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Sulfur Fractions and Carbon-Nitrogen-Phosphorus-Sulfur Relationships in Some Brazilian and Iowa Soils¹

ABSTRACT

Current knowledge concerning the percentage distribution of the various S fractions in soils is mainly derived from studies of S in surface soils of temperate regions. This study was conducted to determine the S fractions and C-N-P-S relationships in some subtropical soils from Brazil and to compare the values in these soils with those in soils of a temperate region from Iowa.

Analyses for S fractions in some Brazilian and Iowa surface soils indicated that, unlike Iowa soils, Brazilian soils contain adsorbed inorganic sulfate S. Expressed as percentage of total S in soils, the Brazilian soils studied contained from 5 to 23% inorganic sulfate S, from 20 to 65% ester sulfate S, from 5 to 12% C-bonded S, and from 24 to 59% unidentified organic S. The corresponding percentages in the Iowa soils were: from 2 to 8% inorganic sulfate S, from 43 to 60% ester sulfate S, from 7 to 18% C-bonded S, and from 31 to 39% unidentified organic S. No inorganic nonsulfate S could be detected in any of the Brazilian and Iowa soils analyzed.

Tests showed that the Brazilian soils studied have capacities for adsorption of sulfate S. There were considerable variations in C, N, P, and S relationships among the Brazilian soils as compared with those among Iowa soils.

¹ Journal Paper no. J-7753 of the Iowa Agr. & Home Econ. Exp. Sta., Ames. Project no. 1845.

² Visiting Lecturer, Assistant Professor, and Professor of Agronomy, respectively, Iowa State Univ., Ames 50010. Present address of senior author: Centro de Energia Nuclear na Agricultura (CENA), Escola Superior de Agricultura "Luiz de Queiroz," Universidade de Sao Paulo, 13400 Pirarcicaba, Estado de Sao Paulo, Brasil.

Received for publication November 12, 1973. Accepted for publication September 17, 1974.