Sulphur–nitrogen interaction effects on the yield and composition of the protein‐N, non‐protein‐N and soluble carbohydrates in perennial ryegrass

In a controlled‐environment pot experiment sulphur fertilisers increased the yields of ryegrass when large dressings of nitrogen were also given. Yield responses to sulphur occurred when the dry matter contained less than 0.20% S. At the third cut, sulphur deficiency decreased concentrations of reducing sugars but had little effect on sucrose and fructosan in the grass dry matter. Only 44% of the nitrogen in the most sulphur‐deficient grass was protein‐N as compared to over 80% in non‐deficient grass. The non‐protein‐N accumulated predominantly as amides especially asparagine. The amino acid composition of the insoluble protein, including the proportions of cystine and methionine, was unaffected by acute sulphur or nitrogen deficiencies.