AbstractThe adsorption of picloram was studied in 28 pasture soils under laboratory conditions. The adsorptive capacities of these soils were expressed in terms of the empirical constants, K and 1/n of the Freundlich equation. The calculated K values ranged from 0.269 to 1.842 for Espinosa sandy loam and Bajura clay, respectively. The 1/n values ranged from 0.27 to 1.68 for Carrizales sandy loam and Mabí clay, respectively. The K values were negatively correlated with sand content of these pasture soils, and positively correlated with organic matter content, cation 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 (Mabí ciay loam). Water samples were collected weekly from two wells adjacent to these pasture plots for three months after each herbicide application. All water samples were analyzed by gas chromatography. No detectable level of picloram concentration was found in any of the water samples collected after the first herbicide application. However, a very low level of picloram (2 µg/L) was detected in one of the wells 10 weeks after the second herbicide application. This finding suggests that there is little possibility that picloram will contaminate groundwater in a heavy soil such as Mabí clay loam.
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