Macroelement composition of nettle in hydroponic production

Nettle (Urtica dioica L.) is a perennial plant used as a medicinal herb and also as a food. Besides numerous phytochemicals, nettle is great source of macro- and microelements which are important for human health. Hydroponic production is a good solution to optimize nutrient supply in order to produce nutritionally high quality nettle. Excessive application of nitrogen can therefore be avoided to reduce negative effects on other nutrients and quality itself. The aim of this research was to determine macromineral compostion of nettle in hydroponic production system in response to different nutrient solutions in order to obtain the highest possible nutritional value. The experiment was conducted in a greenhouse following randomized complete block design with three replicates. Four different nutrient solutions (Johnson, Jensen, Larson, Cooper) which differ in EC value (1.72, 2.34, 2.50 and 3.42 mS cm^‑1, respectively) were tested. Nettle was sown on March 11, 2021 in polystyrene plates filled with perlite and placed in basins filled with nutrient solutions after germination. Harvest was performed manually on May 20, 2021. Samples were first dried, then homogenized which was followed by digestion in the microwave oven with HNO₃ and HClO₄. Phosphorus was determined spectrophotometrically, potassium flame photometrically and calcium and magnesium by atomic absorption spectrometry. Nitrogen was determined using the Kjehldal method. The results showed differences between the nutrient solutions. The highest determined N content was 7.14% N DW (Cooper solution) and 6.90% N DW (Larson solution), P content was 0.93% P DW (Larson and Jensen solutions), K content was 3.94% K DW (Jensen solution) and 3.80% K DW (Larson solution), Ca content was 5.40% Ca DW (Larson solution) and 5.38% Ca DW (Johnson solution), Mg content was 1.13% Mg DW (Jensen solution), all without statistical differences. Considering the results of the first harvest, Larsen solution is the most suitable.