Effect of Pigeon Pea (Cajanus Cajan) Biomass on Nitrogen Nutrition and Yield of Rainfed Rice Using Leaf Color Chart

The high cost and low use efficiency of mineral fertilizers are major constraints to rice production for smallholder farmers in Sub-Saharan Africa. This study evaluated the efficacy of Cajanus cajan biomass as an alternative nitrogen source for rainfed rice, using the Leaf Color Chart (LCC) as a real-time monitoring tool. A field experiment was conducted in Nkolbisson, Cameroon, during the 2025 cropping season using a randomized complete block design with four treatments and three replications: T0 (control, no fertilizer), T1 (200 kg ha⁻¹ NPK 20-10-10), T2 (200 kg ha⁻¹ NPK 20-10-10 + 17 t ha⁻¹ C. cajan biomass), and T3 (200 kg ha⁻¹ NPK 20-10-10 + 100 kg ha⁻¹ urea). LCC readings, yield, and nitrogen use efficiency (NUE) as Partial Factor Productivity (PFP) were assessed. Results showed that T2 maintained significantly higher (p < 0.001) LCC scores throughout the growth cycle, indicating superior and sustained nitrogen nutrition. This translated into a 26.8% grain yield advantage for T2 (5.06 t ha⁻¹) over T1 (3.99 t ha⁻¹). Although the Partial Factor Productivity of Nitrogen (PFPN) was highest for T1 (99.8 kg grain/kg N), the integrated T2 treatment achieved the highest absolute yield, demonstrating its effectiveness for maximizing productivity. The study demonstrates that the integrated use of C. cajan biomass, a key ISFM practice, provides a more stable nitrogen supply and significantly improves rainfed rice productivity, offering a sustainable and efficient alternative to sole mineral fertilization.