Nitrogen management in transplanted rice (Oryza sativa) in mid hill acidic soils of Sikkim Himalayas.

Two field experiments were conducted at Tadong in Sikkim in the humid mid-hill acidic soils during rainy (kharif) season of 2004, 2005 and 2006 to optimize the rate, source and schedule of nitrogen management for increasing the yield and nitrogen-use efficiency of transplanted rice (Oryza sativa L.) under 9 schedules, 4 rates (0, 80, 120 and 160), 3 nitrogen sources (urea, farm yard manure and neem cake-coated urea) in comparison with farmers’ practices. N application @ 80 kg/ha as 1/4 N 10 days after transplanting (DAT) + 1/4 N at maximum tillering (MT) + ½ at panicale initiation (PI) recorded the highest yield (5.44 t/ha), recovery efficiency (82%) and agronomic efficiency (47.9 kg grain/kg N applied). The grain yield increased with increase in the N rate from 80 to 160 kg/ha. Conjunctive application of FYM and urea increased the N uptake by 11.1 to 26.2%, recovery efficiency (11.1 to 46.7%) and agronomic efficiency (5.4 to 14.8%). Basal application of FYM @ 2.5 t/ha and top-dressing 80 kg N/ha through urea as 1/4 N at 10 DAT + 1/4 N at MT+ ½ at PI stage recorded the highest recovery efficiency (66.3%) and agronomic efficiency (38.7 kg grain/kg N applied). At 120 kg N/ha neem cake increased the recovery efficiency by 12.1 and 37.6% and agronomic efficiency by 9.9 and 15.8% over N120 with and without FYM. Farmers’ practice of application of FYM basal @ 5 t/ha and FYM @ 2.5 t/ha along with top-dressing of DAP @ 40 kg/ha at PI gave low yield and N-use efficiency.