HOW MUCH TOPSOIL REMAINS? - QUANTIFYING SOIL LOSS IN THE MIDWESTERN U.S

The development of intensive agricultural practices during the Anthropocene has increased rates of soil erosion world-wide. Numerous studies have documented site-specific increases in erosion, but we have a poor understanding of the total magnitude of anthropogenic soil loss at the scale of entire agricultural landscapes. Here we focus on the Corn Belt region of the midwestern U.S., and present results for novel methods we have developed to: 1) spectrally differentiate between organic-rich topsoil and subsoil using only visible wavelengths; 2) quantify the spatial extent of complete topsoil loss via measurement of subsoil exposed on high-resolution satellite imagery; and 3) scale up soil loss estimates to include areas that lack imagery using relationships between soil spectra and topographic metrics extracted from 360,000 km² of high-resolution LiDAR topographic data. Results from our analyses indicate that topsoil remains on only about half of the agricultural land area in the Corn Belt. Topsoil has been lost primarily from convex hilltops, indicating that tillage is a major driver of soil erosion, which suggests tillage erosion should receive greater attention in soil conservation planning. If soil regenerative farming practices were adopted to restore organic carbon to the degraded soils, our results suggest there is potential to restore $2.9 billion in annual economic losses to farmers while offsetting 2-4 decades of U.S. CO₂ emissions.