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BACKGROUND Selenium is an important, essential element of life. The development of selenium-enriched agricultural products is a safe and effective way to increase the level of human selenium intake in China. The evaluation and utilization planning of selenium-enriched land resources are important aspects of land quality geochemical surveys, to serve the development of characteristic agricultural products and to overcome poverty. OBJECTIVES To improve the methodology for selenium-enriched land assessment and to develop more effective and safe land-use planning methods. METHODS The research results on selenium content in soil and crops, the origin of soil selenium, the soil selenium occurrence and its bioavailability factors, the soil-crop system selenium absorption and transport, and the interaction between selenium and heavy metal cadmium were reviewed in this article. RESULTS The geochemical background of selenium in top soils in China was 0.2mg/kg, significantly lower than the average in world soils (0.4mg/kg). Generally, the soils had a low selenium level, and it was believed that the use of 0.40mg/kg selenium as a selenium-enriched soil standard had a strong scientific basis. Selenium in soils was mostly from a geological setting, however, in some cases anthropogenic activities may be an important source of soil selenium. The genetic mechanism of selenium-enriched soils can be categorized as high geological background, weathering accumulation and anthropogenic input as well as a multi-factor combination. The association of selenium with cadmium and other heavy metals was pervasive because of similar geochemical behavior and geological origin. The species and bio-availability of selenium in soils were mainly controlled by its source and soil physic-chemical properties such as pH, Eh, and contents of organic matter, iron oxides and aluminum oxides. In turn, these factors affect the availability of selenium-enriched land and became the theoretical basis and considerations for formulating local standards for selenium-enriched soil. The accumulation ability of selenium varied greatly between crop cultivars. Selection native crop types with higher selenium accumulation ability and low accumulation with Cd as well as other toxic metals was of practical meaning. Some existing selenium-enriched agricultural product standards did not fully consider the purpose of human selenium supplementation, and there were problems such as poor coordination between standards. It was urgent to strengthen the formulation of selenium-enriched agricultural product standards. CONCLUSIONS Selenium-enriched land suitability assessment, local selenium-enriched soil standard establishment and selenium-enriched crop plantation planning should consider the concentration of selenium and heavy metals in soils, their source and genesis, bio-availability and influencing factors, transport and accumulation in soil-crop system, the synergistic or antagonistic effects between selenium and other chemicals such as cadmium, as well as plantation suitability of crop cultivars under local climate, soil conditions and landscape. According to the availability of selenium-enriched land resources, classification, zoning, scientific planning and reasonable planting management are carried out. In order to meet the needs of investigation and evaluation of selenium-enriched land resources, availability analysis, and research on the health effects of selenium-enriched agricultural products, it is recommended to strengthen the research and application of extraction, separation, analysis, and determination methods for soil and crop selenium content and species. |
