GEOCHEMISTRY OF SELENIUM IN SOIL-CROP SYSTEM OF NEHE CITY, HEILONGJIANG PROVINCE

According to the 1:250 000 scale land quality geochemical survey data of black soil in Northeast China, 1627 groups of surface soil (0-20 cm) samples and 415 groups of deep soil (150-200 cm) samples are collected from Nehe City of Heilongjiang Province to study the Se total content, available content in different types of soil, Se content in crop seeds and distribution characteristics in soil profiles. The results are shown as follows:1) The average Se content in topsoil is 0.239×10^-6, which is lower than that of China and world, and higher than that of Heilongjiang Province and Northeast China Plain. It is characterized by Se sufficiency, and the Se-sufficient land area reaches 84.21%. 2) The Se contents vary in different types of soil. The Se contents in black soil, chernozem and meadow soil are higher than those in dark brown soil, bog soil and alluvial soil. 3) In terms of land use types, the Se contents in traffic land, construction land and cultivated land are higher than those in forest, grassland and water conservancy land, reflecting its close relation with human activity intensity. 4) The Se content in soil profiles decreases with the increase of depth, and that in topsoil is the highest. 5) The average Se content in main crop seeds of corn, soybean and rice is 0.035×10^-6, characterized by low Se. The agricultural technology can be applied to develop Se-rich products and improve grain quality.