Research progress on the simulation model of cultivated loessial soil and anti-sticking and resistance reduction technology of soil-engaging components

Tillage soil is one of the most crucial agricultural resources. Agricultural machinery can continuously interact with the soil during operations. Among them, 278 million acres of arable land in Northwest China account for 13.7% of the total arable land area in China. Loess soil of arable land is widely distributed across six provinces in the middle reaches of the Yellow River in China, with the largest area in northern Shaanxi, followed by central and eastern Gansu. The loess tillage can also suffer the arid and semi-arid climates. However, the loess soil can share the low mechanical stability, resulting in the severe adhesion of the soil-engaging components, such as the soil-cutting shovels, during mechanized ridging. The resulting tillage resistance and machine energy consumption can hinder the emissions reduction and carbon sequestration in agricultural production. It is often required to promote the efficiency of soil-engaging components for low fuel consumption. The adhesion mechanism of the soil-engaging components can also be clarified to reduce the specific soil resistance. Currently, it is difficult to observe the direct micro-interaction between soil-engaging components and soil, due to the limitations in experimental observation. The numerical simulation is then necessary to propose effective anti-sticking and resistance reduction. The constitutive model of the soil is vital to optimize the structure of soil-engaging components, in order to reduce the emissions for the carbon sequestration of agricultural machinery. According to the different algorithms of numerical simulation, the current soil constitutive and contact models can be divided into the finite element method (FEM) and the discrete element method (DEM). But there are a few reports specifically applicable to the tillage loess soil. The layer structure of the loess soil usually presents a granular structure with loose and porous soil. This viscoelastic material can also share the high water and air permeability. The soil particles can fill with water and air, even if there is a small amount of liquid among the soil particles. Thus, the loess soil has stronger cohesion and adhesion, due to the formation of the micro liquid bridges. In this study, the physical and mechanical properties of the loess soil were summarized on the current development of the soil constitutive and contact models using FEM and DEM. Mainstream soil DEM models were compared with the bionic, mechanical, and surface modification in the anti-sticking and resistance reduction for the soil-engaging components. Some challenges were identified in the soil mechanical property, numerical simulation, as well as the anti-sticking and resistance reduction. Advanced experimental technologies were recommended to explore the relationship between microstructures and mechanical behavior. A liquid bridge model was developed suitable for the low saturation soils. The research interest was focused on the compressive plastic deformation and adhesion behavior during the interaction between soil and machinery. Artificial intelligence technology should be used to optimize the machinery's anti-sticking and resistance reduction. These findings can provide valuable technical support and reference for the production challenges, such as the equipment adhesion, high soil-specific resistance, and operational failures caused by soil adhesion and aggregation during mechanized ridging and covering.