Effect of Different Biostimulant Application Forms on Some Geometrical and Mechanical Properties of Soybean Seeds

The physical and mechanical properties of soybean seeds are of fundamental importance for their practical use, as they determine the quality of seed material and the efficiency of technological processes in the food, feed, and oil industries, as well as the seeds’ ability to withstand transport, storage, and processing. Modern agriculture strives to increase productivity sustainably, and plant biostimulants are an innovative solution aiming to support plant development and to improve plant resistance. The purpose of this study was to determine how the form of an application of a biostimulant influences the geometrical and mechanical properties of soybean seeds. Two biostimulants (Asahi SL and Kelpak SL), both applied in three ways (universal spray nozzle, injector spray nozzle, and spray hoses), were tested in conjunction with three levels of moisture (6%, 8%, and 10%) on soybean seeds of the cultivar Abelina. The results demonstrated that the biostimulants did not have a significant effect on the sphericity of seeds, which remained at an average level: 0.74. Lower moisture of seeds resulted in their weaker tolerance to mechanical damage and a higher compression resistance factor. Seeds with a moisture content of 6% treated with Asahi SL using universal nozzle 12004C showed the highest cracking resistance (719.4 N∙mm−1) and ultimate force (245.1 N) compared with untreated seeds (672.4 N∙mm−1 and 216.4 N). The Asahi SL biostimulator increased the compression work up to the maximum force by 12% relative to the control, regardless of the spray application method, while the ceramic universal spray nozzle caused an almost 10% increase in maximum force compared with the control, irrespective of the type of biostimulator used. The findings indicate that biostimulants have a positive effect on the physical quality of seeds, with the choice of spray parameters playing a key role. The results provide practical guidelines for optimising agrotechnical treatments to produce seeds with improved quality parameters. They are also crucial for making an appropriate selection of sowing and seed-processing equipment, minimising seed loss and improving the efficiency of soybean production.