Effects of springtime sodium selenate foliar application and NPKS fertilization on selenium concentrations and selenium species in forages across Oregon

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

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2021
Publication Date: 4/20/2021
Citation: Wang, G., Bobe, G., Filley, S.J., Pirelli, G.J., Bohle, M.G., Davis, T.Z., Banuelos, G.S., Hall, J.A. 2021. Effects of springtime sodium selenate foliar application and NPKS fertilization on selenium concentrations and selenium species in forages across Oregon. Animal Feed Science and Technology. 276. Article 114944. https://doi.org/10.1016/j.anifeedsci.2021.114944.
DOI: https://doi.org/10.1016/j.anifeedsci.2021.114944

Interpretive Summary: Selenium (Se) is an essential trace element for animals and humans. Selenium concentrations in soils and plants are low in many regions of the United States, including the Pacific Northwest, and consequently concentrations in blood of in livestock consuming locally-grown forages are low. Overall, Se deficiencies cause poor livestock performance and compromised animal health because of suboptimal immune function and fertility. Traditional strategies to improve the Se status of livestock include feeding Se-enriched mineral supplements, giving Se injections, or both, but often these approaches fail to maintain consistent blood Se concentrations necessary for optimal health and productivity. An alternative approach is to increase the Se content of feed sources by fertilization, also called agronomic Se biofortification. In this study, we focused not only on our previously tested Se application rates as sodium selenate but also on fertilization with nitrogen-phosphorus-potassium (NPK) for grasses and PK for alfalfa, as well as sulfur(s) fertilization. In addition, we evaluated in forage Se responses among the diverse elevations, climatic and growing zones, precipitation and temperature ranges, soil types, forage species, and harvest procedures across Oregon. Our results showed forage Se concentrations increased linearly with foliar sodium selenate application, and doubling with each additional Se application. There were limited changes linked to forage type, location, NPK/PK fertilization with or withouts, or by year. Nearly all forage total Se was contained in the first two cuts and most of the applied selenate was metabolized to organic Se in plant tissue. Determining the concentration of Se in forage by sending samples to a forage laboratory allows livestock producers the ability to predict desired whole-blood Se concentrations in livestock. In conclusion, foliar selenate application is an effective management strategy to increase forage total Se concentrations and highly bioavailable organic Se concentrations with low interference of site when using recommended NPKS fertilization protocols.

Technical Abstract: Selenium (Se) concentrations in soils and plants are low in the Pacific Northwest, and consequently, in livestock consuming locally-grown forages. Applying sodium selenate with traditional nitrogen-phosphorus-potassium-sulfur (NPKS) fertilizers provides a cost-effective Se agronomic biofortification method for increasing forage Se concentrations and maintaining optimum health and productivity of livestock. This study was conducted on forages grown for two years at three Oregon sites: central Oregon (Terrebonne: orchardgrass), eastern Oregon (Union: grass mixture), southwestern Oregon (Roseburg: grass-legume mixture), and on alfalfa ( Medicago sativa L.) in eastern Oregon (Union). Using a split plot design with double-repeated measures (2017 and 2018 with first, second, third, and residual harvest cuts each year), we determined the best combination of springtime Se application (0, 45, or 90 g Se/ha from sodium selenate; whole plot) and NPKS fertilization (none, NPK/PK fertilization, with or without sulfur; subplot) to improve concentrations of total Se and beneficial organic Se species in forages. Forage Se concentrations increased linearly with foliar sodium selenate application, doubling with each additional 45 g Se/ha application (first cut median: 0.11, 2.06, and 4.15 mg Se/kg dry matter, respectively) with limited changes linked to forage type or site, NPK/PK fertilization with or without sulfur, or year. Nearly all incorporated Se was contained in the first two cuts (87% and 9% in first and second cuts, respectively) and most of the applied selenate was metabolized to selenomethionine in plant tissue. In conclusion, springtime sodium selenate foliar application is an effective management strategy to increase forage total Se concentrations and highly bioavailable selenomethionine concentrations in forage grown across Oregon, with low interference of site when using recommended NPKS fertilization protocols.