A Simulation Model for Prediction of Herbicide Persistence

Abstract

AbstractA simulation model for prediction of herbicide persistence in the field is described. The model combines the effects of soil temperature and soil moisture content on the rates of herbicide loss, determined experimentally under controlled conditions, with the fluctuations in surface soil temperature and moisture content in the field. The computer program includes methods of simulating surface soil temperatures and moisture contents from standard meteorological data. In order to test the model, the degradation of napropamide (2‐(a‐naphthoxy)‐N,N‐diethylpropionamide) was examined. Under controlled conditions, loss of activity followed first‐order kinetics with half‐lives of 54, 63, and 90 days at 28C with soil moisture contents of 10.0, 7.5, and 3.5%, respectively. At 14C, half‐lives at 10.0 and 7.5% soil moisture were 102 and 112 days, respectively. When these data were used in the simulation model in conjunction with the relevant meteorological information, the patterns of loss of napropamide incorporated 2 to 3 cm in the field could be predicted. Napropamide was lost rapidly when applied to the soil surface, and since the model only takes into account losses through microbial or chemical metabolism, this could not be simulated. Some of the limitations and the potential benefit of the simulation technique for prediction of pesticide persistence are discussed.