Effect of tree density in an Acacia auriculiformis-based agroforestry system on rotational food crop yields and on soil fertility parameters

This study compares the effect of four different Acacia auriculiformis tree densities in an alley-cropping agroforestry system (AFS) on food crop yields and some properties of a ferralitic soil. The aims is to identify the one that would allow for settled agriculture. The study was conducted in Yangambi, DR Congo, and lasted eight successive growing seasons. The design consisted of four plots of 1042, 1250, 1563 and 2083 trees per hectare, arranged in corridors of 10 m, 8 m, 6 m, and 4 m respectively, as well as a control field without trees. This design was replicated six times on the ground. Food crops were grown in the corridors in two rotational cycles, each cycle alternating rice, peanuts, maize, and cowpeas crops. The results show that the AFS corridors had a positive impact on yields for all crops. However, the impact of tree density was noted only in cowpea. Acacia auriculiformis also had an acidifying effect on the soil as pH values significantly decreased, particularly in the 6 m corridors. It increased soil carbon, particularly in the 4 m, 6 m, and 8 m corridors, but had no impact on nitrogen. We suggest that the experiment be repeated after 7 years of age to study the long-term impact.