The Effects of Monocalcium Phosphate on Crops Grown
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THE EFFECTS OF MONOCALCIUM PHOSPHATE ON CROPS GROWN IN SOME BUGANDA SOILS A thesis presented by PETER HOTSON LE MARE for the Degree of Doctor of Philosophy in the Faculty of Science of the University of London May 1973 Rothamsted Experimental Station Harpenden Herts 2 ABSTRACT In field experiments at Namulonge, Uganda, in 1961-63 125 kg/ha of triple superphosphate diminished yields of cotton and beans, but larger dressings increased them. This work at Rothamsted investigated the cause of these unusual responses. Ryegrass and cotton were grown in pot experiments in a glasshouse and in controlled environment cabinets. Monocalcium phosphate (MCP) added to Namulonge soil increased the amounts of phosphorus and manganese in ryegrass; this effect was not caused by triple-point solution, formed by hydrolysis of MCP, dissolving soil manganese as. dicalcium phosphate also increased manganese uptake. Manganese concentrations in cotton grown in nutrient solutions without soil, were increased by added phosphorus and decreased by calcium; a small Ca:P ratio in the nutrient medium caused manganese toxicity, but extra calcium prevented it. With large Ca:P ratio, excess manganese was precipitated in older leaves as nodules containing Mn (perhaps Mn02); younger leaves had only slight toxicity symptoms. The Ca:P ratio in the nutrients appeared to be involved in controlling the effect of manganese on auxin oxidation. The ratio of Ca:P in applied nutrient solutions controlled the concentration of manganese in'cotton grown in Namulonge soil without added manganese. Large Ca:P ratios decreased, small ratios increased manganese concentrations; with the mole ratio Ca:P = 1:2, (the ratio in triple superphosphate) the smallest concentrations of calcium and phosphorus in the nutrient solution increased plant manganese, but larger concentrations at the same ratio decreased it. It appears, therefore, that moderate amounts of triple superphosphate depress yield 3 because the Ca:P ratio is too small to prevent harmful amounts of manganese accumulating in plants, not because phosphorus is 'fixed' in the soil. Quartz breccia ridges in Buganda contain much manganese so soils below them have accumulated manganese; crops grown in the soils may take up too much manganese when fertilisers with small Ca:P ratios are applied. 4 ACKNOWLEDGEMENTS I acknowledge help of various kinds that I received whilst I investigated the fertility of the Namulonge soils. When I returned to England in 1969 G. W. Cooke encouraged me to investigate the causes of the field responses at Namulonge, and provided facilities in the Chemistry Department at Rothamsted. He supervised the project and helped by criticising the manuscript. Dr. A. H. Cornfield was Director of Studies at Imperial College, London. E. Jones took soil samples at Namulonge and sent them to Rothamsted. Discussions with him were very helpful, especially during my visit to Namulonge in May 1972. Z. M. S. Kanamwangi provided information on the distribution of'lunyu' soil in Buganda. At Rothamsted J. M. Hill assayed leaf samples for enzyme activities; he, I. F. Bird and A. J. Keys helped by criticising the manuscript of Chapter 10. J. D. D. Mitchell and R. Selby helped with the pot experiments. Other help is gratefully acknowledged: H. A. Smith, M. Roberts, Brenda Messer, V. Cosimini, R. A. G. Rawson (chemical analyses); J. H. A. Dunwoody and A. Todd (statistical analysis); F. D. Cowland and Lynda Woods (photographs and maps); and Mrs. Maureen Broom (typing the thesis). I am also grateful to other colleagues at Rothamsted and Namulonge who helped by discussion, and in other ways, to complete the work. The project was financed by the Overseas Development Administration of H. M. Foreign and Commonwealth Office. 5 CONTENTS Chapter Page Title 1 Abstract 2 Acknowledgements 4 Contents 5 1 Introduction 12 Review of earlier work on response to 12 phosphate in Uganda The unusual response to phosphate at 13 Namulonge Other examples of the effect observed 16 at Namulonge Uganda 16 Kenya 16 India 18 North America 19 Fertilisers that may cause the unusual 20 response Hydrolysis of monocalcium phosphate in 21 soil A first hypothesis for the unusual 24 response at Namulonge 2 The Namulonge Environment 27 Geology of Namulonge Research Station 27 Soils 29 Characterisation of Namulonge soils 29 Sendusu series 3o Nalumuli series 3o Nakyesasa series 33 Climate 33 6 Chapter Page Soils and Crops Used in the Experiments 36 Soils 36 Soil 1 36 Soil 2 36 Soil 3 36 Crops 37 4 Effects of Small Amounts of Monocalcium 38 Phosphate on Ryegrass Grown in Three Namulonge Soils Experimental 38 Results 39 Dry matter 41 Plant phosphorus 41 Plant manganese 41 Discussion 49 5 Laboratory Experiments on Separating the Derivatives of Monocalcium Phosphate Hydrolysis The method 51 Testing the method in Namulonge soil 52 Composition of residues after 52 hydrolysis Movement of phosphate into soil 55 Phosphorus recovered from the 58 soil Time needed for hydrolysis of 58 monocalcium phosphate 6 The Effect of Monocalcium Phosphate, and Its 65 Hydrolysis Derivatives on Manganese in Ryegrass Grown in Namulonge Soils Experimental 67 Soils 67 Phosphate treatments 67 Procedure 68 7 Chapter Page Results 72 Plant density 72 Plant manganese 72 Dry matter 75 Plant phosphorus 81 Discussion 88 7 Possible Effects of Manganese in Cotton 91 Hypothetical causes, of the unusual 91 response The effects of excess manganese in 92 the plant The interaction of manganese and iron 93 Auxin oxidation by manganese 94 Cotton experiments at Rothamsted 94 8 Effects of Triple-Point Solution on Cotton 96 Grown in Two Namulonge Soils Experimental 96 Soils 96 Nutrient treatments 97 Phosphate 97 Iron 97 Basal nutrients 97 Procedure 99 Design 99 Results 100 Observations during growth 100 Leaf production 100 8 Chapter Page Dry matter and plant composition 102 Results for shed leaves 102 Results for plants at harvest 104 Dry matter 104 Plant manganese 106 Plant phosphorus 106 Plant calcium 109 Discussion 109 9 Interactions of Phosphorus, Calcium and 114 Manganese Applied to Cotton Grown in Nutrient Solutions The effects of applying two factors 115 together at various ratios Experimental 116 Treatments 116 Basal nutrients 116 Procedure 117 Results 118 Observations during growth 118 Calcium deficiency 118 Manganese toxicity 119 Dry matter and chemical composition 124 Dry matter 124 Plant manganese 128 Plant phosphorus 137 Plant calcium 137 Discussion 140 9 Chapter Page 10 The Effects of Calcium, Phosphorus and 142 Manganese on Some Enzyme Systems Controlling Auxins in Cotton Experimental 145 Activities of peroxidase and 145 IAA-oxidase Procedure 145 Inhibition of IAA oxidation 146 Procedure 146 Results 147 Activity of peroxidase 147 Inhibition of IAA oxidation 147 Discussion 153 11 The Effects of the Ratio of Calcium to 157 Phosphorus in Nutrient Solutions on Cotton Grown in Namulonge Soil Experimental 157 Treatments 158 Results 158 Presentation of results 158 Dry matter 159 Plant manganese 159 Plant phosphorus 165 Plant calcium 165 Nutrient ratios in plants 168 Calcium : manganese ratio 168 Phosphorus : manganese ratio 171 Soil pH 171 Discussion 174 10 Chapter Page 12 General Discussion : Implications of the 177 Work for Tropical Agriculture Review of experiments at Rothamsted 177 Behaviour of monocalcium phosphate 177 (MCP) in soil Manganese nutrition of cotton 178 Effects of calcium and phosphorus, 180 and their interactions with manganese, in cotton grown in Sendusu soil Results of experiments at Rothamsted 183 related to field results at Namulonge Phosphate fixation and sigmoid 183 response curves Phosphorus concentration in plants 185 The effect of calcium in triple 186 superphosphate Soil physical conditions 187 Effects of other fertilisers 188 Differences in the effects of manganese 189 on various crops and their implications for fertilising at Namulonge The source of manganese in Namulonge soil 192 References 195 Appendices Ia Observations on the Phosphate Potential 203 of Some Tropical Soils Ib Experiments on the Effects of Phosphate 203 Applied to a Buganda Soil II The Geology of South Mengo District, 204 Buganda, with Special Reference to Sources of Manganese III Analysis of Crop Samples 208 IV Yields of Dry Matter, and Concentrations 209 of Phosphorus and Manganese in Crops 11 Chapter Page Appendices (Continued) V Yields of Dry Matter, and Concentrations 212 of Phosphorus and Manganese in Crops (Chapter 6) VI Yields of Dry Matter, and Concentrations 215 of Calcium, Phosphorus and Manganese in the Cotton (Chapter 8) VITA Yields of Dry Matter, and Concentrations 219 of Calcium, Phosphorus and Manganese in Cotton (Chapter 9) VIIB Assays of Peroxidase Activity and 221 Inhibition of IAA Oxidation in Cotton Leaves (Chapter 10) VIII Yields of Dry Matter and Concentrations 222 of Calcium, Phosphorus and Manganese in Cotton (Chapter 11) IX Concentrations of Phosphorus in Water 226 Extracts of Soil 35 and 80 Days After Applying Monocalcium Phosphate and Triple-Point Solution to the Soil Surface (Chapter 5) X Composition of Nutrient Solutions 227 Applied to Cotton Grown in Sendusu Soil (Chapter 11) 12 CHAPTER 1 INTRODUCTION Review of earlier work on response to phosphate in Uganda Traditional peasant agriculture in Uganda is sustained by shifting cultivation that maintains the soil fertile enough for subsistence and a modest cash income from crops sold off the farm; but more intensive farming to increase crops for sale depletes the soil of plant nutrients. Namulonge Research Station was opened in 1950 to find ways of increasing rain-grown cotton in Africa. From the start the farm was used to develop systems of intensive farming suited to the local Buganda environment (Hutchinson & Prentice, 1959) and these entailed bigger demands on the soil's nutrient reserves. Chemical studies of the soil and crops began in 1952 to find how to improve and maintain fertility by using manures and fertilisers correctly. Concurrently with the work similar problems at Ukiriguru, Tanzania, were studied and comparing results from the two places helped to understand both.