Interaction Relationship Research Of Soil-Root Composite And Narrow Tillage Tools On Natural Grassland

Severe degeneration because of hardened soil-layer occurs in northern arid and semi-arid Leymus chinensis grasslands,which causes low productivity,obstructing the effectivity of grassland ecological service function.Improving the degraded grassland through mechanical methods can achieve a better restoration of steppe ecology system,promoting the development of grassland livestock husbandry.However,problems still exist in degraded grassland mechanization restoration system,such as lacking theoretical relationship research between tillage tools and soil of natural degraded grassland,and lacking technical supports for design and optimization of special equipment and key components used for degraded grassland restoration.In order to solve the problems above,the interaction relationship research of soil-root composite and narrow tillage tools on natural grassland was conducted.(1)The soil-root composite mechanical characteristics and its influence factors of degenerated grassland were studied through field investigations and orthogonal experiments.It was found that the roots were densely interspersed transversely and longitudinally within a depth range of 0?10 cm underground,and formed a complex structure with surrounding soil,accelerating the compaction of subsurface soil-layer with the depth range of 0-20 cm.The experiments results showed that the bulk density,moisture content,and root content had significant influences on the soil-root composite mechanical properties(P<0.05).Sequences and interaction effects existed between these factors.The increase in root content of 10 mg/cm3 caused the unconfined compressive strength increased by more than 14%.The shear strength and compressive strength of the composite decreased with the moisture content increasing,and the high water content level(24.68%)made the composite structure broken easily.(2)The failure characteristics of soil-root composite under the action of narrow tillage tools were investigated through the soil bin tests and field experiments based on the finite element method and dicrete element analysis method.The shear failure power function model under the in-situ vane shear test was established,and the model fitting degree exceeded 96%and 83%corresponding to the soil bin tests and field experiments respectively.The influence on model parameters coming from bulk density,and moisture content were analyzed,so did the roots.The interaction model between very narrow tine(thicness?10 mm)and soil-root composite was established,the failure processes caused by half-moon-shaped stress field and velocity field were founded,and the failure resistance analysis methods and calculation formulas based on the four mechanical components of the contact surfaces between the tine and composite were proposed.(3)The interaction relationship between narrow tillage tools and soil-root composite was investigated based on the theory of mechanical soil dynamics.The testbed was set up,and related soil bin tests and field experiments were conducted.A non-linear positive correlation between the very narrow tine contact area and penetration resistance was found(R2 ? 0.94).The resistance prediction model was built,the linear fit degree of the predicted values and trial values exceeded 93%.Based on the theoretical research,field experiments of narrow tillage tools were carried out.The movements and resistance coming from the on-the-go actions of subsoilers and shank openers underground on the grassland were compared and analyzed,as well as the disturbance on the grassland.Compared with the winged subsoiler,the triangular shank opener with cutting edges was more suitable to break the soil-root composite structure in the soil layer on the grassland.The draft force decreased by 9.09%,and disturbed soil-layer cross section area desreased by 84.2%,within the depth of 10?15 cm,compared to the winged subsoiler.Through theoretical analysis and experiment results,a design and optimization principle of tillage tools used for degraded grassland mechanical restoration,based on factors such as the draft force,rate of overturning on the grassland,disturbed soil-layer cross section area,and specific draft was proposed.The research in this paper provides technical support and theoretical reference for improving the degraded grassland mechanization restoration technology and the design and optimization of dedicated narrow tillage tools,as well as enriching the theory system of soil-tool interaction relationship.