Organic and Mineral Sulfur Fractions in Brazilian Soils Submitted to Consecutive Harvests

• Published in: Communications in soil science and plant analysis Vol. 34; no. 3-4; pp. 357 - 373
• Main Authors: Dias, Luiz E., Ribeiro, Emerson S., Alvarez V., Victor Hugo, Mello, Jaime W. V.
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Taylor & Francis Group 01.03.2003; Taylor & Francis
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Mineral components. Ionic and exchange properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil science; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; South America; Brazil; America; Monocotyledones; Organic matter; Extraction process; Soil fertility; Tropical zone; Cultivated soil; Available nutrient; Adsorption capacity; Oxisols; Inorganic element; Hydrogen Peroxides; Cereal crop; Tropical soil; Sorghum bicolor; Absorption; Gramineae; Angiospermae; Nutrient; Spermatophyta; Chemical composition; Application method; Sulfur; Speciation; Organic compounds
• ISSN: 0010-3624; 1532-2416
• DOI: 10.1081/CSS-120017826

Different methods have been used to determine sulfur (S) labile organic forms in tropical soils. Due to variability in their composition, different soil S fractions are solubilized at varying rates, and the contribution of each fraction to long-term availability has not been extensively studied. This study focused on the dynamics of S organic fractions in tropical soils, in the presence and absence of liming, over five consecutive harvests of Sorghum bicolor. A preliminary study was conducted to determine the best dose of H 2 O 2 to oxidize S-organic fractions. Fourteen surface soil samples (0-20 cm) of Brazilian Oxisols with differing levels of S adsorption capacity (SAC) were characterized for the following S-fractions: S-s=ignition of a soil-sodium bicarbonate mixture at 500°C; S-a=S extractable by NH 4 OAc (0.5 mol L −1 ) and HOAc (0.25 mol L −1 ); S-c=S extractable by CaCl 2 (0.01 mol L −1 ); S-p=S extractable by Ca(H 2 PO 4 ) 2 (500 mg L −1 of P in HOAc at 2.0 mol L −1 ); S-r=the difference between S-s and S-a; and S-o=S-c after H 2 O 2 oxidation treatment. Soil-S fractions were determined before the first harvest, and after the second and fifth harvest. Sulfur in the root system and shoot dry matter was determined after each harvest. The results indicated, among the different tested doses, that peroxide oxidation with 0.5 and 1.0 mL g −1 may be used to determine labile S-organic forms. Liming reduced the soluble sulfur content after peroxide oxidation with these two doses. The results denote existence of one more short-term labile S-organic fraction, and a second one, probably formed by more recalcitrant organic forms. In soils with low and medium sulfate adsorption capacity (SAC), the labile S-organic fraction seems to run, in the short term, the S availability to plants. The inorganic fraction seems to be the main controller of S availability in high SAC soils.