Soils and climate change

Abstract

Increasing soil carbon storage has been advocated as a means to both reduce net C emissions and increase the resiliency of soils for climate change (Lal 2004a, b; Lal et al. 2007). In fact, emissions of CO2 from soils since 1850 total approximately 78 ± 12 giga tons (1 Gt = 1 billion tons) of CO2. In comparison emissions related to fossil fuel use over the same time frame total 270 ± 30 Gt of CO2. Considering only cropland, total soil organic carbon sequestration potential in the US is 45–98 Mt (1 Mt = 1 million tons) (Lal et al. 2007). Soil carbon storage is complicated by the fact that increased soil carbon is not simply a case of adding carbon to soils and having that carbon remain in place for decades. Organic matter in soils is part of the annual cycle of growth and decay. At the same time that a portion of the existing carbon in soils is mineralized by soil microbes, more carbon is being added via plant growth and decay. Increasing carbon will result in net increases in primary productivity (plant growth). This increase in productivity will result in increased carbon inputs into soil. A portion of this increased productivity will remain in the soil as detritus from above and below ground plant biomass. While a fraction of this added carbon decomposes and returns to the atmosphere as CO2, a portion becomes incorporated into soil organic matter (Fig. 1).