Parameters Optimization Of Harvester Threshing Unit And Appropriate Agronomic Characteristics Of Machine-harvested Soybean In Relay Strip Intercropping

Maize-soybean relay strip intercropping is the main promotion planting system in Southwest China due to its high productivity and environmental sustainability.The realization of full mechanization of planting process,especially mechanized harvest,is of great significance to the further application of this system.However,problems such as uncertainty of harvest time and differed yield loss rate with different plant type still exist in the process of mechanized harvest.Therefore,based on the GY4D-2soybean combine harvester this study first optimized the threshing device parameters,then checked the effect of harvest time on shearing force of stem,yield and yield harvest quality.Besides,the relationships between yield loss rate and plant agronomic traits were also studied.The major findings are as follows:（1）By using the small feed longitudinal axial threshing apparatus test-bed,single–factor tests of roller-speed,tooth angle and mesh aperture were carried out and the orthogonal test levels were obtained.On this basis,the three factors orthogonal test,including the speed of the roller,the tooth angle and mesh aperture,was researched.The two factors regression experiment,including the roller speed and tooth angle was also studied.Optimum parameters of threshing machine were460r·min^-1 for the roller speed,11°for the tooth angle,and 22mm×25mm for the mesh aperture,which allow the broken rate to be 1.81%,the impurity rate to be25.02%,and the loss rate to be 0.52%.（2）From the R7 to R8 stage of soybean,the moisture content of stem was decreased,while the lignin and cellulose contents of stem increased.The shearing force of stem ranged from 314.33 N to 435.67 N in intercropping soybean and 642.33 N to 844.67 N in monocropping soybean.The moisture content of stem was lower in monocropping soybean compared with intercropping soybean,conversely,the shearing force,lignin and cellulose contents were higher in monocropping soybean at the same sampling stage.In addition,the results of regression analysis showed a significant negative-correlation between the shearing force of stem and the moisture content,while the shearing force was positively correlated with lignin and cellulose content.Therefore,it is necessary to take the power distribution of cutting table into consideration to reduce the yield loss rate in the development of intercropping soybean harvester.（3）Mechanized harvest of soybean started from the R7 stage,the 100-seed weight ranging from 23.77g to 25.33g.As the harvest time progressed,the 100-seed weight increased first and then decreased.The 100-seed weight and grain yield were the highest when harvested on November 3rd.The loss rate resulted by cutting table was increased,but the loss rate resulted by threshing and cleaning,broken rate and impurity rate decreased.The largest reduction of branches moisture content was at80.96%,and the lowest reduction of stem was at 52.08%.The results of multiple linear stepwise regression showed that the loss rate was positively correlated with the water content of shell,so was the broken rate with the seed moisture content.We established a model to analysis the relationship between loss rate,broken rate and plant moisture content.The results showed that the moisture content of shell ranging from 12.70%to 19.57%,and that of seed lower than 25.55%were optimized for mechanization harvest.In terms of plant morphology,the mechanized harvesting was suitable when all leaves fell off,stalk lost moisture,and pods turned into yellow.（4）The variation of agronomic characters in intercropping soybean materials is relatively abundant.Number of branch has the largest variation coefficient up to74.57%,and the smallest is nodes number on main stem,only 17.49%.The correlation analysis showed the loss rate of cutting table was negatively correlated with plant height,height of bottom pod,nodes number on main stem,height of branch,and height of the longest branch.Multiple linear stepwise regression showed that the loss rate of cutting table was closely correlated with three agronomic characters,and the negative effect factors ranked as follows:nodes number on main stem>height of branch>height of bottom pod.Path analysis showed ranking of direct effect to loss rate of cutting table:nodes number on main stem>height of branch>height of bottom pod.The model of the loss rate with agronomic traits showed the suitable morphological characteristics of intercropping soybean for mechanized harvest:nodes number on main stem more than 12,branch height higher than 12.41 cm,and bottom pod height greater than 13.82 cm.