Effect of acid-hydrolyzed soybean waste as a biostimulant on cos lettuce growing using two types of hydroponic systems
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Abstract
Background and Objective: Plant biostimulants produced from agricultural waste have been reported to promote plant growth, stimulate phytochemical content, and promote the valorization of agricultural by-products. This study investigated the impact of soybean-derived protein hydrolysate (SPH) on lettuce production in hydroponic systems using a reduced chemical fertilizer solution concentration (FSC).
Methodology: Cos lettuce (Lactuca sativa L.) was cultivated using both deep-water culture (DWC) and nutrient film technique (NFT) hydroponic systems. The test used a factorial design arranged in a randomized complete block design (RCBD) with two factors: SPH concentration (0 mL/L [SPH0] and 1.0 mL/L [SPH1]) and FSC (half- and full-strength Hoagland nutrient solutions). Each treatment combination was replicated twice with 30 plants per unit, where growth, biomass, and phytochemical parameters were analyzed using two-way ANOVA and Duncan’s multiple range test.
Main Results: SPH1 significantly enhanced plant growth and phytochemical content in both hydroponic systems (P < 0.05). In half-strength nutrient solutions with SPH1, lettuce head diameter and biomass increased by 1.16- and 1.17-fold in deep-water culture, and by 1.16 and 1.61-fold in nutrient film technique, respectively, with greener and more intense color than the control. Additionally, the total phenolic contents, total flavonoid contents, DPPH• scavenging activity, ascorbic acid content, soluble protein content, and nitrate content increased by 1.47, 1.47, 1.11, 1.02, 1.33, and 1.23-fold, respectively, in the DWC system, and by 1.40, 2.40, 2.98, 1.15, 1.69, and 1.71-fold, respectively, in the NFT system.
Conclusions: The findings of this study indicated that adding SPH1 in both systems enhanced lettuce growth, yield, and quality and proved to be an effective method for improving nutritional contents and antioxidant activities while enabling reduced chemical fertilizer use. Although nitrate content increased, levels remained within acceptable daily intakes.
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