Question: What are some things that farmers do to keep soils from eroding?
Answer: What a great question, but let’s not limit it to farmers!
Erosion is a natural process; it is the reason we have valleys, mesas, sand dunes, and the Grand Canyon. There are three processes in erosion:
1) Detachment of soil particles from the surface
2) Transportation of the detached particles
3) Deposition of the particles
Erosion control methods address one or more of these processes.
Keeping a blanket on the soil
The best protection a soil has is a blanket of living vegetation on the surface. Dead plants and plant parts (a.k.a., residues) on the surface and mulches also help.
Farming and construction often remove or decrease the amount of vegetation (both living and dead) on the soil surface, and so increase the potential for erosion. But work activities are not the only danger to soil. Recreational vehicles, hiking off-trail, military drills, and other activities also can destroy vegetation and decrease the plant cover on the soil surface. After the vegetation is gone, the soil is susceptible to blowing in the wind, being pounded by raindrops, and washing away in runoff.
How do farmers keep the surface covered? When possible, they have a growing crop on the field, though not all crops are equally effective at decreasing erosion. Wheat and hay crops cover most of the soil surface, and so limit erosion better than crops like soybeans or cotton. These latter crops are often planted in wide rows, leaving bare soil exposed for a longer time.
After a crop is harvested, farmers in wet and humid regions may plant a cover crop to protect the soil surface until the next growing season when they plant another crop they will harvest. Some farmers use irrigation to plant a cover crop, but in many areas the water available for irrigation is becoming more limited.
Tilling the soil less
Traditional tillage systems turn and mix the soil, much like a rototiller that gardeners often use. When I was a child, my dad and I would turn our garden soil to about 30 centimeters (1 foot) deep with a spade. Then we’d run a rototiller to make the soil nice and fluffy. Intensive tillage systems like these break soil aggregates (natural clumps of soil particles) into smaller chunks.
In semiarid and arid regions, the soil can dry as deep as it was tilled. The powdery soils on the surface are also easily washed away by rain or blown away by wind.
In contrast, more modern tillage systems involve plowing less often, mixing the soil less, creating and leaving large aggregates at the soil surface, and/or leaving plant residues on the soil surface.
Slowing the downhill flow of water
When water erosion is a problem on sloping lands, farmers may plant on contours so that the plant rows follow lines of equal elevation. This limits water from running downhill, and increases infiltration of water into the soil surface. Terraces, grassed waterways, and diversions are other tools used on sloping lands to limit the amount of water running downhill across bare soils.
Similar techniques are used on hiking and biking trails, and on ditches in the roadside right-of-way to slow water movement or divert it away from the trail or road.
What about off the farm?
Construction projects often strip away all the vegetation and much of the surface layer of soil. Heavy equipment compacts and disturbs the soil surface even more. When it rains, water cannot permeate the ground, so there is more runoff. Moving water then carries soil particles with it: The soil goes where the water goes. In some areas, construction projects are also subject to wind erosion.
During a project, special fences, compost, detention ponds, and other techniques are used to protect the soil surface, slow runoff, and limit the amount of water that leaves the construction site. After the project, vegetation is planted, often in two phases. The first phase provides quick ground cover (if there is rain to get the seeds to germinate and grow). The second phase establishes perennial plants that will protect the surface in the future.
In short, the basic principles for controlling erosion are similar regardless of who uses the soil. These include:
1) Keeping the soil surface covered with vegetation or residues to protect it from wind or raindrops. This limits detachment.
2) Slowing down flowing water or wind speeds at the soil surface. This limits detachment and transportation, while encouraging deposition of soil.
3) Improving soil physical conditions at the surface so that it holds together better. This also limits detachment.
–Answered by Clay Robinson, a.k.a., Dr. Dirt
Have a question for Soils Matter? Post it in the comments section below or email us at firstname.lastname@example.org