Impact of historical land-use changes on greenhouse gas exchange in the U.S. Great Plains, 1883–2003

Abstract

European settlement of North America has involved monumental environmental change. From the late 19th century to the present, agricultural practices in the Great Plains of the United States have dramatically reduced soil organic carbon (C) levels and increased greenhouse gas (GHG) fluxes in this region. This paper details the development of an innovative method to assess these processes. Detailed land-use data sets that specify complete agricultural histories for 21 representative Great Plains counties reflect historical changes in agricultural practices and drive the biogeochemical model, DAYCENT, to simulate 120 years of cropping and related ecosystem consequences. Model outputs include yields of all major crops, soil and system C levels, soil trace-gas fluxes (N2O emissions and CH4 consumption), and soil nitrogen mineralization rates. Comparisons between simulated and observed yields allowed us to adjust and refine model inputs, and then to verify and validate the results. These verification and validation exercises produced measures of model fit that indicated the appropriateness of this approach for estimating historical changes in crop yield. Initial cultivation of native grass and continued farming produced a significant loss of soil C over decades, and declining soil fertility led to reduced crop yields. This process was accompanied by a large GHG release, which subsided as soil fertility decreased. Later, irrigation, nitrogen-fertilizer application, and reduced cultivation intensity restored soil fertility and increased crop yields, but led to increased N2O emissions that reversed the decline in net GHG release. By drawing on both historical evidence of land-use change and scientific models that estimate the environmental consequences of those changes, this paper offers an improved way to understand the short- and long-term ecosystem effects of 120 years of cropping in the Great Plains.

Measuring and mitigating agricultural greenhouse gas production in the US Great Plains, 1870–2000

“…The Daycent ecosystem model was used to estimate soil GHG fluxes associated with cropping in each of 476 Great Plains counties (19). The model is driven by county-level weather and soil data (42,43,47) and detailed assumptions about daily agricultural management practices.…”

“…This paper estimates GHG fluxes from "on-farm" activities, and also includes the energy used for irrigation pumping, tractors, and the production of synthetic fertilizer. The Daycent ecosystem model was used to estimate soil GHG fluxes associated with cropping in each of 476 Great Plains counties (19). A complete description of the procedure used to estimate all of the GHG fluxes is provided in SI Materials and Methods.…”

The Community Land Model underestimates land-use CO<sub>2</sub> emissions by neglecting soil disturbance from cultivation

“…We use the models DayCent (Parton et al, 1998;Del Grosso et al, 2006) and CLM4.5bgc, the most recent version of the CLM with biogeochemistry (Oleson et al, 2013;Koven et al, 2013 Hartman et al (2011) Fig. 1 for map).…”

“…We also drive the models with transient atmospheric CO 2 concentration and transient nitrogen (N) deposition data as done by Bonan and Levis (2010), available for years 1860-2010. We prescribe soil texture per site with percent sand/silt/clay values from Hartman et al (2011). Grass is the native vegetation at all sites (Hartman et al, 2011) (Table 1).…”

“…In simulations with the DayCent biogeochemical model at 21 sites around the American Midwest, Hartman et al (2011) account for the loss of soil C from cultivation. Extrapolating to the Great Plains region and accounting for N 2 O and CH 4 in their greenhouse gas calculations, Hartman et al calculate 1.73 × 10 15 g CO 2 -C equivalents emitted from 1860 to 2003 (1 × 10 15 g = 1 petagram = 1 Pg).…”