Measurements and DEM modelling of soybean seed expansion

Abstract

The dynamics of the seed driven by its hydration status has important agronomical implications. However, little research has been done in this area. This study was devoted to the expansion and force of individual seeds hydrated in two different environments: soil and water. The expansion of a soybean seed in soil during imbibition (the uptake of water by dry seed) phase was measured using the computer tomography (CT) scanning technology (non-destructive tests). The expansion force was predicted by a model developed using the discrete element method (DEM). The model was able to predict the expansion force of a seed under different soil compaction levels (Low, Medium, and High). The force potential of a fully hydrated seed was measured. The CT scan results showed that during the imbibition process, a soybean seed continued expanding, and after 36 h, it expanded by 80% of its original length and by 37% of its original volume. The model simulation results showed that as seed expanded in soil, forces arose between the seed and surrounding soil particles. Under the same soil conditions, the expansion force of seed along its length-axis was the highest among all three axes of seed. Within each seed axis, the expansion force increased with the soil compaction level. Measurements showed that a sufficiently hydrated soybean seed was capable of generating a force of 11.3 N along the length-axis. This high force potential suggests that the expansion of soybean seed is unlikely restricted by soil particles during the imbibition process, even the soil is severely compacted. This study provides new information for understanding and improving the process of seed germination.