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, GUOJI - Pennsylvania 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: 4/15/2023
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: Forage selenium (Se) concentrations are low in many regions of the United States, including the Pacific Northwest. Livestock consuming these forages are susceptible to Se deficiency, unless Se supplementation is provided. To minimize the occurrence of Se deficiencies, we have previously shown that the Se status of livestock can be improved by feeding Se biofortified forages, a practice known as agronomic Se biofortification. In Oregon, the Se concentration of forages can be increased by adding Se to fertilizers as an amendment for growing forage crops. The currently recommended application rates of Se are under 30 g Se/ha, however, one question remains unanswered, can higher application rates and different forms of Se fertilizer effectively increase Se concentrations in forage cuttings? In this two-year study, we investigated applying both a high rate of Se as foliar selenate and a lower rate of slow-releasing Se added to the soil. Our results showed that Se levels were only higher in first two cuttings of forage produced from foliar-applied Se compared to lower Se levels in first two cuttings from soil applied Se. However, subsequent cuttings from forage receiving soil amended Se sustained their forage Se levels even the following year in contrast to forage harvest from foliar-applied Se. The results demonstrated that both methods of Se biofortification are effective for increasing forage Se concentrations in first year cuttings, however, soil applied Se as a slow releasing fertilizer, appears to sustain forage Se concentrations in cuttings taking place the following year. This method may be the preferred choice of Se application for sustaining forage Se concentrations on a sustained basis.

Technical Abstract: Selenium deficiencies are still a major concern in livestock production. Consequently, livestock producers pay close attention to Se content in forages fed to their animals. Unlike any other state in the USA, Oregon livestock producers are allowed to add Se as a supplemental fertilizer for growing forage, In this study, we investigated the effects of applying foliar sodium selenate at 900 g Se/ha compared to 45-90 g/ha with a slow-release Se (granular Selcote Ultra® , comprised of 25% selenate and 75% as barium selenate) on forage Se concentrations in different cuttings. The high amendment rate (900 g Se/ha) resulted in higher forage Se concentrations in the first cutting at 49 mg Se kg/ dry matter (DM)] compared to 7.61 mg Se/kg DM with the 90 g/ha amendment rate of Selcote. Forage Se concentrations were also increased in the second cutting the following year but not thereafter with the high rate of foliar Se application. In comparison to foliar selenate, granular Selcote Ultra® resulted in lower Se concentrations in first cutting, yet forage Se concentrations increased in subsequent cuttings, including the following residual spring cuts. The Se species profiles of grass-clover forage amended at 900 g Se/ha showed a much higher percentage for SeMet (75%) compared to a much lower percentage of SeMet (9.1%) with the 45 and 90 g Se/ha application rates. We have shown that a higher application rate of foliar selenate doesn’t prolong the interval before subsequent reapplication of Se amendment is needed. We conclude that forage Se concentrations depend upon the amount and chemical form of Se as a biofortification amendment. Thus, even though higher forage Se concentrations were achieved with an amendment rate of 900 g Se/ha, removal of forage with cuttings quickly resulted in baseline forage Se concentrations in the following spring cuttings. Determining which Se amendment strategy to utilize will depend on the animal type and the potential severity of the Se deficiency. However, the soil application of slow releasing Se appears to maintain forage Se concentrations in year 2 compared to high rates of foilar selenate application.