Studies On The Regulation Of Lodging Traits Variation During Soybean Growth Stages

China is the origin of the soybean, the soybean has become an important grain-oil crop and the goal of high and stable yield in soybean production. Lodging is the barrier factors affecting the formation of soybean yield, the stem lodging is the main form of soybean lodging, studied the relation among morphological traits, mechanical properties and chemical composition of soybean stem, with the lodging resistance, has an important production and theoretical significance. This experiment was conducted from 2014 to 2015, six soybean varieties（Heinong 19, Beifeng 11, Kenfeng 16, Heinong 37, Heinong 42, Heinong 48）were chosen as the test materials. Planting density experiment was carried out with four levels planting densities（150000 plants per hectare, 250000 plants per hectare, 350000 plants per hectare, 450000 plants per hectare）on Heinong 37 and Heinong 42. Determined morphological traits as plant height, fresh weight, stem internode length and stem diameter, mechanical properties as stem break force, deflection, elastic modulus and gravitational moment, stem chemical composition as cellulose, hemicellulose, lignin content. Systematically studied the regulation of lodging traits variation during soybean growth, and its correlation with the plant lodging resistance, provided theoretical basis and reference to soybean high-yield cultivation and breeding work, the test results showed that:Under the condition of experimental planting densities, the soybean resistance factor presented a U-curve, it released during R₁ to R₆, the minimum was in the R₅-R₆ stage, then raised in R8 stage, that showed the most vulnerable lodging period was R₅-R₆ stage. The order of lodging resistance among six varieties was Beifeng 11>Heinong 42>Kenfeng 16>Heinong37>Heinong 48>Heinong 19, the lodging resistance exists obvious difference between varieties. The lodging resistance factor among four planting densities were D₁₅>D₂₅>D₃₅>D₄₅, demonstrated that with planting density increasing, the risk of lodging increased.The soybean lodging resistance factor reduced by plant height, fresh weight increased,and increasing by stem diameter increasing. Plant height, fresh weight were significantly negatively correlative with soybean resistance factor, stem diameter was significantly positively correlative with soybean resistance factor.indicated that with the plant height and fresh weight increasing,the stem diameter reduced, the risk of lodging increased. The lodging resistance is determined by comprehensive among various factors, although the diameter increased during the growth stages, the extent of the stem diameter increased was far less than that of plant height and fresh weight increased, so that the lodging resistance reduced with the growth stages extending. Soybean lodging resistance increased on R₈ stage, was mainly due to the falling leaves reduced fresh weight, and plant height and stem diameter was not significantly reducing.Soybean lodging resistance factor was significantly positive correlation with stem break force, stem deflection, and elastic modulus, and was significantly negative correlation with stem gravitational moment, indicated that with the stem gravitational moment increasing, and the stem break force, stem deflection, and elastic modulus reduced, the risk of lodging increased. Though the stem break force and the stem gravitational moment increased with the growth stages extending, the extent of the increase of stem break force was far less than that of stem gravitational moment increased, so that lodging resistance factor showed lower in the R₅-R₆ stage.Planting density had obvious impact on the mechanical properties of soybean plant and lodging resistance factor. Soybean stem break force, stem deflection, and elastic modulus obviously reduced with planting density increasing, but the extent of the reduce of stem break force was far more than that of stem gravitational moment reduced, so the lodging resistance factor reduced with planting density increasing.Stem cellulose, hemicellulose, and lignin content had certain differences among different varieties, but it didn’t show the obvious regularity with the lodging resistance. The content of cellulose, hemicellulose, and lignin of the stem reduced with planting density increasing, had a consistent trend with soybean lodging resistance factor.Soybean yield presented a single-peak curve trend with planting density increasing, lodging resistance factor decreased with planting density increasing, therefore, when the density reached the high-yield one, it was not appropriate to increase.