Selenium (IV) and Sulphur (VI) as Elements Modifying Plant Quality: Content of Selenium and Sulphur Forms in Wheat

In order to achieve high-quality yields, it is essential to provide plants with the necessary nutrients, including selenium (Se) and sulphur (S), to meet their nutritional requirements. This study aimed to determine the effect of selenium (0, 10 and 20 g Se ha^-1) and the date of its application (in the tillering phase and in the stem elongation phase) and sulphur application (0, 15 and 30 kg S ha^-1) on the content of selenium and various forms of sulphur (total sulphur, sulphate sulphur and organic sulphur) and the N:S ratio in winter spelt wheat and winter common wheat. The research hypothesis assumed that different doses of selenium and sulphur and the timing of their application would have a beneficial effect on the Se and S content in the grain and straw of spelt wheat and common wheat. Selenium fertilisation significantly increased the content of this element in the grain of spelt wheat and common wheat. The concentration of selenium was also influenced by the timing of its application in the plant growth environment. However, the dose of selenium and the timing of its application were not associated with significant changes in the content of both forms of sulphur in the tested plants. The experimental factors used did not contribute to the achievement of selenium levels toxic to humans and animals. The presence of sulphur in the growth environment of spelt wheat and common wheat was associated with an increase in the content of both total sulphur, sulphate sulphur and organic sulphur in their grain and straw, especially in spelt wheat straw by an average of 17%, 29% and 23%, respectively, and in common wheat straw by 26%, 18% and 57%, respectively. The sulphur content in the plant growth environment was not associated with a change in the selenium content in the grain of the tested plants. The results of our study suggest that the optimal dose of selenium for biofortification of humans and animals is 20 mg Se ha^-1 on clay soil, applied during the stem elongation phase of spelt and common wheat. Biofortification of wheat with selenium and sulphur is a good method of supplementing deficiencies of this element in the human diet.