Modified nutrient management protocol for optimum biomass production, nutritional quality, and flavor-related phytochemical properties of hydroponic-grown kale (Brassica oleracea)

Authors: TENG, YANG - South Dakota State University; SAMARAKOON, UTTARA - The Ohio State University; Altland, James

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2025
Publication Date: 8/25/2025
Citation: Teng, Y., Samarakoon, U., Altland, J.E. 2025. Modified nutrient management protocol for optimum biomass production, nutritional quality, and flavor-related phytochemical properties of hydroponic-grown kale (Brassica oleracea). Frontiers in Plant Science. 16. Article 1629432. https://doi.org/10.3389/fpls.2025.1629432.
DOI: https://doi.org/10.3389/fpls.2025.1629432

Interpretive Summary: Kale has higher nitrogen demand compared to other leafy greens, and conventional nutrient management systems struggle to balance nitrogen supplementation while maintaining crop quality. A new approach was evaluated by using only calcium nitrate during the final week of production. This method significantly improved the biomass, nutrient composition, and phytochemical properties of kale. Specifically, calcium nitrate-only treatment increased shoot biomass, shoot-to-root ratio, and uptake of total nitrogen, calcium, and magnesium, while keeping nitrate levels within safe consumption limits. However, it also resulted in reduced levels of total anthocyanins and vitamin C, though glucosinolate levels slightly increased. The accomplishment of this study is the development of a targeted nitrogen supplementation protocol that enhances kale growth and nutrient uptake. This contributes to solving the problem of inefficient nutrient management in hydroponic systems by providing a more balanced and crop-specific nutrient supply, ultimately leading to better crop yield and nutritional quality

Technical Abstract: In hydroponic leafy green production, nutrient supply is not often based on crop-specific requirements. Our research has indicated that nitrogen demand is greater for kale (Brassica oleracea ‘Red Russian’) as compared to other leafy greens. Conventional nutrient management relies on a two-part water-soluble fertilizer system—Part A containing some macronutrients and micronutrients and Part B containing calcium nitrate (Ca(NO3)2) —to maintain electrical conductivity (EC) at a desired level. However, optimizing nitrogen supplementation while maintaining crop quality remains a challenge in EC-based nutrient management. The current study evaluated the effects of enhanced nitrogen supplementation by changing the mixing protocol to using only calcium nitrate (Ca(NO3)2) during the final week of production on the biomass, nutrient composition, and phytochemical properties of hydroponically grown kale. The results showed that Ca(NO3)2-only treatment significantly improved shoot biomass, shoot-to-root ratio and uptake of total nitrogen, calcium, and magnesium by 28.51%, 22.13%, 46.01%, 27.51%, and 14.44%, respectively, as compared to conventional two-part nutrient adjustment. indicating that nitrogen and calcium were key limiting factors for shoot growth. Despite the additional nitrogen supply, nitrate accumulation in kale shoots increased but remained within safe consumption limits. However, phytochemical analysis revealed reductions in total anthocyanins and vitamin C, while glucosinolate levels slightly increased. No significant effects were observed on photosynthetic properties, root growth, or acid and water usage, suggesting that pH stabilization between nitrate and calcium uptake contributed to balanced nutrient dynamics. These findings highlight the potential benefits and trade-offs of targeted nitrogen supplementation in hydroponic kale production. Future studies should explore crop-specific nutrient management for enhancing both crop yield and nutritional quality for other leafy greens.