EFFECTS OF AGRONOMIC AND GEOLOGIC FACTORS ON PESTICIDE MOVEMENT IN SOIL: COMPARISON OF TWO GROUND WATER BASINS IN CALIFORNIA

This paper describes the preliminary results of a study conducted by the California Department of Food and Agriculture which compares the soil dis-tribution of herbicides in two ground water basins in the state. In a pre-vious study, residues of several agricultural chemicals were detected in numerous wells in two inland ground water basins, while only one contaminated well was found in two coastal basins. The present study was designed to provide further information on the effects of cultural practices, climatic conditions, and soil and geologic factors in each basin on pesticide mobility. Soil cores were collected in two citrus-growing regions, one in the San Joaquin Valley, and one on the south coast. Information on agricultural practices and climatic conditions for four years (1981-1984) was obtained from growers and other sources. In order to maximize detection of pesticides in deeper soil layers, sites for soil coring were chosen at locations where the same procedures for application of herbicides had been practiced annuall