Effect on maize growth of the interation between increased nitrogen availability and competition with trees in alley cropping

Maize growing next to Erythrina hedgerows had 44 percent lower biomass (P<0,01) and 35 percent lower N content (P<0,1) than maize growing in the middle of the alleys. Maize growing next to Gliricidia hedgerows had the same biomass but 56 percent higher N content (P<0,1) than maize growing in the middle of the alleys. However, these differences did not develop until 2 months after sowing of the maize. Spatial variability in soil nitrogen mineralization and mulch nitrogen release did not explain any of the differences in growth or N uptake of the maize with respect to distance from the trees. It is hypothesized that the slower growth of the maize next to the Erythrina trees after 2 months is due to increasing light and/or nutrient competition from the trees as the trees recover from pollarding. The apparent lack of competition from Gliricidia may be due to different rates of regrowth or different shoot and root architecture. A theoretical model is described demonstrating that if a crop is to take advantage of the higher nutrient availability under alley cropping it must complete the major part of its growth before the trees recover significantly from pollarding, and start competing strongly with the crop.