Crop rotation is the practice of changing the crop each year on the same piece of ground, in an effort to confuse pests, reduce weed pressure, and ensure the soil does not get depleted of certain nutrients. Eliot Coleman, considered to be one of the godfathers of market gardening, says that crop rotation “is the single most important process in a multi-cropping program” (The New Organic Grower).
Ideally, two crops of the same botanical family would not be planted in succession, nor would they make the same demands on the soil, or attract the same kinds of pests or diseases. The goal for a crop rotation plan then becomes a game of figuring out how best to strategically implement these principles.
Crop rotation principles are age-old, found in early Roman agricultural writings, as well as ancient Greek and Chinese manuscripts. More recently John Jeavons, well known for his contributions to the biointensive agriculture movement, has contributed a succinct way of grouping crops for the purpose of crop rotation. Jeavons organized crops into three main categories, and recommends they be planted in this order when planning your rotation:
- Heavy Feeders
- Heavy Givers
- Light Feeders
When a new plot has been prepared, with plenty of nutrient-rich compost added, the rotation would begin with heavy feeders. Heavy feeders are crops that consume large amounts of nutrients from the soil, especially nitrogen. These would include crops such as corn, tomatoes, squash, lettuce, and cabbage. The three nutrients that plants consume in the highest volume are known as the macronutrients: nitrogen, phosphorus, and potassium. After growing heavy feeders, Jeavons recommends phosphorus and potassium be replenished in the form of compost. However, nitrogen is best replenished by growing what Jeavons refers to as heavy givers.
Following heavy feeders, you would plant heavy givers. Heavy givers are crops primarily in the legume family, nitrogen-fixing plants such as peas and beans. Cover crops such as alfalfa, clover, and vetch are also nitrogen-fixing plants. These plants deposit large amounts of nitrogen into the soil by harnessing it from the atmosphere and transferring it to their root systems. The soil microbes (bacteria and fungi) then make the nitrogen available to other plants by decomposing those root systems.
When growing cover crops to replenish nitrogen in the soil, the best time to cut them down is just after the plants have begun to flower. At this stage of maturity, the root systems will be the most nitrogen rich. As the plants begin fruiting and going to seed, a lot of that available nitrogen will be used up in the process. In addition, you don’t want unwanted cover crop seed in your soil if you plan to plant a cash crop in that same space.
After heavy feeders would come the third category: light feeders. This group is primarily composed of root crops. Planting light feeders after the heavy givers provides the soil an opportunity to rest before the high demand of heavy feeders are planted again. By rotating your crops in this order, you are strategically cycling the nutrients, creating diversity and hopefully biological stability.
Space and Time
As you’re beginning to plan out your crop rotation, the two main factors to consider are space (where the crops are), and time (when the crops will move to). If you’re a very visual/tactile person, it can help to use 3×5 index cards to write the down the crop, or group of crops you’ll be planting in a given bed or field block. You can then move around the cards to strategize your ideal rotation. There are also software programs available to accomplish this on your computer. Below is a good visual illustration that takes into account both space and time in a strategic crop plan. The top columns represent space (beds1-6), and the rows going down the left side of the chart represent time (years 1-6).
Monocultures often produce pest issues. When one crop is continually planted in the same space year after year, harmful insects that are drawn to that particular crop have an endless food supply and will multiply prolifically. Pests may even overwinter in the soil, only to re-emerge and resume their feast the following season. For this reason, moving locations of a given crop can help to confuse pest populations and bring greater balance to the ecosystem of your farm.
A smart crop rotation plan will also factor in weed control. Certain crops, and the cultivation methods used to grow them, may also provide a favorable environment for certain kinds of weeds. If possible, plan your rotation to where the successor crop helps to eradicate the weeds that proliferated with the previous crop.
An example of this would be planting root crops after squash. Squash is considered a “cleaning crop.” It is easier to cultivate with wider-spaced plants, and the once the vines grow out they form a ground cover to naturally smother a second flush of weeds. Roots crops are spaced much closer together and are more susceptible to competition from weeds. When they follow squash in your crop rotation plan, the weed seed bank ought to be lower, making your cultivation/weed management an easier task when growing the root crops.
Most often a disease that affects one crop family, will not affect another. Some disease-causing pathogens can survive in the soil from one year to the next. By rotating your crops, you are moving the host crop away from the plot where it was affected. This can help prevent a build-up of larger populations of pathogens. However, continually growing the same crop in the same location year after year can allow those pathogens to proliferate and get out of control. By mixing it up and growing a crop that is not a host plant for the pathogen that affected the previous crop, that pathogen will die out.
Soil Structure and Nutrition
Rotating your crops also improves the structure of the soil. Different crops send down roots at different depths and also require different cultivation techniques. By moving crop families to different plots from year to year, a grower will contribute to the deepening of the topsoil.
Deeper-rooting crops will extract nutrients and minerals from depths that shallow-rooted crops would not otherwise have access to. Rotating deep-rooted crops to shallow-rooted crops also opens up channels in the soil to make it easier for less vigorous crops to send down roots. The minerals brought up by deep-rooted crops will eventually become available when the crop residue is allowed to decay in the soil. These minerals will now feed the shallow-rooted crops planted there the following season.
Eliot Coleman’s Sample Rotation
Eliot Coleman produced an extremely well-thought-out crop rotation plan that is still referenced by growers still today. It’s an 8-year cycle that incorporates many of the strategies we’ve gone over. Note: Salad crops were not included in this particular crop rotation plan, but instead grown in their own designated space.
The following list is an excerpt from “The New Organic Grower” where Eliot Coleman explains this tried and true crop rotation:
Potatoes follow sweet corn in this rotation because research has shown corn to be one of the preceding crops that most benefit the yield of potatoes.
Squash is grown after potatoes in order to have the two “cleaning” crops back to back prior to the root crops, thus reducing weed problems in the root crops.
3. Root Crops
Root Crops follow squash (and potatoes) because those two are both good “cleaning” crops (they can be kept weed-free relatively easily); thus there are fewer weeds to contend with in the root crops, which are among the most difficult to keep cleanly cultivated. Also, squash has been shown to be a beneficial preceding crop for roots.
Beans follow root crops because they are not known to be subject to the detrimental effect that certain root crops such as carrots and beets may exert in the following year.
Tomatoes follow beans in the rotation because this places them four years away from their close cousin, the potato.
Peas follow tomatoes because they need an early seedbed, and tomatoes can be undersown to a non-winter-hardy green manure crop that provides soil protection over winter with no decomposition and regrowth problems in the spring.
7. The Cabbage Family
The Cabbage Family follows peas because the pea crop is finished and the ground cleared by August 1, allowing a vigorous winter green manure crop to be established.
8. Sweet Corn
Sweet corn follows the cabbage family because, in contrast to many other crops, corn shows no yield decline when following a crop of brassicas. Secondly, the cabbage family can be undersown to a leguminous green manure which, when turned under the following spring, provides the most ideal growing conditions for sweet corn.
Hopefully, this has provided a solid foundation of the main principles when it comes to crop rotation. As with many other aspects of farming, holding a strict dogma when it comes to crop rotation will not always work. You will find some crops don’t fit perfectly into a specific category. You also may want to rotate crops from spring to fall, rather than just every year. Or you might want to rotate with every planting. Ultimately it comes down to what works best for you and your specific context.
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