Impact of selenium biofortification on production characteristics of forages grown following standard management practices in Oregon

Authors: HALL, JEAN - Oregon State University; BOBE, GERD - Oregon State University; FILLEY, S - Oregon State University; BOHLE, MYLEN - Oregon State University; PIRELLI, GENE - Oregon State University; WANG, GUOJIE - Oregon State University; Davis, Thomas - Zane; Banuelos, Gary

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2023
Publication Date: 3/31/2023
Citation: Hall, J.A., Bobe, G., Filley, S.J., Bohle, M.G., Pirelli, G., Wang, G., Davis, T.Z., Banuelos, G.S. 2023. Impact of selenium biofortification on production characteristics of forages grown following standard management practices in Oregon. Frontiers in Plant Science. 14. Article 1121605. https://doi.org/10.3389/fpls.2023.1121605.
DOI: https://doi.org/10.3389/fpls.2023.1121605

Interpretive Summary: Application of Se amendment increases forage Se concentration irrespective of forage fertilization practices. In fact, selenate amendment synergizes with NPK(S) fertilization in promoting forage biomass production and plant uptake of nitrogen and sulfur from fertilizer. In contrast, sulfur fertilizers can decrease forage Se concentrations, when plant available Se is already low. Multiple factors affect forage Se concentrations and Se yields including selenate amendment rate, forage biomass produced, forage species, fertilization practices, soil characteristics, and changing weather conditions from year to year. Because selenate amendment and sulfur application cost extra, and have the capacity to acidify soils, plants, and irrigation water, their concentrations should be routinely measured before application. Combining springtime sodium selenate foliar application and NPKS/PKS fertilizers at amounts adapted to meet local forage and soil requirements is an effective strategy to maintain optimal forage growth and quality on low Se soils.

Technical Abstract: Low selenium (Se) concentrations in soils and plants pose a health problem for herbivores consuming locally-grown forages. Previous studies have shown that Se concentrations in forages can be increased using foliar selenate amendments. However, the effects of foliar selenate amendments applied with traditional nitrogen-phosphorus-potassium-sulfur (NPKS) fertilizers on forage yields, and nutrient contents and agronomic efficiencies are unknown. Using a split plot design, we determined the effects of springtime sodium selenate foliar amendment rates (0, 45, and 90 g Se/ha; whole plot) and NPKS application (none, NPK/PK fertilization, NPKS/PKS fertilization at amounts adapted to meet local forage and soil requirements) on forage growth and nitrogen, sulfur, and Se concentrations, yields, and agronomic efficiencies. This 2-year study was conducted across Oregon on four representative forage fields: orchardgrass (Dactylis glomerata L.) in Terrebonne (central Oregon), grass-clover mixture in Roseburg (southwestern Oregon), and both grass mixture and alfalfa (Medicago sativa L.) fields in Union (eastern Oregon). Without NPK fertilization, grasses grew poorly and were low in nitrogen content. Fertilization with NPK/PK increased forage growth and forage nitrogen concentrations and decreased, in the absence of sufficient plant available sulfur, forage sulfur concentrations. In the absence of sufficient plant available sulfur, co-application of NPK/PK with sulfur increased forage growth, sulfur concentrations, and utilization of nitrogen fertilizer, and lowered forage nitrogen concentrations. Without Se amendment, forage Se concentrations were low and further decreased with NPKS/PKS fertilization. Selenate amendment linearly increased forage Se concentration without adversely affecting forage yields, nitrogen and sulfur concentrations, and nitrogen and sulfur agronomic efficiencies. Importantly, sulfur fertilization did not interfere with Se uptake in Se amended plots. In conclusion, the combination of springtime sodium selenate foliar application to Oregon low Se plants, combined with NPKS/PKS fertilization at amounts adapted to meet local forage and soil requirements are effective strategies to increase forage total Se concentrations, while maintaining optimal forage growth and quality of Oregon forages.