Temperature Effects on Urea Diffusion Coefficients and Urea Movement in Soil
- A. M. Sadeghi ,
- D. E. Kissel and
- M. L. Cabrera
Urea fertilizer is often applied at the soil surface, where it hydrolyzes and can form NH3. To quantify the volatilization of NH3, the molecular diffusion of urea into the soil must be described. The diffusion coefficient of urea in soil is related to its diffusion coefficient in water, which varies with temperature. We initially regressed the value of the urea diffusion coefficient in water from the international critical tables (ICT) on temperature for the range of 10 to 20 °C. Since surface soil temperatures often fall outside this range, additional values for the urea diffusion coefficients were needed. The capillary tube method of Phillips and Ellis was used to measure the diffusion coefficient of urea in water at temperatures ranging from 0 to 50 °C. The laboratory values obtained for the diffusion coefficient of urea in water were higher, by a factor of 1.5, than the ICT values. A comparison was made between measured values of urea concentration in columns of Richfield and Haynie soils and simulated values using regression equations based on laboratory results (new) and ICT data (old). The new regression equation allowed a better agreement between actual and simulated urea concentrations in soil.
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