Selenium availability in soils and its uptake by vegetable plants

Total Selenium (Se) and Se fractions extractable with 1M ammonium nitrate, 1M ammonium acetate or 0.01M calcium chloride + 0.002M diethylene-triamine-pentaacetate (CAT) as well as the Se content in whole shoots of Chinese cabbage (Brassica campestris subsp. pekinensis L.) and kohlrabi (Brassica oleracea var. gongylodes L.) were determined. The content of the element in tubers of kohlrabi (the edible parts) was also measured. Plants were grown in pots with two different soils (loamy sand and silt loam) maintained in a greenhouse. Soils were amended with 0, 5 or 10% (w/w) metallurgical slag and adjusted to pH levels of approximately 5 and 7. Measurements were carried out employing online selenium hydride formation coupled to a graphite tube Atomic Absorption Spectrometer. Total Se content in the soils ranged from about 150 mug kg(-1) in the slag-free treatments to about 400 mug with 10% slag. Se in whole plant shoots increased accordingly from about 20 to 150 mug kg(-1) dry matter. Se in kohlrabi tubers was in the same order if grown on the lighter soil A, however, it ranged from traces to only about 40 mug kg(-1) on the heavier soil B. Correlation between soil Se fractions and Se uptake in whole shoots was also tested by means of two-factorial linear regression analysis. They were best for CAT (Chinese cabbage, R-2 = 0.56 and 0.85; kohlrabi, R-2 = 0.73 and 0.71 at pH 5 and 7, respectively) indicating that this extractant is the most suitable of those tested for the estimation of phytoavailable Se in soils.