Effect of Integrated Pigeon Pea (Cajanus cajan) Biomass and Mineral Fertilizer on Upland Rice Yield, Soil Health, and Economic Profitability in Acidic Soils of Central Africa

Background: The rapid degradation of tropical Ferralsols in Central Africa threatens sustainable rice production. While mineral fertilisers are widely used, they often exacerbate soil acidity and fail to build soil organic matter. Aim: This study evaluated the synergistic effects of integrated pigeon pea (Cajanus cajan) biomass and mineral fertilizers on upland rice performance, soil health, and economic profitability. Methods: A randomized complete block design with four treatments was implemented: T0 (control), T1 (17 t ha⁻¹ pigeon pea biomass), T2 (200 kg ha⁻¹ NPK 20-10-10 + 17 t ha⁻¹ pigeon pea biomass), and T3 (200 kg ha⁻¹ NPK 20-10-10 +100 kg ha⁻¹ urea). Growth parameters, yield components, soil properties, and economic indicators were measured. Results: T2 significantly (p < 0.05) increased grain yield (4.7 t ha⁻¹) by 85% compared to T0 and 82% compared to T1. The integrated treatment maintained higher soil organic matter (-1.90% vs -3.14% for T3), increased available phosphorus (+4.55 ppm), and enhanced exchangeable potassium (+0.13 cmol(+)/kg). Principal component analysis revealed strong correlations between soil fertility parameters and rice yield (r = 0.75-0.82). Economic analysis showed T2 had the highest benefit-cost ratio (2.44) despite higher initial costs. Conclusion: The integration of pigeon pea biomass with mineral fertilisers creates synergistic effects that enhance rice productivity, improve soil health, and increase economic returns, representing a sustainable intensification strategy for acidic tropical soils.