| Rapeseed is an important oil crop in China,and the Middle-Lower reaches of the Yangtze River,whose main cropping pattern is rice-rapeseed or rice-rice-rapeseed rotation,are the main production areas for rapeseed.However,there exists some problems such as shallowing of plough layer,degradation of soil quality,deterioration of till ability,and imbalance of nutrients in plough layer caused by the annual flood-drought rotation and short fallow period.To avoid the influence of the thinning of the tillage layer,thickening of the plow bottom layer and soil hardening caused by the annual use of traditional mechanized tillage in the middle and lower reaches of the Yangtze River on the crop root growth,this study developed a drive-type plough-rotation combined tillage machine based on the requirements of tillage operations.The machine is mainly composed of a drive disc plough group,a rotary tillage machine component,a shoe-like sharp-angle ditch plow,etc.It can return the full straw back to the field,level the crushed soil,and form a reasonable arable layer suitable for rapeseed growth.The main research content and conclusions of this study are as follows:(1)The physical and mechanical parameters of soil and rice straw in the Middle-Lower reaches of the Yangtze River were tested.The results showed that the thickness of plough layer was 135～182 mm,the thickness of the plow bottom layer was 106～163 mm,the average soil solidity was 735.0～1091.6 k Pa,the soil moisture content was 22.86%～32.46%,the height of rice straw was 386mm,the surface straw amount was 1106.7g/m~2,and the straw moisture content was 65.36%.All these data indicated that the soil moisture content,height and amount of rice straw were higher in the rice-rapeseed rotation areas of the Middle-Lower reaches of the Yangtze River.the rice straw had to be reasonably treated before rapeseed planting to improve the passing ability of the tillage machines.(2)The growth status of rapeseed roots during different growing periods and the growth characteristics of rapeseed roots under different tillage modes were tested.The relationship between the reasonable tillage layer and root growth was also analyzed.It could be found that the majority of the vertical roots were shallowand,and the lateral root distributed widely in the soil profile.The roots were basically established from the bolting gestation bud stage to the flowering pod stage without excessive root branches and length growth,making it clear that the annual adoption of a single rotation tillage mode would inhibited the root deep growth,which is not conducive to the growth of rapeseed plant.At the same time,the tests to the growth characteristics of rapeseed root system under different tillage modes showed that the secondary root number of rapeseed had little difference between the rotary tillage,deep plowing tillage,and no-tillage.But the taproot was deeper in the rotary tillage compared with the deep plowing tillage.This indicated that both shallow rotation and deep turning could improve the quality of the soil plough layer to make the soil fertility evenly distributed and improve the absorption of water and fertilizer for the promoting of rapeseed root system and rape growth.The effects of deep turning on these factors is more obvious.(3)The drive-type plow-rotation combined tillage machine was developed,and the planting mode of plow tillage followed by rotary tillage was proposed to form a process plan for a reasonable tillage layer of rapeseed beds with"deeply stubble,upper pine and lower tightness".The overall structural parameters and working parameters of the driven plough-rotary combined tillage machine.The working width of the whole machine was2300mm,the ploughing depth was 200～230mm,the rotary tilling depth was 100～150mm,the ditch depth was 150～250mm,and the ditch width was 200～400mm,which meets the agronomic requirements of rape cultivation.(4)The design and analysis of the key devices of driven plough combined rotary tillage machine were carried out.The contents and conclusions were as follows:(1)The kinematics and dynamics analysis of the interaction between the driven disc plough group and the soil were carried out.The effects of plough depth,the working declination,and the working speed on the working resistance and power consumption were studied.A special disc whose radius and curvature radius were 305mm and 610 mm,respectively,was selected.Based on the analysis results,the working width of the disc was 286～300mm,the working declination was 30°,and the rotation speed was 135r/min.The disc plough group adopted three opposing arrangements on the left and right to improve the stability.(2)According to the structure layout of the whole machine and the agronomic requirements of rapeseed cultivation,the height of the shoe-like sharp-angle ditch plow was 300mm,the width of the upper part of the plow body was 400mm,and the width of the bottom was200mm;Based on the principle of drag reduction characteristics,a circular arc-shaped cutting edge curve with a cutting edge starting angle of 23°and an ending sliding angle of45°was designed;a three-sided wedge model was established to analyze the plow tip,and it was determined that the plow body entry angle was 30°and the opening angle of the plow tip was 60°;Through the kinematic analysis of the interaction between the shoe-like sharp-angle ditch plow and the soil,the relationship between the advance speed of the plow body and the depth of the ditch,the coefficient of dynamic friction of the soil,and the angle of bulldozing were studied,respectively.(3)According to the kinematic analysis of the rotary blades,working conditions,and structural layout requirements,the IT245 rotary blades was used.The rotary blades were arranged in the same direction with double-headed spirals whose outermost blades were arranged symmetrically with 22 rotary blades.(5)The field experiments of the driven plough-rotary combined tillage machine were carried out,and the operation quality was compared and analyzed with the single rotary tillage machine and passive plough-rotated combined tillage machine.The results showed that the driving disc plough could effectively cut straw,and cooperate with the rotary tilling component to bury the straw and soil.At an average depth of 150mm or more,a loose layer of crushed soil could be formed at the plough depth of 200～30mm,which could meet the requirements of reasonable tillage layer of rapeseed bed.The whole machine worked well.The width of the single box surface was 852mm～956mm,the stability of the tillage depth was more than 90%,the flatness of the surface was 15.25～18.60mm,and the vegetation coverage rate was 92.3%.All of these indexes were better than that of the control groups.The soil crushing rate of the designed machine was 80.52～88.43%,which were slightly lower than the control groups.It indicated that the rotation speed of the rotary tillage component was limited by the speed ratio of the zigzag gear box leading to the low speed of blades roller and soil crushing rate.The width and depth of the ditch produced by the shoe-like sharp-angle ditching plow was 200～400mm and 205.6～250.0mm,respectively.The ditch wall and ditch bottom were flat,and the ditch width stability and ditch depth stability were over 90%.Comprehensive analysis showed that the performance of the driven plow-rotary combined tillage machine could meet the agronomic requirements of rapeseed planting. |
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