Gregory Mullins, Lucian Zelazny, Steve Heckendorn, and Marcus Alley. Virginia Tech, Dept. of Crop & Soil Env. Sci., 424 Smyth Hall (0403), Blacksburg, VA 24061
The Virginia Tech Soil Testing Laboratory currently uses a combination of soil pH and soil textural class to determine lime recommendations for Virginia's soils. This approach assumes that soil textural class gives a reasonable estimation of soil buffering capacity. To adopt a more quantitative approach for estimating soil buffering capacity, laboratory and incubation studies were conducted to calibrate the Mehlich Buffer for determining lime recommendation for Virginia's soils. The study included 64 archived soil samples that had been collected from across Virginia for a previous study and 17 soils that were collected state wide in 2003. Soil pH and Mehlich buffer pH was measured on all soil samples. Adams-Evans and SMP Buffer pH were measured on the 17 soils collected in 2003. In addition, titratable whole soil exchangeable acidity was determined on all soils using 1 N KCl. An incubation study was conducted using the 17 soils collected in 2003. Reagent grade CaCO3 was applied to each soil at various rates based on exchangeable soil acidity. The soils were brought to field capacity and allowed to air-dry followed by rewetting at 30-day intervals. Soil pH was measured after 3 months. At a target pH of 6.2 titratable soil acidity was highly correlated (R2 = 0.93) with the Mehlich Buffer lime requirement. Data from the incubation study showed that the Mehlich (R2 = 0.72), Adams-Evans (R2 = 0.66) and SMB (R2 = 0.82) Buffer pH were highly correlated with the amount of CaCO3 required to raise soil pH to a target of 6.2. These laboratory and incubation studies demonstrate that the Mehlich Buffer gives reasonable estimates of lime requirements for Virginia's diverse soils.
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