Productivity benefits from integrating Acacia auriculiformis and agricultural cropping in Java, Indonesia

Agroforestry systems provide smallholder farmers with opportunities to broaden their income base. However, as planting trees can come at the cost of reduced crop yield because of competition for resources, farmers need to understand the consequences of tree growing on crop productivity. This paper explores the impacts of Acacia auriculiformis on agricultural crop productivity during the first three cropping seasons in Gunungkidul, Java, Indonesia; maize then soybean was planted in each season. We also sought to understand whether water competition was a factor in determining productivity in this agroforestry system, as this environment is characterised by a long (~ 6-month) dry season. A randomised complete block design with five replications was used, with three treatments, monoculture A. auriculiformis trees, monoculture agricultural crops, and an agroforestry plot that combined the trees and crop. At the final measure, at age 27 months, the trees were 7.4 and 6.9 m in height and 7.2 and 7.1 cm in diameter in the monoculture and in the agroforestry systems respectively, and treatment had no significant effect on the tree height or diameter. Grain yield of soybean was not affected by treatment in any of the three growing seasons, but both grain and stover yields of maize were significantly lower in the agroforestry system than in the monoculture in the third growing season. Differences in soil water deficit, and pre-dawn and mid-day leaf water potentials in A. auriculiformis and soybean were generally not significant between treatments in all three growing seasons. land equivalent ratios for the A. auriculiformis agroforestry system decreased from the 1st to the 3rd growing seasons but remained > 1.3. As fertilizer was applied it was assumed that there was no nutrient limitation. It was therefore concluded that tree shading was primarily responsible for reductions in productivity, and that this affect was greater on maize than soybean grain yield.