Effect of neem-coated urea and application methods on nitrogen uptake and use efficiency of rice (Oryza sativa) in the coastal rainfed lowlands

Abstract

An experiment was conducted during 2014 and 2015 at Canning Town, West Bengal, to study the influence of neem-coated urea and its application methods on nitrogen uptake and use-efficiency of Amal-Mana rice (Oryza sativa L.).The experiment was laid out in in randomized block design, consisting of 10 treatments, viz., T1, application of 50% N as prilled urea at transplanting and rest N as 6 foliar sprays from active tillering to flowering; T2, 50% N as neem-coated urea at transplanting and rest N as 6 foliar sprays from active tillering to flowering; T3, 50% N as prilled urea 1 week after transplanting (WAT) and rest N as 6 foliar sprays from active tillering to flowering; T4, 50% N as neem-coated urea 1 WAT and rest N as 6 foliar sprays from active tillering to flowering; T5, 50% N as prilled urea at transplanting, 25% N as prilled urea at active tillering and rest N as 3 foliar sprays from panicle initiation (PI) to flowering; T6, 50% N as neem-coated urea at transplanting, 25% N as prilled urea at active tillering and rest N as 3 foliar sprays from PI to flowering; T7, 50% N as prilled urea 1 WAT, 25% N as prilled urea at active tillering and rest N as 3 foliar sprays from PI to flowering; T8, 50% N as neem-coated urea 1 WAT, 25% N as prilled urea at active tillering and rest N as 3 foliar sprays from PI to flowering; T9, 50% N at transplanting, 25% N at active tillering and rest N at PI all as prilled urea; T10, 50% N as neem-coated urea 1 WAT, 25% N as prilled urea at active tillering and rest N as soil application at booting stage. Rice variety Amal-Mana with a common fertilizer dose of 75, 20 and 10 kg N, P2O5 K2O/ha was used. Use of neem-coated urea with 50% applied 1 WAT, and 25% each at active tillering and flowering, resulted in 40 more grains/panicle than current practice (T9). Nitrogen supplied through neem-coated urea resulted in higher (0.6 and 0.7) normalized difference vegetation index, net photosynthesis (>15 mmol/m2/s), and nitrate reductase activity than current N-management practices. Internal efficiency (IEN, 7682 kg grain/kg N uptake) and partial factor productivity (PFPN, 7287 kg grain/kg N applied) of N increased significantly with improved management strategy. Grain yield increased from 3.4 t/ha (existing recommendations) to 4.6 t/ha using 50% N as neem-coated urea 1 WAT, with similar results when the remaining N was applied to the soil or through foliar application