Distribution and Leaching Losses of Applied Urea-N in Sandy Loam and Clay Loam Soils under Wetland and Upland Moisture Regimes

Laboratory studies were conducted in 100 cm long columns (10 cm ID) to study distribution and leaching of applied urea-N in a sandy loam and clay loam soils under upland and wetland moisture regimes. At 2 days after application, movement of N coincided with the wetting front in both the soils and under both the moistures regimes. Urea moved to deeper soil layers in the sandy loam soil as compared to in the clay loam soil. Due to rapid transformation of urea-N to NH4+ and NO3− forms, no urea-N was detected in the soil profile at day 7 or during later samplings. More downward displacement of NH4−-N and NO3−-N was observed in the coarse than in the fine textured soil. Under upland moisture regime, no leaching losses of N occurred beyond 90 cm depth in both the soils. Under wetland moisture regime, no leachate was collected beneath the clay loam soil columns, but leachates collected from the sandy loam soil column contained 12.0 and 26.6% of the applied N as NH4+-N and NO3−-N, respectively. Leaching losses were confined to first two weeks and major losses occurred during first 10 days after urea application. This study suggests that applied urea-N can be lost via leaching beyond 90 cm soil depth in coarse textured soils and under moisture regimes commonly observed under rice.