MEASUREMENT AND PREDICTION OF ISOPROTURON MOVEMENT AND PERSISTENCE IN 3 SOILS

The degradation of isoproturon in three soils at different moistures was measured in the laboratory at a range of temperatures. Measurement of herbicide desorption from the soil at intervals during the laboratory incubation demonstrated an apparent increase in the strength of adsorption with time. Appropriate constants derived from the laboratory data were used with records of air temperature, rainfall and evaporation in a computer model to predict the vertical distributions of isoproturon in three field experiments. One experiment was conducted in 1986 on a sandy clay loam and two in 1987, one on a similar soil and the second on a clay soil. When compared with measured residues in 1986, the model gave good predictions of the pattern and extent of distribution down the profile but amounts of isoproturon in the individual layers were overestimated. Movement down the profile in 1987 was less accurately predicted at either site than at the single site in 1986. Further refinements are required before such a system could be used to give reliable advice on the need to re-treat fields in which weed control from earlier applications of isoproturon appeared to be poor or slow. © 1990.