Relative efficiency of prilled urea coated with major neem (Azadirachta indica A. Juss) oil components in lowland irrigated rice of the Indo-Gangetic plains

The fertilizer nitrogen use efficiency (NUE) in lowland rice is quite low (20-50%) in India. Coating of nitrification inhibitors, such as neem cake or neem oil, onto prilled urea may improve NUE. Hence, a field experiment was conducted at the Indian Agricultural Research Institute, New Delhi, during the wet seasons of 2005 and 2006 to study the effect of prilled urea coated with varying doses of major neem oil components on grain yield and NUE of scented rice. Sixteen treatments comprised of combinations of five major neem oil components (free fatty acid, pure oil, meliacins, saturated and unsaturated fractions)-coated prilled urea with three doses (500, 1000 and 5000 mg kg(-1)). An additional treatment of prilled urea alone (untreated urea) was also taken. The experiment was laid out in a randomized block design with three replications. Results suggest that the coating of prilled urea with meliacins proved the most effective in enhancing yield and NUE of rice as compared to uncoated prilled urea or coated with other neem oil components. Across all the neem oil components, a coating thickness of 500 mg kg(-1) onto prilled urea was sufficient to realize the higher yield and NUE of lowland irrigated rice.