Farms: Manure Slipping Through (Soil) Cracks
Add just enough fertilizer, and crops thrive. Add too much, and you may end up with contaminated surface and groundwater.
Excess nutrients from farms can be transported to groundwater reservoirs by water starting at the surface and flowing through soil. But the flow of water through soil is a “highly dynamic process,” says Genevieve Ali, a researcher at the University of Manitoba. “It can vary from year to year, season to season, or even rainstorm to rainstorm.”
It can also fluctuate depending on soil type and even if organic additions, like manure, are applied.
Ali is lead author of a new study that shows water infiltrates deeper into cracking clay (vertisolic soils) when liquid hog manure is applied.
The study also showed that even though water infiltration went deeper in the presence of manure, it did not reach depths of 39 inches (100 cm). That’s how deep tile drains—designed to remove excess subsurface water—are typically installed in the study region.
“This observation challenges previous studies, which showed that cracks in clay soils can promote the travel of water and associated contaminants from the soil surface into tile drains,” says Ali. “Our study suggests that not all clay-rich soils behave the same.”