Improved Hybrid Percolation–Ultrasound Extraction of Bioactive Compounds and Their Application as Nettle and Sage-Derived Biostimulants in Tomato and Pepper Crops

The present research aimed to improve the extraction efficiency of polyphenolic compounds from nettle and sage, using an improved hybrid ultrasound-percolation extraction method. A factorial experimental design was employed to systematically evaluate the influence of key extraction parameters: pressure (5, 6, and 7 bar), extraction time (60, 90, and 120 min), and ultrasound power (80, 100, and 120 W) on the total polyphenol content (TPC) of the resulting extracts. The obtained extracts were comprehensively analyzed in terms of total polyphenol concentration, micro- and macronutrient content, and antioxidant activity. Based on the results, optimal extraction conditions were determined and subsequently used to formulate a biostimulant solution derived from nettle and sage. To validate the agronomic efficacy of the formulated biostimulant, greenhouse trials were conducted on tomato (<i>Solanum lycopersicum</i>) and pepper (<i>Capsicum annuum</i>) plants. The impact of the treatment was assessed by monitoring vegetative growth (total dry mass), chlorophyll content, and crop productivity. The central hypothesis is that systematic variation of the hybrid ultrasound-assisted percolation process parameters will reveal a range capable of significantly improving the polyphenol yield and antioxidant activity of nettle and sage extracts. We further used these improved extracts to increase certain health indicators and overall productivity in tomato and pepper plants. At the end of the growing period, the treated plants showed an increase in dry mass of 22% for tomatoes and 20% for peppers relative to controls samples. Furthermore, productivity showed a substantial increase, rising by 38.6% for tomatoes and 53% for peppers. Chlorophyll content also increased by up to 20% in tomatoes and up to 22% in peppers, showing better plant health.