What is the fate of ground limestone ("lime") amendmentsin agricultural systems?: Implications for terrestrial carbonsequestration

Kurzman, A.L. and S.K. Hamilton

Presented at the All Scientist Meeting (2003-09-12 )

A recent study (Raymond and Cole 2003) examining the export of alkalinity via the Mississippi River and its tributaries to the ocean suggests that land cover has a significant impact on alkalinity export. The increase in carbon export was not accompanied by an increase in the acidity of atmospheric deposition, the latter having remained relatively constant over the study period. An analysis of the tributaries indicated a positive relationship between area of cropland and stream alkalinity, in contrast to forested sites which showed a strong negative relationship. Carbon exported to the ocean in the form of alkalinity may represent a previously overlooked and significant sequestration pathway.Ground limestone (“lime”) amendments, commonly applied in intensive agricultural settings, may be contributing to the alkalinity export and subsequent carbon sequestration noted by Raymond and Cole (2003). Limestone application represents an anthropogenic transport of carbon from geologic deposits to an actively cycling form that can potentially affect the exchange of carbon dioxide with the atmosphere (Robertson et al. 2000). As agricultural ecosystems occupy an estimated 11% of the earth’s land surface, this has significant implications for the integrated greenhouse gas contribution of intensive agriculture.However, understanding the effect of liming on CO2 trace gas fluxes is difficult as two alternative fates of lime amendments are plausible: strong acid weathering (source) and carbonic acid weathering (sink). The relative importance of these pathways is unknown. Data from the KBS LTER indicate that both reactions are taking place, and that certain treatment replicates favor the carbonic acid weathering pathway. The factors controlling which reaction pathway predominates are not yet fully understood, but it may be that adding more lime, rather than less, may lead to carbon sequestration by creating conditions that favor carbonic acid weathering.

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