Effects Of Bensulfuron-methyl And Nicosulfuron On Soil Microbial Activity

Sulfonylurea herbicide is the main type pesticide which pollutes soil, its dominated situation is difficult to change in the short term, it would be inevitably used for a long time, and causes accumulation of sulfonylurea herbicides in the soil. Therefore, researching the degradation pathway of the herbicide in soil ecological chemical mechanism is significant useful for the rational drug use, lightening the harms of pesticides and improving the quality of soil and water environment. Also, it has important theoretical and practical significance for ensuring agricultural sustainable development. In the present study, a series of laboratory experiments were conducted to determine the biochemical reactions after the pesticide in different soils. The bensulfuron methyl was applied at0(control),0.1,1.0(field rate) and100.0μg g-1in wetland soil, paddy soil and pond soil. The nicosulfuron was applied at0(control),0.1,1.0(field rate) and100.0μg g-1in woodland soil, cornfield soil and uncultivated land soil. At different time points, using the streaked plate to get the number of microorganisms, using indigo blue colorimetric method to obtain the activity of urease, using3,5-dinitrosalicylic acid colorimetry to gain the activity of sucrase, using permanganate titration to acquire the activity of catalase, using high-performance liquid chromatography (HPLC) for determine degradation dynamic, using liquid mass spectrometry for determine degradation products.The main results were summarized as follows:1. The change of microbial population and enzyme activity in water flooded soils at the various concentrations of sulfonylurea herbicides(1)In the wetland soil, populations of microorganisms affected by bensulfuron-methyl increased as the increasing concentration of bensulfuron-methyl, nitrite bacteria were more sensitive to bensulfuron-methyl than other microorganism; At the micro dose, the trend of the urease activity was’incitation-recovery’, at the recommended dose and high dose, the trend of urease activity were’incitation-suppression’; The sucrase activity were suppressed at all levels; The catalase activity were suppressed at the micro dose and the recommended dose,’inspired-suppressed’at the high dose,(2)In the paddy soil, populations of microorganisms affected by bensulfuron-methyl increased as the increasing concentration of bensulfuron-methyl, bacteria, actinomycetes, nitrifying bacteria, denitrifying bacteria were more sensitive to bensulfuron-methyl than other microorganism, fungi were only sensitive to high dose of bensulfuron-methyl; At the micro dose, the trend of the urease activity was’suppression-incitation-recovery’, at the recommended dose and high dose, the trend of urease activity was’incitation’; The sucrase activity and the catalase activity were suppressed at all levels.(3) In the pond soil, populations of microorganisms affected by bensulfuron-methyl increased as the increasing concentration of bensulfuron-methyl, fungi, actinomyces, nitrogen-fixing bacteria, denitrifying bacteria were more sensitive to bensulfuron-methyl than other microorganism; The urease activity were suppressed at all levels; The sucrase activity were suppressed at all levels; The catalase activity were inspired at all levels.(4)The fungi and aromatic compounds degrading bacteria were inspired by bensulfuron-methyl, but other microorganisms were suppressed by bensulfuron-methyl, the number has been changed from10to1000times (Compared with the controls).2. The change of microbial population and enzyme activity in nonirrigated farmland soils at the various concentrations of sulfonylurea herbicides(1) In the woodland soil, populations of microorganisms affected by nicosulfuron increased as the increasing concentration of nicosulfuron, actinomycetes and nitrosation bacteria were more sensitive to nicosulfuron than other microorganism;(2) In the cornfield soil, populations of microorganisms affected by nicosulfuron increased as the increasing concentration of nicosulfuron, nitrosation bacteria were more sensitive to nicosulfuron than other microorganism;(3) In the uncultivated land soil, populations of microorganisms affected by nicosulfuron increased as the increasing concentration of nicosulfuron, fungi, actinomyces and nitrosation bacteria were more sensitive to nicosulfuron than other microorganism;(4) In nonirrigated farmland soils, the urease activity were suppressed at all levels’ nicosulfuron; The sucrase activity were suppressed at all levels’nicosulfuron; The catalase activity were inspired at all levels’nicosulfuron.(5) The fungi and aromatic compounds degrading bacteria were inspired by nicosulfuron, but other microorganisms were suppressed by nicosulfuron, the number has been changed from10to1000times (Compared with the controls). Denitrifying bacteria in the cornfield soil were special, at the micro dose and the recommended dose, the trend was incitation, but at the high dose, the trend was suppression.3. The changes of three main microfloras under the stress of sulfonylurea herbicides The relative proportion of three main microfloras was a measure of soil quality, the high density of bacteria and actinomycetes mean high soil fertility, but the high density of fungi means low soil fertility. At80d, the proportion of actinomycetes in all soils has been suppressed, so the actinomycetes could be used as a sign for polluted soil.The nitrogen-fixing bacteria were less sensitive to sulfonylurea herbicides, but The nitrifying bacteria in water flooded soils were more sensitive to bensulfuron-methyl and the nitrifying bacteria in nonirrigated farmland soils were more sensitive to nicosulfuron.Aromatic compounds degrading bacteria were stimulated at the recommended dose and the high dose.4. The degradation of sulfonylurea herbicides in different soils(1)The microorganism p layed an all-important role in the degradation of sulfonylurea herbicides, the difference of half-life period in sterilized soil and not sterilized soil were more than5days.(2)The soils with rich vegetation and the soils domesticated by pesticides for long time had strong self purification ability, and the degradation rates of sulfonylurea herbicides were faster, and the degradation products were even more.