Effect of Slow-Release Fertilizers and Mahua Oil Cake on Yield of Chakhao Black Rice (Oryza sativa L.)

Abstract

Rice is a globally important staple crop, and nutrient-rich colored varieties like black rice are valued for their nutritional and medicinal benefits. A field experiment was conducted during the kharif season of 2025 at the Agricultural Farm of Himalayan University, Jollang, Itanagar, Arunachal Pradesh, to evaluate the effect of slow-release fertilizers and Mahua oil cake on the yield of Chakhao black rice (Oryza sativa L.). The experiment was laid out in a Randomised Block Design with three replications and eight treatments, comprising varying levels of neem coated urea (NCU) and rock phosphate (RP) along with an additional 25% nitrogen supplied through Mahua oil cake and above the recommended nitrogen dose. The results revealed significant differences among treatments for all yield parameters measured, including grain yield, straw yield, and harvest index. Treatment T4, receiving 50% recommended dose of nitrogen (RDN) through neem coated urea combined with an additional 25% RDN through Mahua oil cake, produced the highest grain yield (1.99 t ha⁻¹), straw yield (11.75 t ha⁻¹), and harvest index (14.48%), and was statistically superior to all other treatments at the 5% level of significance (CD = 0.36 for grain yield; CD = 0.711 for straw yield). The control treatment (T1) recorded the lowest values across all three parameters. The superior performance of T4 is likely attributable to improved nitrogen availability, reduced nutrient losses through the slow-release properties of neem coating, and enhanced soil nutrient dynamics from the organic nitrogen fraction supplied by Mahua oil cake, though these mechanisms were not directly measured in the present study. The study concludes that the combined application of neem coated urea at 50% RDN with an additional 25% RDN through Mahua oil cake may represent a promising integrated nutrient management strategy for Chakhao black rice under the agro-climatic conditions of Arunachal Pradesh, pending validation across multiple seasons and locations.