Nitrogen is an essential input factor required for plant growth and biomass production. However, very limited information is available on how nitrogen fertilization affects the quality of crop residues to be used as lignocellulosic feedstock. In the present study, straw of winter wheat plants grown at six different levels of nitrogen supply ranging from 48 to 288kg nitrogen ha^-1 was analyzed for major cell wall components and mineral elements. Enzymatic digestion of the straw was carried out to evaluate the saccharification efficiency. The nitrogen concentration in the straw dry matter increased linearly from 0.32% to 0.71% over the range of nitrogen treatments. Cellulose and hemicellulose were not affected by the nitrogen supply while lignin peaked at medium rates of nitrogen application. The nitrogen treatments had a distinct influence on the silicon concentration, which decreased from 2.5% to 1.5% of the straw dry matter when the nitrogen supply increased from 48 to 192kgha^-1. No further decline in Si occurred at higher rates of nitrogen application. The most abundant metals in the straw were potassium and calcium and their concentrations almost doubled over the range of nitrogen supplies. The enzymatic saccharification efficiency was negatively correlated with the rate of nitrogen supply. We conclude that the level of nitrogen supply to wheat plants alters the composition of cell wall components in the straw and that this may result in reduced saccharification efficiency.