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This article in SSSAJ

  1. Vol. 66 No. 4, p. 1285-1295
     
    Received: June 21, 2001
    Published: July, 2002


    * Corresponding author(s): alainfplante@hotmail.com
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doi:10.2136/sssaj2002.1285

Intraseasonal Soil Macroaggregate Dynamics in Two Contrasting Field Soils Using Labeled Tracer Spheres

  1. A. F. Plante *a and
  2. W. B. McGillb
  1. a Unité de Science du Sol, INRA Versailles, Route St-Cyr, 78026 Versailles Cedex, France
    b College of Science and Management, Univ. of Northern British Columbia, 3333 University Way, Prince George, BC Canada V2N 4Z9

Abstract

Several studies have hypothesized that increased turnover of soil aggregates promotes soil organic matter losses under cultivation; while others suggest that organic matter protection requires occlusion into aggregates. However, few direct observations of aggregate dynamics are reported in the literature. A 2-yr field study was performed to observe active organic C dynamics and soil macroaggregate dynamics in two contrasting soils. Dysprosium-labelled tracer spheres were applied to field plots to observe soil macroaggregate dynamics, while CO2-evolution during 10-d laboratory incubations was used to measure active C dynamics. Results of biochemical analyses showed higher active C turnover in the low C soil, suggesting a lower proportion of incoming organic matter was protected when compared with the high C soil. No net aggregation or degradation was determined over the long-term, suggesting the soil was at steady-state. However, aggregation followed a cyclical pattern reset by the over-winter period and tillage. Tracer incorporation into large macroaggregates was observed within 9 d after tillage, reaching a maximum of 40 to 60% tracer incorporation into >1-mm aggregates after 72 d. A rapid approach to equilibrium within the study period reflected rapid dynamics of macroaggregates in both soils studied. Slower macroaggregate dynamics in the high C soil were attributed to sustained aggregate stability and resiliency at the end of the growing season. Based on observations of macroaggregate dynamics in soils with contrasting active organic C dynamics, we suggest that rapid macroaggregate turnover not only results in the exposure of labile organic matter but also provides a mechanism for the occlusion and physical protection of particulate organic matter.

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Copyright © 2002. Soil Science SocietyPublished in Soil Sci. Soc. Am. J.66:1285–1295.

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