CROP-TREE INTERACTIONS IN ALLEY CROPPING SYSTEMS ON ALLUVIAL SOILS OFTHE UPPER AMAZON BASIN

A crop/hedgerow interface design was used to test three leguminous spe cies, Inga edulis, Leucaena leucocephala and Erythrina sp., for their potential use for alley cropping on alluvial soils in the upper Amazon Basin. Prunings were applied as mulch at three rates 0, 3.3 and 6.7 M g dry matter/ha/crop. Competition, crop yields, nutrient budgets, and weed control were monitored for three consecutive crops of upland rice . Crop yield reductions were evident up to 1.5 m from each of the hedg erow species, but were more pronounced with Leucaena hedgerows. Additi onal mulch was able to compensate for these reduced yields close to th e hedges in Leucaena leucocephala and Erythrina but not in Inga edulis systems. In general rice yields were higher with Leucaena leucocephal a and Erythrina mulch as compared to Inga mulch, perhaps because of hi gher levels of available N provided by the rapidly decomposing leaves of Leucaena leucocephala and Erythrina sp. as compared to Inga. Weed c ontrol was greater, however, with the slowly decomposing Inga mulch. F or all three hedgerow/crop systems there was a net export of P from th e system which was exhibited by declining soil P levels and decreasing crop yields.