Biostimulant Controls Tipburn in Greenhouse Hydroponic Leafy Greens but Can Cause Phytotoxicity in Some Crops

• Yoko Suzuki, Agriculture and Natural Resources, University of Delaware

• Qingwu Meng, Department of Plant and Soil Sciences, University of Delaware

Title: Biostimulant Controls Tipburn in Greenhouse Hydroponic Leafy Greens but Can Cause Phytotoxicity in Some Crops

Yoko Suzuki and Qingwu Meng

Department of Plant and Soil Sciences

University of Delaware

Abstract

Hydroponics uses nutrient solution, not soil, to grow plants. It is effective for urban food systems and could reduce land and water use compared to open-field agriculture. In leafy greens, tipburn is a physiological disorder that damages crop quality and yield and is caused by calcium deficiency in the youngest leaves. We hypothesized that adding a calcium-mobilizing chemical biostimulant in the hydroponic nutrient solution could decrease the tipburn severity in four leafy greens: arugula ‘Astro’, kale ‘Starbor’, lettuce ‘Rex’, and pac choi ‘Win Win’. After growing seedlings indoors under warm-white light-emitting diode lights, we transplanted 54 seedlings of each crop into 12 deep-water-hydroponics trays in a greenhouse at an average temperature of 24.5 °C and an average relative humidity of 78.6%. In each of three replications, plants were grown in a nutrient solution without and with 0.25 mL⋅L⁻¹ of the biostimulant added to the nutrient solution. After transplanting, plants were grown under natural sunlight with supplemental lighting provided in the last two weeks. The plant tipburn and growth data were collected at 21 and 28 days after transplanting. Lettuce plants without the biostimulant had a higher rate of tipburn while those with it showed less tipburn. Arugula plants without the biostimulant showed tipburn, whereas leaves of arugula plants with the biostimulant turned yellowish and pinkish, which means the biostimulant concentration was too high for arugula. Kale plants grown without the biostimulant had bigger and greener leaves than those with the biostimulant. Pac choi without the biostimulant had bigger leaves but with tipburn. Pac choi without the biostimulant had bigger leaves but with tipburn, whereas pac choi with the biostimulant were smaller but without tipburn. These results show that it is important to identify the optimal biostimulant concentration for each crop to control tipburn without causing phytotoxicity.