THE INHIBITOR EFFECT OF COPPER-SULFATE ON MICROBIAL GLUCOSE DEGRADATION IN RED LATOSOL SOIL

Microcalorimetry has been used in a series of experiments to study the inhibitory effect caused by copper sulphate on soil microbial activit y. This activity was stimulated by addition of 6.0 mg of glucose and 6 .0 mg of ammonium sulphate under a controlled humidity of 53% in a red Latosol soil sample of 1.50 g. Power-time curves were recorded for in creasing amounts of the inhibitor, varying from zero to 6.19 mg. The c urves showed a decrease of the maximum amplitude of the experimental c urve, which shifted to longer times. Increasing masses of copper sulph ate caused a decrease of the original thermal effect to reach a null v alue at 6.19 mg of inhibitor. The results relating the dependence of t he maximum amplitude of the peak time with the considered pollutant ma ss, were fitted to a kinetic model in an attempt to establish the inhi bitory effect of copper sulphate. In this conditions, the data were ad justed to a first power order model for the degradation of glucose. In the absence of inhibitor the consumption of glucose by the microorgan isms is about 10% of the initial mass and decreases with the increase of the copper added to the soil sample.