Sulphur in organic and inorganic combination in pasture grasses

Abstract

THE sulphur content of pastures has recently become a subject of considerable importance both from the point of view of sulphur fertilisation of soils [Alway, 1927] and in relation to the sulphur requirements of sheep for wool-production [Robertson and Marston, 1928]. The question of sulphur deficiency in soils has led to very thorough surveys of the total sulphur content of pastures in different parts of the world, but the organic sulphur content of pastures has received little or no attention. Nevertheless the separation of the total sulphur content of grasses into organic and inorganic components is important in seeking a correlation between the sulphur content of pastures and their value for purposes of wool-production, as only organic sulphur can be made use of by animals in biological synthesis. In the present paper, a method is described whereby the organic sulphur of pastures can be readily determined. It is assumed that all the inorganic sulphur in green leaves is in the form of sulphate, whether free or as ethereal sulphate. This sulphate-sulphur is therefore estimated and deducted from the total sulphur, giving a value for the organic sulphur.As regards the nature of the organic sulphur compounds in grass, they probably occur as constituents of protein. Woodman [1926] finds 27-92 % crude protein in autumn cuts of English grass, while Rigg and Askew [1929] find an average value of 33*37 % crude protein for eight samples of New Zealand pasture. "Crude protein" includes chlorophyll and other nonprotein nitrogen compounds, but the figures are of the right order to account for the organic sulphur present in grass, assuming that grass-protein contains the average amount of sulphur. In this connection it is to be noted that a water-soluble protein prepared from grass, as subsequently described, by the method of Chibnall and Schryver [1921] did not contain sulphur. This substance was a proteose, however, not a native protein, and it represented only a small proportion of the total nitrogen of the grass. Since protein-sulphur in grass would have to form part of an amino-acid, the question of the identity of this sulphur amino-acid immediately arises. Robertson and Marston [1928] apparently make a tacit assumption that the acid is cystine, this being the sulphur constituent of wool and also of widespread occurrence elsewhere in nature [Jones, Gersdorff and Moeller, 1924].

The effect of sulphate of ammonia applications on the sulphur content of various grass and clover mixtures

“…This tendency was even more marked in 1954 and suggests that under conditions of ample sulphate supply, rye-grass absorbs the ion to a greater extent than the grasses in the other mixtures. There is a suggestion in the results of Aitken (1930) who analysed the leaf blades of several grass species in New Zealand and the figures quoted by Bosch (1954) that rye-grass has such a tendency. Strict comparisons between species made at identical stages of growth, however, are necessary before it may be concluded that rye-grass behaves in this way.…”

Studies of the Sulphur of Pasture Grass. I. The Cystine Content of Pasture Grass

“…The Sullivan colorimetric method showed that only a trace of cystine was present, although the addition of cystine to the hydrolysate proved the method to be applicable. 5. Further proof that pasture grass is deficient in cystine was obtained by determining the sulphide sulphur liberated on heating with 30 per cent, alkali.…”

Semimicro determination of inorganic sulfate in plant material

“…In spite of the recognition of the problems associated with this method of separation, few alternatives have been proposed. Benzidine, which had been demonstrated to be the pre-eminent reagent for the determination of sulfate in plasma (Cuthbertson and Tompsett, 1931) and urine (Owen, 1936) did not find favor (Aitken, 1930) and was abandoned for use with plant extracts because of nonspecific precipitation which occurred (Wood and Barrien, 1939). A significant advance was made when Johnson and Nishita (1952), making use of the reaction by which sulfate may be reduced to sulfide, then to be converted to methylene blue (Gustafsson, 1960), developed a method for the direct determination of low concentrations of sulfate sulfur in plant material.…”