Development of universal soil-tool-residue interaction models using the discrete element method (DEM)

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Soil-tool-residue interaction is at the centre of many agricultural field operations. Soil-tool-residue interaction is also one of the fundamental aspects of soil dynamics in agricultural engineering. In a field operation, tillage tools (e.g. plows, chisels, sweeps, etc.) loosen soil for seedbed preparation, or seed openers (e.g. hoes, discs, shovels, etc.) open soil for seed placement. A general term for these tillage tools and seeding openers is “soil engaging tool”. As agricultural fields retain more or less crop residue from previous crops, soil engaging tools interact with both soil and crop residue during field operations. Soil-tool-residue is a complex system, since soil consists of a matrix of discrete particles that are of random, heterogeneous nature, and exhibit sophisticated non-linear behaviours. Such a system cannot be modelled using traditional analytical or numerical methods. THE STATE-OF-THE-ART RESEARCH proposed here will develop a universal model of soil-tool-residue interaction, which can address the complex nature of soil and the existence of residue particles in agricultural fields. In the proposed research program, A NEW, INNOVATIVE NUMERICAL METHOD - DISCRETE ELEMENT METHOD (DEM) - will be used to develop the universal soil-tool-residue interaction model. In the model, basic soil particles will be represented by spherical particles of various sizes. The particle constitutive laws will be defined in such a way that basic particles can form aggregates and have frictional, cohesive, viscous, and deformable behaviours like real agricultural soil (1st INNOVATION). The cohesive behaviour will be described using bonds between soil particles that are in contact. Bonds connect soil particles together, forming soil aggregates, and bonds are breakable under the impact of soil engaging tools. The model must include the microproperties of particles and bonds (such as particle modulus of elasticity, strength of bond, and particle friction coefficient). These microproperties will be defined to be independent of particle sizes, so that they are universal (2nd INNOVATION). As the DEM particle microproperties are not measurable owing to their micro-scales, methods will be developed to calibrate the microproperties. Calibration will be performed using fundamental soil mechanical tests, so that the calibrated microproperties are universal, independent of soil engaging tool (3rd INNOVATION). In the model, a residue particle will be represented by a cluster of basic spherical particles arranged in a way that reflects the shapes of real crop residues. Different sizes of residue clusters will be integrated into soil particles, forming a heterogeneous model domain with a mixture of discrete soil and residue particles (4th INNOVATION). The universal model will be able to predict soil micro dynamics (e.g. forces and displacements of each individual soil particle). Models will be validated using laboratory and field data. DEM modeling of dynamic behaviours of agricultural soil is an emerging field. The universal soil-tool-residue model to be developed will mark a potential BREAKTHROUGH in the area of soil dynamics, in that the model can be used to simulate the micro soil dynamic behaviours for any soil engaging tool, in any soil condition. The simulation results will lead to the emergence of new high performance tillage and seeding tools that consume minimal tractor power and create optimal soil conditions for crop growth. The outcome will be also useful in crop residue management for sustainable agriculture.