Monday, 7 November 2005 - 3:15 PM
91-5

Lime Requirement by Measurement of the Lime Buffer Capacity.

David Kissel, Bob Isaac, Rick Hitchcock, Leticia Sonon, and Paul Vendrell. Soil, Plant, and Water Laboratory, Agricultural and Environmental Services Labs, 2400 College Station Rd., Athens, GA 30602-9105

Soil testing laboratories in the US typically determine the lime requirement of acid soils from the depression in pH of a buffer solution mixed with soil. Most buffers contain toxic chemicals, requiring special safety precautions and hazardous waste disposal. Our objective was to implement for routine use in the laboratory a simple titration procedure based on a single addition of Ca(OH)2 solution to a 1:1 soil:0.01 M CaCl2 solution. The method is based on two pH measurements, the first before addition of Ca(OH)2 and the second taken 30 to 45 minutes following the addition of the Ca(OH)2. The lime requirement was based on the linear extrapolation to the target pH. Successful implementation required a period of testing with client's samples, in which the lime recommendations from the new method were compared to recommendations by the Adams-Evans buffer method used by the University of Georgia soil testing laboratory. Results indicated good agreement between lime recommendations by the new titration method and the Adams-Evans procedure, with about 10 % less lime recommended with the new procedure. Separate incubations in soil of lime recommended by the two methods indicated the recommendations from the new titration procedure were nearer the target pH and with less variation in pH following the application of lime.

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