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Equilibration Reaction from Single Addition of Base to Determine Soil Lime Requirement
Author(s) -
Thompson J.S.,
Kissel D.E.,
Cabrera M.L.,
So L.S.
Publication year - 2010
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2009.0168
Subject(s) - lime , titration , soil water , chemistry , soil ph , acid–base titration , base (topology) , soil test , analytical chemistry (journal) , mineralogy , environmental chemistry , soil science , inorganic chemistry , environmental science , mathematics , materials science , metallurgy , mathematical analysis
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 CaCO 3 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.