ORGANIC SELENIUM DISTRIBUTION IN SELECTED CALIFORNIA SOILS

The distribution of organic Se was determined in seven soils from central California. Six of these soils were in a toposequence from an area thought to be relatively high in native Se. The seventh soil, thought to be low in native Se, was included for comparison. Three of the soils in the toposequence had total Se levels less than 1000 μg kg-1. Organic Se accounted for 50% or more of NaOH-NA4P2O7 extractable Se in all but the poorly drained Ciervo clay, which had about 40% in an organic form. Extracted organic Se compounds were fractionated into humates and hydrophobic and hydrophilic fulvates. The high percentage of extractable Se associated with organic matter in these soils represents a pool of potentially plant-available Se. -from Authors