Is your soil blowin' in the wind?
Friday, May 6, 2011
Soil erosion can be damaging to your fields and the environment. Planting windbreaks and keeping crop residue or cover crops on the surface can help defeat it
by KEITH REID
We have all seen the photos of the dust clouds and drifts of blown soil from the "Dirty Thirties," and that is often what comes to mind when we think of wind erosion.
Unfortunately, thinking of wind erosion only in terms of extreme events means that we ignore the more subtle and more common losses of soil that occur every year.
Wind erosion can occur because the soil naturally has a weak structure, so individual particles can be detached, or because tillage has broken down soil aggregates into fine particles. In either case, the wind will carry the finer and lighter particles further and in larger amounts than the coarse particles.
Since the finer and lighter particles are also the ones that hold the most nutrients and contain the most organic matter, the net effect is that the wind preferentially carries off the best part of your soil.
Even though they don't travel as far, the coarser particles moved by the wind can be even more damaging. These particles, bouncing along the soil surface, will abrade plant tissue, leaving it open to moisture loss and disease entry. In severe cases, this action can cut plants completely off.
Some fields can lose so much soil during wind storms that the soil is blown away from around the seedling, leaving only a tiny fraction of the root clinging to the soil. These plants may survive, but a large part of their potential yield has been lost.
What about off-site effects of wind erosion? Soil particles, except for the very finest ones, tend to drop out of the air as soon as the wind speed drops. This means that most impacts are close to the point of detachment. There have been cases of crops downwind being buried under drifts of wind-blown soil, either because a fence formed a windbreak or because the crop residue in that field slowed the wind enough to trap the soil.
Soil that moves a little farther can be a traffic hazard by reducing visibility where it blows across roadways. This dust can also clog air filters and potentially damage the engines on vehicles that drive through it.
The fine particles that travel long distances can carry nutrients into surface water. This is usually a relatively small part of the total nutrient load entering surface water, but if the water body is particularly sensitive, this can be enough to trigger algae growth, degrading water quality.
The key to keeping the soil from blowing away is to slow down the wind speed at the soil surface. The two usual approaches are to plant windbreaks, or to keep crop residue or cover crops on the soil surface.
Windbreaks will slow the wind over the whole field once they get tall enough, since their influence will extend downwind for 10 times the height of the windbreak. Field trials in Saskatchewan showed that crop yields also improved to the lee of a windbreak, as moisture stress on the crops was reduced with slower wind speeds.
A modification of this approach is used in some high value horticultural crops, where strips of fall rye are left standing between the rows to protect transplanted seedlings from sandblasting.
Crop residue cover on the ground acts like a series of very short windbreaks, breaking the wind velocity close to the soil surface to prevent soil detachment. It actually takes less crop residue cover to prevent wind erosion than it does for water erosion control.
Once the crop has established a canopy, it provides the same protection as crop residue, so the time of greatest risk for wind erosion is around the time of planting when no crop cover has been established yet.
Avoiding clean tillage can reduce the risk significantly during this time. BF
Keith Reid is Manager (Eastern Canada), Soil Nutrient and GHG Management, Agriculture and Agri-Food Canada, based in Guelph.