11.8: General Principles

Try to consider the following principles when you’re thinking about a new rotation:

1. Follow a legume forage crop, such as clover or alfalfa, with a high-nitrogen-demanding crop, such as corn, to take advantage of the nitrogen supply.
2. Grow less of nitrogen-demanding crops, such as oats, barley and wheat, in the second or third year after a legume sod.
3. If possible, grow the same annual crop for only one year to decrease the likelihood of insects, diseases and nematodes becoming a problem. (Note: For many years, the western corn rootworm was effectively controlled by alternating between corn and soybeans. Recently, populations of the rootworm with a longer resting period have developed in isolated regions, and they are able to survive this simple two-year rotation.)
4. Don’t follow a crop with a closely related species, since insect, disease and nematode problems are frequently shared by members of closely related crops.
5. If specific nematodes are known problems, consider planting nonhost plants, such as grain crops for root-knot nematodes, for a few years to decrease populations before planting a very susceptible crop such as carrots or lettuce. High populations of plant parasitic nematodes will also affect the choice of cover crops (see Chapter 10 for a discussion of cover crops).
6. Use crop sequences that promote healthier crops. Some crops seem to do well following a particular crop (for example, cabbage family crops following onions, or potatoes following corn). Other crop sequences may have adverse effects, as when potatoes have more scab following peas or oats.
7. Consider livestock as part of a rotational cropping system. Perennial fodder crops have many benefits, and these benefits are enhanced when livestock are grazing them in pastures. In fact, a rotational grazing system can be incorporated as a rotation of animals within a rotation of crops.
8. Use crop sequences that aid in controlling weeds. Small grains compete strongly against weeds and may inhibit germination of weed seeds; row crops permit midseason cultivation; and sod crops that are mowed regularly or grazed intensively help control annual weeds. Also, rotations including both cool season crops and warm season crops may aid in lowering weed populations. And as weeds develop resistance to more pesticides, it is increasingly important to explore crop sequences that give more opportunities to suppress them.
9. Use longer periods of perennial crops, such as a forage legume, on sloping land and on highly erosive soils. Using sound conservation practices, such as no-till planting, extensive cover cropping or strip cropping (a practice that combines the benefits of rotations and erosion control), may lessen the need to follow this guideline.
10. Try to grow a deep-rooted crop, such as alfalfa, safflowers or sunflowers, as part of the rotation. These crops scavenge the subsoil for nutrients and water, and channels left from decayed roots can promote water infiltration.
11. Grow some crops that leave a significant amount of residue, provide a surface mulch for reduced tillage systems, and, together with their roots, maintain or increase organic matter levels. Examples include sorghum or corn harvested for grain.
12. When growing a wide mix of crops, as is done on many direct-marketing vegetable farms, try grouping into blocks according to plant family, timing of crops (group all early season crops together, for example), type of crop (root versus fruit versus leaf) or cultural practices (for example, if irrigation or plastic mulch are used).
13. In regions with limited rainfall, the amount of water used by a crop may be a critically important issue, usually one of the most important issues. The amount of soil water at the time of planting may determine whether to grow a particular crop. Without plentiful irrigation, growing high-water-use crops such as hay, as well as sunflowers and safflowers, may not leave sufficient moisture in the soil for the next crop in the rotation.
14. Be flexible enough to adapt to annual climate and crop price variations, as well as to development of soil pathogens and plant parasitic nematodes. For example, dryland rotations have been introduced in the Great Plains to replace the wheat-fallow system, resulting in better water use and less soil erosion. (It is estimated that less than 25% of the rainfall that falls during the 14-month fallow period in the Central High Plains is made available to a following crop of winter wheat.) (See the box “Flexible Cropping Systems” and Table 11.2 for discussion and information on flexible, or dynamic, cropping systems.) Growing winter small grains in a rotation offers a number of possibilities depending on weather and the farm’s needs. Winter grains can serve as a cover crop (killed in the spring while still in the vegetative state), be grazed in the spring if feed is needed, or, if it’s very wet in the spring, be allowed to mature and the grain harvested.