Photosynthesis, biomass production, nutritional quality, and flavor-related phytochemical properties of hydroponic-grown arugula (Eruca sativa Mill.) ‘standard’ under different electrical conductivities of nutrient solution

Authors: YANG, TENG - The Ohio State University; SAMARAKOON, UTTARA - The Ohio State University; Altland, James; LING, PETER - The Ohio State University

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2021
Publication Date: 6/30/2021
Citation: Yang, T., Samarakoon, U., Altland, J.E., Ling, P. 2021. Photosynthesis, biomass production, nutritional quality, and flavor-related phytochemical properties of hydroponic-grown arugula (Eruca sativa Mill.) ‘standard’ under different electrical conductivities of nutrient solution. Agronomy. 11(7). Article 1340. https://doi.org/10.3390/agronomy11071340.
DOI: https://doi.org/10.3390/agronomy11071340

Interpretive Summary: Arugula or rocket (Eruca sativa) is a leafy vegetable in the family Brassicaceae. Arugula is cultivated in hydroponics and greenhouses to provide higher quality and greater yields to fulfill year-round demand. Despite the numerous studies on utilization of arugula, scientific studies on cultural practices affecting its commercial production are still lacking, only information available is from anecdotal experience of producers. The present research evaluated the electrical conductivity (EC) effect on yield, physiological and nutritional proprieties of arugula cultivar ‘Standard’ grown with a nutrient film technique (NFT) hydroponic system. Based on yield, quality criteria and human health, the optimal EC treatment would be EC 1.5 to 1.8 dS·m–1 for arugula in NFT. Too low and too high EC would reduce yields, visual quality, phytochemical compounds and lead to a less attractive color and taste to consumer and enhance the negative health effects due to nitrate accumulation.

Technical Abstract: Arugula (Eruca sativa) is a fast-growing leafy green which is cultivated using hydroponic techniques in greenhouses to fulfill high year-round demand. However, nutrient management for hydroponic production of arugula has not yet been standardized, potentially leading to limited quality and productivity. Aiming to optimize the nutrient management in hydroponic system for high productivity and quality, we investigated the effect of electrical conductivity (EC) on yield, nutritional and phytochemical properties of arugula. The model cultivar arugula ‘Standard’ was grown at four different EC levels (1.2, 1.5, 1.8, and 2.1 dS·m–1) with pH adjusted at 5.8. Photosynthetic properties, SPAD and leaf area were measured at the beginning and end of the experiment. After 28 days of transplanting, all plant samples were harvested for yield, nutrient and phytochemical measurements. Our results indicate photosynthetic properties, SPAD, leaf area, yield and dry weight increased with increasing EC from 1.2 to 1.8 dS·m–1. Foliar nutrient content increased with higher EC, but nutrient solution with 2.1 dS·m–1 showed a significant decline in N, Ca and most of the micronutrients including Fe, Zn, Mo, Cu, B and Mn. Total glucosinolates, total chlorophyll and total carotenoids concentrations increased with increasing EC. Glucosinolates are a group of health-promoting phytochemicals and account for bitter/pungent flavor. Thus, a better plant yield, quality and flavor was achieved at 1.5 and 1.8 dS·m–1. In addition, total anthocyanin content was highest in plants grown in EC 1.2 and 2.1 dS·m–1, demonstrating a stress response when grown in extreme EC levels. Our results further indicated a rapid accumulation of nitrate with higher EC, potentially detrimental to human health. This research demonstrated the optimal EC range would be 1.5 to 1.8 dS·m–1 for arugula in hydroponic production systems based on yield, quality criteria and human health considerations.