Temperature-dependent degradation

Degradation in soils is the result of a combination of chemical and, predominantly, biological events (Bollag and Liu, 1990, Wu and Nofziger, 1999). A first-order degradation model is used to simulate the variation of residual mass of a chemical compound in a soil system after its application (Dykaar and Kitanidis, 1996; Walker, 1974). The first-order rate constant or half-life in the degradation model is dependent on soil temperature and the dependence can be approximated by the Arrhenius equation (Rocha and Walker, 1995; Walker, 1974; Walker and Barnes, 1981). Soil temperature under field conditions varies with time and depth. Here it is predicted with a sinusoidal model (Carslaw and Jaeger, 1959; Fluker, 1958; Hillel, 1982; Kirkham and Powers, 1972; Penrod et al., 1960). This program calculates the concentration of chemical as a function of time for a user-defined degradation rate, temperature conditions, and initial concentration. Results are shown for the temperature dependent rate as well as for a constant rate at the reference temperature and a constant rate at a temperature equal to the average of the maximum and minimum annual temperatures.

Send email to david.nofziger@okstate.edu

Last Modified: January 16, 2008.