Nitrogen Use Efficiency, 15N Balance, and Nitrogen Losses in Flooded Rice in an Inceptisol

Abstract

The low efficiency of fertilizer nitrogen (N) in flooded rice is mainly attributed to the losses of nitrogen taking place from rice field through ammonia volatilization, denitrification, leaching, and runoff. A field experiment was conducted during the wet season of 1994 and 1995 on a sandy loam soil (Typic Ustochrept). Objective was to study nitrogen use efficiency and 15N balance in rice (CV Pusa Basmati-1) and nitrogen losses in flooded rice fields through ammonia volatilization, denitrification, and leaching as influenced by sources and levels of N. Rice was grown with three sources of nitrogen, i.e., urea, urea+coated calcium carbide (CCC), and urea+farmyard manure (FYM) each at three levels, i.e., 60, 120, and 180 kg N ha−1. The results revealed that 50% of urea N could be supplemented through FYM for higher N use efficiency. The variety Pusa Basmati‐1 responded only up to 120 kg N ha−1. Application of N, half as urea and half as FYM, resulted in the highest fertilizer N recovery by the crop (30.6%), the highest retention of fertilizer N in soil (39.1%), and the minimum unaccounted‐for fertilizer N (30.3%). Application of coated calcium carbide along with urea significantly improved the fertilizer N recovery by the crop (24.4%) and reduced the unaccounted for fertilizer‐N (47.6%) over that of sole application of urea. The direct measurements of nitrogen losses were less than the unaccounted‐for fertilizer N. Ammonia volatilization was the major pathway of N loss from the rice field. Application of coated calcium carbide along with urea reduced denitrification and leaching loss of N but enhanced the volatilization loss of ammonia over the sole urea application.