Soil pH buffering capacity: a descriptive function and its application to some acidic tropical soils

Nelson, Paul N., and Su, Ninghu (2010) Soil pH buffering capacity: a descriptive function and its application to some acidic tropical soils. Australian Journal of Soil Research, 48 (3). pp. 201-207.

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Calculation of soil acidification rates requires knowledge of pH buffering capacity (pHBC), which is measured using titration methods. The pHBC is often quoted as a single value for a particular soil, implying a linear relationship between pH and the amount of acid or alkali added. However, over its whole range, the relationship is sigmoid rather than linear, and in many soils pH is low or high enough to be outside of the linear range. In this work we fitted a simple sigmoid function to pH buffer curves of 8 tropical Australian soils obtained using one titration method and 58 Papua New Guinean (PNG) soils obtained using another titration method. The function described the curves well for all soils (adjusted r2 > 0.93 for all samples and >0.99 for 90% of samples), irrespective of the titration method, allowing pHBC to be calculated as a function of pH across the range of pH values established. Using the function, the contribution of variable charge to pHBC was calculated for the PNG soils; on average it was 93% at the pH buffer curves’ inflection point, which corresponds with the soil’s minimum pHBC. Factors other than variable charge became important at pH (1 : 5, 0.002 M CaCl2) values <4.8 or >6.0. The relationship between pHBC and soil organic matter content was closest at pH 6.0–6.5. Application of the sigmoid function could facilitate more accurate assessments of acidification risks, acidification rates, and potential management interventions, particularly as soils become increasingly acidic.

Item ID: 11709
Item Type: Article (Research - C1)
ISSN: 1446-568X
Keywords: soil acidification; charge fingerprint; variable charge; organic matter; cation exchange capacity; Papua New Guinea; Andosol; sigmoid function
Date Deposited: 05 Aug 2010 04:11
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050304 Soil Chemistry (excl Carbon Sequestration Science) @ 100%
SEO Codes: 96 ENVIRONMENT > 9614 Soils > 961402 Farmland, Arable Cropland and Permanent Cropland Soils @ 100%
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