DISCRETE ELEMENT MODELING AND PARAMETER CALIBRATION OF THE WHEAT ROOT–SOIL COMPOSITE

Abstract

Due to the anisotropy and small size of wheat roots, as well as the neglect of shear process effects on mechanical properties in existing wheat root-soil composite (WRSC) models, the establishment and parameter calibration of WRSC models remain inaccurate, hindering the precise analysis of the microscopic effects of furrow openers on WRSC during no-till sowing. This study aimed to develop an accurate and reliable WRSC model based on the discrete element method (DEM) using rapid particle filling and the Hertz-Mindlin with bonding contact model. Plackett-Burman tests identified particle shear modulus, inter-particle bonding radius, and bonding stiffness as significant factors affecting the ultimate shear force of wheat roots. Steepest ascent tests narrowed the optimal parameter ranges, and Box-Behnken test results were used to establish a quadratic regression model, leading to the optimal parameter combination: particle shear modulus of 7.96 MPa, inter-particle bonding stiffness of 4.13 GN/m³, and bonding radius of 0.32 mm. Actual and simulated shear tests on WRSC were conducted, and key parameters between wheat roots and soil particles were calibrated via steepest ascent tests with the ultimate shear force on the cutter as the target value: static friction coefficient of 0.8, bonding stiffness of 11 MN/m³, and critical stress of 11 MPa. Validation showed a relative error of 7.35% between simulated and actual shear resistance, indicating that the proposed WRSC model and parameters can effectively simulate field operations such as furrowing and rotary tillage.