ABSTRACT
The pH of soil solutions varies widely, from pH < 3, in pyritic-bearing and other metal suldebearing soils, to pH > 9 in sodium-affected or black alkali soils. Although it is difcult to x a range of soil pH values that encompasses all environments, soils that have pH values less than 4.0-4.5 or greater than 8.5 have usually been impacted by human activities. Excessive soil acidity, which is generally indicated by solution pH values less than 5.0-5.5, is a concern from both an environmental and an agronomic perspective. In excessively acidic systems (such as pyritic spoils), macronutrient availability and microbial activity is restricted, phytotoxic levels of soluble Al and Mn are observed, and the solubility and mobility of many potentially deleterious trace elements is relatively high.
