“We are losing our soil.”
It’s a phrase you may have heard occasionally. Sure, it sounds serious, but how do we lose soil and how do we know we’re losing it?
“Soil erosion is the movement of soil by wind or water, and it’s through erosion that soil is ‘lost,'” explains Nick Comerford, a member of the Soil Science Society of America (SSSA) and center director and professor of soil and water sciences at the North Florida Research & Education Center in Quincy, Florida. “If it is an organic soil, we also lose it by subsidence, which happens when an organic soil is drained and its organic matter decomposes.”
The U.S. loses approximately 1.7 billion tons of soil per year from just its cropland, Comerford points out. “That is a lot, but it’s better than it used to be,” he explains. “Over the past 25 years we have reduced soil erosion by over 40 percent, mainly by conservation practices such as conservation tillage, terracing, cover crops and grass waterways.”
The challenge: It can take roughly 500 to 1,000 years to form 1 inch of soil, depending on the climate and the material from which soil forms, Comerford points out.
Soil erosion 101
Soil erosion occurs when the soil is not protected from the elements. Remove the plants and mulch from mineral soil and things start to happen. Raindrops can break apart the soil, making it easier for wind and water to move it. The water’s ability to enter the soil also reduces, and more water can now flow over the top of it. “Unfortunately, water is powerful and can carry away soil particles if it flows overland,” Comerford warns. “Since water flows downhill, that’s where the soil goes once water erosion begins.”
Where does the soil end up? It might end up at the bottom of a hill or it might end up in a river, stream or ocean. It might even end up in a reservoir, where it limits the space for water and has to be removed by a very expensive process called dredging. If the soil dries out while it is unprotected, then wind can pick it up and move it downwind.
Organic soils can be drained. When drained, they decompose and this is called subsidence. In the Everglades area of Florida where soils have been drained for agriculture, organic soils have lost as much as 5 feet or more of their organic matter. Organic soils are preserved by not draining them. “Letting them stay saturated with water allows them to continue to build over time,” Comerford says.
The ultimate cost of soil erosion
Soil erosion is expensive, costing the U.S. approximately $44 billion per year, Comerford says. “Preventing erosion means taking care of the soil,” he says. “That means protecting it with mulch and plants, not plowing on steep slopes and maximizing the amount of water that enters the soil while minimizing the water that runs over the soil.
“It is not hard to see that soil is a non-renewable resource and worth protecting,” Comerford adds. “Since the soil is the source of water and nutrients for plants as well as a bioreactor to purify and filter water, it is crucial to our quality of life.”