Urea deep placement for minimizing NH3 loss in an intensive rice cropping system

Abstract It is urgently necessary to reduce environmental harm while simultaneously ensuring food security from agriculture in China. Fertilizer deep placement, especially urea deep placement (UDP), has been widely recognized as an efficient way to increase rice yield with less N use in flooded rice fields; however, few studies have explored UDP as a way to abate N loss, particularly ammonia (NH 3 ) volatilization, in intensive rice cropping systems. Therefore, a field experiment was performed in the Taihu Region with five treatments (two surface split broadcasting treatments: a current traditional practice with 300 kg N ha −1 (CT) and a reduced N practice with 225 kg N ha −1 (RN), two one-time UDP treatments: a current traditional practice under UDP (CTDP) and a reduced N practice under UDP (RNDP), and a CK treatment with no urea). The NH 3 volatilization, grain yield and N use efficiency in terms of the N recovery efficiency (NRE) were investigated during the 2014–2016 rice growing seasons. Additionally, N diffusion and 15 N-labeled urea experiments were conducted to explore the N release pattern and the fate of 15 N under UDP. The results demonstrated that little NH 4 + -N could diffuse into surface water under UDP, thus, negligible floodwater NH 4 + -N was detected. The seasonally cumulative NH 3 volatilization of the UDP accounted for only 1% of the total applied N, which decreased by 91% compared to surface broadcasting treatments. As a result, the NH 3 intensity (NH 3 -N loss per crop yield) was reduced by 92% over surface broadcasting. Moreover, the deep placement of urea could supply a higher NH 4 + -N concentration in the soil during the early growth stage and prolong the duration of N availability for 2 months; as a result, UDP remarkably increased the N uptake by 28% compared with surface broadcasting treatments in the 3 years. The UDP treatments significantly increased the yield and NRE by 10% and 55% under favorable weather conditions (2015 and 2016 rice seasons), respectively. The RNDP treatment obtained the lowest N surplus (36 kg N ha −1 ), and the plant 15 N uptake was 62% higher and the 15 N loss was 38% lower with RNDP than surface broadcasting. Therefore, the deep placement of urea can be considered a slow release fertilizer, which better matches the N demand of rice plants and effectively minimizes N losses, especially NH 3 volatilization. The RNDP treatment, with a 25% reduction in the N dose, can represent an effective and promising strategy to achieve environmental integrity and food security in intensive rice cropping systems.