Drought Increases Erosion Concerns
Many crops failed last year in the drought-stricken areas of Alberta, Saskatchewan, and Manitoba. As a result, some fields will be left with little crop residue, raising concerns of increased wind and water erosion.
Erosion decreases soil productivity due to the loss of plant nutrients and degradation of soil structure. The loss of one inch of topsoil has been shown to reduce wheat yields by about 3.5 bushels per acre (bu/ac)/inch of topsoil. Soil erosion also pollutes the air and water with soil particles and associated nutrients and pesticides.
Given time and no further erosion, the soil can rebuild itself at a rate of about one inch in 30 years. Unless erosion is controlled, the loss of topsoil results in a permanent decrease in yield potential which can only partially be restored by large additions of fertilizer or manure.
So what can be done to control erosion? First, leave as much residue as possible on drought affected fields, especially on sands and clay soils. This advice applies particularly to runoff channels which may erode. Try to avoid both spring and fall tillage in order to provide maximum soil protection. Let weeds grow as long as possible before spraying to develop soil cover. When straight combining, leave as much straw standing as possible. On poor yielding crops, leave unharvested strips 1 - 2 metres wide perpendicular to the erosive wind direction to slow down the wind and trap snow.
Prairie farmers rely almost exclusively on crop residue to control erosion. The amount of straw required to keep the soil in place varies according to several factors, including weather conditions, soil type, and topography. A good rule of thumb is to keep at least 1000 pounds per acre (lb/ac) of cereal straw on the soil surface at all times to control erosion. Pulse and oilseed residues are less effective in controlling erosion than cereal straw, while standing residue provides more control than flat straw. Unfortunately, straw production may be much reduced during drought and any subsequent tillage only buries or flattens residue, increasing the erosion risk.
Direct seeding systems generally have the potential to significantly reduce erosion due to less residue disturbance and some carryover from previous years. However, droughts of the last several years and the use of low-residue pulse and oilseed crops have combined to reduce residue levels in many fields.
When there is not much crop residue and no other conservation practices in place, soil conditions control the amount of erosion which occurs during a storm or runoff event. Soils which tend to crust or leave lots of lumps at the surface, such as many loam or clay loam soils, are least susceptible to wind erosion. Loams and clay loams are also quite resistant to water erosion.
Clay soils are often lumpy enough to resist wind erosion but surface aggregates may break down over winter, making them very erodible in open winters and the following spring. Water infiltration into clay soils may be slow under some conditions, resulting in water erosion if runoff volumes are large.
Sandy soils are the most susceptible to wind erosion because they do not form large aggregates. Since sandy soils have low water holding capacity, they tend to be more susceptible to drought and are better managed with permanent forage, particularly in the Brown and Dark Brown soil zones.
Fortunately, much of the Prairies has loam soils, which will reduce the amount and severity of erosion over the next few months. While loam soils will also erode as a result of severe weather events, they will generally lose significantly less soil than clays or sands under the same weather conditions.
If grazing failed crops or stubble, be sure to use low stocking rates and try to avoid putting cattle on sandy soils. Limit driving and heavy livestock traffic, particularly on clay soils, to prevent soil aggregate breakdown. Consider seeding a cover crop to control erosion.
Occasionally, emergency tillage to bring large soil lumps to the surface is the only practical means of controlling wind erosion. Be prepared to respond quickly if roadside ditches start to fill with blow dirt in order to minimize pollution and soil damage
To combat drought and control wind erosion, consider planting shelterbelts of trees or perennial grass barriers. These practices require some compromises in terms of equipment width, tillage flexibility, and use of herbicides. However, they will provide a large measure of erosion control when crops fail, and usually trap extra snow which will enhance future crop yields.
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