The Stability of Different Forms of Selenium Applied to Low‐Selenium Soils

In some acid‐to‐neutral soils, water‐soluble selenite salts react rapidly with the solid phase to form a relatively insoluble adsorption complex. The Se in this complex is less available to alfalfa ( Medicago sativa L. ‘Dupuit’) than the Se added to the same soil as Fe(OH) 3 ‐HSeO 3 . In other soils, or in some acid soils limed to neutrality, the availability of Se to alfalfa from NaHSeO 3 and from Fe(OH) 3 ‐HSeO 3 is essentially the same. The availability of Se from Se o added to the same soils is less than from either NaHSeO 3 or Fe(OH) 3 ‐HSeO 3 sources. Oxidation of Se o is initially rapid in these soils, and does not seem to be pH dependent, but the rate of oxidation varies in different soils. Soluble selenite may be the most practical form of Se to add to low‐Se soils in order to produce crops containing sufficient Se to meet animal requirements.