Effects of Amount and Chemical Form of Selenium Amendments on Forage Selenium Concentrations and Species Profiles.

Abstract

Selenium (Se) agronomic biofortification of plants is effective for alleviating Se deficiencies in human and livestock populations. Less is known about how higher selenate amendment rates, or how foliar compared with granular selenate amendments affect forage Se concentrations. Therefore, we compared the effects of a higher sodium selenate foliar amendment rate (900 vs. 90g Se ha-1), and two selenate amendment methods (liquid foliar sodium selenate vs. granular slow-release Selcote Ultra® at 0, 45, and 90g Se ha-1) on Se concentrations and Se species in forages across Oregon. The 10 × amendment rate (900g Se ha-1) resulted in 6.4 × higher forage Se concentrations in the first cut (49.19 vs. 7.61mg Se kg-1 plant DM, respectively) compared with the 90gha-1 amendment rate, indicating that forages can tolerate higher selenate amendment rates. Most Se was incorporated as SeMet (75%) in the harvested portion of the forage (37mg Se kg-1 forage DM of the first cut) and only a limited amount was stored in the selenate reserve pool in the leaves (~ 5mg Se kg-1 forage DM). Higher application rates of selenate amendment increased forage Se concentrations in first and second cuts, but carry over in subsequent years was negligible. Application of foliar selenate vs. granular Selcote Ultra® amendments, between 0 and 90g Se ha-1, both resulted in a linear, dose-dependent increase in forage Se concentration. Amendments differed in their Se incorporation pattern (Se%), in that, first cut forage Se concentrations were higher with foliar selenate amendment and second, third, and residual (following spring) cut forage Se concentrations were higher with granular Selcote Ultra® amendment. Given the linear relationship between forage Se concentrations and whole-blood Se concentrations in livestock consuming Se-biofortified forage, we conclude that targeted grazing or other forage feeding strategies will allow producers to adapt to either selenate-amendment form.