The effect of the herbicide diuron on soil microbial activity

The inhibitory effect of the herbicide diuron [3-(3,4-dichlorophenyl)-1,1-d imethylurea] on microbial activity in red Latosol soil was followed using m icrocalorimetry. The activity of the microorganisms in 1.50 g of soil sampl e was stimulated by addition of 6.0 mg of glucose and 6.0 mg of ammonium su lfate under 35% controlled humidity at 298.15 (+/- 0.02) K. This activity w as determined by power-time curves that were recorded for increasing amount s of diuron, varying from zero to 333.33 mug g(-1) soil. An increase in the amount of diuron in soil caused a decrease of the original thermal effect, to reach a null value above 333.33 mug g(-1) of herbicide. The power-time curve showed that the lag-phase period and peak time increased with added h erbicide. The decrease of the thermal effect evolved by micro-organisms and the increase of the lag-phase period are associated with the death of micr obial populations caused by diuron, which strongly affects soil microbial c ommunities. (C) 2001 Society of Chemical Industry.