Toxic effect caused on microflora of soil by pesticide picloram application

The toxic effect of the herbicide picloram on the microbial population of a typical Brazilian red Latosol soil was studied in a series of microcalorim etric experiments. The activity of the soil was stimulated by the addition of 6.0 mg of glucose and 6.0 mg of ammonium sulfate, under 34.8% controlled moisture, to a 1.50 mg soil sample, at 298.15 +/- 0.02 K. The net thermal effect due to the addition of the picloram to the soil was determined by in terpreting the power-time curves, which were recorded on the microcalorimet er. The total thermal effect evolved by the microorganisms was affected by the increasing doses of herbicide, and varied from 0 to 10.00 mug g(-1). An increase in picloram exposure caused a decrease of the original thermal ef fect, reaching a null value above 20.89 mug of herbicide per gram of soil. The decreases of the thermal effect evolved by microorganisms and the incre ase of the lag phase period are associated with the death of the microbial population. The effects caused by picloram application in this typical Braz ilian soil resulted in a strong effect on the soil microbial communities.