| Weeds have synchronously growth with soybean in the field,the growth of weeds has caused serious threats to soybean production.At present,herbicides application has been the most important means of weed control in soybean fields.The herbicide application periods h ave been divided into pre-emergence,post-emergence treatment.The pre-emergence herbicides have poor effects on controlling the weeds emerging from the late growth stage of soybean,and the post-emergence herbicides only control the weeds that have emerge d and have a short duration.In the actual production and application process,the post-emergence application period has been greatly affected by the environment,often due to the wrong application period,unreasonable herbicide ratio and blindly increasing the dosage,the effect of controlling weeds was not ideal.To explore the continuous application of acetochlor in pre-emergence and post-emergence,combined with other types of post-emergence herbicides,has great significance to innovate the current application of herbicides in soybean fields and to effectively improve season-long weeds control.It is important to reduce the harm of soybean production,especially late spring weeds.Acetochlor was a commonly used herbicide for pre-emergence application in soybean field in China.In this paper,the pre-emergence puls post-emergence application acetochlor and mixture with other herbicides for weed control and soybean safety were used as an entry point.By using the randomized block group field trial design with three treatments,we use the acetochlor pre-emergence application for the first treatment,both pre-emergence and post-emergence for the second treatment,and two applications which were mixed with fomesafen,quizalofop-p-ethyl and clomazone respectively for the third treatment,the effects of soybean safety,weed control and soybean yield in each treatment area were studied within 4 weeks after application.The main results were as follows:(1)Effect of acetochlor application on the safety of soybean in different periods:1)Effect of acetochlor application on soybean growth in different periods.Compared with weed-free control,acetochlor applied pre-emergence + post-emergence and mixed with fomesafen,quizalofop-p-ethyl,clomazone respectively has certain inhibitory effect on soybean plant height and fresh dry weight of plants.However,there was no significant difference compared with acetochlor applied pre-emergence alone.There was no significant difference compared with weed-free control at 28 days after application.2)Effect of acetochlor application on chlorophyll content of soybean and different canopy light intensity in different periods.The chlorophyll content of acetochlor applied pre-emergence + post-emergence was not significantly different from weed-free control at 28 days after application,but it was significantly higher than untreated control,significantly improved the light intensity near the ground.The application of acetochlor in combination with fomesafen and clomazone w ere more significant in inhibiting chlorophyll content and more effective in enhancing the light intensity,but the effect of improving the light intensity combination with quizalofop-p-ethy was not obvious.3)Effect of acetochlor on antioxidant enzymes in soybean leaves in differ ent periods.The activity of SOD and POD in soybean leaves increased first and then stabilized after acetochlor applied pre-emergence + post-emergence.Finally,there was no significant difference compared with the control groups.The CAT activity and MDA content of soybean leaves increased gradually,the early activity and content were higher than the control groups after application,but there was no significant difference with the control groups at 28 days after application.4)Effect of acetochlor on the α-amylase activity of soybean leaves in different periods.Acetochlor applied pre-emergence + post-emergence and mixture with other herbicides significantly decreased the activity of the target enzyme α-amylase,but there was no significant difference compared with acetochlor applied pre-emergence alone on 28 days after the application.There was no significant difference with the control groups.5)Effect of acetochlor on the root vigor and nodules of soybean in different periods.The root activity of soybean in each treatment area including control group showe d a gradual increase and then stabilized.Compared with weed-free control,acetochlor applied pre-emergence + post-emergence and mixture with other herbicides,the effect on the dry weight of nodule was not significant,and the number of nodules was limited.After application,the activity of nitrogenase in each nodule showed a decreasing trend,and the activity of nitrogenase in root nodule was significantly inhibited,but the activity of nitrogenase could return to normal with soybean growth.(2)Effect of application of acetochlor on weed control in different periods.Compared with acetochlor applied pre-emergence alone,applied pre-emergence + post-emergence the number of emergence of gramineous and broadleaf weeds was significantly reduced,and the decline of control effect was relatively slow.The two-year test showed that the control effect on grass weeds increased significantly by 9.49% and 11.51%,respectively,at 35 days after application.Acetochlor applied pre-emergence + post-emergence significantly increased the control effect on gramineous and broadleaf weeds when mixed with fomesafen or clomazone.Among them,mixed with fomesafen,the average control effect of weeds increased by 8.23% and 12.06% in two years,respectively.(3)Effect of acetochlor application on soybean yield in different periods.The average number of pods per plant and the average number of grains per plant in each treatment treatment area were significantly higher than tha t of untreated control.Compared with weed-free control,the yield was reduced to some extent,but there was no significant difference.Compared with the two-year soybean production,the output of each treatment area in 2017 was higher than 2018. |
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