The Effect of Application of Encapsulated Prolonged-Action Fertilizer to Soil Mix and Foliar Treatment with Lignohumate on Content of Phenolic Compounds in Leaves and Berries of Black Currant (Ribes nigrum L.)

This work studies the effect of complex prolonged-action fertilizers (Ruscote and Osmocote) and Lignohumate AM (LG) bioenhancer on the content of phenolic compounds in blackcurrant leaves and berries in a 3-year microplot experiment. The maximum content of phenolic compounds in the leaves was observed in the first season of the growth and reached 34.4 mg-eq gallic acid g–1 of fresh weight (FW) in the control, whereas this value decreased by a factor of 2.2 (to 17.2 mg-eq gallic acid g–1 FW) by the third year. The variant with a combination of traditional fertilizers and foliar treatment likewise demonstrated a decrease in the content of phenolic compounds in the leaves, from 25.5 to 14.2 mg-eq gallic acid g–1 FW (by a factor of 1.8). On the contrary, the content of phenolic compounds in berries increased. The highest value (12.8 mg-eq gallic acid g–1 FW, which is equivalent to 1280 mg per 100 g–1 FW of raw material) was recorded in the variant with traditional fertilizers in the second growing season. In the Ruscote variant, a threefold increase in the phenol level was observed, that is, from 3.2 to 9.6 mg-eq gallic acid g–1. This suggests redistribution of phenolic compounds from leaves to berries due to the effect of fertilizers and changes in growth conditions. The content of phenolic compounds in blackcurrant berries in variants without LH treatment exceeded the known values (627.9–643.0 mg-eq gallic acid per 100 g FW), which confirms that the bioenhancer has an antistress effect on the plant. Differences in the effectiveness of the Ruscote and Osmocote fertilizers are associated with the 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–1), which excluded the possibility of their significant intake by plants. At the same time, the LH solution contained 14.7–16.1 mg-eq gallic acid g–1 FW of phenolic compounds, which confirmed its potential role as a source of biologically active compounds.