# Environment- and Genotype-Dependent Irrigation Effect on Soybean Grain Yield and Grain Quality
## 1 Introduction  
Soybean (_Glycine max_ (L.) Merr.) is the most important oilseed crop in the world. It is an important source of proteins for food, feed and nutraceutical compounds for the pharmaceutical industry [1]. Although soybean areas have increased from 2,736,400 ha in 2010 to 5,294,214 ha in 2020 [2], the agro-climatic conditions in Europe are not ideal for the widespread cultivation of soybeans [3]. Since European agriculture is mainly rain-fed, with a share of irrigated area of only 6% [4], one way to ensure increased production and yield stability in unstable, extreme weather conditions with limited potential for cropland expansion is to grow cultivars with a shorter life cycle, sufficient drought resistance and high yield potential under European growing conditions [5]. Another suggestion for improving soybean production in Europe is irrigation [6]. Assumed future decreases in water availability in the mid-latitude spatial regions of the world [7], where most of Europe is situated, will require improving the efficiency of water use. Soybeans can withstand shorter-duration droughts in their early vegetative stages without considerable yield reductions [8]. Water needs increase in their reproductive stages, i.e., from the beginning of flowering (R1 stage of soybean development according to [PERSON] [9]) to pod development (R3) and up until full seed development (R6). These reproductive stages occur during the summer, when high temperatures and water shortages are regular in many European soybean-growing regions. As water shortages during this period can have a significant negative impact on yield [10, 11, 12], maintaining production at its present level or increasing it will require precise irrigation scheduling to increase the yield per unitof irrigation water applied. The literature shows that not only the irrigation scheduling has an impact on the soybean yield [13; 14; 15; 16; 17] but different irrigation strategies as well. For example, [PERSON] et al. [18] noted a significant increase in the soybean yield in average climatic years within deficit irrigation (60-80% of the field water capacity, FWC), while full irrigation (80-100% of the FWC) significantly increased the grain yield compared to deficit irrigation only during the extremely warm and very dry growing conditions. In the same agro-ecological conditions, [PERSON] et al. [15] achieved the highest soybean yield under full irrigation, regardless of the weather conditions. A large number of studies have also examined the impact of irrigation on soybean grain quality. The results were inconsistent. Some of the studies reported no impact of irrigation on the oil content [14; 19], some reported an increased oil content [13], and some reported a reduced oil content due to irrigation [11; 20; 21]. Nevertheless, the increase in grain yield as a result of irrigation should compensate for the oil content decrease, increasing the final oil yield. As for the soybean protein content, some authors have reported an increase in the protein content [14], while others [22] have reported a lower protein content in irrigated conditions. All of the mentioned inconsistencies add to the necessity for further studies.  
Considering the given background, the main hypotheses of this study were as follows: (i) the effects of applied irrigation treatments (deficit irrigation maintaining the soil water content (SWC) at 60% of the field water capacity (FWC) and full irrigation maintaining the SWC at 80-100% of the FWC) on soybean grain yield, grain protein content, crude protein yield, grain oil content and crude oil yield will largely depend on the specific environmental conditions and genotypes; (ii) among the tested genotypes and irrigation treatments, we will be able to select the optimal combination that is most productive in the tested environmental conditions. Therefore, the aims of this study were to determine the variability in the irrigation effect on soybean grain yield and grain quality depending on the genotype selection and environmental conditions.