Seed pelleting improves the sowing precision and handling of small-seeded crops, but its effectiveness depends on the coating formulation and architecture. This study evaluated the influence of mineral fillers and coating structures on the physical properties, germination, and early seedling performance of pelleted rapeseed ( Brassica napus ) seeds. Monolayer pellets prepared with eucalyptus fibre, talc, vermiculite or diatomaceous earth were compared to bilayer pellets incorporating a bentonite outer layer. The addition of bentonite markedly increased pellet mass and compressive strength, with strength increasing from approximately 4 N in monolayer pellets to over 11 N in bilayer formulations, improving mechanical integrity but reducing impact resistance. Germination and seedling responses were formulation dependent. Under agar conditions, porous fillers, particularly diatomaceous earth and vermiculite–bentonite bilayers, maintained stable germination and enhanced early growth, whereas denser coatings delayed physiological processes. Under soil conditions, several bentonite-containing formulations maintained emergence comparable to uncoated seeds while promoting greater root elongation ( 8 cm versus 6–7 cm in controls). Overall, pelleted seed performance was governed primarily by the coating formulation rather than the pelleting process itself, providing a practical strategy to balance mechanical robustness with physiological accessibility to improve sowability and early crop establishment.
Li et al. (2026) studied this question.