| The core of corn-soybean belt compound planting is to enlarge the space and keep the shrinking plant secret.This planting mode can keep the corn yield basically unchanged and produce more soybeans for one season.In the planting process of this model,the problem of mixed broad-leaved and gramineous weeds in the field is serious,which directly affects the normal growth of soybean and corn.Therefore,it is of great significance to screen herbicides with good control effect and high safety for corn and soybean.In this study,five soil treatment agents were selected for field efficacy tests to determine their weed control effects.Moreover,high performance liquid chromatography（HPLC）was used to study their degradation dynamics and residual behavior in soil,which provided data support for the safe use of herbicides in corn-soybean composite planting fields.The main results are as follows:（1）The results of the field efficacy test showed that among the five soil treatment agents tested,the control efficiency of 1350 g·hm-2 and 4500g·hm-2 of 96%s-metolachlor and 33%pendimethalin emulsion were the best,both of which reached more than 92.00%,and the control efficiency of fresh weight reached more than 90.00%.The plant and fresh weight control effects of the two treatments on common broad-leaved weeds and gramineous weeds were more than 90.00%.The safety results showed that30 days after application,the above two agents had high safety and good control effect,and the plant damage level was 0,which did not affect the normal growth of corn and soybean.（2）A high performance liquid chromatography method was developed for the simultaneous determination of flumetsulam,s-metolachlor and pendimethalin in the soil of corn and soybean compound planting field.When the concentrations of the three herbicides were 0.05,0.50 and 1.00mg·kg-1,the average recoveries were 87.55%-91.77%and the relative standard deviations（RSD）was 2.61%-4.97%.The average recoveries were84.15%-94.69%,and the relative standard deviations（RSD）was3.74%-6.68%.The average recoveries of pendimethalin in soil ranged from88.08%to 94.02%,and the relative standard deviations（RSD）ranged from2.84%to 8.28%.The method meets the requirement of accuracy and precision,so it can be applied to soil sample determination in field.（3）The degradation dynamic test results of flumetsulam showed that the degradation dynamic in soil conforms to the first-order kinetic equation.After being applied in the field for 2 h at 84.38 g·hm-2 and 126.57 g·hm-2,the deposition amounts were 0.116 mg·kg-1 and 0.131 mg·kg-1,respectively.The degradation rates reached 47.40%and 49.45%at 28 d,and the half-lives were 31.5 d and 28.9 d,respectively.The degradation of s-metolachlor in the field showed that the deposition amount of 1350g·hm-2 and 2025 g·hm-2 in the field for 2 h was 1.945 mg·kg-1 and 2.603mg·kg-1,respectively,and the degradation rate reached 78.00%and 78.91%at 28 d,respectively.The degradation of s-metolachlor in soil conforms to the first-order kinetic equation,and its half-lives in soil are 12.6 d and 13.1d,respectively.The degradation dynamic test results of pendimethalin in the field showed that after 4500 g·hm-2 and 6750 g·hm-2 were applied in the field for 2 h,the deposition amount was 1.254 mg·kg-1 and 1.676 mg·kg-1,respectively,and the degradation rate reached 66.91%and 56.11%at 28 d,respectively.The residual degradation of pendimethalin in soil conforms to the first-order kinetic equation,and its half-lives in soil are 18.2 d and 25.7d,respectively. |
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