## 1 Introduction  
According to the data of the Central Statistical Office [1], the average share of certified seeds in the total amount of cereal seeds used for sowing in Poland in 2020 amounted to only 17.7%. It was even lower, i.e., 15.4%, when cereal mixtures were taken into account. These shares were also similar in 2018, when they amounted to 17.1% and 14.7%, respectively [2]. These data show that uncertified seeds stored directly on farms are sown in more than 80% of farmland in Poland. Globally, this is not an isolated case. According to [PERSON] et al. [3], unclassified seeds from previous harvests are used in more than 60% of the area of rice plantations in Indonesia. Unclassified seeds from previous harvests are stored in flat (usually brick granaries) or vertical warehouses (metal silos) [4], where they come into contact with the atmospheric air of different humidity, which depends on variable weather conditions. Research conducted in Spain [5] revealed a close dependence between air humidity and changes in the moisture content of seeds stored in horreos (traditional grain storage buildings), which ensure natural ventilation. The researchers observed that when the relative air humidity exceeded 90%, the average humidity inside the warehouse buildings decreased by 5.2%. If the relative air humidity was lower than 65%, the humidity inside the warehouse was 3.2% higher. The research showed that the geographical location, altitude, and exposure to wind influenced changes in relative humidity inside the grain warehouse [5]. It is important to store healthy, dry, clean, and pest-free cereal grains. The moisture content is an important parameter affecting the quality of stored seeds. It is taken into account in grain quality standards [6]. Too high moisture content causes biochemical and microbiological changes in seeds, which limit the time of their safe storage. In consequence, seeds warm up, become infested by fungal pathogens, mold, and other microorganisms. On the other hand, too low humidity may increase the susceptibility of seeds to mechanical damage, which will result in a loss [7; 8]. Inappropriate storage conditions reduce the quality of seeds. As a result, they can neither be sown nor used as food or feed [6]. Contemporary storage of cereal grains involves a sequence of treatments protecting them from unfavorable processes lowering their quality. The drying and cooling of seeds enable their long-term storage [9]. Numerous studies have shown that the physical properties of cereal grains and the seeds of other crops depend mainly on their water content [10] and change significantly with it [11; 12]. As results from scientific publications, the water content in seeds affects not only their dimensions, but also the values of the external friction coefficient, angle of repose, and cohesion [13]. For this reason, it is necessary to know the physical properties of agricultural products to predict the quality of the raw material before, during, and after processing. It helps to design technological processes and determine the use by dates [14; 15; 16]. The knowledge of changes in the physical properties of biomaterials caused by moisture is necessary to design technological lines for the sorting, cleaning, separation, transport, storage, processing, and packaging of seeds. This knowledge is also necessary for engineers constructing sowing, planting, and cereal harvesting machinery [17; 18; 19; 20; 21; 22], because, as results from scientific publications, when the dimensions of seeds change, so do their position and the degree to which they fill the space (working volume) in the dispensing units of seed drills., which affects the seed sowing efficiency and uniformity [23]. Simulation methods such as the finite element method (FEM) and discrete element method (DEM) are increasingly often used to design machinery for sorting, cleaning, separation, transport, storage, processing, and packaging. The FEM is used both in strength tests [24] and to test contacts between the elements of machinery [25].