Effect of Circular-Economy-Derived Experimental Biostimulants on Growth and Development of Soilless Strawberry Plants in Greenhouse Conditions

Increasing awareness of the adverse effects of agrochemicals is driving farmers to adopt more sustainable strategies for enhancing plant growth. Biostimulants have gained significant attention in both academic research and the horticultural industry as promising tools to promote growth, improve stress tolerance, and enhance crop performance, while reducing environmental impacts. This study, conducted from March to July 2024, evaluated the effects of different experimental biostimulants (EBs) on the growth, development, and productivity of wild strawberry plants (Fragaria vesca L., cv. "Malga") cultivated under greenhouse soilless conditions. Despite their diverse origins, all tested EBs were sustainably derived from circular economy processes: (i) a suspension of freeze-dried microalgae (Tetraselmis chuii) (MA), (ii) a suspension of a lyophilized microbial mixed culture of purple non-sulfur bacteria (PNSB), and (iii) a hydro-alcoholic extract of pulverized hop biomass (HE). The EBs were applied weekly to the substrate: MA and PNSB at concentrations of 5% and 10%, and HE at 15 and 30 mL/L. Morphological and physiological parameters were recorded weekly until plant uprooting, while biochemical analyses were performed on leaves and fruits at the end of the trial. Application of EBs significantly enhanced plant growth and yield. MA treatments resulted in the greatest plant height, antioxidant activity, and total phenolic content; PNSB promoted the highest total root length and both fresh and dry biomass; and HE at 30 mL/L produced the greatest fruit number per plant. These results underline the potential of biostimulants to optimize strawberry production in controlled environments and contribute to more sustainable agricultural practices.