**1. Introduction**

Rotary tillers are widely used in the seed bed preparation segment of agricultural production [1]. The study demonstrated that a rotation tillage depth of 200 mm could fully mix the straw into the soil and significantly improve the sowing quality and wheat yield [2]. However, there are a significant number of challenges, such as insufficient tillage depth (less than 150 mm), unsatisfactory straw burying effect (low straw burying rate, insufficient straw burying depth), high power consumption, etc., in rice-wheat rotation areas. Moreover, long-term shallow rotational tillage results in a thinning and low-fertility soil tillage layer, which in turn leads to lower crop yields [3]. Simultaneously, inadequate straw mulching resulted in the distribution of straw in the upper part of the tillage layer, which allowed gaps between the top and bottom of the soil tillage layer, thus leading to segregation of the soil. It is easy to cause the next crop to fall dry and die, reducing the seeding rate in the cultivation area of two crops a year [4]. The concentration of a

huge number of agricultural machines in the busy season, coupled with the increase in power consumption, is prone to air contamination [5,6], which is not in accordance with the concept of green development of agricultural machinery and decelerates the achievement of the carbon peaking and carbon neutral development goals.

To meet the above challenges and realize deep plowing, four solutions are applied in production practice as follows. (1) Increase the radius of the rotary blade. The test proved that the machine could achieve a tillage depth of 300 mm, but there are problems with the huge mechanism, heavy tillage load, and low reliability of the machine [7]. (2) Double-axis front shallow and behind deep rotary tillage. The machine sets two rows of knife rollers at the front and behind, the former for the first operation, the latter again, and finally, two operations to achieve deep tillage. In this solution, the soil accumulates in the gap between the front and rear blade axes of the machine, which interferes with the soil and prevents the rear blade axes from sinking into the ground. Moreover, the structure is complicated and heavy and consumes much energy [8,9]. (3) Submerged soil reversal rotary tillage. This solution is a tillage method in which the cutter shaft is reversed and submerged below the ground surface. This form of mechanism resulted in the transmission box and frame being difficult to enter the soil and congestion problems [10–17]. (4) Diagonal submerged soil reversal rotary tillage. This solution effectively solves the problem that the transmission box cannot enter the soil in the above two solutions. The blade roller is angled in the horizontal plane during the operation of the machine, and tillage is carried out obliquely, but there is a significant lateral force, which is not favorable for the operator to control the direction [18,19].

The structure of key components is unreasonable, and the equipment design lacks academic guidance. The above methods restrict the research progress of deep rotary tillage. The systematic study of rotary blade-soil-straw interaction in deep rotary tillage operation is insufficient, and the design of rotary tiller parameters and whole machine design lack theoretical support. This study synthesizes the research results in related fields of agricultural engineering and conducts research and discussion on the mechanism of rotary blade-soil-straw interaction in deep rotary tillage operation based on the discrete element method. The Discrete Element Method (DEM) is a numerical simulation method for basic research on solving discontinuous media problems [20]. It is different from the Finite Element Method (FEM) for solving continuous media problems. The basic principle of this method is to separate the research object into a set of rigid units. In order to make each unit conform to Newton's second law, the motion equation of each unit is calculated by means of central difference, and the whole motion state and parameters of the research object are obtained. This method is favored by most researchers in the field of agricultural engineering. In this paper, the discrete element method is used to deal with the fact that the soil model is a discontinuous medium [21,22].

We have developed a discrete element model of rotary blade-soil-straw for issues such as soil breakage rate, straw displacement, and power consumption during observation of rotary tillage operation. After that, the prototype was tested according to the 3D model of the machine designed on the basis of this study, and field verification tests were done. Finally, the validity of the model was determined by comparing the results of field tests and simulation analysis. The structural arrangement of the remainder of this article is as follows: Part 2 describes the analysis of the relevant phenomena during the simulation test. Part 3 shows the relevant results. Part 4 presents the discussion of the test. Part 5 concludes and summarizes the whole article. In this study, a blade-soil-straw interaction model was established for rice-wheat rotation. The model can provide a theoretical basis and technical reference for the interaction mechanism between rotary tillage and soil straw, the optimization of machine geometry, and the selection of operating parameters.
