The American Midwest is Losing an Inch of Topsoil Per Decade (This is fast!)
Author and Geologist David R. Montgomery, PhD, explains how fast topsoil is being lost, to the detriment of our soil fertility, water quality and carbon footprint.
From my interview with David R. Montgomery, PhD.
HART HAGAN: What is the status of soils in the United States and what we should be doing differently?
DAVID MONTGOMERY: Well, if you look at soils, not just the United States but all around the world, there's been significant soil degradation that comes in two forms.
One is the loss of the topsoil itself. And if you think about how soil erosion works, it works from the top down. The topsoil is generally the most fertile part of the soil profile. So you lose the best stuff first. But there's also the loss of soil quality and that relates to soil organic matter, the once-living organisms that are integrated into the soil that are a source of nutrients to support new life that can draw upon those nutrients.
And if you look at those two different dimensions, the loss of the top soil and the degradation of soil organic matter and the soil life--and the soil health that flows from organic matter--you come up with different ways of thinking about the state of the soil in the U.S.
There was a paper that was put out in 2015--I believe it was in the Journal of Sustainability-- that looked at the organic matter and changes in the organic matter content, the carbon content of soils across the U.S. The paper concluded that we've reduced our organic matter by about 50% on most farmland across the U.S.
If we look at in terms of soil erosion, there are estimates that in certain regions up to half the top soil has eroded off others, like the Piedmont of the American Southeast. From Virginia down to Alabama, almost the whole topsoil A horizon--that really top soil--has been eroded off that fairly large area. So it depends where you're at as to how much erosion has happened and how much erosion can be tolerated in the future and still be able to farm the land.
But there's two different dimensions to it. There was a study that came out in 2020 or 2021 that looked at the top soil erosion across the whole U.S. Corn Belt and the whole U.S. Midwest. And those two studies basically confirmed that we're losing on average about an inch of topsoil every decade and that's screamingly fast compared to how fast soils can be built by natural systems.
And if you look at the magnitude of soil organic matter loss, we're again at about the fifty percent level in terms of the total losses. There was a study that looked, again, at the Corn Belt, that concluded that over one-third of the area in the US Corn Belt, the entire topsoil has already been eroded off and that high yields are supported simply by high rates of fertilizer application, because the natural fertility of the soil is shot.