## 4 Discussion
However, the plant variety can greatly impact the influence of plant variety on the concentration of elements. For example, in a study on broccoli by [PERSON] et al. [42], the phosphorus content was greatest in the plants grown with the largest spacing, which was similar to the finding in this study about stevia plants. In the study by [PERSON] [39], stevia plants had an average phosphorus level similar, though slightly lower (0.27%), to the concentration in stevia plants grown in the spacing of 50 cm \(\times\) 30 cm. However, the total potassium content in plants analysed by [PERSON] [39] was almost two times lower than the content of potassium in the stevia plants grown in Poland. The stevia plants analysed by [PERSON] et al. [38] had similar potassium concentrations. However, the phosphorus content of stevia plants grown by [PERSON] et al. [38] was similar to that in plants grown in spacings of 45 cm \(\times\) 25 cm and 30 cm \(\times\) 30 cm, but it was lower than in stevia plants grown in the spacing of 50 cm \(\times\) 30 cm. This suggests that plant spacingcould affect the total concentration of phosphorus in stevia plants. Different results were seen in the concentration of calcium and magnesium. The average concentration of these elements in stevia plants grown in the study by [PERSON] et al. [38] was 20-25% higher. Additionally, plant spacing can affect the root system, influencing nitrate capture, which might explain why stevia plants grown at the largest spacing (50 cm \(\times\) 30 cm) had the highest nitrate content [43]. However, stevia plants grown by [PERSON] et al. [38] had similar nitrate concentrations to those grown in the spacing of 30 cm \(\times\) 30 cm and lower than those grown in the spacing of 50 cm \(\times\) 30 cm. This suggests that it may not be the plant spacing directly but the availability of nitrogen that influences nitrate concentration, as nitrogen fertilization was applied per area, not per plant, giving plants in larger spacings access to more fertilized soil. Currently, there are no data on the influence of plant spacing on the concentration of phenolic compounds or vitamin C in stevia plants, but similar analyses have been performed on other species. For example, a study by [PERSON] et al. [44] on cabbage (_Brassica oleracea_ L. var. _capitata_) found that various planting densities (four, six and eight plants per square meter) did not significantly affect the concentration of phenolic compounds or vitamin C. However, a study by [PERSON] and [PERSON] [45] on the _Lactuca sativa_ showed that denser planting resulted in a lower concentration of vitamin C and carotenoids. Similar results were noted for stevia, where in September, plants grown in the smallest spacing (30 cm \(\times\) 30 cm) had lower vitamin C concentrations than those grown in the 50 cm \(\times\) 30 cm spacing. The study by [PERSON] et al. [38] on stevia plants grown with different nitrogen fertilization showed that the plants had phenolic compound concentrations similar to those in plants grown at spacings of 50 cm \(\times\) 30 cm and 45 cm \(\times\) 25 cm. The stevia plants also had similar vitamin C content to those in the spacing of 50 cm \(\times\) 30 cm. Carotenoid and chlorophyll (a + b) concentrations were not affected by plant spacing, which was similar to findings in garlic cultivation described by [PERSON] and [PERSON] [46]. This results contrast with a study by [PERSON] et al. [47] on maize, where increasing planting density increased the concentration of carotenoids, but it did not significantly impact chlorophyll concentration at the time of harvest. The dry mass content of stevia leaves was similar in July, but before harvest, plants grown in the spacing of 30 cm \(\times\) 30 cm had higher dry mass content. A meta-analysis by [PERSON] et al. [48] over hundreds of plant species has shown that it is a typical phenomenon during plant cultivation. All these results indicate that different spacings of stevia plants can significantly impact the quality of the plant material.