Sulphur oxidation capacity of some soils of the south central area of Chile

Hernán Figueroa P., Luis Longeri S. e Iván Vidal P.1

Sulphur is an important element in plant nutrition. The elemental sulphur oxidizing capacity of30 soils belonging to five series ofthe South Central region ofChile was determinated. The series were Cauquenes (Ultic Paleustalf), Collipulli (Typic Haplohumult), Diguillín (Typic Dystrandept), Santa Bárbara (Thaptic Haploxerand) and San Carlos (Ultic Palexeralf). Soil samples at 75% field capacity were amended with 500 mg S kg-1 and S-SO4 content was measured after incubation at 25°C for 10, 20 and 30 days. Non S-amended samples were also incubated as a comparison. Sulphur oxidation followed a zero-order kinetic with ko ranging from 0.02 to 4.98 mg kg-1 day-1. The average sulphur oxidation rate was 3.44; 2.85; 1.35; 0.61 and 0.45 mg S-S04 kg-1 day-1 in series Diguillín, San Carlos, Cauquenes, Santa Bárbara, and Collipulli, respectively. Stepwise multiple regression analysis (r2=0.87**) selected soil interchangeable Na, K and Ca, P-Olsen and sand percentage contents as predictors of the S oxidation rate (T), according to the equation:
T = -3.69 + 2.13Na + 1.45K + 0.38Ca + 0.038P-Olsen + 0.039Sand

Keywords: sulphur, oxidation rate, soils.
1 Universidad de Concepción, Facultad de Agronomía, Casilla 537, Chillán, Chile. ividal@udec.cl.