Effect of Sulphur Fertilization on Amino Acid and Fraction Composition of Protein of White Mustard Seeds

In view of the increasing sulphur deficiency in Poland’s soils, in 2007-2010, a field experiment was performed with white mustard (Sinapis alba L.) in Haplic Luvisol with low sulphur content (mean – 9.4 mg kg-1). The aim of the research was to evaluate the effect of varied sulphur application methods (foliar and pre-sowing soil application), forms (elemental and ionic), and rates (0, 20, 40, 60 kg S ha-1) on the content of protein in mustard seeds, as well as on its amino acid and fraction composition. The research showed that of all the studied factors, the sulphur application rate affected the protein content the most. As compared with the control, sulphur application increased the overall sums of essential and dispensable amino acids in the mustard seeds as well as their quantitative ratio. The biological protein value indices (Chemical Score and Essential Amino Acid Index) point to a clearly positive effect of sulphur on the amino acid composition of the protein, including sulphur-containing methionine, an amino acid limiting protein biosynthesis. The sulphur rate significantly affected the content of all the protein fractions assayed, except for glutelins.