Sulphur in Nitrogen Metabolism of Legumes and Non-Legumes

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Abstract
A study was made of the influence of S on the N metabolism of subterranean clover and the non-legumes oats, flax and linseed. All spp. responded to S on the 3 soils used. Sulfates of ammonium. K, Na, and Mn were all effective. Non-legumes deficient in either S or N were pale green and contained a lower % of protein N than the dark green, treated plants. N deficiency decreased the percentages of non-protein and total N. S deficiency increased the percentages of both non-protein and total N. High nitrate accumulation occurred in the S-deficient plants where nitrate was the source of N. Thus S was needed by the non-legumes for protein formation from the absorbed combined N. N-deficient non-legumes responded little in color or growth to S. The S-N yield interaction was positive. Clover, under Mo supply inadequate for symbiotic nitrogen fixation, reacted to S and N treatments in the same way as the non-legumes, normal growth occurring only where both S and N were provided. No effect of S on the yield or visual symptoms was obtained where Mo and N were deficient. The Mo_S and N-S yield interactions were positive. The added S and N were needed for protein formation in the legume as in the non_legumes. In clover provided with Mo and dependent upon symbiotic N fixation for its N supply, deficiency of S decreased the % total N as well as the yield. Thus symbiotic N fixation was greatly reduced by S deficiency. Clover deficient in S showed visual symptoms of N deficiency, and contained a low % of protein N. However, the % of non-protein N in the clover was increased by S deficiency. The S-deficient clover responded little in color or growth to applied N. Thus the restricted growth of the S-deficient clover was not due to poor N fixation consequent on defective nodulation, but to a deficiency of S in the host legume. Clover deficient in S had fewer nodules than the treated plants. Nodulation reflected the N demand of the host legume. S deficiency decreased the demand for N and decreased the number of nodules, in contrast to deficiencies of N and Mo, which increased the demand for N and the number of nodules.