Deep placement of nitrogen fertilizers reduces ammonia volatilization and increases nitrogen utilization efficiency in no-tillage paddy fields in central China

Deep placement of nitrogen fertilizer affects the fate of fertilizer nitrogen through influencing nitrogen transformation. Few studies have examined ammonia (NH3) volatilization and nitrogen-utilization efficiency under deep placement of nitrogen fertilizers in no-tillage (NT) paddy fields. Therefore, a field experiment was conducted to investigate the different application methods of nitrogen fertilizers [no fertilizer, traditional nitrogen broadcasting (S), and point deep placed at 5 cm, 10 cm and 20 cm depths as basal fertilizer + nitrogen broadcasting as topdressing (e.g., 5D, 10D and 20D)] on NH3 volatilization, nitrogen recovery efficiency (NRE), nitrogen partial factor productivity (NPFP), nitrogen agronomic efficiency (NAE), and grain yield in NT paddy fields during the 2012-2013 rice growing seasons in central China. Nitrogen deep placement significantly decreased mean floodwater pH by 2-4% and mean floodwater NH4+-N concentration by 29-98% compared with nitrogen broadcasting. Nitrogen deep placement treatments significantly decreased cumulative NH3 volatilization by 20-45% in 2012 and by 15-40% in 2013 compared with S treatment. On average, nitrogen deep placement treatments significantly increased NRE by 26-93%, NPFP by 10-16%, NAE by 31-51%, and grain yield by 5-11% in both seasons compared with S treatment. In addition, 10D treatment showed the highest nitrogen utilization efficiency and grain yield, implying that this measure can be effective in increasing agricultural economic viability and decreasing NH3 volatilization. However, given high labor requirement for manual deep placement, developing mechanical fertilization technology is necessary to overcome this difficulty in future.