Models in mode for agroforestry
Intuitively, the concept of growing trees and crops together is appealing - it seems closer to what nature intended rather than the artificiality of monocultures that are the norm in the agricultural systems of developed countries. Yet, despite the millions of dollars that have been spent over the last 15 years, senior agroforestry researchers admit that they are still unable to predict which agroforestry systems or particular tree/crop combinations will do well in a given environment. Research so far has concentrated on categorising existing agroforestry systems and testing a limited number of agroforestry technologies at specific sites. However, the very nature of systems containing trees means that such research takes several years before conclusive results can be obtained, even at one location. If it turns out to be successful, researchers may then want to test the same system at other sites, requiring more time. Then, if a new idea of managing this agroforestry system is developed, more experiments are needed to test in which environments this idea may be successful. The whole process of identifying successful agroforestry systems and adapting them to a particular location can take many years. Clearly, there is a need for a tool to help in the initial screening of agroforestry systems in new areas, or to help evaluate new ideas on the management of these systems.
Crop simulation models have been used for a number of years now to help researchers, extension workers, and farmers understand and make better informed decisions regarding management of annual crops such as maize, wheat, barley, and soybeans, to name but a few. These models are based on an understanding of the processes occurring in the crops, and draw together expert knowledge from a range of disciplines, including soil science, agronomy, and agro-meteorology. The same model can be used for a number of different environments, provided the appropriate input data for weather, soils and crop varieties are used.
To some extent, existing models for various crops and trees can be linked but, in addition, it is essential to understand the principles of tree/crop interactions, and build these into the models. For this, it is not enough to know that a certain agroforestry system works or doesn't work at a specific site, as current research is telling us - we need to know why it performed in the way that it did. It is only then that results obtained from a limited number of experimental sites will be able to be extrapolated with some confidence to other regions. This approach does take time and money, but the rewards are large - efficient identification of promising technologies that may benefit millions of subsistence farmers in the developing world.
Robin Matthews
Department of Natural Resources Management, Silsoe College,
Cranfield University, Silsoe, Bedfordshire MK45 4DT.
