Degradation of Isoproturon in Soil in Relation to Changes of Microbial Biomass and Activity in Small-Scale Laboratory and Outdoor Studies

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Abstract
The soil degradation of isoproturon under standardized laboratory conditions was compared to that carried out in an outdoor experiment using lysimeters. After application of 14C-labelled formulated isoproturon (1.5 kg A.I./ha), radiochemical analysis, as well as microbial investigations, were performed to relate changes in soil microbial biomass to its capability of degrading isoproturon. The results showed that the microbial biomass, as well as its dehydrogenase activity, varied under field conditions due to fluctuations of temperature and soil moisture. In the laboratory experiment the microbial biomass decreased during the 100 day experimental period, this reduction being the result of the experimental conditions. Consequently, the herbicide was degraded more quickly in the outdoor experiment where leaching, formation of 14CO2 uptake by plants, and photolysis also took place, than in the laboratory experiment. Further microbiological investigation in the laboratory experiment showed that specific populations known to be responsible for the metabolic degradation of the compound were enhanced in the isoproturon-treated soil.