GoKawiilA plot of experimental land at Joe Collins’ Field near Harper Adams University, where University of Washington researchers travelled to collaborate on an agroseismology experiment examining the impact of tilling on soil moisture. Photo: Marine Denolle/University of Washington Researchers (from left to right) Ethan Williams, Joe Collins, Simon Jeffrey lay the fiber optic cable just below the surface of a test near Harper Adams University. Photo: Marine Denolle/University of Washington Senior author Marine Denolle, a UW associate professor of Earth and space sciences, poses in front of the test field with her daughter, Catherine, on a rainy field day. Photo: Marine Denolle/University of Washington Ethan Williams, a former UW postdoctoral researcher in Earth and space sciences, now an assistant professor at UC Santa Cruz, uses the highly portable DAS data collection system at the experimental farm. Photo: Marine Denolle/University of Washington Previous image Next image
Plowing, or tilling, is an age-old agricultural practice that readies the soil for planting by turning over the top layer to expose fresh earth. The method — intended to improve water and nutrient circulation — remains popular today, but concerns about soil degradation have prompted some to return to regenerative methods that disturb the soil less.
In a new study, a team led by University of Washington researchers examined the impact of tilling on soil moisture and water retention using methods originally designed for monitoring earthquakes. Researchers placed fiber optic cables alongside fields at an experimental farm in the United Kingdom and recorded ground motion from plots receiving different amounts of tillage and compaction from tractor tires pulling farm equipment.
The study, published March 19 in Science, shows that tilling and compaction disrupt intricate capillary networks within the soil that give it a natural sponge-like quality.
“This study offers a clear explanation for why the process of tillage, one of humanity’s oldest agricultural activities, changes the structure of soil in ways that affect how it soaks up water,” said co-author David Montgomery, a UW professor of Earth and space sciences.
The link between tilling and soil degradation has been established for quite some time, but the rationale is less robust.
“It’s counterintuitive,” Montgomery said.
Tilling is supposed to create holes for water to reach the roots of plants, but it breaks these small channels in the soil instead, causing rain to pool on the surface and form a muddy crust. Over time, this can increase erosion and flood risk. The researchers observed this phenomenon in detail using seismological methods.
For the past decade or so, physical scientists have been exploring ways to harness the fiber optic cable network to make remote observations. They use a technique called distributed acoustic sensing, or DAS, that records ground motion based on cable strain. Because the technology is so sensitive, it can also capture the speed at which sound waves pass through a substance, which is called seismic velocity.
When soil gets wet, seismic velocity changes. Sound moves slower through mud than dry dirt.
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