Comparison Of Soil Available Selenium Extraction Methodsand Its Bioavailability

Selenium is an essential nutrient element for human beings due to its great importance to human health. Selenium in the soil enters human body mainly via the food chain, Se uptake from soil by plant depends mainly on the bioavailability and fractions of soil Se. In this study,14of different chemical extractants and10of Se-enriched soils from Enshi, Hubei were employed to screen for best chemical analytical method of soil available Se by soil pot seedling experiment. The relationship between soil Se contents and the Se uptake of plant and the effect of Se application on the growth of rice were studied through the rice soil pot experiment, and the effect of different chemical additives on the Se release from Se-enriched soils was examined through cultivation experiments. This research intended to provide the theoretical basis as well as the practical measures for the diagnosis of soil Se fertility and regulation in Se-enriched soils. The main results were as follows:1. The soil available Se content determined by14different methods in10soils, with the total Se content of0.46-9.22mg/kg, were0.00-292.94ug/kg, accounting for0%-15%of soil total Se. The available Se content by Sodium Bicarbonate (including organic Se) method was the highest, and had the greatest coefficient with Se contents and accumulation in Nicotiana tabacum, Brassica juncea and Oryza saliva, and thus, was the best chemical method for analysis of soil available Se.2. Soil Se fractionation was carried out by a sequential extraction procedure, and the results showed that the significantly positive correlation was observed between the Se contents and accumulation of N. tabacum and the Exchangeable Se and Fe-Mn oxides-Se, indicating that exchangeable Se and Fe-Mn oxides-Se could be easily absorbed and accumulated by plant.3. Since the soils used were all Se-enriched soils, with the lowest available Se content of0.11mg/kg, the Se contents of rice was higher, with the range of0.20-1.50mg/kg, which meet the national standard of Se-enriched rice. The result showed that Se-rich rice could be obtained by growing paddy rice in these soils.4. The Se uptake of rice increased gradually from tillering stage to booting stage, and at mature stage, the Se began to transfer to rice spike. Application of Se fertilizer in Se-rich soils increased Se contents in shoots and rice grain significantly, with the average increase by590%and272%in tillering and booting stage, respectively, and by412%in rice grain at mature stage. In addition, Se application significantly increased rice yield by18%.5. Addition of pig manure and straw could increase the release of soil Se. In addition, results showed that fly ash, which is an industrial solid waste, could be used in paddy soils to increase Se availability.