Influence of rock phosphate on growth and biomass production of pigeonpea ( Cajanus cajan (l.) millsp.) in different farmers' fields and its residual effect on maize in the derived savanna of Bénin

One of the options to alleviate soil fertility constraints for sustainable agriculture in West African’s savanna is to develop soil nutrient management technologies from an adequate supply and feasible share of organic and inorganic fertilizers. The impact of combined application of organic input (fresh Cajanus cajan pruning residues) and inorganic fertilizers (Togo phosphate rock) on maize performance was investigated on 2 sites (Zouzouvou and Eglime) in the derived savanna benchmark of Benin, where 2 main geological units can be distinguished, giving rise to distinct soil associations. One (Zouzouvou) is a Rhodic Ferralsol and one (Eglime) a complex pattern of Acrisols, Lixisols, Luvisols and Leptosols with inclusions of Vertisols and Cambisols. The application of rock phosphate increased the shoot dry weight of Cajanus cajan by 29 to 145 % in 5 out of 12 farmers’ fields at Zouzouvou and 17 to 53 % in 3 out of 12 farmers’ fields at Eglime. The dry matter of the leaves increased by 13 to 227 % in 6 out of 12 farmers’ fields at Zouzouvou, while at Eglime, in 6 out of 11 fields, it increased by 7 to 31 %. A significant increase was obtained with symbiotic parameters of Cajanus cajan such as % AMF, nodule number and nodule fresh weight with rock phosphate application, at both places. Only 40 % of farmers’ fields at Zouzouvou had a subsequent maize grain increase (by 17 to 90 %) as a result of the residual effect of combining organic (Cajanus cajan ) and inorganic input. There was no effect at Eglime.