Alley cropping systems can positively utilize deep soil water and leached nitrogen in the dry season, and help prevent soil and water erosion in the rainy season. In the surface soil, however, competition for nitrogen and water, and above the ground the competition for sunlight between the components may occur. The objective of this paper was to assess the alley cropping system, consisting of Choerospondias axillaris trees and peanut (Arachis hypogaea) plants in subtropical China in terms of uses of soil water, soil nitrogen and light. 15N injection experiments were carried out to determine N use by tree and crop. Spatial variations of photosynthetic available radiation (PAR) were measured to determine the shadowing effect. Spatial and temporal variations of soil water regime were monitored to determine the competition for water between the trees and peanut plants. In addition, crop and tree growth were also recorded.
Compared to the tree alone systems, alley cropping systems encouraged the fast growth of the trees, and depressed the biomass and yield of peanut by 20% to 50%. The impact of PAR was profound and had a negative relationship to the biomass and yield of peanut plants. The spatial and temporal variations of soil water regime indicated that the tree utilized soil water beneath the surface layer and alleviated the seasonal drought. Competition for soil water between the tree and peanut plant occurred at the beginning of the dry season. Compared with the mono-peanut cropping system, the alley cropping system decreased 15N recovery by peanut plant and increased ¹⁵N recovery by the tree, indicating that the tree utilized soil nitrogen leached to 60 cm depth. The yield and biomass of peanut plants were influenced mostly by light, but also by fertilizer and water. The results suggest that these competitions for resources must be taken account to optimize the alley cropping system.