Effect Of A Legume Cover Crop (Mucuna Pruriens Var. Utilis) On Soil Carbon In An Ultisol Under Maize Cultivation In Southern Benin

Abstract. Long term fallow is no longer possible in densely populated tropical areas, but legume cover crops can help maintain soil fertility. Our work aimed to study changes in soil carbon in a sandy loam Ultisol in Benin, which involved a 12￢ﾀﾐyear experiment on three maize cropping systems under manual tillage: traditional no￢ﾀﾐinput cultivation (T), mineral fertilized cultivation (NPK), and association with Mucuna pruriens (M). The origin of soil carbon was also determined through the natural abundance of soil and biomass 13C. In T, NPK and M changes in soil carbon at 0￢ﾀﾓ40 cm were ￢ﾈﾒ0.2, +0.2 and +1.3 t C ha￢ﾈﾒ1 yr￢ﾈﾒ1, with residue carbon amounting to 3.5, 6.4 and 10.0 t C ha￢ﾈﾒ1 yr￢ﾈﾒ1, respectively. After 12 years of experimentation, carbon originating from maize in litter￢ﾀﾐplus￢ﾀﾐsoil (0￢ﾀﾓ40 cm) represented less than 4% of both total carbon and overall maize residue carbon. In contrast, carbon originating from mucuna in litter￢ﾀﾐplus￢ﾀﾐsoil represented more than 50% of both total carbon and overall mucuna residue carbon in M, possibly due to accelerated mineralization of native soil carbon (priming effect) and slow mulch decomposition. Carbon originating from weeds in litter￢ﾀﾐplus￢ﾀﾐsoil represented c. 10% of both total carbon and overall weed residue carbon in T and NPK. Thus mucuna mulch was very effective in promoting carbon sequestration in the soil studied.