Effect of Compost and NPK Fertiliser on Soil Fertility and Cowpea Yield in Katsina State, North West Nigeria

This study evaluates the effects of compost, NPK fertiliser, and their combination on soil fertility parameters and cowpea grain yield in Katsina State, located in Nigeria's North West geopolitical zone. Cowpea is a critical food security crop in the semi-arid North West zone, and integrated soil fertility management combining organic and inorganic inputs has been advocated as an effective and affordable approach for sustaining productivity in resource-poor smallholder systems. A field experiment was conducted in a randomised complete block design with five treatments: no input control, compost alone at 5 tonnes per hectare, NPK fertiliser at recommended rate, compost at 2.5 tonnes combined with half-rate NPK, and compost at 2.5 tonnes combined with full-rate NPK. Soil samples were collected before planting and after harvest and analysed for pH, organic carbon, nitrogen, available phosphorus, and exchangeable cations. Cowpea grain yield was determined at maturity. Findings revealed that the combined compost plus half-rate NPK treatment produced cowpea grain yield not significantly different from full-rate NPK alone, while significantly improving post-harvest organic carbon and nitrogen levels compared to NPK-only plots. The combined treatment also reduced soil acidity relative to NPK-only treatment. The study demonstrates that integration of compost with reduced NPK can maintain crop yields while improving soil fertility at lower input cost, and recommends this integrated approach as the preferred nutrient management strategy for smallholder cowpea producers in Katsina State. Keywords: compost, NPK fertiliser, cowpea yield, soil fertility, Katsina State.