A Comparative Study of Four Extractants on the Extraction of Available Selenium in Vegetable and Orchard Soils

Abstract

BACKGROUND Available selenium is an important index to evaluate the supply capacity of selenium from soil to plants. However, there is no national standard method to test available selenium in China. The selection of extractants is very important for the accurate determination of available selenium. OBJECTIVES To determine the optimum extractant based on the correlation between available selenium and selenium species. METHODS Four extractants, sodium bicarbonate, potassium dihydrogen phosphate, nitric acid and hydrochloric acid, were selected to extract the available selenium from vegetable and orchard soils in Tianjin. Atomic fluorescence spectrometry was used to determine the content of various forms of selenium, and the minimum, 25 percentile, median, 75 percentile, maximum value of the effective selenium and water-soluble+ion-exchange+carbonate-combined selenium were used for comparative analysis and the difference. RESULTS The average content of available selenium extracted from vegetable soils by sodium bicarbonate and potassium dihydrogen phosphate was 0.039mg/kg, which was higher than that of nitric acid and hydrochloric acid. The contents of available selenium extracted from orchard soils by sodium bicarbonate, potassium dihydrogen phosphate, nitric acid and hydrochloric acid decreased in turn. The minimum, 25 percentile, median, 75 percentile, and maximum values of available selenium extracted by potassium dihydrogen phosphate in the two soils were closer to the content of sum of water-soluble, ion-exchange and carbonate combined selenium. CONCLUSIONS Potassium dihydrogen phosphate with a concentration of 0.1mol/L was the optimum extractant of available Se for vegetable and orchard soils in Tianjin.

Keywords

• soil
• selenium
• available form
• speciation analysis
• extractants
• potassium dihydrogen phosphate
• atomic fluorescence spectrometry