Different nitrogen rates and methods of application for dry season rice cultivation with alternate wetting and drying irrigation: Fate of nitrogen and grain yield

Improvement of nitrogen use efficiency (NUE) is a challenging task because of its several losses through ammonia volatilization, surface runoff, leaching and nitrification-denitrification. Fertilizer deep placement (FDP) has been proven effective in increasing grain yields and NUE under continuous standing water (CSW) condition. However, the impacts of FDP have not been investigated under alternate wetting and drying (AWD) irrigation. Field experiments were conducted in the dry seasons during 2014-2016 to determine the interaction effect of fertilizer x water regime on N losses as floodwater ammonium and ammonia volatilization, grain yields and NUE. Broadcast prilled urea (PU), deep placement of urea briquettes (UB) and nitrogen-phosphorus-potassium fertilizer briquettes (hereafter NPK) at varied N rates and zero N were tested under AWD and CSW conditions. The deep placement of UB and NPK, irrespective of N rates and water regimes, reduced floodwater ammonium and ammonia volatilization significantly compared to broadcast PU. Deep placement of either UB-N78 or NPK-N104 increased grain yields under both AWD (21-26%) and CSW (13-20%) conditions compared to broadcast PUN104. The magnitude of increase was larger under AWD, because AWD significantly reduced grain yields (8%) compared to CSW at PU-N104. However, yields of deep-placed UB were similar between AWD and CSW. Deep placement of UB and NPK increased N recovery up to 57-66% from 36% of PUN104. These results suggest that UBN78 and NPK-N104 can be utilized under AWD not only for increased grain yield and NUE but also to reduce additional pumping cost for irrigation water. Moreover, combined approach of AWD and FDP might be a good option for improving water and fertilizer use efficiencies in rice cultivation. (C) 2017 Elsevier B.V. All rights reserved.