ACIDITY
N S Bolan, Massey University, Palmerston North, New Zealand
D Curtin, New Zealand Institute for Crop and Food Research,
Christchurch, New Zealand
D C Adriano, University 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+) quring 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 generate sufficient soil acidity that ceral crop cultivation has had to be abandoned due to aluminum (AI) 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, theeby 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. p. 11-17. In Encyclopedia of Soils in the Environment, edited by D. Hillel. Elsevier Academic Press. Amsterdam, The Netherlands.
