Liming is the addition of calcium and magnesium to soil to neutralize acidity and increase the activity of soil bacteria. The amount of lime needed to reach the desired acidity depends on the pH and the buffering capacity of the soil. The pH is a measurement of acidity or alkalinity. Buffering capacity refers to the soil's ability to resist change to its pH.

Additionally, liming improves nutrient efficiency by encouraging fertilizer uptake. However, there are important limits to liming, as oversupply may cause harm to plant life (Axelrod, 2004). The most common liming materials come from grinding natural limestone.

Limestone is composed mostly of calcium carbonate (CaCO3) and by most state laws must contain 6 percent magnesium for purposes of liming. In addition to buffering the soil, the main way to reverse acidification in freshwater is through liming the water body or its surrounding drainage basin. Carbon dioxide (CO2) does not absorb the Sun's energy, but it does absorb the heat energy released from the Earth. Some of the released heat energy returns to Earth and some goes out into space. This describes the greenhouse effect of CO2; that is, CO2 lets light energy in, but not all of the heat energy can get out. Soil liming can act as either a source or a sink for CO2. A heat sink absorbs and dissipates the heat energy.

Some studies indicate that rather than all of the carbon in lime becomingCO2, the lime may sequester up to half of its carbon content, thus becoming an effective carbon sink. If this is so, liming might even be part of the strategy to moderate climate change (Botterill, 2003). Streams draining agricultural watersheds generally show a net CO2 uptake. However, as nitrate (a common fertilizer ingredient) concentrations increase, lime may switch from a net CO2 sink to a CO2 source.

Peat soil contains large amounts of carbon and therefore is a significant emission source of greenhouse gases--especially of methane. When farming acidic peat lands, adjustment of the acidity through liming is essential. However, when adding lime to these soils often rich in carbon and methane, CO2 production increases. In addition, because of the enhanced decomposition of organic matter through liming, soluble organic carbon increases and may factor into climate change. Finally, it is important to note that the amount of CO2 emissions from liming is not completely clear. This is because the amount of carbonate lime applied to soils is unclear, as is the net amount of carbon from liming that is released as CO2.

References

1. Axelrod, Regina S., David Leonard Downie, and Norman J. Vig, eds. The Global Environment: Institutions, Law, and Policy. 2d ed. Washington, D.C.: CQ Press, 2004.

2. Botterill, Linda C., and Melanie Fisher, eds. Beyond Drought: People, Policy, and Perspectives. Collingwood, Vic.: CSIRO, 2003.

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