Effect of soil type, exchangeable sodium percentage, water content, and organic amendments on urea hydrolysis in some tropical Indian soils

Urea has emerged as one of the most extensively used sources of nitrogen fertiliser in recent years because of its low cost per unit nitrogen. Urea hydrolysis in soils is an enzymatic decomposition process by the enzyme urease. The effects of soil type, exchangeable sodium percentage, moisture regime, and organic manures and their levels on the kinetics of urea hydrolysis were studied in a series of laboratory incubation experiments at 25 +/- 1degreesC. Urea transformation followed first-order kinetics, and the first-order rate constants for soils varied from 0.0321 to 0.1182/h. The rate of urea hydrolysis in the different soils increased with greater clay content and followed the order: Gulkani clay loam > Dadupur loam > Hisar sandy loam > Jakhol silty clay loam > Bawal loamy sand > Balsamand sand. Increasing the exchangeable sodium percentage in soils decreased the rate of urea hydrolysis both at field capacity and flooded conditions (2 cm standing water). Application of vermicompost, sheep manure, poultry manure, pig manure, and urban waste to soil at the 1% level increased the rate of hydrolysis over the untreated soil.