Soils on a Warmer Earth

Developments in Soil Science 20

SOILS ON A WARMER EARTH

Further Titles in this Series 1. I. VALETON BAUXITES 2. IAHR FUNDAMENTALS OF TRANSPORT PHENOMENA IN POROUS MEDIA 3. F.E. ALLISON SOIL ORGANIC MATTER AND ITS ROLE IN CROP PRODUCTION 4. R. W. SIMONSON (Editor) NON-AGRICULTURAL APPLICATIONS OF SOIL SURVEYS

5A. G.H. BOLT and M.G.M. BRUGGENWERT (Editors) SOIL CHEMISTRY. A. BASIC ELEMENTS 5B. G.H. BOLT (Editor) SOIL CHEMISTRY. B. PHYSICO-CHEMICAL MODELS 6. H.E. DREGNE SOILS OF ARID REGIONS

7. H. AUBERT and M. PINTA TRACE ELEMENTS IN SOILS

8. M. SCHNITZER and S. U. KHAN (Editors) SOIL ORGANIC MATTER

9. B.K.G. THENG FORMATION AND PROPERTIES OF CLAY-POLYMER COMPLEXES 10. D. ZACHAR SOIL EROSION 11A. L.P. WILDING, N.E. SMECK and G.F. HALL (Editors) PEDOGENESIS AND SOIL TAXONOMY. I. CONCEPTS AND INTERACTIONS 11B. L.P. WILDING, N.E. SMECKand G.F. HALL (Editors) PEDOGENESIS AND SOIL TAXONOMY. 11. THE SOIL ORDERS 12. E.B.A. BISDOM and J. DUCLOUX (Editors) SUBMICROSCOPIC STUDIES OF SOILS 13. P. KOOREVAAR, G. MENELIK and C. DIRKSEN ELEMENTS OF SOIL PHYSICS

14. G.S. CAMPBELL SOIL PHYSICS WITH BASIC-TRANSPORT MODELS FOR SOIL-PLANT SYSTEMS 15. M A . MULDERS REMOTE SENSING IN SOIL SCIENCE 16. I.B. CAMPBELL and G.G.C. CLARIDGE ANTARCTICA: SOILS, WEATHERING PROCESSES AND ENVIRONMENT 17. K. KUMADA CHEMISTRY OF SOIL ORGANIC MATTER 18. V. VANCURA and F. KUNC (Editors) INTERRELATIONSHIPS BETWEEN MICROORGANISMS AND PLANTS IN SOIL 19. L.A. DOUGLAS (Editor) SOIL MICROMORPHOLOGY: A BASIC AND APPLIED SCIENCE

Developments in Soil Science 20

SOILS ON A WARMER EARTH effects of expected climate change on soil processes, with emphasis on the tropics and sub-tropics Edited by

H.W. SCHARPENSEEL Institute of Soil Science, University of Hamburg, Allende-Platz, 0-2000 Hamburg 13, F.R. Germany and

M. SCHOMAKER and A. AYOUB UNEP, P.O. Box 30552, Nairobi, Kenya Proceedings of a n International Workshop on Effects of Expected Climate Change on Soil Processes in the Tropics and Sub-tropics, 12-14 February 1990, Nairobi Organized by United Nations Environment Programme (UNEP) International Society of Soil Science (ISSS) Sponsored by United Nations Environment Programme (UNEP ) UNEP International Society of Soil Science (ISSS) EC Technical Centre for Agriculture and Rural Development (CTA)

(ISSS)

ELSEVIER Amsterdam - Oxford -New York - Tokyo

1990

ELSEVIER SCIENCE PUBLISHERS B.V. Sara Burgerhartstraat 25 P.O. Box 211,1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER SCIENCE PUBLISHING COMPANY INC. 655, Avenue of the Americas New York, NY 10010, U S A .

ISBN 0-444-88838-1

0Elsevier Science Publishers B.V.. 1990 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Science Publishers B.V./ Physical Sciences & Engineering Division, P.O. Box 330,1000 AH Amsterdam, The Netherlands. Special regulations for readers in the U S A . - This publication has been registered with the Copyright Clearance Center Inc. (CCC ), Salem, Massachusetts. Information can be obtained from the CCC about conditions under which photocopies of parts of this publication may be made in the USA. All other copyright questions, including photocopying outside of the USA, should be referred to the copyright owner, Elsevier Science Publishers B.V., unless otherwise specified. No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. This issue is printed on acid-free paper. Printed in The Netherlands

V

CONTENTS Forewords Pn=face Conclusions and recommendations Chapter 1

Chapter 2

Chapter 3 Chapter 4

Chapter 5

Chapter 6

Chapter 7

Overview of the greenhouse effect. Global change syndrome, general outlook H .W . Scharpenseel and P . Becker-Heineman

Chapter 9

1

Inputs to climatic change by soil and agriculture related activities. Present status and possible future trends A.F. Bouwman and W.G. Sombroek

15

Processes that affect soil morphology R .W . Arnold

31

Influence of climatic change on soil moisture regime, texture, structure and erosion G.Y. Varallyay

39

Resilience against climate change? Soil minerals, transformations and surface properties, Eh, Ph R. Brinkman

51

Impact of climatic change on soil attributes. Influence on salinization and alkalinization I . Szabolcs

61

Soil organic matter and biology in relation to climate change P.B. Tinker and P . Ineson

Chapter 8

ix xiii xv

71

Influence of climatic change on development of problem soils, especially in the alluvial domains W.R. Fisher Addendum: Methane formation in waterlogged paddy soils and its controlling factors Y.Takai and E . Wada

101

Potential influence of climate change on soil organic matter and tropical agroforestry E.H. Franz

109

89

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Contents

Chapter 10 The use of models of soil pedogenic processes in understanding changing land use and climatic conditions 121 J.W.B. Stewart, D.W. Anderson, E.T. Elliott and C.V. Cole Addendum: Modeling nitrous oxide production by denitrification 133 J.R.M. Arah and K.A. Smith Chapter 11 Impacts of anthropogenic atmospheric pollution on soils, with special relevance to tropical and subtropical soils, and possible consequences of the greenhouse effect N . Van Breemen

137

Chapter 12 Changes in soil resources in response to a gradually rising sea-level H . Brammer and R . Brinkman

145

Chapter 13 Soils on a warmer earth: tropical and subtropical regions W.G. Sombroek

157

Chapter 14 Soils on a warmer earth: subtropical and Mediterranean regions 175 D. Yaalon Chapter 15 Impact of climate warming on arid region soils D.H. Dregne

177

Chapter 16 Soils of the subboreal region on a warmer earth B.G. Rozanov and E.M. Samoilova

185

Chapter 17 Climate induced changes of the boreal and subpolar soils S.V. Goryachkin and V.O. Targulian

191

Chapter 18 Approaches to mitigate tropical deforestation by sustainable soil management practices P.A. Sanchez, C.A. Palm and T.J. Smyth

21 1

Chapter 19 Managing global change by curtailing emission sources and creating new sinks R. Grantham

22 1

Chapter 20 Implications of the greenhouse effect for African agriculture R.S. Odingo

23 1

Contents

vii

Chapter 21 The agricultural environment of Latin America and the Caribbean and the greenhouse effect N . Ahmad

249

Chapter 22 The Asian agricultural environment and the greenhouse effect L. Venkutaratnam

267

This Page Intentionally Left Blank

ix

FOREWORDS The motivation for organizing the International Workshop ‘Effects of Expected Climate Change on Soil Processes in the Tropics and Subtropics” was threefold. Soil Science is heavily involved in the problems of trapped radiation in the atmosphere by greenhouse effect (GHE) promoting gases. The e€fect of soils on the GHE syndrome was analyzed in a preceding conference: the International Conference on Soils and the Greenhouse Effect, Wageningen, the Netherlands, August 1989, organized by the International Soil Reference and Information Centre (ERIC). An answer was needed regarding the effect of climate change on sustainable productivity of soils, with emphasis on tropical and subtropical regions. The confusing dispute in scientific and popular science journals regarding the predictions of effects of temperature and eustatic sea-level rise, as well as a wide array of possible advantages and disadvantages due to especially C02-rise, had to be thoroughly evaluated against the background of impacts on soil changes. A state of the art of predictive approaches, recognized by the majority of scientists, had to be elaborated. In this volume some 24 scientists contributed to such an evaluation and inventory, each in their own specific field. Though differences in opinion on assumptions, approaches and predictions still exist, these proceedings clearly bring the discussion a great step forward, and it is hoped that they will be of assistance to the soil science community in deciding on concepts for soil related core programmes of the forthcoming International Geosphere Biosphere Programme. The editors

x

Forewords

What once were local incidents of environmental damage, confined to one area and region now involve the whole world. Concern on the global environment has indeed become more and more pressing. All people concentrate their attention to this matter, regardless of their wealth. The United Nations Congress, the Alsh Summit and the Tokyo Conference on Global Environment and Human Response Towards Sustainable Development in 1989, issued the statements that the human race may be making our planet uninhabitable. They are concerned about the rapid decrease in land which should be set aside for forests and other vegetation, essential for maintaining the balance of atmospheric gases, and about the increasing deterioration of soil, water and air, that support the continued existence of all life on the earth. These threatening developments call for an increased emphasis on studies specifically aimed at problems of global change. In a broader perspective the need to expand the role of soil scientist's approaches to global environmental and resources utilization is evident. May these proceedings become an important milestone, which will amongst others contribute to a fruitful discussion during the 14th International Society of Soil Science Congress and its symposium "Global Soil Changes Under Influence of a Changing Environment" (Kyoto, Japan, August 1990). Professor Y. Takai Vice-president, ISSS

Fore words

xi

The theme of this book is a far reaching one and should attract great interest, both in industrialized as well as in less developed countries. Although the question of climate change and its effects on soil productivity is overshadowed by so many current events, it is almost certain that this subject will remain on the international agenda for the years to come; not only as science and research are concerned but also in relation to development policies, agricultural policies and others, especially since poor, rich, developed and developing countries are equally threatened by these problems. The Technical Centre for Agricultural and Rural Co-operation (CTA), provides ACP states with better access to information, research and innovations in the spheres of agricultural and rural development. CTA gives great attention to increasing agricultural production on a sustainable basis and CTA is prepared to strengthen and expand these activities in the years to come. Within this context the recommendations in these proceedings and the subsequent follow-up will be of great interest to us and we are certainly prepared to continue our collaboration in this respect with the United Nations Environment Programme (UNEP) and the International Society of Soil Science (ISS S ) . Dr. W. Treitz Deputy Director, CTA/ACP-EEC Lorn6 Convention

xii

Forewordr

Each day, we are getting a clearer understanding of the growing pressures that threaten our planetary biosphere. Each day, pressures are mounting, due to demographic momentum and rising industrialization. Though uncertainties remain about the magnitude of climate change, scientific evidence confirms human activity has undoubtedly altered, and continues to alter, the atmosphere. While the principle greenhouse gas is carbon dioxide from fossil fuels, agricultural practices are having important impacts on possible changes in global climatic regimes. Recent studies suggest burning of savannahs for agriculture contributes three times more carbon dioxide per hectare to the atmosphere as does burning of tropical forests. Savannah clearing and increase in cattle and rice paddies are just three greenhouse gas sources from agriculture. Studies suggest soil processes involving inputs and outputs of water, gases, soluble salt and organic matter are likely to be influenced by global mean temperature increases. Such changes could in turn reduce land productivity, further threaten biodiversity, exacerbate soil loss and disrupt sediment budgets. Productive cropping areas could turn into deserts, while coastal storms could inundate or degrade fertile lands. Restoring the balance between the sources and the sinks of greenhouse gases will likely not be achieved solely through carbon emission reductions. Conserving existing carbon sinks (oceans, rainforests, grasslands, mangroves, coral reefs, etc.) and significantly increasing the productivity on degraded soils would be cost effective measures to achieve both environmental and economical sustainability. Massive reforestation, regrassing and amelioration of degraded lands are needed. A growing challenge to soil experts and agriculturalists is to produce more food for our growing world-wide population (currently already at 5.2 billion) from finite and shrinking productive lands. Of the total world-wide area of potential arable land, nearly half (about 1.5 billion ha) is already cultivated. There are very few virgin lands easy to exploit for additional food production. With these proceedings, a serious effort has been made to: 1) discuss latest knowledge on the expected impact of climate change on soil processes, with emphasis on the tropical and sub-tropical regions; 2) agree on recommendations for meaningful and useful future research and monitoring programmes; and 3) formulate policy responses to the expected impact in the form of preventive and adaptive measures. I hope that with these proceedings, we have moved forward to a better understanding of soil processes and their relationship to climate change. Mostafa K. Tolba Executive Director, UNEP

...

Xlll

PREFACE The Plan of Action for the implementation of the World Soils Policy was endorsed by UNEP’s Governing Council in 1984. The document identified the international action required to promote the sound use of land and soil resources. It also highlighted the need for internationally acceptable methods for assessing and monitoring the existing status and risk of soil degradation. The importance of ensuring that practices to prevent soil degradation, improve land productivity and reclaim degraded areas are appropriate to Iocal physical, economic, social and cultural conditions had been recognized in the document. At the same time, it is also recognized that serious gaps exist in knowledge of the extent, mechanisms and economic consequences of soil degradation as well as in knowledge of costeffective means for controlling erosion and other forms of land degradation. Consequently, there is an equally urgent need for a long term commitment by international organizations and Governments to support research on mechanisms and effects of soil degradation on the development for combatting soil erosion, as well as for the identification of critical areas and for a standardized assessment of soil resources and of the seriousness of soil degradation, through surveys and inventories. Methods are required which can reliably detect significant changes in those soil and land characteristics which directly or indirectly affect the quality and quantity of the land and its liability to produce food, fibre and timber. The manipulation of the pedosphcre by man is substantial and is likely to increase strongly until at least the year 2050, whcn the world population is expected to peak. This manipulation certainly has an impact on global climate and should be taken into account in connection with the increasing greenhouse effect on climate. The present status and future trends concerning the effects of soils and land cover on the fluxes of greenhouse gases, the surface energy balance and the water balance are discusscd in Bouwman (1990). The current publication explores and assesses the concept, the trends and impacts of the possible global warming on soil processes in the tropics and sub-tropics. Hierarchical research requirements and response stratcgies nccessary to meet the ncgative impacts of climate change on soils are also outlined. UNEP sees that the great task for the world community is therefore three fold: 1) to reduce greenhouse gascs; 2) to prepare for the impacts of global warming; and 3) to provide technical and financial assistance to developing countries so that their strive towards legitimate economic expansion is not hampered by measures addressing global warming. UNEP welcomes thc concern expressed on global warming at the highest levels. Thcse and other priorities, such as protection of land resources by combatting dcsertification and

x iv

Preface

deforestation, have bcen constant pre-occupations of UNEP for well over a decade. The preparatory work for global conventions on climate change and biological diversity are but a few of the many actions of UNEP to safeguard our planet. A.T. Ayoub, Senior Programme Officer, UNEP

xv

CONCLUSIONS AND RECOMMENDATIONS OF THE INTERNATIONAL WORKSHOP ON THE EFFECTS OF EXPECTED CLIMATE CHANGE ON SOIL PROCESSES The workshop discussed how soils in specific ecosystems respond to changes of climate and the needfor soil scientists to work with other disciplines.It also listed research priorities and discussed how the use and management of soil resources can mitigate climate change and at the same time adapt to it.

ECOSYSTEM DYNAMICS, INTERACTIONS WITH THE ATMOSPHERE AND THEIR EFFECT ON SOIL AND LAND USE A scenario and some predictions

We assumed: over a time span of about 50 years a gradual warming of the atmosphere of about 3°C with 2°C in tropics and 5°C in sub-polar areas; 10% increase of precipitation, a sea level rise of 50 cm, and an equilibrium world population of 10 billion; by about the year 2100 a doubling of the atmospheric C 0 2 content. The results of geophysical, geochemical, and biogeochemical processes vary widely in current soil ecosystems. Within a decade changes of temperature and precipitation will influence soil temperature and moisture regimes, pH, base saturation, fertility status, surface litter and biological activity, and the presence of salic and fluvic soil properties where appropriate. Over a period of several decades changes of climate are manifested in soils through the depth and kind of humus in the topsoil, relative fertility, erosion, and in peatiness, swell-shrink features, degree of bleaching and calcareoumess. We believe that soil ecosystem responses to changes in land cover and climate differ mainly due to different degrees in sensitivity of soils to disturbance and modification. It is recognized that there are likely to be very large regional and local variations in the manifestation of warmer earth conditions. Nevertheless the following general statements can be made for some major ecosystems. In a Tropical Rain Forest ecosystem (hot, humid) one might expect increases of forest growth, nutrient cycling, and mineral weathering. Ferralsols are common in such biomes and with more percolation through the soil we would expect a decline of the fertility status, slight decreases of pH and base saturation, more litter production but also more biological activity with little change in humus content in the topsoil. Additional Weathering of minerals would occur, however, due to the great thickness of many saprolites there would be little change in relative fertility over time. Although soil processes would respond to the changes of climate and vegetation the overall impact would be minimal compared to the present ecosystcm. Thcse kinds of soils have low sensitivity to the assumed

xvi

Conclusions and recommendarions

climatic changes. In a Steppe or Grassland ecosystem (warm, semiarid) the increase of precipitation would increase biomass production and movement of water through and on the soil. In such ecosystems, Chernozemic soils are common; they are moisture sensitive and the humus content in the topsoil would increase, carbonates and other soluble salts would leach deeper and salinization might occur in adjacent lower areas. Soil pH and base saturation would decrease slightly but the nutrient supply would remain high. Increased erosion would occur on slopes where vegetation would become stressed. In a subpolar Boreal Forest ecosystem (cold, subhumid) we would expect an increase of biopmductivity and biogeochemical cycling. For the dominant soils in this ecosystem, Podzols, the humus content, base saturation, relative fertility status and pH would become higher. The litter and liistic horizon, if any, would become thinner, leaching would tend to intensify, and the spodic horizon would likely become thicker. The vegetative cover would minimize erosion of the soil. The soil processes in this ecosystem are fairly sensitive to the assumed climate changes, especially temperature. We conclude that the changes in soil processes will be substantially more pronounced in cold and temperate regions than in the tropics because the soils outside the tropics are more temperature sensitive and the temperature changes are expected to be greater there. As one approaches the transitional zones between ecosystems ("ecotones") it is more difficult to make general predictions about soil changes because of the strong interactions of climate and biota that often occur in such zones. In coastal swampy areas and tropical mountains a global warming can have dramatic effects on the ecosystems. Rising sea levels would generate a host of events such as flooding, salinization, and new erosion and sedimentation patterns that would affect many soil ecosystems. In mountainous areas the ecological zones respond to elevation, thus a warming would push the climatic belts up the mountains, creating new conditions. The essential contribution of soil science to climate change studies The impact of climate change will be extremely diverse and difficult to predict. The consequence for soils and their associated vegetation will be even more complex, and will have the most wide ranging and diverse consequences for agriculture, forestry, ecology, conservation, and all forms of land use. Progress in understanding and pedicting these effects can only be made by multidisciplinary studies. Soil science forms an essential component of such work. Soil is the basis for plant growth, and the full effects of climate change will be mediated by complex interaction between the two. There will also be direct effects of increase in atmospheric C02.At the highest level, full scale ecosystem studies are essential to understand changes resulting from broad shifts of vegetation bands and biomes. Major modeling programmes will be needed at

Conclusions and recommendarions

xvii

several different scales of size and complexity. Apart from these vital studies on impact, it must not be forgolten that soils have major sources and sinks for important greenhouse gasses: carbon dioxide, water vapor, methane, nitrous oxide. These fluxes require much more accurate measurement, and the understanding of all underlying processes. We also need to know how the expectcd climate changes will interact with these greenhouse gas processes in positive or negative feedbacks. Major research programmes are bcing dcvcloped on these themes in a number of countries, many with a strong international component. It is critically important that the central position of soil science in such studies is recognized at an early stage, so that these programmes are fully balanced and complete. This also demands from the soil science community that it is prepared to collabotate freely and widely with other essential disciplines having a bearing in this issue. These studies require new techniques, which are only just being introduced into soil science, such as molecular biology, natural abundance stable isotope studies, and the newest methods of remote sensing. A crucial group of soil processes arc tcrmed "anthropogenic", referring to those brought about by the activitics of man. Thcsc processes likely override all others. The implications of man's direct influence on soil processes, on ecosystems, and on the earth systcm as a whole are such that they tend to overshadow our attempts to deal with natural ecosystems and climate-induced changes. Such anthropogenic processes have the potential to change the course of civilization especially if they are ignored.

RESEARCH PRIORITIES ON EFFECTS OF EXPECTED CLIMATE CHANGE ON SOIL PROCESSES, WITH EMPHASIS ON THE TROPICS AND SUBTROPICS The soil research priorities identified during the workshop can be categorized in 6 main groups: Collection of baseline data; Study of soil processes; Study of land use dynamics; Modelling of soil processes; Long-term monitoring of global soil change; Management and mitigation measures of global soil change. Furthermore, to carry on many of thc soil studies, data have to be collected and processed in a whole hcarted collaborative effort with other disciplines, such as those dealing with climatology, ecology, and crop production. No priorities were identified for research on emission of greenhouse gases, because these were considered during the recent conference on "Soils and the

xviii

Conclusions and recommendafions

Greenhouse Effect" in August 1989 in Wageningen (see Bouwman 1990). The following specific subjects in each of the six categories were identified as priority research subjects. Base line data A large number of data bases pertaining to the nature and state of the worlds soil cover exist. To prcdict effects of climatic change on soil properties and on quantitative and qualitative aspects of ground water recharge and on surface water, it is necessary to identify gaps in these data bases. A first brief survey indicated the following gaps (some of which may overlap with each other): Soil information on a scale of 1:1 million, or even smaller (such as the FAOAJnesco Soil Map of the World at a 1 : 5 million schale), of large parts of Africa, South America, and Asia is not accurate enough for predictive and interpretative purposes; larger scales (up to 1:250,000) are needed. The state of soil/land degradation is generally poorly understood and quantified, although an overview will be available soon through the UNEPDSRIC Global Assessment of Soil Degradation (GLASOD) Project. Special attention should bc paid to mapping of (potentially) saline, alkaline and acid sulfate soils. Global data bases on actual land use are either out-of-date or too general. These baseline data should be organizcd and made available through the development of Land Information Systems (LIS) such as the ISSSDSRIC Soil and Terrain Digital Database (SOTER). Paleopedological maps of the world (1:2.5 million) of 2 or 3 climatic periods in the Pleistocene and Holocene will be very hclpful in analogue studies to forecast the effect of climatic change on present-day soils and for estimating the carbon cycle changes. As a first priority it would be sufficient to prepare such maps for a numbcr of selected, promising areas, whcre more background data are available. The Unesco-initiated project of mapping continental soil salinization and potential soil salinization should be cornpletcd. Soil processes and their dynamics In studying soil processes, priorities should be given to processes that operate on a time scale of 1 to 100 years, including those that may change suddenly or catastrophically. We bclieve that these are (in order of decreasing

Conclusions and recommendations

xix

potential rate of change): Changes in soil salinity and alkalinity (one month to 10 years); Changes in soil meso- and macro fauna important for bioturbation and homogenization (1 to 10 years); Changes in structural stability and moisture characteristics (1-10 yrs); Changes in amount and quality of organic C and N levels (1-10 yrs); Changes in nutrient status, acidity, redox regime (10 to 100 years); Changes in susceptibility to erosion (10 to 100 years); Changes in iron and amorphous minerals (10 to 100 years). A number of methods are available for this purpose: Analogue studies, using soil chronosequences or using situations where the soil climate has actually changed substantially (due to deforestation, artificial drainage, ponding, etc.) Manipulation studies in the field (small chamber, small watershed), greenhouse or laboratory. Field studies on soil processes should preferably be camed out in areas involved in a network for long-term monitoring (see below). An important problem to be addressed is the methodology of scaling down experimental (as well as modeling) results to values that are relevant at less detailed scales.

Changes in land use For a number of other disciplines (agronomy, animal husbandry, economics, general politics, medicine) it will be important to predict the changes in land use resulting from climatic change and related changes in soil properties. Soil scientists will be asked to provide data needed to help forecast optimal land use on the short (0-10 y) medium (10-30 y), and long (40-60 y) run. GIs- or LIS-based expert systems should be very helpful in this regard.

Mo dei i n g Process oriented simulation models describing changes in soil properties, as a function of temperature and precipitation (time scale of days, weeks, months, or years) are urgently needed. Research on soil processes and collection of longterm monitoring that should provide parameters and opportunities for calibration and validation of these models.

Long term monitoring To detect ecologically relevant changes related to climate change, and to provide opportunities for research, a network of stations for long-term

xx

Conclusions and recommendations

monitoring of vegetation-soil properties - topography-hydrology-hydrochemistryclimate of a number of globally representative,natural, rangeland and agricultural ecosystems should be set up. Priority should be given to: Transitional regions where rapid climate change is expected; Coastal areas where sea level changes are expected; Irrigated areas in semiarid regions; Deforested areas; Natural wetlands. Besides detailed monitoring at field/small catchment scale on the ground, detailed remote sensing monitoring of the general region, representative for the ecosystem, should be carried out. Remote sensing should be directed to estimating vegetation (cover), net primary production, evapotranspiration, surface temperature, IR radiation and, where applicable, surface soil properties. The monitoring research sites should be run by local organisations and coordinated internationally to promote the use of common methodologies and exchange of data. Data from other disciplines Climatologists

In addition to forecasts about mean annual temperature and precipitation, it will be very important to obtain estimates of the ranges of year to year and month to month variability, especially in rainfall, and the expected frequency of high intensity, highly erosive rainfall. Ecologists and crop production physiologists Effects of increased CO;!on organic matter return to the soil, estimated on the basis of crop production models. In addition to quantity, qualitative aspects of the organic matter (possible changes in biodegradability) should be considered.

ADAPTATION TO CLIMATE CHANGE: SOIL RESOURCES USE AND MANAGEMENT The workshop participants discussed strategies to counteract increases in greenhouse gases and defend present soils and their uses against adverse effects of climate change. The resulting recommendations are directed at policy makers and at the users of the soils. Management strategies were identified that are desirable in their own right as well as in the context of the greenhouse effect. Four sets of concerns with accompanying recommended management strategies are reported:

Conclwionr and recommenda~iom

xxi

Increasing C 0 2 sinks The following measures are advocated, recognizing that soil- and land management-related methods of C02 sequestering on-their-own would only remove a fraction of the increased atmospheric carbon. Besides removing CO2, each of these measures would provide direct production benefits to the land user. Conditions that favour C retention in soil and biomass include wetness, low temperatures, increased mineral nutrition (soil fertility), deep root development as well as biological activity. Management strategies should aim to preserve and, where possible, increase standing biomass and residues in soils. On many soils this will involve appropriate use of mineral fertilizers. On acid soils, selection of aluminium-tolerant crops or cultivars and liming of the acid subsoil to encourage deep root development are recommended. Irrigation in arid areas, either to produce grassland or annual field crops or to establish perennial vegetation, will increase standing biomass and soil organic matter. In the case of hardpans or other root barriers, subsoiling would enable deeper root development.

Reducing N2O and CH4 emissions Conditions favouring N2O emission from soils include high concentrations of mineral N species and alternation of reduction and oxidation. Conditions favouring methane emission include deep reduction in the absence of sufficient active iron oxides as well as of sulfate. Management measures to avoid such conditions include the following: Proper dosage. timing and placement of nitrogen fertilizers in accordance with crop growth stages, to minimize periodic excess N. Drainage or cultivation or other measures to avoid topsoil compaction and periodic reduction in cropland or pastures. In wetland soils, efficient water management so as to avoid periodic oxidation. Under rainfed conditions, this may involve land shaping, bunding, puddling, supplementary irrigation where feasible. Methane emission from wetland soils can be rninimizcd by avoiding incorporation of readily decomposable organic matter, and by addition of material rich in ferric iron, where practical, on soils low in active iron oxides. Also the use of fertilizers with the sulfate anion suppresses methanogenesis.

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Conclusions and recommendations

Adapting to sea-level rise Sea-level rise causes a destabilized coastline, inland extension of areas affected by salinity and increased flooding depth and wetland conditions in inland parts of coastal plains. These problems can be combatted by one or more of the following measures: Sea defense including structural works such as embankments, as well as planting or preservation of protective mangrove forest belts. Embankment and pump drainage, or tidal drainage where feasible, of the impoldered land. Changing land use to fish farming where protection of the land against fresh-water or saline flooding is not practical. Changing to more salt-tolerant crops or cultivars in salt-affected areas. Selection of cultivars for higher yield under deep flooding or brackish water conditions.

Adapting to climatic variability The main problems to be considered are high-rainfall events and drought. Soil management measures to mitigate their effects in dryland soils should aim to maintain a complete soil cover, minimizing rainfall impact and non-beneficial evaporation; assure good macroporosity, infiltration and aeration; promote deep root penetration. Such measures include mulching, use of cover crops, relay cropping to improve cover and bioporosity; and subsoil liming where needed and appropriate deep ferlilization, especially with P, to increase rooting depth. Additionally, water harvesting methods and terracing and other recognized water conservation methods would increase amounts of water available to crops. Response farming techniques including, for example, late topdressing in amounts will capture the benefits of years with good rainfall or minimize costs in poor rainfall years. Finally, it should be mentioned that a rise in atmospheric C02 can have a positive effect on plant growth through increased photosynthesis ("CO2 fertilization"), and on the water use efficiency of plants due to reduced stomata1 openings. Global temperature rise will moreover result in higher precipitation due to greatly increased evaporation over the oceans - which in places will significantly enlarge the amount of fresh water that can be used for irrigation purposes.

1

Chapter 1

OVERVIEW OF THE GREENHOUSE EFFECT Global change syndrome; general outlook H.W. Schapenseel and P . Becker-Heidmann Institute of Soil Science, University of Hamburg Allende-Platzz, D-2000 Hamburg 13. Federal Republic of Germany

ABSTRACT Accumulation of cosmic dust and planetesimals was most likely the mechanism that created our planet. Due to dominance of hydrogen, the extruded gases produced a primordial reducing atmosphere. enriched with methane and ammonia. Then, after a slow start, continued oxidation with oxygen, released from photolysis of water, and the later development of life from photosynthesis caused the atmosphere to become dominated by COz, water vapor and N. The two former components were able to trap IR radiation and to produce a warming greenhouse effect of 33"C, shifting the surface temperature to +15"C. Oxygen from photosynthesis (at present yearly c a 330 bil t from terrestrial photosynthesis) was used over at least 2 billion years, for sustaining respiration of the various facets of life and for iron oxidation in marine and terrestrial sediments. During the last billion years oxygen began to enrich in the atmosphere, parallel to reducing CO2 concentration, due to its consumption by photosynthesis, chemical weathering and the carbonate precipitating pumping effect of the oceans. C02 replenishment occurs via volcanism and release from subduction zones. The faster biochemical cycle of smaller pool size (organic matter production, respiration, humification, kerogene formation, and biotic-abiotic-photochemical organic matter turnover) and over longer geological periods especially the slow but very large geochemical cycle (exchange of carbon between atmosphere, ocean, biosphere, and sediments), are decisive for CO2 concentration and its contribution to temperature. Some features of the biochemical cycle against the background of climate changes, including those due to Pangaea/Gondwana shifting, are discussed. Life is on a carbon trip. Wasteful consumption of fossil C based fuel, due to rising living standard and population explosion in conjunction with increasing release of greenhouse active (radiatively active) gases - which are fingerprinted - threatens to exert climate changes detrimental to our life conditions and civilization. Arguments to characterize the situation are assessed, also those expressing potential advantages of increasing C02 concentration for crop yields and expansion of the farmland area, doomed to shrinking at the present level of population explosion. The need for a change from the carbon trip to a mixed carbon - hydrogen trip is evident.

INTRODUCTION Environmental consciousness, especially watchfulness with focus on all anthropogenic activities causing pollution, tend to deviate our attention from tf-e dominant natural processes, underlying the whole web of contributing factors,

2

H.W. Schorpenseeiand P.Beckr-Heidmann

actions and feed-back systems in our unique earthly environment. A predictive analysis of the possible effects of a global climate change on soil processes and land degradation should be preceded by a short review of the scene as it existed, before a steadily growing human population created the syndrome of changing climate, basic to our worries. Its background is population explosion in conjunction with carbon-based energy sources and technologies, accompanied by steadily increasing release of nitrogen oxides (N20,NO), that absorb IRradiation or consume ozone in the stratosphere and produce ozone in the troposphere, as well as by increased infrared radiation trapping and stratospheric ozone destroying CFCs (chloro-flouro carbon compounds). These compounds, C02, CH4, N 2 0 , 0 3 , CFCs are expected by the majority of atmospheric chemists to lead to a further indirect temperature increase at the earth surface and decrease in the stratosphere. The estimated temperature rise of 3 to 5°C in the next 50 to 100 years may cause an eustatic sea level rise of 0.7 to 3 m due to water expansion and melting of polar ice masses. How did it all dcvelop and finally become a problem ?

OVERVIEW Basic facts, relating to this question in a nutshell expose the following tableau: Within the sun 700 mil t of hydrogen are fused per second into helium, i.e., ca 4.3 mil t of solar mass are converted into radiation energy, equal to 1.2 x 1015t per year (Wunderlich 1968). From the total solar mass of 2.2 x t , ca 1/40,000 has so far been consumed. The share of the solar radiation hitting the earth, the solar constant, amounts to 2.0 k 0.04 cm-2min-1.This solar radiation with wave lengths of less than 3,000 is absorbed in the ozone layer. Besides, light waves of 3,000 - 20,000A, till near-IR and radiowaves of 1 - lo3 cm wave length enter the atmosphere. The energy invested in the sun radiation is the origin and source of all important features of climate and environment, such as temperature, wind, clouds, precipitation and autotrophic organic matter production. The fact that the earth possesses an atmosphere, is taken as indication, that the origin of the earth is unlikely the result of a cosmic catastrophe, e.g. a collision of the sun with another cosmic body. I may have been formed however, by contracting dust and planetesimals with gaseous inclusions, giving rise after its compaction to extrusion of gases. Provided the gravitational forces are strong enough, those gases will be retained by the planet to form its atmosphere. The very light elements, such as H, He and Ne dissipated into space. This is revealed by comparison of the remaining atmospheric concentration with the share of these elements of the matter in the universe. Estimates are, that about 1 of 50 bil original Ne atoms in the primordial gas cloud is still left; He of the atmosphere is held 10 be almosr entirely radiogenic. The very wasteful atmospheric H, the major

Ilistorical overview of the greenhouse effect

3

cosmic element, may be representing 1 out of 5 mil H atoms in the original dust cloud; the even more reactive 0 about 1 of former 6 atoms; the less reactivc N about 1 of 800,000 N atoms (Asimov 1981). The high cosmic excess of the element H, also early earth, led to an initially reducing atmosphere of chiefly methane (CH4, carbon plus hydrogen) and Ammonia (NH3, nitrogen plus hydrogen). Depending on the amount of oxygen available, water (H20, oxygen plus hydrogen) was formed, which howcvcr was progressively precipitated and collected in depressions and marine basins together with the water vapor emitted by volcanic exhalations, thus leavingCH4, N H 3 , and water vapor as dominating atmospheric gases (Urey's work). Photodissociation of water (H2O + h.v = H+ + OH- ) led to slow oxidation of methane and ammonia into C02 and N2, producing an N2 and C02 atmosphere. With progressing integration of N2 into nitrates, C02 gained dominance till its rising conccntration increasingly blocked the photodissociation of water. Furthcrmorc, ozone formation from free 0 2 in the higher atmosphere absorbcd the UV-radiation and prevcntcd its penetration into the lower atmosphere and action of photolysis. As a rcsult, a stable C02 dominated atmosphere came into existcncc (scc also Habcr 1965). The high C02 concentration could have strongly promoted the greenhouse effect. Due to a rising temperature, water evaporation would have bcen further enhanced, with its additional promotion of the GHE and atmosphcric tcmpcrature rise until a hot earth would have emerged, envclopcd by a water vapor cloud and C02 dominated atmosphere. (For comparison, planct Venus built up a hot and stable COz atmosphere of ca 450" C). But planct earth took a completely different turn in the development of life, probably already slowly bcginning under the reduced CH4/NH3 atmosphere, whcre NH3 was decomposed, releasing N2 into thc aunosphcre, whilc excessive C 0 2 precipitated with Ca, Mg or Fc, which were dissolved by weathering procedures (without oxygen participation) in thc marine basins (not the least enclosed in phytoplancton). Thus, only a moderate GHE occurred due to water vapor and C02 built up, increasing carth's mean temperature by 33" C from - 1 8" C to +15" C (Arrhcnius 1896). This is a temperature level suitable for the liquid state of water and thc colloidal state within living organisms. Other conditions supported the sustainability of life as well, such as: 1 ) the Van Allen belt (the magnetosphere); 2) the shield against cosmic radiation; 3) similarly, the ozone shield for absorption of UV light; 4) the earth magnctic field, although changing its polarity rcpcatcdly in the course of earth history, giving furlher radiation protcction and orientation; 5 ) the high altitude cirrus clouds, heating the atmosphere; 6) the lower altitudc vapor saturated clouds exerting a cooling effect; 7) the inclined earth axis (23.5"), producing annual seasons of climate; 8) the earth rotation, causative for day and night change for regeneration of the metabolisms; and 9) the atmospheric currents for transportation of moisture, heat and dissipation of products of pollution.

4

H.W. Scharpenseel and P . Becker-Heidmann

Soil and humus formation, CO, and 0, trends

&M 0 Quaternary Ter t iar y

.

70

Cretaceous plus humus of Angiosperms

. 140

Jurassic

.

180

-

225

Triassic Permian . 275

first complete soil cover Carbonian plus humus of Gymnosperms

345

'

Devonian . 400

.

Silurian 440 Ordovician

. 490

Cambrian '

580

C02 trend decreasing 0 trend increasing

Fig. 1.1

Soil and humusformation in earth is history

Life on earth was slowly turning the N/C02 atmosphere into a N/O atmosphere. The 0 2 concentration increased by almost one order of magnitude (Fig. 1.1) during the last ca 600 million years, that is since the beginning of terrestrial plant growth (the Phanerozoic; flowering plants, the angiosperms since just ca 150 million years) . This is mainly the effect of oxygen release during the photosynthesis process of organic matter production from CO2, and 0 and H from H20, previously dissociated by sunlight energy (light reaction of photosynthesis). The slow development of our oxygen rich atmosphere after exhaustion of the enormous demand for marine and terrestrial Fe-oxidation is shown in Fig. 1.2. Meanwhile the total free oxygen pool in the atmosphere and dissolved in the oceans is estimated to amount to 1.3 x 1021 g. Most of the biologically produced oxygen, at present ca 3.3 x 1017g of 0 2 per year (corresponding with ca 1.2 x lOI7 g of C per year by terrestrial photosynthesis) plus ca 1.3 x 1017 g of 0 2 per year (corresponding with ca 5 x 10l6 g of C consumed by marine photosynthesis), is bound in the earth crust as metal oxide, sulfate, silicate, and carbonate and represents about 6 x g of oxygen (Chem. Ind. 1987). Considering the high reactivity of oxygen, its existence as free 02-gas in the atmosphere is possibly only the result of constant new 0 2 production and

5

Historical overview of the greenhouse effect

addition. Without replenishment by photosynthesis, our atmospheric oxygen may

be consumed in about 3000 years due to oxidation processes in the earth crust (Haber 1965, 1971). But also atmospheric C02 needs replacement outside the biochemical cycle of photosynthesis and respiration due to consumption of C02 by silicate weathering, where from 2 molecules of C02 involved in the bicarbonate reaction always only one is returned to the atmosphere, whereas the second one is precipitated as carbonate, which would use up the present atmospheric CO2-pool in about 10.000 years (2 COz + H 2 0 + CaSi03 t Ca2' + 2 HCO3- + Si02) (Berner and Lasaga 1990). Similarly the gas exchange pump of the oceans induce C02 intake to replace C02 of precipitated carbonate. After longtime involvement of the geochemical cycle, these carbonates may under high pressure and temperature be subjected to metamorphic processes and eventually release the C02 through volcanism or expulsion by subduction zones.

4 B I L L I O N Y E A R S AGO

3 TO

Primordial m l m o ~ p h e r e

Formallon 01

co2

S o l u l l o n O d 0, I " w a t e r

S O l U l l O " I " "11*,

4

B I L L I O N Y E A R S AGO

0, I n

water

CA

2 B I L L I O N Y E A R S AGO

Formillon 01

0, I n w a t e r

T B ~ l d S l I 1 ~l 1l x a l l o n 01

0,

......~

CA

0 5 B I L L I O N Y E A R S AGO

T e r r e $ t r i a l o r m ~ t i a n0 1

0, R I S E

0,

I N ATMOSPHERE

IIIIII 0 2

0 A C T E A IA

W E AT H E R I N G

CaCO, A

I

Fig. I .2

Fe*O 3

-

MUD

,

History of oxygen formation and dynamics

This gas exchange process would exhaust atmospheric C02 in about 300,000 years (Bemer and Lasaga 1990). Planet earth, its atmosphere and biosphere become vitally predetermined by the consequences of the vast but slow geochemical and faster biochemical cycle, which however represents a much smaller carbon compartment.

6

H.W. Scharpenseel and P . Becker-Heidmann

FEATURES OF THE BIOCHEMICAL CYCLE Only carbonaceous materials, produced by abiotic processes till ca 3 billion years ago are exclusively geochemical (Rankama 1948). All others also have a biochemical component. The organic matter residues of living organisms are preserved almost exclusively in aquatic sediments as carbonates or in contact with shales and clay minerals. The latter as clay domains provide also the matrix for organo-mineralcomplexation of younger or even today's terrestrial organic matter (Aylmore and Quirk 1960; Theng and Scharpenseel 1975; Theng 1979) (Fig. 1.3). 70-

60-

50I

P

E" 40-

1

H m i c acid concentration (mg/rnl)

Fig. 1.3

Isotherms at 20°C f o r the adsorption of 14 C-humid acid by montmorillonite saturated with diflerent cations (Theng and Scharpenseel 1975)

Most of recent as well as ancient sediment's organic matter stcms from phytoplancton and bacteria (Bordowsky 1965; Murphy et al. 1966); this forms the major sink of organic C and of CO2. Sediments, produced by precipitation, such as evaporites and carbonates, rarely contain large amounts of allochthonous organic matter. Detrital rocks like sandstone or shales engulf, usually diagenetically formed, relatively stable, secondary polymerized compounds, such as humic acids as oxidative or kerogene as reductive products (Tappan and Loeblich, ref. Welte 1963). Both together represent the major organic carbon sink

Historical overview of the greenhouse effect

7

at a level of ca 3.6 x loi5t, compared with petrol or coal with stocks of the order of 10l2- l O I 3 t only (Degens 1967). Finally, climatic and tectonic events have a great influence on the organic compound production and preservation, e.g. bituminous sequences often seem to be related to orogenic phases or epimgenic oscillations with corresponding eustatic lifts, trans- and regressions (Bitterli 1963). The C02 and 0 2 balance in ocean water and in the atmosphere changed with the organic matter production in the course of earth history, with its carbonate precipitation as well as the emergence of higher plants and animals (Tappan and Loeblich, ref. Welte 1969). During sediment diagenesis organic matter supports the microbial metabolism and it exerts influence on chemical reactions through pH and Eh changes, especially those involving C02 - SO2 CH4. After microbial activity terminates, chemical interactions with the inorganic matrix occur, leading to complexation and chelation, and reactive chemical groups like carboxyl, hydroxyl, and amino groups are released. The origin of life is believed to have occurred in an aquatic milieu, which provides more continuity due to less zoographic isolation than terrestrial life which developed later. According to Schilder (1956), 63 among 68 animal classes live in a marine environment, but, due to geographic/ecologic isolation in terrestrial environments, the differentiation in species is more pronounced, comprising ca 83 % of all known animal species. The transition from marine to land based life, that contributed most to an oxygenation of the atmosphere and that became a major sink for C02 excess in the biochemical cycle, must have begun preferably in marginal shelf fringes of the epipelagial, the euphotic zone, mostly under tidal influence, such as in marshy or mangrove environments and in shallow littorals. Since organisms sustaining the biochemical cycle by photosynthesis (C02 consumption) and respiration (C02 release) survive in evolutionary processes, due to their capability to adopt flexibly to environmental changes and to find ecological niches or refuges, the eco/geographical boundaries governing the distribution of species are constantly shifting due to climate changes as well as to tectonic effects. This applies particularly to stenothermic animal species requiring a narrow temperature regime. In biomes, animal life usually is more flexible and stretches further into critical environments than growth of vegetation (Wurmbach 1971). The spread of terrestrial life has also been largely influenced by plate tectonics in conjunction with the dissolution of Pangaea, the Gondwana and Europe-Angara drifting with the corresponding climate changes. In this context, the most striking process of soil degradation, a land fossilization and lateritic cuirass formation, occurred due to changed erosion and drainage patterns. These cuirasscs represent an extreme form of humid tropical weathering under the changing climate of the floating Gondwana subcontinents (mainly Jurassic to Oligocene) (Valeton 1984). A sporadic soil blanket (pers. comm. Dudal 1990)

8

H . W . Scharpenseel and P . Becker-Heidmann

existed probably since the end of thc Silurian, a soil continuum came into being some time after the cold spell during the Permian.

IMPACTS OF GEOCHEMICAL AND BIOCHEMICAL CARBON CYCLE A comparison of the magnitudes of the compartments of carbon in the (bio)geochcmical (exchange of C between sediments, atmosphere, biosphere and ocean) and biochemical (organic matter production, respiration, turnover) cycle shows the dominance in pool size of the former, which over geological time pcriods is all decisive with its enormous buffer capacity (Table 1.1). Shortcuts in the biochemical cycle and short-term excessive inputs may produce a flicker, strong enough though for consequences on the GHE, the earth temperature, the prccipitation and the circulation, which may damage or even exterminate species causativc of the disturbance. Thus, in our short historical span we can not rely on the buffcr capacity of the large but slow gcochcmical cycle to neutralize the consequcnces of our mistakes. Table 1.1

Comparison of carbon pool sizes in biochemical and geochemical cycle*

Componcnts CaC03 in sediments CaMg (CO& in sediments Organic sediments (kerogcne) HCOf and C032- dissolved in sea Fossil fuel (coal, gas, oil) Dead soil biomass (humus) C02 in atmosphere Living biomass (plant, animals) * Data slightly modified from Berner and

C-amount in 10'2 t of c 35,000 25,000 15,000

42 5

2 0.72 0.56 Lasaga 1990.

LIFE ON EARTH, A CARBON TRIP Lifc on earth is on a carbon trip. We must get aware of the need for changing course in time to avoid an erratic trip back into chaos, from which evolution made us ascend. Looking at the biochemical carbon cycle (Fig.1.4). about 115 to 120 x l O I 5 g of C are turned over annually in the terrestrial ecosystems by photosynthesis and inversely by respiration through the bio- and pedosphere. Worrysome is the surplus due to respiration of ca 1.5 x lOI5 g of C from annual land clearing (slash and bum) as well as the 5.5 x l O I 5 g of C from

9

Historical overview of the greenhouse effecr

combustion of fossil fuel, which are adding up at a ca 50% rate to the 720 x 10'5 g of C in the atmospheric carbon pool. However, recent results of Esser (1990) suggest that the C-sink due to C02 fertilization is already overcompenzating the C02 source from forest clearing (ca. 1.5 Gt C y - l from 10 to 15 mil. ha of clearing a year). Principally, carbon oxidation products, C02 and CH4, although being greenhouse active trace gases, are minor in importance compared with water vapor (1:5) in generating the temperature rising greenhouse effect of 33"C, lifting the surface temperature from -18°C to +15"C. According to Ramanathan (1989) as well as Raval and Ramanathan (1989), the total natural 33°C greenhouse effect generated by water vapor plus C02 equals 155 Wm-2 (ca 145 W at clear sky, 180 W at cloudy sky). Doubling of the C 0 2 concentration would add ca 4 Wm-2 only; human activities so far have enhanced the GHE of the atmosphere by ca 1.5 % only.

CARBON CYCLE

l

120

I

n

A

2'

B'OSPHERE + PEDOSPHERE

i...ca.?3P..!!.!v!na.! .......

$.

C6 2000 (dead)

ca 100

ca 100

ca 60

01

5"

,

DEPOSITS 5000 i ......COAL, . ...........OIL, .........GAS ............................................ SEDIMENTS/LITHOSPHERE 66 000 000 o,2 from l o r e s t a n d sol1 d e g r a d a t i o n

OCEAN SURFACE WATER c a 700 ................................................................... DEEPER OCEAN WATER c a 37000

l r o m c o a l , 011.

gas combusllon

a m o u n t s ~n G I ( I O " ~ ) , f l u x e s i n G I I ~

Fig. 1.4

Carbon compartments in biochemical and geochemical cycle

But the increments of C02, CH4, as well as the other radiatively active trace gases, such as the CFCs, N20 and tropospheric ozone, are wholly or to greatest extent the product of anthropogenic activities. Human civilization was in its earlier phases sustained by the direct products of photosynthetic C reduction and

10

H.W. Schorpenseel and P.Becker-Heidmann

photolysis of water (Calvin 1962). Since beginning craftsmanship and industrialization it progressively built up a dependency on minable and consumable forms of organic matter, produced mainly throughout the last 350 million years, such as coal, kerogene/petrol and methane. While the first scientists, expressing the vision of an expanding greenhouse effect with temperature and in consequence an eustatic sea level rise (Arrhenius 1896; Callendar 1938; Flohn 1941, cited in Lausch 1989) found little attention or enthusiastic response, at present an almost overheated scientific climate and preferably apocalyptic predictions thtcaten to misinterpret the real facts, needs and situative, curative potentials. We also should not ignore the main trend of decreasing C02 concentration over most of the geochemical and biochemical evolutionary phases of the past, with at least five times the present level still during Tertiary times and about 200 ppm after fluctuations during glacial and interglacial periods at the end of last Wisconsin-, Wurmian-, Weichselian glacial. Since even the present 350 ppm are at the lower end of the plant physiologically suitable C02 range, could there have been an acute C02 deficiency developing, and the C02 rise since begin of industrialization in reality being beneficial in our endeavour to increase food production for the growing world population ? The temperature rise of 0.7"C since 1860 and a sea level rise of about 17 cm are acknowledged by most climate research units, but a highly rated group of scientists from the G.C. Marshall Institute in Washington, D.C. draws attention to a better correlation between the observed trend in temperature and the solar activity/sun spot activity than the more commonly considered increasing C02 concentration (ref. Economist Vol. 313, No. 7633, 1989). R.S. Lindzen from M.I.T. Boston a.0. reported to be expecting nominal temperature increases only. Other critical observations focus in many different ways on the overestimation of the C02 concentration change and neglect of the importance of changes in atmospheric moisture level, which, as mentioned before, is undisputed the major promoter of the basic greenhouse effect. While the determination to reduce the release of the other greenhouse active trace gases, such as CH4, N 2 0 , CFCs, tropospheric ozone (see overview in Table 1.2) is apparently worldwide accepted, a production oriented pedologist/plant nutritionist can argue, whether the rise of C02, which is expected to enhance especially C3 photosynthetic efficiency and to improve the water economy of plants due to closing of stornatal aperture with increasing C02 concentration, which even under rising temperature and water evaporation may also conserve precious water (Schleser and Kirstein 1990), would be really all that bad. Fig. 1.5 shows the wide range of C02 concentration versus light intensity capable of increasing photosynthetic efficiency. The relative effect of increasing C02 on the major cultivated plants as well as the most obnoxious weeds requires thorough attention.

Historical overview of the greenhouse effect

Table 1.2

Greenhouse active and other (polluting)trace gases, basic pool sizes

Trace gases

% share of antrogenic

GHE co2 CH4 CFCs 0 3 (tropospheric)

co2

50 19 17 8 6 Residence time Concentration 100 y 350 ppm

co

1 - 6 months

CH4 CFCs (ClOx -radicals)

10 Y 50 - 150 y

100-150ppb N 40-80 ppb S (N, S. hemisphere) 1.7 ppm 0.2 - 0.3 ppb

N20

170 y few days only

0.31 ppm 0 - 100 ppb

N20

Components

NOx (NO, NO21 0 3 (stratospheric) 0 3 (tropospheric)

OH (atmospheric)

so2 Atmospheric C-pool Photosynthesis (terrestr.) Soil organic matter pool Ocean C-cycle flux

Fossil fuel C

11

few seconds only

10 ppm (35 km) 0.02 ppm (0.1 ppm max.) < O.oooO1 ppb

GHE-rising potential of trace gases rel. to c02 1 32 14 - 17,000 2000 150 Increase per year (1800->280, 1950>310); ca. 0.5% variable

1.1 % (18 ppb) 5% 4% 0.3 % (ca 1 ppb) 0.2 - 0.3 % (stratospheric)

0.5 %

50 ppb (max.) 740 bil t 115 bil t (ca 1/2 respired, ca. 1/2 Wmpo@ 1.8 x 10l2 t

38.5 x 10l2 t (3x 109tpery precipitated as carbonate) 5 - 10 x 1012 t

The vegetation belt, which may be particularly affected by increasing heat and drought, the inigation-dependent and responsive sub-tropics, may hopehlly

12

H.W. Scharpemeel and P . Becker-Heidmann

replenish water deficits by stepped up sea water distillation, which may become technically feasible in nearer future. Besides, the leading Russian climatologist from Leningrad, M.I. Budyko (ref. Spiegel 1990) expects even for the (semi)arid tropics more rainfall and a vegetation cover similar to that of the Pliocene. Increase of temperature and precipitation in the boreal belt could bear grave consequences due to enhancement of organic matter decomposition and consequent COs release, but may also hold unforeseeable opportunities to increase agricultural production in vast areas of so far low productive boreal lands, which may even become important carbon sinks (see for more details Chapters 16 and 17). The catalogue of pros and contras of effects of climate change is certain to expand. I

Net photosynthetic rate for different light intensities and C 0 2 concentrations Rp (mg C O P / q m

I Fig. 1.5

s)

I light Intens.. Rp net photosynth. r a t e

Influence of light intensity and CO;, on photosynthesis. (modified from Mengel and Kirkby 1979,acc. to Warren-Wilson 1969)

We should be critically alert towards the climate change syndrome, but as critically open to the more constructive and may be even optimistic arguments before destroying productive structures without having replacements in panic, through poorly conceived legal actions as well as preventive or curative measures, . The most important reaction, though, should be to prepare t k follow-up phase of a mixed hydrogen plus carbon trip. In geological times the geochemical cycle is absolutely dominating and decisive for CO2 concentration and its influence on temperature. However, the anthropogenic shortcut of the

H k l o r i c a l overview of the greenhouse effect

13

biochemical cycle that we practice with wasteful consumption of fossil fuel reserves, with rising population and living standards, may suffer under t k unsentimental regime of natural processes, such as temperature and sea-level rise, to destroy our species and civilization (only a fast forgotten flicker in earth history), We must therefore concentrate all our efforts on the development of the photovoltaic hydrogen technology for replacement of C-based fossil fuels, as well as on the methodology for use of sun energy in desalination of sea and brackish ground water to stabilize life and productivity in the (semi)arid lands.

REFERENCES Asimov, 1. (1984). Asimov’s new guide to science. Basic Books Publ., New York. Aylmore, L.A.G. and J.P. Quirk (1960). Domain or turbostratic structure of clays. Nature 187. 1046- 1048. Berner, R.A. and A.J. Lasaga (1990). Simulation des geochemischen Kreislaufs. Spektrum der Wissenschaft 5, 56. Bitterli, P. (1963). Aspects of the genesis of bituminous rock sequences. Geol. Mijnbouw. 42, 183-201. Bordovskij, O.K. (1965). Accumulation and transformation of organic substances in marine sediments. Marine Geology 3, 3-1 14. Calvin, M. and J.A. Bassham (1962). The photosynthesis of carbon compounds, W.A. Benjamin Inc., New York. Degens, E.T. (1967). Diagenesis of organic matter. In: Diagenesis in sediments, Larsen, G. and G.V. Chilingar, Eds., Elsevier, Amsterdam, chap. 7. Dudal, R. (1990). Global Soil Change, report of an IIASA-ISSS-UNEP Task Force Meet. on the Role of Soil Global Change, Chap. 3 (in print). Esser, G. (1990). Modeling global terrestrial sources and sinks of COz with special reference to soil organic matter. In: Soils and the greenhouse effect, A.F. Bouwman (Ed.) (1990). John Wiley and Sons, Chichester. Fond der Chemischen Industrie, Umweltbereich Luft (1987). Vol 22, p. 15. Haber. H. (1965. 1971). Die Entwicklungsgeschichte der Erde, Deutsche Verlags Anstalt, Stuttgart, p. 79, p. 208. Lausch, E. (1989). Treibhaus Erde. CEO (Gruner u. Jahr, Hamburg) 37,46-49. Mengel, K. and E.A. Kirkby (1979). Principles of Plant Nutrition. Int. Potash Institute, Bern, Switzerland, 233. Murphy, M, B. Nagy, G. Rouser, and G. Kritchevsky (1965). Analysis of sulphur compounds in lipid extracts from the Orguiel meteorite. J. A. Oil Chem. Soc. 43, 189.196. Ramanathan, V. (1989). Spurengase, Treibhauseffekt und weltweite Erwrmung, In: Das Ende des blauen Planeten ? Crutzen and Muller (Eds) Beck, Federal Republic of Germany, 6576. Rankama, K. (1948). New evidence of the origin of pre Cambrian carbon. Bull. Geol. Soc. Am. 59, 389-416. Raval. A. and V. Ramanathan (1989). Observational determination of the greenhouse effect. Nature 342, 758-761. Schilder, F.A. (1956). Lehrbuch der Allgemeinen Zoogeographie, Jena, German Democratic Republic. Schleser, G. and W. Kirstein (1989). Der Treibhauseffekt. Ursachen und Konsequenzen fur

14

H.W. Scharpenseel and P . Becker-Heidmonn

Klima und Biosphre. Seminar Technik und Gesellschaft, KFA Jlich, Federal Republic of Germany (preprint). Spiegel (1990). M.I. Budyko - Interview. Der Spiegel, Hamburg, 1, 143. Theng, B.K.G. (1979). Formation and Properties of Clay Polymer Complexes, part 3, Chap. 12, 283-314. Theng. B.K.G. and H.W. Scharpenseel (1975). The adsorption of 14-C labelled humic acid by montmorillonite. Proc. Internatl. Clay Conf., Mexico City, 643-653. Valeton, I. (1983). Klimaperioden, lateritische Verwitterung und ihr Abbild in den synchronen Sedimentationsrumen. Z. Dtsche Geol. Ges. 134, 2. Warren-Wilson, I. (1969) Maximum yield potential. In: Transition from extensive to intensive agriculture with fertilizers, Proc. 7th Coll. Intern. Potash Institute, Bern, Switzerland, 34-56. Welte, D.H. (1969) Organic matter in sediments. In: Organic Chemistry, Springer, Berlin, 262-264. Wunderlich, H.G. (1968). Einfhrung in dic Geologie, Vol. 1, Exogene Dynamik. Bibliographisches Institut, Mannheim. Federal Republic of Germany. Wurmbach, U. (1971). Zoologie. Vol. 2, G. Fischer Verlag, Stuttgart.

15

Chapter 2

INPUTS TO CLIMATIC CHANGE BY SOIL AND AGRICULTURE RELATED ACTIVITIES Present status and possible future trends A.F. Bouwman and W.G. Sombroek International Soil Reference and Information Centre P.O. Box 353, 6700 AJ Wageningen, the Netherlands

ABSTRACT The most important soil borne and land use related greenhouse gases are carbon dioxide

(COz), methane (CHd and nitrous oxide (N20). The present annual increase of atmospheric CO2 is 0.5%. The total emission of C 0 2 is 6.5 to 7.5 Gt C y-'. Fossil fuel combustion contributes 5.7 Gt C y-*. The present global rate of deforestation of 10 to 20 million ha y-l causes an emission of 1 to 2 Gt C y-' including the release of C 0 2 from soil organic matter oxidation. There is uncertainty about the sinks of C02. The oceanic uptake is less than 1 Gt C y-1, while the atmospheric accumulation accounts for approximately 3.5 Gt C. Increasing net primary production and other terrestrial sinks balance the budget. The emissions from fossil fuel use will probably increase, and projections of efficiency and magnitude of future energy use are rather uncertain. Deforestation will continue in the coming decades to satisfy the growing demand for agricultural land. The atmospheric concentration of CH4 is rising at a rate of 1% y-'. The major part of this fast increment is caused by increasing emissions, while a minor part can be attributed to decreasing destruction in the atmosphere. The total annual emission from all sources is 400 to 640 Tg CH4. Biotic sources make up about 80% of the total annual emission, the rest is from fossil sources. The biotic sources of CH4 are: wetland rice cultivation (20%of the total source), natural wetlands (20%). ruminating animals (15%). landfills (10%). oceans and lakes (5%) and biomass burning (15%). The contribution by termites is very uncertain. Most sources are increasing at present. Nitrous oxide is increasing at a rate of 0.2 to 0.3% and its sources are almost exclusively biogenic. Nitrous oxide is inert in the troposphere, but it destroys stratospheric ozone ( 0 3 ) . The causes of the increase in atmospheric N 2 0 are not well known. Fossil fuel combustion is a minor source of N20. Increasing use of N-fertilizers in agriculture is a growing source of N2O. The emissions from natural ecosystems are not well known at present .

INTRODUCTION Atmospheric gaseous constituents which are able to absorb thermal radiation and thus contributc to Lhe trapping of heat in the atmosphere are water vapor (H,O), carbon dioxidc (CO,), methane (CH,), nitrous oxide (N,O), ammonia (NH,), halocarbons (the most important are the chlorofluorocarbons, CFCs), and ozone ( 0 3 ) . Of Lhcse, CO;?, CH4, N 2 0 and NH3 are produced in natural and

16

A T . Bouwman and W . G . Sombroek

agroecosystems. To assemble a complete picture of the role of soils and land use in the greenhouse effect, it is necessary to attend to indirect effects of other gases as well. Indirect effects of a source change (i.e. soil change or land use change) are induced changes in a chemical species which affect a given valued atmospheric component through an intermediate influence on another chemical species. Atmospheric constituents with biotic sources having indirect effects on concentrations of the greenhouse gases listed above are carbon monoxide (CO), non-methane hydrocarbons (NMHC, isoprene, C5H8, and terpenes), nitric oxide (NO) and nitrogen dioxide (NO,; NO and NO, as a group are denoted by NO,), ammonia (NH3), oxides of sulphur (SO,), and organic S compounds. Ammonia has indirect effects as well: about 10% of atmospheric ammonia is oxidized to NO and NOz, which play a catalytic role in various photochemical reactions in which 03,CH,, CO and OH are involved. Carbon monoxide is oxidized to CO, thereby affecting many other atmospheric constituents, such as ozone (03). hydroxyl radicals (OH) and CH4. Non-methane hydrocarbons are oxidized by O3 to CO in the atmosphere.

Table 2.1 Residence time of the major greenhouse gases, their rise, atmospheric concentration, radiative adsorption potential and contribution to global warming Type

co2 co CH4 N20 03 CFCs'O

Residence time (y)

Annual

1985

rise (%)

concentration

0S3 0.6-1.07 15 0.256 2.02 3 .02

100' 0.24 8-123 100-2006 0.1-0.32 65-1102

Radiative Contribution absorption to global potential 9 warming 9 345 ppm3 1 50 90 ppbz n.a. n.a. 32 19 1.65 ppm7 300 ppb6 150 4 n.a.8 2,000 8 0.18-0.28 ppb > 10,000 15

-',

Total sources Q is 5-7 Gt C y and atmospheric burden B is 720 Gt. The following relation exists: B = Q x T (see Cicerone and Oremland 1988). The lifelime of C 0 2 must thus be f 100 y (strictly speaking the residence time of C 0 2 is shorter when exchanges between atmosphere and biosphere on the one hand and atmosphere and oceans are allowed for. In that case however, the true importance of C 0 2 is underestimated; Ramanathan et al. (1985) (data for 1980); Bolin (1986); The residence time of CO is not a single constant number, because spatial and temporal variations of sources and sinks are not identical. Total sources and average atmospheric concentration are not known accurately, bu1 accounting for the uncertainties Cicerone (1988) estimates the residence time of CO at 2-2.5 months; Cicerone and Oremland (1988); Crutzen and Graedel (1986); Bolle et al. (1986); 0, vanes from 25 ppb at surface to 7 0 ppb at 9 km (Ramanathan et al. 1985); Enquete Kommission des 11. Deutschen Bundestages "Vorsorge zum Schutz der Erdatmosphare" (1988); "Data presented are for the two major CFCs. Reprinted, with adaptations from Bouwman (1990). by permission from Wiley & Sons, Chichester.

D~

~, ....

-O.

. I . . I -

......

C"

I,

The role of water vapor will not be discussed here. By far the most important other atmospheric greenhouse gases from soil and agriculture related sources are C02, CH4 and N20. These will be discussed in more detail in this paper. We will discuss some chemical aspects of CO in the context of atmospheric chemical reactions of methane. For an overview of the sources and sinks of CO, the reader is referred to Cicerone (1988). A review of the other trace gases not discussed here is presented in Mooney et al. (1987). Due to their relatively long atmospheric residence times C02, CH4 and N20 have important effects on the radiative balance. Some of their characteristics are compared with a number of non-biogenic gases in Table 2.1. The information on the sources and sinks of C02, CH4 and N20 and the possible causes of their increase will be summarized below. In Table 2.3 the global sources and sinks of the three major gases discussed in this paper are summarized.

CARBON DIOXIDE Sources of CO,

The major sources of CO;! are fossil fuel combustion, gas flaring and cement manufacturing, which produced 5.3 Gt CO2-C y-1 in 1984 (Rotty 1987) (Gt = gigaton; 1 Gt = 1015 g), while the 1987 emission was 5.7 Gt C y - 1 (CDIAC 1989). The C02 emission from these sources will amount 2 to 20 Gt C y-l (Keepin et al. 1986), depending on hture efficiency of energy use and shifts to non-carbonaceous sources of energy. Past release of C02 from land use modifications has contributed significantly to the present atmospheric CO;? concentration. Today deforestation and increasing shifting cultivation are responsible for only 1-2 Gt C y-' (Table 2.2). The disagreement between the different suweys of deforestation shown in Table 2.2 is in the fate of fallow lands in shifting cultivation, which at present is being replaced by non-sustainable systems called "sedentary shifting cultivation" or "forest farming" (Houghton et al. 1985), whereby the forest is often not able to re-establish on fallow lands due to soil nutrient depletion. Data presented by INPE (1989) suggest that the deforestation in the Brazilian Amazon region is much slower than the rates presented by the authors quoted in Table 2.2. Part of the CO;?sources shown in Table 2.2 stems from soil organic matter oxidation. Detwiler and Hall (1988) estimated that this soil C 0 2 emission is 0.1 10.25 Gt C y-I for the tropics. Armentano and Menges (1986) estimated that the net release from wetlands as a consequence of drainage, calculated as the sum of loss of sink strength and gain of source strength as a result of wetland drainage, is 0.15 to 0.1 8 Gt C y-l. The role of weathering on fluxes of C02, which often is totally neglected, is discussed in Van Breemen and Feijtel (1990).

18

A P . Bouwman and W.G.Sombroek

Sinks of C O ,

The release of C02 from fossil sources and from land use modifications is being balanced by atmospheric accumulation uptake of C02 in the world's oceans and by the terrestrial biosphere. The increase of 0.5 % y - l in the C 0 2 concentration in the atmosphere accounts for about 3.5 Gt C y-l. The uptake of C02 by the oceans may be less than 1 Gt y - l (Tans et al. 1990). Increased atmospheric C02 concentrations stimulate net primary productivity considerably, and moreover plants will utilize water more efficiently (see Sombroek, Chapter 13 of this volume, for some details). Modelling results (Esser 1987, 1990) suggest that the C02 fertilizing effect is responsible for a growth in net primary productivity which since around 1970 would overcompensate the losses from clearings. The terrestrial biosphere was a small sink of CO;! of about 0.3 (Goudriaan and Ketner 1984) to 0.5 Gt C y-l (Esser 1990) in the early 1980s. The world's wetlands may sequester carbon, while formation of caliche (calcium carbonates) in desert areas is proposed to be a small but important sink. An additional sink of carbon may be the formation of charcoal or inert C , one of the products of biomass burning, which may even amount up to 0.5 - 1.7 Gt C (Seiler and Crutzen 1980). Table 2.2 Annual release of COZ for the early 1980sfrom terrestrial biota including soils caused by deforestation and increasing areas of shifting cultivation, demonstrating uncertainties in estimates. Release rates in Gt C y-I; areas cleared in 106 hay"

2 References

World

Tropics

Houghton et at. (1987)

1.0 - 2.6

0.9 -2.5

Detwiler and Hall (1988)

0.3 - 1.7

0.4

- 1.6

Area of permanent clearing

in the tropics low: 6.0 a high:15.2 low: 3.0 medium: 10.6 high: 15.2

F A 0 (1983); Myers in Houghton et al. (1985); Seiler and Crutzen (1980); Lanly (1982); ' Detwiler and Hall (1988) concluded from results in other studies that temperate forests contributed -0.1 to +0.1 Gt C y - ' in 1980; their own analysis considers only tropical deforestation. B o ~ hlow and high figures of forest biomass were used in the presented estimates. The low estimate for the tropics is based on forest volume figures: 90 t C h a - ' for closed and open forests, respectively (Brown and Lug0 (1984). The other estimate which is based on destructive sampling yields higher values of between 164 and 40 I ha-' for different types of tropical and subtropical forests (Brown and Lugo, 1982). Reprinted with adaptaoons form Bouwman (1990b). by permission of Butterwonh Scientific Ltd, UK.

Inputs to climatic chonge by soil and agriculture related activities

Table2.3

19

Global emissions and sinks of major greenhouse gases. G t = gigaton, 1 Gt = g, Tg = teragram, I Tg = 10l2 .

co2 Global annual 6.5- 7.5 Gt C emission* % Biotic 20-30

CH4

N20

400-640 Tg CHq

11-17 Tg N

70-90

90-100

Sources*

fossil fuel use (5.7 Gt) deforestation and shifting cultivation (1-2 Gt)

rice paddies (60-140 Tg) cultivated soils (S Tg?) wetlands (40-160 Tg) natural soils (?) ruminants (65-100 Tg) fossil fuel (?) termites (10-100 Tg) landfill sites (30-70Tg) oceansflakes(15-35) biomass burning (50100 Tg) fossil (50-95 Tg), coal mining/gas exploitation

Sinks*

atmospheric accumulation (3.5Gt) Oceans (1WC

C '

300-2500

Period with Annual soil temp. < precipitation O", months (P),mm -24-36 >8pf (per 250-800 mafrost) +1-26 0-8 400-800

100-1000

+10+20 +15+18

500-3500 1000-1600

+6-28 -12-28

0-8 5-8

450-2200 500-800

100-1000 180-300

PC

+12+22

1500-3500

+6-20

0-8

600-2500

150-1700

PC

+12+16

500-1000

-36-40

>8pf

300-500

50-200

st

+10+12

500

-6-16

5-8

250-400

100-200

st

+14+20

800-2000

-6-25

5-8

500-700

100-350

January

P-ETo, mm

0-300

. s d '/1 e

f:aR a

it

5

st

+16+20

1500-2500

+6-20

0-5

600-1000

50-450

9

St

st

+4+10 +12+20

300 500-2200

-8-38 +I-25

>8 pf 0-8

200-600 500- 1000

100-400 50-450

Do

st

+16+20

1500-3500

+5-20

0-8

500-1000

50-450

st

+4+12

500

-17-38

>8 pf

300-500

100-300

St

+8+18

300-1000

-24-50

>8pf

200-600

0-300

PC

+8+16

300-1000

-24-36

>8pf

300-800

0-400

PC

+12+18

1000-2000

-1-34

2->8 pf

500-1000

200-600

T t

9'

3.PV 19-

Soils on a wormer earth: boreal and subpolar regions

3 o S P I PZ-

3 O Z I + I p+

.-U

3052-I I+

309I+I ZI+

d

3.0Z+1OI+

SLEP

.000I

SLEP OP

SLEP OSI-09

.00zz-o001

001-OP .00zz-o00 I

193

194

S.V. Goryachkin and V.O. Targulian

major part of soils alteration was so far studied by reconstructing the rather slow soil evolution, connecting it with long-term climatic changes, but seldom as forecasts of fast changes in the future. Pedologists proposed some ideas which can be used for predicting soil change (Jenny 1941; Rode 1947; Nikiforoff 1949; Hekstra 1988; Walker and Graetz 1989).

PRESENT CONCEPTS AND THEORETICAL BACKGROUND Some existing pedological concepts can be used as an approach to this problem: 1) The concept of soil evolution as proposed by Rode (1947) has been further developed in many publications. Climate induced soil changes can be considered to be analogous to natural soil evolution caused by long-term climate change; 2) The concept of “soil sensitivity” (Sokolov and Targulian 1976; Fedoroff 1987; Yassoglou 1987) supposes that individual soils have their own ways of responding to climate changes; 3) The concept of characteristic response time of soil properties or processes (Armand and Targulian 1974) assumes that soil processes need varying periods of time to come into quasiequilibrium with the environment after its change; and 4) The concept of soil chronosequence (Jenny 1941; Yaalon 1971) supposes that some soil changes in space could be assumed as time changes if the soils have similar environments but different ages. Pedologists have experience in substituting soil change in space for temporal soil change. This experience can be used as the basis for predicting future climate induced changes of soils. Above theoretical concepts serve as a starting point for our study. The most important sources of world and boreal soil information are the world soil maps, particularly the most comprehensive ones. Soils of the World (USDA 1972), Soil Map of the World (FAOKJNESCO 1977) and Soil Map of the World (Glazovskaya and Fridland 1982). One can obtain information about the: 1) distribution of the main soil units, including the distribution of diagnostic soil horizons (USDA and FAO) and soil temperature and hydrological regimes (partially USDA, Glazovskaya and Fridland); 2) distribution of the main texture classes (FAO, Glazovskaya and Fridland); 3) soil phases (FAO); 4) slopes (FAO); and 5) soil cover patterns (Glazovskaya and Fridland). This information is mainly static, whereas in order to predict soil changes we nced some facts about soil dynamics. Unfortunately, there is no temporal data base for world or boreal soils. This knowledge is disseminated in many publications on soil chronosequence investigations and on monitoring station data. One of the most serious obstacles in predicting climate induced soil changes is the lack of data on quantitative relationships between labile soil features and climatic characteristics. The main approach to predict climate induced rapid soil changes is the consecutive expert evaluation of soil properties, processes, bodies and soil cover changes.

Soils on a warmer earth: boreal and subpolar regiom

195

BOREAL SOILS: THEIR ENVIRONMENTAL CHARACIERISTICS AND "ECOLOGICAL GROUPS" Based on soil map analysis, 26 boreal and 5 subboreal and subpolar soil units were selected that represent more than 90% of the soil cover. Every soil unit area was compared with some maps of the World Agroclimatic Atlas (1972) and the climatic range for every soil unit was determined. The information on textural classes was taken from FAO/UNESCO (1977), the hydrological regimes from Glazovskaya and Fridland (1982). The result of this analysis is shown in Table 17.1. As shown in the table, soil units which developed on calcareous and coarse parent material, and soil units with stagnant hydrological regimes, have t k largest climatic amplitudes. This analysis allows us to create a matrix table in which soil units are distributed according to their environmental characteristics. Using this table, t k main environmental soil groupings were made. The result of this exercise is shown in Table 17.2. Some cells of this table are empty due to the lack of such combinations of climate, relief and substrata. Using the knowledge about soil property dynamics gathered from monitoring stations and based on soil chronosequence investigations, we compiled the ranged sequence of soil properties in accordance to their characteristic response times or time changeabilities. These soil properties are used for soil unit and subunit diagnostics in the revised legend of the Soil Map of the World (FAOAJNESCO 1988). We added a wide set of soil regimes, biotic and other characteristics to those properties (see Table 17.3).

QUALITATIVE EVALUATION OF THE MAIN BOREAL AND SUBPOLAR SOILS AND CHANGES IN THEIR PROPERTIES DUE TO CLIMATE CHANGES. Nine subpolar and boreal soil units, including 14 soil subunits, were analyzed on probable future changes. Other soil subunits have much in common with their ecological neighbors, so we evaluated only their possible classification position change. We did not analyze all the soil properties listed in Table 17.3. For example, we left out the properties with characteristic times of more than 1000 years, because it is not reliable to analyze relatively stable properties. Orthic, humic and ferric Podzols

These 3 soil subunits (Table 17.4) are distributed widely in boreal, subboreal and even polar belts, both in their humid and subhumid segments, and are closely connected to coarse acid parent materials. The temperature regime and moisture content of Podzols change rapidly, in close correspondence to climate

196

S.V. Goryachkin and V.O.Targulian

change: less precipitation - lower moisture content, more heat - warmer temperature regime, etc: Table 17.3 Soil features and properties with differeni characreristic time

Characteristic Time in Years

Soil Features and Properties

10'

heat regime, aeration regime, composition of gases, composition of solutions, moisture content, microbiota moisture regime, fertility regime, annual biota, litter properties, pH, base saturation, salinity/alkalinity,fluvic, gleyic and stagnic properties, permafrost, gelundic phase, inundic phase, salic phase humus content and composition (topsoil), relative fertility status, salic, calcareous, sodic, vertic properties, histic (< 20 cm), ochric A, gypsic, albic E (in podzols), spodic (immature) horizons, placic phase

n.10' - 10'

n.10' - lo2

(Weak)

n-102 - lo3

tree roots, color (yellowish,reddish), Fe-concretions, depth (in loose parent material), clay cutans, interfingering,smeary consistence, andic properties, histic (> 20 cm), mollic, umbric, calcic, albic E (in soils of medium and fine texture), cambic, spodic (mature) horizons, placic phase

The waterhydrological regime remains percolative because of the enormous permeability of the coarse textured substrata. Due to increasing temperature, th? intensity of bioproductivity and biogeochemical cycles would escalate, and characteristics such as base saturation, humus content, relative fertility status and pH would increase. The litter and histic horizons, if any, would become thinner, and at the same time an ochric A horizon would occur in the upper part of the Podzol profile. Due to humidity and temperature increase, the leaching would intensify and there could be some discrepancy between processes of accumulation connected with increased bioproductivity, and leaching processes that could result in changes of pH and humus content. Gleyic properties are correlated with humidity - if it becomes less humid, there will be less or even no gleyic properties. In the case of increased temperature and moisture, an albic E horizon could remain the same or become thicker, and it could be replaced by an ochric A horizon due to warming and aridization. A spodic B horizon would remain the same or become thicker in accordance with future warming and humidization. So, the sequence of Podzol alteration after climate change would be: < 10 years - alterations of some properties within the same sub-units; 10-100years transformation of some humic Podzols into orthic ones and some orthic Podzols into ferric ones (warming + aridization ) .

197

Soils on a warmer earth: boreal and subpolar regions

Table 17.4 Orthic, humic andferric Podzols

Characteristic Time in Years

Properties

100 years - transformation of some Podzoluvisols into orthic and gleyic Luvisols (warm humidization) or into orthic Greyzems (warming + aridization). Table 17.5

Dystric Podzoluvisols

Characteristic Time in Years

Properties

< 1

heat regime moisture content water regime PH base saturation litter thickness gleyic properties humus content rel. fert. stat. histic horizon ochric A horizon clay cutans interfingering mollic horizon albic E horizon

1-10'

n.10' - lo2

n.1o2 - lo3

Result

Climatic Scenarios H um idization Aridization Warming Warming warmer warmer more less Same same, impercolative same, higher higher same, higher higher same, thinner thinner same, more distinct loss more more higher higher, same no, Occurrence no no, Occurrence occurrem more same more distinct same no occurrence same, thinner thinner orthic and orthic Greyzems gleyic Luvisols

D yst ric Cambisols Dystric Cambisols occur in the humid segments of the boreal belt on basic, intermediate and even acid paEnt material of coarse and partially medium texture. These soils would have some alterations similar to those of Podzols (Table 17.6). The percolative hydrological regime of some dystric Cambisols could change more distinctly in comparison with Podzols - it could become periodically impercolative in the case of aridization because of its partially finer texture. Humus content change is similar to that of Podzoluvisols, as there is no complicated combination of accumulative and illuvial humus (as in Podsols) in

199

Soils on a warmer earlh: boreal and subpolar regions

dystric Cambisols. Cambic B horizon would remain the same (aridization) or even become thicker (warm humidization) because of the increase in weathering intensity. The umbric A horizon would become thicker (warming + humidization) or even transform into mollic A horizon (warming + aridization). Thus, we suppose the following succession of dystric Cambisols change: c 100 years appearance of humic Cambisols among eutric ones (in the case of aridization); > 100 years - transformation of some humic Cambisols into haplic Phaeozems (warming + aridization). Table 17.6

Dyszric Cambisols

Climatic Scenarios Characteristic Time in Years

Properties

< 1

heat regime moisture content water regime

1-10]

PH n.10' - lo2

n.1O2 - lo3

Result

base saturation litter thickness humus content rel. fert. stat. histic horizon spodic B horizon mollic horizon umbric A horizon cambic B horizon

Humidization

Warming warmer more same same, higher same, higher thinner more

higher thinner, loss no more thicker

thicker dysmc and eutric Cambisols

Aridization Warming warmer

less same, impercolative higher higher thinner more higher loss no occurrence trans. to mollic same

eutric and humic Cambisols, haplic Phaeozems

Rendzinas Rendzinas develop on calcareous substrates of different textures (predominantly coarse) in both humid and subhumid segments of boreal, subboreal and polar belts. These soils have a very wide ecological amplitude (Table 17.7). The hydrological regime of these soils would remain percolative in spite of any climate alteration because of the high permeability of coarse or wellstructured soil material. There could be some alterations of pH but it would still remain alkaline or neutral and weakly acid only in the upper horizon. They would be base-saturated even in spite of humidization. The litter thickness would decline due to warming because of more intensive transformation of litter. Permafrost

200

S.V. Goryachkin and V . O . Targulian

could change or disappear due to various climatic alterations but it would never play a role in the formation of these soils because of its dryness. Humus content and composition will remain the same or change slightly due to calcareous soil mass, but the store of organic carbon could increase with climate warming because of the upper horizon thickness alteration. In spite of the expected change of leaching intensity, calcareous properties would remain the same. Perhaps long leaching after the climate has become warmer and more humid would result in a notable decline of CaC03 content. In this case even a cambic B horizon could occur in a few Rendzinas. Mollic horizons could become thicker or occur in Rendzinas due to higher bioproductivity in a warmer climate. Thus, Rendzinas have only slight changes after climate changes; only after more than n"100 years some Rendzinas could become calcaric cambisols (warming + humidity) Table 17.7 ~

~~

~~

Rendzinas ~

Characteristic Time in Years < I 1-10'

n-10' - lo2

n.10~- lo3 Result

~

Climatic Scenarios Humidization Aridization Warming Warming heat regime warmer Warnla moisture content more less water regime same same lower same PH base saturation same same litter thickness thinner thinner gleyic properties no no permafrost no, deeper no, deeper humus content same same rel. fert. stat. same same calcareousproperties less distinct same histic horizon no no mollic horizon thicker, Occurrence thicker, Occurrence cambic B horizon no, Occurrence no Rendzinas, rarely Rendzinas calcic Cambisols Properties

Eutric and dystric Gleysols

Eutric and dystric Gleysols have poor or very poor drainage caused by their relief and/or substrata conditions. They occur less in semihumid than in humid segments of boreal and subboreal belts, on acid, coarse, medium and fine parent materials. Their hydrological regime is stagnant. Some parts of these soils get

Soils on a warmer earlh: boreal and subpolar regions

20 1

their moisture not only from the atmosphere directly, but also from neighboring soils occupying higher positions. That is why expected changes of these soils are connected not only with climate changes directly but also with future changes of their neighbors (Table 17.8). The water regime of Gleysols of the present humid climate would remain the same in spite of different humidity alterations, but in some places in semihumid regions, aridization could cause the presence of some periods of water pulsation. Base saturation and pH would depend on climate change as well as on their initial values: in the case of warming, the bioproductivity would increase but it could result in a contrast change of these two properties only in dystric Gleysols, which would become more eutrophic. Gleyic properties are closely Connected with humidization: less humid - less distinct gleyic properties. Histic H horizon would increase in the case of humidization and decrease or even become replaced by an ochric A and then a mollic A horizons due to warm aridization. In some Gleysols of the semihumid regions (in hydromorphic relief positions), aridization could result in fundamental soil profile changes - the occurrence of mollic A, albic E, cambic B or Bt and spodic B (coarse substrata) horizons. The possible succession of Gleysoils may be the following: c 10 years - in accordance with climatic change some eutric Gleysols would be transformed into dystric ones; 10-100 years - some Gleysols would be transformed into Histosols (humidization) and some of them into gleyic Cambisols (aridization); > 100 years - in the case of warm aridization, some Gleysols and gleyic Cambisols would become mollic Planosols (or Luvisols) and gleyic Podzols (on coarse substrates). Eutric and dystric Histosols Eutric and dystric Histosols are soils of very poor drainage occurring in both humid and semihumid segments of boreal, subboreal and subpolar belts. These bog soils change very little in spite of different climate changes because of the extreme water content in the peat and because they occupy relief depressions which always get more water than any other relief position. This is why eutric and dystric Histosols are the only soils in our analysis which almost never change their moisture content due to humidization or aridization (Table 17.9). The majority of their properties remain the same. Only in some cases due to aridization and subsequent increase of ground and soil water mineralization, some Histosols get higher pH and base saturations. Only one property would certainly change wiLh climatic and bioproductivity changes - the thickness of a histic H horizon. In the case of warm humidization it would become thicker. In the case of warm aridization, the processes of peat growth due to higher bioproductivity would be hindered by peat mineralization processes due to less humidity, and the histic H horizon thickness could remain the same.

202

S.V. Goryachkin and V.O. Targulian

All possible changes, supposed to be very slight, could change a Histosol classification in 10 or n 10 years. Some dystric Histosols could become eutric (aridization) and vice versa (humidization). Table 17.8 Eulric and dysrric Gleysols

Characteristic Time in Years

Properties

1600 mm. Light shaded area: 200-800mm. Cross marks: rainfall observation stations. Thin broken line: 1OOOmm contour (derived from Nicholson African data set, in Makomura (Ed.)1989)

African ogriculiwe and ihe greenhowe effecl

237

CLIMATIC CHANGE AND LAND USE AND AGRICULTURE IN AFRICA Before tackling the more specific impacts of climate change on the African scene in general, and global warming in particular, it should be instructive to work at the general picture of land use on the continent. The current land use is very much governed by water availability whether this be in the form of rainfall, or in the form of water available for irrigation.

0

Fig. 20.3

UOE

Coefficient of the variability of annual rainfall (standard deviation of annual totalslannual mean). Unit: %. Shaded area: 20-40%. (derived from the Nicholson African data set, in Kadomura (Ed.) 1989)

238

R.S. Odingo

Fig. 20.4 is a generalised map showing the extent of water resources which can support agriculture on the continent, including irrigated areas, areas with adequate rainfall and the semiarid, and and extremely arid areas where water for crops becomes a problem progressively. In this map one cannot fail to notice the pcrennial problem areas where inadequacy of rainfall coupled with the lack of imgation water have resulted in the impossibility of any meaningful form of agriculture. Fig. 20.5 illustrates the expected response to the water situation which has evolved over centuries. I

I

I

Water ulitization for agriculture ze%zydams,

@

canals

...........

Main irrigation schemer

Water resources in relation to present economic requirements Areas with adequate rain

Semiarid areas

Fig. 20.4

Water availability for agriculture

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Fig. 20.5

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Lund use in Africa

This land use map shows areas where arable land is in abundance (largely because water for agriculture is available), pasture lands, tropical grazing (usually associated with the savannahs with adequate rainfall), dry steppe and semidesert grazing (where the shortage of moisture keeps out agriculture), the deserts , and the closed forests. The foregoing section has briefly sketched the current climatic background to agriculture in Africa. It is also possible to go into detailed agro-climatological zoning of the whole continent, as has been carried out by the United Nations

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Food and Agriculture Organization (FAO) and the International Institute of Applied Systems Analysis (IIASA) who prepared an Agro Climatological Map of Africa and followed this with an analysis of the potential population supporting capacities of the various agroecological zones for tropical Africa (FAO/UNFPA/IIASA 1986). The point that needs emphasising is that currently Africa is relying rather heavily on rainfed agriculture. However, in the projected climate change scenarios, there is likely to be increased availability of rainfall, hence soil moisture even if this is not evenly distributed regionally. It therefore now only remains to comment on the likely impacts on agriculture of the changed conditions which are expected to accompany global warming.

TYPES OF AGRICULTURE IN AFRICA AND THE LIKELY EFFECTS OF GLOBAL, WARMING Thc likely effects of global warming on African agriculture are expected to be uneven even if one were to assume a generally increased rainfall because the current agriculture is already sensitive to temperature in two particular subregions and subzones, namely: The subtropical parts of Africa in the "Mediterranean North" and "Mediterranean South" are currently referred to as areas of Mediterranean agriculture with cereals like wheat, orchards, vineyards and specialized crops which are all sensitive to even minor temperature changes and therefore likely to be impacted by the envisaged temperature increases ( I S O C ? ) under a global warming. High altitude areas within the tropics where currently temperate crops (including cereals like barley and wheat) are grown because of the reduced temperatures brought about by altitude.

For the rest of Africa and especially for tropical Africa current agricultural practices are likely to shield the agriculture from the adverse effects of a changed climate, in particular a warmer climate. Fig. 20.6 which shows the main types of agriculture in Africa brings out certain important features. There is for instance a preponderance of mixed cropping which is thought to be advantageous even in a changed climate because some crops will benefit from temperature increases where others suffer. In general, areas dominated by tropical crops are expected to bcnefit rather than suffer from increased temperatures. Even more important is the fact that the GCMs do not envisage very large temperature increases (1S"C) for these tropical areas. It is therefore somewhat hypothetical to try and guess how the agriculture is likely to respond to a changed climate where the possible change is expected to remain within the ranges which have always been experienced, at

African agriculture and the greenhouse effect

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least in the last 200 years. In the final analysis each crop will have its own unique response to changed or changing climatic conditions and it is here where some instructive information may be sought. Unfortunately, the bulk of the studies on these aspects has been carried out in temperate latitudes, so one can only infer what is likely to transpire in the tropics and subtropics where similar crops are found, as will be summarised briefly in the next section.

Fig. 20.6

Types of agriculture in Africa

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CLIMATIC EFFECTS ON SELECTED CROPS RELEVANT TO THE AFRICAN SITUATION Bach (1978) briefly analysed the effects of rainfall and temperature changes on corn (maize in Africa), and these are summarized in Figs. 20.7 and 20.8. In these illustrations it is shown that corn is very sensitive to both temperature and rainfall changes particularly during those months (July and August) where the combincd effects of temperature and rainfall are critical to their growth. The accompanyingprojected yield changes linked to temperature and precipitation are also summarised in Table 20.1 obtained from Bach (1978). According to this table expected changes would be significant enough to depress corn yields by up to 11%. 85

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Response of corn yields to temperature in the US corn belt (from Biggs a d Bartholic 1973, as cited in Bach 1978)

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Response of corn yields to rainfall during diferent stages of growth in the US corn belt Cfrrom Biggs and Bartholic 1973, as cited in Bach 1978)

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Table 20.1. Estimatedpercent change in corn yield due to changes in temperature and precipitation

Temperature Change in precipitation (% of normal *) change,"C -2 -1 0 +1.0 +2.0

-20 19.8 8.4 -2.9 -14.2 -25.6

-10 21.2 9.8 -1.5 -12.8 -24.2

0 22.7 11.3 0 -9.8 -22.7

+10 24.2 12.8 1.5 -8.4 -21.2

+20 25.6 14.2 2.9 -8.4 -19.8

Source: Benci et al. (1975) quoted in Bach (1978) p.155 * Normal = 85+16 bu/acre. 1901-1972 average for selected stations in Missouri, Dlinois, Indiana, Nebraska, Iowa and Kansas.

Two other crops which are also grown abundant in Africa and for which there are research results from other parts of the world are wheat and rice. Fig. 20.9 and Fig. 20.10, obtained from Yoshida (1978) and Asama (1976) respectively, show the intimate link between temperature changes and rice productivity, and between day/night temperature changes and wheat productivity. There is no doubt whatsoever that changed temperatures such as those exptected under a global warming will be highly significant for continued rice and wheat production with available evidence pointing clearly in the direction of possible drastic declines in the yields of these two key crops.

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Effect of increasing temperature on (he productivity of rice at different rates of radiation Cfrom Yoshida 1978)

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Effect of increasing temperature on grain development in wheat (from Asana 1976)

As far as the rice crop is concerned, it has hitherto been assumed that it should thrive under conditions of high temperatures, so that global warming could even be conducive to a higher rice productivity. Unfortunately, this is untrue. Sinha et al. (1988) have shown that rice yields tend to decrease markedly as temperature rises above 28°C (see also Fig.20.9). Table 20.2 based on Stansel and Huke (1975) and quoted in Bach (1978) gives some indication of expected percent deviation from world rice production when influenced by changes in temperature and precipiation, and from this it can be seen that global warming will bring with it many conditions, some of which will be clearly undesirable, even for Africa where rice cultivation though still insignificant has been increasing in the last few decades. Table 20.2 Percent deviation from world rice production, as influenced by changes in temperature and precipitation* P change Temperaturechange Total P in % in "C change in % -2" -lo -0.5" +0.5" +lo +2" % -15 -19 -13 -8 4 0 3 -8 -10 -17 - 1 1 -6 -2 2 5 -6 -5 -13 -7 -2 2 6 9 -2 +5 -9 -3 2 6 10 13 2 +10 -5 1 6 10 14 17 6 +15 -3 3 8 12 16 19 8 Temp. -11 -5 0 4 8 11 change

* Based on world production of 300 Mt.

Source: Stansel and Huke (1975)

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As far as agriculture in Africa is concerned, it is important to underline the fact that it is not the absolute magnitude of a climate change that will determine the nature of the effects as much as the change in climate relative to the existing or baseline conditions. For example, in tropical Africa, in theory, there will be a lengthening of the potential growing seasons in areas where it is now short due to the latitudinal as well as the altitudinal position. But in other cases there might even be a shortening of the required growing period because of local soil moisture and altitudinal circumstances. Such changes will also affect the maturation period of certian crops differently. As far as changes in crop yields are concerned, moisture, and especially soil moisture has been paramount in tropical and subtropical Africa. Unfortunately, a look at the GCMs does not provide consistent or confident estimates (Parry et al. 1986 and 1990) of regional precipiation changes. Second to rainfall (and hence soil moisture) is temperature and higher temperatures may ultimately rule out some crops alltogether. The work by Sinha et al. (1988) already quoted shows that beyond 28OC, rice yields for instance will be depleted. In the final analysis, if the climate changes projected are severe enough, the present crop cultivars may cease to be suitable for the changed circumstances. Fortunately for Africa, according to current GCMs, no conditions envisaged should be so severe as to rule out many crops. Much of tropical Africa has tended to rely on crops such as cocoa, rubber, oil palm, coffee and tea. Some of these crops should be able to absorb increased temperature if there is a corresponding increase in rainfall. As a result, higher yields may even be anticipated, but one is not always sure how the crops will react because of the lack of specificity in the projected conditions. What is known for certain is that climate change will first and foremost be felt in soils, and in turn in plant growth through changed photosynthesis. For those areas in Africa where there is currently high altitude farming (a.0. tea and coffee), global warming may bring drastic changes. It is possible that the current altitudinal zoning (agroclimatological zoning) may be seriously disoriented by increased temperatures, so that crops which now grow well at the higher altitudes (temperate crops) may totally disappear. Experimental results in Africa as to what to expect in crop plant performance under the changed soil moisture and temperature conditions are few and it may be safer to make some inferences from work in the tropics in other parts of the world. For example, it is fair to assume that under increased C02 there should be an increase in leaf photosynthesis, but it is not clear how this will affect African plants. In general carbon dioxide fertilization effects can partially offset the adverse climate, particularly for C3-plants (see also Chapter 13 by Sombroek), but i t would be unwise to rush to conclusions before field and laboratory experiments are carried out in Africa to establish the expected scientific results. According to Sinha et al. (1988) the higher yields in C3-crops are obtained

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around a daily mean temperature of 15°C and in C4-crops around 30"C, but it is necessary to accompany such generalisations with more detailed information on physiological requirements of each individual crop.

AGRICULTURAL ADJUSTMENTS TO COPE WITH GREENHOUSE WARMING Much of the agriculture practised in Africa is operated at a low to medium scientific level, so that even weather advises are rare. Because of this it would be unwise, if not impossible, to suggest very precise adjustments which could be made to cope with expected changes in climate. Among the existing options for adjustment, which are already being practised and some of which could be brought into full practice in the event of a climate change, would be the following: Germplasm improvements for drought-tolerance (this is already being implemented in Kenya with Katumani Composite Maize and other dryland maize composites like Taboran Composite in Tanzania), or for heat stress resistence could be undertaken; Appropriate research should now be commenced on simulated situations such as crop production responses to high temperatures to establish suitable germplasm requirements for the changed conditions; There is already the possibility for the substitution of crop species e.g. pigeon peas (Cujunus cujun) for soy beans (pigeon peas are already a very successful crop in the dryland areas of Kenya); Agricultural management changes could be introduced including multiple cropping already much practised in much of tropical Africa, and early planting, already a successful weather advisory practice in some countries like Kenya and Uganda; Africa (tropical) already has good experience with tree crops (e.g. coffee, cocoa, tea, oil palm etc.) and this should be the focus of intensified research to understand their place in a changed climate.

SUMMARY AND CONCLUSIONS The likely impacts of a changed climate due to increased levels of (maily) C02 are still difficult to project, largely because the models of change are still rather vague. That there will be significant effects on African agriculture cannot be doubted. There is evidence of some existing resilience in African agriculture which could enable it to cope wilh a changcd climatic situation, but it is quite clear that more intensive research will be required at national, regional, and global levels. to establish more accurate scientific facts which can form the basis for

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more informed policy formulation.

REFERENCES Asama, R. (1976). Plupiological approach to breeding of drought resistant Crops. ICAR Technical Bulletion, New Dehli. Bach, W. (1978). The potential consequences of increasing C 0 2 Levels in the atmosphere. 1. Williams J (Ed) (1978). pp. 141-167. F A 0 (1982). Methodology of agroecological studies in Africa. Rome. F A 0 FAO/UNFPA/IIASA (1986). Potential Population Supporting Capacities of Lands in the Developing World. Rome. FA0 Hansen, J. et al. (1981). Climate impact of increasing atmospheric carbondioxide. Science 213:957-66. Hansen, J., A. Lasis, D. Rind, S. Lebedeff, R. Ruedy and G. Russel (1988). The greenhouse effect: projections of global climate change. In: Effects of changes in stratropheric ozone and global climate. Nairobi, UNEP and EPA Kellogg, W.W. (1977). Effects of human activities on global climate. WMO Technical Note No. 156. WMO. Geneva. Kellogg, W.W. and R. Schware (1981). Climate change and society -consequences of increasing carbondioxide. Boulder Colorado, Westview Press. Manabe, S. and R.T. Wetherald (1986). Reduction in summer soil wetness induced by an increase in atmospheric carbondioxide. In: Effects of changes in stratrospheric ozone and global climate. Nairobi, UNEP/EPA. Nicholson, S.E. (1976). A climatic chronology for Africa: synthesis of geological, historical, and meteorological information and data. Unpublished Ph.D. dissertation, University of Wisconsin, Madison, 324 pp. Nicholson, S.E. (1978). Climatic variations in the Sahel and other African Regions during the past five centuries. Journal of And Environments. 1:3-24. Nicholson, S.E. (1979). The methodology of historical climate reconstruction and its application to Africa. Journal of African History. 20:3 1-49. Nicholson, S.E. (1980). Saharan climates in historic times.In: The Sahara and the Nile. M.A.J. Williams and H. Faure (Eds). Balkema Rotterdam. Nicholson, S.E. (1981). The historical climatology of Africa. In: Climate and history. T. Wigley. M. Ingram, and G. Farmer (Eds). Cambridge University Press, Cambridge. Pany, M.L. and T.R. Carter (1986). Effects of climatic changes on agriculture and forestry. In: Effects of changes in stratropheric ozone and global climate. Nairobi, UNEP. Parry, M.L., T.R. Carter and N.T. Konijn (Eds) (1990). The impact of climatic variations on agriculture. Vols 1 & 2, Reidel, Dordecht.. Sinha S.K., N.H. Rao and M.S. Swaminathan (1988). Food security in the changing global climate. In: Conference Proceedings on the Changing atmosphere. WMO, Geneva, pp. 167- 191. Stansel, J. and R.E. Huke (1975). Rice. In: Impacts of climatic change on the biosphere, CIAP Monograph 5 . pt. 2, Climatic Effects 4-90 amd 4-132. Washington, W.M. and G.A. Meehl (1984). Seasonal cycle experiment on the climate sensitivity due to a doubling of C 0 2 with an atmospheric general circulation model coupled to a simple mixed-layer ocean model. J. Geophys. Res. 89:9475-9505.

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Williams. J. (Ed). (1978). Carbondioxide, climate and society. Oxford, New York, Toronto, Sydney, Paris, Frankfurt, Pergamon Press. Yoshida. S. (1978). Tropical climate and its influence on rice. IRRI Research Paper Science 20. IRRI. Manilla.

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Chapter 2 I

THE AGRICULTURAL ENVIRONMENT IN LATIN AMERICA AND THE CARIBBEAN AND THE GREENHOUSE EFFECT N . Ahmad Department of Soil Science The University of the West Indies St. Augustine. Trinidad, West.Indies

ABSTRACT The Latin American region is diverse, representing a land mass of over 20,340 million km2. The area is not densely populated and only about 7% of it can be considered too dry for agriculture. There is a wide range of soils with all the orders represented, the six major ones are Ferralsol/Oxisols. Acrisols/Ultisols, Luvisols/Alfisols, Cambisols/ Inceptisols, Fluvisols/Entisols, and Phaeozems/Mollisols. The region is well known for very high levels of management for several perennial crops such as coffee, banana, citrus, cacao, oil palm and sugar cane. These individual crops probably approach forest conditions in terms of total photosynthetic activity and no serious fires are involved. The projected climatic change would lead to changes in rainfall distribution in different parts of the region which would necessitate a high level of technology in agriculture. The effect of the projected sea-level rise could be disastrous in several areas. Subsistence agriculture in the region is based on slash and bum and shifting cultivation with little capital inputs. Depending upon the soil nutrient reserves, the effect of this treatment on the soil is very variable. On the Oxisols, Ultisols and Alfisols of the Amazon basin with a total estimated area of nearly 7 million km2, soil deterioration is extremely rapid due to low reserves of fertility; shifting cultivation leads to large annual clearings of virgin forest, estimated at present at about 10 million ha. The burning which takes place probably adds about 625 million tons of CO, to the atmosphere annually besides reducing the capacity of the vegetation to absorb CO, in photosynthesis. The total contribution can be quite important in the global greenhouse effect. The cultivation of rice which is elsewhere associated with increased concentrations of methane does not have this objection in Latin America since over 75% of the crop is grown in upland conditions. On the other hand, the continually rising pasture fed cattle population throughout the region with subsequent methane production could be an important factor in the overall greenhouse effect. Ways to improve land use and crop production without increasing the concentration of greenhouse gases and adverse climatic change have been suggested.

INTRODUCTION The countries of South and Central America cannot be regarded as densely populated and the area has the highest percentage of land still under forest (63%) compared to the world average of 58% (Espig 1989). From areas with a suitable climate for crop production, only 6% are actually cultivated, 23% is under pasture

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and 46% under forests. Potentially, 35% could be cultivated, 40% can be used for pastures and/or forests and 25% should be reserved. The Caribbean area is an outstanding example within the region of an area having a high population density and hardly any unused land resources. In this paper, the possible effects of climatic change within the region on agriculture and land use are discussed. The present agricultural environment, the ways in which it contributes to the amount of greenhouse gases and global warming and what can be done to alleviate the problem are presented.

POSSIBLE EFFECTS OF GLOBAL WARMING TO AGRICULTURE IN LATIN AMERICA Changes in precipitation and temperature According to the predictions of Washington and Meehi (1984) and the Commonwealth Secretariat (1989), there are likely to be important rainfall distribution changes in at least the tropical and subtropical parts of Latin America. The wet seasons are likely to get wetter and the dry seasons drier. Sombroek in Chapter 13 summarizes the predicted changes with up to 30 mm increase in soil moisture during the period December - February for Eastern Amazonia but up to 30 mm decrease for Western Amazonia and Central Brazil. There is also expected to be a 10 - 20 mm increase in Eastern Amazonia and in Central Brazil in JuneAugust which is at present a dry season in that region. No change is predicted in Western Amazonia during this period which is normally wet at this time. The models also predict a temperature increase of 5°C for the higher latitudes but only 2°C for thc equatorial region. Sombrock also discusses the possible direct effect of increased air temperature on tropical crop plants. The expected increase in atmosphere CO2 production and associated temperature increase could result in a 25% increase in biomass production world wide although for the tropics the combined effect might be smaller. No precipitation changes are predicted for the rest of Latin America except that Uruguay, Northern Argentine and Chile are expected to be somewhat wetter in June-August. Such a change is likely to increase agricultural production in this part of the region which normally has a deficiency of rainfall. The predicted changes in precipitation would probably affect the water balance of the Amazonian region and the discharge of water by the Amazon River, especially if this is associated with increased clearing of natural vegetation with a resulting increased runoff. The full effects of this are likely to be felt not only in the Amazon basin but also on the South American coast. In Central Amazonia, the expected precipitation changes may lead to a better rainfall distribution for crops. The projected decrease in the rest of the area in DecemberFebruary would make cropping more risky than it is at present, this period being

.!An

American and Caribbean agriculture and the greenhouse effect

25 1

presently the short wet season for a good part of this region with already unpredictable rainfall. This moisture supply problem is likely to be exacerbated by the tendency for higher biomass production and higher yields due to increased atmospheric COz. Changes in crops and land use may be involved in which more drought tolerant species may have to be grown. These trends are also likely to encourage more extensive cattle rearing in areas with low population densities which is characteristic for the whole region. There are also likely to be wider annual fluctuations of water levels in the Amazon River system which could lead to great flooding in the wet season. With appropriate soil management to cope with wider soil moisture fluctuations, the effects on agriculture need not be traumatic. If the climatic changes are accompanied by a higher level of farming especially in soil and water management and including greater use of irrigation, the adverse effects can be minimized. In association with the climatic changes, changes in the crops grown, especially the commercial crops must be viewed as a possibility. New technologies would have to be adopted. Thc increase in temperature could have an important beneficial effect in extcnding the cropping area and widening the range of crops produced in Southern Argentina and other cold areas of Latin America. However, in this event there would be greater evapotranspiration demands with implications for appropriate crop management. Rise in sea-level The projected rise in sea levels due to global warming has been estimated to be about 0.5 to 1.0 m over the next hundred years (Brammer and Brinkman in Chapter 12, Commonwealth Secretariat 1989, Sombroek in Chapter 13; Washington and Meehl 1984). The consequences of this are frightening for several Latin American and Caribbean countries. Some present land masses would be inundated, particularly the flat, low lying coastal fringes which are so important in Guyana and Surinam. The present coastal plain in those countries which are now below the level of the highest tides would be completely submergcd; so would several areas in the region that have been formed from coral and marl. This would lead to obvious catastrophic situations in which parts of countrics may disappear. Another result would be salinization of groundwater. As an example, in Barbados and Jamaica the groundwater of low lying limestone areas is being used for domestic purposes and for irrigation. A significant rise in sea-level will disturb thc existing delicate balance between fresh and saline waters in these aqui fcrs, leading to salinization. Any risc in sea-levels would cause greater encroachment of salt water in the rivers of the regions which would lead to reduced potential for irrigation throughout and would create the need to replace, modify or expand domestic

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water supply systems. Damage from saline intrusions into fresh water wells is already a problem in parts of the region. Many low lying coastal areas in the Caribbean and South America are protected either by coral reefs or mangroves. Both are under pressure from human activity such as pollution and sedimentation as a result of bad land use and construction processes and excessive cutting of mangrove for poles and fuel. A rising sea-level would tend to narrow the band of mangrove between the sea and human occupation and it might outstrip the growth capacity of some coral reefs. The vulnerability of the coasts to erosion and flooding would increase. These events would also greatly upset marine life in coastal and estuarine areas which could lead to the disappearance of presently valuable fishing grounds. Even if the full expected rise in sea-level is not attained, any further rise would pose problems to several areas in the region. There is already much coastal erosion occumng along the coastal plains of Surinam and Guyana. While the full causes for this are not known, one factor could be greater runoff in the Amazon Basin and greater discharge by the Amazon River due to clearings for agricultural purposes. This phenomenon is likely to increase due to greater precipitation in parts of the the Basin and from runoff from further agricultural clearings. As can be seen from the above, the consequences of any appreciable global warming to agriculture in Latin America and the Caribbean can have traumatic results. Therefore, it would be very germane to this problem if the present agricultural pursuits in the region can be considered in the light of possible contributions to atmospheric greenhouse gases and climate change.

THE AGRICULTURAL ENVIRONMENT Climate Much of the land area lies in equatorial latitudes and it has the earth’s greatest continental extent of humid tropical climates - areas in which plant growth is restricted by moisture stress only for very short periods of the year. These areas, about 42% of Tropical America, have a udic moisture regime. Another 43% has an ustic moisture regime. In these areas, there may be several dry months in any year. Examples are Northeast Mexico. Only 7% of the area is aridic. Although there are few areas in lowland Latin America where low temperatures may inhibit plant growth (mainly in temperate Brazil) low temperatures caused by high elevation are common in much of the Andean Region and to a lesser extent in parts of Central America and the Caribbean.

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Soils All the soil orders are represented in the region. Soil classification in this text is according to the USDA Soil Taxonomy System (Soil Survey Staff 1975); between brackets the approximately equivalent names are given according to the legend terminology of the FAO-Unesco Soil Map of the World (FA0 1974). Oxisols and Ultisols (Ferralsols) cover the largest area of tropical Latin America followed by Inceptisols, Entisols and Mollisols with minor occurrence of the other orders. Oxisols are the dominant well drained soils of the areas affected by the Guyana and Brazilian Shields, including the Cerrado, the Llanos and the Eastern Amazon basin. According to Sanchez and Buol(l974) there are about 5 13 million ha. Oxisols occur on many of the old erosion surfaces and also on the more recent depositional plains. An important area of Oxisols is in the Greater Antilles where they have developed on hard limestone. Here the soils are commonly bauxitic and are mined as aluminium ore. Ultisols (Acrisols; most Nitosols) are extensive in Latin America, covering some 371 million ha (Sanchez and Isbell 1978). They are fairly common in the higher rainfall areas of Central America but are more widespread on gently sloping outwash plains of the Amazon and Orinoco basins. Typically, they occur in South and Central America on an old coastal plain which was dissected at the end of the Quaternary Period and upon which the new coastal plain has been built. Alfisols (Luvisols; some Nitosols) occur throughout the region. In South America they occur in Northeast Brazil, the North coast of Colombia and Western Venezuela and occupy approximately 160 million ha. In Central America and the Caribbean there are about 32 million ha, derived generally from basic materials. In the Caribbean, Alfisols occur on old volcanic materials and on intermediate and basic rocks of igneous and metamorphic origins. Inccptisols (Cambisols) are widespread in Andean South America and mountainous areas of Central America and the Caribbean where they are associated with volcanic materials (Andepts/Andosols). Other Inceptisols are also common in these upland areas and in Eastern Brazil. Large areas of Aquepts (Gleysols) are widespread in the seasonally flooded areas on the coast of South America and along the major river systems. Vertisols (Vertisols) are widespread through Latin America and the Caribbean and may be more common than previously thought. They are distributed from Mexico to Argentina and occur in practically every country. They are common in the less humid regions where they are developed on basic igneous and mctarnorphic rocks and on volcanic materials and calcareous rocks. Vertisols are also common in high rainfall areas on very fine marine, lacustrine or riverine sediments which have since been uplifted. In some of these areas, Vertisols occur on fairly steep slopes and they are naturally unstable. Due to the nature of the parent materials, acid Vertisols are frequent in parts of Coastal South America and

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the Caribbcan where they form important agricultural soils. Entisols (Arenosols; Regosols and Lithosols; Fluvisols) are another soil order which may be more important in Latin America than previously thought. In Central and Eastern Brazil, the chief forms are deep red or yellowish sands formed from siliceous parent materials on old erosion surfaces. In the Amazon basin, the Guyanas and Venezuela they are widespread and occur on whjte sand deposits. There are very large areas of quartz sand in Brazil, Guyana, Surinam, French Guyana and Venezuela. In Brazil alone 70.9 million ha of these soils are distributed (Bowen and Lobato, 1989). Many of these have spodic subgroups. Entisols occur throughout the steeper parts of the Andean system and other mountainous areas. In similar locations they are important in Central America and the Caribbcan. In this area exploitive use over a long period of time results in the occurrence of these soils where they should not normally be. Entisols are also very important on deltaic, estuarine, coastal and marshy areas where they can have sulphiric properties and intergrade with Histosols. Mollisols (Chemozems; Phaeozems; Kastanozems) are productive soils and are locally important in subhumid parts of Latin America. Examples are in Central Mexico and the Yucatan Peninsula, in some drier inter-Andean valleys of Peru and Colombia, in Northwest Argentina and in Northern Paraguay. They are also important in the Caribbean where they are associated with less humid climates on calcareous and other basic rocks and on volcanic parent materials. Aridisols (Xerosols and Yermosols; Solonchaks) are distributed on the coastlines of Surinam, Guyana and Venezuela and Northern Brazil where salinity is due to the constant influence of the sea. They also occur in dry areas of desert or near desert climates in Mexico and Peru. Histosols (Histosols) are widespread throughout the region but do not occur in large expanses in any one location. Commonly they are associated with brackish inland swamps along coastlines and may be complicated with both salinity and sulphiric features. Spodosols (Podsols) are important in the Amazon (Klinge 1965; Bleakley and Khan 1963) and are also known to occur in Venezuela. They were first described by Richards (1941) in Guyana as giant Podzols. A most characteristic feature is the dark colored chemically pure drainage water from these Podzol soil areas from which the Rio Negro derives its name (Herrera et al. 1978); the same dark colored water is characteristic of the rivers of the Guyanas and the Orinoco. These soils are infertile but can be managed for crop production (Ahmad 1989). The region’s soil resources have been very little studied. Some soil situations have been studied with nonproportional intensity compared to their area of occurrence (i.e Spodosols) due to special interest of visiting scientists. The detailed distribution and classification of the soils is not known with the exception of certain restricted areas, so that their management for agriculture is based more on sociological conditions than soil properties. Soil surveying is an essential,

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initial step. A notable exception is the Commonwealth Caribbean where the soils of the entire region have been mapped to at least semidetailed level and the soils have been studied to a good extent.

LAND USE Cropland and cropping systems Only 1 1 % of the cultivable area is tilled at present in Latin America (Schaffer 1980). There is much unused land and the population densities are relatively low. The exception is the Caribbean area which has long been colonized and settled with labour intensive enterprises and therefore the population density is now high and there is literally no untilled land which is suitable for farming. Agricultural land use can be divided into areas with farming systems where the land is occupied by permanent crops and those in which short term food crops are produced largely on a subsistence level. The permanently farmed areas produce a number of important crops such as coffee, banana, sugar cane, cacao, rubber, oil palm and citrus; and the levels of management and productivity of thesc crops are very high. When fully established, the extent of ground cover can approach forest conditions, Therefore, this form of agriculture may not contribute to the greenhouse effect. Exotic tropical fruits are not yet produced in large quantities for export. The other important aspect of permanent land use is pasture and livestock production. Land use for short term crops includes cultivation of the important food crops of the region such as rice, beans, maize, other temperate cereals, manioc, sweet potato or white potato. The distribution of land for these uses is not exactly known; probably pasture and livestock production would be the overall dominant land user which has increased consistently in recent years throughout the region (Kohlhepp 1986). There are no land zoning policies, at least none that are effectively applied. Even in the Commonwealth Caribbean whett land resources are extremely scarce and valuable, here are no effective land zoning laws. Throughout the Caribbean, land use is largely determined by the landowner. In effect, the flatter areas and better soils are generally in occupation as large blocks and are in permanent plantation agriculture. The small, landless cultivator is forced to squat on steeper lands with fragile soils, cultivating short term food crops. Since the farmer does not own the land and in any case for economic reasons, hardly any inputs except the farmer's labour are made; hence, there is rapid deterioration. This level of farming exists alongside highly efficient, capital intensive production of major export crops. Land use for food crop and livestock production is generally based on shifting cultivation. The traditional form is cutting of the vegetation, allowing

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time for it to dry, burning to clear the land, and begin with alternate cropping; this is a cyclical land use technique in which short term cropping alternates with long periods of forest fallow. In the system, soil ameliorants or crop rotations are not used. It begins when trees, bushes and lianes of a forest are felled or slashed and after a certain amount of drying, burned (Walters 1971; Goodland and Irwin 1975; Neugebauer 1988). The rain forest contains up to 500 tons ha-1 of biomass and a considerable part of the mineral nutrients present in the soiVplant system. Fire destroys this biomass with much of the N, S and P while the other nutrients are mineralized to suffer loss through surface runoff and leaching. With the beginning of the favorable rainy season, seed is sown in the burned untilled land. In the first year there is a high yield and very little labour input, but even for the second harvest, considerably more labour is required because of weeds and the deterioration of soil structure. This is due to the accelerated loss of fertility caused by heat, moisture and extreme insolation and soil compaction. By the third year competing weeds can become uncontrollable. As soon as the labour requirements become too high, or the harvests too low, the shifting farmers desert their area. Using the same technique as before, they open a new area by the same process with at least 25 years of fallow. Profound soil deterioration both physically and chemically results from the practice. The changes have been well documented both in South America (Sanchez 1981) and in West Africa (Nye and Greenland 1960). If there are large areas available with a low population density shifting farming allows continuous high yields. However, where cultivation and regeneration are practised without the necessary care, or where population density has risen so high that the land is not left fallow for long enough, soil erosion and reduced soil productivity results. This induces successive changes in the vegetation structure and in climate and edaphic conditions, and finally brings about destruction of the tropical forest. At a population density of 25 people per km*, the carrying capacity in this farming system has been reached (Neugebauer 1988). The rate at which the deterioration of the vegetation takes place is of course dependent on the reserves of fertility. In areas of volcanic soils or soils developed on calcareous materials, an initially cleared area can be used for a long time for agricultural production and such areas can support a higher population density. The resistance of volcanic soils to lapid deterioration can be seen in some pans of Indonesia for instance, where the population density which lives on subsistence agriculture is over 400 per km2. The same also occurs in Latin America and the Caribbean. In such areas probably total deterioration never results. In Central America for instance land initially cleared by the Mayas, cultivated and then deserted, is today in a fairly productive secondary forest vegetation. Traditionally, the method of managing land in these areas is somewhat different from where the soil environment is poorer. The "milpa" and the "conuco"

L d i n American and Caribbean agriculture and the greenhouse effect

257

systems of land use are examples in which the land is semipermanently used for agriculture. Livestock and production systems The ultimate result of shifting agriculture in Latin America, especially in South America, is the wellknown man made savannahs or the replacement of magnificent forests with coarse grass scrub. The resulting savannahs can be beneficially used for cattle rearing but it forms such poor pasturage that unless more productive plants can be adapted, the productivity is extremely low and without improvement it is an unproductive form of land use. Besides, annual fire is a component of management since burning of the savannah stimulates young growth so that for a short time at least after the burn, the stock can have a more nutritious forage. (Medina 1982 and Medina et al. 1978). This adds to the greenhouse effect. An estimate of the area of these man made savannahs throughout the region is not readily known but it is very large. Throughout the region, there are also examples in most agroecological zones of high production levels of pasture management and livestock production. These areas are not burned and they remain in production on a permanent basis. This type of land use presents the other extreme in livestock production and is at least an alternative to the extensive grazing on man made savannahs. Although not without exception, livestock production in Latin America has been at some to the environment. The area is a net exporter of beef and has a high per capita consumption of meat products. Production has been increasing in many of the countries during the last 10 years while most other agricultural commodities have decreased during that period. Throughout the tropical area of Latin America the clearing of land for livestock production occurs mainly through the subsistence farmers' slash and bum with shifting agriculture, so that pastures result from a degradation process with atmospheric COz enrichment. Further, the animals are all grass fed and therefore livestock production adds to atmospheric methane. Due to the abundance of land and principal lack of inputs, livestock production is extensive and stocking rates are usually quite moderate. Where the nutrient reserves in the soil are very low, such as in the Amazonian region of South America, the deterioration of the vegetation is very rapid and manmade savannahs can be formed probably after only two cycles of land clearing for shifting cultivation. There are, however, examples in the region where the quality and quantity of vegetation is greatly improved by agriculture. The Cerrado of Brazil is the best example of this situation, where the typical scrub vegetation is cleared, all the needed inputs of soil ameliorants and fertilizers are made and the land is being transformed into agricultural land either for cultivation or improved pastures with high production. This could be an example of a positive effect of human interference on the environment.

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AMMONIA

The environment and its exploitation In recent times the rate of deterioration of the environment has accelerated in the Amazon Region, caused by the traditional slash and bum shifting cultivation and other activities such as mining, forest exploitation and cattle rearing. 'Ihe possible global effect on the environment this ecological transformation is likely to exen, has the world's population sensitized to what is happening in this vast region. Thc drainage basin of the Amazon River is still by far the world's largest area of continuous forest. The whole catchment area exceeds 7 million km2, and while i t comprises 40% of the area of Brazil, it extends into French Guyana, Surinam, Guyana, Venezuela, Colombia, Peru and Bolivia. The natural vegetation is like non other anywhere else in the world with over 100,OOO species and an equally varied fauna. It has an abundance of water - about 20% of all water flowing on the earth's surface runs down the Amazon to the sea. The typical rainforest vegetation has developed, in which the biomass exceeds 500 tons per ha and the annual production is 25 tons per ha. The area is as yet only sparsely populated - about one person per km2. Characteristic for the vegetation, apart from the great variety of species, are its vertical division into 2-3 levels of trees of different heights, the highest storey being up to 50 m, its fewer appendages of epiphytes hanging from the trees as compared to the tropical mountain forest and its sparse ground vegetation due to lack of light. Only from the river banks, largely concealed by dense vegetation, is the impression of impenetrability created. At the present time, the forest is being cleared at the rate of 10 million ha per year. It was estimated that in 1987 up to 25 million ha of land in the basin was burned but most of this area consisted of already deforested pasture and plantations. Up to 1980 only 2.45% of the Brazilian Amazon forest region was cleared. Even if this is doubled in the last decade, less than 5% of the region would have bcen cleared so far, but there is a rapid rate of increase. During the 1970s and even later, the Brazilian Government positively encouraged settlement in the Amazon Basin. Incentives to cattle ranchers exceeded one billion dollars over the last decade but this activity brought little success and much damage to the fragile environment. It also embarked on the construction of the Trans-Amazon Highway, a system of roads that runs West from Recife toward the Peruvian border. The idea was to prompt a land rush. To encourage settlers, the Government offered transportation and other incentives, allowing them to claim the land that they had improved by deforesting. However, most of the 8000 families that responded at least between 1970 and 1974 have bcen disappointed due to rapid deterioration of crop yields. A later development is the Grandc Carajas Programme to develop mineral resources. The principal iron

Latin American and Caribbean agricdfure and the greenhouse effeci

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ore mine began production in 1985 but the ore melters are powered by charcoal which is produced from the wood of the surrounding vegetation; it is feared that this venture would be a repeat of the experience of the state of Minas Gerais in Central Brazil, where pigiron production consumed nearly two-third of states forests. In another huge project, Polonoroeste, the Government is trying to develop the State of Rodonia. Instead of model settlements, the project has produced impoverished itinerants. Settlers grew rice, maize, coffee and manioc on a shifting basis in which the farming and burning became a perpetual cycle of degradation. Since 1980, the percentage of the State covered by native forest has dropped from 97 to 80%. Earlier in the 1920s Henry Ford was unsuccessful in a bold attempt to promotc large scale rubber cultivation in a part of the Amazon Basin and in the late 1960s and 1970s Ludwig was also unsuccessful in a project to produce wood pulp and rice along the Jan River. Apparently, the only reasonably successful agricultural production in the region has been the production of black pepper, a crop which was introduced by Japanese scttlers in 1933. In the culture of this crop, the forest vegetation is not completely cleared and the soil never fully exposed. Besides, the crop is managed at a high agronomic level. The fires during a five to six months dry season can release up to 620 million tons of C02 into the atmosphere, an amount equivalent to 10% of all the C 0 2in the world's atmosphere. This result is caused by the activities of relatively few pcoplc. Instead of contributing to atmospheric C02 levels, the forest can in fact serve as a filter for up to 25% of the 5 billion metric tons of C02 released by the burning of fossil fuels each year. The burning of the forest therefore, not only releascs more C 0 2 but it also destroys a unique system for purification of the atmosphere. It must be pointed out that the rapidly increasing use of alcohol as fuel in Brazil is ecologically better than the use of only fossil fuels and in this respect this country is pioneering. Clearly, the results of human activity in the Amazon so far has tragic results overall. Not only is the forest being destroyed and the whole environment deteriorated, but the people involved in the process have been leading miserable lives as well. Cutting of the forest and burning is obviously too harsh an initial treatmen1 for this fragile ecosystem, posing a great shock to the environment from which it cannot rccovcr. I t is imperative that more is known about the ecological conditions of this uniquc area so that man's activities can be adaptable. One outlook is ihat enough land has already been cleared of its forest cover and what is nceded now is to develop management techniques and the necessary input to make these areas agriculturally productive on a permanent basis. There is already some information about how this can be done from the work of Sanchez and his colleagucs in the Peruvian Amazon area (Sanchez 1981; Bandy and Sanchez

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h d

1982). This approach would obviously lead to a more settled population and eventually a much better quality of life. The other approach is practice of more ecologically adapted farming and more and better use of the natural products of the forest. This approach would not have such negative impacts on the environment, and the hazards of an increasing global greenhouse effect would be diminished. It would require much more research, product development and promotion, a greater variety in the diet of the population and adoption and creation of appropriate technology for mining systems for the Amazon Region. The actual and potential agricultural systems in the region can now be examincd in the light of the above. Annual crops The main annual crops are rice, maize, cassava and peanut. Valverde and Bandy (1982) concluded that the growing of annual food crops in Amazonia requires the use of modem technology, to be developed in situ and to be sensitive to the local socioeconomic conditions. If crops are grown in rotation or interplanted, the overall performance is better. Also, the native method of land clearing is superior compared to bulldozing. The crop variety is too small to provide a wide enough range for intercultivation and crop rotations. More legumes should be involved and an obvious crop is pigeon pea (Cajanus cajan) which can be grown as a perennial. This applies LO Latin America as a whole. According to Valverde and Bandy (1982), soy bean has shown promise and winged bean and yam have been tried. Carbohydrate crops, aroids and some yams are well adapted to grow with a certain amount of shade and may be adaptable to Amazonian conditions as they are to forest conditions in West Africa. However, the initial problem with these new food crops is the existing dietary habit of the population, with traditional food consisting of maize, rice, beans and manioc. As far as the greenhouse effect is concerned, the cultivation of annual crops leads to atmospheric enrichment with C 0 2 due to frequent burning for land clearing. Rice production is a notable exception. Although in Latin America a lot of rice is grown, over 75% of it is produced in upland conditions and this does not lead to methane emissions. However, about 2 million ha flat lands capable of producing irrigated rice exist in the Amazon Basin and its development would contribute to the methane problem (Alvim 1982). Perennial crops Alvim (1 982) recommended certain potentially suitable perennial crops for

the Amazon Region. Such crops, replacing forests, would have the potential of largely substituting the beneficial ecological effect of the forest. In this

L o h American and Caribbean agriculiure and the greenhouse effect

26 1

connection, it is interesting to note that two of the most important tropical perennial crops i.e. rubber (Hevea brasiliensis) and cacao (Theobromacacao) evolved in the Amazon, but until recently Amazonian countries paid little attention to research and development of these crops. In the case of rubber only 1% of the world's crop is grown in Brazil, the country producing only about 25% of its requirements. With improved techniques of controlling the South America Leaf Disease (using fungicides), in areas with a marked dry season and where suitable production techniques are propagated, rubber production can be greatly increased. Brazil produces only about 0.2% of the world's supply of cacao. It was believed that the soils of the Amazon were not productive enough for commercial production of this crop but according to Alvim (1982) about 10 million ha of land with fcrtility comparable to the currently best cacao soils elsewhere in Brazil have been identified in the Amazon Region. Experiments have demonstrated that very high yields of cacao can be obtained in these soils without the use of fertilizers or liming. Oil palm (Elaies guineenis) is a crop which may have important prospects in the region. As far as climate and soils are concerned, the environment seems ideal and in fact its adaptability has been proved. Crossing of the African oil palm with an Amazonian species (E. Melanoccoca) has produced very interesting material for use in the Amazon (Alvim 1982). Some Latin American countries already produce palm oil but the potential for expansion is great. Sugar cane (Saceharum officinarum) especially for alcohol production is a semiperennial crop, which is suitable in large areas of the Amazon Basin. This crop is widely grown in other parts of Latin America which is the world's largest producing area. It requires a fairly high level of management for efficient production. However, the annual burning of the crop prior to harvest destroys up to 5 tons per ha of biomass and together with the use of nitrogen fertilizers, have certain environmental implications. Black pepper (Piper nigrum) is the most popular crop in the Brazilian Amazon at present and Brazil is now the third largest producer. The crop lasts for about 10 years after which it usually succumbs to a root disease and it is replaced with crops such as cacao, rubber, papaya or passion fruit, while a new area is cleared for pepper growing. These crops benefit from the residual fertility left in the soil from the well managed pepper crop. Potential perennial crops These include cashew (Anacardium oflicinale - Amazon native), achiote (Bixa oreffan- Amazon native), Brazil nut (Berrholleria excelsa - Amazon native), and several palms such as pejibaya (Guilielma gasipaes) or peach palm, palmito (Euterpe oleracea), seje (Jessenia s p p ) , piquia (Caryocar villosum), buriti (Mauritia flexuosa) and copaiba (Copaifera spp), all of which produce either

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edible fruit or palm hearts. Breadfruit (Arrocarpus aftifis) should also be mentioned as being a prolific, high yielding tree, the fruit of which is an excellent source of carbohydrates. There are several exotic tropical fruits which have possibilities as fresh fruit, nectars or other preserves and among the most adaptable species may be avocado (Persea arnericana),citrus (Citrus spp.). carambola (Averrhoa carambola),guava (Psidium guajava), Malacca apple (Eugenia malaccensis), mammey apple (Mummeaamericana),mammey sapote (Calocarpum mammosum), sweet and sour sops (Anonu spp.) and several spices. Systems of cultivation would have to be developed for trees and would require genetic improvement, product development and international promotion.

Pa st 11 re s What is needed, not only in the Amazon but also elsewhere in Latin America, is an improvement of the existing pastures to increase the carrying capacity rather than clearing more land and expand the current extensive system. Research on pasture plants adaptable to poor soils has been in progress at CIAT for years, and this research could now support pasture improvement in the region. Agraforestry This is a farming system which is being projected in the tropics as a substitute for shifting cultivation; it combines the protective and soil improvement roles of spccific highly desirable trees and crop production in various geometrical arrangements. It has most appeal in overpopulated areas of the world, where there is almost an equal shortage of food as of forest products such as fire wood, poles and livestock fodder. The forest component contributes soil protection and improvement, and wood products and fodder which are all in high demand, while the arable crops grown in association provide human food. In Latin America and especially in Amazonia there is as yet not a great appeal for agroforestry. In the Caribbean area a form of agroforestry incorporating forest food plants as a top storey cropping and crops at the ground surface with an almost random distribution of the various components of the system has been practised for at least 150 years. This system is popular as it offers many advantages for the farmer and it protects and enriches the soil. This form of agroforestry may well be applicable to the Amazon Region.

Forest improvement

Tropical rain forests of the Amazon Region are unique as far as flora and fauna species diversity is concerned. However, the growing stock and

263

Lo& American and Caribbean agriculture and Ihe greenhome effect

commercial volumes are not as high as generally assumed and it is commonly stated that these forests are more impressive than useful (Von Maydell 1984). In Table 2 1.1 an analysis is given of the tree species of forests of Latin America, compared to those of forests elsewhere. Table 21 .I

Comparison of characteristicfigures of closed tropical lowland rainforests a

Wood charactcristics Atiica Total nurnbcr of stems 60 - 80 Numbcr of species 40 - 50 Numbcr of commercial 5 - 20 species 3 Volurnc per stcm, all species (in m3) Total growing stock in rn3 180 - 250 Growing stock of commer- 20 - 70 cia1 specics (m3) Net timbcr rcrnovals 10 - 20 a

Latin America Asia 70 - 90 120- 150 50 - 70 70 -90 3 - 10 10 - 30

Maxima 200 150 10 - 30

2

3

4

140 - 200 15 - 40

200 - 400 80 - 200

450 - 800 450

2 - 10

4 0 - 100

150

All data are averages per ha for trees over 30 cm diameter growing stock; data refer to sternwood (from Von Maydell 1984) above buttress

Table 21.2 presents an indication of the relative productivity of Latin American forests. There is much scope for improving the productivity of the forests for actually harvesting more from much less land. In Trinidad, the shelterwood system of forest regeneration has improved forest from 6 to 10 productive trees to 60 to 80 productive trees per ha in 30 to 40 years. In this case, the new forest itself can be maintained, while the harvest is useful timber (Bruenig 1986). Table 21.2 Slatistics of individual wood production in the tropics and subtropics, 1980 ~~

Type of wood

World

Latin

Africa

America

Roundwood mill m3 Lumber mill m3 Woodbasepanels mill m3 Pulp mill t Papx,cxdboard mill t

*

excluding USSR and Japan

1393.5 428.7 102.0 126.8 174.2

76.9 24.2 4.2 5.1 7.1

50.4 7.9 1.2 1.2

1.6

Asia* Tropics and Australia Subtropics in Oceania %ofworld production 173.6 21.6 46.4 18.3 8.4 13.5 3.5 7.7 14.2 13.1 (from Von Maydell 1984)

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REFERENCES Ahmad, N. (1989). Acid sandy soils of the tropics with particular reference to the Guyanas. In: Farming systems for low fertility acid sandy soils. D. Walmsley (Ed.). CTA Seminar Proceeding, Georgetown, Guyana. Alvim, P. de T. (1978). Agricultural production potential of the Amazon Region. In: Pasture production in acid soil of the tropic. P.A. Sanchez and L.E. Tergas (Eds.). C U T , Colombia. 13-23. Alvim, P. de T. (1982). A perspective appraisal of perennial crops in the Amazon Basin. In Amazonia: agriculture and land use research. B. Hecht (Ed.). C I A T 311-328. Bandy, D.E. and P.A.Sanchez (1982). Continuous crop cultivation in acid soils of the Amazon Basin of Peru. In: Management of low fertility acid soils of the American humid tropics. J.F. Wienk and H.A. de Witt (Eds.). IICA, San Jose, Costa Rica; 153174. Bleakley, D. and E.J.A. Khan (1963). Observations on the white sand areas of the Berbice Formation, British Guyana. J. Soil Sc. 14: 44-51. Bowen, W.T. and E. Lobato (1989). Possibilities and constraints for crop production on acid sandy soils (quartz sands) in Brazil. In: Farming system for low fertility acid sandy soils. D. Walmsley (Ed.). CTA Seminar Proceedings. Georgetown, Guyana. Bruenig. E. (1986). The tropical rain forest as an ecosystem. Plant Res. & Dev. 24: 18-30. Commonwealth Secretariat (1989). Climatic changes: Meeting the challenge. Report by a Commonwealth Group of Experts. Commonwealth Secretariat, Marlborough House, London. Espig, C. ( 1 989). Ecological problems and environmental stresses caused by agricultural production in the tropics. Natural Resources and Development. Institute for Scientific Cooperation, Tubingen. 55-68. F A 0 (1974). FAO-Unesco Soil Map of the World 1:5,000,000 Volume I Legend. UNESCOParis. Glauner. H.J. and H. Keil (1988). The approaches, goal and methods of eco-farming in tropical and subtropical regions of developing countries. Plant Res. and Dev. 28: 4762. Goodland, K.J.A. and J.S. Irwin (1975). Amazon jungle: green hall to red desert. Elsevier, Amsterdam. Hecht, S . B . (Ed) (1982). Amazonia: agriculture and land use research. CIAT. Herrera, K., C.F. Jordan, H. Klinge, and E. Medina (1978). Amazon ecosystems; Their structure and functioning with particular emphasis on nutrients. Interciencia 3: 223232. Klinge, H. (1965). Podzol soils in the Amazon Basin. J. Soil Sci. 16: 95-103. Kohlhepp, G. (1986). Problems of agriculture in Latin America. Production of food crops versus production of energy plants and export. Appl. Geog. and Dev. 27:60-92. Medina, E. (1982). Nitrogen balance in the Trachypogon grasslands of Central Venezuela. Plant and Soil 67:305-314. Medina, E.. A . Mendoza and R. Montes (1978). Nutrient balance and organic matter production in the Trachypogon savannahs of Venezuela. Trop. agric. (Trin.) 55: 243254. Neugebauer, €3. (1988). Starving in the forest. Plant Res. and Dev. 28: 7-31. Nye. P. and D.G. Greenland (1960). The soils under shifting cultivation. Tech. Comm.51. Cornmonwealch Bureau of Soils, Harpenden. Richards, P.W. (1941). Lowland tropical Podzols and their vegetation. Nature, London, 148 : 129-131.

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Sanchez, P.A. (1981). Soil management in the Oxisol savannahs and Ultisol jungles of tropical South America. In: Characterization of soil. D.J. Greenland (Ed.). Clarendo Press, oxford. Sanchez, P.A. and S.W. Buol (1974). Properties for some soils of the upper Amazon Basin in Peru. Soil Sci. SOC.of Amer. Proc. 36: 117-121. Sanchez, P.A. and R.F. Isbell (1978). A comparison of the soils in tropical Latin America and tropical Australia. In: Pasture production in the acid soils of the tropics. P.A. Sanchez, and L.E. Tergas (Eds.). CIAT. Colombia: 25-53. Schaffer, G. (1980). Ensuring man's food supplies by developing new land and preserving cultivated land. Applied Geog. and Dev. 16: 7-27. Soil Survey Staff (1975). Soil Taxonomy; a basic system of soil classification for making and interpreting soil surveys. SCS-USDA. Agricultural Hand book 436. Washington DC . Valverde, C. and D.E. Bandy (1982). Production of annual crops in the Amazon. In: Amazonian: Agriculture and Land Use Research. S.B. Hecht (Ed.). CIAT: 243-280. Von Maydell, H. (1984). The role of forestry in rural development. Plant Res. and Dev. 19:52-70. Washington, W.M. and G.A. Meehl (1984). Seasonal cycle experiment on the climate sensitivity due to a doubling of CO2 with an atmospheric general circulation model coupled to a simple mixed layer ocean model. J. Geophys. Res. 89: 9475-9505. Walters. R.F. (1971). Shifting cultivation in Latin America. FAO, Rome.

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Chapter 22

THE ASIAN AGRICULTURAL ENVIRONMENT AND THE GREENHOUSE EFFECT L. Venkataratnam National Remote Sensing Agency Balanagar, Hyderabad - 500 037. India

Modem agriculture depends heavily on four technologies: mechanization, irrigation, fertilization and chemical control of weeds and insect diseases. Each of these technologies has made an important contribution to the earth’s increased capacity for sustaining human population and each has perturbed the cycles of the biosphere. In the technologically advanced agriculture of today, even in some of the Asian countries, the expenditure of the fossil fuel energy per acre is often substantially greater than the energy yield embodied in the food produced. In the poorer countries, man’s expanding need for fuel has forced him to cut forest far in excess of their ability to renew themselves, making the soils vulnerable to soil erosion. The inorganic nitrates and phosphates discharged in to the lakes or ponds provide a rich medium for algae. The massive growth of alae in tum depletes the water of oxygen and thus endangers fish life. In the end, the eutrophication or overfenilization of lakes slowly brings about its death as a body of the fresh water converting into a swamp. In spite of rapid advances achieved in the agricultural sector during this decade, enabling developing countries to increase their agricultural production at the rate of 3.6% per year. Over 200 million people in Asia alone wills till continue to be undernourished. Even assuming a linear growth in agricultural output, the annual global cereal production in AD 2000 is estimated to fall short of demand by almost 140 million tonnes. Year to year variations in the food production due to climatic changes, drought and flood damages, pests and diseases further compounds the problem leaving a gap of over 20% between production and demand (Rao 1989). For an accurate prediction of the climatic changes, we have to clearly understand three fundamental issues: 1) the forces such as solar radiation, atmospheric dynamics, and chemistry which initiate global changes; 2) the response of the earth to these forcing functions involving complicated interactions between climate, ocean, land, biota, and the atmosphere; and 3) accurate modelling and reliable long range prediction of global changes (Rao 1989). In addition to h e problems created by increased emissions of greenhouse gases (see Bouwman and Sombroek in Chapter 2), the progressive destruction of the ozone layer in the upper atmosphere (1 5 to 30 km altitude) has been observed

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L. Venkatorotnom

particularly during spring season in Antarctica. This is attributed to an increase in the use of CFCs and fluorocarbons for purpose of refrigeration, air-conditioning, propellants for aerosols, expanded foam for packaging etc. Thus the world is faced with a multidimensional problem directly related to the patterns of energy consumption, life styles, industrial and urban expansion and agricultural technology. As of today, out of the estimated total emission of CO, (6.5 to 7.5 Gt C y-') only half is contributed by the developing countries having 75% of world population. The present contribution of all developing countries of CFC emission is less than 15% of the total global estimates of 1.2 m tons y-l, the per capita annual contribution ranging from 1.22 kg in USA and 0.9 kg in Europe and Japan to just 0.006 kg in India and China (Rao 1989). National Environmental Engineering Research Institute (NEERI) in India has been collecting air quality data in and around Agra, India since 1976 and its findings are given in Table 22.1. Table 22.1 Air quality data for Agra

Component Sulphur Dioxide

Data Annual average :

24 hrs average : 2 hrs average : Nitric Oxide

15 to 20 pg m-3 7 to 42 pg m-3 20 to 160 pg m-3

Negligible

Suspended particle matter 24 hrs average : 2 hrs maximum :

66 to 448 pg m-3 106 to 803 pg m-3

In general, the levels of different pollutants are well within the permissible limits laid down by International Agencies, and also recommended by Indian Standards Institute, the optimum level to cause a atmospheric hazards being 80 pg m-3 (0.03 ppm). It is however, observed that the two hourly maximum value of SO2 crosses 100 pg m-3) at times and this increase even for shorter duration is harmful (Tripathi and Prasad 1984).

GLOBAL WARMING DUE TO AGRICULTURE The crucial role played by vegetation (crops and forests) in the global cycling of C02 is well known. The vegetation and the soil of our earth together hold more than two trillion tons of carbon, three times the amount stored in the atmosphere. When the trees are felled or the crops are harvested, the carbon they

Asian agriculture and the greenhouse effecl

269

contain along with soil carbon is oxidized and released to the air by decay or by burning. Since 1860, deforestation has contributed 90- 180 billion tons of carbon to the atmosphere compared with at least 150-190 billion tons from the burning of fossil fuel and natural gas. Agricultural practices lead to the emissions of several gases as well. The burning of forests and savanna grasses in tropical and sub-tropical regions to create pastures and crop land yields additional large amount of carbon monoxide, methane and nitrogen oxides. Moreover soils exposed after forest clearing emits nitrous oxide, as do nitmgen rich fertilizers spread over fields. The concentrations of many gases, given in parts per billion (ppb) are expected to be significantly higher 40 years from now (see Bouwman and Sombroek in Chapter 2) if anthropogenic emissions continue to increase. The concentrations of NO2 and SO2 over highly industrial sites may not rise much in 40 year, but the number of polluted sites can be expected to grow, particularly in the developing nations as in Asia (Graedel and Crutzen 1989). The reduction in the rate of deforestation and initiation of afforestation programmes can delay the onset of global climatic changes in the world. India has more than 50 million hectares of land which is lying wasted. The National Wasteland Development Board established in 1985 was entrusted with the task of transforming the degraded land every year into viable plantations to supply fuel wood as well as fodder in addition to acting as C02 sink. Increased carbon dioxide in the atmosphere could have a favorable impact on crop yield provided it is not simultaneously accompanied by higher temperatures. A study carried out by Sinha, Rao and Swaminathan indicated higher mean temperature will adversely affect the wheat production (Swaminalhan 1989). This is because, for every 0 . 5 " ~increase in temperature and subsequent limited moisture reserves there could be a reduction in crop duration by seven days leading to a loss in yield of 4.0 quintals per hectare.

DEFORESTATION It is a fact that C02 fixed by the forest vegetation from the atmosphere would return when the plants are cut and burnt or when they decay. However, forests account for about two thirds of the photosynthesis taking place on the land and since the forests are long lived, they tend to spread the replenishment of COz to the atmosphere over a long period of time. Deforestation, has far reaching direct and indirect consequences and is one of the most serious human impacts on environment. Deforestation as a cause of ecological degradation has been recognized since long (Thomas 1956) and the current awareness of this problem in developing countries demonstrate the seventy of environmental damage and wood shortage attributable to deforestation (Allen and Bamess 1985). According to the estimates of F A 0 (1981) developing countries will loose 40% of their

270

L. Venkalaralnam

existing forests by the year 2000 at the present rate of exploitation. Available studies indicate that countries like Bangladesh, Nepal, Sri Lanka and Thailand record annual deforestation at a rate of 4%, 3%, 1% and 2% respectively, in 1960s and 1970s (USAID 1979; Revelle 1980; Eriksson 1979). The US InterAgency Task Force on Tropical Forests (1980) concluded, that with the present trend of deforestation, the worlds' tropical forests outside Central Africa and the Amazon Basin, would be nothing but scattered remnants by the year 2025. In India, official estimates show that the country has lost about 4.04 million ha of forest land or about 12% of its total geographical area under forest between 1951-52 and 1975-76 (Puri et al. 1983). According to NRSA (1983) forest cover in India has been reduced from 17.05% to 14.10% of the total geographical area of the country in a span of 7 years (Table 22.2). Table 22.2

Forest cover in India (km2)(NRSA 1983)

Forest type

Closed forest Open forest Mangroves Total Percentage forest area to the total geographical area

1972-75

1980-82

4,64,226 87,683 3,28 1 5,55,180

3,60,229 1,00,592 2,649 4,63,470

16.89%

14.10%

HTMALAYAS The Himalayan mountainous chain, about 2,400 km long and 240-400 km wide rising from low lying Indian plains to well over 8,000 m has a complex physiography situated between the latitudes of 27"-37"N and longitudes 73"-97"E. It is thus a mountainous region cutting across many latitudes, covering the entire tenitorics of Nepal, Bhutan and all or parts of five states of India namely Jammu & Kashmir, Himachal Pradesh, Uttar Pradesh, West Bengal, Sikkim and Arunachal Pradesh. The Himalayas ranges run from West to East. In h e longitudinal plain, South to North, the Himalayas can be viewed as four broad physiographically distinct zones parallel to each other. The outer Himalayas confirm to the climatic zones based on the attitudes as follows: W a n tropical Warm subtropical Cool temperate Alpine Arctic

below 800 m; 800 m -1200 m; 1200 m-1400 m; 2400 m - 3600 m; Above 3600 m.

27 1

Asian agriculture and the greenhouse effecl

In each of the above zones, there is a great variation in precipitation, temperature, wind pattern, humidity, radiation and sunshine which determine the local climates. Kawasa (1988) has prepared vegetation maps of the Himalaya region using Landsat imagery (MSS) of the years 1972-75. The modelling of the Himalayan system has indicated its biological extinction within a matter of a few decades if the present rate of disturbances continues. Forest area lost for various purposes in the Himalayan region including Uttar Pradesh, Jammu & Kashmir, Himachal Pradesh, Arunachal Pradesh, Sikkim and West Bengal as well as Nepal and Bhutan are given in Table 22.3. Table 22.3

Forest area lost for various purposes in the Himalayan region from 19521976

Agriculvalley tural projects purposes River

Country/statcs in India

Jamrnu & Kashrnir Himachal Pradesh Uttar Pradmh Nepal Sikkim & W. Bengal Bhutan Arunachal Pradesh Source: India's Forest

(1980)

10% 0.1 7.7 16.2

10% 0.3 12.2 14.54

Roads

Industries

Miscellanews purposes

Total

10% 0.2 1.2 0.79

10% Nil Nil 3.36

10% 90.2 5.7 3.56

10% 90.8 26.8 38.45

6.1

40.0

Negligible

-

0. I

26.3

0.4

7.1 - :

No information available

EFFECT OF GLOBAL WARMING ON COASTAL AND LOW LYING AREAS Coastal erosion is one of the major environmental hazards faced by maritime states. It assumes great importance for a country like India which has a long coast line of nearly 7000 km with numerous fishing villages, settlements and other establishments right on the shore. Fluvial transport of materials and erosion processes become a focus of attention. Periodic become a focus of attention. Periodic surveys of river basins can provide a reasonable estimates of sediment yields from a drainage basin. Continental fluvial processes and their impact on the ocean require detailed studies of medium size rivers in Asia. Of the total sediment yield to the world oceans, the Indian subcontinent alone contributes about 35% (Milliman and Meade 1983). This will result in silting of the reservoirs reducing their capacity to hold rain water year by year resulting in the reduction of the commandable area.

272

L. Venkataratnam

This would further result in a geographical shifting of the cropping patterns. Conservative scientific estimates revealed that the likely rise in global temperature over the next few decades would result in an eustatic sea-level rise of about 0.5 to 1 m, threatening the islands, low lying areas of deltas and coastal areas. The worst affected areas in Asia would be the Maldives, Indian islands, Bangladesh, and few other countries with long coast lines.

REMOTE SENSING OF LAND DEGRADATION Systematic earth orbital observations began in the year 1960 with the launch of TIROS-1, the first meteorological satellite and since than more than 40 meteorological and environmental satellites with steadily improving sensor data collection capabilities and resolution of the data have been sensing the land surface. In addition to the Landsat, the first satellite designed specifically to collect the data of the earth’s surface, other satellites withe earth resources experiments packages launched by USA, are Skylab, Seasat, HCMM, and space shuttles. Other present and planned satellites around the earth include ERTS & SPOT (Europe), MOS (Japan), IRS (India), Chinasat (China), Radarsat (Canada) and TERS (Netherlands) in addition to the satellites from USSR. In spite of the great strides taken in the machine and manual processing of these data in recent years, so far no uniform methodology or an agreed global albedo data set exists which could lay the basis for current and future research in this field. In order to arrive at comparable interpretations, many scientific groups are mobilizing the scientific community into using satellite data with a prime objective of developing a uniform methodology and albedo data sets for various surface features to ensure a wise usage of the data and their usefulness and repeatability. Twelve July integrations were made with the GLAS (Goddard Laboratory for Atmosphere) GCM (General Circulation Model) to investigate the influence of the surface albedo, surface roughness and evapotranspiration over the Indian subcontinent on the monsoon circulation and rainfall (Sud and Smith 1985). The surface albedo and the surface roughness are governed primarily by vegetation. Any reduction of vegetation increases the surface albedo and decreases the surface roughness. For example, changing forests to agricultural or bare land may imply about a 6- 10% increase in the surface drag coefficient. Their studies also demonstrated that major modifications of the biosphere in the Indian subcontinent might be expected to influence its monsoon circulation and rainfall by altering: 1 ) the surface energy balance; 2) the Planetary Boundary Layer (PBL) motion fields and the moisture convergence; and 3) the hydrological cycle. The results further suggested that the excessive land use via destruction of vegetation would reduce the rainfall and weaken the monsoon. The authors inferred that the feedback effects of changes in land, surface albedo and roughness produced by

273

Asian agriculture and the greenhouse effect

deforestation of the Indian subcontinent, may in turn be partial contributors to the progression of the Thar desert into neighboring arable regions. Robinove et al. (1981) used multitemporal Landsat generated albedo images for studies of indicators of desertification. Comprehensive investigations of atmospheric influence on satellite imagery and derivation of surface albedo from digital Landsat data were presented by Otterman and Fraser (1976) and Otterman et al. (1980). A method for derivation of surface albedo from Landsat data only, without any atmospheric models or ancillary data on the atmosphere, was presented by Robinov et al. (1981). Satellite data have a unique capability in monitoring and mapping natural resources such as crops, forests, water, soils and thus whole environments and provide timely information on the agricultural situation, droughts and floods etc. In India, forest vegetation has been mapped for the years 1972-75 and 1980-83. Wastelands in India have also been mapped for the whole country on a 1:l million scale with village boundaries superimposed on the maps. Similar work is in progress to map the soils affected by salinity and alkalinity at a 1:250,000 scale for the whole country. Once such information is made available, using the remote sensing data, necessary planning can be done for the development of wastelands, reclamation of saline/dkaline soils and conservation of other degraded lands for their optimum utilization. In densely populated South and Southeast Asia, where both food and arable land are scarce, about 90 million hectares of land, climatically, physiographically and hydrologically suited for rice are uncultivated, largely because of land degradation (Table 22.4) (Ponnamperuma 1984). Greening of such vast lands, after proper reclamation measures, by growing crops, forests and grasses would contribute to the creation of new C02 sinks by fixing a significant portion of C02. Table 22.4 Country

Bangladesh Burma India

Indonesia Kampuchea Malaysia

Pakistan Philippines Thailand Vietnam Total

Distribution and extent of problem rice lands, South and Southeast Asia.

Saline soils

Alkali soils

2.5 0.6 23.2 13.2 1.3 4.6 10.5 0.4

0.5 2.5

0.7 0.2 0.4 2.0 0.2 0.2

Peat soils

Total

0.8

4.3 0.8 26.1 31.2 1.5 7.2 14.5 0.4 2.3 3.5 91.8

16.0 2.4

4.0

1.5 1 .o 58.8

Extent, lo6 ha Acid sulfate soils

0.6 1

7.0

.o

5.3

0.2 1.5 20.9

274

L . Venkataratnam

REFERENCES Allen, J.C. and D.F. Bamess (1985). The causes of deforestation in developing countries. Annals of Association of American Geographers. 75: 164-184. Eriksson, J.R. (1979). Energy, environment, and forestry in Sri Lanka: Some major issues. Paper presented in U S AID Asia Bureau Conference on Energy, Forestry and Environment Manila. F A 0 (1981). F A 0 Production Year Book, FAO, UNO, Rome. Graedel, T.E and P.J. Crutzen (1989). The changing atmosphere. Scientific American, 261: 58-68. India's Forests 1980 Compiled by Central Forestry Commission, Ministry of Agriculture (Forestry Division) Govt. of India. Kawasa, M.A. (1988). Remote Sensing of the Himalaya. Natraj Publishers, Dehra Dun, India. Milliman, J.D and R. Meade (1983). World wide delivery of river sediment to the oceans. I. Geology. 91: pp 1-21. NRSA (1983). Mapping of forest cover in India from satellite imagery, 1972-75 and 198082. Summary Report. National Remote Sensing Agency, Dept. of Space, Govt. of India. Otterman, J and R.S. Fraser (1974). Earth-atmosphere system and surface reflectivities in arid regions from Landsat MSS data. Remote Sensing of Environment 5: 247-266. Otterman, J., S. Ungar, Y. Kaufman and M. Podolak (1980). Atmospheric effects on radiometric imaging from satellites under low optical thickness conditions. Remote Sensing of Environment 9: 115-129. Ponnamperuma, F.N. (1984). Adverse soil conditions: their diagnosis and delineation by remote sensing in Applications of Remote Sensing for rice production Edited by Deepak A. and K.R. Rao (1984). A. Deepak Publishing, Hampton, Virginia, USA. Puri, G.S., V.M. Meher - Homji, R.K. Gupta and S. Puri (1983). Forest ecology Phytogeography and forest conservation. Oxford & IBH Publishing Co., New Delhi. Rao. U.R. (1989). The next 4 0 years in space - A view point of developing countries. Presented at the Theme Session. The 40th congress of the International Astronautical Federation, Malaga, Spain 7-13 Oct. 1989. ISRO Special publication No. ISRO-SP4689, India Space Research Organization, Bangalore, India. Revelle, R. (1980). Energy dilemmas in Asia: the need for research and development. Science: 209, pp 169-174. Robinove. C.J., P.S. Chavez (Jr), D. Gehjring, and R. Homgren (1981). Arid land monitoring using Landsat Albedo different images. Remote Sensing of Environment, 11: 133-156. Sud, V.C and W.E. Smith (1985). Influence of local land - surface processes on the Indian monsoon: A numerical study. J. of Climate and Applied Meterology, 24: 1015-1036. Swaminathan, M.S. (1989). Danger of greenhouse gases. Published in Hindu, 5 June 1989. Thomas, W.L. (1956). Man's role in changing the face of the earth. University of Chicago Press, Chicago, USA. Tripathi, C and U. Prasad (1984). Environmental degradation in the marble rocks of Tajmahal, Agra, Uttar Pradesh, India. Proc. Seminar on India's environment, problems and perspectives, Trivandrum, Kerala, India. USAID (1979). Considerations for Bangladesh. Paper presented at the US AID Asia Bureau Conference on Energy, Forestry and Environment, Manila. US Inter Agency Task Force on Tropical Forest (1980). The worlds' tropical forest: A policy, strategy, and program for the Untied States. Report to the President, Washington D.C. U.S Govt. Printing Office.