Water flow through tilled soils can make land vulnerable to flooding and drought.
For thousands of years, humans have prepared for planting by tilling and turning the soil to manage moisture, air flow and nutrients. But the deep plowing and heavy machinery of modern agriculture do more harm than good, disrupt the natural pathways by which water infiltratesthe researchers report on March 19 in Science. According to the team, breaking this network is not only counterproductive for the crop: it also makes the soil less resilient to flooding and drought.
To observe the subsurface, geophysicist Qibin Shi of the Chinese Academy of Sciences in Beijing and his colleagues made a dense array of seismic sensors from fiber-optic cables. Fiber optic cables are not only intended for high-speed Internet; they are powerful tools for seismologysensitive enough to detect even tiny vibrations triggered by the movement of water in the ground.
The team installed the cables along the boundaries of 27 plots of land at the Harper Adams University Test Farm, an agricultural research site in Newport, England. For this study, the plots were prepared with different plowing depths: one third was plowed, one third was plowed to a depth of 10 centimeters and the last third was plowed to a depth of 25 centimeters. These thirds were then distributed based on the weight of the machines used to plow them, which affects soil compaction.
Over three days in March 2023, the team collected continuous seismic data, tracking the ground’s response to precipitation. In deeper tilled and compacted soils, rainwater tended to accumulate near the surface rather than infiltrate downward. This also meant that water evaporated quickly in the sun. The less the soil was reworked, the more easily the water was distributed.
To understand the mechanisms at work, the team designed a computer model that recreated this data. Rainwater, they discovered, moves through porous soil via dynamic capillary pressure. Because the tiny passages between soil patches are very thin, like blood vessels, the flow of water through them is not driven by gravity. Instead, it moves by capillary action, a back-and-forth between water adhering to soil particles and cohesion with other water molecules. When pathways are disrupted or compacted, these suction forces become stronger, impeding water movement.
Fiber optic sensing offers farmers a quick and inexpensive way to monitor soil moisture on a large scale, according to the team. Such monitoring could also provide real-time alerts regarding natural hazards, including floods And liquefaction caused by an earthquakewhen the ground is saturated, it can suddenly become unstable due to shaking.