研究了除草剂百草枯在3种不同浓度下对土壤微生物的种群数量及其部分活性的影响。结果表明，施用百草枯对土壤微生物有明显的影响。0.05~5mg/kg的百草枯在施药后30d内，真菌种群严重被抑制；硝化细菌种群和纤维素分解菌种群均呈刺激效应；低浓度的百草枯刺激土壤细菌和放线菌种群的生长，而高浓度的百草枯则抑制其生长。结果同时表明，百草枯对土壤硝化作用和纤维素分解强度的影响均表现为刺激效应。随着加药时间的延长，这种刺激或抑制作用又逐渐恢复或接近正常水平。

The effects of paraquat on the population amount of soil microflora and their activity in soil at three different densities were studied in this experiment. The results indicated that paraquat had a significant effect on soil microflora in thirty days. Paraquat of 0.05~5mg/kg inhibited the growth of funguses, but stimulated the growth of the population of cellulose utilizing microorganism and nitrifying bacteria. The low-density paraquat stimulated the growth of bacteria and actinomyces, but high-density paraquat inhibited their growth. The results also showed that soil nitrification and soil cellulose decomposition was stimulated. And the effect of stimulating or inhibiting had recovered normal level with prolonging of time of adding pesticide.