Evidence for carbon sequestration by agriculturalliming

Hamilton, S.K., A.L. Kurzman, C. Arango, L. Jin, and G.P. Robertson

Presented at the All Scientist Poster Reception (2006-05-09 )

Agriculture 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 Ca and Mg to carbonate alkalinity in soil solutions beneath unmanaged vegetation vs. limed row crops, and of streams and rivers in agricultural vs. 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 half of its C content, in contrast to the prevailing assumption that all of the carbon in lime becomes CO₂. The ~30 Tg/y of agricultural lime applied in the U.S. could thus sequester 1.9 Tg C/y, about 15% of the annual change in the U.S. CO₂ emissions (12 Tg C/y for 2002-2003). The implications of liming for atmospheric CO₂ stabilization should be considered in strategies to mitigate global climate change.