PICLORAM GROUNDWATER CONTAMINATION FROM PASTURE USE

The adsorption of picloram was studied in 28 pasture soils under labor atory conditions. The adsorptive capacities of these soils were expres sed in terms of the empirical constants, K and 1/n of the Freundlich e quation. The calculated K values ranged from 0.269 to 1.842 for Espino sa sandy loam and Bajura clay, respectively. The 1/n values ranged fro m 0.27 to 1.68 for Carrizales sandy loam and Mabi clay, respectively. The K values were negatively correlated with sand content of these pas ture soils, and positively correlated with organic matter content, cat ion exchange capacity, clay content and silt content of the soils. In a field study on picloram groundwater contamination from pasture use, picloram at 2.47 L/ha was applied twice to two pasture plots (Mabi cla y loam). Water samples were collected weekly from two wells adjacent t o these pasture plots for three months after each herbicide applicatio n. All water samples were analyzed by gas chromatography. Mo detectabl e level of picloram concentration was found in any of the water sample s collected after the first herbicide application. However, a very low level of picloram (2 mu g/L) was detected in one of the wells 10 week s after the second herbicide application.This finding suggests that th ere is little possibility that picloram will contaminate groundwater i n a heavy soil such as Mabi clay loam.