The Study Of Pendimethalin On The Impact Of Microorganism And Enzyme Activity And Its Degradation

Pendimethalin was a soil-treated herbicides which was normally used to control weeds in tobacco, cotton and vegetable field. This paper had established the methods which was about the effects of pendimethalin to soil environment. The effects of pendimethalin to soil enzymatic activity under laboratory conditions was assessed; and the studies further analyzed the effects of different concentrations of pendimethalin to soil enzymatic activity in different time and different soil depths; in cotton field of Xinjiang, the influence of pendimethalin on soil microorganisms that contain the dynamics of microbial species, population and community; at the same time, the influence of different concentrations of pendimethalin at different times and different residues in soil was studied. The results of the studies are listed as follows :1) The results of greenhouse studies showed that the soil’s urease activity was increased with the treatment of high concentrations of pendimethalin(2000 g a.i./hm2) during the whole incubation period(0-60 d). On the contrary, when concentrations of pendimethalin was low(400 、 800 、 1200 g a.i./hm2), it inhibited urease activity and with the pendimethalin concentrations decreasing, the inhibitory effect was enhanced gradually; for alkaline phosphatase enzyme, the enzyme activity changed acutely in different pendimethalin concentration; for dehydrogenase enzyme and sucrose enzyme, the pendimethalin was shown activation effects to both of them, and the enzyme activity increased with increasing concentration.2) The results of microbial population in field studies showed that the number of bacteria and fungi in the soil which was treated with pendimethalin was mainly inhibited, and with the pendimethalin concentrations decreasing, the inhibitory effect was enhanced gradually; during the upper course of experiments(60-90 d), inhibitory effects on bacterial population gradually reduced until the recovery. The results also show that low concentrations of pendimethalin has stimulation effect and high concentrations showed a slight inhibition on actinomyces.3) The enzyme activity of soil in field indicated that the sucrose and dehydrogenase enzyme in different concentrations of pendimethalin was activated; pendimethalin on alkaline phosphatase activity in general is inhibited, but the catalase activity of soil was a slight activation. Long-term applying pendimethalin caused soil nutrient unbalance.4) The analysis of residue dynamic of pendimethalin in field experiment revealed that under the level of addition of 0.05-5 mg, the recovery rate of pendimetalin was 92.97-94.33%, with the relative estimation deviation(RSD) 3.79-4.57 and limit of detection(LOD) 0.05 mg. The increase of the residue of the pendimethalin in the soil is companied with increasing concentration. The dissipation of the pendimethalin in the cotton field follows the first-order kinetics, with half-time period 7.8-1.1 days that relative to the depth of soil.Overall, the studies of residual kinetics revealed that less impact was on the soil when the concentration of pendimethalin was 800-1200 g a.i./hm2. Farmland experiment studies revealed that the microorganisms were mainly inhibited by the pendimethalin. The effect of inhabitation was directly proportional to the concentration and inversely proportional to the depth of soil. The long-term administration of pendimethalin would cause the out-of-balance of microorganisms in the soil. The influence of pendimethalin to the soil enzyme activities would be complicate, which affected the out-of-balance of nutrient of soil. Pendimethalin is a relatively safe herbicide but unfavorable use for long term, because the residue time in the cotton field was short.