SOME FACTORS AFFECTING UREA HYDROLYSISRATES IN SOILS

With incubation experiments, 2 manural loessial soil were used to study the effects of temperature, moisture, soil pretreatment, glucose and urease on the rate of urea hydrolysis in soil; 1 dark loessial soil, 1 loessial soil ,2 manural loessial soil and 1 yellow cinnamon soil were used to study the effects of original urea concentration on the rate of urea hydrolysis; and 2 manural loessial soil, 1 dark loessial soil, 1 loessial and 1 yellow cinnamon soil were used to study the effects of soil properties on the rate of urea hydrolyses. The results showed that the temperature ranged from 5 to 35 has obvious effect on urea hydroysis rate and the average temperature coefficient (Q10) is 1.73, the time in hour reguired to hydrolyse half the applied urea-N decrease with the raising of temperature. Althorgh the urea hydrolysis rates are stable at 20%30% of soil water content, the hydrolysis rates decrease apparently at the 15%, and rapidly decline after air-drying soil. Adding glucose and urease respectively, the urea hydrolysis rate increase pointedly, but the former treatment lasts longer period and the latter one quickly drops to previous level. Highly significant correlation is found between the urea hydrolysis rate and the organic carbon (correlation coefficient r is 0.93*) and original urea concentration (r 0.95* *).