| Black soil is an important soil resource,and the black soil in Northeast China,concentrate most of the black lands.It is also one of the four major regions of black land in the world and is an important commercial grain base of China.Strengthening the protection and utilization of black soil in major grain producing areas is of great significance to ensure Chinese food security.It is for the reason that excessive reclamation and neglect of the combination of planting and rearing in the traditional cultivation and utilization of black land led to thinning of the black soil layer,decreased soil organic matter,and intensified wind and water erosion,which poses a severe challenge to national food security.In order to effectively protect the black land,the"giant panda in the cultivated land",the majority of scientific and technological workers actively explore suitable technical models and promote the protection and utilization of black land in an orderly manner.Conservation tillage technology is a green agricultural tillage technology with mechanization as the means and"cover no-tillage,soil and water conservation"as the essence.It has positive benefits in reducing soil wind erosion and water erosion,increasing soil fertility and improving soil water storage and moisture conservation ability.As a kind of straw treatment and water storage tillage construction method in the protective tillage technology system,the technology of straw incorporation returning to the field adopts the combination of pine harrow and ground preparation machine to work directly on the cultivated land covered with full amount of straw after the corn machine is harvested in autumn to complete the deep mixed burying of straw.The technology of straw incorporation returning to the field effectively solves the problems of slow ground temperature rise and low rot rate of corn straw in spring sowing period,and has the advantage of sustainable development of green agriculture.In this paper,based on the actual needs of black land protection,mechanical design,discrete element and finite element simulation,indoor soil trough test and field test were used to study the straw incorporation returning technology suitable for the northeast black soil area.The key components of the technology are studied,so as to provide effective solutions for the protection of black land.This paper provided experimental basis and equipment support for the research and demonstration of overlying straw incorporation returning technology.The main research contents include the following aspects:(1)Research on soil moisture infiltration and maize seedling growth caused by straw returning in straw incorporation returningTo explore the effect of corn stalks on soil moisture infiltration performance in straw incorporation returning,according to the Box-Behnken test principle and by using the software of Design Expert.The indoor soil column simulation test was used to determine the depth of mixed stover and the quantity of mixed stover,the length of stover as the influencing factor,and the water seepage amount as the index to carry out the quadratic regression orthogonal test with three factors and three levels.By establishing a response surface mathematical model,the influence of various factors on soil water infiltration performance was analyzed,and the influencing factors were comprehensively optimized.The test results showed that the water seepage amount reached the optimal value when the depth of mixed stover is 20 cm,the quantity of mixed stover is 80%,and the length of stover is 9 cm.The effects of straw returning in straw incorporation returning on maize seedling stage and seedbed characteristics were revealed,and different straw burial depths,different straw burial amounts,and different repression pressures were evaluated on maize seedling stage growth and seedbed characteristics.The test indicators include:corn emergence rate,average emergence time,corn plant height and stem diameter,corn root dry weight,corn plant stem and leaf dry weight,soil firmness and soil moisture content.From the analysis of the test results,it can be seen that the depth of mixed straw,the amount of mixed straw,and the repression force have significant effects on the emergence rate of corn,average emergence time,corn plant height and stem diameter,corn root dry weight,and corn plant stem and leaf dry weight.Besides,it had no significant effect on soil firmness and soil moisture content.Compared with the suppression strength of 22 k Pa,the growth characteristics of maize with the suppression strength of 12 k Pa were better,and the high degree of compaction had affected the root extension of the plant.When the quantity of mixed stover increased from 60%to 80%,the soil firmness decreased but the soil moisture content gradually increased,indicating that burying straw in the soil could reduce the soil firmness and enhance soil water holding capacity.(2)Research on simulation model of soil-straw mixture and design and experiment of ball-type subsoilerTaking the soil-straw mixture in the black soil area as the research object,a discrete element simulation model of the soil-straw mixture was constructed.The method of combining physical test and EDEM simulation test was adopted,and the contact model of Hertz Mindlin with JKR was used to calibrate the contact parameters of discrete element simulation.The actual accumulation angle of the soil-straw mixture was determined by the method of cylinder lifting,and the parameters that had a significant effect on the accumulation angle were screened out by the Plackett-Burman test in the software of Design Expert.Furthermore,the optimal value range of the four parameters was determined through the steepest climbing test,and the optimal parameter combination was determined according to the Box-Behnken test principle:straw-soil rolling friction coefficient is 0.16,soil-soil rolling friction factor is 0.24,soil-steel static friction factor is 0.75,soil JKR surface energy is 0.67 J/m~2.Combined with discrete element analysis and mechanical design,the ball-type subsoiler structural scheme and structural parameters of each component was determined and a mechanical model of the subsoiler was established.Based on the discrete element method,the soil disturbance performance and tillage of the ball-type subsoiler and traditional subsoiler was analyzed.By using the indoor soil tank test,the soil disturbance performance and tillage of the ball-type subsoiler and traditional subsoiler at different speeds was analyzed.The result showed that the ball type subsoiler could reduce the tillage resistance by 8.74%?13.38%and the subsoiling stability coefficient is above 93%compared with the traditional subsoiler.(3)Structural design and finite element analysis of bionic disc harrowIn order to solve the problem of low cutting efficiency of single stalk buried in the disc harrow,based on the principle of bionics,the analysis was carried out from the perspective of the motion of the golden cicada.The MATLAB software was used to fit and extract the outer contour curve of the golden cicada,and the image processing module of the MATLAB software was used.To convert the outline image of the golden cicada into a mathematical model to determine the accurate function coordinates,and used the overall method to perform curve fitting,which is used to design the notch curve of the bionic disc harrow blade,and design the bionic disc harrow blade.The motion of the bionic disc harrow blade mechanism was explored,and its tillage resistance during operation was analyzed.The finite element software ANSYS/LS-DYNA was used to analyze the influence of the bionic disc harrow blade on the cutting performance of straw and soil,the configuration of the bionic disc harrow blade on the combined soil preparation machine was optimized,a dynamic performance test experiment of the bionic disc harrow blade was built.The bench was used to analyze the quantity of mixed stover after operation at different operating speeds,different raking angles,and different raking depths.The test results showed that,The operating speed of the machine tool is 7 km/h,the angle of the blade is 25°,the depth of the blade is 16 cm,and the straw returning rate in the maximum value of 64.78%.(4)Integration of key components of straw incorporation returning and test of combined ground preparation machineBased on the research results of straw incorporation returning and the key components of subsoiler and bionic disc harrow,a combined ground preparation machine suitable for the mulch tillage was designed and a prototype test was carried out.The field test results showed that the machine can complete a number of processes such as cutting stubble,burying,subsoiling,crushing,and pressing,and complete the ploughing operation of the field with full straw coverage.The effects of different machine operating speeds,raking depths,and subsoiler on the straw coverage rate and straw returning rate were studied.The interaction between different factors was analyzed through the response surface graph,and the software optimization solver was used to obtain:the operating speed of the machine tool was 9 km/h,the depth of the rake blade was 13 cm,the depth of the subsoiler was 30 cm,and the straw coverage reached the maximum value of 60.13%,the straw returning rate reaches the maximum value of 79.80%.The optimized parameters were verified by experiments,and the relative error between the optimal value and the optimal value of the model was less than 5%.The research results can provide theoretical reference for the straw incorporation returning technology and optimization and improvement of the machine. |
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