The acidity measured in a soil and water mixture is designated as active acidity and is a measure of the pH environment of the root. This does not represent the total amount of acid in a soil. Soils have a large reserve supply of acidity held by clay and organic matter particles or in aluminum and iron compounds. As calcium and magnesium carbonates from aglime neutralize the active acidity in the soil solution, more acidity is released into solution from the reserve supply and the pH does not rise. This resistance to a pH change is called buffering. Buffering capacity of a soil is a function of the clay and organic matter content as well as the amount of aluminum and iron compounds. Soils that are highly buffered require more lime to raise the pH because they have a larger supply of reserve acidity that must be neutralized. Florida soils are aparantly "lightly buffered", allowing the PH to be easily neutralized with small amounts of lime.

In most laboratories, the buffering capacity (total acidity) is determined by mixing a special solution (buffer solution) with soils and measuring the change in pH. This test is labeled "Lime Index" (also called "SMP Buffer pH&quot. Lime requirements are calculated on the basis of change in pH of the buffer solution.



Edited by - Sag...again on 10/03/2002 10:46:25