[en] Tree and crop components of an alley cropping system may compete for nutrients and water in the surface soil while the deeper-rooting tree may have better access to resources in the subsoil. The objectives of the present study in an alley cropping system were to monitor runoff and soil loss, spatial variation of soil water, and tree sap flow to determine competitiveness for water between the tree and peanut. Plant and root growth were also recorded to evaluate competition. The tree competed for water in the surface soil at some critical period as indicated by the spatial variation of monitored soil water content. The tree used deep soil water and reduced deep drainage as indicated by modelling of soil water fluxes and direction of water movement. Trees in the alley cropping system used less soil water than peanut, and more water than trees alone, as indicated by water balance modelling. The magnitude of the reduction of deep drainage increased with tree age. The alley cropping system increased system water use efficiency by using deep soil water as indicated by water balance modelling. The alley cropping system promoted Choerospondias axillaris growth by 50 to 100% and reduced peanut biomass and yield by 20 to 50%. Field management should aim to prevent water competition between trees and crops in the surface soil. (author)