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.