WaNuLCAS, a model of water, nutrient and light capture in agroforestry systems

Models of tree-soil-crop interactions in agroforestry should maintain a balance between dynamic processes and spatial patterns of interactions for common resources. An outline is given of, and major assumptions discussed, underlying the WaNuLCAS [Water, Nutrient and Light Capture in Agroforestry Systems] model of water, nitrogen and light interactions in agroforestry systems; this is a prototype model now at the testing stage. It uses the Stella Research modelling shell linked to Excel spreadsheets for data input and output, and represents a 4-layer (vertical) soil profile, and water and nutrient (at this stage only N) balance and uptake by a crop and a tree. The model was developed to deal with a wide range of agroforestry systems - hedgerow intercropping on flat or sloping land, fallow-crop mosaics, or isolated trees in parklands - with a minimum of parameter adjustments. Examples are presented for simulation runs of hedgerow intercropping systems at different hedgerow spacings and pruning regimes, a test of the safety-net function of deep tree roots, lateral interactions in crop-fallow mosaics and a first exploration for parkland systems with a circular geometry