ORGANIC SELENIUM AND ITS DISTRIBUTION IN SOILS
中国几种土壤中的有机态硒及其分布特征

Organic selenium and its distribution in soils of typical groups in China were studied using 0.1 mol L-1NaOH+0.1 mol L-1Na4P2O7 extraction techniques. Organic selenium accounts for 3.46 %-59.86%, on average, 28.6% of the total Se for 16 soils tested. Factors affecting organic Se content in soils include total Se content, organic carbon, exchangeable acidity, and pH. The C/S eratio of organic matter extracted by the NaOH-Na4P2O7 mixture ranges from 0.58 × 106 to 42.93×106, on average, 6.38×106. Soils from low Se areas where Kashan and Kaschin-Beck disease once happened, have much higher C/Se ratio than those from areas without Se deficiency. Of the organic selenium, 66% (the average) was associated with fulvic acid (FA-Se) and 34% with humic acid fraction (HA-Se). The percentage of HA-Se is, in general, higher in Se deficient soil than in normal soil.