Nitrogen, sulphur and other mineral elements in white clover and perennial ryegrass grown in mixed swards, with and without fertiliser N, at a range of sites in the UK

Perennial ryegrass (Lolium perenne L. cv. S23) and white clover (Trifolium repens L. cv. Blanca) were grown in mixed swards, with and without fertiliser N as ammonium nitrate, at 12 sites in the UK. Grass and clover separated from herbage harvested in May, July and September, have been examined for N, S and other major mineral elements, in relation to the nutrition of both the crop and ruminant animals. The total N content was greater in the clover than in ryegrass at each site, both with and without fertiliser N. The S content of the clover was similar to that of ryegrass at the first harvest in May, but was lower in July and September. There were large differences between the species in the ratio N:S, the average being 17.1:1 in white clover and 8.6:1 in ryegrass. The proportions of the total S present as sulphate were higher in ryegrass, with a mean of 48%, than in the clover, with a mean of 16%. The contents of Mg, and particularly of Ca, were higher in clover, while K was generally higher in ryegrass. Consequently, the ratio K: (Ca+Mg) was always at least twice as high in the ryegrass as in the clover. In some of the ryegrass, but none of the clover samples, it exceeded 2.2:1, the value above which there is an increasing risk of hypomagnesaemia in ruminant animals. The content of total cations (Ca + Mg + K + Na) was on average 37% greater in the clover than in the ryegrass, while the content of total inorganic anions (but including organic P) was much less in the clover. The content of organic anions, as calculated from the difference between the contents of total cations and inorganic anions, was at least twice as great in white clover as in ryegrass.