SREL Reprint #2832

Acidity

N. S. Bolan1, D. Curtin2, and D. C. Adriano3

1Massey University, Palmerston North, New Zealand
2New Zealand Institute for Crop and Food Research, Christchurch, New Zealand
3University of Georgia, Aiken, SC, USA

Introduction: Soil acidification is a natural process that can either be accelerated by certain plants and human activities or slowed down by careful management practices. Industrial and mining activities lead to soil acidification due to acid produced from pyrite oxidation and from acid precipitation caused by the emission of sulfur (S) and nitrogen (N) gases. In managed ecosystems, soil acidification is mainly caused by the release of protons (H+) during the transformation and cycling of carbon (C), N, and S, and fertilizer reactions. Soil acidification caused by these processes can have adverse impacts where soils are unable to buffer against further pH decrease. For example, in parts of North America and Europe, soil acidification caused by acid precipitation has resulted in forest decline and, in some parts of Australia, continuous legume cultivation and inappropriate use of N fertilizer have generated sufficient soil acidity that cereal crop cultivation has had to be abandoned due to aluminum (Al) and manganese (Mn) toxicity.
Historically, liming is the most common management practice used to neutralize soil acidity. Most plants grow well in the pH range 5.5-6.5, and the usual objective of liming programs is to maintain pH in this range. Liming enhances the physical, chemical, and biological properties of soil through its direct effect in ameliorating soil acidity and through its indirect effects in mobilizing plant nutrients, immobilizing toxic heavy metals, and improving soil physical conditions. In variable-charge soils, liming can be used as a management tool to manipulate the surface charge, thereby controlling the reactions of nutrient ions and heavy metals. Liming provides optimum conditions for a number of biological processes, including N2 fixation and mineralization of N, phosphorus (P), and S.

SREL Reprint #2832

Bolan, N. S., D. Curtin, and D. C. Adriano. 2005. Acidity. pp. 11-17 In D. Hillel (Ed.). Encyclopedia of Soils in the Environment. Elsevier Academic Press. Amsterdam, The Netherlands.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).