Effects Of Longterm And Repeated Application Of Herbicide Chlorimuron-Ethyl On Soil Microbes

Chlorimuron-ethyl is a sulfonylurea herbicide developed by Dupont Corporation in1980s. It is mainly used in soybean fields to control the broadleaf weeds, sedge family weeds and the grass family weeds since it has been widely used in1990s. However, it is a kind of long residual herbicide that is the herbicide is persistent in soil. Longterm and repeated application can not only cause succeeding crop injury, but also damage the soil ecosystem and the sustainable use of soil resources. In this paper, the effects of longterm and repeated application of chlorimuron-ethyl on soil microbial populations, soil micobial community structure and functional diversity were systematically investigated by incubation experiments in the greenhouse. The microbiological mechanism that how chlorimuron-ethyl affects soil biology quality was also discussed. The main results were summarized as follows:1. A method for the determination of chlorimuron-ethyl residue in soil was eatablished. Soil samples were extracted with acetonitrile (containing1%formic acid), then purified by30mg PSA and150mg anhydrous magnesium sulfate, and finally detected by UPLC-MS/MS under multiple-reaction monitoring (MRM) mode. The ion pair m/z414.8>212.9were chosed to identify chlorimuron-ethyl and the ion pair m/z414.8>185.9was used to quantify the compound. Average recoveries of chlorimuron-ethyl in soil samples were at the range of78.73to101.91%at three spiking levels from0.01mg/kg to1mg/kg with relative standard deviations from2.83to7.43%. Limit of quantification of chlorimuron-ethyl was3.3μg/kg. The method is sensitive, simple and suitable for fast determination of chlorimuron-ethyl residue in soil in lagre amounts.2. The soil for incubation experiments in greenhouse was collected from Xiangfang Farm, Harbin, Heilongjiang Province, with no use of chlorimuron-ethyl before. The blank soils were treated with chlorimuron-ethyl technical at doses of one, ten and a hundred fold of the recommended doses after preincubation for10days in the greenhouse. According to the experiments design, chlorimuron-ethyl was applied to the soil one time within a year, two times within a year, two times within two years and four times within two years.1,7,15,30,45,60,90and120days after the treatment each time, soil samples were collected to test the chlorimuron-ethyl residue, the basal respiration of soil microbes, soil microbial biomass C, average absorbance of soil microbial community (BIOLOG Ecoplates method) and soil microbial PLFA content. The effects of longterm and repeated application of chlorimuron-ethyl on soil microbes were studied by applying the herbicide to the soil two times each year with three different concentrations in continuous two years. The results of the incubation experiments showed that the degradation dynamics of chlorimuron-ethyl in soil was in accordance with a first order kinetics model and the half-time was24.7-51.0d in soil, indicating that longterm and repeated use of chlorimuron-ethyl can prolong its half-life. The results of soil microbial respiration determination displayed that during the initial time after application of chlorimuron-ethyl two times within a year, two times within two years and four times within two years, the basal respiration of soil microbes in each treatment was obviously different with the control, but it recovered to be similar with the control after60d,30d,45d, respectively. The results of BIOLOG Ecoplates indicated that:after application of chlorimuron-ethyl two times within a year, the microbial metabolic activity was obviously influenced at the initial stage of different doses treatment and the activity was positively correlated with the concentration of chlorimuron-ethyl, the difference was gradually turning minor after60d; within45days after application of chlorimuron-ethyl two times within two years, the A WCD value of soil microbes was higher than the control and the time to recover was differed in different doses treatments; within60days after application of chlorimuron-ethyl four times within two years, the AWCD value was higher than the control and recovered after90d. The results of PLFA content determination showed that:after application of chlorimuron-ethyl two times within a year, the PLFA content in10-fold treatment was obviously higher than the control in the first15days and recovered after30days, then was obviously lower than the control; there was no detectable effects in1-fold treatment; after application of chlorimuron-ethyl two times within two years, the PLFA content was lower than the control and inhibiting effect was positively correlated with the concentration of chlorimuron-ethyl, it then recovered after60days in each treatment; after application of chlorimuron-ethyl four times within two years, the PLFA content in10-fold treatment was obviously lower than the control in the first15days, then recovered after30days, there was also no detectable effects in1-fold treatment. Simpson and Shannon indexes of different treatment soil changed in the whole incubation process, but finally recovered similar to the blank; McIntosh indexs obviously increased in100-fold treatment and repeated10-fold treatment. During the initial time, the soil microbe was restrained after the application of chlorimuron-ethyl. The microbial PLFA content and soil microbial biomass C in different treatment soil were much lower than the blank soil at first and rised along with the days after application.The GN/GP ratio was obviously different from the control at the early and late stage after treatment, but it changed similarly with the control in the middle stage. The Fungi/Bacteria ratio was higher at first and later lower than the control, and then it gragually recovered to be similar with control. Principal component analysis of the PLFAs showed that the microbial community structure was obviously changed in one hundred fold treatment.