In-situ mineral nitrogen following soil incorporation Crotalaria grahamiana and Mucuna pruriens biomass and financial benefits of legume short-fallow in Eastern Uganda

Abstract Improved fallows have been promoted in Uganda as alternative soil fertility management options to enhance sustainable land management. The major contribution of improved is through biological nitrogen fixation and high quality soil organic matter. An on-farm study was conducted in eastern Uganda to determine the mineral nitrogen contribution of improved fallow and the consequent increased in maize yield and economic benefits to the farmers. Improved fallow of Crotalaria grahamiana (Sunhemm) and Mucuna pruriens (Velvet bean) were studies because they have gained dominance amongst smallholder farmers in Uganda. The short-duration C. grahamiana and M. pruriens fallows were compared to farmers' practices of natural vegetation fallow, compost manure and continuous cropping. It was noted that C. grahamiana and M. pruriens fallow significantly (p<0.05) increased soil mineral N at Site 1 at end of fallowing, then a week and the fifth week after incorporating the biomass (p< 0.05). Maize yield significantly increased (p<0.05) following improved fallows subsequently positively responded to supplement doses of inorganic fertilizer at 60 kg N ha-1. However, high varied and opportunity costs of improved fallows reduced their profitability (p <0.001). Consequently, continuous cropping with application of inorganic fertilizer at a rate 60 Kg N ha-1 was cost effective with the marginal rate of return of 156% and 65% at Sites 1 and 2, respectively. Therefore, improved fallowing is only a viable soil fertility management option in low income subsistence farming systems.