Modelling of soil-seed contact using the Discrete Element Method (DEM)

It has long been recognised that soil-seed contact is vital to seed germination, as good soil-seed contact promotes water transfer from soil to seed. However, until today, it has not been possible to quantify soil-seed contact, due to the non-homogeneous nature of agricultural soil. This study has made a significant step in advancing the field through modelling the soil-seed regime using the Discrete Element Method (DEM). In the soil-seed model, the seed was simplified as a spherical particle, and agricultural soil was represented by an assembly of completely random individual spherical particles exhibiting cohesive and frictional behaviours. Seed placement was simulated in a fashion similar to the field planting process. Model results showed that the number of active contacts between a seed and soil particles varied from 0 to 33, and the contact area varied from 0 to 41 mm2, depending on the size and properties of the seed and soil particles. The greatest contact area was observed when the size ratio of soil to seed is 1.33 or 1.75. Higher soil particle stiffness resulted in a reduced number of contacts and smaller contact area. Simulations of press wheel effects in the model showed that when soil is compacted, both number of contacts and contact area are significantly increased.