Mechanical subsoiling is an effective practice to promote better water infiltration and crop root development. The bending subsoiling tool (BST) is a primary subsoiling tool and is used to remove soil compaction and restore soil productivity. In this study, a discrete element model was developed and validated using laboratory soil bin tests to investigate the effects of the mounting angle of the BST (5°–33°) on soil disturbance behaviors and draft forces. The results show that the upheaval, failure and fragmentation of soil was achieved by successive shearing, uplifting, extrusion, tension and turning actions from the cutting share and cambered shank of the BST. Increasing soil depths gave smaller soil disturbance ranges in lateral, forward and upward directions. With an increase in mounting angle, both the draft force and soil rupture distance ratio initially decreased and then increased, whereas the soil loosening efficiency initially increased and then decreased. Overall, increasing the mounting angle of the BST from 5° to 33° gave a greater soil surface flatness that increased rapidly when the mounting angle increased from 26° to 33°. Appropriately increasing mounting angle of the BST from 5° to 26° could lift more moist soil from the deep seed and middle layers (5.0–15.5% increase) into the shallow seed layer (depth of <50 mm) without seriously affecting the mixing of the deep layer and other layers. Considering both the soil disturbance characteristics and draft forces, a mounting angle of 26° appeared to outperform the other angles.

Discrete element modelling (DEM) parameters are of great importance for the accurate prediction of soil properties and disturbance. This study aimed to provide an efficient method for accurately determining the DEM parameters of a paddy soil with a high moisture content (45.66%). The DEM parameters of the paddy soil modelled using the Hertz–Mindlin with JKR contact model were determined by using the Plackett–Burman (PB), steepest ascent, and central composite tests. The accuracies of the developed DEM models were evaluated using actual slumping tests. Based on the PB test, the surface energy of soil, coefficients of soil–soil rolling friction, and coefficients of soil–steel static friction exerted larger influences on the overall relative error (δ_ZH). The optimization results showed that to achieve a minimum δ_ZH (5.96%), the surface energy of soil, the coefficients of soil–soil rolling friction, and the coefficients of soil–steel static friction should be 0.808 J m⁻², 0.11, and 0.6, respectively. The optimized DEM model had an overall relative error of 7.27% with a coefficient of variation of 1.32%, indicating that the DEM parameters of the calibrated paddy soil had good accuracy.

Oil peony is an important oil crop that is primarily sown by using artificial methods at present. Its seeder encounters the problems of low efficiency of seeding that significantly limits the highly efficient mechanized production of high-quality peony oil. In this study, Fengdan white oil peony seeds were used as the research object and repose angle as the response value to establish a discrete element model (DEM) and parameter calibration. The range of parameters of oil peony seeds was first obtained through an experiment, and their repose angle was obtained by an inclinometer. A three-dimensional DEM of oil peony seeds was then established. The Plackett–Burman (PB) test was utilized to screen the parameters that had a significant influence on the repose angle, and the steepest ascent (SA) test was applied to determine their optimum range of testing. Following this, based on Box–Behnken (BBD) test results, a second-order regression model between the important parameters and the repose angle was constructed. Finally, the absolute minimum difference between simulated and measured repose angles was utilized as the objective of optimization to obtain the following optimum combination of parameters: The values of the seed–steel collision recovery coefficient (CRC), seed–seed static friction coefficient (SFC), seed–steel SFC, and seed–seed rolling friction coefficient (RFC) were 0.704, 0.324, 0.335, and 0.045, respectively. This optimal combination of parameters was confirmed through simulations, and the error between simulated and measured repose angles was only 0.67%, indicating that the calibrated DEM of oil peony seeds was reliable.

The discrete element computer simulation method is an effective tool that enables the study of the interaction mechanism between the pulping components and the paddy soil during the paddy field pulping process. The findings are valuable in optimizing the parameters of the paddy beating device to improve its working quality and efficiency. However, the lack of accurate soil models for paddy soil has limited the application and development of the discrete element method in paddy pulping research. This study selected the Hertz-Mindlin with Johnson-Kendall-Roberts discrete element model for the pre-pulping paddy loam soil and used the slump error as the test index to select nine parameters, including soil Poisson’s ratio and surface energy, as test factors to calibrate the model parameters. The Plackett-Burman test identified soil shear modulus, surface energy, and soil-iron plate static friction coefficient as significant factors affecting the test index. The steepest ascent test results determined the test range of the above parameters. The Box-Behnken test obtained the regression model between the significant factors and the test index, and the regression model was optimized using the slump error as the target. The optimal combination of parameters was surface energy of 3.257 J/m², soil shear modulus of 0.709 MPa, and static friction coefficient between soil and iron plate of 0.701. The slump simulation test using this combination of parameters yielded an average slump error of 2.04%. The collective results indicate the accuracy of the calibrated discrete element simulation parameters for paddy loam soil. These parameters can be used for discrete element simulation analysis of the paddy pulping process after paddy field soaking.

Agricultural and Biological Engineering

Subsoiling is an effective practice to promote better soil water infiltration and crop growth. The information regarding the variation and persistence of subsoiling effects with different soil disturbance on soil properties and crop growth was absent in previous research. In this study, the effects of wing mounting height (h) (75–155 mm) during subsoiling on soil disturbance at various layers, soil properties and crop performance were investigated using in situ field experiments from 2019 to 2021 in winter wheat–summer maize rotations. The experimental field soil was covered with crop stubble and crop straw was removed before subsoiling or sowing the next crop. The analysis of variance (ANOVA) was used to assess different subsoiling treatment effects on tested variables, including soil moisture content, bulk density, plant diameter, plant height, dry root weight, root number, yield, and yield components of crops. Means between subsoiling treatments were compared using Duncan’s multiple range tests. Based on ANOVA outputs, the h significantly (p < 0.05) affected soil moisture content in the first growing season of winter wheat (WW1), soil bulk density, number of roots and panicle number and grain yield of WW1, and thousand kernel weight (TKW) of both WW1 and summer maize (SM). Decreasing h overall gave better soil properties and crop performance. Decreased subsoiling effects were found on aspects of insignificant difference in subsequent grain yield of SM and winter wheat in the second growing season (WW2). These findings had implications for designing higher-performance winged subsoilers, as well as selection of subsoiling frequency.