Effects Of Lead And Bensulfuron-methyl Combined Pollution On Degradation Of Bensulfuron-methyl And The Size Of Microbial Biomass In Soils

With the rapid development of industry and agriculture and excess application of agricultural chemicals, combined pollution of lead and bensulfuron-methyl in agricultural ecosystems has become more and more popular. However, study on the effects of the combined pollution on soil quality was neglected. In this research, three different paddy soils (paddy field on quaternary red soil, blue clayey paddy soil, paddy field on desalting muddy polder) were used. The soils were treated with different concentrations of lead (0,100,300,500,800mg/kg), bensulfuron-methyl (0, 5.10mg/kg) and their combinations, and incubated to study the effects of combined pollution of lead and bensulfuron-methyl herbicide on the degradation of bensulfuron-methyl, the size of the microbial biomass in soils and the dynamics of Cmic, Nmic and Cmic/Nmic ratio with time. The interactive effects of lead and bensulfuron-methyl on microbial biomass were also evaluated. The study is important for the remediation of soils contaminated by herbicides, establishment of criteria of soil environmental capacity, improvement of soil quality, safety of agricultural products, and sustainable development of agriculture. The main results were summarized as follows:1. In this research, bensulfuron-methyl was an easily degradable herbicide. Its half-life of degradation was 27.2-45.3 days. The degradation was mainly affected by soil pH and the size of soil microbial biomass. In all three soils, the degradation of bensulfuron-methyl herbicide was significantly inhibited by addition of lead. The more lead was added, the longer the half-life of degradation of bensulfuron-methyl herbicide was. Under the same treatment, the half-life of bensulfuron-methyl herbicide degradation showed significant difference because of different pH values among the soils. The higher the pH value was, the longer the half-life of degradation was: with the order of paddy field on desalting muddy polder (pH=7.38)> blueclayey paddy soil (pH=6.10) > paddy field on quaternary red soil (pH=4.96).2. The results indicted that the soil Cmic and Nmic were decreased significantly with the treatments of combined pollution of lead and bensulfuron-methyl during the whole incubation period (180d). Similar patterns of decrease were observed for Cmic and Nmic. Low Cmic or Nmic was observed in the treatments of high lead or bensulfuron-methyl concentration. The inhibitory effects on Cmic and Nmic were strong during the initial 7-14 days and then became less strong after 30 days.3. In the soils, the combined pollution of lead and bensulfuron-methyl resulted in an increase of the Cmic/Nmic ratios during the initial 7-14 days. However, the differences were not significant for most treatments. After 30 days, no differences were found between the treatments and the check.4. Statistical results indicated that the interactive effects of lead and bensulfuron-methyl on the Cmic and Nm;c were significant in most sampling days, being synergistic inhibitory effects on Cmic and Nmic.