Study On The Competition And Chemical Control Of Echinochloa Crusgalli(L.) Beauv. And Polygonum Lapathifolium L. On Soybean

Soybean[Glycine Max?Linn.?Merr.],as an important grain and oil crop in China,has been cultivated for more than 5,000 years.Heilongjiang is a major province of soybean production in China,and the soybean planting area and output rank first in the country,with a significant strategic position.As an important limiting factor affecting soybean pro duction,weeds not only compete with soybeans for growing resources such as light,nutrients,water and space,but also act as an intermediate host and habitat for a variety of diseases and insects,which is one of the main factors restricting soybean yield in China.In recent years,with the adjustment of farming patterns,changes in planting systems,and changes in agricultural operations such as fertilization and herbicides,the succession of farmland weed communities has been accelerated.Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.are two major malignant weeds in soybean field in heilongjiang province,with large amount of occurrence and high reproduction rate,which have serious harm to soybean growth and serious loss to soybean pro duction.There are many kinds of weeds in soybean field and the community structure is complex.We investigated the occurrence hazards of weeds in soybean fields in 6 villages and towns around Harbin city,and identified the dominant weed populations in the region;analyzed the effects of mixed hazards of dominant weeds on soybean yield loss at different densities and coexistence,Screened and obtained new herbicide mixed formula for controlling dominant weeds,in order to obtain the control index and herbicide mixed formula that match the actual occurrence of weeds in soybean fields,and provide a scientific basis for the comprehensive management of weeds in soybean fields;In addition,the effects of dominant weed communities on the photosynthetic physiol ogical characteristics of soybean were further analyzed,so as to preliminarily identify the physiological mechanism of the decline of soybean yield caused by dominant weeds from the aspects of photosynthetic mechanism and chlorophyll fluorescence quenching.The main findings are as follows:1.Investigation of weed occurrence in soybean fields in Harbin,Heilongjiang ProvinceThere are 24 species of common weeds in soybean field in Harbin,belonging to 13 families.Among of them,18 species of broad-leaved weeds accounted for 75.00%and 6 species of gramineous weeds accounted for 25.0%.There were 19 species of annual weeds,accounting for79.17%,and 5 species of perennial weeds,accounting for 20.83%.There were 12 species of weeds in 8 families with relative abundance of more than 10,among which Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.had relative abundance of more than 30.2.Effects of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.on soybean yield.With the increase of weed density and coexistence time,the number of pod per plant and yield of soybean decreased,while the empty pod rate increased,weed density and coexistence time and yield loss rate were significantly positively correlated.The effect of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.on the yield of soybean was mainly direct,and the influence degree of the two is different.Polygonum lapathifolium L had a greater impact on soybean yield loss rate,with a direct diameter coefficient of 0.799,which was 43.43%higher than Echinochloa crusgalli?L.?Beauv.Polygonum lapathifolium L had a greater impact on soybean yield loss rate,with a direct diameter coefficient of 0.799,which was 43.43%higher than Echinochloa crusgalli?L.?Beauv..The relationship between weed density,coexistence time and yield loss rate of soybean was analyzed by curve fitting and regression.The results show that the power function Y=0.685x1.046?R²=0.898;F=87.646;P=0.000?has the best fitting effect on the relationship between the mixed density of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.and soybean yield loss;The quadratic curve function Y=-0.01x²+1.899x-24.134?R²=0.995;F=193.542;P=0.005?can better express the relationship between the coexistence time of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.and soybean yield loss rate.According to the local production level of soybean,the allowable level of economic harm in the artificial control of weeds in soybean field was 12.23%,the economic threshold value of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.were 15.73-23.18 plants/m²,and the critical period of control was 13.7-21.6 days.3.Screening of soybean field weed herbicide mixed formulations with Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.as dominant species?1?In this study,the whole plant bioassay was used to determine the sensitivity of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.to common stem and leaf treatment agents in soybean fields.It is:propaquizafon>quizalofop-p-ethyl>quizalofop-p-tefuryl>clethodim>fluazifop-p;the ED₅₀ of the three broad-leaf herbicides is:fluoroglycofen>fomesafen>bentazone;ED₅₀ increases with the age of weeds.?2?The Gowing method was used to evaluate the combined action type of the three herbicides on the Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv..The result showed that propaquizafon had synergistic effect when used in combination with fomesafen and bentazone.The best weeding effect was achieved when propaquizafon was combined with the active components of fomesafen?1:3?and bentazone?1:10?.The safety test showed that 900 g a.i./ha of propaquizafon combined with bentazone?1:10?could significantly inhibit the fresh weight of soybean,and the other test doses were all safe for the tested soybean varieties.4.Effects of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.on the Photosynthetic Physiological Characteristics and Yield of Soybean.It was found that with the increase of total weed density,the number of main stem nodes,Chla/b,net photosynthetic rate and Rubisco activity of soybean all decreased to different degrees.The effect of Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.on photosynthetic physiological characteristics and yield of soybean at different growth stages were determined by pot culture.Under the condition of the same total density of weeds,the number of mai n stem nodes,Chla/b,photosynthetic rate,PS?maximum photochemical efficiency and Rubisco activity of Soybean Polygonum lapathifolium L planted alone were the largest declines,and Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.mixed secondly,Echinochloa crusgalli?L.?Beauv.alone is the lowest.Soybean chlorophyll fluorescence parameters did not change significantly during the pod setting period.It can be seen that competition between Polygonum lapathifolium L and Echinochloa crusgalli?L.?Beauv.reduced the Rubisco activity,photosynthetic capacity and light energy conversion efficiency of soybean,which was the main physiological reason leading to the decrease of soybean yield.