## 4 Discussion
The obtained image of changes in the climatic risk for soybean cultivation in the area of Central Poland is generally consistent [46] and it confirms certain aspects of the theses related to climate warming [47]. This problem also occurs in other soy-growing regions, for example in the Krasnodar region, where the sum of active temperatures (above 10 \({}^{\circ}\)C) increased up to 218 \({}^{\circ}\)C/10 year and precipitations decreased down to 20.9 mm/10 year from 1987-2015 [48]. Generally, predictive models indicate precipitation decreasing insouthern Europe and increasing in northern Europe. Although, the position of the exact border line at which the positive or negative climate change signal starts is not certain; it varies over a broad band somewhere between mid-Scandinavia and the Alps, within which Poland is located [49]. Hydrothermal coefficient (\(K\)), which combined two meteorological parameters, i.e., temperature and rainfall, based on our data and according to the trends recorded by [PERSON] and [PERSON] [36] was estimated. We believe that \(K\) is a convenient and appropriate solution in two aspects: 1. the pattern of temperature and precipitation expressed in one value of \(K\) alters two distributions into one, ready for the statistical analysis (multi regression, ANOVA, cluster analysis); 2. the incidences of space-time in four terms (dry, relatively dry, optimal humid, and humid) provide the rank classifications of entire periods, which are easy and legible to describe. In 2018, in all locations where the research was conducted, \(K\) indicated drought or relative drought. In 2019, the three locations were classified into dry and relatively dry conditions, and the three others had optimal humid conditions. In 2020, humid conditions for soybean were applied at all sites. We propose the \"optimal humid\" for soybean, when \(K=1.3\)-\(1.6\), and \"humid season\" when \(K>1.7\). Actually, the most humid season in this investigation (with \(K=2.4\), at Jedrzejewo in 2020) did not reveal severity for soybean plantations, except for the need to dry soybeans up to 14% after harvest, which is standard practice for sale or storage seed. Such a weather pattern prompted us to analyze the soybean yield along with the hydrothermal coefficient, which is original and may be very useful in practice. We found a relationship between \(K\) and the yield of soybean that indicated an increase in yield of 120 kg per ha for each increase of 0.1 of \(K\). A study in the Pennsylvania region showed that total rainfall is positively correlated with the yield of soybeans, and the determination ranges between 57-67%, with yield variability up to 72% in [50]. In response to drought stress, soybeans experience reduced growth to alleviate the stress effect and activate tolerance pathways to ensure an adjusted metabolism, which is similar to other plants, for combating drought stress [51; 52]. The primary metabolites (carbohydrates, amino acids, lipids) are differentially accumulated in soybean leaves, although they decrease to a lesser extent than under heat stress [53]. Drought stress is mostly responsible for the accumulation of major carbohydrates, such as glucose, fructose, sucrose and raffinose, which indicates that in response to drought, soybean growth is restricted, and more carbohydrates are stored [54]. A study on drought-tolerant and drought-sensitive soybean cultivars indicated that under drought stress, more than 50% of genes related to various metabolic processes increased in expression independent of the tolerance factor [55]. In this study, protein and oil contents were investigated, as they are the two most important parameters of seeds of global usefulness for humans and animals. Soy protein is a more important component in the Polish market because most high-protein feeds come from soybeans. The analyses showed here that the percentage of protein in seeds depends on hydrothermal conditions and cultivar selection.