Batch Equilibrium Procedure Research Articles

Sorption of Bromacil, Chlortoluron, and Diuron by Soils

AbstractSorption of bromacil (5‐bromo‐3‐sec‐butyl‐6‐methyluracil), chlortoluron [3‐(3‐chloro‐4‐methylphenyl),1,1‐dimethylurea], and diuron [3‐(3,4‐dichlorophenyl)1,1‐dimethylurea] by soils containing contrasting organic carbon (OC) content was studied. The sorptive capacity of the soils was assessed at 4 and 25°C by the batch equilibrium procedure over a broad range of aqueous phase herbicide concentrations. The herbicides showed the following order of increasing tendency to be sorbed: diuron > chlortoluron > bromacil. Sorption constants (Kf) were from 50‐ to 120‐fold higher for the organic soil than for the loamy sand soil, reflecting sorption dependence on soil OC. This variation in Kf was reduced to less than twofold variation in Koc by normalizing sorption to OC. Although sorption was higher at 4 than at 25°C, the difference was only minor at this temperature range. The isosteric heats of sorption (δHs) were relatively small and exothermic, suggesting the involvement of entropy driven mechanism. Water solubility (S) and octanol‐water partition coefficient (Kow) of the herbicides were determined and used to derive equations for estimating Koc with r2 ≥0.989. The practical utility of these correlations is that they allow reasonable estimates of Koc from more easily determined molecular parameters.

SOLUBLE AND EXCHANGEABLE CATION RATIOS IN SOME SOILS OF ISRAEL1

SummarySodium‐absorption ratio–exchangeable sodium ratio relationship was tested on some Israeli profiles. Two approaches were used: firstly, a survey on existing relationship in about 250 soil samples representing twenty soil types, and secondly, a comparison of the exchange isotherms of five soil types obtained by a batch equilibrium procedure. The results of the survey extended over a small range of S.A.R., a fact which was an obstacle for making any conclusions. By the second approach it was found that the examined soil types showed a difference in their exchange properties. Determination of the exchange isotherms and calculation of the parameters for each soil separately gave a better insight into their exchange behaviour.