Keep your soil from 'Blowin' in the Wind'

Thursday, May 2, 2013

Once you see wind erosion occurring, it is generally too late to do anything about it. Prevention is easier, cheaper and more effective, so you should be planning ahead if your soil is susceptible to erosion

by KEITH REID

I recently watched a documentary on the Dust Bowl, which described the severe drought and wind erosion that affected Kansas, Oklahoma and northern Texas during the "Dirty Thirties." The images of the "dusters" were compelling, as were the pictures of the human misery they caused.

While we in Ontario have not experienced this devastation, unlike parts of the Canadian Prairies, it is worth considering the more subtle impacts of wind erosion. Aside from removing the most productive part of the soil, wind erosion can damage crops by sandblasting the tender stems (cutting them off completely in some cases) or burying seedlings under drifts of soil.

Windblown soil can also create a traffic hazard by reducing visibility and fine dust can cause breathing problems or be carried for long distances to deposit nutrients into lakes and rivers, leading to water quality impairment.

Wind erosion processes. Any type of erosion is divided into two parts:  detachment and transport. Wind does not carry nearly as much energy as water (imagine trying to stand up in a river with a 20-kilometre-per-hour current, compared to a 20-kilometre-per-hour breeze), so it can only detach particles that are already loose.

Any soil that has a structure that holds the individual particles together is almost impervious to wind erosion. This means that sandy soils are generally the most sensitive to wind erosion, although some silt soils are also susceptible. We create the only other situation where detachment can easily occur by breaking down soil structure through excessive tillage.

The smooth drum packer is probably the worst culprit in this regard, pounding the surface of the soil into fine particles and leaving a smooth surface with nothing to impede the wind. Muck soils, where the surface has been loosened and dried out by tillage, are at extreme risk for wind erosion.

Once soil particles have been detached by wind, the way they are carried will depend on the size of the particles. Sand grains are too heavy to be easily suspended in the air, so they will either roll along the top of the soil (surface creep) or bounce in a series of arcs (saltation).

Saltation can generate more wind erosion by dislodging more particles as the bouncing sand grains hit the soil surface. These sand grains travelling near the soil surface are responsible for most of the plant damage from wind erosion, abrading the stems of tender seedlings. Even if the plants are not cut off by the sandblasting, the wounds opened up cause moisture loss and allow disease organisms to enter. Lighter particles in the fine sand and silt fraction can be carried high into the air where they travel for long distances.  

The greatest risk for wind erosion occurs when there is no cover over the soil to obstruct the wind and the soil surface is dry. While this can occur during the winter, it is usually most severe around planting time in the spring. Wind erosion is seldom a concern once a crop canopy has been established.

Controlling and preventing wind erosion. Once you see wind erosion occurring, it is generally too late to do anything about it. Prevention is easier, cheaper and more effective, so you should be planning ahead if you know your soils are susceptible to wind erosion. A few options for emergency control of wind erosion that have been used with limited success include:

Tillage perpendicular to the wind to bring up clods and roughen the soil surface.  Effectiveness is generally short-lived, as the clods dry out and start to break apart.

Applying manure or other organic materials (one to two tons per acre) to provide some cover over the soil. Concerns include uneven nitrogen applications to the field.

Erecting temporary wind barriers. This is labour intensive and suitable only for high-value crops.

Measures to prevent wind erosion should be standard practice on any farm with susceptible soils. These include:

Windbreaks. Planted perpendicular to the prevailing wind direction, these will provide protection from wind erosion up to 15 times the height of the windbreak on the downwind side, and five times the height on the windward side. This means that on a 100-acre lot (80 by 200 rods), one windbreak along each side and one up the middle would provide full protection for the lot, if properly oriented.

Wind strips. These are really small temporary windbreaks, created within the field with winter cereal crops. This practice has become quite common for processing vegetables grown on sandy soils, since the protection from the wind strips not only prevents erosion but also creates a microclimate that helps the transplants to get established.

Residue cover. Keeping the residue from the previous crop on the soil surface, or planting a cover crop to create living residue, are both effective at protecting the soil from wind erosion. It actually takes less residue to prevent wind erosion than water erosion, so there should be fewer concerns about heavy residue interfering with planting operations or delaying crop emergence. BF

Keith Reid is Manager (eastern Canada), Soil Nutrient and GHG Management, Agriculture and Agri-Food Canada, Guelph.