Nitrogen Release Characteristics of Controlled Release N Fertilizers and their Effect on Yield and N Nutrition of Rice in Alluvial and Laterite Soils

Cumulative N release from four grades of controlled release N (CRN) fertilizer was studied in a laboratory incubation experiment using alluvial and laterite soils both at 60% water holding capacity (WHC) and waterlogged condition maintained at 30°C. The functional relationship between cumulative release of N from CRN fertilizers and the time of their incubation in soil at varying water regimes was quadratic in nature. A linear relationship was also established between these two variables by their natural log transformation. From these established relationships, the patterns of N release from CRN fertilizers were predicted to synchronize N supply from the polymer coated urea (PCU) fertilizers with the N demand patterns of rice varieties. The controlled release fertilizer CRN-6C exhibited smaller initial N release but subsequent faster release than CRN-2D. The cumulative N release gradually increased with time of soil-fertilizer interaction and reached 80% of total N content after 41–78, 29–52, 44–81 and 29–50 days of incubation in CRN-lC, CRN-3C, CRN-6C and CRN-2D, respectively, depending upon the type of soil and moisture regimes. In a green house experiment on alluvial and laterite soils, basal application of CRN fertilizers like CRN-IC and CRN-3C along with prilled urea (PU) at 3: 1 ratio was as efficient as conventional split application of PU in terms of grain yield and N uptake pattern of rice (cv. IR 36). In on-farm trials on improvement of N use efficiency in direct sown rice (cv. Durga) grown on alluvial soil under unfavourable rainfed lowland conditions of Cuttack district of Orissa, basal furrow placement of CRN-6C +PU at 3: 1 proportion registered 25% higher grain yield and larger N use efficiency (25 kg grain kg⁻¹ N added) than the conventional practice of basal broadcasting of PU (14 kg grain kg⁻¹ N added).