Laboratory studies on rape seeds, conducted at the Institute of Agrophysics, PAS, were aimed at the determination of their strength properties in the aspect of the susceptibility of the seeds to damage. Limit values were determined for loads causing the disruption of the seed cover, with relation to varietal features, agrotechnical measures applied (crop spraying, time of harvest - plant ripeness, sowing density), temperature, and seed moisture content. The value of force causing seed cover cracking, the corresponding strain, or the value of energy and the apparent modulus of elasticity clearly defined the resistance of individual seeds under loading. The mechanical parameters studied were differentiated for particular plant varieties, however, differences in particular years of the study were statistically insignificant, while the differences between successive years of the study but for the same variety were significant. Generally it was observed that seeds of all the varieties in 1993 were more resistant to external loads. No statistically significant changes were observed in seed strength with relation to plant ripeness (time of harvest). Assessing the effect of chemical preparations used for rape spraying, no statistically significant effect on the strength parameters under study was noted for any of the preparations with relation to the control. Experiments concerned with the effect of sowing density on the strength properties of rape seeds did not show any significant differences of the particular parameters with relation to four sowing densities (50, 35, 20 and 10 plants/m²). The strongest differentiation of the properties under study was noted in the case of seeds with increased moisture content. An increase in the seed moisture content was accompanied by a distinct decrease in the values of force, strain, energy, and modulus of elasticity, the greatest decrease in the values of the parameters being observed for moisture content between 11 and 17 %. Also, a significant effect of seed temperature on the strength parameters under study was observed. With increasing temperature, the values of all the parameters decreased. The effect of seed temperature was stronger for diy seeds and decreased with increasing seed moisture content.
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