Considering the problems of a low soil fragmentation rate and low straw mulching rate in the traditional rotary tiller tillage mode in the saline-alkali land, the layered stubble and soil crushing rotary tillage knife was designed, and the key structural parameters were determined by the analysis of rotary tillage knife-soil-straw movement. The soil-straw movement behavior in saline-alkali land under different working parameters of rotary tillage was analyzed, and the discrete element modeling of soil-straw-rotary tillage in saline-alkali land was established. In addition, the dynamic process of soil-straw aggregate fragmentation in saline-alkali land from a microscopic perspective was systematically explored. Combined with experimental optimization analysis, the optimum working parameters of the saline-alkali rotary tiller were obtained with a forward speed of 2.02 km/h, a working depth of 178.83 mm, and a rotation speed of 324.48 r/min. To verify the field performance of the machine, the soil fragmentation rate, straw burial rate, and tillage depth stability were chosen as test indices for the field trial. The average soil fragmentation rate was 91.85%, the average straw returning rate was 91.09%, and the average stability of tillage depth was 91.12%, indicating that the designed rotary tiller can effectively improve soil crushing and straw burial in saline-alkali land and meet the basic requirements of high-performance seedbed preparation in saline-alkali land.

In this study, a simulation model of peanut pod particles during harvest in saline soil was tested to calibrate contact parameters. Discrete meta-fill models of peanut pods were generated by a 3D meter and EDEM software. The range of values of contact parameters for peanut pods was measured by conducting collision and other tests using a homemade test rig. The parameters that affect the significance of the simulation process of stacking angle were screened by the Plackett-Burman experiment, the steepest ascent experiment, and the Box-Behnken experiment. An optimization test determined the optimal simulation model parameters: The peanut pods had a Poisson’s ratio of 0.386 and a shear modulus of 3.04 MPa. The coefficient of recovery for pods-pods collisions was 0.335, the coefficient of static friction was 0.854, and the coefficient of rolling friction was 0.346. The coefficient of recovery of collision between the pods-65Mn steel was 0.339, the coefficient of static friction was 0.589, and the coefficient of rolling friction was 0.159. The test results showed a relative error of 0.42% between the stacking angle bench and simulation tests. The results can provide data support for studying the discrete metamaterial characterization of peanut pods.

Considering the problems of low soil crushing rate and poor straw mulching performance of the traditional rotary tiller on saline-alkali soils, a two-axis layered rotary stubble cutter for saline-alkali soils with front-axis positive rotation of the front axle and rear-axis counter-rotation of the rear axle was developed, focusing on the kinetic properties of the straw and soil under positive and counter-rotation. In addition, the most important structural parameters and the arrangement of the front-axis stubble cutting knife and the rear-axis return knife were analyzed and determined. Hertz-Mindlin with bonding was used to create a discrete element model of the agglomerate of implement, straw and soil. The forward speed, horizontal distance and vertical distance were used as test factors, and the straw return rate and soil fragmentation rate were used as test indexes to analyze the straw-soil transport law under different operating parameters from a microscopic point of view, and then Design-Expert was used to conduct the test 1.07 km/h, horizontal distance of 569.55 mm, vertical distance of 176.59 mm. To validate the performance of the two-axis, layered rotary tiller, a field trial was conducted and the results show that the straw return ratio was (91.59±0.41)%, soil fragmentation ratio was (91.90±0.29)% and tillage depth stability was (91.52±0.46)%, which met the requirements for peanut seedbed preparation on saline-alkali land.