Studies on the leaching of urea in sodic soils

Abstract

SUMMARYLaboratory experiments were conducted in PVC columns to study the leaching and transformation of applied urea in sodic soils (Gharachon loam-Aquic Natrustalf and Domeli silty clay loam-Aquic Camborthid) reclaimed by gypsum application and kept submerged for 7 or 14 days after fertilizer application. The effect of different depths of irrigation water (5, 7·5, 10, 20 and 30 cm) on urea leaching was studied in a sandy loam sodic soil. In another experiment, the effect of time interval (0 or 4 days) between urea application and initiation of submergence with distilled water (for 7 or 14 days) was investigated involving two recently reclaimed sodic soils (Gharachon loam and Domeli silty clay loam). The results showed that the extent of urea leaching mainly depended upon soil texture. In Domeli silty clay loam, urea penetrated to 20 cm depth with peaks in concentration at 12·5 cm at both 7 and 14 days of submergence. In Gharachon loam urea-N moved to 25 cm depth after 7 days and to 35 cm after 14 days. In the sandy loam sodic soil peaks of urea-N concentration were observed at 12·5, 22·5 and 27·5 cm depths after infiltration of 5, 7·5 and 10 cm depth of water, respectively. Leaching with 20 and 30 cm depths of water moved urea deeper (below 50 and 70 cm, respectively). In recently reclaimed soils, leaching initiated immediately after fertilizer application displaced urea to slightly deeper layers compared with leaching initiated 4 days after urea application. Leaching may not be an important loss mechanism of urea-N in loam or silty clay loam sodic soils. However, in light-textured sandy loam sodic soils leaching beyond the root zone can be expected to create fertilizer management problems.