Evidence for carbon sequestration by agricultural liming

[1] Agricultural lime can be a source or a sink for CO2, depending on whether reaction occurs with strong acids or carbonic acid. Here we examine the impact of liming on global warming potential by comparing the sum of Ca2+ and Mg2+ to carbonate alkalinity in soil solutions beneath unmanaged vegetation versus limed row crops, and of streams and rivers in agricultural versus forested watersheds, mainly in southern Michigan. Soil solutions sampled by tension indicated that lime can act as either a source or a sink for CO2. However, infiltrating waters tended to indicate net CO2 uptake, as did tile drainage waters and streams draining agricultural watersheds. As nitrate concentrations increased in infiltrating waters, lime switched from a net CO2 sink to a source, implying nitrification as a major acidifying process. Dissolution of lime may sequester CO2 equal to roughly 25 - 50% of its C content, in contrast to the prevailing assumption that all of the carbon in lime becomes CO2. The similar to 30 Tg/yr of agricultural lime applied in the United States could thus sequester up to 1.9 TgC/ yr, about 15% of the annual change in the U. S. CO2 emissions (12 Tg C/yr for 2002 - 2003). The implications of liming for atmospheric CO2 stabilization should be considered in strategies to mitigate global climate change.