Influence of Chlorsulfuron Contamination on Ratios of Biomass Carbon and Nitrogen to Total Organic Carbon and Nitrogen in Soil

The extent and seriousness of the colltamination of soils by pesticides still remain to bedetermined. In agricultural systems, herbicides are the largest class of pesticides used (Shea,1985). Chlorsulfuron is one of the most important sulfonylu-rea herbicides with importantfeature of very high herbicidal activity, which results in extremely low application rates of10~40 g ha-1 (Blair and Martin, 1988). The sulfonylurea herbicides can persist in the soil formore than 1 year (Brown, 1990). Therefore, there has been considerable interest in the sideeffects of these chemicals on non-target organisms, including soil microorganisms (Greavesand Malkomes, 1980). It is generally recognized that the microbial biomass is the eye of theneedle through which all organic materials that enter the soil must pass (Jenkinson, 1988).Changes in the microbial biomass-C (C.i.) can provide an early indication of long-termtrends in the total organic-C (Corg) of soils (Carter, 1986). The Cmic/Corg ratio has beenfound useful as an index of changes in soil organic matter resulting from land managementchanges (Hart et al., 1989). Many studies were done on relatitre effect of heavy metals on theratio of Cmic/Corg. but few studies have laid particular attention to the effect of herbicideson 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.