Annual Barriers for Special Crops

More than 450,000 acres of Manitoba farmland is used to grow special crops such as potatoes, sugar beets and pulse crops. This land is generally light-textured and very prone to wind erosion if not properly protected. Complicating the issue is the fact that special crops produce very little crop residue to protect the soil.

Wind erosion does more than remove valuable topsoil. It also removes the organic matter that holds the soil together and conserves moisture, while improving its tilth and structure. Soils that have lost much of their organic material become even more susceptible to wind erosion. It also provides a kind of nutrient bank, releasing nutrients for crop use.

The best way to protect erosion-prone soils is to use a complete management system including shelterbelts, cover crops, proper residue management and crop rotations. Annual barriers can also be a component of the system.

The Annual Barrier Alternative

The most common species for annual barriers is silage corn, although sunflowers are also popular. Plant the barriers in the spring or early summer to allow the plants to mature before the time comes to harvest the special crop. Barriers may be planted before, during, or after planting the special crop. For corn, plant the belt before June 30.

When properly used, annual barriers will protect the soil from wind erosion after the harvest of a special crop and before the next crop is mature enough to protect the soil itself the following spring.

Use Annual Barriers in These Situations

With late maturing varieties of potatoes. Late potatoes are harvested too late for a cover crop to become established before freeze-up.
With sugar beets. Sugar beets are also harvested too late in the year to seed a cover crop.
With early potatoes as an alternative to cover crops if you foresee a problem of finding time to plant cover crops during or after harvest.
In addition to cover crops. On especially erodible land, annual barriers will provide protection while the cover crop is becoming established, whether it is potato or pulse crop land.
With pulse crops as an alternative to cover crops.
When you have reason to believe that soil moisture at harvest time may not be adequate to germinate a cover crop.
As a method of trapping snow to enhance spring moisture conditions.

Advantages of Annual Barriers

Reduces loss of topsoil.
Snow catch - one foot of snow translates roughly into one inch of water.
Provides some protection to the crop during the growing season.
Modification of the field microclimate can enhance crop growth and yield and conserve moisture.

Disadvantages of Annual Barriers

If planted as a separate operation, extra time is required in the spring when time is at a premium.
Requires special equipment or modification to existing equipment.
Takes land out of production.
Divides fields into narrow strips.

It's A Fact

1/32 of an inch, the thickness of a five cent piece, equals five tons of soil per acre.
When visibility is reduced to 1/2 mile in blowing dust, fields may be losing as much as 3/4 of a ton of topsoil per hour.
Of the water that falls on cropland, an average of 66% evaporates, 25% runs into ponds or streams and only 9% enters the soil.

Planning the Pattern

Most wind erosion damage occurs during the late winter or early spring, therefore, annual barriers are most effective when planted across the direction of the prevailing spring winds. Spring winds are not necessarily from the same direction as the prevailing wind for the remainder of the year. For example, spring winds in the Red River Valley are generally from the south, while winds during the remainder of the year are from the west, northwest and north.

The closer the annual barriers can be placed, the more protection they provide. The most effective spacing is about 60 feet. However, to minimize the inconvenience of working around the belts, plan the spacing to coincide with the width of your field equipment. For example, if your planter is 18 feet wide, plant the barriers at spacings that are multiples of 18 - 72, 90, etc. don't forget to consider your sprayer width, as well.

Note: The barriers themselves take up space. So, add the width of the barrier itself to the spacing when calculating where to plant them. It is the space between the barriers that must be multiples of your equipment width.

One Row, Two Row or More?

A two-row corn barrier provides the best combination of effectiveness and efficiency. An eight-foot high, two-row belt will reduce wind speed by 35 per cent for a distance of five times its own height, or 40 feet. Wind speed will be reduced significantly for a distance of nine times, or about 70 feet.

Single row corn barriers reduce wind speed only slightly, providing little in the way of erosion protection. However, single barriers will capture snow, enhancing spring moisture conditions.

A four-row barrier does not reduce wind speed significantly more than a two-row barrier and it uses more land. Two rows of corn use about four acres on an eighty-acre field if barriers are spaced 70 feet apart. Four rows use twice that. However, some producers use three or four rows to ensure continued protection if the outside rows of the belt are damaged by spray drift.

One Bad Day in May

On May 20, 1992, a strong south wind filled the air with dust over the Red River Valley. Soil scientists monitored its destructive force on a field in the Winkler area. The field was corn, seeded into potato residue on dry, sandy soil. Effective soil cover was negligible and the field was smooth and large. Wind speeds ranged from 50 km/hr to 75 km/hr.

Wind-blown soil was collected at two sites and the total soil loss per acre was calculated. Soil loss from the field during this single windstorm ranged from 7.25 to 8.23 tons per acre!

Soil Loss By Type (kg/metre width)
Movement	Site 1	Site 2
Creep	7.5	7.3
Saltation	529	507
Suspension	115	225
Total (kg/m)*	652	740
Soil loss (tons/acre)	7.25	8.23
*The field length was 400 metres. Soil loss was calculated in kilograms on an area one metre wide and 400 metres long.

Creep: The largest soil particles roll or otherwise move along the ground. They generally end up in the roadside ditch or fenceline.

Saltation: Soil particles bounce and fly near the soil surface, dislodging other particles each time they impact the soil surface. These particles also form banks along fences, roads and other wind barriers.