Selenium deficiency is a widespread problem amongst grazing livestock in many areas of
Britain. The pathway of selenium from soil to plants and hence to livestock is not clear and no simple
relationships appear to exist between selenium concentration in soil and that in herbage. This study
aimed to elucidate the soil factors influencing selenium accumulation by plants.
A field sampling programme was carried out in England and Wales, collecting herbage,
topsoil and subsoil samples from 16 agricultural sites seasonally over a two year period. Seasonal
variations in plant selenium concentrations were noted, with lower concentrations during the spring
and summer due to increased plant growth rate. This seasonal difference was independent of seasonal
soil contamination of pasture.
A significant correlation of r=0.41 was found between soil and herbage selenium
concentrations; previous research had not found a significant correlation. Selenium concentrations in
soil were closely associated with the organic matter content of the soil, but the association was not
significant for herbage selenium. No correlations between soil sulphur and herbage selenium
concentrations were found. The relationship between soil and herbage selenium concentrations and
soil pH was complicated by the effect of organic matter on both selenium concentrations and soil pH.
The lowest soil-plant uptake of selenium was found on an improved moorland farm site.
The field work was augmented by two greenhouse pot trials; i) the effect of fertilisers on the
uptake of selenium in grass and clover species grown on vermiculite; ii) the influence of organic matter
on selenium accumulation in Lolium perenne grown on soils from three of the field sites. Nitrogen
fertilisation produced lower herbage selenium concentrations due to growth enhancement and dilution
effects. No competition between selenium uptake and sulphur added in fertilisers was seen at the low
concentrations of selenium and sulphur used in the experiments. The influence of phosphate fertilisers
on selenium uptake was not clear. Selenite uptake was greater than selenate uptake in the plants
grown on vermiculite, but those grown on soil accumulated selenate to a greater extent than selenite.
Organic matter additions to soil increased the uptake of selenium in herbage; growth was also
increased but no corresponding decrease in selenium concentration was found, in contrast to the results
following nitrogen fertilisation.
