# Environment- and Genotype-Dependent Irrigation Effect on Soybean Grain Yield and Grain Quality
## 2 Materials and Methods
The weather data (rainfall (mm), air temperature (\({}^{\circ}\)C), humidity (%), wind speed (m s\({}^{-1}\)) and sunshine (h)) were obtained from a weather station located 1.5 km from the study location. The climatological characteristics classification for each study year was performed according to the distribution analysis of the climatic elements, probability \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & & & & \\ \hline Depth & Silt & Clay & Sand & P & RC & AC & PWP & PD \\ \hline (cm) & \% & \% & \% & \% & \% & \% & \% & g cm\({}^{3}\) \\ \hline
0–30 & 64.7 & 32.5 & 2.8 & 44.8 & 39.6 & 5.2 & 23.7 & 2.75 \\ \hline \multicolumn{8}{c}{**Chemical Properties**} \\ \hline Depth & \multicolumn{2}{c}{pH} & \multicolumn{2}{c}{Al-P\({}_{2}\)O\({}_{5}\)} & \multicolumn{2}{c}{Al-K\({}_{2}\)O} & SOM & CaCO\({}_{3}\) \\ \hline (cm) & H\({}_{2}\)O & KCl & & mg/100 g & & \% & \% \\ \hline
0–30 & 5.59 & 6.60 & 26.40 & 29.70 & 2.55 & 1.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical and chemical properties of the soil at the study site (P = porosity; RC = retention capacity; AC = air capacity; PWP = permanent wilting point (vol.%); PD = particle density; SOM = soil organic matter). Figure 1: Amount of rainfall (mm), ETo (mm/month) and air temperatures (\({}^{\circ}\)C, Tavg) during the four growing seasons (A1–A4), rainfall long-term averages (RLTAs) and temperature long-term averages (TLTAs). percentiles and estimation of the extremes performed by the Croatian Meteorological and Hydrological Service (2022). Weather data for the growing seasons A1 to A4 were compared with long-term (1961-1990) average data (Figure 1). The Penman-Monteith methodology [25] was applied to calculate the reference evapotranspiration (ETo). The soybean crops were irrigated with a traveling sprinkler system, and the irrigation time was determined by measuring the soil water content (SWC) with granular matrix sensors (GMSs) that were placed in the soil at two depths (20 and 30 cm), while the irrigation time was determined according to the SWC at the average depth (25 cm). Before use, the GMS sensors were calibrated for the soil at the study site. The calibration curve is presented in Figure 2, in which the red line represents the relationship between the SWC and the sensor readings. According to the calibration results, the 40 cbar represents the irrigation time for the B3 irrigation treatment, i.e., 80% of the FWC, while the 60-80 cbar represents the irrigation time for the B2 irrigation treatment, i.e., 60% of the FWC. The SWC was measured after an irrigation event or after considerable rainfall (>5 mm). The irrigation rate (35 mm) was the same during the growing period, i.e., the study period, and was determined according to the following equation [25]:  
\[\text{IR}=100\times\text{vt}\times\text{h}\times\text{(FWC}-\text{SWC)}\]  
where IR stands for the irrigation rate, vt stands for the soil bulk density (g cm\({}^{-3}\)), h stands for the irrigation depth (m), FWC stands for the field water capacity (%) and SWC stands for the soil water content (%). The irrigation rate was adjusted to the management allowable depletion (MAD) for field crops, i.e., 70% of the FWC. The irrigation depth was determined for shallow rooting crops (30 cm), that is, for shallow rooting crops grown on clayey soil [26]. The monthly water balance (\(\Delta\)W) was calculated as the difference between the rainfall amount (mm) and the ETa rate (mm). The soybean grain yield was measured for each plot after the harvest, converted to 13% grain moisture and expressed in kg ha\({}^{-1}\). The soybean grain protein and oil contents were determined from grain samples collected after the harvest each year on the grain analyzer InfrateTM 1241 (Foss, Hillered, Denmark) based on near-infrared transmittance technology and expressed as % of grain dry matter (DM). The crude protein and crude oil yields in kg ha\({}^{-1}\) were calculated by multiplying the grain yield converted to 13% moisture by the grain protein and oil contents, respectively.