For millennia, humans have tilled the soil to prepare for planting, aiming to regulate moisture, airflow, and nutrients. However, modern agricultural practices involving deep plowing and heavy machinery have been found to be detrimental. According to a report published on March 19 in Science, these methods disrupt the natural channels that allow water to permeate the soil. Researchers emphasize that this disruption not only hinders crop growth but also reduces the soil’s resilience against flooding and drought.
In a bid to explore what lies beneath the surface, geophysicist Qibin Shi from the Chinese Academy of Sciences in Beijing and his team utilized a sophisticated network of seismic sensors crafted from fiber-optic cables. While commonly associated with high-speed internet, fiber-optic cables are also highly effective in seismology, capable of detecting even the smallest vibrations caused by water movement through soil.
The research team installed these cables around the borders of 27 plots at Harper Adams University’s test farm in Newport, England. The plots were subjected to varying tilling depths: a third remained untilled, another third was plowed to a depth of 10 centimeters, and the final third to 25 centimeters. Furthermore, these sections were divided based on the weight of the machinery used, affecting the level of soil compaction.
Over a period of three days in March 2023, the researchers gathered continuous seismic data to observe how the soil responded to rainfall. In areas where the soil was tilled more deeply and compacted, rainwater accumulated on the surface instead of penetrating deeper. This led to rapid evaporation in sunlight. Conversely, less-disturbed soil allowed water to spread more effectively.
To decipher the underlying mechanisms, the team developed a computer model reflecting their data. They discovered that rainwater travels through porous soil by dynamic capillary pressure. The narrow pathways between soil particles, akin to blood vessels, enable water to flow not by gravity but through capillary action—a balance between water’s adhesion to soil and cohesion among water molecules. When these pathways are disrupted or compacted, stronger suction forces impede water movement.
The researchers suggest that fiber-optic sensing can provide a fast and cost-effective method for farmers to monitor soil moisture over large areas. This technology could also offer real-time alerts for natural hazards such as flooding and liquefaction caused by earthquakes, where saturated soil can become destabilized by shaking.
