Effects of climate change on soil carbon and nitrogen storage in the US Great Plains

Soils of the US Great Plains contain enormous stocks of soil organic carbon (SOC) and soil organic nitrogen (SON) that are vulnerable to predicted climate and land use change. Climate change scenarios predict a 2.2 degrees C to 3.6 degrees C (4 degrees F to 6.5 degrees F) increase and more variability in precipitation across most of the United States. This study quantifies management effects (native grassland, Conservation Reserve Program [CRP], and cropped) on SOC and SON stocks across the region and assessed soil variables (soil texture, cation exchange capacity and others) and climatic drivers (precipitation and temperature) to predict future changes in carbon (C) and nitrogen (N) stocks. Across all sites, cropped land had significantly lower C and N stocks in the 0 to 5 cm (0 to 2 in) and 0 to 10 cm (0 to 3.9 in) depths than native sites, while CRP sites were intermediate. Mean annual temperature (MAT), the ratio of mean annual precipitation to potential evapotranspiration (MAP:PET), soil bulk density (BD), and clay content were important covariates for SOC and SON stocks within land use. Soil C and N stocks under all three land uses were strongly negatively related to MAT and positively related to MAP:PET, suggesting that they are equally vulnerable to increased temperature and decreasing water availability Based on these empirical relationships, a 1 degrees C (1.8 degrees F) increase in MAT could cause a loss of 486 Tg SOC (536 million tn) and a loss of 180 kg SON ha(-1) (160 lb SON ac(-1)) from the top 10 cm (3.9 in) of soil over 30 years, but the decrease will be mediated by water availability (MAP:PET). Combined, increased temperature and conversion from CRP to cropland could decrease the existing SOC sink, but improved soil management and increased water availability may help offset these losses in the US Great Plains.