A Chemical Biostimulant Enhances Growth of Greenhouse Lettuce, But Not Some Cruciferous Vegetables, in Aerated Hydroponics

Abstract

A calcium-mobilizing chemical biostimulant has been developed to improve crop growth and quality by promoting calcium uptake and mobilization. Although designed to be applied as a foliar spray, it can potentially be added to the nutrient solution in controlled-environment hydroponic systems. Although it has been shown to mitigate calcium deficiency–induced tipburn while maintaining biomass in hydroponic lettuce (Lactuca sativa), its efficacy in other emerging hydroponic leafy greens remains unclear. The objective of our study was to determine the influence of this biostimulant, when added to the nutrient solution, on the growth traits of four hydroponic leafy greens: arugula (Eruca sativa), ‘Astro’; kale (Brassica oleracea var. sabellica), ‘Starbor’; lettuce ‘Rex’; and pac choi (Brassica rapa var. chinensis), ‘Win-Win Choi’. After 11 days of germination and seedling propagation under indoor sole-source lighting, we transplanted seedlings of all crops into actively aerated deep-water culture trays in a summer greenhouse environment. The trays had the same nutrient solution with and without the added biostimulant at a concentration of 0.25 mL·L–1 in three blocks of a randomized complete block design. Plant growth data were collected 21 and 28 days after transplanting (DAT). At 21 DAT, the added biostimulant decreased shoot fresh and dry mass of arugula, kale, and pac choi by 21% to 31%, but increased that of lettuce by 23% to 25%. At 28 DAT, the added biostimulant also increased shoot fresh and dry mass of lettuce by 24% to 29%, did not influence shoot fresh mass of the other crops, and decreased shoot dry mass of kale and pac choi by 14% to 21%. Tipburn incidence was minimal without or with the added biostimulant at 21 and 28 DAT, although tipburn reduction was observed in arugula and pac choi with the added biostimulant. In general, the chlorophyll concentration index was unaffected by the added biostimulant, except for an 11% increase in lettuce with the added biostimulant at 28 DAT. Extension growth of all crops except lettuce had a 9% to 15% reduction with the added biostimulant at 21 DAT, but was unaffected by the added biostimulant at 28 DAT. We conclude that the added biostimulant boosted the growth of lettuce, but not the cruciferous vegetables tested, in summer greenhouse aerated hydroponics.