Chemical and Biochemical Properties of Common Nettle (Urtica dioica L.) Depending on Various Nitrogen Fertilization Doses in Crop Production

Fertilization in sustainable agriculture aims to provide optimal nutrients to plants while minimizing negative impacts on the environment and human health. This study aimed to determine the effect of various nitrogen fertilizer doses of 0, 50, 200, and 300 kgN ha−1 on the chemical and biochemical composition of the leaves of nettle (Urtica dioica L.). Nettle leaves were harvested in late April to early May, before flowering. The contents of Zn, Cu, Mn, and Fe, as well as chlorophylls a and b, carotenoids, ascorbic acid, antioxidant, and catalase activity were determined. The result of catalase activity in nettle leaves was used to calculate the resistance index and the actual value of this enzyme activity, which was given as percentage change. Based on the analysis, nitrogen fertilization was found to have a statistically significant effect on the formation of the tested chemical and biochemical parameters in nettle leaves. The highest dose of nitrogen caused a statistically significant increase in the content of Zn, Mn, and assimilation pigments. The content of ascorbic acid ranged from 8.7 to 115 mg 100 g−1 f.m. and, in contrast to the antioxidant and catalase activity, decreased with increasing nitrogen dose. The relative change index (RCh) showed the following effect of nitrogen dose on catalase activity: N300 > N200 > N50. The low value of the plant resistance index (RP) for the nitrogen dose of 300 kg N ha−1 indicates that this dose had the greatest effect (lowest resistance) on catalase activity. Thus, the impact of the stress factor (nitrogen fertilization) was greatest at the highest dose. No statistically significant differences in catalase activity were found between N0 and N50. It was also demonstrated that the contents of Zn and Mn had a statistically significant and positive correlation with chlorophyll a and chlorophyll b.