Trees, crops, and soil fertility : concepts and research methods

1. Impacts of Trees on the Fertility of Agricultural Soils 1 G. Schroth and F.L. Sinclair 1.1 Trees and the Development of Agriculture 1 1.2 Objectives and Structure of the Book 9 2. Economic Aspects of Soil Fertility Management and 13 Agroforestry Practices A.-M.N. Izac 2.1 Introduction 13 2.2 Factors Influencing Farmers’ Decisions About Soil 14 Fertility Management Practices 2.3 Hierarchy of Agricultural Systems as a Background to 18 the Understanding of Farmers’ Constraints 2.4 Anatomy of a Decision at the Farm Scale and Economic 18 Methods for Understanding such Decisions 2.5 Landscape and Global Scales: Soil Fertility and 32 Agroforestry Trees as Part of Natural Capital 3. Designing Experiments and Analysing Data 39 R. Coe, B. Huwe and G. Schroth 3.1 Synopsis 39 v 3.2 Experimental Objectives, Treatments and Layout 40 3.3 Fallow Experiments 48 3.4 Measurements and Sampling Designs 52 3.5 Analysing the Data 61 3.6 Spatial Structure and Its Analysis 67 4. Soil Organic Matter 77 G. Schroth, B. Vanlauwe and J. Lehmann 4.1 Synopsis 77 4.2 Methods for Total Soil Organic Carbon 86 4.3 Physical Fractionation Methods 86 4.4 Chemical Methods 88 4.5 Biological Methods 89 5. Soil Nutrient Availability and Acidity 93 G. Schroth, J. Lehmann and E. Barrios 5.1 Synopsis 93 5.2 Methods for Soil Nitrogen 104 5.3 Methods for Soil Phosphorus 112 5.4 Methods for Soil Sulphur 121 5.5 Methods for Potassium, Calcium and Magnesium in Soil 125 5.6 Methods for Soil Acidity 127 6. Decomposition and Nutrient Supply from Biomass 131 G. Schroth 6.1 Synopsis 131 6.2 Methods for Biomass and Nutrient Input with Litter 140 6.3 Methods for Decomposition and Nutrient Release from 143 Biomass 6.4 Measures of Resource Quality 148 7. Nutrient Leaching 151 J. Lehmann and G. Schroth 7.1 Synopsis 151 7.2 Methods for Soil Solution Composition 158 7.3 Tracer Methods for Nutrient Leaching 163 7.4 Dyes as Tracers for Preferential Flow Paths 165 8. Nutrient Capture 167 G. Schroth and J. Lehmann 8.1 Synopsis 167 8.2 Tracer Methods for Nutrient Uptake 174 vi Contents 9. Nutrient Exchange with the Atmosphere 181 G. Schroth and J. Burkhardt 9.1 Synopsis 181 9.2 Methods for Atmospheric Nutrient Inputs 185 9.3 Methods for Nutrient Losses from Burning 188 10. Soil Structure 191 M. Grimaldi, G. Schroth, W.G. Teixeira and B. Huwe 10.1 Synopsis 191 10.2 Methods for Soil Bulk Density 195 10.3 Methods for Aggregate Stability 196 10.4 Methods for Soil Porosity and Pore Size Distribution 198 10.5 Measuring the Role of Soil Organic Matter in Aggregate 204 Stability 10.6 Soil Micromorphology and Image Analysis 207 11. Soil Water 209 W.G. Teixeira, F.L. Sinclair, B. Huwe and G. Schroth 11.1 Synopsis 209 11.2 Methods for Soil Water Content 215 11.3 Methods for Soil Water Potential 221 11.4 Methods for Soil Hydraulic Properties 225 11.5 Estimating Topsoil and Subsoil Water Use with Stable 232 Isotopes 12. Root Systems 235 G. Schroth 12.1 Synopsis 235 12.2 Methods for Studying Root Distribution 240 12.3 Distinction of Roots of Different Species 245 12.4 Methods for Root Dynamics, Production and Turnover 246 13. Biological Nitrogen Fixation 259 K.E. Giller 13.1 Synopsis 259 13.2 Microbiological Methods for Studying Rhizobia 265 13.3 Simple Methods for Determining Whether a Legume 265 is Fixing Nitrogen 13.4 Isotope-based Methods for Measurement of Nitrogen 266 Fixation 13.5 Estimating Nitrogen Fixation in Field Settings 268 13.6 Methods Based on Nitrogen Fixation Transport 269 Products 13.7 Estimating Total Amounts of Nitrogen Fixation 270 Contents vii 14. Mycorrhizas 271 D.L. Godbold and R. Sharrock 14.1 Synopsis 271 14.2 Inoculation Methods 280 14.3 Sampling of Plant Roots for Mycorrhizal Studies 281 14.4 Quantification of Mycorrhizas 281 14.5 Identification of Mycorrhizal Fungi 283 14.6 Estimation of Mineral Nutrient Uptake Through 286 Mycorrhizas 15. Rhizosphere Processes 289 D. Jones 15.1 Synopsis 289 15.2 Obtaining a Representative Sample of Rhizosphere Soil 294 15.3 Methods for Rhizosphere Soil Chemistry 297 15.4 Methods for Rhizosphere Biological Activity 298 15.5 Quantification of Root Carbon Loss into the 300 Rhizosphere 15.6 Rhizosphere Mathematical Modelling 300 16. Soil Macrofauna 303 P. Lavelle, B. Senapati and E. Barros 16.1 Synopsis 303 16.2 Sampling of Macrofauna: the TSBF Methodology 318 16.3 Other Sampling Methods 320 16.4 Manipulative Experiments 322 17. Soil Erosion 325 M.A. McDonald, A. Lawrence and P.K. Shrestha 17.1 Synopsis 325 17.2 Quantitative Methods 336 17.3 Qualitative Methods 341 References 345 Index