The Degradation Trends Of Iodosulfuron-methyl Sodium And Its Effects On Several Biological Indicators In Soil

The degradation behaviours of iodosulfuron-methyl sodium in soil and water and its effects on urease, catalase, neutral phosphatase, microbial biomass carbon in soil and soil respiration are studied under various control conditions by stimulating methods in laboratory. The main results are follows:(1) Under control conditions, the degradation of iodosulfuron-methyl sodium in soil follows a first-order of degradation kinetics, and it was mainly degraded by soil microorganisms, the chemical and photo degradation are subsidiary.(2) The degradation rate of iodosulfuron-methyl sodium had a positive correlation with soil temperature and moisture content, but had an inverse correlation with soil pH and the concentration of iodosulfuron-methyl sodium. The higher of soil temperature and moisture content, the faster degradation of iodosulfuron-methyl sodium; but the higher of soil pH and iodosulfuron-methyl sodium concentration, the slower degradation of it. When the temperature from 5°C rise to 35°C and soil moisture from 25% saturated water contents rises to 75% saturated water contents, the degradation rate of iodosulfuron-methyl sodium was increased by 2.77 times and 4.13 times separately. But when the soil pH from 5.14 rise to 9.42 and the concentration of iodosulfuron-methyl sodium from 2.5mg/kg rise to 10mg/kg, the degradation rate of iodosulfuron-methyl sodium was decreased by 3.18 times and 1.38 times respectively.(3) In Hunan three typical soils, the degradation rates of iodosulfuron-methyl sodium are in the order of red soil , purple soil , river tidal soil.(4) The hydrolysis of iodosulfuron-methyl sodium in phosphate buffer was conducted in buffer solution of different pH value showed that the higher pH of buffer solution, the lower hydrolysis rate of iodosulfuron-methyl sodium, and the hydrolysis rate constant has an inverse correlation with pH of buffer solution(R2=0.9663), and the hydrolysis rates were in the order of pH 4>pH 7>pH 10.(5) Under different temperature, the hydrolysis of iodosulfuron-methyl sodium was follow Arrhenius law, and the higher temperature, the faster of its hydrolysis rate. When the temperature from 5°C rise to 35°C, the hydrolysis half-time were shortened 14.6 days, 7.8 days and 4.7 days respectively.(6) The urease activity, neutral phosphatase activity and microbial biomass carbon are decreased notably at the first 4-14 days as the soil treated with iodosulfuron-methyl sodium at a level of 1 mg/kg. But with the extension of time, iodosulfuron-methyl sodium was decreased in soil, its effects on urease, neutral phosphatase and microbial biomass carbon are diminished gradually after 14 days, and slowly become consistent with CK.(7) The effects of iodosulfuron-methyl sodium on catalase activity is complicated. At first 9 days, the catalase activity of soil was lightly restrained, then stimulated, and after 28 days it come consistent with CK as the soil treated with iodosulfuron-methyl sodium at a level of 1 mg/kg.(8) Iodosulfuron-methyl sodium also had some effects on soil respiration, the...