# Environment- and Genotype-Dependent Irrigation Effect on Soybean Grain Yield and Grain Quality
## 2 Materials and Methods  
The field study was conducted at an experimental station of the Agricultural Institute Osjiek (45\({}^{\circ}\)32\({}^{\prime}\) N and 18\({}^{\circ}\)44\({}^{\prime}\) E, 90 m above sea level), Republic of Croatia, during a four-year period (A1 = 2010; A2 = 2011; A3 = 2011; A4 = 2012). The location has a temperate continental climate (Cfwbx climate class) with an annual precipitation of 650 mm and an average annual air temperature of 12 \({}^{\circ}\)C [23]. The first growing season (A1) was extremely wet and warm, with rainfall that was 308.6 mm (83.69%) higher than the rainfall long-term average (RLTA, 368 mm) and an average air temperature that was 1.8 \({}^{\circ}\)C higher than the temperature long-term average (TLTA, 17.5 \({}^{\circ}\)C; Figure 1). The second growing season (A2) was extremely dry and very warm, as it had 123.1 mm (33.45%) less rainfall than the RLTA and an average air temperature that was 1.2 \({}^{\circ}\)C higher than the TLTA. The third growing season (A3) was dry and very warm, with 76.8 mm (20.87%) less rainfall and an average air temperature that was 1.8 \({}^{\circ}\)C higher than the TLTA. The fourth growing season (A4) was wet and warm, with 52.3 mm (14.21%) more rainfall and an average air temperature that was 1 \({}^{\circ}\)C higher than the LTA (Figure 1). According to the WRB soil classification [24], the soil at the study site is classified as anthropogenic eutric cambisol with a silty clay loamy texture. The physical and chemical properties of the soil are given in Table 1.  
The soil was analyzed in the first year of the study before sowing according to ISO 11464 in a drying oven. A pH analysis was performed according to ISO 10390, i.e., in a 1:5 (\(v\)/\(v\)) suspension of soil in water and a 1M potassium chloride (KCI) solution. The SOM was analyzed by a method prescribed in ISO 14235 using organic carbon (C) by sulfochromic oxidation. The plant-available phosphorus (P\({}_{2}\)O\({}_{5}\)) and potassium (K\({}_{2}\)O) were extracted using an AL solution (ammonium lactate-acetate) and detected by spectrophotometry and flame photometry, respectively. According to the soil analysis results, the soil reaction (pH) at up to 30 cm depth is neutral, with low organic matter and high levels of P and K.  
The field study was carried out in a split-plot design with three factors (environmental conditions/growing season, irrigation and soybean genotype) in three replications. The factors included the following: four environmental conditions/growing seasons (A1-A4), three irrigation levels (B1 = rain-fed conditions (control); B2 = deficit irrigation maintaining the soil water content (SWC) at 60% of the field water capacity (FWC); B3 = full irrigation maintaining the SWC at 80-100% of the FWC), and four genotypes (C1-C4), resulting in 12 treatment combinations and 36 experimental plots in total. The basic plot area for each soybean genotype (C) was 3 rows (0.5 m inter-row space) = 1.5 m \(\times\) 20 m row length = 30 m\({}^{2}\). Prior to the sowing and during vegetation, all conventional agricultural management practices were applied. The plant material consisted of four elite soybean lines originating from the Agricultural Institute Osijek. Genotype C1 belonged to the 00 maturity group (MG), and it had the shortest growing cycle (100-105 days from sowing to maturity); C2 belonged to the 0 MG with a 115-125-day life cycle; C3 and C4 belonged to the I MG with 130-135-day life cycles. The sowing was performed at the end of April at the recommended plant densities, which varied depending on the MG (70, 65 and 60 plants m\({}^{-2}\) for the 00, 0 and I MGs, respectively). The environmental/growing season effect (A) was observed as the impact of meteorological conditions, i.e., the amount and distribution of precipitation (mm) and air temperatures (\({}^{\circ}\)C) on soybean grain yield and grain quality. Plot harvesting was performed with a small plot combine harvester at full maturity, usually in the first half of September.