Influence on the content of phenolic compounds in leaves and berries of black currant (Ribes nigrum L.) when applying encapsulated fertilizers of long-release to the soil (and the rate of release of nutrients from them) and foliar treatment with Lign

In this work, the effect of complex prolonged-release fertilizers (Ruscote, Osmocote) and the biostimulator Lignohumate AM (LG) on the content of phenolic compounds in blackcurrant leaves and berries in a 3-year small-plot experiment was studied. The maximum content of phenolic compounds in the leaves was observed in the first year of vegetation, reaching 34.4 mg-eq gallic acid / g fresh weight in the control, but by the third year this figure decreased by 2.2 times (to 17.2 mg-eq gallic acid / g fresh weight). The variant with a combination of traditional fertilizers and foliar treatment also demonstrated a decrease in the content of phenolic compounds in the leaves — from 25.5 to 14.2 mg-eq gallic acid / g fresh weight (by 1.8 times). The content of phenolic compounds in berries, on the contrary, increased. The highest value (12.8 mg-eq gallic acid/g fresh weight, which is equivalent to 1280 mg per 100 g fresh weight of raw material) was recorded in the variant with traditional fertilizers in the second year of vegetation. In the Ruscote variant, a threefold increase in the phenol level was observed — from 3.2 to 9.6 mg-eq gallic acid/g. This indicates a redistribution of phenolic compounds from leaves to berries under the influence of fertilizers and changes in vegetation conditions. The content of phenolic compounds in blackcurrant berries in variants without LH treatment exceeds the known values (627.9–643.0 mg-eq gallic acid per 100 g fresh weight), which confirms the anti-stress effect of the biostimulant on the plant. Differences in the effectiveness of Ruscote and Osmocote fertilizers are associated with their different rates of nutrient release. During the first 20 days, Ruscote capsules released 99.9% of nitrogen, 49.9% of phosphorus and 15.9% of potassium, while Osmocote demonstrated a more balanced release (70% nitrogen, 30% potassium and 11% phosphorus). Fertilizer analysis showed that Osmocote and Ruscote contained extremely low concentrations of phenolic compounds (0.2 mg-eq gallic acid/g), which excluded the possibility of their significant entry into plants. At the same time, the LH solution contained 14.7–16.1 mg-eq gallic acid/g fresh weight of phenolic compounds, confirming its potential role as a source of biologically active compounds.