This study was undertaken to determine the effects of various substances on soil contaminated with cobalt (Co) on the mass and content of cobalt in the main crop—spring barley (Hordeum vulgare L.)—and the after-crop—white mustard (Synapis alba L.). Manure, clay, charcoal, zeolite, and calcium oxide were used for phytostabilization. Cobalt was applied in the form of CoCl2 in doses of 0, 20, 40, 80, 160, and 320 mg/kg soil. Amendments in the form of manure, clay, charcoal, and zeolite were

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... in an amount of 2% in relation to the weight of the soil in a pot, with calcium oxide at a dose of 1.30 g CaO/kg of soil. The highest cobalt doses resulted in a significant reduction in yield of both plants and in tolerance index for cobalt. Increasing contamination of soil with cobalt resulted in a major and significant increase in its content in plants and a reduction in cobalt translocation factor in both plants. Amendments used in phytostabilization had a significant effect on growth and development of oat and content of cobalt in plants. The strongest effect on the yield of above-ground parts was exerted by manure (both plants) and calcium oxide (white mustard), while the strongest effect on weight of roots was exerted by calcium oxide (both plants) and zeolite (white mustard). The addition of manure, zeolite and calcium oxide to soil caused an increase of the tolerance index for both plants, while the addition of clay only had a positive effect for white mustard. All substances used in phytostabilization (except zeolite) decreased cobalt content of roots, and manure and calcium oxide in above-ground parts of spring barley; manure and zeolite only in above-ground parts, and calcium oxide in both organs of white mustard. Most of them also reduced bioconcentration of cobalt in above-ground parts, calcium oxide decreased cobalt content in roots of both plants, and manure in roots of spring barley. The effect on cobalt translocation was less clear, but most substances used in phytostabilization increased the transfer of cobalt from the soil to plants. White mustard had higher ability to accumulate cobalt than spring barley.