11.9: Rotation Examples

It’s impossible to recommend specific rotations for a wide variety of situations. Every farm has its own unique combination of soil and climate, and of human, animal and machine resources. The economic conditions and needs are also different in each region and on each farm. You may get useful ideas by considering a number of rotations with historical or current importance.

A five- to seven-year rotation was common in the mixed livestock-crop farms of the northern Midwest and the Northeast during the first half of the 20th century. An example of this rotation:

Year 1. Corn
Year 2. Oats (mixed legume–grass hay seeded)
Years 3, 4 and 5. Mixed grass–legume hay
Years 6 and 7. Pasture

The most nitrogen-demanding crop, corn, followed the pasture, and grain was harvested only two of every five to seven years. A less-nitrogen-demanding crop, oats, was planted in the second year as a “nurse crop” when the grass-legume hay was seeded. The grain was harvested as animal feed, and oat straw was harvested to be used as cattle bedding; both eventually were returned to the soil as animal manure. This rotation maintained soil organic matter in many situations, or at least didn’t cause it to decrease too much. On prairie soils, with their very high original contents of organic matter, levels still probably decreased with this rotation.

In the Corn Belt region of the Midwest, a change in rotations occurred as pesticides and fertilizers became readily available, animals were fed in large feedlots instead of on integrated crop-livestock farms, and grain export markets were developed. Once the mixed livestock farms became grain-crop farms or crop-hog farms, there was little reason to grow sod crops. In addition, government commodity price support programs unintentionally encouraged farmers to narrow production to just two feed grains. The two-year corn-soybean rotation is better than monoculture, but it has a number of problems, including erosion, groundwater pollution with nitrates and herbicides, soil organic matter depletion, and in some situations, increased insect problems. Soybeans leave minimal amounts of residues. But research indicates that with high yields of corn grain in a soybean-corn rotation there may be sufficient residues to maintain organic matter. For many years, the Thompson mixed crop-livestock (hogs and beef) farm in Iowa practiced an alternative five-year Corn Belt rotation similar to the first rotation we described: corn-soybeans-corn-oats (mixed/grass hay seeded)-hay. For fields that are convenient for pasturing beef cows, the Thompson eight-year rotation is as follows:

Year 1. Corn (cereal rye/hairy vetch cover crop)
Year 2. Soybeans
Year 3. Oats (mixed/grass hay seeded)
Years 4 to 8. Pasture

Organic matter is maintained through a combination of practices that include the use of manures and municipal sewage sludge, green manure crops (oats and rye following soybeans, and hairy vetch between corn and soybeans), crop residues and sod crops. These practices have resulted in a porous soil that has significantly lower erosion, higher organic matter content and more earthworms than neighbors’ fields.

A four-year rotation researched in Virginia used mainly no-till practices as follows:

Year 1. Corn, with winter wheat no-till planted into corn stubble

Year 2. Winter wheat grazed by cattle after harvest; foxtail millet no-till planted into wheat stubble and hayed or grazed; alfalfa no-till planted in fall

Year 3. Alfalfa harvested and/or grazed

Year 4. Alfalfa harvested and/or grazed as usual until fall, then heavily stocked with animals to weaken it so that corn can be planted the next year

This rotation follows many of the principles discussed earlier in this chapter; it was designed by researchers, Extension specialists and farmers, and is similar to the older rotation described earlier. A few differences exist: this rotation is shorter; alfalfa is used instead of clover or clover-grass mixtures; and there is a special effort to minimize pesticide use under no-till practices. Weed-control problems occurred when going from alfalfa (fourth year) back to corn. This caused the investigators to use fall tillage followed by a cover crop mixture of cereal rye and hairy vetch. Some success was achieved suppressing the cover crop in the spring by just rolling over it with a harrow (with similar effects as a roller/crimper) and planting corn through the surface residues with a modified no-till planter. The heavy cover crop residues on the surface provided excellent weed control for the corn.

Traditional wheat-cropping patterns for the semiarid regions of the Great Plains and the Northwest commonly include a fallow year to allow storage of water and more nitrogen mineralization from organic matter for the next wheat crop to use. However, the two-year wheat-fallow system has several problems. Because no crop residues are returned during the fallow year, soil organic matter decreases unless manure or other organic materials are provided from off the field. Water infiltrating below the root zone during the fallow year moves salts through the soil to the low parts of fields. Shallow groundwater can come to the surface in these low spots and create “saline seeps,” where yields will be decreased. Increased soil erosion, caused by either wind or water, commonly occurs during fallow years, and organic matter decreases (at a rate of about 2% per year, in one experiment). In this wheat monoculture system, the buildup of grassy weed populations, such as jointed goat grass and downy brome, also indicates that crop diversification is essential.

Farmers in the dryland regions trying to develop more sustainable cropping systems are considering using a number of species, including deeper-rooted crops, in a more diversified rotation. This would increase the amount of residues returned to the soil, reduce tillage, and lessen or eliminate the fallow period. (See “Flexible Cropping Systems” box.) In the 1970s some farmers began switching from the two-year wheat-fallow system to a three year rotation, commonly winter wheat-grain sorghum (or corn)-fallow. When this rotation is combined with no-till, accumulated surface residues help maintain higher soil moisture levels. A four-year wheat-corn-millet-fallow rotation under evaluation in Colorado was found to be better than the traditional wheat-fallow system. Wheat yields have been higher in this rotation than wheat grown in monoculture. The extra residues from the corn and millet are also helping to increase soil organic matter.

Many producers are including sunflowers, a deep-rooting crop, in a wheat-corn-sunflower-fallow rotation. Sunflowers are also being evaluated in Oregon as part of a wheat cropping sequence.

Another approach to rotations in the semi-arid Great Plains of North Dakota combines crop and livestock farming; it uses a multi-species rotation in place of continuous hard red spring wheat. This five-year rotation includes only two cash crops (wheat and sunflowers) with grazing crops grown for three years:

Year 1. Hard red spring wheat (cash crop) with winter triticale and hairy vetch planted after wheat harvest in September

Year 2. Triticale-vetch hay harvested in June. A cover crop consisting of a seven- to 13-species mix is seeded as soon as possible after the hay harvest and then grazed by either cows or yearling steers

Year 3. A silage-type corn variety is planted and grazed first by yearling steers and then by cows in a “leader-follower” grazing plan

Year 4. A field pea-forage barley mix is grazed by yearling steers

Year 5. Sunflowers (cash crop)

Sodic seeps and subsurface sodic clay layers are sometimes found in semi-arid regions and may limit crop growth. (See Chapter 6 for discussion of saline and sodic soils, and for their reclamation see Chapter 20). During the cover crop year of a multi-crop rotation such as the one discussed just above, including adapted crop-types with taproots such as tillage radishes, sunflowers, safflowers, mustard, and canola, as well as sodium-tolerant crops like barley, aids in remediating problem soils when coupled with a diverse crop rotation on all farm acres.

Flexible Cropping Systems

As discussed in point 14 under “General Principles,” it may be best for many farmers to adopt more “dynamic” crop sequences rather than to strictly adhere to a particular sequence. Many things change from year to year, including prices paid for crops, pest pressures and climate. And many farmers do deviate from plans and change what they plant in a particular field; for example, in a wetter-than-normal field a dry spring opens the opportunity for a vegetable farmer to plant an early season crop, thus potentially enhancing the diversity of crops grown in that field. However, this issue is especially important for dryland farmers in water-limiting regions such as the Great Plains. In dryland agriculture, low water availability is usually the greatest limitation to crop growth. In such regions, where much of the water needed for a crop is stored in the soil at planting time, growing two heavy water users in a row may work out well if rainfall was plentiful the first year. However, if rainfall has been low, following a heavy-water-using crop (such as sunflowers or corn) with one that needs less water (such as dry peas or lentils) means that water stored in the soil may be enough, along with rainfall during the growing season, to result in a reasonable yield. Caution is needed when making flexible cropping decisions because carryover of herbicides from the previous crop may interfere with your ability to use a different crop than the one planned. University Extension weed control guides are reliable sources of information relating to herbicide chemical plant-back intervals for various crops (including cover crops). Overall, using an adaptive approach to cropping makes sense for many farm operations but requires a solid understanding of the agronomic principles on the part of the farmer.

Table 11.2 Comparison of Monoculture, Fixed-Sequence Rotations and Dynamic Cropping Systems

	Monoculture	Fixed-Sequence Rotations	Dynamic Cropping Systems
Numbers and types of crops	Single crop	Multiple crops; number depends on regionally adapted species, economics, farmer knowledge, infrastructure	Multiple crops; number depends on regionally adapted species, economics, farmer knowledge, and infrastructure
Crop diversity	None	Diversity depends on the length of the fixed sequence	Diversity high due to annual variation in growing conditions and marketing opportunities, as well as changes in producer goals
Crop-sequencing flexibility	None	None, although fixed-sequence cropping systems that incorporate opportunity crops increase flexibility	High; all crops, in essence, are opportunity crops
Biological and ecological knowledge	Basic knowledge of agronomy	Some knowledge of crop interactions is necessary	Extended knowledge of complex, multiyear crop and crop-environment interactions
Management complexity	Generally low, though variable depending on crop type	Complexity variable depending on the length of the fixed sequence and diversity of crops grown	Complexity inherently high due to annual variation in growing conditions, market and producer goals
Source: Modified from Hanson et al. (2007)

Crop Rotation On Organic Farms

Crop rotation is always a good idea, but a sound crop rotation is essential on organic farms. Supplying nitrogen and controlling weeds is more challenging, and options for rescuing crops from disease are limited, making proactive planning through good crop rotations more important. Disease and weed management require a multiyear approach. Nutrients for organic crop production come largely through release from organic matter in soil. Therefore manure, compost, cover crops, and a crop rotation with regular organic matter inputs and large amounts of nitrogen and active soil organic matter are critical.

Organic farmers usually grow a high diversity of crops to obtain the benefits of a diverse crop rotation and to take advantage of specialty markets. Thus, organic field crop producers commonly grow five to 10 crop species, and fresh market vegetable growers may grow 30 or more. However, because of the large variation in acreage among crops and frequent changes in the crop mix due to weather and shifting market demands, planning crop rotations on highly diversified farms is difficult. Therefore, many organic farmers do not follow any regular rotation plan but instead place crops on individual fields (or parts of fields) based on the cropping history of the location and its physical and biological characteristics (e.g., drainage, recent organic matter inputs, weed pressure). Skilled organic growers usually have next year’s cash crops and any intervening cover crops in mind as they make their placement decisions but find that planning further ahead is usually pointless because longer-term plans are so frequently derailed.

Although precise long-term rotation plans can rarely be followed on farms growing a diverse mix of crops, some experienced organic farmers follow a general repeating scheme in which particular crops are placed by the ad hoc approach described above. For example, some vegetable operations plant cash crops every other year and grow a succession of cover crops in alternate years. Many field crop producers alternate some sequence of corn, soybeans and small grains with several years of hay on a regular basis, and some vegetable growers similarly alternate a few years in vegetables with two to three years in hay. These rest periods in hay or in cover crops build soil structure, allow time for soilborne diseases and weed seeds to die off, and provide nitrogen for subsequent heavy-feeding crops. Some vegetable growers alternate groups of plant families in a relatively regular sequence, but this generally requires growing cover crops on part of the field in years when groups that require less acreage appear in the sequence. Within all of these generalized rotation schemes, the particular crop occupying a specific location is chosen by the ad hoc process described above. Organizing the choices with a general rotation scheme greatly simplifies the decision-making process.

Dividing the farm into many small, permanently located management units also greatly facilitates effective ad hoc placement of crops onto fields each year. By this means, a precise cropping history of every part of each field is easy to maintain. Moreover, problem spots and particularly productive locations can be easily located for planting with appropriate crops.

—Charles Mohler, Cornell University

Vegetable farmers who grow a large selection of crops find it best to rotate in large blocks, each containing crops from the same families or having similar production schedules or cultural practices. Many farmers are now using cover crops to help “grow their own nitrogen,” utilize extra nitrogen that might be there at the end of the season, and add organic matter to the soil. A four- to five-year vegetable rotation might be:

Year 1. Sweet corn followed by a hairy vetch/cereal rye cover crop

Year 2. Pumpkins, winter squash or summer squash followed by a rye or oats cover crop

Year 3. Tomatoes, potatoes or peppers followed by a vetch/cereal rye cover crop

Year 4. Crucifers, greens, legumes, carrots, onions and miscellaneous vegetables followed by a cereal rye cover crop

Year 5. (If land is available) oats and red clover or buckwheat followed by a vetch/cereal rye cover crop

Another rotation for vegetable growers uses a two- to three-year alfalfa sod as part of a six- to eight-year cycle. In this case, the crops following the alfalfa are high-nitrogen-demanding crops, such as corn or squash, followed by cabbage or tomatoes, and, in the last two years, crops needing a fine seedbed, such as lettuce, onions or carrots. Annual weeds in this rotation are controlled by the harvesting of alfalfa a number of times each year. Perennial weed populations can be decreased by cultivation during the row-crop phase of the rotation.

Most vegetable farmers do not have enough land, or the markets, to have a multiyear hay crop on a significant portion of their land. Aggressive use of cover crops will help to maintain organic matter in this situation. Manures, composts or other sources of organic materials, such as leaves, should also be applied every year or two to help maintain soil organic matter and fertility.

Alternating cotton with peanuts is a common, simple rotation in the Southeast coastal region. The soils in this area tend to be sandy, low in both fertility and waterholding capacity, and have a subsoil compact layer. As with the corn-soybean alternation of the Midwest, a more complex system is very desirable from many viewpoints.

A rotation including perennial forage for at least a few years may provide many advantages to the cotton-peanut system. Research with two years of Bahia grass in a cotton-peanut system indicates greater cotton root growth, more soil organic matter and earthworms, and better water infiltration and storage.

The rapid expansion and intensification of agriculture in South America, notably Brazil and Argentina, is strongly driven by the increased global demand for grain crops like corn and soybeans. Many areas in this region also experience extended dry seasons. The system can be made more ecologically sustainable by using no-till and growing soybeans and corn. It is followed into the dry season by a tropical grass like brachiaria that is interseeded into the corn and grazed by beef cattle. While this makes the corn-soybean system less damaging, the participation of these countries in production for global distribution has resulted in the loss of significant portions of important tropical forests and the homelands of the people living in those forests.