Plot-scale modelling of coffee agroforestry systems in Central America

The productivity and environmental impact of coffee agroforestry systems depend on many factors: environment, management coffee cultivar, tree species. We present a simple dynamic model of coffee agroforestry systems that can help analyse the impact of the different factors (van Oijen et al., 2008). The model includes the physiology of coffee plants, and its response to different growing conditions. This is integrated into a plot-scale model of coffee and shade-tree growth that includes competition for light, water and nutrients. The model can simulate management treatrents such as spacing, thinning, pruning and fertilising. Model outputs are the variables that we want the model to calculate, as a function of the inputs. The major outputs of the model are. - Productivity: coffee-bean yield, tree-stem volume. - Environmental impact: rate of N-leaching to groundwater and of N-emission to the atmosphere, rate of loss of organic carbon and nitrogen in surface runoff. We analysed to what extent the literature has sufficient information to allow parameterisation of the model for various coffee-tree combinations. Information on weather, coffee and trees is found to be limited, but soil information seems adequate. In particular, missing are multifactorial experiments to examine interactive effects of different environmental factors. Although model parameterisation thus remains uncertain, model behaviour seems consistent, with observations. We show examples of how the model can be used to examine trade-offs between increasing coffee and tree productivity, and between maximising productivity and limiting the impact of the system on the environment.