Spatial And Temporal Distribution Of Chlorothalonil And Chlorpyrifos In The Facility Soil And Their Effect Mechanism

The greenhouse, on account of the warm and humid environment,provides pests appropriate living conditions. So, it results in excessively and frequently pesticides application. Chlorothalonil(CHT) and Chlorpyrifos(CHP), as two kinds of commonly used pesticides in agricultural production, have been widely used, especially in greenhouse vegetable production. They not only pollute the agriculture ecological environment,but also threaten the quality safety of agricultural products. In order to evaluate the pesticide safety in the soil,it is the premise to understand the spatial and temporal distribution of CHT and CHP in the facility soil and their effect mechanism.The paper adopts the combining method of field investigation and laboratory study. We investigated the spatial and temporal distribution of CHT and CHP in the facility soil and discussed the correlation of between soil physico-chemical properties (moisture content, temperature, Eh and pH) and pesticides residues. And the characteristic of pesticides degradation in the root soil gotten from tomato and cucumber greenhouse were studied under laboratory conditions. The main results were as follows:The recommended doses of CHT and CHP (0.4003 g/m~2 and 0.1124 g/m~2,respectively), were used to study. The degradation dynamics of two pesticides in the soil were not compatible with the first-order kinetic equation, instead they behaved more fluctuant. In tomato greenhouse soil, CHT residue concentration fluctuated in the range of 1.396-18.42 mg/kg, while CHP residue concentration fluctuated in the range of 0.255-4.075 mg/kg. And in cucumber greenhouse soil, CHT residue concentration fluctuated in the range of 0.208-18.22 mg/kg, while CHP residue concentration fluctuated in the range of 0.228-2.641 mg/kg. However under laboratory, the degradation dynamics curves of the two pesticides fitted well with first-order kinetic equation. The half-lives of CHT and CHP were among 5.90-11.89 d and 4.68-11.98 d, respectively. The differences pesticides degradation between shed monitoring and laboratory observation indicated that pesticides degradation in the shed soil were more uncontrollable and complex. In addition,pesticides application would affect the microorganisms (bacteria, fungi) amounts. The results showed that in the spraying period, the numbers bacterial and fungal were inhibited from 4.9-4.8×10~7 to 3.6-3.8×10~7 and 1.6-1.8×10~5 to 1.1-1.5×10~5, repesctively. Until the 21st day after pesticaies application the number of bacteria and fungi were resumed to previous level.Pesticide residues in different ridges in the greenhouse soil existed spatial difference. The two pesticides residues were higher in the south ridges than those in the north ridges, especially for CHT. In cucumber greenhouse, the average CHT residues was 24.71 mg/kg in the south side soil while it was 8.776 mg/kg in north side soil, the former was higher than the latter by 15.93 mg/kg. And in tomato greenhouse, the average CHT residues in the south side soil was 25.35 mg/kg, much higher than that of north soil of 10.81 mg/kg. Our study declared that the residues of CHT and CHP were correlated positively with soil water and Eh with correlation coefficient of 0.784 and 0.775, respectively.