Effects of Acidity and Alkalinity on Urea Transformation in Soil

Changes of pH,volatilization of ammonia(NH_3) volatility,transformation of urea-N and activity of Al in 3 acidic and 3 alkali soils as induced by urea were studied.The results indicated that effects of acidity and alkalinity of soil on urea hydrolysis was related to the concentration of urea.At 25℃,the changes of pH in 3 acidic soils increased quickly,however,the changes of pH in 3 alkali soils increased at the beginning and then fell to some extent,but rose again after sometime,The dynamic experiment revealed that the increase of soil pH was short-lived,with a subsequently slow decline after reaching its maximum.Ammonia volatilization intensity,NH_4~+-N and NO_3~——N followed the changes of soil pH.The peak of NH_3 volatilization occurred between the 7~(th) and 9~(th) day of urea fertilizer addition in the 3 acidic soils,but on the 3~(rd) day in alkali soils,NH_4~+-N and NO_3~——N in the 6 soils increased to maximum after 2-4 weeks,and then decreased to a constant value.Soil exchangeable Al decreased sharply with the increasing concentrations of urea in the 3 acidic soils.and there was an obviously negative relationship between soil exchangeable Al and soil pH in a short-term period.Applying urea to acidic soils could obviously decrease the content of exchangeable Al in the acidic soils in the short-term.