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This article in AJ

  1. Vol. 79 No. 6, p. 1079-1083
     
    Received: July 15, 1986
    Published: Nov, 1987


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doi:10.2134/agronj1987.00021962007900060026x

Particle Size and Soil Texture Effects on Elemental Sulfur Oxidation1

  1. M. R. McCaskill and
  2. Graeme J. Blair2

Abstract

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%.

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