Growth and chemical composition of white clover as affected by sulphur supply

Plants of white clover (Trifolium repens L. var. Ladino) were grown in sand culture with four levels of sulphur supply. Growth increased with increasing sulphur supply, all plants except those at the highest sulphur level showing deficiency symptoms. As the severity of the deficiency increased, the root system formed a proportionately larger part of the plant, and the stems and petioles smaller proportions; the proportion of the whole plant formed by the laminae was reduced to only a slight extent. Nitrogen and sulphur fractions were examined in the laminae, nitrogen at each of three harvests and sulphur at the second harvest. The percentages of protein nitrogen and of total nitrogen increased as sulphur supply increased, protein nitrogen forming a greater proportion of the total nitrogen at the higher sulphur levels. In contrast, protein sulphur formed the bulk of the total sulphur in deficient plants, but as sulphur supply approached an adequate level for growth, there was a marked increase in non-protein organic sulphur and a smaller increase in sulphate sulphur. In this respect, white clover appears to differ from legumes other than Trifolium spp. and from non-legumes, all of which accumulate sulphur mainly as sulphate.