*3.5. Influence of Air Temperature on Tuber Yield*

The temperature conditions in the April–May period and the precipitation and temperatureprecipitation conditions described by the Sielianinov hydrothermal index in April–September had a decisive influence on the potato yield in the southeastern part of Poland. The influence of air temperature in this period was described by the power function equation in the following form.

$$\mathbf{y} = 13.52 \mathbf{x}^{0.1349} \tag{7}$$

This indicates that a positive influence of air temperature in April–May is decisive for plant emergence, rooting and the formation of stolons and tubers. The value characterizing the yield increased with the temperature increase in this period. The coefficient of determination of this equation was 88.63%, which makes it significant and reliable (Figure 5).

Similar relationships were proven for the June–July period. During this period, there was also a positive impact of ever higher air temperature on the shaping of the potato yield described by the equation on Figure 6.

The temperature in the first part of the growing season had a positive effect on potato yields. This fact is confirmed by the coefficient of determination (R2 = 87.4%).

**Figure 6.** Partial dependence of tuber yield on air temperature in the June–July period.

The results of the regression analysis of the yield with air temperature in the second part of the growing season (August–September) are described by the formula in Figure 7. As a result of the air temperature increase in this period of time, there was a systematic decrease in yield value. The value of the coefficient of determination, amounting to 84.67%, makes the equation highly reliable [19].
