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FORMS OF SULFUR, AND CARBON, NITROGEN AND SULFUR RELATIONSHIPS, IN IOWA SOILS

1972; Lippincott Williams & Wilkins; Volume: 114; Issue: 5 Linguagem: Inglês

10.1097/00010694-197211000-00009

1538-9243

M. A. Tabatabai, J. M. Bremner,

Nitrogen and Sulfur Effects on Brassica

Although it has long been known that sulfur is essential for plant growth, very little is known about the nature and availability of the sulfur compounds in soils. Early work indicated that most of the S in well-drained soils of the humid regions is organically combined, and recent work indicates that most of this organic S occurs in two distinct forms: (a) organic S which is not bonded directly to carbon and is reduced to hydrogen sulfide by hydriodic acid, and (b) organic S which is directly bonded to carbon and is reduced to inorganic sulfide by Raney nickel in alkaline medium (3, 5, 6, 7, 8, 13, 14, 15). Fraction (a) is believed to consist largely, if not entirely, of S in the form of ester sulfates (organic sulfates containing C–O–S linkages; e.g., choline sulfate, phenolic sulfates, sulfated polysaccharides), and fraction (b) is believed to consist largely of S in the form of S-containing amino acids such as methonine and cysteine. The occurrence of S-containing amino acids in soils has been confirmed by chromatographic analyses of acid hydrolysates of soils and soil organic matter preparations (for review, see ref. 2), but attempts to isolate ester sulfates from soils have not thus far been successful and there is no unequivocal evidence that a substantial fraction of soil S is in the form of organic sulfates. Current knowledge concerning the forms of S in soils has been derived largely from investigations of Australian and Canadian surface soils, and no studies to determine the distribution of ester sulfate S and carbon-bonded S in U.S. soils have been reported. The main objective of the work reported here was to characterize the S in Iowa soils and to study the effect of sample depth on the distribution of different forms of S in soils. An additional objective was to compare the carbon, nitrogen, and sulfur relationships in Iowa soils with those in soils from other regions.