| Soil quality of cultivated land is one of the key factors to ensure grain yield and quality.China's cultivated land has a long-term high load output,soil fertility has been seriously reduced,the speed of soil erosion has been intensified,the area of soil erosion has been expanding year by year,and the growth of grain yield is in a bottleneck period.Conservation tillage is a new agricultural farming system and technology system with soil quality as the core,whose goal is to protect,improve and utilize effectively natural resources,and to further achieve sustainable agricultural production in the sense of economy,ecology and society.Stubble mulching is an important part of conservation tillage technology,which can improve soil structure,increase the content of soli organic matter,improve the ability of soil drought resistance and water conservation,reduce wind erosion and water erosion,and reduce the amount of chemical fertilizer and pesticide.The core of stubble mulching and returning is the technical mode and equipment.Aiming at the characteristics of the unique cold temperate continental monsoon climate and the current situation of large-scale and intensive production in Heilongjiang Province,it is very important to develop a stubble treatment device,which can be suitable for full coverage of corn stubble condition,match wide and in-situ no tillage sowing and fertilizing device and realize the functions of stubble surface covering and no tillage sowing and fertilizing in order to protect soil and increase grain yield.In this paper,in the condition of full coverage of corn stubble in Heilongjiang province,based on the principle of high-speed,wide-range,in-situ no tillage sowing and stubble mulching and returning,the key technologies and devices of stubble treatment,including straw cleaning technology,stubble removing technology,stubble multi-stage lateral ejecting and transporting technology and stubble breaking,throwing,regulating and controlling technology were studied.Theoretical analysis,mathematical modeling,dynamic simulation,discrete element simulation and other methods were used to deeply explore and research the key mechanism of stubble treatment.On the basis of it,quadratic regression orthogonal rotation center combination test,orthogonal test,fuzzy comprehensive evaluation and other methods were used to optimize the structure and working parameters of stubble treatment device and key parts,which laied a foundation for the design of stubble treatment device based on theory and experiment.The main contents and results are as follows.(1)Technical scheme design of lateral multi-stage stubble treatmentAiming at farming mode of no tillage sowing and stubble mulching under the condition of full remain of corn stubble in spring sowing season in cold region of Heilongjiang Province,a new multi-stage ejection lateral movement stubble treatment technology plan matching wide and in-situ no tillage sowing and fertilizing device was designed,which can realize the functions of straw cleaning,stubble removing,lateral movement of stubble,moderate breaking of stubble and stubble mulching and returning in the whole width between ridges in corn stubble field,creating conditions for the seeding device to plant seeds in moist,well permeable and straw barrier-free soil,thereby forming a high-quality seed bed structure with solid bottom and virtual top.In addition,the problems that ground temperature rising was hindered and crop yield decreased were solved effectively,which were caused by that all corn stubble was returned to field,covering the soil surface in spring in cold regions.Moreover,the technology plan mentioned above can match with the existing wide range sowing and fertilizing device,realizing the compound operation at the speed of more than 10.8 km/h.(2)Research on the axis-fixed type seed bed construction deviceIn this paper,a kind of axis-fixed type seed bed construction device was designed,which could complete the functions of straw cleaning,stubble removing and stubble lateral movement under the condition of full coverage of corn stubble.The mechanism of straw cleaning and stubble removing was explored,and the structure and working parameters affecting the working performance were deeply analyzed and experimented.First of all,in order to explore the influence of lateral straw cleaning cutters on straw winding degree,vibration intensity,power consumption and straw covering uniformity in the device operation process,the mechanism of lateral straw cleaning was analyzed,the mathematic model of the sliding section working curve was developed and the design of the sliding section working curve was completed,and the key structure and working parameters affecting the working performance of lateral cleaning-straw blade were determined.Four factors with three levels orthogonal experiment method was applied,the initial radius,initial sliding angle,knife roll angular speed and device operation speed were selected as the influencing factors,and the straw winding degree,vibration intensity,equivalent power consumption and straw covering uniformity were used as evaluation indexes to optimize the structure and working parameters affecting the lateral straw cleaning cutter operation performance.The results showed that under the condition of that the initial radius was 200mm,initial sliding cutting angle was 30°,knife roll angular speed was 42 rad/s,and device operation speed was 7.2km/h,straw winding phenomenon did not occur,the vibration intensity was 159 m/s~2,the equivalent power consumption is 4.9 k W,and straw covering uniformity was 0.075.Compared with the existing lateral blade,the vibration intensity was reduced by 46.5%,the equivalent power consumption was reduced by 29.6%,and there was no blockage phenomenon in the working process;Secondly,aiming at the problems of the blocking of soil touching parts of sowing and fertilizing device and the reduction of sowing quality caused by corn stubble and fibrous root in the process of in-situ no tillage sowing and fertilization,a lateral cleaning-stubble blade for removing corn stubble was designed.The operation processes of the lateral cleaning-stubble blade such as stubble cleaning,movement,throwing,etc were analysed,the mathematical model of tangent edge curve was developed,and finally,the lateral cleaning-stubble blade structure and the tangent edge curve were designed,key structure and working parameters affecting its operation performance were determined.Three factors and three levels orthogonal experiment and fuzzy comprehensive evaluation method were used,the stubble clearing angle,tangent edge width,and lateral stubble blade angle velocity were selected as the influencing factors,and stubble cleaning rate,soil disturbance rate,and equivalent power consumption were selected as the performance indexes to optimize the structure and working parameters affecting the operation performance.The results showed under the condition of that the cutting speed was 7.2 km/h,lateral cleaning blade angle was 0.86 rad,the cutting edge width was 50 mm and lateral stubble blade angle velocity was52 rad/s,the stubble removal rate was 94.3%,the soil disturbance rate was 54.3%,and the equivalent power consumption was 3.4 k W.(3)Mechanism analysis of single stage movement of corn stubble and research on rectifierIn order to solve the problem of multi-stage ejection and lateral movement process retention of corn stubble,which could affect the straw cleaning rate in the sowing and fertilizing area,and reduced the machine working quality and efficiency.Based on the analysis of the movement law of single-stage spreading of corn stubble,a rectifier for stubble movement was designed,and the key structure parameters affecting the working performance of the deflection device were determined.Based on the quadratic regression orthogonal rotation center combination experiment method,the virtual simulation parameters combination optimization experiment was carried out on the experimental platform of rectifier built in EDEM software,with the entry angle,guiding flow angle and guiding flow radius as the experimental factors,and the straw cleaning rate and straw cleaning consistency between rows as the performance evaluation indexes,the results showed that each factor has the performance evaluation index.The results showed that combination of parameters was optimal with entry angle at 60°,guiding flow wrapping angle at 105°and rectification radius at 425 mm.As a result,the straw cleaning rate was 92.4%,and the straw cleaning consistency between rows was 93.2%.According to the optimization parameters combination obtained from virtual simulation,the field validation experiment was performed after guiding flow device was processed,and the resulted showed that the straw cleaning rate was93.1%,and the straw cleaning consistency between rows was 92.5%,which was basically consistent with the virtual simulation experiment results.(4)Research on stubble breaking and throwing device based on lateral straw cleaning principleAiming at the wide range operation of multi-stage ejection and lateral movement for corn stubble,a scheme that corn stubble was moderately broken,threw compound,and returned to the soil surface between ridges was proposed,and a stubble breaking and throwing device was designed,which can realize the operation procedures such as picking,breaking,throwing,etc.Relevant mathematical model was established based on the mechanism of stubble picking,breaking and throwing of stubble.It could be concluded that the main factors affecting stubble picking were the rotary diameter and the rotation angular speed of the long stubble breaking cutter.The main factors affecting the stubble breaking rate were the length,the weight,the cutting edge angle,the cutting edge thickness,the position of mass center and the rotation angular speed of the long stubble breaking cutter,and the rotary radius of the cutter seat.The main factors affecting stubble throwing were the rotary diameter and the rotating angular velocity of the long stubble breaking cutter,and the length,the width and the inclination angle of the negative pressure blade.According to the key structure and working parameters affecting the breaking performance of stubble,the discrete element simulation experiment was carried out.The cutting edge angle,the cutting edge thickness,the weight and the rotation angular speed of the long stubble breaking cutter were taken as the experimental factors,the stubble picking rate,the stubble breaking rate and the power consumption were taken as the performance evaluation indexes.When cutting edge angle was 15°-18°,the cutting edge thickness was 0.51-0.62 mm,the weight was 0.3 kg,and the rotating speed was 1415 r/min,the result was optimal,the stubble picking rate was more than 80%,the stubble breaking rate was more than 80%,and the power consumption was less than 7 k W.In this paper,the CFD-DEM coupling method was used to analyze the movement characteristics of corn stubble particle group in the stubble breaking and throwing device.It was determined that the negative pressure blade was conducive to increase the stubble picking,movement and throwing efficiency,and could realize the surface covering and returning of corn stubble between ridges.In order to explore the influence of structure parameters of negative pressure blade on stubble picking rate,straw covering consistency between ridges and power consumption,a three factor and five level quadratic regression orthogonal rotation center combination experiment method was adopted.The length,the width and the inclination angle of negative pressure blade were taken as experimental factors,and the stubble picking rate,straw covering consistency between ridges and power consumption were dependent variables.The results showed that when the width of negative pressure blade was 27.5-41 mm,the inclination angle of negative pressure blade was 121°-127°and the length of negative pressure blade was 53 mm,the stubble picking rate was more than 85%,the straw covering consistency between ridges was more than 75%,and the power consumption was less than 7.6 k W.(5)Effect of stubble mulching technology on soil physical structure and crop yieldIn order to explore the effect of stubble mulching technology between ridges on soil structure characteristics of the plough layer and crop yield in Heilongjiang Province,the field positioning comparative experiment was carried out for continuous three years in Xinxing Village(the third accumulated temperate zone)of Beilian Township,Keshan County,Qiqihar city from 2017 to2019.The effect of five tillage techniques on dependent variables including soil bulk density,soil porosity,soil organic matter content and crop yield were analyzed.The results showed that there was no significant difference between MRNT,SRNT and SCST on soil bulk density of 0-25cm soli layer,but it was significantly different between SONT and MRNT,SRNT and SRNT,and significantly different between CK and MRNT,SONT and SRNT.There was no significant difference on soil bulk density of 50-75cm soil layer among MRNT,SONT,SRNT and SCST,and between SONT,SRNT,SCST and CK,but there was significant difference between MRNT and CK.There was no significant difference between MRNT,SRNT and SCST in soil porosity of 0-25cm soil layer,but there was significant difference between SONT,CK and MRNT,SRNT and SCST,and there was no significant difference between SONT and CK.For the effect of soil porosity in 25-75 cm soil layer,there was no significant difference between MRNT,SONT,SRNT and SCST,but there was significant difference between CK and MRNT,SONT,SRNT and SCST For the effect of soil organic matter content in 0-50 cm soil layer,there was no significant difference between MRNT,SRNT and SCST,but significant difference between SONT,CK and MRNT,SRNT and SCST,and there was no significant difference between SONT and CK.For the effect of soil organic matter content in 50-75 cm soil layer,there was no significant difference among MRNT,SONT,SRNT,SCST and CK.Soil bulk density,soil porosity and soil organic matter content of 0-50 cm soil layer were affected by different stubble mulching and returning to field cultivation modes.MRNT and SRNT had better effect on improving soil structure,MRNT,SRNT and SCST had better effect on improving soil organic matter content,MRNT and SRNT had significant yield increase effect.In 2017,there were significant differences between MRNT,SRNT and SONT,SCST,but there was no significant difference between MRNT and SRNT.The corn yield of MRNT and SRNT increased by 12.6%and 10.6%respectively compared with that of CK;There were significant differences between MRNT,SRNT,SCST and SONT,CK in 2018,and the yield of MRNT and SRNT increased by 7.6%and 7.2%respectively compared with that of CK;In2019,there were significant differences between MRNT,SRNT,SCST and SONT,CK,the yield of MRNT and SRNT increased by 9.2%and 10.4%respectively compared with that of CK. |
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