Effect of Compost Application on Soil Carbon and Cowpea Yield in Gombe State

Soil carbon depletion in the seasonally dry farming systems of North East Nigeria reduces soil water-holding capacity and nutrient cycling efficiency, and compost application offers an affordable and locally available carbon restoration strategy. This study examined the effect of three compost application rates (0, 3, and 6 tonnes per hectare) on soil organic carbon content and cowpea grain yield in Akko Local Government Area, Gombe State, North East Nigeria. A field experiment was conducted during the 2023 rainy season at a farmers' demonstration plot using a randomised complete block design with three replications. IT90K-277-2 cowpea variety was used. Soil samples collected before and after the season were analysed for organic carbon, pH, and available phosphorus. Cowpea yield parameters including pods per plant, grain weight, and grain yield were measured at harvest. Results showed that compost application at 6 t ha-1 increased soil organic carbon content from 0.83 percent to 1.21 percent over the cropping season, a 45.8 percent increase. Grain yield at 6 t ha-1 compost was 1.67 tonnes per hectare, significantly higher than the control (0.98 t ha-1) and the 3 t ha-1 rate (1.34 t ha-1). Soil pH and available phosphorus also improved with compost application. The study concludes that compost application at 3 to 6 t ha-1 is beneficial for both soil carbon status and cowpea productivity in Gombe State and recommends its integration into the state organic resource management extension programme.

Keywords: compost application, soil organic carbon, cowpea, Gombe State, soil fertility