Foliar Application of Hempseed Press Cake-Derived Protein Hydrolysate Enhances Yield, Fruit Quality, and Antioxidant Properties of Strawberry (Fragaria × ananassa Duch.) Grown Under Smart Greenhouse Conditions

Hempseed press cake-derived protein hydrolysate (HPH) is a promising plant biostimulant, but its effects on strawberry fruit production under smart greenhouse conditions remain unclear. The objective of this study was to evaluate the effects of foliar HPH application on growth, mineral accumulation, reproductive traits, yield, fruit quality, and antioxidant properties of strawberry cv. ‘Pharachatan 80’. Plants were grown in a smart greenhouse and treated with water (control), a commercial biostimulant, and HPH at 7.5 and 10.0% (w/v) (HPH7.5 and HPH10.0, respectively). Foliar application was initiated 25 days after transplanting and repeated weekly for five applications. HPH applications showed clear concentration-specific improvements in vegetative growth, mineral accumulation, reproductive performance, fruit yield, and antioxidant quality. As the most effective treatment for overall crop performance, HPH7.5 enhanced plant growth and mineral accumulation, particularly K and Mg. Consequently, it improved both yield components (fruit set, number, weight, size, and total yield) and fruit quality attributes, such as total soluble solids, total phenolics, flavonoids, ascorbic acid, and ABTS radical-scavenging activity. Conversely, HPH10.0 was more closely associated with N, P, Ca, Fe, Zn, and Mn accumulation, as well as fruit firmness and total anthocyanin content, and DPPH radical-scavenging activity. Principal component analysis confirmed distinct response patterns between HPH concentrations. Thus, HPH7.5 serves as an effective foliar biostimulant to improve strawberry productivity and quality in smart greenhouses.