Evaluating the Use of Biostimulants for Indoor Hydroponic Lettuce Production

Abstract

Biostimulant products have various reported benefits for plant production in the field or using hydroponic systems in protected structures. However, limited information is available describing their potential use for indoor farming applications. Considering that lettuce (Lactuca sativa) is one of the most popular crops produced in commercial indoor farms, the objective of this study was to compare growth and quality of lettuce grown indoors using nine biostimulant products derived from humic substances, amino acids, hydrolyzed proteins, or seaweed extracts. ‘Monte Carlo’, ‘Fairly’, and ‘Lalique’ lettuce were grown hydroponically for 30 to 33 days under a daily light integral, day/night temperature, relative humidity, and carbon dioxide concentration of ≈13 mol·m‒2·day‒1, 22/21 °C, 70%, and 800 µmol·mol‒1, respectively. There were no positive effects from using any of the biostimulant products evaluated in our study as growth (leaf area, leaf number, shoot diameter, and shoot and root dry weight), yield (shoot fresh weight), and quality (bolting, tipburn index, leaf color, and SPAD index) of treated plants were generally similar to those from the untreated control. Applications from one seaweed extract caused slight negative growth effects, possibly due to phytotoxicity. Cultivar differences showed that Fairly plants had the highest susceptibility to tipburn and bolting, and none of the biostimulant products countered these symptoms. Overall, the products evaluated provided marginal advantages for indoor hydroponic lettuce production.

Effect of Biostimulants on Leafy Vegetables (Baby Leaf Lettuce and Batavia Lettuce) Exposed to Abiotic or Biotic Stress under Two Different Growing Systems

“…A meta-analysis of the plant growth response to humic substances conducted by Rose et al revealed that plants are more likely to respond positively to applications of humic substances when they are submitted to high or moderate stressful conditions [52]. Moreover, for nine biostimulants derived from humic substances, amino acids, hydrolyzed proteins, or seaweed extracts, Gómez and Gómez reported no beneficial effect on the growth, yield, or quality of treated lettuce plants grown hydroponically where stressors were minimal or non-existent, and one biostimulant even generated a slightly negative effect on growth [53]. In the present study, detrimental effects of biostimulants were also observed.…”

A Biostimulant Containing Humic and Fulvic Acids Promotes Growth and Health of Tomato ‘Bush Beefsteak’ Plants

“…Similarly, Martins et al reported that Micromate promotes growth in petunias grown under low and optimal fertility and that FulviPro reduces petunia growth under both low and optimal fertility [21]. Also, no effect on shoot dry weight was observed in petunias or hydroponic lettuce treated with HumaPro [21,28] Humic substances are reported to increase N, P, Fe, Zn, Mn, and Cu uptake by the plant [5]. Principal component analysis (PCA) was performed to compare the shoot nutrient concentration profiles of each treatment.…”