Soil selenium treatments to ameliorate selenium deficiency in herbage

Sodium selenite, sodium selenate, and sodium selenate in a pill formulation were applied to three soils known to produce Se‐deficient herbage ( < 100 μg Se kg −1 dry matter (DM)). The ability of the salts, applied in spring 1985, to ameliorate Se deficiency was followed over 3 years by taking four harvests each year. Selenate treatment at 10 g Se ha −1 and selenate prill treatment at 20 g Se ha −1 produced herbage with Se levels (geometric means) of between 0.57‐0.86 and 1.79‐1992 mg kg −1 DM respectively in the first spring harvest after treatment. Selenite was less potent and selenite at 100 g Se ha −1 produced a response in herbage closely similar to that of selenate at 10 g Se ha −1. Even at 300 g Se ha −1 the selenite treatment produced herbage with only 1.00‐1.36 mg Se kg −1 DM at the first harvest. Application of selenate in the prill form at 60 g Se ha −1 produced herbage potentially toxic to grazing animals with 4.81‐4.94 mg Se kg −1 DM. The addition of fertiliser N to Se‐treated plots increased total Se uptake at the first harvest by a factor of 4 and had a small effect on Se concentration. The Se concentration levels in herbage from Se‐treated plots declined exponentially ( t 1/2 = 21‐43 days). On one soil derived from Lower Old Red Sandstone and lava, selenite at 300 g Se ha −1 gave herbage with Se contents significantly above background ( P < 0.05) in all harvests over 3 years.