Selenium Fertilization of Pastures for Improved Forage Selenium Content

Selenium (Se) was applied to perennial ryegrass (Lolium perenne) and subterranean clover (Trifolium subterranean) pasture as a fertilizer to determine the effect of Se form and concentration on Se accumulation in subsequent forage growth. Treatments were a no Se control, 0.6 kg/ha Se as sodium selenate, and 0.6, 1.1, and 2.2 kg/ha Se as sodium selenite, all applied to pasture plots with low soil Se concentration in southwestern Oregon (n = 3 plots per treatment). The plots were protected from grazing by use of electric fence, and total forage DM production and Se concentrations were measured after the spring growing season in yr 1. Pastures were grazed by sheep over the fall growing season, but then were protected from spring grazing to enable sampling of residual forage Se concentrations during yr 2. Application of 0.6 kg/ha selenate provided greater (P < 0.01) average forage Se content in yr 1 (8.44 ± 0.08 mg/kg) than all other treatments. Compared with the control (0.09 ± 0.06 mg/kg), the plots in the 0.6 and 2.2 kg/ha selenite treatments contained greater (P < 0.01) forage Se content (1.17 ± 0.05 and 4.24 ± 0.35 mg/kg, respectively), whereas the 1.1 kg/ha selenite treatment tended (P = 0.06) to increase forage Se content (3.11 ± 0.79 mg/kg). Two years after Se application, only the plots treated with 0.6 kg/ha selenate and 2.2 kg/ha selenite had forage Se concentrations (0.43 ± 0.04 mg/kg and 0.51 ± 0.06 mg/kg, respectively) that differed (P = 0.04 and P = 0.01, respectively) from the control. Fertilization with Se had no effect (P = 0.37) on forage yield during yr 1. These data suggest that selenite and selenate fertilization increases forage Se concentrations for up to 2 yr. This may be a cost-effective method of supplying Se for grazing livestock.