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This article in SSSAJ

  1. Vol. 74 No. 2, p. 517-524
     
    Received: Oct 29, 2008


    * Corresponding author(s): Martin.Chantigny@agr.gc.ca
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doi:10.2136/sssaj2008.0347

Influence of Temperature on Water-Extractable Organic Matter and Ammonium Production in Mineral Soils

  1. Martin H. Chantigny *a,
  2. Denis Curtinb,
  3. Mike H. Beareb and
  4. Laurie G. Greenfieldc
  1. a Agriculture and Agri-Food Canada, 2560 Hochelaga Blvd, Québec, QC, Canada, G1V 2J3
    b New Zealand Institute for Plant & Food Research Ltd, Private Bag 4704, Christchurch Mail Centre, Christchurch 8140, New Zealand
    c School of Biological Sciences, Univ. of Canterbury, Private Bag 4800, Christchurch, New Zealand

Abstract

Cold (room temperature) and hot water (70–80°C) extraction methods have been used to assess the availability of organic matter and N in soil; however, the influence of temperature on their extractability is largely unknown. Twenty-one mineral soils from New Zealand and eastern Canada were incubated for 16 h in water (1:6 soil/water ratio) at temperatures ranging from 20 to 80°C. After centrifugation and removal of the supernatant solution, the soil residue was extracted with 2 mol L−1 KCl to recover NH4–N released during incubation. In all cases, water-extractable organic C (WEOC) and N (WEON) increased exponentially with temperature. The temperature dependence of organic matter solubility differed considerably among the soils (estimated increase in WEOC and WEON: 1.1–5.3% °C−1). These differences were not explained by management history or soil physicochemical properties, although there was evidence that organic matter extractability in some clay soils was less sensitive to temperature. Ammonium N was released in significant amounts at all temperatures. Peak NH4–N release typically occurred at 50°C, where NH4–N comprised an average of 49% of the total recovered N (WEON plus NH4–N). Factors that may account for NH4–N production during the 16-h incubation include mineralization at the lower temperatures and abiotic processes (e.g., release of clay-fixed NH4 and thermal degradation of organic N) at higher temperatures. The possibility that mineralization made a significant contribution to NH4–N production at temperatures as high as 50°C warrants further investigation.

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