Distribution and Transformation of Band-Applied Urea in Soil Following Incubation Under Isothermal and Temperature Gradient Conditions

Urea was added as a band in the middle of 12-cm-long columns of Wellwood clay loam (pH 6.6) and the soil was incubated at constant uniform temperatures of 10, 15 and 20 C. A similar set of the soil samples was incubated in columns which had a temperature of 23 C at one end and 8.5 C at the other end. At uniform temperatures the rate of disappearance of ammonium and the formation of nitrate from the banded urea was found to increase with increasing temperature. Nitrite was found to accumulate during the incubation period but disappeared with the prolonged incubation at 15 and 20 C. At 10 C incubation, the maximum nitrite accumulation occurred at 12 wk, the longest incubation time used. Various ionic species, NH4 + , NO 2 − and NO 3 − were found to be nearly symmetrically distributed from the point of placement. When the soil was incubated under a temperature gradient, NO 3 − and to a lesser degree NH 4 + accumulated near the end of the column.