Particle Size and Soil Texture Effects on Elemental Sulfur Oxidation¹

Abstract

Most previous experiments examining factors affecting the conversion of elemental S into plant‐available forms have used indirect methods, such as measuring sulfate accumulation, and have at times resulted in exaggerated estimates of elemental S oxidation rates. Direct measurement of residual elemental S offers a more reliable estimate of conversion rate, but only some of the factors known to affect conversion rate have been investigated by direct methods. A pot experiment was conducted over 238 days to measure conversion rates under a range of elemental S particle sizes (0.1–2.0 mm) and soil textures, and with and without inoculation with sulfur‐oxidizing bacteria. Conversion rates were measured by two indirect methods—S uptake by plants and 35SO4 dilution‐and one direct method—acetone extraction of remaining elemental S. Initial surface area of elemental S was the prime determinant of conversion rate, but three other factors had to be considered to fully explain observed release characteristics. These were (i) a gradual particle disappearance in 0.1‐ and 0.2‐mm particles, which caused a reduction in conversion rate with time, (ii) a depression in conversion rate for particle sizes ≧ 0.4 mm on noninoculated treatments, and (iii) shape considerations that were imputed to the observed lower conversion rates for the more spherical 2.0‐mm size. Three of the four soils—an Arenic Haplustult, a Plinthic Haplustult, and a Typic Torrert—showed increased conversion rates in response to inoculation, with inoculation responses most marked for the larger (> 0.4 mm) particle sizes. The other soil—a Udic Ustochrept—was not responsive to inoculation. No relationship was detected between soil texture and elemental S conversion rate over a range of clay contents from 9 to 52%.

Sulfur in agriculture

“…The particle shape also influences the total surface area; the more spherical the shape, the smaller the mass/area ratio (Germinda & Janzen, 1993). Several mathematical models have been described for the determination of the oxidation rate depending on the size and shape of S 0 particles over time, and there is an ongoing debate over which is the best model (Blair, 1987;Janzen & Bettany, 1987;McCaskill & Blair, 1987;Blair et al, 1993;Watkinson, 1993;Watkinson & Blair, 1993). …”

Relação entre atributos de solos e oxidação de enxofre elementar em quarenta e duas amostras de solos do Brasil

“…Os resultados obtidos neste estudo contrariam algumas investigações, nas quais se concluiu que as taxas de oxidação foram inversamente relacionadas ao teor de argila e diretamente relacionadas ao teor de areia (Janzen & Bettany, 1987a;Lawrence & Germida, 1988;Deng & Dick, 1990). Entretanto, concordam com outros trabalhos que não obtiveram relações significativas entre a textura do solo e a taxa de oxidação de S-elementar (Rehm & Cadwell, 1969;McCaskill & Blair, 1987;Watkinson, 1989). Segundo Germida & Janzen (1993), essas observações aparentemente contraditórias são, provavelmente, reflexos indiretos do estado de aeração dos solos, e o efeito inconsistente da textura pode ser parcialmente explicado pelas diferentes condições de umidade em vários experimentos.…”

Kinetic model of elemental sulfur oxidation by Thiobacillus thiooxidans in batch slurry reactors

“…Microbial oxidation of sulfur in soils [13,20] or mine spoils [8,15] has been studied rather extensively because elemental sulfur is an increasingly important component of many fertilizers and is produced in surface deposits from mining operations of sul®de minerals.…”