Crop Rotations for Increased Productivity

EB-48 (Revised), January 1998

Introduction
General Effects of Rotations
Results of Crop Rotation Experiments
Economic Considerations with Crop Rotations
Selecting a Rotation
Suggested Rotations
Bibliography

Results of crop rotation experiments

The results of crop rotation experiments from several locations are summarized in this section.

Rotational benefits to corn and sorghum

Corn yields following alfalfa and soybean, even with 300 pounds of applied nitrogen per acre, were greater than with continuous corn (Table 8). The data in Table 8 also illustrate the beneficial effects of alfalfa on corn yields during the second and third years following alfalfa. Even with 75 to 150 pounds of added nitrogen, the residual benefits of alfalfa are still evident. First-year corn yields were the same after either soybean or alfalfa.

Table 8. Effect of rotation and nitrogen on corn yields at Lancaster, Wisconsin, 1967-76.

Data in Table 9 illustrate the beneficial effects of soybean in the rotation on yield of grain sorghum. Grain sorghum yields after soybean remained greater than yields after sorghum even when 160 pounds per acre of nitrogen was applied to both treatments.

Table 9. Three-year average yield of grain sorghum grown either continuously or in rotation with soybean. University of Missouri (15).

Results from five years of a 10-year study indicated yield increases for both corn and soybean when the two crops were rotated versus continuous cropping the same species (Table 10). The results suggest that rotation of corn hybrids or soybean varieties increased yields; however, when the potential for disease development is high, such as with scab or tan spot on wheat, rotation to the same crop regardless of variety is not advisable.

Table 10. Comparison of yields of corn and soybean under continuous cropping, rotation of crops and rotation of varieties.

Rotational benefits to small grains

Barley yields (Table 11) were increased when barley followed soybean or fababean rather than barley. Barley yields were similar with barley seeded into fababean and legume stubble plus 54 pounds per acre of nitrogen and barley seeded into barley stubble plus 107 pounds per acre of nitrogen. Barley yield on fababean stubble was equal or superior to barley yield on soybean stubble.

Table 11. Yield and Protein content of barley in different crop rotations (1). Brandon, Manitoba.

Data represents 6 station years. 31 lbs/A of P₂O₅ applied at planting.

Wheat yield following dry bean has been shown to be equivalent to wheat yield after soybean (Table 12). Fallow in regions where rainfall exceeds 16 inches annual precipitation is generally not a profitable practice. A yield benefit of growing wheat after barley was observed, but the yield advantage of rotating wheat with a legume or other broadleaf crop is even greater (Table 2).

Table 12. Effect of preceding crop on grain yield of spring wheat at four locations.

Sugarbeet rotations

Yields and quality are usually highest when sugarbeet follows barley or wheat in the crop rotation. Yields are usually high when sugarbeet follows corn, potatoes or summer fallow in rotation, but higher than desirable soil nitrogen levels may reduce crop quality. Three years research in Minnesota indicates sugarbeet yielded significantly less when following soybean versus barley in rotation. One year of research indicates sugarbeet yields were reduced following dry edible beans in rotation. Several possible explanations for reduced yields when sugarbeet follows soybean include: (1) herbicide carryover; (2) lack of available soil water; (3) increased rhizoctonia root rot; or (4) alleopathic effects.

Typical Red River Valley sugarbeet rotations include: Sugarbeet — soybean or dry edible bean — small grain - small grain or, if using a three year rotation, only one year of small grain. In areas where corn is more common, a desirable rotation is sugarbeet — soybean — corn. Soybean following sugarbeet is desirable because the soybean may adjust to periods of moisture stress better than small grains following sugarbeet. Planting small grains prior to sugarbeet reduces root rot potential in the sugarbeet. Early harvested small grains also allow time for sugarbeet growers to soil sample, apply fertilizer, and prepare seedbeds for the subsequent sugarbeet crop.

Sugarbeet rotation guidelines

• Three year rotations are the absolute minimum length of an acceptable rotation.
• Four year or longer rotations are desirable to minimize root disease, Cercospora leaf spot and herbicide carryover.
• Avoid canola in crop rotations with sugarbeet if at all possible, because it is an alternate host for sugarbeet cyst nematode.
• Avoid herbicide carryover that may damage sugarbeet or rotational crops.
• Manage fertilizer nitrogen use throughout the rotation.
• American Crystal Sugar Company data shows a trend toward more sugar production per acre in rotations of five years or more (Table 13).

Table 13. Length of rotation in relation to sugarbeet yield and quality, 10 year average (1987-1996)* D. Hilde, American Crystal Sugar Co.

*Data from representative fields (beets delivered on correct contracts).

Economic considerations with crop rotations

The job of the farm manager is to combine the resources of land, labor, management, and capital to provide the most farm profit. Since these resources are scarce, maximizing returns to each resource is important.

Each crop grown in North Dakota has risk and uncertainty in terms of yield and/or price. Farmers differ in their ability to bear risk and in their attitude toward accepting risk, and these differences will have a direct bearing on the selection of a cropping program. Federal farm programs no longer provide stability to income from crops such as wheat. Other crops, such as dry bean, may offer a chance for more profit per acre but at some increase in risk. Federal Crop Insurance, which covers most crops, may be purchased to protect against yield and income risk.

In deciding which crops to grow once the agronomic factors have been considered, the farm manager should gather information concerning costs of production and economic outlook and then budget the potential costs and returns from each enterprise. Computer assisted decision models available from the NDSU Extension Service will help analyze alternatives, both short and long term.

Income stability

Crop rotations provide income diversification. If something happens to reduce profitability of one crop, income is not as likely to be adversely affected as if the total farm was planted to this crop; provided a profit potential exists for each crop in a rotation. This is especially important to the farmer with limited capital or a heavy debt.

Price and yield variability won't necessarily always be reduced by diversification. Weather that affects barley will affect wheat and oats in the same way. Prices and yields for oilseeds (sunflower and soybean) are correlated with each other in the same manner. Therefore a crop rotation with cereals and row crops will likely lead to greater income stability, because crop price movements and yield variability due to weather will be less than diversification with only row crops or only cereal crops.

Time management

Many crops are competitive where labor is concerned, particularly at seeding and harvest. It is possible to spread these operations over a longer period of time with a crop rotation. Spring seeded cereal grains generally compete with each other for labor, while row crops may be planted and harvested later than cereals. (Winter wheat fits well into a rotation with other cereals because of fall seeding and earlier harvest while equipment needs remain essentially the same.) This tends to even out labor requirements. The addition of forage and feed crops, combined with a livestock enterprise, can further utilize labor, spreading it into the winter months.

It may be helpful to calendarize the operations required to plant and harvest each crop, with special attention to the labor needed for each operation. The labor needed can be compared to the labor available (combined with a particular complement of machinery) to determine if the farm operations can be done in a timely manner.

Machinery efficiency

Efficiency in machinery use comes from either getting the job done in a more timely manner at a low marginal cost or from spreading fixed costs over more hours or acres. The efficacy of a rotation may be limited by available machinery. The ability of the additional crop(s) in the rotation to pay the additional cost must be determined when implementing a new rotation requires the purchase of new equipment.

Weather and pest damage

Too little or too much precipitation is the most common weather problem in North Dakota. Within limitations, crop rotations can be used to adjust to rainfall limitations and moisture needs. Crops seeded or harvested at different times of the year will not be affected in the same manner by freezes, drought, or hail, lending stability to income.

Rotations provide control and limit the spread of insects and diseases. This is possible because most diseases and insects affect only one or a few crops. Rotations help reduce disease buildup when host plants are confined to one or two seasons of cropping. Some insects may be controlled similarly, and infestations that do appear may be later and of little economic importance when compared to fields with a continuous single crop. Rotations, therefore, can reduce the need for pesticides, but they will not eliminate the need for pesticides entirely, nor will rotations be effective against all insects and diseases.

Climatic considerations

Climate is the greatest factor limiting the choice of crops for rotations in North Dakota. The freeze-free growing season varies from year to year but averages from about 110 days in the north central area along the Canadian border to over 130 days in the southeast corner of the state (Figure 1). The climate permits warm season crops such as corn, soybean and sunflower as well as cool season crops such as small grains and flax to be grown in some regions. In the cooler regions of the state, fewer growing degree days and a shorter season limit the choices to legumes, canola, small grains, flax, sunflower, and several specialty crops such as mustard, millet, buckwheat, safflower and canaryseed. Early corn hybrids can be grown but grain will not always mature.

Figure 1. Average number of frost-free days across North Dakota.

Variations in temperature from year to year can cause detrimental effects in all crops. Years with below normal mean temperatures tend to favor higher yields of the cool season crops, especially if there are few hot days. Maximum temperatures greater than 90�F during flowering and grain filling can cause substantial yield reductions in the cool season crops. Warmer season mean temperatures favor higher yields of the warm season crops.

Foliar disease problems are highly dependent on weather conditions. Many are favored by high humidity and warm temperatures. These conditions are more apt to occur in eastern North Dakota than in the western regions.

Annual precipitation declines from southeast to northwest (Figure 2). It ranges from less than 14 inches in the northwest areas of the state to more than 20 inches in the extreme southeast. In regions west of the 18-inch rainfall zone, dryland production of such crops as soybeans, sugarbeets, and potatoes has not been economically feasible. Fortunately nearly half of the annual precipitation occurs during the growing season months of June, July and August (Figure 3).

Figure 2. Average annual precipitation, in inches, in North Dakota.

Figure 3. Mean monthly precipitation in North Dakota.

Accumulated growing degree days (GDDs) can be calculated for various crops from daily temperature records. Accumulated growing degree days can be useful in many ways, including crop maturity predictions and crop development stages. The same formula is used for all crops except that the base temperature and maximum temperatures may be different.

If the daily maximum is greater than specified for a specific crop, the maximum temperature is used. The same applies for daily minimum temperatures.

Base plus maximum. Temperatures for four crops common to North Dakota.

On a day when the maximum temperature reaches 84^o F and the minimum temperature is 68^o F wheat would accumulate 40 GDDs {[(76 + 68)/2] - 32 = 40}, and corn would accumulate {[(84 + 68)/2] - 50 = 26}.

Reduced risk

Crop rotations add diversity to farm operations and can help reduce risk, provide income stability, spread labor requirements, help control pests, and may add to efficient machinery use. Maintaining some flexibility within rotations to take advantage of price changes can help increase returns with little change in risk.

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[Introduction] [General Effects of Rotations]
[Selecting a Rotation] [Suggested Rotations] [Bibliography]

EB-48 (Revised), January 1998