Urea Hydrolysis and Transformation in Some Illinois Soils
1963
Simpson, D. M. H. | Melsted, S. W.
Samples of several representative Illinois soils, ranging in pH from 4.9 to 7.2, were incubated under different conditions of temperature (1° and 25°C.), soil moisture content (24 and 60%), and urea concentration (200 and 400 ppm. N). The samples were analyzed for residual urea and NH₄⁺ formed after time intervals ranging from 1 day to 4 weeks. Urea hydrolysis occurred at a nearly constant rate for an individual soil under given conditions. Hydrolysis rates varied widely among the different soils and environmental conditions studied, ranging from a minimum of about 6 ppm. N per day to a maximum of about 225 ppm. N per day. Urea hydrolysis rates were from 2 to 6 times greater at 25°C. than at 1°C., depending upon the particular soil involved. An increase in pH resulted in an increase in the hydrolysis rate. Different soil moisture contents and urea concentrations caused little change in the urea hydrolysis rates for individual soils. Nitrification of 400 ppm. urea-N was followed over a period of 8 weeks for several soils. No measurable nitrification occurred in any of the soils at 1°C. The amount of nitrates formed at 25°C. varied from a minimum of 102 ppm. N in a Herrick silt loam, pH 4.9, to a maximum of over 400 ppm. in a Muscatine silt loam, pH 6.3.
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