## 2 Material and Methods
### Statistical Methods  
Analysis of variance (ANOVA) was determined (Table 6) using a mixed model with cultivar and site effect as fixed and year as a random block replication model. The characteristics (yield, protein, oil, VPD and \(K\)) were checked for normality by [PERSON]'s test. The [PERSON]'s test was used for the means significance differences (\(p=0.05\)) and for the visualization of the means separation on figures. The multivariate regression by the forward method was calculated, taking yield, protein and oil as dependent attributes from year \(K\) and VPD as independent variables. The goodness of fit of the regression parameters was evaluated by Student's \(t\)-test (\(p=0.05\)). The division of soybean cultivars into groups that differed significantly in terms of yield, protein, oil and VPD (also in tillage and no-tillage cultivation) was made using cluster analysis (CA) with the \(k\)-means method. Confirmation of significance between groups was performed via ANOVA with the grouping variable. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Month**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} & \multirow{3}{*}{**Method**} \\  & & & & & & & & & & & & & & \\ \hline \multicolumn{12}{c}{2018} \\ April & 40.0 & 36.4 & 71.0 & 46.0 & 15.0 & 46.0 & & 12.0 & 12.0 & 11.1 & 9.9 & 11.8 & 11.2 \\ May & 14.2 & 9.8 & 5.5 & 30.0 & 7.0 & 8.0 & & 16.9 & 17.0 & 17.0 & 16.8 & 16.5 & 16.8 \\ June & 26.7 & 19.2 & 21.0 & 40.0 & 16.0 & 38.0 & & 18.4 & 18.3 & 17.8 & 18.5 & 17.6 & 19.2 \\ July & 86.0 & 34.6 & 44.0 & 15.0 & 70.0 & 86.0 & & 20.5 & 20.2 & 20.7 & 20.7 & 20.2 & 20.1 \\ August & 23.7 & 20.8 & 31.5 & 28.0 & 15.0 & 42.0 & & 19.9 & 20.2 & 20.6 & 18.6 & 19.3 & 19.5 \\ September & 17.0 & 11.4 & 32.5 & 34.5 & 26.5 & 76.5 & & 15.6 & 15.5 & 16.7 & 16.0 & 16.3 & 15.8 \\ _Sum_ & _207.6_ & _132.2_ & _205.5_ & _193.5_ & _149.5_ & _296.5_ & _Mean_ & 17.2 & 17.2 & 17.3 & 16.8 & 17.0 & 17.1 \\ \hline \multicolumn{12}{c}{2019} \\ April & 1.5 & 4.2 & 9.0 & 30.0 & 45.0 & 5.0 & & 9.3 & 9.3 & 9.1 & 8.5 & 8.7 & 8.9 \\ May & 89.2 & 58.2 & 86.5 & 95.0 & 55.0 & 39.0 & & 12.1 & 12.0 & 13.5 & 14.1 & 15.0 & 14.6 \\ June & 17.7 & 19.2 & 33.5 & 65.0 & 75.0 & 21.0 & & 21.9 & 21.6 & 22.0 & 21.5 & 22.0 & 22.3 \\ July & 22.4 & 16.8 & 45.0 & 50.0 & 15.0 & 52.5 & & 18.6 & 18.5 & 19.0 & 19.3 & 19.2 & 18.9 \\ August & _37.7_ & 36.2 & 35.5 & 61.0 & 1.5 & 45.0 & & 19.7 & 19.7 & 20.2 & 20.3 & 19.9 & 20.5 \\ September & 98.5 & 72.6 & 76.5 & 45.0 & 19.5 & 87.0 & & 13.5 & 13.2 & 14.2 & 14.2 & 13.9 & 14.6 \\ _Sum_ & _267.0_ & _207.2_ & _286.0_ & _346.0_ & _211.0_ & _249.5_ & _Mean_ & 15.9_ & _15.7_ & _16.3_ & _16.3_ & _16.5_ & _16.6_ \\ \hline \multicolumn{12}{c}{2020} \\ April & 0.7 & 3 & 13.4 & 56.5 & 50.6 & 26.7 & & 8.2 & 8.2 & 7.9 & 7.5 & 8.0 & 8.1 \\ May & 34.6 & 23.8 & 35.6 & 76.8 & 67.4 & 98.6 & & 10.9 & 10.8 & 10.8 & 10.9 & 11.0 & 10.8 \\ June & 153.9 & 114 & 123.0 & 95.4 & 87.6 & 123 & & 17.9 & 17.7 & 17.6 & 17.5 & 18.0 & 17.9 \\ July & 85.1 & 78.6 & 65.0 & 75.6 & 55.4 & 65.7 & & 18.0 & 18.0 & 17.9 & 18.1 & 17.7 & 18.1 \\ August & 90.0 & 60.4 & 76.8 & 65.4 & 78.8 & 59.5 & & 19.2 & 19.3 & 19.5 & 19.3 & 19.0 & 19.1 \\ September & 71.2 & 70.4 & 67.5 & 56.9 & 67.7 & 89 & & 14.4 & 14.6 & 15.3 & 14.2 & 14.3 & 14.4 \\ _Sum_ & _435.5_ & _347.2_ & _367.9_ & _370.1_ & _356.9_ & _435.8_ & _Mean_ & _16.1_ & _16.1_ & _16.2_ & _16.0_ & _16.0_ & _16.1_ \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Monthly sum of precipitation and monthly mean temperatures during seasons at the sites of the study.