Responses Of Some Soil Enzymes To Atrazine And Tribenuron-methly Spiking In Soils Of Different Fertility

Pesticide is one of the most important means of crop production in modern agricultural,but pesticide residues can contaminate soils and lead to a drastic decline or even losses of some soil functions, and therefore soil productivity. Hence, understanding the responses of soils with different soil fertility levels to pesticide contamination is of great significance in improving soil fertility and ecological environment. We investigated the effects of two kinds of commonly used herbicides on the dynamics of microbial biomass carbon and some selected enzymes’ activities in soils based on a 26-year long-term experiment on a loess soil in Guanzhong Plain, Shanxi Province, China. Long term fertilizers treatments at the site included CK(no fertilizered control), NPK(synthetical fertilizers of nitrogen, phosphorus and potassium), SNPK(Maize stalk incorporation with NPK), M1NPK(Lower dose of organic manure plus NPK), M2NPK(High dose of organic manure plus NPK). Herbicide treatments included no herbicide spiking(0 mg/kg), and spiking 0.5 mg/kg benzene sulfonic and 5 mg/kg atrazine into soils stated above with tribenuron-methly and atrazine as sources, respectively.The main results obtained are as follows:1. Long-term fertilization had significant influence on soil catalase, invertase, urease activities and microbial biomass carbon. Overall, soil enzyme activities and microbial biomass carbon in soils receiving fertilizers were higher than those in control. Treatments receiving organic manure(MNPK) had significantly higher urease activity and microbial biomass carbon than NPK. The application of the organic material(SNPK、M1NPK、M2NPK)markedly increased the activity of catalase than the NPK.2. Atrazine had significant inhibitory effect on catalase of all soils at the beginning of the incubation.. Atrazine showed a significant inhibitory effect on urease, with an inhibition rate of 50-60%, particularly in soil of CK where inhibition rate can reach to a value higher than65%. Atrazine spiking showed an activation effect to some extent on invertase in all soils at the beginning of incubation, but inhibited invertase activity after one week of incubation with a mean inhibition rate of about 30% and the lowest inhibition rate of 20% was observed on CK. Soil microbial biomass carbon has also been significantly inhibited by atrazine, overall the inhibition of microbial biomass carbon of CK treatment is minimal.3. Tribenuron methyl inhibited soil catalase activity to some degree, with the inhibition rate between 1% to 6%, and the soil catalase activity raised to the initial level at the end of the incubation. Tribenuron methyl decreased the soil urease activity in soils receiving organic manure in the first three weeks, but showed no effect on other treatments. Tribenuron methyl had significant inhibitory effect on soil invertase of CK treatment with an inhibition rate of about 10%, but only had a slight inhibition on treatments those receiving fertilizers. At the beginning of the incubation, tribenuron methyl significantly increased soil microbial biomass carbon content of all treatment; at the end of the incubation, it only had significant inhibitory effect on soil microbial biomass in CK and SNPK treatments with a mean inhibition rate of about 20%.