What you need to know
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Small grains almost always yield better following another crop than when following other small grains.
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Rotations can control or reduce disease, insect and weed pressure.
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Rotations can improve soil fertility and soil structure.
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Rotations help manage available soil moisture.
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Diversity in crops grown can spread out fieldwork and harvest time, as well as reduce risk.
Crop rotation is the order specific crops are planted on the same field. The order a small grain crop is included in a rotation can significantly impact grain yield and/or grain quality.
How to select a crop rotation
When selecting a rotation, consider the long-term viability of that rotation to reduce weed, insect and disease pressure, and its economic viability.
Always follow a well-developed plan that can be altered when necessary. Otherwise, the desired crop sequence may be interrupted and you won’t get the maximum benefits of the rotational effect.
Important questions to consider when designing a crop rotation, regardless of location are:
How will previous crops affect subsequent crop production?
Will the previous crop increase or decrease concerns? Consider several dimensions, including disease, insect, weed pressures, soil fertility and soil structure.
Research findings
Research directed toward developing crop rotation recommendations is complex to implement and difficult to interpret. This is because of the diversity of crops grown in Minnesota and North Dakota, plus the large number of potential crop sequences.
Guiding principles
However, research has established several principles to consider when creating a rotation plan. Principles include:
Small grains almost always yield better following another crop than when following other small grains.
Rotations can control or reduce disease, insect and weed pressure.
Rotations can improve soil fertility and soil structure.
Rotations help manage available soil moisture.
Diversity in crops grown can spread out fieldwork and harvest time, as well as reduce risk.
Yield advantages
Rotations consistently offer a yield advantage over continuous monocropping. Numerous studies have demonstrated the yield advantage of rotating small grains compared to continuous small grain cropping.
You can often trace the rotation’s yield advantage to reduced levels of diseases or insects. However, sometimes the yield advantage can’t be attributed to any known, observable factor; the crop just grows better. This is often referred to as the rotation effect.
Study results
Rotation studies in Fargo over a nine-year period showed a 40, 20 and 15 percent increase in grain yield when wheat followed soybeans, sunflowers or flax, respectively, compared to continuous wheat.
Research conducted by the Department of Agriculture’s Agricultural Research Service lab in Mandan, N.D.—where more than 100 crop combinations were grown in rotations—found spring wheat was invariably the lowest yielding when preceded by spring wheat (Table 1). Similarly, barley following barley was lower yielding than when it followed any of the other preceding crops.
This study is a rich source of information on cropping sequences, particularly for environments like south-central North Dakota. Study results are available on an interactive CD called the Crop Sequence Calculator.
Research clearly shows that, to optimize yield, don’t grow a small grain crop after a previous small grain crop of the same species.
Effects of rotation
Table 1 shows yield in the third year of selected crop sequences. Adapted from the Crop Sequence Calculator.
Table 1: Grain yield of hard red spring wheat
| Crop sequence | Wheat yield in year three |
|---|---|
| Barley-wheat-wheat | 42 bushels per acre |
| Wheat-wheat-wheat | 44 bushels per acre |
| Wheat-dry beans-wheat | 49 bushels per acre |
| Barley-dry beans-wheat | 54 bushels per acre |
| Soybean-dry beans-wheat | 58 bushels per acre |
Rotations can be an important method of controlling or reducing disease, insect and weed pressure. Pests that are more mobile are more difficult to control with crop rotation.
For many environments in Minnesota and North Dakota, the most important reason for rotating small grains is to reduce disease pressure. Table 2 summarizes some of the small grain diseases that rotation controls or reduces in severity.
Given the severity of Fusarium Head Blight (FHB) in Minnesota and North Dakota, avoid rotations where wheat or barley follows another small grain crop or corn. Residues of these crops can harbor Fusarium spores and predispose a subsequent small grain crop to FHB damage when environmental conditions are favorable.
Table 2: Common diseases entirely or partially controlled by rotation
| Small grain disease | Crop affected | Control methods |
|---|---|---|
| Common root rot | Wheat, barley, oat | Rotation, seed treatment |
| Ergot | Wheat | Rotation, tillage |
| Bacterial blights | Wheat, barley, oat | Rotation |
| Fusarium Head Blight | Wheat, barley | Rotation, resistant varieties, fungicide |
| Tan spot | Wheat | Rotation, resistant varieties, fungicide |
| Septoria | Wheat, barley, oat | Rotation, resistant varieties, fungicide |
Several small grains insect pests can be controlled or reduced with appropriate rotations (Table 3). Furthermore, rotations offer options for reducing weed pressure and controlling problematic weeds.
Using crops with a different planting date, growth habit or herbicide than a small grain crop may help control weeds that could become problematic in a continuous cropping situation.
For example, you can control perennial weeds such as Canada thistle and quackgrass in a preceding crop of Roundup Ready soybeans. However, these same weeds could quickly become problematic in a continuous wheat rotation.
Table 3: Common insects partially or entirely controlled by rotation
| Insect pest | Crop affected |
|---|---|
| Wheat stem maggot | Wheat |
| Wheat stem sawfly | Wheat |
| Wheat stem sawfly | Wheat |
Crops have different water requirements and rooting depths. These can be important factors to consider, particularly in environments where water is frequently the most limiting factor of crop production.
Table 4 summarizes the water use and rooting depth of select crops near Mandan, N.D. Corn wasn’t included in the study summarized in the table, but can have a rooting depth of 4 to 4.5 feet and is a relatively heavy water user.
Growing two heavy-water-using crops in a row can increase the risk of crop losses. Furthermore, sequentially growing crops with different rooting depths is a good way to exploit water that may not be available to a shallower rooting crop. Too few water-using crops, on the other hand, may result in saline seep problems.
Table 4 shows crop water use and maximum observed rooting depth averaged over two years (1999 and 2000) in Mandan, N.D. Adapted from the Crop Sequence Calculator.
Table 4: Crop water use and rooting depth
| Crop | Water use | Root depth |
|---|---|---|
| Barley | 11.8 inches | N/A |
| Canola | 12.8 inches | 4.0 feet |
| Dry beans | 12.8 inches | 3.3 feet |
| Field peas | 11.8 inches | 3.2 feet |
| Flax | 12.4 inches | 4.1 feet |
| Hard red spring wheat | 12.4 inches | 4.1 feet |
| Soybean | 13.3 inches | 3.5 feet |
| Sunflower | 15.0 inches | 5.0 feet |
Potential crop rotations: Minnesota and North Dakota
Table 5 includes crops adapted for production in Minnesota and North Dakota with potential for rotations. You can maximize rotational benefits if crops from a common group don’t follow one another in a rotation.
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You can substitute a crop for another of the same group in a rotation without destroying rotational benefits.
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Achieve the best rotational benefits when crops from groups I and II precede group III.
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Crops from group IV should never precede group III.
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Including warm- and cool-season crops in a rotation will spread planting and harvest workloads.
Table 5: Crops adapted for Minnesota and North Dakota
| Crop type | Group I | Group II | Group III | Group IV |
|---|---|---|---|---|
| Cool-season crop | Field pea, canola, mustard, crambe | Potato, sugarbeet, flax | Wheat, barley, durum, oats, winter wheat, rye | -- |
| Warm-season crop | Dry bean (pinto, navy, black, turtle), soybean, sunflower | Buckwheat, flax | -- | Corn, sudangrass, millet |
| Perennial | -- | Alfalfa | -- | -- |
Table 6 shows potential rotations in Minnesota and North Dakota that include small grains.
Key: Roman numerals refer to the crop group, C = cool-season, W = warm-season and P = perennial.
Table 6: Potential rotations
| Rotation | Year 1 | Year 2 | Year 3 | Year 4 | Year 5 |
|---|---|---|---|---|---|
| One | Wheat (III-C) | Corn (IV-W) | Soybean (I-W) or canola (I-C) | ||
| Two | Barley (III-C) | Dry bean (I-W) | Dry bean (I-W) Wheat (III-C) | Sunflower (I-W) | |
| Three | Sugarbeet (II-C) | Wheat (III-C) | Soybean (I-W) | Wheat (III-C) | |
| Four | Wheat (III-C) | Canola (I-C) | Barley (III-C) | Flax (II-C) | Soybean (I-W) |
| Five | Wheat (III-C) | Canola (I-C) | Barley (III-C) | Sunflower (I-W) | Dry pea (I-C) |
| Six | Wheat (III-C) | Canola (I-C) | Corn (IV-W) | Sunflower (I-W) | Dry pea (I-C) |
| Seven | Winter wheat (III-C) | Canola (I-C) | Barley (III-C) | Field pea (I-C) | Flax (II-C) |
| Eight | Wheat (III-C) | Corn (IV-W) | Canola (I-C) | Flax (II-W) | Alfalfa (II-P) |
Strengths and weaknesses of each rotation
Strengths
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Two years between any one crop.
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Less potential for scab than growing continuous small grains.
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Legumes in the rotation provide nitrogen for the following crop.
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Two years between broadleaf reduces the potential for sclerotinia.
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Includes both cool- and warm-season crops.
Weaknesses
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Using corn in the same rotation with small grains leaves the potential for Fusarium (scab) fungus to survive on corn residue.
Strengths
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Two years out of wheat or barley can break foliar and head diseases common to wheat and barley.
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Legumes provide nitrogen for the small grains grown in following years.
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Including both cool- and warm-season crops spreads planting and harvest time, and reduces the potential for wheat midge.
Weaknesses
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Only one year between wheat and barley can increase the potential for scab, spot blotch and root rot.
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One year between broadleaf crops increases the potential for Sclerotinia. Substituting flax in the second or fourth year will reduce this problem.
Strengths
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Includes two unrelated broadleaf crops.
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Nitrogen advantage from sugarbeet tops and legumes.
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Includes both warm- and cool-season crops.
Weaknesses
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Sugarbeet production isn’t an option when sugarbeet contract acreage isn’t available.
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Potential herbicide carryover to sugarbeet.
Strengths
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Achieves a two-year break between barley and wheat crops, but not between wheat and barley. This reduces head and foliar disease potential.
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Wheat does well following soybeans. Herbicide rotation is possible and volunteers are controllable.
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Volunteer flax control in dry beans or sunflowers is difficult.
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Residue management is achievable.
Weaknesses
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Sclerotinia soil levels may be maintained, although the risk is low.
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Only one opportunity to change planting dates.
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A frost risk with soybeans.
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Herbicide carryover is a potential problem.
Strengths
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A two-year break from small grains. This reduces the probability of small grain disease and makes residue management achievable.
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Volunteer crop management is also achievable.
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The wheat protein and yield is good following peas.
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Includes legumes in rotation.
Weaknesses
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Canola, sunflowers and dry peas are susceptible to Sclerotinia.
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Only one late-planted crop.
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Canada thistle control is difficult.
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Crop insurance doesn't cover peas lost to disease.
Strengths
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Two warm-season crops.
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High water-use intensity.
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Three years between wheat and barley.
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Manageable volunteer and resistant weed control.
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Residue management possible.
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Herbicide rotation possible.
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Perennial weed control possible.
Weaknesses
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Three crops susceptible to Fusarium (scab fungus).
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Two crops sensitive to Sclerotinia.
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Frost risk to corn.
Strengths
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Only one crop with high sensitivity to Sclerotinia and scab.
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Low surface residue production.
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Good weed control is possible.
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Includes legumes.
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Fall planting helps with spring seeding workload.
Weaknesses
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No warm-season crop.
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Only one deep-rooted crop.
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Possible winter kill of winter wheat.
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Compressed harvest schedule.
Strengths
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Three or more years of a deep-rooted crop.
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Low risk of Sclerotinia and scab on wheat.
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Minimized potential for insect problems.
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Multiple choices for weed control.
Weaknesses
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Three years of deep-rooted crops may create a moisture shortage for wheat.
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The market for alfalfa may be limited, and requires additional equipment for haying or hiring a custom operator.
Reviewed in 2018