Effects of Nitrogen Nutrition on the Nutraceutical and Antinutrient Content of Red Beet (Beta vulgaris L.) Baby Leaves Grown in a Hydroponic System

Efficient nitrogen fertilization is critical for maximizing crop productivity while minimizing environmental and health risks. Red beet baby leaves are valued for their vibrant color, flavor, and antioxidant content, particularly betalains, but they are also prone to accumulating antinutritional compounds such as nitrate and oxalate. Excessive nitrogen supply can exacerbate this accumulation, highlighting the need to optimize nitrate input to balance yield, nutritional quality, and safety. This study examined how different nitrate concentrations (1 mM and 10 mM NO3−) in hydroponic systems influence red beet baby leaf yield, quality, and levels of beneficial and harmful compounds. The plants were sampled at 10 and 17 days after planting (DAP), and the effects of the treatments in relation to plant age were assessed. Both sampling time and nitrate concentration significantly influenced red beet baby leaf growth and quality. Extending cultivation to 17 days improved yield and antioxidant levels (phenols, flavonoids, betalains) but also increased soluble oxalates. Low nitrate (1 mM) reduced both yield and antioxidant content, regardless of harvest time. However, after 17 days, low nitrate also lowered total oxalate levels, likely due to increased oxalate oxidase activity. Although 1 mM nitrate reduces fertilizer input, it compromises yield and quality. Therefore, intermediate nitrate levels should be explored to optimize both fertilizer use and product quality.