Selenium biofortification and growth of onions as affected by Se application, biochar and irrigation

Authors: Banuelos, Gary; CENTOFANTI, TIZIANA - Fresno State University; ZAMBRANO, MARIA - Fresno State University; Arroyo, Irvin; Wang, Dong

Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2025
Publication Date: 4/1/2025
Citation: Banuelos, G.S., Centofanti, T., Zambrano, M.C., Arroyo, I.S., Wang, D. 2025. Selenium biofortification and growth of onions as affected by Se application, biochar and irrigation. Journal of Food Composition and Analysis. 140. Article 107217. https://doi.org/10.1016/j.jfca.2025.107217.
DOI: https://doi.org/10.1016/j.jfca.2025.107217

Interpretive Summary: Worldwide, selenium deficiencies are exasperated by a low Se intake from a plant-based diet. Reportedly, more than one billion of the world’s population suffers from some degree of Se-deficiency in many regions in China, Oceania, Africa, and Europe. Consequently, increasing Se content in select food crops is an effective means to increase Se intake in humans. A process called biofortification can increase Se content in food crops by utilizing Se as a fertilizer for growing selected crops. For example, onions have a physical affinity for Se and may accumulate Se when exposed to an application of Se. Se-enriched onion can serve as an excellent dietary source of Se when consumed as a biofortified food product. To develop effective Se biofortification strategies in light- textured soils, it is essential to gather more data on the impact of biochar addition on water and Se uptake by plants. In this 3-year study in a light-textured soil, we tested the co-application of biochar and different forms of Se applied to the soil or applied directly to field-grown onions. We also included irrigation treatments where different amounts of water were applied due to California’s drought-stricken conditions. Our results demonstrated that spraying Se onto plants and irrigating with medium to normal amounts of water was the most effective for increasing Se concentrations in onion bulbs. Except for one year, the addition of biochar in the light textured soil had no significant effect on Se accumulation by onions. We conclude that Se biofortification strategies in onions established in light-textured soils in California were not consistently enhanced with the addition of biochar. Selenium biofortification in onions is best served by foliar application of Se and by irrigation at rates near to normal or normal water requirement.

Technical Abstract: Worldwide, selenium (Se) deficiencies are exasperated by a low Se intake from a plant-based diet. Consequently, to increase Se intake by humans it is essential to select food crops that can efficiently assimilate Se from different Se sources into the edible plant parts. This biological process is called biofortification and it can be applied to a variety of crops, especially sulfur-loving plants like onion. In this multi-year study in light-textured soil of California, we examined strategy possibilities for enhancing Se accumulation in field-grown onion by 1) applying biochar as an organic soil amendment to increase retention of water- and applied water-soluble Se, 2) using deficit irrigation to minimize leaching of Se, and 3) applying Se directly to the soil and/or to the plant. Selenium treatments included applying either selenate, selenite or selenomethionine at a rate of 100 g/ha to the soil or foliar to the plants, irrigating at 50, 75 or 100% Eto, and growing in soils with added or not added biochar. Results from the 3-year-study showed that the accumulation of Se in onion bulb ranged from 0.3 to 1.3 mg Se/kg DW across all treatments that included the addition of Se. In general, the Se concentration was higher in onions treated with foliar application of selenate compared to other forms of Se at irrigation rates of 75 and 100% Eto., irrespective of biochar added to soil (except in 2nd year). Our results clearly demonstrate that the foliar application of selenate with or without biochar and a medium or high irrigation rate were most effective for enhancing Se biofortification in onion bulb grown in light-textured soil. The addition of biochar in light textured soil does not appear to consistently result in an increased accumulation of Se in onion bulbs used as a crop in Se biofortification.