*3.6. Influence of Precipitation on the Formation of Tuber Yield*

The factor used to assess the influence of meteorological conditions on potato yielding was also the sum of atmospheric precipitation. Among the periods in which their impact on the variability of potato yielding was the most frequent, the rainfall in the April– May period turned out to be the most impactful. The regression model described by the following equation.

$$\mathbf{y} = \mathbf{21}\mathbf{\bar{z}}\mathbf{936x}^{-0.051}\text{.}\tag{8}$$

This indicates a negative impact of increasing sum of rainfall in the analyzed time interval on tuber yield (Figure 8). The coefficient of determination of this equation amounting to 77.02% indicates its high credibility. It was shown that the potato yield assessed on the basis of data from the Central Statistical Office, limited by excess water in April–May, turned out to be 39% lower than the actual yield and as much as 65% lower than the potential yield in the experiments obtained in the Central Research Center for Testing in Poland.

**Figure 8.** Partial dependence of tuber yield on total rainfall in April–May.

The results of polynomial regression analysis of tuber yield versus rainfall total, performed with the stepwise method, in the case of other time intervals turned out to be insignificant. The coefficients of determination of these equations were also low, which means that other environmental factors not considered in the analysis could have contributed to tuber yields.
