The Study On Weeds Control Threshold And Competition Between Soybean And Weeds

The soybean is one of the main food crops in Heilongjiang province, because it has long growth period, The weeds were given large space and sufficient time to develop, and result in many problem such as the soybean's output reduction and descend with quality. To solve these problems and control the weeds, it is very necessary to make further research of the competition between the soybean and weeds and the economic threshold level.In this project the characters of e competition between the soybean and weeds and economic threshold level was study by field experiments and investigation.The result are brought forward as following:1. Weeds can be divided into three kinds of clusters by their height in the soybean field in which Echinochloa and amaranth were main weeds, weed-free periods and soybean weight and leaf area and output are the positive correlation. They are represent S shapes Logisticcurve, the equation is: . The critical period of weed-free periods is theperiod of five weeks after the soybean seedlings come out, and the critical period of constant competition is the period of four weeks after the soybean seedling come out.2. With the Se-taria irdis competition increasing, the output of soybean reduce gradually. In the different density the Se-taria irdis come into being competition in it's breed.The density of Se-taria irdis and the loss of soybean output(P) make a quantity relation: P = 4.5477+1.0203Lgx.3.the Amaranthus retoflexus and the loss of soybean output(P) make a marked andunsymmetrical S shape curve: P=4.1003+0.35941gx.if the rate of Amaranthus retoflexus reach 0.5(stub/m2),the soybean output will reduce 19.1%,it is the critical density.4.1mitated Chenopodium album density and the loss of the soybean output make amarked and unsymmetrical S shape curve: P =4.9290+0.99661gx.5.the critical density of Echinochloa in the Spring soybean field is 1-2(stub/m2), and thedensity of it to the loss of soybean output is P=4.0178+0.76811gx.In the latter period ofsoybean growth, the competition of Echinochloa increase strongly, can reduce the soybean output.