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This article in SSSAJ

  1. Vol. 74 No. 2, p. 663-669
     
    Received: May 1, 2009


    * Corresponding author(s): dkissel@uga.edu
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doi:10.2136/sssaj2009.0168

Equilibration Reaction from Single Addition of Base to Determine Soil Lime Requirement

  1. J.S. Thompsona,
  2. D.E. Kissel *a,
  3. M.L. Cabrerab and
  4. L.S. Sonona
  1. a Agricultural and Environmental Services Laboratories, 2400 College Station Rd, Univ. of Georgia, Athens, GA 30602
    b Dep. of Crop and Soil Science, 3111 Miller Plant Sciences Building, Univ. of Georgia, Athens, GA 30602

Abstract

The University of Georgia Soil, Plant, and Water Laboratory (SPW) uses a single-addition titration for estimating soil lime requirement. The lime requirement depends in part on a soil's pH buffering capacity (described as lime buffer capacity [LBC] in mg CaCO3 kg−1 per pH unit), which is estimated from the rise in soil pH after Ca(OH)2 is added and allowed to react for 30 min. The 30-min reaction time has not been sufficient to reach equilibrium between the soil and Ca(OH)2, resulting in an underestimation of the LBC. As a corrective measure, the SPW adjusts the agricultural lime recommendations to account for the lack of equilibrium. This study investigated the rate of pH change after Ca(OH)2 is added to acid soils. Specifically, the objectives of this study were to: (i) determine the time in which the Ca(OH)2–treated samples reached pH equilibrium; and (ii) determine if a relationship exists between the LBC estimated from a 30-min equilibration and the LBC estimated from the time in which the sample had reached an equilibrium pH. The 25 soils used in this study were equilibrated for up to 96 h. Results indicated that the soils had reached an equilibrium pH by 84 h after the addition of Ca(OH)2 The ratio (mean of 84- and 96-h LBC/30-min LBC) could be predicted with the equation 1.4742 + 0.0023(30-min LBC) (r 2 = 0.82). This relationship allows the current titration procedure with 30-min equilibration time to be used to predict the equilibrium LBC, which in turn can be used to calculate more accurate lime recommendations.

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