This study has shown that there exists positive correlation between microbial population and soil organic matter and that the variation in soil microbial activity represents the capacity of microorganisms to respond to inputs of herbicides. Microbial activity increased as an adaptation to the stress caused by increase in concentration of the herbicides over weeks of treatment. The results obtained demonstrate a potential capacity for adaptation of the microorganisms in soils when large amounts of herbicides are added. Dehydrogenase activity