Integrated Use of Pigeon Pea Residues and Mineral Fertilizers Enhances Rainfed Rice Productivity and Soil Health in a Humid Forest Zone

Abstract Sustainable intensification of rainfed rice systems in sub-Saharan Africa is constrained by low soil fertility and limited access to mineral fertilizers. Integrated nutrient management that combines organic and mineral sources offers a promising pathway to enhance productivity and soil health. A field experiment was conducted in Nkolbisson, Cameroon, to evaluate the effects of pigeon pea (Cajanus cajan L.) biomass and mineral fertilizers on the growth, yield, and soil properties of rainfed rice (variety NERICA 8). The experiment employed a randomized complete block design with four treatments: control (T0), NPK only (T1, 200 kg ha-¹), NPK + pigeon pea biomass (T2, 200 kg ha-¹ NPK + 17 t ha-¹ biomass), and NPK + urea (T3, 200 kg ha-¹ NPK + 100 kg ha-¹ urea). Results showed that T2 significantly (p<0.05p<0.05) improved plant height, tiller number, and leaf nitrogen status compared to other treatments. Grain yield under T2 reached 5.06 t ha-¹, a 40.5% increase over NPK alone (3.99 t ha-¹) and 28.5% higher than NPK + urea (4.39 t ha-¹). The integrated treatment also enhanced key yield components: panicle density (85 m-²), grains per panicle (58.4), and 1000-grain weight (27.0 g). Post-harvest soil analysis indicated that T2 significantly increased available phosphorus (+29.8%) and exchangeable potassium (+37.1%), while maintaining a more favorable C/N ratio (9:1) than mineral-only treatments. Economic analysis revealed the highest gross value added under T2 (1,310,500 FCFA ha-¹), despite higher initial costs. We conclude that integrating pigeon pea residues with reduced-dose NPK fertilizer is an agronomically effective and economically viable strategy for enhancing rainfed rice productivity and soil fertility in humid tropical Africa. This practice supports sustainable intensification by improving nutrient use efficiency, building soil organic matter, and reducing dependency on external mineral inputs.