Efficiency of Legumes in Increasing Yam Yield under Sandy Ferrasol in the Forest Zone of Southwestern Côte d’Ivoire

The cropping system is based on traditional farming in rural areas. In this way, yields of some food crops like yam are very low considering their high need for nutrients. The nutrient-rich land is under high land pressure as it is occupied by cash crops such as oil palm and rubber at the expense of food crops and soil fertility is declining. The study was conducted in Grand-Lahou to assess the effect of organic matter provided by legumes in increasing yam yield. The randomized complete block design included four (4) treatments: Arachis hypogaea？+ yam association (T1), Acacia mangium +？yam association (T2), Arachis？+？Acacia mangium？+ yam association (T3) and pure yam crop (T0). The parameters measured were: the soil nutrients content, the rate of mineralization of organic matter through the C/N ratio as well as the yield of yam through different techniques that allowed the objective of the study to be achieved. It was noted a slight improvement of nitrogen and organic carbon in all treatments with a higher value recorded in the T2 treatment. The C/N ratio decreased to 12 in all treatments compared to the control, which reflects a normal decomposition of the organic matter. Treatment T1 increased yam yield (8.4 t/ha) in contrast to treatments T2 (4.1 t/ha) and T3 (2.8 t/ha). Legume-based treatments T2 and T3 were associated with a significant decrease in yam yield, resulting in losses of −46.34% to −25.09%, while treatment T1 resulted in a gain of 28.57%. As a result, the treatments involving legumes contributed to normalizing the organic matter content of the soil. The simultaneous association of these two legumes led to a decrease in yam production, contrary to the treatment associating only groundnut.