Management of agroforestry systems for enhancing resource use efficiency and crop productivity

Agroforestry is a low-input system which combines trees with crops in various combinations or sequences. It is an alternative to intensive cropping systems, which rely on large inputs of manufactured fertilizers and other external inputs to sustain production. Agroforestry also has the potential to reduce risk through diversification of a variety of products, including food, fuelwood and animal fodder. Other perceived benefits include enhanced nutrient and water use efficiencies, reduced nutrient leaching to groundwater and improved soil physical and biological properties. The use of leguminous or actinorhizal trees may further enhance these benefits because of their capacity to fix atmospheric nitrogen. Depending on the type of agroforestry system and the management practices employed, a substantial portion of this fixed nitrogen can be transferred to companion crops and to the soil. In considering the overall productivity of agroforestry systems, it is essential to investigate the competition or complementarity in the capture and partitioning of resources between tree and crop components. This is especially true for nutrients and water, usually the two most limiting factors influencing crop growth. The focus of this coordinated research project (CRP) was to evaluate the efficacy of various agroforestry systems used in Member States in terms of crop productivity, resource use efficiency and improvements in soil properties. The use of isotopes and nuclear techniques was essential for understanding the dynamics of nutrients and water in agroforestry systems. The contribution of nitrogen from fertilizers and leguminous trees to soil and crops was studied using both direct and indirect 15N labelling techniques. The cycling of carbon from trees or crops to soil was studied using natural variations in the 13C signatures of the soils and the different species. The soil moisture neutron probe in conjunction with tensionics was used to monitor soil water status and balance, and differences in the 18O composition of rain, surface and groundwaters were used to identify the sources of water used by trees and crops. This CRP was implemented through a research network that initially included nine contract holders from Benin, China, Chile, Costa Rica, Kenya, Malaysia, Sri Lanka, Uganda and Zambia, and five agreement holders from Australia, France, Kenya, Nigeria and the UK. The CRP was conducted in collaboration with National Agricultural Research Systems in Africa, Asia and Latin America, and with three CGIAR Centres, the International Centre for Research in Agroforestry (ICRAF, Kenya), the International Institute of Tropical Agriculture (IITA, Nigeria) and CIAT's Tropical Soil Biology and Fertility Institute (TSBF, Kenya). This IAEA-TECDOC contains 15 manuscripts prepared by the project participants