Combined Effects of Soil Disinfestants and Foliar Biostimulants on Growth and Quality of Baby Leaf Lettuce (Lactuca sativa L.)

In line with sustainability goals, biological alternatives to chemical fumigants are increasingly in demand to support intensive baby leaf lettuce cultivation systems. This study evaluated the combined effects of soil disinfestation strategies and foliar biostimulants on crop performance and nutritional quality. With the aim of evaluating the interactive effects of biofumigation and the application of Trichoderma spp., Ascophyllum nodosum extract, and vegetable protein hydrolysate, an experiment was conducted under controlled growing conditions, integrating microbial and foliar treatments on two lettuce cycles. Soil microbial load, plant biometric traits, ionic profiles, antioxidant activity, and polyphenolic compounds were quantified. Biofumigation induced a marked recovery of bacterial populations, while both soil treatments resulted in sustained fungal suppression and the absence of detectable Fusarium spp. Biofumigation consistently increased fresh and dry biomass, highlighting its dual sanitizing and fertilizing role. Foliar biostimulants, particularly vegetable protein hydrolysate, significantly enhanced dry matter accumulation, reduced nitrate concentration, and improved cation uptake. Antioxidant activity and phenolic metabolism were strongly stimulated by Trichoderma spp. and protein hydrolysate, with significant synergistic effects on key hydroxycinnamic acids and flavonoids. These findings indicate that integrating biological soil disinfestation with foliar biostimulation improves yield stability and nutritional quality, supporting a sustainable framework for high-value baby leaf lettuce production.