The extent and seriousness of the contamination of soils by pesticides still remain to be determined,In agricultural systems,herbicides are the largest class of pesticides used (Shea,1985),Chlorsulfuron is one of the most important sulfonylurea herbicides with important feature of very high herbicidal activity,which results in extremely low application rates of 10-40g ha^-1(Blair and Martin,1988),The sulfonylurea herbicides can persist in the soil for more than 1 year(Brown,1990),Therefore,there has been considerable interest in the side effects of these chemicals on non-target organisms,including soil microorganisms(Greaves and Malkomes,1980),It ios generally recognized that the microbial biomass is the eye of the needle through which all organic materials that enter the soil must pass(Jenkinson,1988), Changes in the microbial biomass-C(Cmic) can provide an early indication of long-term trends in the total organic-C(Corg) of soils(Carter,1986),The Cmic/Corg ratio has been found useful as an index of changes in soil organic matter resulting from land management changes(Hart et al.1989).Many studies were done on relative effect of heavy metals on the ratio of Cmic/Corg but few studies have laid particular attention to the effect of herbicides on this ratio,The present paper reports on the Cmic/Corg and microbial biomass-N/total N (Nmic/Ntotal)ratios in soil as affected by chlorsulfuron.
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