Salt effects on urea hydrolysis and nitrification during leaching through laboratory soil columns

Summary

We studied the transport and transformation of urea under steady-state conditions in two soils and at three water salinities (1.0, 5.0, and 10.0 dS/m) using laboratory soil columns. A mathematical model that considers diffusion, convection, adsorption and first-order kinetic transformation of nitrogen was used to describe measured effluent concentration of the two nitrogen species. Increasing salt levels in the applied water decreased the hydrolysis of urea in the two soils studied with first-order rate coefficients decreasing from 0.015 to 0.009 h⁻¹ in the fine sandy loam, and from 0.075 to 0.015 h⁻¹ in a silty loam. Similarly, the nitrification rate decreased by 50% and 70% in the two soils as salinity increased. The rate coefficients measured in the leaching studies were much smaller than measured in incubation-type experiments. Calculated half-lives for urea and NH ⁺₄ provided a method interpreting the kinetic rate coefficients as a function of the experimental conditions.