Advances in Agronomy, Volume 50

VOLUME 50

d:.

Advisory Board Martin Alexander

Eugene J. Kamprath

Cornell University

North Carolina State University

Kenneth J. Frey

Larry P. Wilding

Iowa State University

Texas A&M University

Prepared in cooperation with the American Society of Agronomy Monographs Committee M. A. Tabatabai, Chairman D. M. Kral S. E. Lingle R. J. Luxmoore W. T. Frankenberger, Jr. S. H. Anderson P. S. Baenziger

G. A. Peterson

S. R. Yates

D V A N C E S IN

Agronomy VOLUME 50 Edited by

Donald L. Sparks Department of Plant and Soil Sciences University of Delaware Newark, Delaware

ACADEMIC PRESS, INC. A Division of Harcourt Brace & Company San Diego New York Boston London Sydney Tokyo Toronto

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Contents CONTRIBUTORS .......................................... PREFACE ................................................

vii ix

AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

1.

I1 .

I11.

IV . V.

R . K . Downey and S. R . Rirnmer Introduction ............................................. Improving Yield .......................................... Improving Resistance to Pests ............................... Future Prospects.......................................... Summary and Conclusions .................................. References ..............................................

1

10 24 39 49

so

POPULATION DIVERSITY GROUPINGS OF SOYBEANBRADYRHIZOBIA Jeffry J . Fuhrrnann

1. Introduction ............................................. I1 . Genotypic Groupings ..................................... Ill . Phenotypic Groupings ..................................... IV . Summary of Phenotypic and Genotypic Relationships ............ V . Taxonomic Srarus of Bradyrhizobium japonirum ................. VI . Concluding Remarks ...................................... References ..............................................

67 68 69 93 93 95 96

CROPRESPONSESTO CHLORIDE Paul E . Fixen I . Introduction ............................................. I1 . Chloride in Plants ........................................ Ill . Yield and Quality Responses to Chloride ...................... IV . Chloride Sources, Losses, and Application ..................... V Predicting Crop Response to Chloride ........................

VI . Summary and Future Research Needs ......................... References .............................................. V

107 108 12.5 133

135 141 143

CONTENTS

vi

REDOXCHEMISTRY OF SOILS Richmond J . Bartlett and Bruce R .James I . Introduction ............................................. I1 . Nature of the Electron ..................................... I11 . Derivation of Thermodynamic Relationships for Electron Activity in Soils ................................................. IV . Kinetic Derivation of Thermodynamic Parameters for Redox ...... V . Uses of pe - pH Thermodynamic Information. . . . . . . . . . . . . . . . . . . VI . Uses of pe - pH Diagrams ................................... Reduction Status of Soils ............ VII . Measurement of Oxidation . Free Radicals in Redox Processes ............................ VIII . IX . Manganeseandlron ....................................... X . Soil Chromium Cycle ...................................... XI . Photochemical Redox Transformations in Soil and Water . . . . . . . . . XI1. Humic Substances ........................................ XI11. Wetland and Paddy Properties and Processes ................... XIV . Empirical Methods for Characterizing Soil Redox . . . . . . . . . . . . . . . References ..............................................

152 153

155 158 160 165 172 176 178 187 188 190 195 198 205

PLANTNUTRIENT SULFURIN THE TROPICS AND SUBTROPICS

N. S. Pasricha and R. L . Fox 1. Introduction .............................................

I1. Extent of Sulfur Deficiency ................................. Ill . Forms of Sulfur in Soil ..................................... IV . Sulfur Cycling in the Tropics ............................... V . Effects of Acid Rain ....................................... VI . Sulfur in Irrigation Waters ................................. VII . Sulfate Retention in Soil ................................... VIII . Diagnosis of Sulfur Needs .................................. IX . Critical soil Solution Concentration .......................... X . Crop Responses .......................................... XI . Sulfur Fertilization and Crop Quality ......................... XI1. Sulfur Interactions with Other Elements ....................... XI11. Summary and Conclusions .................................. References ..............................................

INDEX

.................................................

210 211 215 217 223 226 227 237 241 246 252 256 257 260 271

Contributors Numbers in parentheses indicare the pages on which the authors’ contriburions begin.

R I C H M O N D J. B A R T L E T T (1 5 l ) , Department of Plant and Soil Science, University of Vermont, Burlington, Vermont 05405 R. K . D O W N E Y (l), Agriculture Canada Research Station, Saskatoon, Saskatchewan, Canada S 7 N OX2 P A U L E. FIXEN (107), Potash 6 Phosphate Institute, Brookings, South Dakota 57006 R. L. F O X (209), Department of Agronomy and Soil Science, University of Hawaii at Manoa, Honolulu, Hawaii 96822 JEFFRY J. F U I I R M A N N (67), Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 1971 7 B R U C E R. JAMES (1 5 l ) , Department OfAgronomy, Univerdy of Maryland, College Park, Maryland 20742 N. S. PASRICHA (209), Department of Soils, Punjab Agricultural University, Ludhiana, India S. R. RIMMER ( l ) , Department ofplant Science, University o f Manitoba, Winnipeg, Manitoba, Canada R 3T 2 N 2

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Preface Volume 50 includes state-of-the-art reviews written by recognized experts on several topics of interest to crop and soil scientists. The first chapter discusses advances in agronomic improvement in oilseed brassicas. These cruciferous crops are cultivated throughout the world as vegetable crops for human consumption, as condiments and spices for improved flavor of human diets, and as fodder crops for livestock feeding. However, the largest cultivation of these crops is for edible vegetable oil production. The first chapter also reviews the world socioeconomic importance of the oilseed brassicas, ways to improve yields and resistance to pests, and future improvement of oilseed brassicas through molecular genetics and other biotechnological means. The second chapter presents a comprehensive overview of population groupings of soybean bradyrhizobia, including discussions on genotypic groupings; phenotypic groupings include serology, intrinsic antibiotic resistance, uptake hydrogenase, dissimilatory nitrate reduction, rhizobitoxine, surface polysaccharides, protein profiles, rhizobiophage typing, plant growth regulating substances, and other phenotypes; a summary of phenotypic and genotypic relationships, and the taxonomic status of Bradyrhizo-

bium japonicum. The third chapter is a comprehensive review of crop responses to chloride. Topics covered are aspects of chloride in crops, including biochemical functions, osmoregulatory functions, disease suppression, crop development, and interaction with other nutrients, plus yield and quality responses of various crops to chloride, chloride sources, losses, and application, and ways to predict crop response to chloride. The fourth chapter presents a thorough treatment of redox chemistry in soils, a topic of immense interest to soil and environmental scientists, and which Advances in Agronomy has not reviewed in many years. Discussions on the nature of the electron, derivation of thermodynamic parameters for redox, use of pe- pH diagrams, measurement of oxidation - reduction status of soils, free radicals in redox processes, manganese and iron, the soil chromium cycle, photochemical redox transformations in soils and waters, humic substances, wetland and paddy properties and processes, and empirical methods for characterizing soil redox are included in this review. The fifth chapter is concerned with plant nutrient sulfur in the tropics and subtropics. Topics reviewed include the extent of sulfur deficiency in these areas, sulfur cycling in the tropics, effects of acid rain, sulfur in ix

X

PREFACE

irrigation waters, sulfate retention in soil, diagnosis of sulfur needs, critical soil solution concentrations, crop responses, sulfur fertilization and crop quality, and interactions of sulfur with other elements. Many thanks to the authors for their excellent chapters. DONALD L. SPARKS

AGRONOMIC IMPROVEMENTIN OILSEED BRASSICAS R. K. Downey' and S. R. Rimmer2 'Agriculture Canada Research Station, Saskatoon, Saskatchewan, Canada S7N OX2 'Depanmenr of Plant Science, Universiry of Manitoba, Winnipeg, Manitoba, Canada R 3 T 2N2

1. Introduction

I!. 111.

IV.

V.

A. World Socioeconomic lmportance of the Oilseed Brassicas B. Brossira Oilseed Species Improving Yield A. Seed Yield B. Oil and Protein Yield Improving Resistance to Pests A. Diseases B. Development of Herbicide-Tolerant Cultivars Future Prospects A. Interspecific Hybridization B. Improvements Based on Biotechnologies C. Uses of DNA Markers Summary and Conclusions References

I. INTRODUCTION Brassica and other closely related cruciferous crops are widely cultivated throughout the world as vegetable crops for human consumption, as condiments and spices for improved flavor of human diets, and as fodder crops for livestock feeding. However, the largest cultivation of these crops is for edible vegetable oil production. In recent years, a number of monographs and reviews (Tsunoda et al., 1980; Downey, 1983; Stefansson, Adwnrtr rn A ~ w n a n y Yo/ , $0 Copyrighi 0 1993 by Academic Press, Inc. All nghts of reproducuon in MY form reserved.

1

2

R. K. D O W N E Y A N D S. R. RIMMER

1983; Scarisbrick and Daniels, 1986; Downey and Robbelen, 1989) have dealt in detail with many aspects of oilseed Brussicu improvement, especially those which relate to improvements in fatty acid composition and the reduction in levels of glucosinolates in the residual meal. Substantive changes in the quality of seed oil and meal composition have resulted in dramatic increases in areas of production in Canada and western Europe (see below). Unfortunately, this has also resulted in a rather narrow germ plasm base of cultivated oilseed brassicas, especially in Brussicu nupus L. Emphasis in plant breeding has consequently shifted from quality improvement toward increasing seed yield, incorporating resistance to diseases and pests, and improving tolerance to stress. This review focuses on recent developments and current and future trends for agronomic improvements in oilseed Brussicu crops.

A. WORLD SOCIOECONOMIC IMPORTANCEOF THE OILSEED BRASSICAS Historically, human consumption of vegetable oil obtained from Brussicu spp. was primarily concentrated in asiatic countries, predominantly in the northern Indian subcontinent and in China. The cultivation in these countries of oilseed types of Brussicu rupu L. (syn. Brussicu cumpestris L.) and Brussicu junceu (L.) Czern. dates back to approximately 1500 BC (Prakash, 1980), and these areas today are still major producers and consumers of Brussicu vegetable oils. Since the second world war, a dramatic increase in Brussicu oilseed production has occurred worldwide. In Canada and in Europe this was associated with seed quality improvements through plant breeding involving the modification of the fatty acid composition (elimination of erucic acid) and the reduction of glucosinolate content in the residual meal. The large production increase in Europe was also related to economic support from the Common Agricultural Policy of the European Economic Community (EEC). Thus, in the 1948- 1952 period, 70% of a world total oilseed Brussicu production of 2.8 million tonnes was produced in Asia, but by 1984, Canada (20%) and Europe (35%) produced more than half the total world production of 15.9 million tonnes, with the Indian subcontinent ( 18%) and China (25%) producing the balance (Bunting, 1986). Total world production values of oilseeds, edible vegetable oils, and residual protein meals for the years 1985-1989 are given in Table I. Oilseed brassicas account for approximately 10% of total world oilseed production and 14- 15% of the total edible vegetable oil production. Production by the primary producing regions of oilseed brassicas is shown in Table 11. Total world production is now in excess of 20 million tonnes annually.

AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

3

Table I World Production of Oilseeds, Edible Vegetnble Oils, and Derived Protein Meals, 1985 - 1989a

Millions of t o n n e produced by years Commodity

1985- I986

1986- 1987

1975- 19Mb

1988- 1989'

Oilseeds Soybean Cottonseed Peanuts Sunflowerseed Rapeseed Flaxseed Coconut Palm kernel

97.03 30.63 19.94 19.56 18.57 2.36 5.32 2.56

97.92 27.13 20.44 19.25 19.46 2.69 4.72 2.60

103.17 3 1.05 19.72 20.5 1 22.97 2.28 4.24 2.67

93.13 32.24 21.56 20.96 21.72 1.75 4.56 2.89

195.57

194.21

206.61

198.81

13.85 3.47 2.94 6.65 6.19 1.63 3.3 I 1.11 8.17

15.19 3.05 3.10 6.57 6.83 I .56 2.95 I .09 8.09

15.20 3.46 2.85 7.20 7.65 I .90 2.59 8.53

14.85 3.62 3.35 7.57 7.27 1.41 2.76 I .26 9.36

47.32

48.43

50.56

5 1.45

6 1.07

1.89 1.33

67.12 9.83 4.42 7.54 11.09 I .20 1.72 I .32

67.37 11.17 4.01 8.13 12.51 1.14 1S O 1.41

65.54 11.62 4.77 8.59 11.80 0.99 1.60 I .49

98.6 1

104.24

107.30

106.40

Total Edible vegetable oils Soybean Cottonseed Peanuts Sunflowerseed Rapeseed Olive Coconut Palm kernel Palm Total Protein meals Soybean Cottonseed Peanuts Sunflowerseed Rapeseed Flaxseed Coconut Palm kernel Total

11.10

4.22 7.66 10.19 1.15

From United States Department of Agriculture, 1988. Preliminary estimates. 'Forecast estimates. a

1.18

R. K. DOWNEY AND S. R. RIMMER

4

Table 11 Production of Oilseed Brassicas by Main Producing Countries/Regions, 1982- 1989' Millions of tonnes by years Average Country or region

1982/1983- 1986/1987

1987- 1988'

1988- 1989'

India China Canada EEC Europe (excluding EEC) Other

2.64 5.13 3.1 I 3.18 I .70 1.06

3.10 6.61 3.85 5.95 2.16 1.31

3.50 5.04 4.24 5.3 I 2.18 1.45

16.82

22.98

21.72

Total

From United States Department of Agriculture, 1988.

'Preliminary estimates. Forecast estimates.

B. Brcusica OILSEED SPECIES Four species of Brassica have been widely cultivated as oilseed crops, Brassica carinata Braun, B. rapa, B. juncea, and B. napus. Where conditions are appropriate, namely cool temperate climates with good moisture availability, winter forms of B. napus are preferred and are the most productive. Most of the land area cultivated to oilseed brassicas in Europe and China is sown to winter oilseed rape. However, as latitude or altitude increases, the winter form of B. nupus is supplanted by the summer form of B. napus or the winter or summer form of B. rapa. In Canada, cultivation consists of approximately equal amounts of the summer types of these two species. Brassica juncea is well-adapted to drier conditions and is relatively fast maturing. On the Indian subcontinent B. juncea is the dominant species grown, although large areas are also sown to B. rapa types (toria and sarsons) (Prakash, 1980). In these climates, with hot dry summers, nonvernalization types of oilseed brassicas are cultivated in the cool moist winter season. Brassica juncea is also grown in many parts of China outside of the Yangtse/Yellow river flood plains (Stinson et a!., 1982). In western Canada B. juncea is grown as a crop for condiment on some 8 1,000 ha but has strong potential as an oilseed crop for this region (Woods et al., 1991). Brassica carinata may perform well under long season growing conditions.

AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

5

Its distribution presently is largely confined to North East Africa, principally Ethiopia. Clearly, these oilseed crops are well adapted to many different parts of the world. 1. Genomic Relationships

The genomic relationships among the four oilseed Brassica species are well known [see Mizushima ( 1980), Olsson and Ellerstrom ( I 980), and Downey and Robbelen (1989)l. Our modem understanding of these relationships was initiated by Morinaga and co-workers (Morinaga, 1934), who provided cytological evidence to show that Brassicu nigra (n = 8; B), Brassica oleracea (n = 9; C), and B. rapa (n = 10; A) are primary species and that 8. carinuta ( n = 17; BC), B. junceu (n = 18; AB), and B. napus (n = 19; AC) are amphidiploids resulting from crosses between corresponding pairs of the primary species. These relationships were later confirmed by U (1935), who succeeded in the artificial synthesis of B. napus from crosses between the diploid species B. rapa and B. oleracea. Synthesis of B. juncea and B. curinata has subsequently been accomplished by the interspecific hybridization between B. nigra and B. rapa or B. oleracea [see Downey et al. (1975) and Olsson and Ellerstrom (198O)J. Understanding the relationship among these Brassicu species has enabled plant breeders to create synthetic amphidiploids and to transfer useful agronomic characteristics from species to species through interspecific hybridization. No cultivars have as yet been released as a direct result of artificial reconstitution of a species through interspecific crosses, although some desirable characteristics have been successfully transferred from one species to another through artificially synthesized amphidiploids that function as a “bridge.” For instance, the first double-low (low erucic acid content in the oil and low glucosinolate content in the meal) strains of turnip rape were developed from interspecific crosses among turnip rape (B. rupa), rape (B. napus), and oriental mustard (B. junceu) (Downey et al., 1975). Similarly, the development of low-glucosinolate B. juncea involved interspecific hybridization of B. rapa and B. junceu (Love et al., 1990).The transfer of resistance to blackleg disease from B. junceu to B. nupus (Roy, 1984) is another example. In China and Japan, interspecific crosses between B. rupa and B. napus have often been used to transfer characteristics such as early maturity, cytoplasmic male sterility, self-incompatibility, and yellow seed coat, from the former to the latter, and to broaden the genetic basis of B. nupus through genome substitution (Liu, 1985).

6

R. K. DOWNEY AND S. R. R I M M E R

2. Plant and Seed Description

Brassica rapa (AA, 2n = 20) is one of the primary diploid species and occurs wild in the high plateaus of the Irano-Turanian regon (Hedge, 1976), where it is well adapted to the cool, short season environment of this area. This species has a high relative growth rate under cool temperatures and can produce abundant seed. Both spring and winter forms are cultivated and the most cold-hardy cultivars of the oilseed brassicas occur within this species. This species is considered to be of the seed vernalization type. Full clasping of the upper leaves around the stem, the positioning of the terminal buds below newly opened flowers, and a high ratio of beak to pod length are characteristic of this species. Both dark- and yellow-seeded types occur. Brassica carinata (BBCC, 2n = 34) is the amphidiploid between B. oleracea and B. nigra. It shows a slow steady growth, probably derived from the B. oleracea genome. Leaves, which are generally waxy and light green in color, are attached to the stem with a true petiole. Though seeds are predominantly dark, some types have yellow seed. Cultivation is limited to the Ethiopian plateau and adjacent areas of east Africa. It is currently under evaluation and shows promise agronomically in many other parts of the world. Brassica juncea (AABB, 2n = 36) is the amphidiploid of B. rapa and B. nigra. It has a high leaf area ratio and a high relative growth rate, comparable to B. rapa (Sasahara and Tsunoda, 197 1 ). Asia, especially China, is rich in variations of cultivated forms of this species. It is grown widely for oil in the north Indian subcontinent and in various regions of China (Xinjiang Autonomous Region, Szechuan). This species is also characterized by having leaves with true petioles. Leaves vary considerably in shape but are generally of a dark green coloration. Seeds may be dark or yellow and the “bold” types from India have a large seed size. It has considerable potential as an oilseed crop in many other parts of the world. Brassica napus (AACC, 2n = 38) is the amphidiploid of B. rapa and B. oleracea. The existence of a wild form of B. napus is uncertain; if it does exist it will probably be found in the European-Mediterranean region ( McNaughton, 1976). Olsson (1 960) suggested that the amphidiploid B. napus (genome AACC) might have arisen at different locations by hybridization of various forms of B. oleracea (genome CC) and B. rapa (genome AA). Leaves of this species lack a true petiole as does B. rapa, but only partial clasping of the stem occurs. Seeds are dark, generally larger than those of B. rapa, and no natural yellow-seeded types are known. Development of a yellow seed form that is known to be associated with a thinner seed coat (and thus reduced fiber content in the meal) is one of the current

AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

7

objectives in many breeding programs. Production of oil in Europe from B. nupus occurred as early as the thirteenth century, when it was used primarily as lamp oil (Appelqvist, 1972). 3. Mode of Pollination

Brussicu rupu is primarily a self-incompatible species, as are the other diploid brassicas, although some types of B. rupu, e.g., yellow sarson, are self-compatible. The self-incompatibility (SI) in cruciferous species is of the homomorphic sporophytic type determined by a single S locus. About 50-60 alleles are known at the S locus in B. oleruceu (Nasrallah and Nasrallah, 1989). The allelic interactions at the S locus are dominant, codominant, or recessive depending on the alleles involved. This system ensures that B. rupu is normally 100% outbreeding and consequently breeding methodologies for this species are designed to take advantage of this natural heterozygosity. The amphidiploids, B. nupus, B. junceu, and B. curinutu, are normally self-compatible species, though S alleles from B. rupu have been introduced into some genotypes of B. nupus in order to develop SI-based F, hybrids. Such hybrids have recently been registered for commercial production in Canada. Generally, self-pollination occurs readily in the amphidiploid species and selfed seed may easily be obtained by enclosing the flowering racemes in bags. Under field conditions, outcrossing, from pollination due to insects and wind, has been estimated to range from 5 to 15% (Huhn and Rakow, 1979)to about 27 to 35% (Olsson, 1952; Persson, 1956) in winter rape, 22 to 36% in summer rape (Persson, 1956; Rakow and Woods, 1987), and 19% for B. junceu (Rakow and Woods, 1987). 4. Oilseed Quality Improvements

At present, cultivars of two species (B. nupus and B. rupu) have been developed with both low-erucic and low-glucosinolate (double low, or canola) quality, and these are now widely grown commercially. In North America the term “canola” has been coined to describe cultivars that meet specific requirements for erucic acid in the extracted seed oil (less than 2% erucic acid as a percentage of total fatty acids) and aliphatic glucosinolate content in the residual meal (less than 30 pmol g-I). [For a discussion of the development of low-erucic acid cultivars of B. nupus and B. rupu and the genetics of the inheritance of erucic acid in these species, see Stefansson ( 1983).] It is likely that canolaquality cultivars of B. junceu and perhaps B. curinutu will be developed in the near future, and, if this occurs, it will significantly influence the choice of oilseed Brussicu species in some areas.

Table I11 Fatty Acid Composition of Oilseed Brassicu Crops and Other Common Vegetable Oils

Fatty acid composition (%)" CY2

Species, crop, cultivar, and type Brussicu nupus (rape) Victor winter Jet Neuf winter Hero summer Westar summer Stellar summer Brussicu rupu (turnip rape) Duro winter Yellow sarson Echo summer Tobin summer Brussicu junceu (mustard) Indian origin Cutlass

Ref!

14:O

16:O

16:l

18:O

18:l

18:2

18:3

20:O

20:l

22:O

22:l

24:O

0.3 0.4 0.2 0. I tr

0.8 1.4

9.9 56.4 12.9 57.7 59.1

13.5 24.2 12.2 20.8 28.9

9.8 10.5 9.0

0.6 0.7 0.8 0.6 0.5

6.8 1.2 7.5 1.4 1.4

0.7 0.3 0.8 0.3 0.4

53.6 0.0 50.2 0.5 0.1

0.0 0.0 0.3 0.3 0.2

13.4 12.0 18.8 24.0

9.1 8.2 8.9 10.3

0.7 0.9

9.6 6.2 12.0 1.0

0.2 0.0 0.0 0.1

49.8 55.5 23.5 0.3

0.0 0.0

1.2

12.9 13.1 32.5 58.6

1.2 1.2

8.0 17.2

16.4 21.4

11.4 14.1

6.4 11.4

1.2 0.4

46.2 25.8

0.1

1

0.0

2 3 4 4

0.0 0.0 0.0 0.0

3.0 4.9 2.8 3.6 4.1

I 2 2 2

0.0 0.0 0.0 0.0

2.0 1.8 2.5 3.8

0.2 0.2 0.2 0.1

5 6

0.0 tr

2.5 3.3

0.3 0.3

1.O

1.6 I .4 I .o

0.9 1.O

11.5

3.3

0.6 0.6 1.2 0.1

0.0 0.0 0.2

24:l 1 .o

0.0 1.2 0.0 0.0 1.1

1.2 0.0 0.0 I .9 1.7

2km 1

2

tr

3.6

0.4

2.0

45.0

33.9

11.8

0.7

1.5

0.3

0.1

0.2

0.5

6

tr

3.2

0.2

0.9

9.8

16.2

13.9

0.7

7.5

0.7

41.6

0.6

2.0

7

0.0

15.3

0.0

4.2

23.6

48.2

8.7

0.0

0.0

0.0

0.0

0.0

0.0

8

0.1

5.8

0.1

5.2

16.0

71.5

0.2

0.2

0.1

0.7

0.0

0.1

0.0

9 9

9.2 6.7

0.0 0.0

0.0 0.0

3.1 4.3

57.2 71.4

23.4

0.0 0.0

1.4 1.6

1.4 1.0

2.6 2.7

0.0

11.1

0.0

1.8 1.3

0.0 0.0

10

tr

11.5

0.0

2.2

26.6

58.7

0.8

0.2

0.0

0.0

0.0

0.0

0.0

11

0.0 1.0

7.6 23.4

0.0 0.8

2.0 2.5

10.8 17.9

79.6 54.2

0.0 0.0

0.0 0.0

0.0 0.0

0.0 0.0

0.0 0.0

0.0 0.0

0.0 0.0

Brassicu carinafa Ethiopian mustard Glycine may (soybean) Group 1 variety Helianrhus annuus (sunflower) Peredovik Arachis hypoguea (peanut) Virginia Bunch Cook Jumbo Zea mays (corn) United States sources Curlhamus finctorius (safflower)

us10 Gossypium hirsutum (conon)

12

Fatty acids represented by carbon chain length and number of double bonds; tr, trace amounts. References: (1) Appelqvist (1969), (2) Downey (1983), (3) R.Scarth (unpublished), (4) Scarth ef al. (l988), (5) Appelqvist (1970). (6) R. K. Downey (unpublished), (7) Hymowitz ef al. (1972), (8) Earle ef ul.(1968). (9) Worthington and Hammons (1971), (10) Beadle ef al. (1965), ( 1 1) Knowles (1968). and ( 1 2) Anderson and Worthington (197 1). a

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R. K. DOWNEY AND S. R. RIMMER

In developed countries, the production of edible oil from oilseed brassicas is now obtained exclusively from low-erucic acid cultivars and this trend is expected to continue for production in developing countries. Low-erucic acid strains of B. juncea have been recently obtained. These strains were obtained by crossing plants from an accession with intermediate levels of erucic acid content and screening for low erucic acid in the F, progeny using the half-seed technique (Kirk and Oram, 1981). The development of low-glucosinolate B. junceu required interspecific hybridization of B. rupu and B. juncea (Love el ul., 1990) in order to transfer the Bronowski block for aliphatic glucosinolate synthesis from a B. rupu line producing low glucosinolate to a strain of B. juncea that produced 3-butenyl glucosinolate but no 2-propenyl (allyl) glucosinolate. Continued improvement for oilseed quality includes development of strains with modified fatty acid composition. These include development of strains with lower levels of linolenic acid, higher levels of linoleic acid, high oleic acid levels, and other modifications (see Table 111 for a comparison of the fatty acid compositions of oilseed brassicas and other vegetable oilseed crops). A cultivar with low levels of linolenic acid (60%) levels of erucic acid would also be desirable for industrial purposes. Breeders have found it extremely difficult to achieve levels of erucic acid higher than 55% of the total oil content. Because of the inability of acyl transferases to insert erucoyl moieties in the 2-position of the triglyceride there may be a natural upper limit of 66% erucic acid obtainable in Brussicu spp. (Taylor el ul., 1992).

11. IMPROVING YIELD

A. SEEDYIELD 1. Yield Components and Breeding Methods

Although improved nutritional quality of the oil and meal has been a major breeding objective of Brussicu oilseed breeders, yield of seed, oil, and protein must all be maintained and improved if these crops are to remain competitive. Because seed yield is probably the most difficult and costly trait to measure accurately, numerous attempts have been made to identify the most important yield component(s). Positive relationships have fre-

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11

quently been cited between the seed yield and the numbers of pods per plant and per main raceme, as well as the numbers of seeds per pod and seed weight per pod (Thompson, 1983; Shabana et al., 1990). In examining yield and yield components of 10 European winter rape cultivars over a 3-year period, Grosse et al. (1992) concluded that high yields could be attained from different combinations of three yield components- seeds per pod, number of pods, and individual seed weight. However, as noted by Thurling (1974b) and others, compensation among the various yield components in response to environment occurs to such an extent in oilseed brassicas that few breeders practice selection for one or even a few yield components. Observations on the contribution of various yield components to the observed heterosis in hand-crossed hybrids have confirmed earlier findings. Heterosis effects varied for each yield component depending on the environmental and/or genotypic effect when number of pods per plant, number of seeds per pod, single seed weight, and plant density were considered (Lefort-Buson and Dattke, 1982; Schuster et al., 1985; Uon, 1989; Schuler et al., 1992). Given the importance of the oilseed brassicas, very few studies have been undertaken to determine the physiological basis for increased yield. Thurling ( 1974a), who studied three Australian cultivars, found that correlations of total dry matter and yield were positive and highly significant (r = 0.70). Allen and Morgan (1975) reported that leaf area index at first flower was correlated to yield and concluded that a greater photosynthetic source at flowering and after first flower would result in higher yield. Campbell and Kondra (1978), studying single plants of three B. napus cultivars, found that seed yield was significantly correlated with total dry matter production (r = 0.2 1 to 0.52) per plant. Thurling (199 1) concluded from a series of experiments with cultivars and breeding lines that early flowering and maximum light penetration of the crop canopy are required to maximize seed yield. The importance of light penetration of the crop canopy is supported by the findings of Mendham et al. ( 1991). Comparing the seed yield of an apetalous strain to a closely related petalous variety, they attributed the higher yield of the apetalous strain to the 30% greater solar radiation transmitted through the apetalous canopy. Although these studies provide the breeder with some insight into the plant type that may be highly productive, the measurement of such parameters is normally not as efficient or effective in oilseed brassicas as the total measurement of yield. In conventional B. napus and B. juncea breeding programs for yield, various forms of the pedigree system are employed [see Thompson (1983), Downey and Rakow ( 1987),and Downey and Robbelen ( I989)]. However,

R. K. DOWNEY AND S. R. RIMMER

12

Table IV Average Relative Yield of Winter Rape Parental Lines and Cultivars Compared to Performanceof Syn-1 Synthetics and Seed Mixtures of P a r e d seed yield as percentage of parents Average of parents

Syn- I synthetic

seed mixtures

Reference

100 100 100 100

I04 I14 I06 108

97 I05 106 104

Grabiec and Krzymanski ( 1 984) Schuster and Friedt ( 1985) E o n ( 1987) Lkon and Diepenbock (1987)

'After Becker (1988). the parameters of these systems differ from pedigree cereal programs in two important respects. First, the oilseed brassica crops have a high multiplication rate per generation (- 1000: I), and second, the plant-to-plant outcrossing rate is much higher, ranging from 5 to 36% (see Section I,B,3). Thus replicated progeny testing can begin as early as the F, and a certain level of heterosis from the initial cross can be captured and retained in subsequent generations. In a comparison of winter rape selection techniques, Sauermann (1989) found that in winter B. napus visual selection in the F, for yield was superior to a random line selection, but the highest yielding lines were identified by measuring yields of single-row F, progenies in a three-replicate test at one location or by testing sublines in the F4 with one replicate at each of three locations. Because of the potential for significant levels of heterosis for yield in the oilseed brassica species, the degree of natural interplant crossing, and the absence of a highly efficient system of pollen control, synthetics have been suggested as a means of capturing part of the available heterosis. Becker ( 1988) compared the performance of experimental synthetics of winter B. napus to their parent lines or cultivars and noted that the synthetics yielded some 4 to 14% more seed (Table IV). He postulated that even higher levels of heterosis could be captured if the parents were selected on the basis of their combining ability. On the other hand, in three of the four experiments, sowing mixed seed of the parents in the same drill run also resulted in yield increases, which in some instances approached or equaled the yield of the synthetics (Table IV). U o n (199 I ) found that cultivar mixtures and Syn- 1s displayed greater yield stability than their corresponding F, hybrids or any of the individual cultivars, suggesting that heterozygosity and het-

AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

13

erogeneity of both cultivar mixtures and synthetics have a positive effect on yield stability. In B. rupu, where self-incompatibility ensures a high degree of heterogeneity, recurrent selection has been the most effective method for increasing seed yield as well as oil content (Downey and Rakow, 1987). However, with the numerous agronomic and quality traits that must now be incorporated into any new B. rupa canola cultivar, more than one specialized recurrent selection program, to be run in parallel with the main recurrent selection program, may be required. After sufficient progress is made within each specialized composite, two or more may be combined to create a new composite cultivar source. The presence of the natural self-incompatibility (SI) system in most B. r a p cultivars suggests that synthetic cultivars would be attractive alternatives to F, populations derived by recurrent selection. Falk (1991), using four parental cultivars of B. rupu, compared the seed yield of the parent cultivars and all possible F,s with their various two-, three- and four-component Syn- Is and Syn-2s. It was found that the agronomic performance of the synthetics could rival the single-cross F,s. On average, hybrids yielded 15 to 30% more seed than their parent cultivars over 2 years of testing. However, the Syn-1 populations averaged only 1% less seed than the F,s in each testing year, while the average of the Syn-2s in the last year of testing yielded only 3 and 2 percentage points less than the F,s and Syn-ls, respectively. 2. Heterosis and F, Hybrids

Although B. nupus is usually classified as a largely self-pollinating species, significant levels of heterosis for yield have been obtained in F, hybrids of both the spring and the winter forms. Based on the results from reciprocal top crosses of seven summer rape cultivars with the Canadian cultivar Regent, Sernyk and Stefansson ( 1983) concluded that it should be possible to develop hybrid cultivars of summer rape with a commercial heterosis for yield of about 40%. Also, in spring rape Grant and Beversdorf ( 1985)found high-parent heterosis for seed yield of up to 72%, with specific combining ability being more important than general combining ability. In winter rape, several researchers have documented the potential for hybrids, reporting heterosis for seed yield up to 60-70% (Schuster and Michael, 1976; Lefort-Buson and Dattke, 1982, 1985). Lefort-Buson et al. (1987) related heterosis to genetic distance in crosses between and within groups of European and Asiatic B. nupus cultivars and strains. As might be expected, hybrids between distant groups showed greater heterosis than

14

R. K. DOWNEY AND S. R. RIMMER

within-group hybrids. Additive and dominant genetic variance was more important for the within-group than the between-group hybrids. In the self-incompatible B. rapa species, Arunachalam and Bandyopadhyay ( 1984)were also able to relate the magnitude of heterosis exhibited in the F, to the genetic divergence of the parental phenotype. Singh and Gupta (1985) outlined a procedure to identify diverse genotypes using 3 1 B. rapa strains tested in 12 different environments. Indian researchers have reported varying degrees of heterosis for yield within and among Indian oilseed types of B. rapa (i.e., Toria and brown- and yellow-seeded sarson). In general, such hybrids have shown positive high parent heterosis for seed yield with a high proportion showing commercial heterosis. Unfortunately, many of these observations are based on single plant yields (Prasad and Singh, 1985; Yadav and Yadava, 1985; Singh and Gupta, 1985) or have been taken from space-planted, single-row plots (Devarathinam ef al., 1976; Labana et al.. 1978), and the results reported are often based on only I year and a single location. In most of the studies, combining-ability analysis has indicated yield to be primarily under the control of nonadditive gene action. High parent heterosis reported from Indian studies has been as great as 63% on single plant yields in yellow sarson (Labana et al., 1978). In Canada, a natural top cross of a canola breeding line onto the yellow sarson rapeseed cultivar, R500, yielded 46% more seed than the commercial B. rapa canola cultivar Candle (Hutcheson ef al., 1981). Further studies over a 2-year period, using R500 as the female parent in crosses with three Canadian oilseed cultivars and strains, showed high parent heterosis for seed yield between I6 and 37% (Hutcheson, 1984). Schuler (1989) tested hand-crossed hybrids between the B. rapa canola cultivar Tobin and 19 European and Canadian parental strains and cultivars at four locations over a 2-year period. He reported the highest average commercial heterosis for seed yield to be 64%, the same range as that found by Labana et al. ( 1978). However, the best canola-quality hybrid yielded only 22% over the commercial cultivar Tobin. Falk ( I99 1) reported that 4 of 12 hybrids from diallel crosses between four B. rapa Canadian and European cultivars exhibited high parent heterosis for seed yield. The maximum high parent heterosis found in the 2-year multilocation study was 26%, whereas the best commercial heterosis for seed yield, between canolaquality parents, was 22%. Studies of heterosis in B. junceu have for the most part been camed out on the Indian subcontinent and, as in the B. rapa studies, are largely based on single plant yields in space-planted plots. Singh (1 973) reported that six B. juncea hybrids showed an average high parent heterosis of 49% over 2 years of testing. Banga and Labana (1 984) found the range of seed yield

AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

IS

heterosis to extend from -76 to 263% over the high parent whereas commercial heterosis ranged from -77 to 172%. However, yields were measured using only 20 selected single plants per entry. Singh and Singh ( 1989, also using single plant yields, observed a heterotic yield response ranging from 9 to 9 1% over the high parent. It would appear that the greatest opportunity for commercial exploitation of the heterosis phenomenon within the oilseed brassicas occurs in B. nupus and B. junceu. In general, higher levels of heterosis have been found within these species than in B. rupu. In addition, these self-compatible amphidiploid species do not exhibit the same degree of inbreeding depression as found in the self-incompatible B. rupu during the development of high-combining parents. It is also important to keep in mind that heterosis is measured as a percentage of actual yield. As a result, the commercial advantage of a hybrid cultivar is highly dependent on the average yield of the crop being grown. Given that the average yield of winter B. nupus in some countries is over 3000 kgjha, while average yields of summer B. nupus and B. rupu are, respectively, closer to 1500 and 1000 kgjha, the level of heterosis in the latter two crops would have to be substantially higher to return to the growers the same number of extra kilos. Given the extra cost of producing hybrid seed and the moderate yield and level of heterosis found in B. rapu studies, the development of synthetic varieties of this species appears to be a more attractive alternative to hybrids. To date, no investigations have been published on the potential level of heterosis that might be obtained in B. curinutu. 3. Pollination Control Systems

The potential for increased yield from hybrid cultivars in oilseed brassica crops is substantial and has generated considerable commercial interest. However, to capture the heterotic potential exhibited in hand-crossed hybrids, some form of pollination control is required. The pollen control systems investigated include chemical gametocides, various cytoplasmic male sterility (CMS)- nuclear male fertility restorer systems, genic male sterility (GMS), and sporophytic incompatibility (SI). a. Gametocides Although gametocides have been extensively investigated in cereal crops ( McRae, 1985), only limited work on Brussicu species has been reported. Van der Meer and Van Dam (1979) were able to maintain some plants of several B. oleruceu cultivars in a completely male sterile condition for up to 24 days by repeatedly spraying with varying concentrations of GA 417 in isopropyl alcohol. Reversion to complete male fertility occurred a few days

16

R. K. DOWNEY AND S. R. RIMMER

after treatment. In B. junceu, Banga and h b a n a (1984) induced male sterility with 2-chlorethylphosphonic acid (etherel). Although they reported 54% hybridity in seed harvested from the treated plants, only shriveled seed was obtained. In general, the indeterminate flowering habit of the oilseed brassicas suggests that gametocides will be of questionable value for the commercial production of hybrid seed. b. Self-Incompatibility In the Cruciferae, SI systems, where present, are of the strong sporophytic type, characterized by an interaction between the papilla cells of the stigma and the pollen or pollen tube (Hinata and Nishio, 1980). Genetic analysis of self-compatibility(SC) and SI revealed that SI expression is not only controlled by a multiple series of alleles at a single locus but also by alleles at a complementary modifying locus (Hinata el ul., 1983; Hinata and Okazaki, 1986). Self-incompatibility has been used since the 1940s to produce hybrid cruciferous vegetables (Tsugimoto and Minato, 198 1) and since the 1960s to produce hybrid marrow - stem kale (Thompson, 1967). Thompson ( 1983) proposed the development of a three-way B. nupus hybrid, using a dominant self-compatible line as the third parent. Recently, B. nupus SI hybrids of spring canola have been registered in Canada. The first SI hybrids were produced using a system patented in Canada by Kingroup Inc. (Scott-Pearse, 199 1 ) that involves using microspore culture to produce doubled haploid plants that are homozygous for either SC or dominant SI alleles. When pollen from SC plants is transferred to SI plants, a heterozygous, self-incompatible parent is produced. This SI parent is used as the female in hybrid seed production fields, with an SC line serving as the pollen parent. Although one-half of the resulting hybrid plants in commercial fields will be self-incompatible, the surrounding non-SI plants can provide an effective pollen source. Banks (1989) provided the SI genes for these hybrids by introgressing S alleles from B. rupu and B. oleruceu into oilseed B. nupus, demonstrating their effectiveness as a practical means of pollination control. Unlike Schweiger and Eicke (1981), he found that the stability of the SI system in B. nupus was sufficient for hybrid seed production. Banks (1989) reported a good correlation between pollen tube growth and degree of seed set and concluded that this test was effective in S allele identification. One of the major constraints to the use of the SI system is the need to suppress the SI bamer so that sufficient parental seed can be produced for hybrid seed production. Various methods have been used to overcome SI [see review by Ito (198 I)], but the most efficient method for the large-scale maintenance of B. nupus SI parental lines appears to be the use of high CO,

AGRONOMIC IMPROVEMENT IN OILSEED BRASSICAS

17

concentration in an enclosed environment when plants are flowering (Nakasishi and Hinata, 1973, 1975; Thompson, 1978). An alternative method is to apply a series of salt (NaCl) sprays to the flowering plants (Guan and Wang, 1987; Monteiro et uf., 1988). The use of the SI system for hybrid development could be extended to B. junceu as well as B. rupu, which already has an SI system. However, the use of the SI system in B. rupu has two limitations. First, the level of heterozygosity within the crop is already high, which tends to limit the expected level of heterosis, and second, unlike B. nupus and B. junceu, inbreeding to maintain the SI parent results in a significant loss in vigor and seed set in B. rupu, thus increasing production costs for such hybrids. c. Cytoplasmic Male Sterility The cytoplasmic male sterile- nuclear restorer system in brassica oilseeds parallels systems in maize and sunflower and has been reviewed by Shiga (1980) and Rousselle et ul. ( 1983). Several cytoplasms have been reported to induce male sterility in B. nupus. The nap cytoplasm was identified independently by Shiga (1980) and Thompson (1983), in progeny of crosses between winter and spring cultivars, where the male parent was the Polish cultivar Bronowski (Shiga et ul., 1983). Bronowski camed the recessive male sterility rfallele together with a male fertility (F)-conditioning cytoplasm. Nearly all B. nupus cultivars carry the dominant restorer, R/;and a sterility-inducing cytoplasm. Unfortunately, the male sterile lines with an (S) rf $genotype become male fertile at moderate temperatures (26/20°C) (Fan and Stefansson, 1986) and two to five genes are involved in maintenance and restoration (Grant, 1984). Because of these complications little research is now being done on this system. The ogu cytoplasmic male sterility system, found in Japanese radish (Ruphunus sutivus L.) by Ogura (1968), was transferred to B. oleruceu and then to B. nupus (Bannerot et ul., 1977). The male sterility of the recovered CMS B. nupus plants was highly stable under a wide range of environments ( Bartkowiak-Broda et ul., 1979). However, the leaves of these plants were chlorotic at low temperatures (6, and catalase enzymes both destroy H,O, by catalyzing its dismutation [Eq. (34)]. The rate of dismutation is a better indication of quantities and activities of catalytic substances present than is amount of H,02 dismutated, because a small amount of catalyst will act on a large amount of substrate. The rate of dismutation can be evaluated by adding 5 ml of 0.5 M H,O, solution to 2.5 g of moist soil, on a dry weight basis, and clocking the time required for the soil to evolve enough bubbles to displace 24 ml of H 2 0 (1 mmol of 0,).

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K. INTERFERENCES Most colorimetric tests useful in studying redox processes in soils also involve redox reactions, and because we are trying to measure colorimetrically quantities of particular redox species in the presence of other redox species, we have many opportunities for color-interfering interactions among the various reactions. Manganese oxides produce positive interference in measuring nitrate by the hydrazine reduction method (Prochazkova, 1959) and also with brucine or diphenylamine, positive interference in nitrite by the diazonium salt method, but no interference with the diphenyl carbazide color for Cr( VI). Nitrite, citrate, and hydroxylamine negatively interfere with the Cr(VI) test, and nitrite and Cr( VI) positively interfere with determination of nitrate by brucine. Highly oxidized hypochlorite and peroxides and highly reduced substances, such as thiosulfate, sulfides, amines, and ascorbic acid, interfere with everything imaginable. Nitrate is too inert to interfere with most tests, which tells us something about the reactivity of nitrate. Wariness, ingenuity, and flexibility are required for redox titrations.

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Ehrlich, H. L. (1976). Manganese as an energy source for bacteria. Environ. Biogeochem. Proc. Int. Symp. 2nd, 2. Farrell, R. E., Swerhone, G. D. W., and van Kessel, C. (199 I). Construction and evaluation of a reference electrode assembly for use in monitoring in situ soil redox potentials. Commun. SoilSci. Plant Anal. 22, 1059- 1068. Fridovich, 1. (1975). Superoxide dismutases. Annu. Rev.Biochem. 44, 147- 159. Fridovich, 1. (1978). The biology of oxygen radicals. Science (Washinglon. D.C.) 201, 875880. Fruton, J. S., and Simmonds, S. (1961). “General Biochemistry.” Wiley, New York. Carrels, R. M., and Christ, C. L. (1965). “Solutions, Minerals, and Equilibria.” Freeman, San Francisco, California. Halliwell, B. (1974). Manganese ions, oxidation reactions and the superoxide radical. Neure tOXiCOlOgY 5, 1 13 - 1 18. Harter, R. D., and Smith, G. (1981). Langmuir equation and alternate methods for studying “adsorption” reactions in soils. In “Chemistry in Soil Environments” (D. Baker, ed.),pp. 167- 182. Soil Sci. Soc. Am., Madison, Wisconsin. Hines, M. E., Knollmeyer, S. L., and Tugel, J. B. (1989). Sulfate reduction and other biogeochemistry in a northern New England salt marsh. Limnol. Uceanogr. 34, 578590.

James, B. R. (1989). Electron activity in soils: A key master variable. Agron. Abstr., 20 1. James, B. R., and Bartlett, R. J. (1983). Behavior of chromium in soils. VI. Interactions between oxidation-reduction and organic complexation. J. Environ. Qual. 12, 173176.

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Liem, H. H., Cardenas, F., Tavassoli, M., Poh-Fitzpatrick, M. B.,and Muller-Eberhard, U. (1979).Quantitative determination of hemoglobin and cytochemical staining for peroxdihydrochloride, a safe substitute for benzidine. ide using 3,3’,5,5’-tetramethylbenzidine Ann. Biochem. 98,388-390. Lindsay, W. L. (1979).Chemical Equilibria in Soils,” pp. 386-412. Wiley-Interscience, New York. Liu, C. W., and Narasimhan, T. N. (1989).Redox-controlled multiple-species reactive chemical transport. I . Model development. Waier Resour. Res. 25,869-882. Loach, P. A. (1976).Oxidation-reduction potentials, absorbance bands, and molar absorbance of compounds used in biochemical studies. Handb. Biochem. Mol. Biol. 3rd Ed. Loganathan, P., Burau, R. G., and Fuerstenau, D. W.(1977).Influence of pH on the sorption of Co2+,Zn2+and Ca2+by a hydrous manganese oxide. Soil Sci. Soc. Am. J. 41,57-62. Lutz, H. J., and Chandler, R. F. (1946).“Forest Soils,” pp. 140-480. Wiley, New York. McBride, M. B. (1982).Electron spin resonance investigation of Mn2+ complexation in natural and synthetic organics. Soil Sci. Soc. Am. J. 46, 1137- 1142. Magdoff, F. R., and Bouldin, D. R. (1970).Nitrogen fixation in submerged soil-sand-energy material media and the aerobic-anaerobic interface. Plant Soil 33,49- 53. Marschner, H. (1990).“Mineral Nutrition of Higher Plants,” pp. 336-337. Academic Press, San Diego, California. Masscheleyn, P. H., Delaune, R. D., and Patrick, W. H. (1991). Arsenic and selenium chemistry as affected by sediment redox potential and pH. J. Environ. Qual. 20, 522527. Matia, L., Rauret, G., and Rubio, R. (1991).Redox potential measurement in natural waters. Fresenius Z. Anal. Chem. 339,455-462. Moore, J. N., Walker, J. R.. and Hayes, T. H. (1990).Reaction scheme for the oxidation of As(lI1) to As(V) by birnessite. Clays Clay Miner. 38, 549-555. Mueller, S. C., Stolzy, L. H., and Fick, G. W. (1985).Constructing and screening platinum microelectrodes for measuring soil redox potential. Soil Sci. 139, 558-560. Pohlman, A. A,, and McColl, J. G. (1988).Organic oxidation and metal dissolution in forest soils. Soil Sci. Soc. Am. J. 52, 265-27 I. Ponnamperuma, F. N. ( I 972).The chemistry of submerged soils. Adv. Agron. 24,29-96. Prochazkova, L. (1959).Bestimmung der Nitrate in Wasser. Frescnius 2. Anal. Chem. 167, 254-260. Rabenhorst, M. C., and James, B. R. (1992).Iron sulfidization in tidal marsh soils. In “Biomineralization processes of iron and manganese” (H. C. W.Skinner and R. W. Fitzpatrick, ed.). (Catena Suppl. 21.)Catena Verlag, CremCngen-Destedt, Germany. Rabenhorst, M. C., James, B. R., and Shaw, J. N. (1992).Evaluation of potential wetland substrates for optimizing sulfate reduction. Proc. Nail. Meet. Am. Soc. Surf Min. Reclam.. Duluth, Minnesota (in press). Reddy, K. R., and Patrick, W. H. (1980).Evaluation of selected processes controlling nitrogen loss in a flooded soil. Soil Sci. Soc. Am. J. 44, 1241 - 1243. Ross, D. S..and Bartlett, R.J. (1981).Evidence for nonmicrobial oxidation of manganese in soil. SoilSci. 132, 153-160. Rowell, D.L.( I98I ). Oxidation and reduction. Chem. Soil Processes, 40I -463. Russell, E. W. (1973).“Soil Conditions and Plant Growth,” 10th Ed., pp. 670-695.Longman, London, England. Schnitzer, M., and Khan, S. V. (1972).“Humic Substances in the Environment,” p. 300 Dekker, New York. Senesi. N., and Schnitzer, M. (1978).Free radicals in humic substances. Environ. B i o g w chem. Geomicrobiol., Proc. Inr Symp., 3rd, 2,467-480. Shindo, H. (1990).Catalytic synthesis of humic acids from phenolic compounds by Mn(1V) oxide. Soil Sci. Plant Nutr. (Tokyo) 36,679-682.

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Shindo, H., and Huang, P. M. (1982). Role of Mn(1V) oxide in abiotic formation of humic substances in the environment. Nuture (London) 298, 363-365. Shindo, H., and Huang, P. M. (1984). Significance of Mn(IV) oxide in abiotic formation of organic nitrogen complexes in natural environments. Nature (London)308, 57- 58. Sillen, L. G. (1967). Master variables and activity scales. Adv. Chem. Ser. Silver, M., Erlich, H. L., and Ivarson, K. C. (1986). Soil mineral transformation mediated by soil microbes. In “Interactions of Soil Minerals with Natural Organicsand Microbes” (P. M. Huang and M. Schnitzer, eds.).pp. 497-5 19. Soil Sci. Soc. America, Madison, WI. Sparks, D. L. (1985). Kinetics of ionic reactions in clay minerals and soils. Adv. Agron. 38, 23 I -265. Sparrow, L. A., and Uren, N. C. ( I 987). Oxidation and reduction of Mn in acidic soils: Effect of temperature and soil pH. Soil Biol.Biochem. 19, 143- 148. Sposito, G. (198 I). “The Thermodynamics of Soil Solutions.” Oxford, New York. Sposito, G. (1989). “The Chemistry of Soils.” Oxford, New York. Stone, A. T., and Morgan, J. J. (1984). Reduction and dissolution of manganese(ll1) and manganese(1V) oxides by organics: 2. Survey of the reactivity of organics. Environ. Sci. Technol. 18,617-624. Stumm, W., and Morgan, J. J . (1981). “Aquatic Chemistry,” 2nd Ed.,pp. 418-504. WileyInterscience, New York. Sullivan, J. C., Gordan, S., Cohen, D., Mulac, W., and Schmidt, K. H. (1976). Pulse radiolysis studies of uranium (VI), neptunium (VI), neptunium (V), and plutonium (VI) in aqueous perchlorate media. J. Phys. Chem. 8, 1684- 1686. Sunita, J. M., Loll, M. J., Snipes, W. C., and Bollag, J. M. (1981). Electron spin resonance study of free radicals generated by a soil extract. Soil Sci.131, I45 - 150. Thompson, 1. J. (1923). “The Electron in Chemistry.” Franklin Institute, Philadelphia, Pennsylvania. Thorp, H. H., and Brudvig, G. W. (1991). The physical inorganic chemistry of manganese relevant to photosynthetic oxygen evolution. New J. Chem. 15,479-490. Vincent, A. (1985). “Oxidation and Reduction in Inorganic and Analytical Chemistry.” Wiley, Chichester, England. Wang, T. S. C., Huang, P. M., Chou, C.-H., and Chen, J.-H. (1986). The role of soil minerals in the abiotic polymerization of phenolic compounds and formation of humic s u b stances. Interact. Soil Miner. Nat. Org. Microbes Proc. Symp., 1983, 25 I - 28 1. Weaver, J. H. (1987). “The World of Physics.” Simon and Schuster, New York. Westcott, C. C. ( I 978). “pH Measurements.” Academic Press, New York. Zumdahl, S. S. (1986). “Chemistry,” pp. 931 -935. Heath, Lexington, Massachusetts.

PLANTNUTRIENT SULFURIN THE I~OPICS AND SUBTROPICS N. S. Pasricha’ and R. L. Fox’

’

Department of Soils, Punjab Agricultural University, Ludhiana, India Department of Agronomy and Soil Science, University of Hawaii at Manoa, Honolulu, Hawaii 96822

1. Introduction 11. Extent of Sulfur Deficiency 111. Forms of Sulfur in Soil A. Sulfur Transformation Products B. Sulfate Sulfur IV. Sulfur Cycling in the ‘Tropics A. Sulfur Supplies of Atmospheric Origin B. Sulfur Accession through Precipitation V. Effects of Acid Rain A. Effect on Crop Plants B. Effect on Forest Vegetation C. Effect on Soil Acidification VI. Sulfur in Irrigation Waters A. Sulfur in Streams B. Sulfur in Groundwater VII. Sulfate Retention in Soil A. Sulfate Adsorption and Desorption B. Sulfate Adsorption Curves C. Mechanism of Sulfate Adsorption VIII. Diagnosis of Sulfur Needs A. Soil Tests B. Plant Analysis IX. Critical Soil Solution Concentration X. Crop Responses XI. Sulfur Fertilization and Crop Qualiry A. Effect on Protein Oualiry B. Effect on Oil Content

Adwnrti m Abmnary. C‘ol 10 Copyright 0 1993 by Academic Press, Inc. All rights of reproduction in any form reserved

209

210

N. S. PASRICHA AND R. L. FOX

C. Effect on Glucosinolate Content D. Effect on Nitrate Content XU. Sulfur Interactions with Other Elements A. Interaction with Phosphorus B. Interaction with Other Elements XI11. Summary and Conclusions References

I. INTRODUCTION Many generalizations of doubtful validity have been promulgated and postulated about “tropical soils.” One example is the concept that soils of the tropics are highly weathered. In fact, many soils of the tropics are so highly weathered that little remains except sesquioxides and some 1 : 1 layer silicates, but there are also numerous examples of tropical soils in which 2 : 1 clays influence, or even dominate, soil chemistry and physics. Because many soils of the tropics have reached an advanced stage of weathering, it is frequently assumed that chemical weathering in the tropics is greatly accelerated as compared with the temperate zone. However, in most of the tropics, rainfall is seasonal. The dry season may retard chemical processes just as effectively as the cool season does in the temperate zone. But even in the tropics, rejuvenating influences have operated in soils (Jackson et al., 1971; Syers ef al., 1969). Inasmuch as some concepts about tropical environments may be inappropriate, if not inaccurate, it follows that some of the concepts about the chemistry and nutritional status of soils of the tropics based on those assumptions should be reexamined. It is probably safe to say that there is nothing unique about the types of soil fertility problems encountered in soils of tropical and subtropical regions. Soil fertility problems are not necessarily more complex either, although multiple nutrient deficiencies tend to be the rule rather than the exception for leached and weathered soils of the humid tropics. A more unique feature of the tropical and subtropical zones is the magnitude of soil fertility problems in relation to the resources that are being committed, or being advocated, for alleviating those problems. Sulfur deficiencies in tropical and subtropical regions have been recognized for many years. The deficiency is particularly widespread in the semiarid and subhumid savannas of tropical America and Africa. BoleJones (1964) reviewed the early work on S deficiencies in Africa. He concluded that deficiencies are most likely on fermginous and ferrallitic soils developed on very old erosion surfaces that separate major drainage systems south of the Sahara. Sulfur deficiency was described by McClung

PLANT NUTRIENT SULFUR

21 1

and de Freitas (1958) as a major fertility problem for developing the Brazilian Campos. Sulfur was second only to P as a nutritional factor limiting growth of grasses. McClung ef al. ( 1958) believed that responses to S in central Brazil would be more common if N and P were plentifully supplied and if cropping were intensive. de Freitas et al. (1972) reported benefits from applying S fertilizer to coffee in Sao Paulo State, Brazil. Sulfur deficiencies have been reported from other tropical and subtropical areas, including islands in the Caribbean (Haque and Walmsley, 1973) and Hawaii (Fox et al., 1965). There is considerable evidence of S deficiency in subtropical regions (Kanwar and Mohan, 1962; Kanwar, 1963) and of the response to its application (Dalal et al., 1963; Chopra and Kanwar, 1966; Pasricha and Randhawa, 1971). However, there is less evidence of S deficiencies in areas of tropical rain forests in Nigeria (Kang and Osiname, 1976). The sandy surface soil therein contains a modest amount of adsorbed sulfate with a solubility of 8 p g S m1-I. The subsoil, which contains more clay, is relatively rich in adsorbed sulfate but the solubility is low (Fox and Blair, 1986). It now seems probable that better sulfur nutrition of crops in forest zones is related to the capacity of subsoils to retain sulfate. Although detailed data are lacking, savanna soils seem to be much poorer in adsorbed sulfate than are soils of rain forests. In this review we intend to give an interpretive account of developments in various aspects of sulfur as a plant nutrient in subtropical and tropical soils.

11. EXTENT OF SULFUR DEFICIENCY An examination of the pattern of S deficiency on a global basis leads at once to the conclusion that areas prone to S deficiency are those which are remote from smelting industries and from heavy industrial or domestic burning of fossil fuels; areas in which weather is controlled by air masses originating from such regions; and areas which have marked wet-dry rainfall patterns giving rise to a savanna-type vegetation that is frequently burned. The situation becomes locally worse where soils are derived from basic igneous materials, especially volcanic ash, at intermediate or high elevations and some distance from the sea. Generally these are the areas in which low quantities of SO, are deposited in precipitation. Many tropical and subtropical areas fall into one or more of these categories. Thus, it is not surprising to observe that S deficiencies are frequently encountered in the tropics and subtropics. Numerous observations on a variety of crops in the tropics have demon-

212

N. S. PASRIClIA AND R. L. FOX

strated that incipient S deficiencies do abound. This is related to low concentrations of S in rainwaters and generally low levels of organic S in soils (Fox and Blair, 1986). Organic matter contents of tropical soils are not so low as is sometimes supposed. This fact is evidence for the stability of such organic matter that persists. It should not be assumed, however, that the availability of S in the resistant organic matter will be as readily available to plants as that which has already decomposed. The implications of this for the future are clear; organic S will be decreasingly important with increasing time of arable agriculture. To complicate the problem, some of the soils of the humid tropics adsorb S q - strongly, especially in subsurface horizons. These soils may be S deficient even though they contain much SO, (Hue et al., 1990). Sulfate solubility, and presumably its availability to plants, is related to the quantity of adsorbed SO, in relation to the capacities of soils to adsorb SO,. Most soils developed in weathered volcanic ash adsorb SO, strongly. Widespread S deficiencies in groundnut in the West Africa savanna have been recognized for 40 years and are well documented. Fox (1980a) estimated that exported S in 750,000 tons of groundnut kernels would amount to 1500 tons S per year, assuming a nominal content of 0.2% S in the kernels. Although this is not a large quantity by the standards of S reserves in most temperate zone soils, it is a serious drain for a system in which S deficiency has been chronic. The magnitude of the problem is placed in better perspective by considering that the total expected S content of rain for the groundnut-growing belt of northern Nigeria ( 1.2 million hectares) amounts to about 1400 tons, essentially equivalent to S being exported (Bromfield, 1974). Kang et al. (198 1) reported results of laboratory and greenhouse expenments comparing the S status of savanna and forest upland soils of 30 surface soil samples (0- 15 cm) from Nigeria. The S status was not related to parent material or soil type. Total and extractable S levels were in the following order: forest zone > derived savanna > Guinea savanna. Observed sulfur deficiency was most acute in soils from Guinea savanna and least acute from the forest zone. Sulfur responses are most frequently observed in the savanna zone (Enwezor, 1976). Sulfur deficiencies have been reported from several locations in the humid tropics and a few studies on the sulfur status of soils there have been reported (Bornemisza and Llanos, 1967). However, much more needs to be done before accurate predictions can be made on the magnitude of S problems, or probable requirements and effectiveness of S fertilizers. Many Central American soils, particularly those under more or less permanent crops such as coffee, cocoa, sugarcane, or pastures, have accumulated organic matter in the surface and consequently contain high organic S levels (Bornemisza et al., 1978; Burbano and Blasco, 1975; Granados,

PLANT N U T R I E N T SULFUR

21 3

1972; Hardy and Bazan, 1966). However, a favorable C :S ratio is more important than a large store of organic matter for S response under tropical conditions (Bromfield et af.,1982). This is because the ratio influences amounts of S that will be mineralized (or immobilized) during microbial decomposition of organic matter. Bornemisza ( 1990) reported detailed information on S distribution and S problems in Central America. About half of the soils in the Entisol and Inceptisol orders respond to S, especially after N and P deficiencies have been corrected. Soils that are coarse textured are most responsive because of the leaching that is associated with them. Cordero et af. (1986) reported that in some of these soils, S deficiencies are the main production-limiting factor. Andisols are important in the area because of widespread volcanic ash influence, and research on S problems of these soils has been reported (Jimenez and Cordero, 1988).The more highly weathered Andisols adsorb large amounts of SO, on exchange sites below the A horizon (Gebhart and Coleman, 1974). However, SO, can be displaced by phosphate fertilizers, which can result in deficiencies, as has occurred in El Salvador (Muller, 1965). Sulfur deficiencies have been reported on Mollisols particularly after the P status was improved by P fertilization (Kass et af., 1984). Research in Panama and Costa Rica indicates considerable variation in S status of Alfisols. Research in Panama has confirmed S problems in these soils both in pot studies and in field conditions. Comparable soils in Brazil have shown strong pH-dependent SO, adsorption capacity (Couto ef al., 1979). In the Pacific lowland of Central America, S deficiency in Vertisols becomes evident only after correcting P deficiencies and consequent leaching of SO, (Bornemisza et al., 1978). In Brazil, accumulations of SO, results in increased cation retention, which can partially compensate for low exchange capacities of soils. Insufficient S usually becomes a problem for sugarcane after problems of N, P, and sometimes K have been corrected. Williams and Andrew (1970) were unable to outline any major occurrence of S deficiency in tropical Australia. It cannot be inferred, however, that S is adequate on all soils and one must look further for an explanation of this apparent sufficiency of S. The accession of S by the plant/soil system in this nonindustrialized area, if indeed it does accrue, can be considered a redistribution rather than a gain (Wetselaar and Hutton, 1963), and in any case must be low. At Townsville (near the sea) and Woodstock (20 km inland), depositions of 5.7 and 2.6 kg S ha-' annum-', respectively, have been measured (Jones et af., 1975). Other records are available from coastal stations further south in Queensland (Sedl, 197 l), where annual deposition of 3.7 to 25.2 kg S ha-' was measured. The higher figures were registered during periods of intense rainfall associated with cyclones. In tropical regions with little industrial activity, SO4-S concentrations in

214

N. S. PASRICHA AND R. L. FOX Table I Sulfate S in Soils along Tmsects in Rwanda as Determined by Repeated Phosphate Extraction" Surface Mean Transect no.

Soil

Solyinyo ( I ) Karisimbi (3) Karisimbi (2) Ruhengeri-Kigali (4) Kigali-Kibuye (5) Cyangugu-Gikongoro (6) Butare (6) Bugesera (7) Kigli-Kibungo(8) Gabiro-Ryumba (9)

Andept Andept Andept Udult Tropept/Humult Tropept/Humult Tropept Ustox/Orthox Ustox/Ustalf Ustox/Usdult

Mean

Range

Subsoil Mean

( M g-')

27 64 29 23 19 45 5.6 I1 11.5

27 26.2

2-84 6 - I36 2-66 2-46 2-54 4 - I80 0- 16 0-32 4-28 4 - 120

Range g-9

19 50 15 28 26 48 4 34 41 24

2-24 14- I38 2-44 8-50 8-72 8-94 1-12 6-62 6 - 1 372b 4- 102

29

Adapted from Vander Zaag ef a[. (1984). bvalues > 200 not included in the average.

rainwater are usually less than 1 pg m1-I. In Rwanda, SO, was generally a little more abundant in subsoil samples than in 0- to 15-cm samples (Table I). Information on availability of subsoil sulfate is limited, but deep-rooted crops are likely to benefit from subsoil sulfate. Sulfate levels determined in these soils appear to be deficient or near deficient. For soils from volcanic ash (Dystrandepts) 25 pg g-l was inadequate (Fox et al., 1965), but 810 pg g-l may be adequate for soils that do not adsorb sulfate in appreciable quantities (Kang and Osiname, 1976). Sulfur deficiency is widespread in rice fields in Bangladesh (Hoque and Hobbs, 1978; Hussain, 1990). About 44% of the cultivated land in Bangladesh is estimated to be S deficient. Crops grown on these soils respond to S application. The major cause of S deficiency seems to be extremely low redox conditions in wetland rice, although SO, is the last compound to undergo reduction, after NO3-, Mn (IV), and Fe (111) compounds, when reducing conditions set in. In soils with fine texture and appreciable decomposable organic matter, SO, reduction to H,S is likely. Decreased incidental addition of S is a probable reason why S deficiency is now appearing more frequently than formerly. Besides smaller accretions of S by rain, a drastic decrease in incidental S additions in fertilizers is

PLANT NUTRIENT SULFUR

215

100 h

a

0 1950

1960

1970

1980

1990

Figure I . Trends in consumption of S-bearing N and P fertilizers in India during 19501990 (Pasricha and Aulakh, I99 I ; by permission of The Sulphur Institute, Washington, D.C.)

a probable cause for the appearance of S deficiency in crops in India (Pasricha and Aulakh, 199I). In 1950, sulfur-containing fertilizers were commonly used sources of N and P. At that time 28,900 tons of N as ammonium sulfate and 4279 tons of P as single superphosphate were applied. The consumption of fertilizer N and P has increased sharply since then to 7,396,000 tons of N and 1,315,000 tons of P in 1990. However, use of N and P fertilizers that contain S has relatively decreased, thus resulting in a drastic decrease in the use of S (Fig. 1). An analysis of 1164 soil samples collected from all over India indicated S deficiency to the extent of 4 1 % (Singh, 199I). In Thailand, Hoult et al. ( 1983) estimated that 50% of the northeast plateau, 30-40% of the southeast coast, and 30-40% of the northern highland area are S deficient and would respond to S fertilization.

111. FORMS OF SULFUR IN SOIL

A. SULFURTRANSFORMATION PRODUCTS Sulfur is continuously cycled between inorganic and organic forms. Three broad fractions of organic S have been identified: (1) ester sulfate, (2) C-bonded S (mainly amino acids), and (3) residual S (Tabatabai, 1982). The nature of the compounds formed and their transformations are

216

N. S. PASRICHA A N D R. L. FOX

strongly influenced by biologically mediated processes, which in turn are affected by environmental conditions. Perhaps 95% or more of the total S in arable soils in temperate regions is organic S. This generalization does not apply in the tropics. Inorganic SO, vanes seasonally in soils. Castellano and Dick ( 1991) observed that during rainy winter seasons, SO, levels ranged from 7 to 13 mg kg-' in gypsum-treated plots compared with 2 to 7 mg kg-' in control plots. In the months from March to May, biomass S increased and SO, level decreased (.E \f

3

H

z

53 0 c

a

(1

' a *

" 3 :: 2 4 vr

$9

x

D

A

n 22 Transfer to ocean

3.

95

(T) Figure 2. Global sulfur cycle (units: lo6tons S/annum) (Robinson and Robbins, 1968).

Another pathway is the atmosphere-plant-soil route. This is called dry deposition and is important in industrial and residential areas where fossil fuels are burned. In the tropics, burning of vegetation is relatively more important. Areas that have a marked wet-dry rainfall pattern giving rise to savanna-type vegetation that is regularly burned no doubt lose much of the S that accrues to them in rainfall in this way. Large areas of the tropics are so affected. Burning is generally done in the dry season. Thus there is little likelihood that S volatilized by agricultural burning will be redeposited on land from which it came. A disproportionate quantity will accrue to downwind locations and to nearby areas where soils are moist and vegetation is green (Fox and Blair, 1986). Burning is likely to be important in the redistribution of S in tropical Australia. Most native vegetation is subject to fire (Tothill, 1971), but we were unable to find reports on S losses from such fires. Losses are likely to be appreciable, if data from burning of heather (36% loss) are a guide. Sulfur is one of the main components of atmospheric deposition. Atmospheric deposition impacts S cycling both directly and indirectly. The inputs of S may be relatively large (60 kg S ha-' yr-l) in some ecosystems (Johnson, 1984) and very few studies have been done on the effect of these inputs on S cycling. Increased numbers of S oxidizers have been measured,

PLANT NUTRIENT SULFUR

219

but effects on S oxidation have been mixed (Wainwright, 1979, 1980). The sulfur cycle is important in understanding the S budgets of soil. One estimate of the global S cycle (Robinson and Robbins, 1968) is presented in Fig. 2. Major components of the S cycle system are gaseous S in the atmosphere, dissolved S in rainwater, S in surface and groundwater (imgation), inorganic S in soils, organic S in soils and plant residues, and S in vegetation. In areas of coarse-textured, low-organic-matter soils that lack significant capacities for surface sorption, the limit of S uptake (S yield) by crops is approximately equal to dissolved S in precipitation. If incoming S is in the range of 1 to 4 kg S ha-', sulfur deficiency becomes a major constraint, even for low levels of production, in areas as diverse as the United States (Alabama, Nebraska, and Hawaii), Nigeria, Australia, and New Zealand (Fox and Hue, 1986). Gaseous S may contribute 20% or more of the S taken up by plants, but this S source is not a significant factor in most tropical areas.

A. SULFURSUPPLIES OF ATMOSPHERIC ORIGIN Because the atmosphere is the major S source for most upland soils, the S budget can be understood better if it is viewed in the context of the total environment. It is, therefore, important to know the S compounds in the atmosphere and their concentration and chemical behavior, the source of S in the atmosphere, and the quantity of S supplied to soils from the atmosphere. Atmospheric S is generally present in gaseous form as H,S and SO,, and as particulate forms as sulfate. Considerations of the global S budget show that HzS, SO,, and particulate SO, are present as trace constituents. These are primarily of natural origin except in polluted areas where anthropogenic emission may dominate. There are few reliable data on atmospheric H,S. Concentrations of this gas are greatest near natural swamps, anaerobic waters, industrial sources, volcanoes, geothermal wells, etc. Hydrogen sulfide has a background concentration between 5 and 50 parts in lo', parts of air by volume (Slatt et al., 1978). It has been proposed that reaction of carbaryl sulfide and CS, is an important source for both HzS ( McElroy ef af.,1980)and SO, (Logan et af.,1979). The latter author postulated that the source of atmospheric SOz formed from CS, and COS can be quite large. A major source of sulfides from the oceans is dimethyl sulfide produced by phytoplankton. Estimates of the total quantity of S released to the atmosphere in this way are greater than estimates of anthropogenic S sources. Although the quantity of this product is relatively large, the concentration is so low and the half-life is so

220

N. S. PASRICHA AND R. L. FOX

short that dimethyl sulfide is not an environmental problem. We assume that sulfide is a major contributor to background S in the tropics, without which S deficiency would be an even more serious problem than it is already. Such considerations suggest that S emission control measures such as are now being instituted, although locally effective, will be of little significance on a global basis. For SO,, an average concentration in the troposphere is about I p g m-3 STP. A generalized value for SO, is given as 0.9 ppb, but a value of 0.3 ppb is given for central Brazil. Values are higher in Panama (Lodge et al., 1973). Although the United States generates 35% of the world’s electricity and consumes a corresponding fraction of fossil fuel, its production of SO, may be less than 35% of the world’s production from energy sources (Kellog et al., 1972).We will adopt the figure 100 X lo6tons of SO, per year for total man-made contributions to the atmosphere. This corresponds to I50 X lo6 tons per year of SO,, into which most of the SO, is converted. This is a global figure. It is significant that only about 6.5% was produced in the Southern Hemisphere [Massachusetts Institute of Technology (MIT), 19701. Because seawater contains SO,, SO, concentrations in the air in coastal areas usually are higher than they are further inland. In polluted surface air the SO,: SO, ratio is about 10 times greater than in clean air (Junge, 1970). Thus, SO4 concentration does not vary as much as SO, concentration. Oxidation products of SO, are further oxidized to SO, by a variety of processes. The net residence time for SO, in the atmosphere must be similar to that of SO, because the overall ratio of SO, :SO, concentration in the atmosphere seems to be close to unity (Georgii, 1970). Quantitative estimates of global sources of S compounds in the atmosphere are presented in Table 11. The total amount of about 2 X lo8 tons/annum is of the same order as global industrial production or consumption of s. Sulfate aerosols are primarily produced naturally from sea spray over the ocean. Most of it is deposited over the ocean by rain. The large figures for H,S production were obtained indirectly by budget considerations and these may not be reliable. The range of maritime sulfate concentrations, 0.22 - 2.72 p g m-3, determined around Asia by Horvath et al. (1981) are in good agreement with results obtained over oceans in other parts of the world (Nguyue et al., 1974a,b). The value of excess SO4 (0.87 pg m-3) is similar to the value of 0.9 pg m-3 reported by Grevenhorst (1978) for the North Atlantic. Although the origin and nature of precursor gas is not well understood, one possibility is anthropogenic SO,. However, taking into account the residence time of SO, ( 1 -2 days) as well as wind direction observed during sampling rules SO, out as a major source in favor of submicron sulfate

PLANT NUTRIENT SULFUR

22 1

Table 11 Estimates of Sources of Atmospheric S per Yeara

Land (tons S)

Ocean (tons S)

-

Source

Anthrowgenic

Natural

Anthrowgenic

Total

-

-

7 0 X lo6 1 3 X lo6$'

4 4 x 106 3 0 X 106

-

3 x 106

4 4 x I06 103 X 106 73 x 106

Natural

so, H2S

so2

-

-

-

220 x 106

Grand total Adapted from Robinson and Robbins (1968). Total (natural anthropogenic).

f,

+

particles from a sulfur gas of natural origin, namely, dimethyl sulfide, the oceanic release of which is estimated at 27 Mt yr-'.

B. SULFURACCESSION THROUGH PRECIPITATION The relationship between soil sulfate and rainfall is complex. Rainfall amount seems to have influenced soil sulfate in five ways: (1 ) SO, accession, (2) SO, retention, (3) SO, utilization, (4) S immobilization, and (5) SO, leaching. Sulfate accessions are the combined effects of rainfall quantity and rainfall quality. Muller (1975) analyzed rainwater and lysimeter leachates for total S for 20 years at the Otara Research Station, Auckland, New Zealand. Losses of SO, in leachates from fertilized and unfertilized soils were also determined. An average of 13 kg ha-' S was received annually in the rainfall, with extremes of 6.6 and 17.6 kg ha-'. The proximity of tidal flats and accessions from aerial top-dressing may have been responsible for contributions not exceeding 25%. Sulfur concentration in rainwater in the continental tropics is usually low. The deposition of S in rainfall was measured at 10 locations in Central Kenya, monthly for 1 year (1977- 1978) by Bromfield el al. (1980). Amounts deposited ranged from 1.58 to 3.81 (mean 3.47) kg S ha-'. Concentrations ranged from 0.10 to 0.17 (mean 0.12) mg S liter-'. Low S concentration in rainwater and depleted organic matter reserves of soils are associated with S deficiency in the seasonally dry West African Savanna. Mean annual S in rainfall for northern Nigeria is about 1.14 kg S ha-' (Bromfield, 1974), suggesting that yields of cowpea, an important crop in the seasonally dry savanna, are limited by S deficiency (Fox et al., 1977).

N. S. PASRICHA AND R. L. FOX

222

1 .o

0.8 0.6

0.4

0.2

I

I

I

lo3

lo4

lo5

Distance (km) x altitude (m)

Figure 3. Influence of distance and elevation from the sea on the concentration of S in rainwater (Fox el al., 1983).

On the other hand, rainfall, air deposition, and particulate matter contributed approximately 10.7, 1.8, and 3.0 kg S ha-' per year, respectively at one location in the southern United States (Suarez and Jones, 1982). No relationship was obtained between applied S and crop response for several crops. Suarez and Jones (1982) emphasized the need to keep in view contributions of atmospheric deposited S when making fertilizer recommendations. Influence of the sea as a S source diminishes in proportion to a product of distance and elevation from the source (Fox et a/., 1983). Sulfur concentration in rainwater dropped exponentially with increasing distance from the coast in both New Zealand and Hawaii (Fig. 3). For example, in Hawaii, rainwater contained 4.5 mg S liter-' 0.5 km from sea, 1.0 mg S liter-' 3 km inland, and only 0.1 mg S liter-' 24 km from the coast. Estimated total S inputs from rain were 24, 10, and 1 kg S ha-' at 0.5, 3, and 24 km distance, respectively (Hue et al., 1990). Although New Zealand is only subtropical in its northern latitudes, data on the S composition of rainwater should provide a useful example of the importance of the sea in tropical regions. Maximum distance from the sea in New Zealand was 100 km. At that distance the sea was of little consequence but, even so, 0.2 mg S kg-' in rainwater has some agricultural significance. Fox et af.,

PLANT NUTRIENT SULFUR

223

1979) demonstrated that 0.2 mg SO,-S liter-’ was sufficient for approximately one-half maximum yield of banana. In the Southern Hemisphere and in the tropics generally, background atmospheric S is low because atmospheric S does not move readily across the tropical convergence zone. Thus, the influence of the oceans can be more readily discerned there than in the North Temperate Zone, where, because of pollution, the influence of oceans is relatively less important.

V. EFFECTS OF ACID RAIN The effects of acid rain (precipitation) are widely debated. Some of the chemical compounds associated with acid deposition are important nutrients for both plants and animals. Water in equilibrium with CO, in the atmosphere has a pH of approximately 5.6. As usually defined, “acid rain” is rain with pH below 5.6 resulting from the solution of other acid-forming constituents, such as SO,, directly from the atmosphere. This process is known as “wet deposition.” The term “acid deposition” represents the total deposition of acid from the atmosphere. With adequate precautions, the acidity of precipitation can be measured with reasonable ease and precision, but dry deposition is not so easily determined and little is known of the magnitude or significance of dry deposition [Council for Agricultural Science and Technology (CAST), 19851.

A. EFFECTON CROPPLANTS Experiments with simulated acid rain within the observed pH range of acid precipitation have sometimes decreased crop yields, although Irving (1983) concluded that the effects appear to be very small, and that when responses are observed, they may be positive or negative. There is no convincing evidence that acid precipitation as such is detrimental to crops in the field. Increased incidence of blossom-end rot of tomatoes has been associated with volcanic activity in Hawaii, suggesting that acid rain may have brought on a Ca deficiency. Faller ( 1 97 l), observed that crop yields increased with increasing concentration of SO, in the atmosphere (Table 111). For tobacco, total dry weight increased up to 48%. The yield of leaves and stems increased by SO%, reflecting reduced root yield frequently associated with improved S status. Additions of SO, increased plant inorganic sulfate. Simulated acidic rain on radish plants decreased hypocotyl growth but not shoot growth

N. S. PASRICHA AND R. L. FOX

224

Table 111

Effect of Atornospheric SO,on Relative Dry Matter Yields of Sunflower, Cow and Tobacco" Relative yield, dry weight (per x mg SO, M-' air) Crop Sunflower TOP Root Corn TOP Root Tobacco TOP Root

N=O

0.2

0.5

1.o

1.5

100 100

I49 93

I52 89

I78 45

I59 60

100

112

100

100

I24 98

I I7 87

I I3 87

100 100

147 99

165 79

I77 75

I85 75

Adapted from Faller ( 197I); by permission of The Sulphur Institute, Washington, D.C.

0

3

6

9

1 2 1 5

Internal flux of SO, (nrnol ern-' hc')

Figure 4. Relationship between the internal deposition of SO, and the inhibition of net photosynthesis in Viciu fubu (Black and Unsworth, 1979;Reprinted with permission from Nuiure (London), Macmillan Magazines Limited.)

PLANT NUTRIENT SULFUR

225

(Jacobson et al., 1986). Heggestad and Lesser (1990) studied the effects of SO, in concentrations from 0.005 to 0 . 2 2 4 ~ 1liter-’ (4 hr day-’, 5 days week-’) from seedlings to mature soybean. They observed a negative impact on bean yields and seed size. Black and Unsworth ( 1979)observed that CO, assimilation in Viciafaba associated with low levels of SO, exposure was highly flux dependent, exhibiting first-order reaction kinetics at fluxes less than 1 nmol cm-* hr-I (Fig. 4). At higher fluxes, CO, assimilation was typical of second-order reaction kinetics achieving a trend indicative of saturation at fluxes greater than 8 nmol cm-, hr-’.

B. EFFECTON FORESTVEGETATION Much of the literature on SO, deposition has been reviewed by Voldner ef al. (1986). While most of the measurements were done on field crops, studies on watersheds in forests suggest that pollutant effects on ecosystems can be more important than direct effects on vegetation. Near large anthropogenic sources of SO,, accretions of SO, by forests may be the largest source of S in the watershed S balance. Even at some distance from these sources, inputs from dry deposition of SO, may be nearly as great as the input from acid rain (Garland, 1977). For this reason, it is necessary to make accurate estimates of the input of SO, to forested watersheds and to know how the S from this source is redistributed in the forest system. Gay and Murphy (1989) attempted to measure the deposition and fate of 35S02 in a pine plantation. Sulfur dioxide is a much discussed air pollutant in relation to a “new type” of forest damage, but owing to the spatial distribution of SO, deposition, it cannot be singled out as the causative agent. Atmospheric concentrations of SO, are highest in industrial and densely populated areas, but the most serious forest damage occurs in remote areas. In fact, SO, concentrations in urban areas have decreased significantly (Kandler, 1985). A decreasing SO, emission trend over western Germany has been shown by Huettl ( 1989). In areas where forest damage is observed, SO, concentration may be below well-established International Union of Forest Research Organization (IUFRO) standards (1983). Thus direct SO, damage is not the overall cause for “new type” forest damage. This conclusion is supported by histological observations by Fink (1986). So far there are no research results indicating that acid precipitation, within the range of pH values usually encountered, directly damages forest vegetation [Council for Agricultural Science and Technology (CAST), 19851.

226

N. S. PASRICHA AND K. L. FOX

C. EFFECTON SOILACIDIFICATION The evidence for widespread accelerated acidification of soils by acid precipitation is not very strong. Acid soils are predominant in humid regions from the tundra through the tropics, irrespective of their proximity to industrial emissions. They have been acid for a long time. Even strongly acid precipitation in a humid region with well-buffered soils probably would be detectable only after several decades. However, in Hawaii, and in many tropical areas, some of the soils are so delicately poised with respect to pH that only small amounts of acid might push them over the edge (Fox and Hue, 1986).

VI. SULFUR IN IRRIGATION WATERS

A. SULNR IN STREAMS Surface waters and groundwaters may be important sources of S for irrigated or flooded crops. Sulfur in imgation waters varies greatly depending on whether it is surface water or groundwater. Much runoff water from high mountains is S deficient, and so is water from some aquifers. Sulfur deficiencies have been discovered in newly reclaimed Swamp soils in the lower Amazon Basin (Wang, 1978). A general deficit in S in the environment of tropical South America has been known for many years (McClung and de Freitas, 1959; McClung ef al., 1959). The amount of S in a stream depends on contributions from geologc formations and other inputs contributing to the water. For example, the upper Yakima river in Washington State contains only 0.7 mg liter-' of S and crops irrigated with it respond to S fertilization, but the lower reaches of the river, contain 1.4 mg liter-' and irrigated crops do not respond to S applications. At its mouth, the river water contains 5.1 mg liter-' (Dow, 1976). Yoshida and Chaudhry (1972) observed that imgation waters carrying more than 2.7 mg S liter-' met the S requirement of rice. Wang el al. (1976) suggested this limit is 6 mg liter-'. Severe S deficiency in rice in South Sulawesi, Indonesia, was not prevented by imgation with waters having 2.8 mg liter-l (Blair ef al., 1978). Generally, irrigation waters carrying more than 4 to 6 mg liter-' S will supply enough S for most crops. Applicability of this guideline will depend on (1) the amount of water applied per growing season, (2) crop requirement, (3) redox potential of the system, and (4) yield expected.

PLANT NUTRIENT SULFUR

227

Sulfate contents of nine selected Indonesian irrigation waters ranged from 1.28 to 20.2 mg liter-' of SO,-S with all but two samples being 6. I7 mg liter-' or less (Ismunadji and Zulkamaini, 1978). These two were associated with extractable SO4-S of < 4 mg kg-l. A survey of 254 rice fields indicated that 31% were deficient and 42% were marginal in S ( 1000 mg SO,-S kg-I (Fig. 6). These soils were well leached and acidic. Sulfur was extracted with

24 3

PLANT NUTRIENT SULFUR Table VII Status of Sulfate S in Some Tropical Soil Profilesa Sulfate as sampled

Saturation at 5 pg l i t e r ' in solution

s g-9

(%I

(%I

32 27 145 220

78 67 39 51

herto Rico, Dagney (Orthoxic Tropohumult) 0- 10 10 0.6 10-30 I70 3.0 30 - 60 250 I .5 60-95 373 I .5

51 435 548 67 I

20 39 46 56

herto Rico, Catalina (Tropeptic Haplothox) 0- 16 414 6.0 16-35 1080 16.0 35-60 1310 16.0 I267 2.0 60 - 80 80- 120 1225 5.0 120-130 195 3.0

930 I I80 1430 I720 1730 860

45 92 92 74 71 23

Hawaii, Hanipoe (Typic Dystmndept) 0- I 5 25 0.4 15-30 18 30 - 60 16 17 60-90

220 -

11 -

-

-

-

-

Depth increment (cm)

Adsorbed sulfate (pg g-')

Sulfate in solution (pg s m1-9

Nigeria, alagba (Oxic Paleustalf) 0- 15 25 15-30 18 30 - 60 56 I12 60 - 90

8.0 4.5 I .2 0.7

Hawaii, Akaka (Typic Hydmndept) 0-15 220 15-30 1210 30 - 60 3730 60 - 90 5480 -

Sulfate adsorption maxima h 3

Adapted from Fox ( I980a); by permission of The Sulphur Institute, Washington, D. C.

Ca( H2P04)2solution and by short-term growth of ryegrass seedlings. Plant S percentage increased linearly with increasing log SO,-S until soil S reached 250 mg kg-'. Maximum uptake was attained at 1000 mg kg-I, after which uptake decreased. Apparently, the low-concentration mechanism of SO4 retention (presumably adsorption) began to phase out after soil SO4 reached 250 mg kg-' and a second mechanism (presumably a compound of low solubility) controlled availability (solubility) as soil

N. S. PASRICHA AND R. L. FOX

244 1 .o

0.8

0.6 9 al

.-x al > .-c

04

m -

2 0.2

0 0

2 4 6 8 Phosphate-extractable S (pprn)

10

Figure 9. Relationship between relative yield of legumes and weighted profile mean of extractable sulfer. Fitted curves are as follows: A = I - Y d Y , = exp(-0.7228 S ) , R = 0.43. 19 D F B = 1 - Y d Y , = exp(-0.7262 S ) , R = 0.58, 18 DF. 0, Siratro; 0, various Stylosanthes spp. (Probert and Jones, 1977).

SO,-S content approached 1000 mg kg-'. Further studies of this type are needed, but it is probable that both adsorbed and precipitated SO, are major factors in the S economy of highly weathered soils. That probability offers a plausible explanation for why S deficiencies have been slow to develop in such soils. In negatively charged soils that may have no sulfate buffering capacity, the magnitude of external S is such that movement of S to roots by mass flow in the transpiration stream is suggested (SO, concentration in soil solution X transpiration ratio = plant S). In variable-charge soils, the concentration of SO,-S may be lower than necessary for adequate nutrition, even though deficiency of S may not be obvious (Fox, 1984). Yield response curves that relate plant growth to the external SO,-S concentration demonstrate that substantial yields can be made at solution concentrations that require SO4 movement to roots along concentration gradients. These observations suggest that in some well-buffered soils, adsorbed SO, is moving to plant roots by diffusion. A constant but low SO, concentration in solution in relation to large amounts of P-extractable SO, from chemically similar soils suggests that S-bearing minerals, such as basaluminite, are controlling soil solution concentrations (Fig. 10). However, a smooth plot of concentration versus

PLANT NUTRIENT SULFUR

245

22

B+ Q

20

s -J

Qa

18

-

Jurbanite

I

1

1

I

I

I

I

quantity suggests adsorption. There are reasons to believe that both mechanisms are involved in controlling sulfate solubility in highly weathered soils. Sulfate adsorption isotherms of volcanic ash soils generally show biphasic properties and suggest that 40-8Ofig SO4-S g-' is required to maintain 3 - 6 mg SO,-S liter-' in soil solution, a concentration range considered adequate for growth of most crops (Hue et al., 1990). A rational approach to S nutrition is to detem'ine the required sulfate concentration in the soil solution (the external S requirement) and the amount of S fertilizer needed to produce that concentration. Investigations to define specific external S requirements of plants have been conducted using four lines of approach: 1. The minimum S content of imgation water associated with near maximum production (Blair et a/., 1979; Wang, 1978; Yoshida and Chaudhry, 1972). 2. Yield curves as a function of SO4-S in solution based on sulfate sorption curves. This approach is appropriate for soils that have a high capacity for sulfate sorption (Hasan et al., 1970). 3. Solution or sand culture experiments with SO, concentration as a variable (Fox, 1976). 4. Frequent leaching of soils with dilute sulfate solutions to establish and

246

N. S. PASRICHA AND R. L. FOX

maintain a range of SO, concentrations in “soil solutions,” in which plants are grown (Fox ef al., 1976, 1977, 1979). From results of these investigations, using several crops, it seems reasonable to generalize that the external S requirements of crops in the subtropics and tropics are approximately 2 - 5 mg liter-’ S in solution.

X. CROP RESPONSES Numerous papers have been published on responses to S by crops growing on highly weathered or intensely leached soils. An extensive listing has been prepared by Blair (1979). That S deficiency is a problem in the tropics and subtropics, and that the deficiency has a potential for becoming worse, is abundantly clear from papers on sugar, fiber, and oil crops (Aulakh and Pasricha, 1988; Pasricha el al.. 1987, 1988, 1991; Pasricha and Aulakh, 199 1 ; Braud, 1969; Stanford and Jordan, 1966; Fox, I976), legume forages (Metson, 1973; Pasricha and Randhawa, 197 1, 1975), grain legumes (Fox ef al., 1987; Aulakh and Pasricha, 1986; Aulakh et al., 1990; Pasricha ef af.,1987; 1991), rice (Wang, 1978; Mazid, 1986), corn (Kang and Osiname, 1976; Pasricha et al., 1977a), coffee (de Freitas et al., 1972), and banana (Fox ef al., 1979). Sulfur deficiencies in tropical, subtropical, and warm temperate areas are being reported with increasing frequency (Blair, 1974; Jones ef af., 1975; Tandon, 1991). Sulfur probably is the fourth most limiting nutrient in highly weathered soils, and if only the tropics are considered, it probably ranks third. Furthermore, if effectively nodulated legumes are being grown, S moves up one place in the ranking to third or second. The relative adequacy of 12 nutrients for clover on seven mountain soils from Equador is summarized in Table VIII, which clearly shows that S is second only to P for legume growth in these soils. Fox et al. ( I 977) observed that the S content of the seeds of cowpea increased with increasing S fertilization of soil. The levels of S adequate for seed yield were also sufficient for near maximum S content in the seed. Sulfur percentage associated with 95% of maximum yield was 0.26%. Seed yield increased 15-fold as soil solution concentration increased from near zero to 1.8 mg m1-I. The S: N values were in the range 0.03-0.04 at S concentrations less than 2 mg liter-’, to 0.07-0.08 at > 5 mg liter-’. These results imply that to obtain maximum yield of cowpeas in the tropics, S fertilization will be required in many areas. The S concentration in rainwater in northern Nigeria during high-rainfall months is about 0.2 mg

247

PLANT N U T R I E N T SULFUR Table VIII Mean Relative Yields of Trifolium mpens as Intluenced by Withholding Nutrients from Plants Grown in Seven Mountain Soils of EquadoP

Relative yield (%) Nutrient(s) withheld None (all added) All (none added) P S K Ca B

General responseb

Mean

-

Range

100

-

Deficient, 7 soils

16

Deficient, 6 soils NS'

41 95 92 96

0-45 0-46 17-84 80- I15 67- I17 66-134

NS Deficient, I soil Toxic, 1 soil

17

-

-

Calculated from data of Poultney (1975). ' No statistical evidence that Mg, Zn, Fe, Mn, Mo, or Cu increased yield.

'NS, Not statistically significant.

liter-' (Bromfield, 1974), a level far below adequacy for either good yield or high seed S content. However, S contents of rainwater that infiltrates the soil are augmented by S leached from the standing crop and crop residues and are further concentrated by water evaporation and transpiration. The final concentration may be more favorable than is indicated by rainwater composition. Laurence et a/. (1976) observed that in Malawi, S applied either as a foliar dust or soil treatment increased yields of groundnut, although the effects of complementary treatments were not fully additive. Besides improving yield, S application also produced kernels of better size and quality than untreated samples. There is great pressure to achieve breakthrough in human nutrition by introducing new foods into diets or by developing new cultivars of staple crops that have high protein contents and at the same time produce high yields. The improbability of accomplishing either goal (much less a happy combination) on a sustained basis given the S nutrition constraints of vast areas in the tropics is evident from research in West Africa (Bromfield, 1974; Fox ef al., 1977). On the other hand, it is possible to increase the S amino acid content of cowpea, groundnut, and mustard and at the same time achieve greater yields of grain by increasing the S supply (Pasricha et al., 1970; Evans ef al., 1977; Fox ef al., 1977). Likewise, S fertilization

N. S. PASRICHA AND R. L. FOX

248

Table IX Elemental Composition of 11 Cultivars of Cowpea Grain Produced at IITA, Ibadnn, Nigeria and Calculated Quantities in Harvested Grain for Two Levels of Production'

Elemental yield (kg ha-') Concentration (%) Element

Mean

Range

N P

3.97 0.47 I .63 0.10 0.23 0.25 0.0044

3.64-4.36 0.44-0.54 1.50- 1.80 0.10-0.1 I 0.21 -0.23 0.2 I -0.28 0.0038-0.0051

K Ca Mg S Zn

Typical yield'

Agronomicall possible yield

8.9

59.7 1.4 24.4 I .5 3.4 3.8 0.07

1.1

3.7 0.2 0.5 0.6 0.01

i

Adapted from Fox et al. ( 1977). A typical yield is 224 kg ha-I; 1500 kg ha-l is believed to be agronomically feasible.

improves the quality of rice (Jones el al., 1975; Yoshida and Chaudhry, 1972). Summerfield et a/. (1974) placed cowpea (Vigna unguiculata) among the grain legumes, with immediate potential for alleviating human malnutrition in the tropics. Cowpea is relatively rich in protein. The leading area of production is in the West African Savanna. Per season yield in Nigeria was 224 kg ha-', but it is feasible to produce much higher yields. It is obvious from Table IX that such agronomically feasible yields will require much higher outlays of nutrients. Fox ef al. (1977) examined what these numbers mean with respect to S supply. Assuming typical yields of 224 kg ha-', a mean sulfur percentage of 0.2596, and 50%partition of plant sulfur into the grain, a projected value of 1.12 kg S ha-' in the cowpea is obtained. Mean annual sulfur in the rainfall for northern Nigeria is about 1.14 kg ha-' (Bromfield, 1974). These estimates suggest that cowpea production in the dry savanna is already limited by a nutritional (S) constraint. To attain near-maximum yield, the indicated requirement for sulfur will exceed natural inputs by an order of magnitude. Obviously, production cannot be sustained with such a deficit. Few studies have been reported on responses of millets to S. Relatively large difference between yields of millet fertilized with single superphosphate and triple superphosphate after 7 years of cultivation (Fig. 1 1 ) are evidence of the need for S in the soils of West Africa. The implications for

PLANT N U T R I E N T SULFUR

1400 1200

1 -

249

Single superphosphate

1000 800 .-C

s

600 400 L

200

I

I

I

I

I

4.4

80

130

175

P-applied (kg P/ha)

Figure 11. Effect of P sources and rates of application on pearl millet grain yield at Sadore, Niger. Rainy season, I988 (Bationo and Mokwunye, I99 I ; Reprinted by permission of Kluwer Academic Pub1ishers.l

S fertilization are discussed by Friesen ( I99 I ). Single superphosphate, rather than more concentrated fertilizers, may be a preferred source for crops that require both P and S to increase crop yields (Aulakh and Pasricha, 1988; Aulakh et al., 1980b; Pasricha et al., 1987, 1991). Table X presents a summary of yield responses to sulfur applications in Bangladesh. In most cases, 500 ppm P extracted approximately 10 p g g-' soil. Yield increases in various crops attributable to S were 5-95% where S was applied in conjunction with N, P, and K. Yield responses to applied S were observed in corn grown in the Dominican Republic (Pierre et al., 1990). Sulfur deficiency is intensified by burning, which volatilizes up to 75% of S contained in residues (Sanchez, 1976). Because much of the total S in soils of subhumid regions is in organic forms (Tabatabai, I982), total and available S are expected to be low in conventionally tilled soils where residues are burned. In Thailand, S applied along with NPK fertilizers significantly increased yields of cassava, corn, and sesame growing on coarse-textured soil with less than 8 - 12 mg kg-I phosphate-extractable SO,-S (Parkpian el al., 1991). Intensive cropping and use of S-free fertilizers has caused 60 - 70% of rice in South Sulawesi, Indonesia, to become S deficient; pastures respond to S

Table X Average Yield Increase of Crops Due to S Application in Bangladesh'

Yield (tons ha-l)b Crop

Increase in yield (%)

Response ratio (kg extra yield per kg S)

Trials

Locations

NPK

NPKS

Rice

50

8

4.26

4.53

6.34

9

Wheat Maize Mungbean Chickpea

39 10

10

3.2I 4.62 0.59 1 .oo

9.93 40.85 9.26 9.64

45 2 6

10

1

1

3

1

2.92 3.28 0.54 0.84

Mustard

4

3

0.81

1.27

56.79

15

Groundnut Potato

3 3

3

I

1.69 22.I3

1.85 22.80

9.41 3.03

5 22

Sugarcane

6

3

16.39

81.31

6.44

164

Conon

5

1

1.67

1.83

9.58

5

18

7

2.31

2.42

2.1 1

18

4

1

1.91

2.00

4.7I

4

Jute Tobacco

a

2

Reference(s) Bangladesh Agricultural Research Council (BARC)(1981,1982, 1983) -do-doAhmed er al. ( 1 984) Talukder er 01. (1984)and Bangladesh Agricultural Research Council (BARC) (1981,1982) Bangladesh Agricultural Research Institute (BARI) (1981,1982) Noor and Islam (1983) Bangladesh Agricultural Research Council (BARC) (1981,1982) Bangladesh Agricultural Research Council (BARC) (1981,1982, 1983) Bangladesh Agricultural Research Council (BARC)(1981, 1982) Bangladesh Agricultural Research Council (BARC)(1981, 1982, 1983) Bangladesh Agricultural Research Council (BARC) (1981,1982)

Adapted from Hussain (1990). NPK, Addition of nitrogen, phosphorus, and potassium; NPKS, addition of nitrogen, phosphorus, potassium, and sulfur.

PLANT NUTRIENT SULFUR

2s 1

4

z Figure 12. Response in Centrosema pubescence to sulfur applications in South Sulawesi, Indonesia (Blair ef a/.. 1978).

application (Blair et al., 1978), and responses to these applications were greater than to P applications (Fig. 12). In the Sahelian and Sudanian zones of West Africa, soil organic matter is being exploited to supply S to crops (Bationo and Mokwunye, 1991). Friesen ( 1991) reported on the fate and efficiency of S fertilizer applied to food crops in West Africa. Sulfur fertilizer increased grain yields from 10 to 65% in 14 out of 20 site-years in semiarid and subhumid West Africa. Substantial leaching losses resulted in low crop recovery of fertilizer S. Low S fertilizer rates were required, which suggests that S deficiencies in the region can be corrected at relatively low cost. Leaching losses probably explain the poor residual value of sulfate fertilizers on highly permeable soils of West Africa. The low organic matter content of soils provides a very small sink for S immobilization. Most of the residual S (about 71%) remained as SO, in the profile (Fig. 13) and is again subject to leaching at the onset of the next rain. The high mobility of SO, in this region is a result of sandy soil texture. Considerable interest has developed in acid subsoil amelioration by

252

N. S. PASRICHA AND R. L. FOX Fertilizer-S(% applied)

0

10

20

30

15

30

5

v

45

%.a n

60

75

Figure 13. Soil profile distribution at harvest of S derived from phosphogypsum applied to millet at Sadore, Niger (Friesen, 1991; Reprinted by permission of Kluwer Academic Publishers.)

applying large quantities of gypsum on the surface of highly weathered soils and letting natural leaching move Ca and SO4 into the subsoil. The primary purpose, A1 inactivation, deals only indirectly with S as a nutrient, but S in solution and S nutrition of crops will be influenced, irrespective of the primary purpose. The physical chemistry and mineralogy of what happens in the subsoil is complicated (Fig. 10) and crop performance may be influenced in ways that are unexpected (Farina and Channon, 1988). In this regard, it will be appropriate to remember that SO4-S concentrations in solution greater than 15 mg liter-' have depressed the growth of banana (Fox d al., 1979) and cowpea (Fox et al., 1977).

XI. SULFUR FERTILIZATION AND CROP QUALITY The contribution of soil fertility to crop quality should not be overlooked. In areas of highly weathered soils, but especially in tropical areas

PLANT NUTRIENT SULFUR

253

where leached and weathered soils constitute the majority of soils used for local food production, crop quality becomes especially important. One concern is amino acid deficits in diets. It is in the tropics, with low anthropogenic additions of S and intensively leached soils, that S deficiency is most likely; and it is in the tropics and subtropics, generally, that protein intake is low and primary dependence is placed on plant protein sources, usually grain legumes and cereal grains.

A. EFFECTON PROTEIN QUALITY Sulfur applied to crops grown on S-deficient soils not only increases crop yields but also favorably affects crop quality. Concerns about protein quality have led to interest in increasing the sulfur amino acid content of edible legumes (Luse er al., 1975; Pasricha er al., 1991). Pasricha ef al. (1970) observed increased S-containing amino acids in response to S fertilization of groundnut and mustard. For some lupine varieties, S fertilization increases the S amino acid content of seeds. This increase is associated with a change in the proportion of various proteins with differing amino acid ratios (Blagrove ef al., 1976). Sulfur-containing amino acid content is a better predictor of protein efficiency than is total S (Sandhu er al., 1974), but relative ease of determination makes the N: S ratio desirable for screening purposes. For human nutrition, legume seed proteins are deficient in sulfo-amino acids. A possible remedy for this deficiency is to increase the sulfo-amino acid levels in seeds by S fertilization. Concerns about protein quality have created interest in using N : S ratios of cowpea cultivars as a tool for screening for protein quality (Porter et al., 1974). The protein S : protein N ratio of IVu 76 cowpea meal increased 27% over the control when cowpea was supplied with 5 mg liter-' of SO4-S, and that of variety Sitao Pole increased 100%when cowpea was supplied with 1.8 mg liter-' of SO,-S (Evans er al., 1977). Further details are presented in Table XI. Sulfur concentrations, S : N ratios, and S amino acid contents in cowpea seeds increased with increasing levels of S fertilization. For cowpea variety Sitao Pole, concentrations of methionine and cyst(e)ine increased approximately twofold as adequacy of S supply increased from severe deficiency to sufficiency for maximum yields (Evans er al., 1977). For variety IVu 76, methionine content was increased by 14%, cysteine increased 32Y0, and S-methyl-L-cysteine increased 470%. Of the 53% increase in S percentage associated with 5 mg liter-' SO,-S, 16% was derived from increased methionine plus cysteine and 3 I % from increased S-methyl-L-cysteine.

254

N. S. PASRICHA AND R. L. FOX Table XI

Ratio of S in Methionine

+ Cysteine to Amino Acid N in Cowpea Varieties under Various Sulfate S Fertilition Levels'

Recovered Cowpea Treatment amino acid N Met + Cys cultivar (SO,-S mg liter') (g/IOO g meal) (a100g meal)b %Met + Cys):N(amino acid) IVu 76

0 0.2 0.6 I .8 5.0 15.0 45.0

3.38 3.77 3.62 3.68 3.19 3.13 3.33

0.1 10 0.104 0.1 14 0. I29 0.134 0.122 0. I52

0.033 0.028 0.03 I 0.035 0.042 0.039 0.046

Sitao Pole

0 0.2 0.6 I .8 5.0 15.0 45.0

3.90 4.36 4.22 3.6 I 3.85 3.48 4.04

0.070 0.093 0.1 I I 0.128 0.143 0.133 0.150

0.018 0.02I 0.026 0.036 0.037 0.038 0.037

'Adapted from Evans et a/.(1977). Dry weight basis of cowpea.

B. EFFECTON OILCONTENT Improving the S nutrition of S-deficient oil seed crops increases oil contents in peanut (Aulakh et al., 1980b; Singh, 1968), Brussica species (Aulakh er af.,1980a; Pasricha el af., 1988), linseed (Aulakh et af., 1989), and soybean (Aulakh et af., 1990) (Table XII).The relative concentration of different fatty acids in some oilseeds determines their use. Sulfur fertilization with an adequate supply of N and P resulted in a large decrease in percentage of stearic, oleic, and linoleic acids with a concurrent increase in the content of linolenic acid (Aulakh et af., 1989).

C. EFFECTON GLUCOSINOLATE CONTENT Plant S is the major factor in the glucosinolate content of oilseed rape (Zhao et ul., 1991). Excessive S can result in unacceptability due to high glucosinolate levels and inadequate S may substantially decrease yields. Both situations markedly reduce the profitability of oilseed rape crops. Therefore, the effects of S application should be quantified for both yield and quality in order to obtain optimum benefits.

PLANT NUTRIENT SULFUR

255

Table XI1 Influence of Applied S on the Oil Content, Protein Content, and Oil Yield of Dierent Oil Crops'

Oil content

Oil yield (kg ha-')

(%)

Protein

Crop

No S

S

No S

S

No S

Peanut Brassica juncea Brassica compestris Linseed Soybean

39.0 36.4 41.5 41.6 21.7

48.0 42.6 47. I 43.2 23.6

659 540 300 1285 317

859 670 450 1480 412

-

-

22.5 23.3

30.8 28.1

28. I

31.9

-

S

-

Adapted from Pasricha and Aulakh (1991); by permission of The Sulphur Institute, Washington, D. C.

D. EFFECTON NITRATE CONTENT Sulfur plays an important role in secondary plant metabolism, which is related to parameters determining the nutritive quality of vegetables (Schnug, 1990). Nitrate concentration in vegetables has become an important criterion for food quality (Corre and Breimer, 1979; Schuphan, 1976; Vetter, 1988). A shortage of S adversely affects utilization of N during plant metabolism. Thus S deficiency causes an accumulation of nonprotein N compounds, including NO3 (Fig. 14). Such a condition indicates severe S deficiency and is invariably associated with S deficiency symptoms

Y = 69.35 Exp(-l.l28X)+ 0.643

0

1

2

3

4

5

6

S-Content (mg g-')

Figure 14. Nitrate concentration in the dry matter of lettuce as influenced by plant S status of the plant (Schnug, 1990; by permission of The Sulphur Institute, Washington, D.C.)

2 56

N. S. PASRICHA AND R. L. FOX

(Schnug, 1990). Murphy (1 990) observed that S fertilization affected N : S ratios and significantly reduced NO3 contents. An inadequate S supply hinders protein formation and results in accumulation in forage crops of soluble N compounds such as nitrate N and amide N (Pasricha and Randhawa, 1975).

XII. SULFUR INTERACTIONS WITH OTHER ELEMENTS A. INTERACTION

WITH

PHOSPHORUS

The fertilizer P and S interaction may be positive or negative depending on (1) the level of each when applied in combination and (2) soil conditions that control availability of each nutrient. If applied P induces SO, leaching in soils in which the S level is marginal, onset of S deficiency may be hastened. In such cases the interaction is antagonistic. On the other hand, in highly weathered soils that may retain adsorbed SO,, added P may mobilize the SO,, increasing its availability in the soil. In such a case, application of S along with P may be without benefit. For example, crop responses to applications of P and S were synergistic at fertilizer rates of 20-40 kg P and 43 kg S ha-' (Pierre et al., 1990), but others have shown antagonistic effects (Barrow, 1969; Aulakh et al., 1990).

B. INTERACTION

WITH OTHER ELEMENTS

Sulfur fertilization may lower the concentration of B and Mo in plants. This antagonistic effect has been used to suppress Mo in forages growing on Mo-toxic soils (Pasricha and Randhawa, 1971, 1972; Pasricha et al., 1977b). On coarse-textured soils with marginal to low amounts of B and Mo, S fertilization of Brassica species can create deficiencies for these crops (Schnug and Haneklaus, 1990). Sulfur fertilization is a feasible technique by which to decrease plant uptake of some toxic or otherwise undesirable elements on polluted soils. In areas where Se toxicity exists, Se uptake can be suppressed by S fertilization (Dhillon and Dhillon, 1991). Antagonistic relationships between S and anionic trace elements such as arsenic, bromine, and antimony have been reported. Grill et al. ( 1990) reported that excess S fertilization may also increase concentrations of cations such as Cu, Zn, and Cd in roots, while reducing levels in shoots. This results from stimulated production of phytochelatines (metallothioneins) in roots, induced by metals in the growth medium, and

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perhaps by enhanced S supply. By this mechanism, plants may avoid excess uptake. Thus, S fertilization may be a feasible technique to enhance the quality of crops grown on polluted soils.

XIII. SUMMARY AND CONCLUSIONS Sulfur deficienciesin the tropics and subtropics have been recognized for more than 50 years, but even today the extent and magnitude of the problem is ill-defined. In recent years S-deficient areas of considerable extent have been discovered and delineated, including, for example, much of Bangladesh and South Sulawesi. Sulfur deficiency has been slow to develop, or at least slow to be recognized, for several reasons: the atmosphere is a ubiquitous source of S; other nutrients, especially N and P, are usually even more deficient than S; S has been applied in irrigation water and as adjunct to other nutrients (a factor that is rapidly decreasing in importance); SO, is more efficiently used by plants than NO3, with which it is frequently compared; as soil organic matter is exploited, S cycling between organic and inorganic forms is net positive for inorganic S; adsorbed SO,, which is usually abundant at some depth in profiles of highly weathered soils, is continually being released. The pattern of S deficiency on a global scale leads at once to the conclusion that areas prone to S deficiency are those that are remote from industrial and domestic burning of fossil fuels, areas where weather patterns are controlled by air masses originating in remote regions, and areas that have marked wet-dry seasons giving rise to savanna-type vegetation that is burned frequently. Much of the tropics and subtropics is included in one or more of these categories. Sulfur sources in much of the continental tropics are meager. Long-term yields there will not exceed those that can be supported by the incoming S supply. In some areas S yields in crops are approximately equal to incoming S in the rainfall. In the case of soils that do not adsorb sulfate, S supply is controlled by S currently accruing as rainfall (wet deposition) and directly from the atmosphere (dry deposition), plus S mineralization from organic matter. Other sources may be locally important: irrigation water, fertilizers, animal manure, and plant residues. Adsorbed SO, and/or sparingly soluble SO,-containing minerals are major factors in the S supply of highly weathered subtropical and tropical soils. In most highly weathered soils, large quantities of SO, have accumulated somewhere in the profile. Usually the accumulation approaches maximum at about a 1-m depth. Total SO,-S in some leached profiles

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exceeds 16,000 kg ha-'. These forms of SO, are usually associated with acid soils that contain hydrated oxides of iron and aluminum. Adsorbed SO, can be extracted with phosphate solutions, presumably by ligand exchange. This has led to the use of phosphate solutions as extractants for soil-testing purposes. Success has been mixed; the availability of SO, so extracted should not be inferred from quantity alone. Sulfate concentration in highly weathered soils is low, but, although many of these soils contain copious amounts of adsorbed SO, within the root zone, and although availability to plants of adsorbed SO, has been demonstrated, crops may be mildly S deficient. Sulfur concentrations in rainwater and irrigation water can be used as a rough guide to the level of S nutrition of crops and long-term requirements for S fertilizers. It is obvious that sustained production cannot remove more S than has been put into the system. In remote areas of the subhumid tropics in the Northern Hemisphere, S inputs are in the range 1 -2 kg ha-'. Even lower values can be expected in similar situations in the Southern Hemisphere. Estimates of S being removed in some crops (cowpea and peanut) in subhumid tropical Africa are approximately equal to S inputs. It is reasonable to believe that, without additional S inputs, there can be no significant yield increases unless additional S is introduced. The oceans are important sources of S. However, the influence of oceans decreases rapidly with distance and elevation from the coast. Global estimates of S inputs suggest that biological sources, among which those of the oceans are dominant, contribute more S to the atmosphere than manmade pollutants. Sea spray across the sea-land boundary contributes relatively little to the total global system. The list of crops for which S fertilizer has been beneficial is almost as long as the list of cultivated crops. Some crops that formerly were not considered to be susceptible to deficiency, rice, for example, are now considered as being so. Seasonal burning of vegetation during the dry season is widely practiced in the tropics. Without doubt, burning represents a severe drain on already meager S resources. Probably much of the S volatized is recovered in adjacent areas of green vegetation and accounts for the relatively better S status of these areas. Because S accrues to plants from numerous sources, instances of acute S deficiency are not common in the field. Even in S-deficient areas, typical yield increases resulting from S fertilization are in the range of 5 - 20%. Thus much evidence for S deficiency can be overlooked by an ultraconservative approach to data interpretation. As a first approximation the fertilizer requirement should be that which will establish and maintain 3-5 mg SO,-S liter-' in solution. For me-

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dium-textured soils that contain little adsorbed S, this amounts to approximately 10- 15 mg SO,-S kg-' on a dry soil basis. For soils in which adsorbed SO, controls SO, concentrations in soil solutions, a rational approach to predicting whether S fertilizer is required, and how much, can be based on sorption curves. The approximate fertilizer requirement is that which will establish a level of SO, in solution appropriate for the crop being grown. Most soil testing for advisory purposes uses turbidimetric methods for SO, analysis. Most of these procedures are not satisfactory for extracts of highly weathered soils. Some substances inhibit BaSO, precipitate formation in extracts of such soils. Many of the data on SO, in tropical and subtropical soils are probably underestimates. A more reliable, although more complicated, method has been developed. Although SO, concentration in rainfall can be used as a rough guide to the adequacy of sulfur supply, it should not be taken at face value. Wet deposition of S is augmented by dry deposition as rainwater passes through plant canopies, plant residues, and into soils, and it may be concentrated further in the soil by surface evaporation. Sulfur contents of plants increase with increasing concentrations of S in soil solutions. For many crop species maximum yield requires approximately 0.2% S in leaves. Although crop yield and plant composition are sensitive to the level of S supply, foliar diagnosis of the S status has been little used in the tropics and subtropics. For survey work foliar analysis is probably superior to soil analysis, and seed analysis has advantages over both. Best results require that all appropriate tools be used. This is especially true for evaluating the S status of crops in the tropics, where, in many areas, background information is lacking. Care must be exercised in selecting tissues for foliar analysis. Because S is one of the less mobile nutrients, it may accumulate in old tissues even though young tissues are deficient. Deficiency symptoms, if they are expressed at all, can be confused with symptoms of other nutrient deficiencies. Because S is relatively immobile in plants, upper leaves are first to show symptoms of deficiency-just the reverse of N. However, S-deficient plants are often more distinctly yellow than are N-deficient plants. An interveinal chlorosis develops in maize leaves that is similar to Zn or Fe deficiency. The external requirements for SO,-S in soil solutions is in the range of 3-5 mg S liter-' for some important crops of the tropics and subtropics; however, yields of approximately 80% of the maximum attainable yield may be obtained with as little as 1 mg liter-'. A need for special attention to S in the tropics and subtropics arises from the importance of S for human nutrition. The essential S-containing

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amino acids of foods are of particular concern. Their concentration in plant products can be enhanced by appropriate use of S fertilizers. Finally, a word about the environmental impact of anthropogenic S in the atmosphere on S as a plant nutrient. On a global scale, excess S appears as local problems. In the subtropics, and especially in the tropics, levels of S from all sources are below those that are optimum for plant nutrition. From this perspective, burning low-sulfur fuel to avoid contaminating vast areas is nonsense.

ACKNOWLEDGMENTS The senior author is grateful to Dr.M. S. Bajwa, Professor and Head, Department of Soils, Punjab Agricultural University, Ludhiana for providing facilities. Special thanks are due to Mr.Subhash Chander Gossain for typing the manuscript.

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Index A Acidification, soil, 226 Acid rain, effects on crop plants, 223-225 forest vegetation, 225 soil acidification, 226 Adsorption SO,, mechanism, 234-236 sulfate by soils, 227-232 Adsorption curves, sulfate, 232-234 A horizons development, 191 - 192 oxidative polymerization by Mn oxides, 193 stabilization of organic matter in acid soils, I93 - 194 CO, from added organics, 195 in near-neutral soils, 194- 195 Albugu candida white rust, in Brassica spp., 28-32 Alfalfa, chloride deficiency, I10 Amphidiploids, among oilseed brassicas, 5 a-Amylase, chloride activation, I I I Anther culture, oilseed brassicas, 41 -42 Antibiotic resistance, intrinsic, Bradyrhizugbum japonicum and DNA homology groupings, 74-75 methods, 72-73 phenotype diversity, 72 - 74 and symbiotic performance, 74 Asparagine synthetase, chloride activation, Ill Atmosphere, sulfur sources, 219-221

B Eacillits thicringiensis toxin, production by oilseed brassicas, 46 Barley, chloride deficiency, I10 Beans, chloride deficiency, I10 Blackleg, resistance in oilseed brassicas, 2428

27 1

Black spot, resistance in oilseed brassicas, 34 - 36 Boron, sulfur fertilization effects, 256 Bradyrhizogbum japonicurn dissimilatory nitrate reduction and DNA homology groupings, 80 methods, 78 phenotype diversity, 78 and symbiotic performance, 79 fatty acids, 93 genotypic groupings, 68-69 hemoproteins, 92 - 93 hydrogenase system and DNA homology groupings, 78 phenotype diversity, 75-71 and symbiotic performance, 77- 78 intrinsic antibiotic resistance and DNA homology groupings, 74-75 methods, 72-73 phenotype diversity, 72-74 and symbiotic performance, 74 nitrogenase activity ex planfa, 92 phenotype/genotype relationships, summary, 94 plant growth-regulating substances and DNA homology groupings, 91 - 92 phenotype diversity, 90-91 and symbiotic performance, 9 I protein profiles and DNA homology groupings, 88 methods, 87 SDS-PAGE phenotype diversity, 8788 and symbiotic performance, 88 rhizobiophage typing and DNA homology groupings, 89-90 phenotype diversity, 89 and symbiotic performance, 89 rhizobitoxine and DNA homology groupings, 83-84 phenotype diversity, 80-82 and symbiotic performance, 82-83 serology and DNA homology groupings, 72

272

INDEX

methods, 69 phenotype diversity, 69-70 and symbiotic performance, 70-72 surface polysaccharides and DNA homology groupings, 87 methods, 84-85 phenotype diversity, 81 -85 and symbiotic performance, 85-86 taxonomic status, 93-95 Brussicu spp., oilseed, see Oilseed brassicas Breeding programs, for Erussicu seed yield, 10-13 Bromoxynil tolerance, oilseed brassicas, 39

C Cabbage, chloride deficiency, 109- I10 Cadmium sequestration by transformed oilseed brassicas, 47 sulfur fertilization effects, 256 Canker, stem, in oilseed brassicas, 32-34 Carbon pe-pH diagrams, 170- 172 reduction half-reactions, 163 Cation transport, chloride role, 1 I2 Chitinase, production by Erussicu spp.. 47 Chloride fertilizers, 134- I35 Chloride, in plants additions with no effects, 124 biochemical functions, 109- I I I enzyme activation, I I I photosynthesis, 110- I 1 I crop development responses, 124- I25 deficiencies, 109- 1 10 disease interactions, I I7 - I24 enhanced host tolerance and, 112- 114 IOSS~S, I33 - I34 manganese interactions, 1 16- 1 17 nitrogen interactions, 114- I I5 osmoregulatory functions, I 12- 1 13 phosphorus interactions, I I5 - I I6 quality responses corn, 129-131 oats, 129 potatoes, 132 soybeans, I3 I - I32 research needs, I4 I - 143 sources, 133- I34 suppression common root rot, I 19

foliar diseases, 1 19- I22 take-all root rot, I 18- I I9 uptake, 113-114 yield responses, I25 - I26 barley, I26 - 128 wheat, 126- 128 Chlorsulfuron tolerance, oilseed brassicas, 38 Chromium cycle, soil, 187- 188 Chromium, net oxidation test interferences, 205 protocol, 202-203 Coconut palm, chloride deficiency, I10 Copper, sulfur fertilization effects, 256 Corn chloride deficiency, 1 10 chloride effects, 129- I 3 1 Crop responses acid rain effects on plants, 223-225 to chloride developmental effects, I24 - I25 plant analyses, I35 - I38 soil testing, 138- 140 to sulfur, 246-252 Cultivars, oilseed brassicas, canolaquality, 7 Cytoplasmic male sterile-nuclear restorer system, in Erussicu spp., I7 -20

D Deposition dry, 218 wet, 2 I7 Desorption, sulfate by soils, 227 - 232 2,2’-Dipyridyl tests, for Fe oxides, 202 Disease resistance, in Brussicu spp. blackleg, 24 - 28 black spot, 34-36 light leaf spot, 36 stem rot, 32-34 turnip mosaic virus, 36 Verticillium wilt, 36- 37 white rust, 28-32 Dismutation, of H,O,, 204 Dissimilatory nitrate reduction, Brudyrhizogbumjaponicum and DNA homology groupings, 80 methods, 78 phenotype diversity, 78 and symbiotic performance, 79 DNA homology groupings, Erudyrhizogburn japonicum. phenotypes

27 3

INDEX dissimilatory nitrate reduction, 83 - 84 fatty acids, 93 hemoproteins, 92-93 hydrogenase system, 78 intrinsic antibiotic resistance, 74-75 nitrogenase activity ex plunfu,92 plant growth-regulating substances, 9 1 - 92 protein profiles, 88 rhizobiophages, 89-90 serogroups, 72 surface polysaccharides. 87 DNA markers, in oilseed brassica breeding random amplified polymorphic, 48 restriction fragment length polymorphisms, 48 Doubled-haploid technique, for oilseed brassicas, 4 I - 42

E Electrons activity in soils, thermodynamic relationships, 155-158 characteristics, I53 - I55 Equilibrium constant, for redox equilibria, I59 Erucic acid, in extracted seed oils, 7- 10

F Fatty acids Brudyrhizogbum japonicum, 93 oilseed brassicas, 8 -9 Fertilizers chloride-containing, 134- I35 sulfur-containing, 252- 256 Foliar diseases, chloride effects, I 19- I22 Free radicals behavior, I77 - I78 formation in soils, 176- I77 oxidizing, field tests for. 20 I - 205

G Gametocides, for Erussiccl spp., I5 - I6 Gel electrophoresis. SDS-polyacrylamide. soybean bradyrhizobia phenotypes, 87 88 Genomic relationships, among oilseed brassicas. 5

Ghcosinolate, sulfur fertilization effects, 254 Glyphosate tolerance, oilseed brassicas, 38 Groundwater, sulfur in, 227 Gum guaiac, tests for Mn and Fe oxides and oxidizing free radicals, 202

H Heavy metals, sequestration by Brussica SPP., 47 Hemoproteins, Bradyrhizogbum juponicum, 92-93 Herbicide resistance, in oilseed brassicas, 37 - 39 Heterosis, Brussicu F, hydrids, I3 - I5 Horizons A. see A horizons E, development, 191 Host tolerance, enhancement by chloride, 112-114 Humic substances A horizon development, 19 I - 195 E horizon development, I9 I manganese role, 190- I9 I Hybridization in identification of genetic groupings of Bradyrhizogbum juponicum, 68 interspecific, oilseed brassicas, 5 , 40-4 I Hydrogenase system, Bradyrhizogbum j u p onicirm and DNA homology groupings, 78 phenotype diversity, 75-77 and symbiotic performance, 77 - 78

I lmidazolinone tolerance, oilseed brassicas, 38 Insect control, gene-based, in Brussica spp., 46 Iron catalytic oxidation of organics, 180- I8 I disproportionation, I8 I - I82 oxides, field tests for, 20 I -205 pe-pH diagrams, 170 proportionation, I8 1 - I82 redox system, I79 reduction half-reactions, 162- 163 Irrigation water, sulfur contents, 226-227

2 74

INDEX L

Leaf diseases, chloride effects, I I9 - 122 Leaf movement, chloride role, I 13 Leaf rust, chloride effects, I2 1- I22 Lepfosphaeria maculans blackleg, resistance in oilseed brassicas, 24 - 28 Lettuce, chloride deficiency, 109 Light leaf spot, resistance in oilseed brassicas, 36 Linkage mapping, oilseed brassicas, 48-49

M Manganese chloride interactions in plants, I 16- 1 17 as electron acceptor, I8 I field tests, 20 I - 205 humus formation, 190- 191 Mn-nitrogen transformations, 186- I87 Mn(II1)-organic acid reductants, 182184 oxidation in soils mechanism, 185- 186 oxygen restriction effects, 184- I85 oxides dismutation of H,O,, 204 interferences, 205 pe- pH diagrams, I67 - I69 redox system, I79 reduction half-reactions, 162- 163 synthetic amorphous Mn(1V) preparation, 202 Manganese electron demand (MED) determination, 204 Metals, heavy, see Heavy metals Methionine, levels in oilseed brassicas, 46 Microspore culture, oilseed brassicas, 41 -42 Molybdenum, sulfur fertilization effects, 256 Mutagenesis,with haploid Brassica spp., 42

N Nitrate reduction, dissimilatory, see Dissimilatory nitrate reduction Nitrification, inhibition by chloride, 114 Nitrogen -chloride interactions in plants, 114- I15 -manganese transformations, 186- I87 pe-pH diagrams, 166- 167

reduction half-reactions, 162 sulfur fertilization effects on plant nitrate content, 255 - 256 Nitrogenase, activity in Bradyrhizogbumjaponicum, ex planta, 92

0 Oats, chloride effects, I29 Oil quality Brassica spp., Agrobacierium-mediated transformation techniques, 44 - 45 sulfur fertilization effects, 254 Oil quantity Brassica spp., Agrobacleriurn-mediated transformation techniques, 45 -46 oilseed brassicas, 22 - 23 sulfur fertilization effects, 254 Oilseed brassicas disease-resistant cultivars, 24- 37 DNA markers, 48 -49 fatty acid compositions, 8-9 genomic relationships among species, 5 haploid production in viiro, 4 I -42 herbicide-resistant cultivars, 37 - 39 heterosis and F, hybrids, 13- I5 interspecific hybridizations, 40-41 oil yield, 22-23 plant descriptions, 6-7 pollination control systems, I5 - 22 modes, 7 production, 2-4 protein yield, 22 - 23 protoplast fusions, 43 -44 quality, improvements in, 7- 10 seeds, descriptions, 6- 7 seed yield breeding methods, 10- 13 components, 10- I3 somaclonal variations, 42-43 transformation, 44-48 world socioeconomic importance, 2- 3 Organic compounds, catalytic oxidation by iron, 180- 181 Osmoregulation, chloride role, I 12 Osmosis, adjustments, chloride role, I I2 Oxidation - reduction reactions, see Redox reactions

INDEX Oxygen pe-pH diagrams, I65 - I66 reduction half-reactions, 162

P PP

definition, I56 empirical, determination, 200 PP-PH diagrams carbon species, 170- I72 iron species, 170 manganese oxide species, 167- I69 nitrogen species, I66 - I67 oxygen species, I65 - I66 sulfur species, 170- I72 thermodynamic information from, 160165 PH definition, 156 pe-pH thermodynamic data, 160- 165 Phage typing, Bradyrhizogbum japonicum and DNA homology groupings, 89-90 phenotype diversity, 89 and symbiotic performance, 89 Phenotype, oilseed brassicas dissimilatory nitrate reduction, 78-80 fatty acids, 93 hemoproteins, 92-93 intrinsic antibiotic resistance, 72-75 nitrogenase activity ex planta, 92 plant growth-regulating substances, 90-92 protein profiles, 87-88 rhizobiophage typing, 88 -90 rhizobitoxine, 80- 84 serology, 69 - 72 summary of relationships, 94 surface polysaccharides, 84-87 uptake hydrogenase, 75-78 Phosphinotricin tolerance, oilseed brassicas, 39 Phosphorus, interactions with chloride in plants, I I5 - I I6 sulfur in plants, 256 Photosynthesis, chloride role, 110- I I I Plant analyses crop response to chloride, 135- 138 sulfur deficiency, 239- 24 I

275

Plant growth-regulating substances, Bradyrhizogbumjaponicum and DNA homology groupings, 9 I - 92 phenotype diversity, 90-91 and symbiotic performance, 9 1 Pollen control, in Brnssica spp. cytoplasmic male sterile- nuclear restorer system, I7 - 20 gametocides, I 5 - I6 genic male sterility, 20-21 self-incompatibilitysystems, I6 - I7 transgenics, 2 1 -22 Pollination, oilseed brassicas control systems, 15 -22 modes, 7 Pollutants, reduction half-reactions, 163 Polysaccharides, surface, Bradyrhizogbum japonicum and DNA homology groupings, 87 methods, 84-85 phenotype diversity, 8 I - 85 and symbiotic performance, 85-86 Population diversity groupings, Bradyrhizogbum japonicum dissimilatory nitrate reduction, 78-80 fatty acids, 93 hemoproteins, 92-93 hydrogenase system, 75-78 intrinsic antibiotic resistance, 72- 75 nitrogenase activity explanta, 92 plant growth-regulatingsubstances, 90-92 protein profiles, 87-88 rhizobiophage typing, 88-90 rhizobitoxine, 80-84 serology, 69 - 72 summary of genotype/phenotype relationships, 94 surface polysaccharides, 81 -85 Potatoes chloride deficiency, I I0 chloride effects, I3 1 - 132 Precipitation, and soil sulfate, 22 I -223 Protein profiles, Bradyrhizogbumjaponicum and DNA homology groupings, 88 methods, 87 SDS-PAGE phenotype diversity, 87-88 and symbiotic performance, 88 Protein quality crop responses to sulfur, 253-254 oilseed brassicas, 46

INDEX

276

Protein yield, oilseed brassicas, 22-23 Protons, characteristics, 153- 155 Protoplast fusion, in oilseed brassicas, 43 -44

Q Quality response to chloride corn, 129-131 oat, 129 soybeans, 131 - I32 to sulfur, 252 - 256

nitrate, dissimilatory, see Dissimilatory nitrate reduction -oxidation reactions, see Redox reactions Rhizobitoxine, Bradyrhizugbum japonicum - related and DNA homology groupings, 83 - 84 phenotype diversity, 80-82 and symbiotic performance, 82-83 Root rot common, chloride effects, 119 take-all, chloride effects, I I 8 - I 19 Rot, see Root rot; Stem rot Rusts, see specific types ofrust

R Redox reactions characterization, empirical methods empirical pe determination, 200 lab incubations, 199-200 soil handling, 198- 199 free radicals behavior, 177- 178 formation, 176- 177 iron, 178- I79 log K determination, 157 manganese, 178- 179 measurement in soils electrochemical relations in reverse, 174-175 empirical pe values, 175- I76 platinum electrodes, I72 - I74 pe, definition, 156 pH, definition, I56 photochemical transformations in soil and water, I88 - I90 reduction half-reactions, 155- 156 thermodynamic parameters for electron activity, I55 - I58 kinetic derivation, 158- 160 pe-pH information, 160- 165 wetlands interfaces, 197- 198 preservation, I96 Reducing capacity, soil, 203 - 204 Reducing intensity, soil, 203 Reduction half-reactions characterization, I55 - 156 for N, 0, Mn, Fe, S, C and pollutants, 162- I63

S Sclerotinia sclerotiurum, stem rot, resistance in oilseed brassicas, 32 - 34 Seeds, oilseed brassicas, 6 - 7, 10- I 3 Selenium, sulfur fertilization effects, 256 Self-incompatibility systems, for Brassica spp. pollination control, 16- 17 Serology, Bradyrhizugbum japonicum and DNA homology groupings, 72 methods, 69 phenotype diversity, 69 - 70 and symbiotic performance, 70-72 Somaclonal variations, in oilseed brassicas, 42-43 Soybean brad yrhizobia, see Bradyrhizugbum japonicum Soybeans, chloride effects, I3 I - I32 Spinach, chloride deficiency, 109 Stem canker, in oilseed brassicas, 24-28 Stem rot, Sclerutinia sclerutiorum, resistance in oilseed brassicas, 32- 34 Sterility, genic male, in Brassica spp., 2021 Stomata operation, chloride role, 1 I2 - 1 13 Streams, sulfur in, 226-227 Stripe rust, chloride effects, 120- 12 I Subtropics, sulfur deficiency, 2 1 I -2 15, 257-258 Sugar beets, chloride deficiency, 109 Sulfur critical soil solution concentration, 24 1 246 crop responses, 246-252 fertilization effects, 252-256

277

INDEX interactions with phosphorus, 256 with various elements, 256-257 in irrigation water, 226- 227 pe-pH diagrams, 170- I72 reduction half-reactions, 162 requirements of plants, 241 -246 SO, adsorption mechanisms, 234-236 sulfate form accession through precipitation, 22 I 223 adsorption by soils, 227-232 adsorption curves, 232-234 characterization, 2 16- 2 I7 desorption by soils, 227-232 transformation products, 2 15 -2 16 Sulfur cycling accession through precipitation, 22 I -223 supplies of atmospheric origin, 219-22 I in tropics, 2 I7 - 2 I9 Sulfur deficiency plant analyses for, 239- 24 I soil tests for, 237-239 tropical/subtropical, 21 1-215, 257-258 Sulfur tetroxide, adsorption mechanism, 234-236

T Tanspot, chloride effects, I22 Tests, soil crop response to chloride, I38 - 140 sulfur deficiency, 239-24 I Tetramethylbenzidine, tests for Mn, Fe oxides, and oxidizing free radicals, 20 1 202 Thermodynamics, redox reactions electron activity, I55 - I58 kinetic derivation, I58 - I60 pe-pH information, 160- 165 Tomato, chloride deficiency, I09 Transformation ARrobactprium-mediated, in Brassicu spp., 44-48 disease resistance, 47 heavy metal sequestration, 47 insect control, 46-47 molecular farming, 47-48 oil quality modifications, 44-45

oil quantity modifications, 45 -46 protein quality, 46 redox, photochemical, 188- 190 Triazine tolerance, oilseed brassicas, 37- 38 Tropics sulfur cycling, 2 17- 2 I9 sulfur deficiency, 21 1-215,257-258 Turnip mosaic virus, resistance in oilseed brassicas, 36

V Vegetation, forest, acid rain effects, 225 Verticillium dahliae wilt, in Brassica spp., 36-37

W Water irrigation, sulfur contents, 226 -227 ground-, sulfur in, 227 Wetlands characterization, 195- 196 preservation, redox-related reasons for, I96 redox interfaces, 19?- 198 White rust, resistance in oilseed brassicas in Brassica napus, 3 1 - 32 race 2 resistance, 29 - 3 I race 7 resistance, 3 1 selection for, 32 Wilt, see Verticillium dahliae wilt

Y Yellow rust, chloride effects, I 19- I20 Yield oilseed brassicas oil, 22-23 protein, 22-23 seeds, 10- 13 wheat and barley responses to chloride, 126- 128

Z Zinc, sulfur fertilization effects. 256