Abstract

“ No other single chemical soil characteristic is more important in determining the chemical environment of higher plants and soil microbes than the pH. There are few reactions involving any component of the soil or of its biological inhabitants that are not sensitive to soil pH. This sensitivity must be recognized in any soil-management system.” “ Lime is truly a foundation for much of modern humid-region agriculture. Knowing how pH is controlled, how it influences the supply and availability of essential plant nutrients as well as toxic elements, how it affects higher plants and human beings, and how it can be ameliorated is essential for the conservation and sustainable management of soils throughout the world.” (Brady and Weil, 1999) Under areas where rainfall exceeds evapotranspiration, soil acidification is an ongoing natural process, which can either be accelerated by the activity of plants, animals and humans or can be impeded by careful management practices. In areas affected by industrial activities, soil acidification is caused by acid drainage from pyrite oxidation and also from acid precipitation. In areas that remain unaffected by industrial pollution, soil acidification in managed ecosystems is mainly caused by the release of protons (H + ) during the transformation and cycling of carbon (C), nitrogen (N) and sulfur (S). Just like in managed ecosystems, soil acidification in natural ecosystems caused by acid drainage and acid precipitation can have adverse impacts where soils have low pH buffering capacity. Liming is the most common management practice aimed at neutralizing the acid produced, thereby overcoming the adverse impacts of soil acidification. This review brings together fundamental aspects of soil acidification and recent developments on the implications of liming in relation to soil processes, particularly nutrient and heavy metal transformation and bioavailability in soils. The article first outlines the various soil, plant and microbial processes that generate acid (protons; H + ions) both under natural and managed ecosystems. It then discusses the effects of soil acidity on soil chemical and biological properties. The effect of liming to overcome the problems associated with soil acidity is examined in relation to the transformation of nutrient ions and heavy metals. The practical implications of liming to overcome heavy metal toxicity have been discussed in relation to the adsorption, leaching and phytoavailability of these metal ions. Future research should aim to focus on the development of methods to quantify lime-enhanced (im)mobilization of nutrient ions and heavy metals in soils and to explore further the role of liming in remediating contaminated soils.

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