Assessment of soil factors limiting growth and establishment of Mucuna in farmers' fields in the derived savanna of the Benin Republic

Mucuna pruriens was been used to control Imperata cylindrica and improve so il fertility in maize and cassava cropping systems in the derived savanna o f the Benin Republic, West Africa. However, field observations showed that Mucuna had poor establishment in some farmers' fields. This could be due in part to the poor symbiotic effectiveness of Mucuna and/or its poor nutriti on because of mineral deficiencies in the soil. A short-term survey was car ried out in 34 farmers' fields located in four different sites (Zouzouvou, Eglime, Tchi, and Niaouli) in the derived savanna to assess the natural nod ulation and mycorrhizal infection of Mucuna. This survey was followed by a nutrient-omission trial conducted in a pot experiment using soil collected from two groups of farmers' fields at Zouzouvou where Mucuna had poor estab lishment. Mycorrhizal infection ranged from 2 to 31% and correlated positiv ely with nodulation and shoot dry matter production of plants grown only in one site at Zouzouvou. The number of rhizobia ranged between <0.05 (near t he detection limit) and 15 cells gl soil depending on the plot history and the fields. Nodulation occurred in 79% of the fields with numbers of nodule s ranging from 0 to 135 plant(-1). The nutrient-omission trial showed that when N and P were absent in the complete fertilizer treatment, biomass prod uction decreased significantly, on average by 69% (N) and 33% (P). Mg, S, K and micronutrient deficiencies did not reduce significantly the biomass pr oduction in the two groups. However, N fertilizer applied additionally each week to some treatments drastically reduced Mucuna nodulation. Strategies to enhance Mucuna establishment and growth are discussed.