Simultaneous Movement of Water and Herbicides in Unsaturated Soils

Since weed killers were developed in the early part of the decade beginning in 1940, herbicides have been increasing in use until they are now widely used to control weeds . The application of herbicides has thus become a regular agricultural and ecological practice. Some of the herbicides are applied directly to soils and accompanied by a light irrigation to wash them into the soil in order to increase their efficiency . Some of these chemicals accumulate in the soil and should be removed in order to avoid toxic effect on succeeding plants (Klingman, 1961) . The toxic effect of herbicidal residues in soil and water to human subjects , livestock , and wildlife has been repor•ted (Paynter et al., 1960; Carpenter et al., 1961). When these materials are leached out of the soil , they may pollute the water supply. The movement of water and herbicides in soils is thus closely connected to both their herbicidal and toxic effect and is becoming a serious economic problem. It is the purpose of this investigation to study the simultaneous movement of water and herbicides in unsaturated soils by using the thermodynamic theory of irreversible processes. The adsorption of herbicides, the energy of adsorption, and the break-through curve will also be studied