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This article in SSSAJ

  1. Vol. 70 No. 1, p. 287-296
     
    Received: Nov 23, 2004


    * Corresponding author(s): alainfplante@hotmail.com
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doi:10.2136/sssaj2004.0363

Impact of Soil Texture on the Distribution of Soil Organic Matter in Physical and Chemical Fractions

  1. Alain F. Plante *a,
  2. Richard T. Conanta,
  3. Catherine E. Stewarta,
  4. Keith Paustianab and
  5. Johan Sixac
  1. a Natural Resource Ecology Lab., Colorado State Univ., Fort Collins, CO 80523
    b Dep. of Soil and Crop Sciences, Colorado State Univ., Fort Collins, CO 80523
    c Dep. of Plant Sciences, Univ. of California, Davis, CA 95616

Abstract

Previous research on the protection of soil organic C from decomposition suggests that soil texture affects soil C stocks. However, different pools of soil organic matter (SOM) might be differently related to soil texture. Our objective was to examine how soil texture differentially alters the distribution of organic C within physically and chemically defined pools of unprotected and protected SOM. We collected samples from two soil texture gradients where other variables influencing soil organic C content were held constant. One texture gradient (16–60% clay) was located near Stewart Valley, Saskatchewan, Canada and the other (25–50% clay) near Cygnet, OH. Soils were physically fractionated into coarse- and fine-particulate organic matter (POM), silt- and clay-sized particles within microaggregates, and easily dispersed silt- and clay-sized particles outside of microaggregates. Whole-soil organic C concentration was positively related to silt plus clay content at both sites. We found no relationship between soil texture and unprotected C (coarse- and fine-POM C). Biochemically protected C (nonhydrolyzable C) increased with increasing clay content in whole-soil samples, but the proportion of nonhydrolyzable C within silt- and clay-sized fractions was unchanged. As the amount of silt or clay increased, the amount of C stabilized within easily dispersed and microaggregate-associated silt or clay fractions decreased. Our results suggest that for a given level of C inputs, the relationship between mineral surface area and soil organic matter varies with soil texture for physically and biochemically protected C fractions. Because soil texture acts directly and indirectly on various protection mechanisms, it may not be a universal predictor of whole-soil C content.

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