Diffusion of Herbicides in the Adsorbed Phase
1974
Scott, H. D. | Phillips, R. E. | Paetzold, R. F.
Equations were presented which describe the diffusion of the soil-adsorbed herbicide phase. Assuming (i) no precipitation and volatilization, (ii) a linear adsorption isotherm, and (iii) no net change in herbicide concentration in the adsorbed phase, the data needed to make such a calculation can be determined experimentally and are as follows: soil bulk density, distribution coefficient, apparent self-diffusion coefficient of the herbicide in soil, self-diffusion coefficient of the herbicide in water and the transmission factor. The results indicated that the magnitude of the diffusion coefficient of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H) one] in Dubbs soil depends primarily upon the amount in the adsorbed phase and on the moisture content. The magnitude of the adsorbed phase diffusion coefficients of ¹⁴C-metribuzin was less than the apparent self-diffusion coefficients and decreased with decreasing soil water content. Since negative adsorbed phase diffiusion coefficients were observed at the lower soil water contents, the data suggested that the amount of metribuzin in the adsorbed phase increased as soil water content decreased.
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