## 3 Results and Discussion  
### Yield of Stevia  
Table 2 presents yield of _Stevia reaudiana_ grown in Poland, while using different irrigation practices throughout the growth period. Presented in Figure 1 are percentages of particular components of stevia (a leaf, shoots or so-called plant waste, i.e., dried leaves or stems) in the total yield of stevia grown using different irrigation practices. Total average yield of stevia plants in the three-year period of the experiment was in the range of 2.08 kg to 2.58 kg\(\cdot\)m\({}^{-2}\). Sample 0 W was characterised with the lowest total yield, while the result of 2.58 kg\(\cdot\)m\({}^{-2}\) was determined in the sample NR. Increasing the frequency of the irrigation of stevia plants had no significant impact on the total yield of the acquired biomass. Only 0 W was characterised with a different yield than other samples. These data suggest that the optimisation of the type of watering of stevia is not as important as just simple use of watering procedures to avoid drought periods during stevia cultivation. However, all of the analysed samples were characterised with a similar yield of stevia leaves, despite the differences in the total yield of the whole plants. The average yield of stevia shoots from the three-year period was greatest in the samples NR and 1 W (0.95 and 0.90 kg\(\cdot\)m\({}^{-2}\)) and smallest in 0 W (0.66 kg\(\cdot\)m\({}^{-2}\)). Yield of plant waste was similar for all analysed irrigation regimes and ranged from 0.10 to 0.22 kg\(\cdot\)m\({}^{-2}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Treatment** & **Year** & \multicolumn{3}{c}{**Stevia Plant 1**} & **Stevia Leaves** & **Stevia Shoots** & **Stevia Plant Waste** \\ \cline{3-6}  & 2014 & 1.21 \(\pm\) 0.15 e & 0.83 \(\pm\) 0.06 e & 0.33 \(\pm\) 0.04 f & 0.06 \(\pm\) 0.01 e \\
0 W & 2015 & 2.56 \(\pm\) 0.22 ab & 1.64 \(\pm\) 0.09 ab & 0.78 \(\pm\) 0.07 d & 0.15 \(\pm\) 0.04 c \\  & 2016 & 2.46 \(\pm\) 0.23 ab & 1.50 \(\pm\) 0.08 ab & 0.87 \(\pm\) 0.06 cd & 0.09 \(\pm\) 0.03 cde \\ Average for 0 W in the years 2014-2016 & 2.08 & 1.32 & 0.66 & 0.10 \\  & 2014 & 2.08 \(\pm\) 0.18 c & 1.14 \(\pm\) 0.03 d & 0.79 \(\pm\) 0.06 d & 0.12 \(\pm\) 0.03 cde \\ NR & 2015 & 2.82 \(\pm\) 0.27 a & 1.57 \(\pm\) 0.10 ab & 1.02 \(\pm\) 0.05 bc & 0.23 \(\pm\) 0.06 b \\  & 2016 & 2.83 \(\pm\) 0.28 a & 1.63 \(\pm\) 0.18 ab & 1.10 \(\pm\) 0.05 ab & 0.10 \(\pm\) 0.02 cde \\ Average for NR in the years 2014–2016 & 2.58 & 1.45 & 0.97 & 0.15 \\  & 2014 & 1.89 \(\pm\) 0.18 d & 1.04 \(\pm\) 0.05 d & 0.75 \(\pm\) 0.05 d & 0.10 \(\pm\) 0.02 cde \\ \(1\) W & 2015 & 2.33 \(\pm\) 0.21 bc & 1.15 \(\pm\) 0.04 d & 0.76 \(\pm\) 0.04 d & 0.42 \(\pm\) 0.07 a \\  & 2016 & 3.05 \(\pm\) 0.19 a & 1.75 \(\pm\) 0.15 a & 1.21 \(\pm\) 0.09 a & 0.09 \(\pm\) 0.02 cde \\ Average for 1 W in the years 2014–2016 & 2.42 & 1.31 & 0.91 & 0.20 \\  & 2014 & 1.70 \(\pm\) 0.16 d & 1.07 \(\pm\) 0.05 d & 0.55 \(\pm\) 0.06 e & 0.08 \(\pm\) 0.01 de \\
2 W & 2015 & 2.24 \(\pm\) 0.20 bc & 1.12 \(\pm\) 0.13 d & 0.70 \(\pm\) 0.03 de & 0.42 \(\pm\) 0.06 a \\  & 2016 & 2.67 \(\pm\) 0.22 ab & 1.42 \(\pm\) 0.12 bc & 1.12 \(\pm\) 0.08 ab & 0.14 \(\pm\) 0.02 cd \\ Average for 2 W in the years 2014–2016 & 2.20 & 1.30 & 0.79 & 0.21 \\ \hline \hline \end{tabular}  
* Values are expressed as the mean (\(n\) = 30) \(\pm\) standard deviation. Mean values with different letters within the same column are significantly different (\(\alpha\) = 0.05) according to Duncan’s test; 0 W—not irrigated, 1 W—irrigated once a week, 2 W—irrigated two times a week, NR—irrigated only during the dry periods (no rainfall).  
\end{table} 
Table 2: Influence of irrigation on the yield of stevia plants. The percentage of particular components in the total yield of stevia plants shows lesser homogeneity than yield of various stevia components. Samples 1 W and 2 W were characterised with a lower percentage of the leaf weight (53.73% and 55.27%, respectively) in the total yield than sample 0 W (64.47%).