Competition for light between hedgerows and maize in an alley cropping system in Hawaii, USA

Successful agroforestry systems depend on minimizing tree-crop competition. In this study, field experiments and a simulation model were used to distinguish between tree-crop competition for light and belowground competition in an alley cropping system. Maize (Zea mays L.) was harvested periodically in three treatments: between vertical barriers of shade cloth, hedgerows of Flemingia macrophylla (Willd.) Merr., and sole maize. Radiation intercepted by the maize was calculated using a simulation model based on measured values for direct and diffuse light, hedgerow dimensions and leaf area, and solar trajectory. Radiation use efficiency was calculated as biomass production per unit of intercepted radiation. Maize biomass and yield in both the alley crop and the shade cloth treatment were greatest in the center of the alleys. Grain yield between hedgerows was 3.5 Mg ha(-1) (averaged across the alley), significantly less than in the shade cloth (7.4 Mg ha(-1)) or the sole maize (7.7 Mg ha(-1)) treatments. Light intercepted by the maize in the alley crop was about half that intercepted by the maize in the sole crop. The shade cloth intercepted less light than the hedgerows because it did not have an appreciable width. Radiation use efficiency in the three treatments was 0.75 g mol(-1) PAR and did not differ significantly among treatments. Tree-crop competition was overwhelmingly for light.