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In a discovery that has repercussions for everything from domestic agricultural policy to global food security and the plans to mitigate climate change, researchers at the University of Massachusetts recently announced that the rate of soil erosion in the Midwestern US is 10 to 1,000 times greater than pre-agricultural erosion rates. These newly discovered pre-agricultural rates, which reflect the rate at which soils form, are orders of magnitude lower than the upper allowable limit of erosion set by the U.S. Department of Agriculture (USDA).
The study, which appears in the journal Geology, makes use of a rare element, beryllium-10, or 10Be, that occurs when stars in the Milky Way explode and send high-energy particles, called cosmic rays, rocketing toward Earth. When this galactic shrapnel slams into the Earth's crust, it splits oxygen in the soil apart, leaving tiny trace amounts of 10Be, which can be used to precisely determine average erosion rates over the span of thousands to millions of years.
[...] The numbers are not encouraging. "Our median pre-agricultural erosion rate across all the sites we sampled is 0.04 mm per year," says Larsen. Any modern-day erosion rate higher than that number means that soil is disappearing faster than it is accumulating.
Unfortunately, the USDA's current limit for erosion is 1 mm per year—twenty-five times greater than the average rate Larsen's team found. And some sites are experiencing far greater erosion, disappearing at 1,000 times the natural rate. This means that the USDA's current guidelines will inevitably lead to rapid loss of topsoil.
[...] Yet, there's no reason to despair. "There are agricultural practices, such as no-till farming, that we know how to do and we know greatly reduce erosion," says Quarrier. "The key is to reduce our current erosion rates to natural levels," adds Larsen.
Journal Reference:
Caroline L. Quarrier, Jeffrey S. Kwang, Brendon J. Quirk, et al.; Pre-agricultural soil erosion rates in the midwestern United States. Geology 2022;; 51 (1): 44–48. doi: https://doi.org/10.1130/G50667.1
(Score: 2, Disagree) by khallow on Sunday January 22 2023, @01:20AM
The model is broken. If erosion matches soil creation exactly under every condition, then how do you get soil in the first place? For example, about 14k years ago much of their sites would have been under a kilometer of ice. Meaning there might be a great base for soil under that ice, but no actual soil. And at a glance, their model has net soil growth not of 0.04 mm per year, but zero.
My take is that a better model here for pre-agricultural soil is a logistics model [wikipedia.org] where soil growth starts high when you have thin soil and slows down as soil thickness increases until it reaches the above stable point. My take is that human agriculture has an artificially high level of soil creation due to fertilizer use and the practice of recycling plant material back into the soil.