Problem of Applying Sodium Selenate to Increase Selenium Concentration in Grassland Plants in Southern Belgium

In a survey of grasslands, mean selenium (Se) concentration in Holcus lanatus was 83 μg kg−1 (less than 100 μg kg−1, the minimal concentration protecting mammals from deficiency disorders). Despite rather high levels of soil extractable Se, plant Se availability was supposed to be low because of high soil humus concentration. A pot experiment with common grassland species showed contrasting responses to selenate addition (9 g Se ha−1 yr−1). Lolium perenne leaves reached 470 μg kg−1, and Trifolium pratense reached 292 μg kg−1. The controls were less than 100 μg kg−1. Leaves of others species showed greater values both in control and treated series and no significant difference. In a second pot experiment, Melilotus albus, a supposed secondary accumulator, and Lolium perenne as a control were submitted to moderate increased selenate additions (up to 45 g Se ha−1 yr−1). The results confirmed that Melilotus albus was a better accumulator with a leaf concentration that could reach the toxicity level of 2 mg kg−1.