Effect of nitrogen-15 labelled urea application alone and in combination with farmyard manure or green manure on yield of and nitrogen use efficiency by rice

A field experiment was conducted to study the nitrogen (N) use efficiency in lowland rice (Pusa-834). Nitrogen was applied at three levels, viz. 0, 90 and 120 kg ha⁻¹ through N-15 labelled urea alone or in combination with green manure (GM) or farmyard manure (FYM) in two ratios (2:1 and 1:1). Urea applied alone or its combined application with organics resulted in a similar grain yield. However, substitution of N up to 50% either through GM or FYM resulted in reduction of straw yield as compared to urea alone. There was hardly any accumulation of NO₃-N in soil, though NH₄-N content remained sufficiently high up to 55 days after transplanting (DAT). Application of urea along with FYM or GM significantly improved its use efficiency (8–15%) over that of urea alone.