pH. For example, at pH 4.6, the Al concentration at Haskell
was 35.6 mg kg−1, whereas, at Lahoma it was 58.4 mg kg−1. At
similar pH level, the soil at Perkins resulted in an Al con-
centration of 96.0 mg kg−1, which indicates that pH threshold
may differ among locations due to the inherent differences
among soil types. A significant inverse exponential relation-
ship existed between soil pH and AlKCl at all sites, with