Simulation of cotyledon-soil dynamics using the discrete element method (DEM)

Abstract For epigeal seeds, cotyledons experience soil resistance as they move up through soil during the emergence process. Understanding cotyledon-soil dynamics is important for seedbed preparation to promote good seedling emergence. A discrete element model (DEM) was developed to simulate soybean seedling emergence. The cotyledon of soybean was represented by an ellipsoid according to the measured shape. Soil particles were represented by an assembly of spherical particles. As the cotyledon moved upwards through the soil particles, the cotyledon-soil dynamic characteristics were monitored for different cotyledon sizes and orientations (from lying flat to standing vertically). The cotyledon-soil dynamic characteristics (soil resistance, number of soil-cotyledon contacts, and soil kinetic energy) significantly increased as the cotyledon size increased, and generally decreased as the cotyledon angle increased. The simulated soil resistance to cotyledon was 7.08 N that was comparable with the experimental value of 8.02 N reported in the literature. The soil resistance increased from 1.64 to 15.4 N as the cotyledon size increased from 4 to 14 mm, which indicated that smaller seeds would have advantages in terms of soil resistance. A more vertically inclined cotyledon had less resistance force from the soil, which partially explained why hypocotyl tends to pull or push the cotyledon to a relatively upright position during the emergence of a seedling. The proposed model was able to provide useful insights into the micro-mechanics of the seedling emergence through soil.

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