Iron (Fe) is an essential and versatile micronutrient in plants and humans, and inadequate levels of dietary Fe can cause impaired development in children and poor physical and cognitive functioning in adults. Iron deficiency is the leading micronutrient deficiency worldwide, affecting around 1.6 billion people, with the most vulnerable demographic being pregnant women and infants. Contributing factors include diets that, particularly in developing regions, are predominantly comprised of cereal grains which are characterized by relatively low bioavailable Fe levels. Additionally, 30% of cultivated soils globally have low Fe availability. Defining effective ways to increase Fe content and availability in edible plants is therefore of utmost importance, and an agronomic approach to Fe biofortification could be a viable solution. Microgreens are an ideal candidate crop for tackling nutrient deficiencies. They are nutrient dense, have low antinutrient levels, can be grown in a relatively short amount of time, and can be consumed raw, making them a convenient target for agronomic Fe biofortification. Unfortunately, Fe uptake by plants is problematic, especially in alkaline and oxidizing conditions. Previous studies have suggested the potential of using ascorbic acid (AA) as an enhancer of Fe uptake. However, this approach has not been tested before in microgreens. Therefore, a study was conducted to investigate in a soilless system the effect of different Fe sources with and without organic acids (Ferric sulfate, Ferric sulfate 0.1% Ascorbic acid, Ferric citrate), applied via fertigation at different concentrations (0, 15, 30, 45 mg/L of Fe), on radish and pea microgreens’ Fe content. Treatments were arranged in a randomized factorial experimental design using three replications. We discovered that Ferric sulfate 0.1% AA was the most effective source in increasing Fe uptake, while Ferric citrate was the least efficient. Fertigating with 45 mg/L Ferric sulfate with 0.1% AA resulted in an approximately 110% increase in Fe accumulation in radish and pea microgreens, compared to the untreated control. However, using sodium hydroxide (NaOH) to adjust the nutrient solution pH, the same treatment was associated with an increased level of Na and resulted in a 3-30% reduction in fresh and dry biomass in both microgreen species. In conclusion, this study provides promising evidence that through fertigation, supplementation of AA with Fe fertilizers is effective in increasing Fe uptake in two microgreens species. However, careful consideration of Fe sources and concentrations needs to be made to not compromise yield and nutritional quality.
