Estimating Net CO2 Emissions From Agricultural Lime Applied to Soils in the U.S.

Agricultural lime in the form of crushed limestone and dolomite is applied to U.S. agricultural soils at a rate of 20-30 Tg yr-1. Understanding the ultimate fate of applied lime and associated carbonate species is important for estimating net CO2 emissions from agricultural lime. We provide a history of lime use in the U.S., estimate the fraction of dissolution by acid species, discuss transport of lime constituents through the soil profile, and estimate the transport of these constituents in rivers and to the ocean. Previous estimates of net CO2 loss from agricultural lime assume that all CO2 in lime is eventually released to the atmosphere. Our analyses suggests that, as a first approximation, about 50% of the CO2 in lime is released to the atmosphere. This estimate translates to 0.059 Mg C per Mg limestone and 0.064 Mg C per Mg dolomite, and 4.4-6.6 Tg CO2 emissions in 2001, depending on the total application of agricultural lime in the U.S. This estimate largely depends on the pathways of lime dissolution and the fraction of bicarbonate leached through the soil profile. If carbonate species are accumulating lower in the soil profile, then our estimates of net CO2 emissions from agricultural lime may be overstated. However, if carbonate from lime is transported down rivers to the ocean, as is suggested by data from the Mississippi watershed, then the application of aglime may be impacting carbon cycling in the coastal ocean. A more complete understanding of net CO2 emissions from aglime will contribute to bottom-up estimates of CO2 emissions from agricultural lands, and these estimates are also applicable to terrestrial carbon accounting.