Effect of Water Depth and Initial Soil Water Content on the Volatilization Losses of Ammonia

A laboratory study was conducted to investigate the effects of flood water depth and initial soil water content on ammonia volatilization losses from applied urea. The ammoniacal N concentration decreased with the increase in flood water depth. It reached a maximum of 10.6g N m⁻³ in Hisar soil (Typic Camborthid) and 8.3 gN m⁻³ in Kaul soil (Typic Ustochrept) in 1 cm floodwater five days after urea application, whereas, the maximum values in the 10 cm floodwater were 5.4 and 4.1 g N m⁻³ in Hisar and Kaul soils, respectively. Floodwater pH increased over initial soil pH values due to submergence and attained a maximum value five days after fertilization. The ammonia volatilization losses decreased significantly with the increase in floodwater depth in both the soils and this was attributed to NH_4⁺-N concentration of the floodwater. The losses were higher and ranged from 21.8 to 24.6 per cent at 1 cm floodwater depth as compared with 15.6 to 16.7 per cent at 10 cm floodwater depth. The soils maintained at −0.5 MPa water potential showed higher ammonia losses as compared with the soils maintained at −0.03 or -0.1 MPa water potential. The minimum losses were observed at −0.0 MPa water potential in both the soils. Ammonia losses from applied urea decreased by 10 to 13 per cent when soil water potential decreased from -0.5 to -1.5 MPa. The losses from applied urea were higher from Hisar soil as compared to Kaul soil, irrespective of floodwater depth and initial soil water potential.