The effects of soil properties and applied water on the leaching of atrazine, simazine, diuron and DCPA in soil columns

Today, there is an increasing demand for information regarding the disappearance of herbicides from soils. Such information is important from at least two standpoints. First, it is essential that a soil applied herbicide remain in an active state long enough to do the job for which it was intended. Second, its phytotoxicity should become dissipated rapidly enough so that sensitive crops which follow will not be injured. Not only is it possible for frequently applied herbicides to build up to toxic levels even for tolerant crop plants, but often residues from spring-applied herbicides remain in the soil to affect sensitive fall seeded plants. Little is known at the present time about what happens to herbicides under a variety of edaphic and climatic conditions. Even when herbicides are applied directly to plants, a substantial amount eventually reaches the soil. The problem of persistence of herbicides in soils is one which faces both farmers and research workers. Disappearance of herbicides from soils is a complex process which is affected by several interacting variables. These variables include type and rate of application of the herbicide, physical and chemical soil properties, amount of leaching by rainfall, microbiological activity, chemical decomposition, volatilization, photo-decomposition, and plant uptake. The persistence of a herbicide in a given situation is governed by the prevailing combination of these variables. This study deals with leaching which is one of the most important factors affecting disappearance of herbicides from soils. In humid agricultural regions particularly, leaching is a major factor influencing the success or failure of preemergence herbicides. The purpose of this study was to determine the effects of three rates of applied water on movement of four herbicides in columns of four soils.