Selenium fractionation and bio-availability in some low-Se soils of central Jiangsu Province

Three types of soils in central Jiangsu Province was studied using seuential extraction techniques .The results showed that Se concentration of the tested soils is relatively low and the soils derived from sediments of Yangtze River fall in category of that for low-Se soils. Se extracted by 5%K2S2O8-1:1HNO3 is the predominated Se fraction in these soils, followed by residue Se, making a total contribution of 70%～80% of soil Se. Generally, Se is richer in the topsoil than in the plowpan except for Se exractaed by 2.5mol/L HCl. Water soluble Se concentration is shown to be affected by soil pH, while exchangeable Se is strongly positively related to other fractions except for to water soluble Se. Among the five extractants, only Se extracted by 0.5 mol/L NaHCO3 is in close relation to shoot Se content. Thus 0.5 mol/L NaHCO3 can be used as indicator of bio-available Se in these low-Se soils.The sum of Se extracted by 0.25 mol/L KCl and 0.7 mol/L KH2PO4 can also be used as indicator of bio-available Se in these low-Se soils.