Better explicating the strengths and shortcomings of these models will help refine projections and improve transparency in the years ahead.
Image credit: Witsawat.S.
Edited by David Tilman, University of Minnesota System, St. Paul, MN, and approved December 29, 2020 (received for review December 20, 2019)
Significance
Conventional agricultural practices erode carbon-rich soils that are the foundation of agriculture. However, the magnitude of A-horizon soil loss across agricultural regions is poorly constrained, hindering the ability to assess soil degradation. Using a remote-sensing method for quantifying the absence of A-horizon soils and the relationship between soil loss and topography, we find that A-horizon soil has been eroded from roughly one-third of the midwestern US Corn Belt, whereas prior estimates indicated none of the Corn Belt region has lost A-horizon soils. The loss of A-horizon soil has removed 1.4 ± 0.5 Pg of carbon from hillslopes, reducing crop yields in the study area by ∼6% and resulting in $2.8 ± $0.9 billion in annual economic losses.
Abstract
Soil erosion in agricultural landscapes reduces crop yields, leads to loss of ecosystem services, and influences the global carbon cycle. Despite decades of soil erosion research, the magnitude of historical soil loss remains poorly quantified across large agricultural regions because preagricultural soil data are rare, and it is challenging to extrapolate local-scale erosion observations across time and space. Here we focus on the Corn Belt of the midwestern United States and use a remote-sensing method to map areas in agricultural fields that have no remaining organic carbon-rich A-horizon. We use satellite and LiDAR data to develop a relationship between A-horizon loss and topographic curvature and then use topographic data to scale-up soil loss predictions across 3.9 × 105 km2 of the Corn Belt. Our results indicate that 35 ± 11% of the cultivated area has lost A-horizon soil and that prior estimates of soil degradation from soil survey-based methods have significantly underestimated A-horizon soil loss. Convex hilltops throughout the region are often completely denuded of A-horizon soil. The association between soil loss and convex topography indicates that tillage-induced erosion is an important driver of soil loss, yet tillage erosion is not simulated in models used to assess nationwide soil loss trends in the United States. We estimate that A-horizon loss decreases crop yields by 6 ± 2%, causing $2.8 ± $0.9 billion in annual economic losses. Regionally, we estimate 1.4 ± 0.5 Pg of carbon have been removed from hillslopes by erosion of the A-horizon, much of which likely remains buried in depositional areas within the fields.
Footnotes
- ↵1To whom correspondence may be addressed. Email: thaler.evan{at}gmail.com.
Author contributions: E.A.T., I.J.L., and Q.Y. designed research; E.A.T. performed research; E.A.T. analyzed data; and E.A.T., I.J.L., and Q.Y. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1922375118/-/DCSupplemental.
Data Availability.
Data are cataloged at the Oak Ridge National Laboratory Distributed Active Archive Center (https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=1774) (65). The archive includes spatial raster data for topographic metrics (elevation, slope, and curvature), soil organic carbon index values, and the probability of B-horizon soil. Spatial vector data and tabular data with county-, state-, and farm-level erosion and economic loss values are also archived. The soil organic carbon index values derived from the RaCA samples and used to develop the logistic regression and receiver operator characteristic curve for each site (such as those shown in SI Appendix, Fig. S8) are also archived.
Published under the PNAS license.
References
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The extent of soil loss across the US Corn Belt
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