Effects of amount and chemical form of selenium amendments on forage selenium concentrations and species profiles

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

Submitted to: Biological Trace Element Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2022
Publication Date: 1/5/2023
Citation: Hall, J.A., Bobe, G., Filley, S.J., Pirelli, G.J., Bohle, M.G., Wang, G., Davis, T.Z., Banuelos, G.S. 2023. Effects of amount and chemical form of selenium amendments on forage selenium concentrations and species profiles. Biological Trace Element Research. 201:4951-4960. https://doi.org/10.1007/s12011-022-03541-8.
DOI: https://doi.org/10.1007/s12011-022-03541-8

Interpretive Summary: Forages in certain areas of Oregon are deficient in selenium (Se) often resulting in deficiencies in livestock that graze them. Increasing the sodium selenate (900 g Se ha-1) application rate 10-fold to grass-clover forage resulted in 7x higher forage Se concentrations in the first cut compared with the 90 g ha-1 amendment rate. After two cuttings of forage nearly all of the Se is accounted for, predominantly as selenomethionine, in the harvested forage and thus additional applications are needed to increase the Se content of the forage once again. Forage Se concentrations after granular Selcote Ultra® amendment are lower in the first cuts, but higher in later and residual cuts compared with foliar selenate amendment. Selcote Ultra® amendment should be reapplied every two years for effective agronomic Se biofortification. Depending on the rate of application, Se content in the forage can exceed 5 mg Se kg-1 which could potentially be toxic to livestock if fed for an extended period. Therefore, if Se is applied as a foliar amendment, the resulting forage should be tested and diluted with other forages, if necessary, before feeding to livestock.

Technical Abstract: We previously reported the effects of springtime sodium selenate foliar amendment rates (0, 45, and 90 g Se ha-1) and nitrogen, phosphorus, potassium, and sulfur (NPKS) fertilization on Se concentrations and Se species in forages across Oregon. The objective of the current report was to examine the effects of a higher sodium selenate amendment rate (900 g Se ha-1) and slow-release Se (granular Selcote Ultra® at 45 and 90 g Se ha-1). The 10x amendment rate (900 g Se ha-1) resulted in 7x higher forage Se concentrations in the first cut (49 mg Se kg-1 plant DM) compared with the 90 g ha-1amendment rate (7.6 mg Se kg-1 plant DM) with 75% of selenate converted to organic selenomethionine. In comparison to foliar selenate amendment, granular slow-release Se (Selcote Ultra® at 45 and 90 g Se ha-1) resulted in lower first cut Se concentrations yet more sustained increases in forage Se concentrations in later cuts. We conclude that forage Se concentrations will depend on amendment rates for both foliar selenate and granular Selcote. For effective agronomic Se biofortification, foliar selenate amendment should be reapplied after two cuts and Selcote every two years.