Adsorption, Desorption and Mobility of Metsulfuron Methyl Herbicide in Malaysian Agricultural Soils

The adsorption, desorption and mobility of metsulfruon methyl, a commonly used herbicide in Malaysia, was investigated in some selected agricultural soils namely Persit, Segamat, Kiol, Sedu and Penor as a means to understand the potential of the herbicide to contaminate the Malaysian soil environment. The range of organic matter content of the soil samples was 2.3 to 33.8, while the range of pH was 3.2 to 6.5. The adsorption of metsulfuron methyl to soils was found to best fit a Freundlich adsorption isotherm with distribution coefficients (1C4) ranging from 0.45 - 46.23. A positive correlation (r=0.95) between organic matter content and adsorption was observed, while a significant negative correlation (r =-0.821) was seen between soil pH and adsorption. The extent of desorption of metsulfuron methyl was also observed to decrease with increasing organic matter content of the soil. Simulated rainfall following the application of metsulfuron methyl at a field application rate of 75 g/hectare in the Segamat soil resulted in the leaching of the herbicide to up to 15 cm of the soil column. Much of the chemical was found in the 10-15 cm zone of the packed column. Complete leaching of the chemical through the soil column was not observed under the conditions of the present study, as the chemical was not detected in the leachate. It was observed that the influence of organic matter content and soil pH was consistent with reports on soils from temperate countries. It was also noted that the relatively low pH, low organic matter content and high clay content of the Segamat soil resulted in limited leaching of the chemical.