By Chad King
Crop rotation has been used since Roman times to improve plant nutrition and to control the spread of disease. A study published in Nature’s The ISME Journal reveals the profound effect crop rotation has on enriching soil with bacteria, fungi and protozoa.
Crop rotation simply means changing the type of crop grown on a particular piece of land from year to year which includes cyclical and non-cyclical rotations. Good crop rotation includes planning ahead two or more years. A lack of planning can lead to problems including the buildup of soil-borne diseases or imbalances in soil nutrients and an increase in pests.
“Changing the crop species massively changes the content of microbes in the soil, which in turn helps the plant to acquire nutrients, regulate growth and protect itself against pests and diseases, boosting yield,” said Professor Philip Poole from the John Innes Centre.
Soil was collected from a field near Norwich and planted with wheat, oats and peas. After growing wheat, it remained largely unchanged and the microbes in it were mostly bacteria. Crop rotation by growing oat and pea in the same sample caused a huge shift toward protozoa and nematode worms.
Seven Crop Rotation Steps
A good crop rotation plan should include the following steps:
Step 1. Identify and prioritize your goals. Your goals may to be build better, healthier soils, control pests, minimize soil-borne diseases, reduce weed pressure and to produce the most nutritious foods possible.
Step 2. Write down the mix of fruits, vegetables and cover crops that you plan to grow next season along with each crop’s planting and harvesting dates.
Step 3. Write the plant’s family name next to each crop and then add up the amount of garden space in square feet that will be allocated for each family. If one family will be grown on more than 25 percent of your garden, then consider increasing the diversity of your crop mix. Having a high proportion of your garden in one family might mean that a location will rotate back to that family too soon, which can lead to soil-borne diseases.
Step 4. Make a crop rotation planning map. Think about how you will divide your garden into small units of somewhat equal sizes. These units could be long rows or individual beds of any shape. Making this map and having your garden divided into these units allows you to keep track of what you planted on a piece of ground years later. The map of your garden will show every unit. The map should be large enough so that information can be written inside each unit. For this mapmaking, 12 x 16 sketch paper or a computer works well. When you are done making your map and before you start filling in each unit’s information, make at least six to eight copies. Next, assign a color for each plant family, cover crop, mulch and fallow periods.
Step 5. On another copy of your map, designate each crop to as many units as you need to meet the area of your specific crop mix. If a unit will be double or triple cropped, separate their names with dashes such as May lettuce-buckwheat cover-fall spinach. If you plan on growing two or more of the same crop family on a unit, use slashes to indicate this (tomato/peppers/potato). When placing a crop onto a unit, try to pair crop families together on a given unit, but avoid placing a family onto a unit that has had that same family on the unit in the previous few years. At this time you may match the colors you’ve chosen for families and color them onto the appropriate units.
Step 6. Once you have your maps finished with the crops written inside each unit, numbered and colored, along with any other usable information, then take your maps and walk your garden. Imagine how it will look and consider the tillage, planting, care and harvesting of your crops and if the proposed crop sequence makes sense for a given location. At this time also take into consideration equipment, irrigation and labor needs.
Step 7. Develop a backup plan by thinking ahead to any problems that may arise with growing a crop within a unit, such as if a spring may be too wet for early planted crops or certain transplants are unavailable at a critical time or who will take over your labor duties if something happens to you and you have to be away for an extended period of time. Write down your backup plans for coping with various problems and make provisions for these possible problems.
Every garden is unique and each gardener will have their own specific needs, but there are principals and general rules of thumb that should be followed when thinking about a new rotation.
- Follow legume cover crops such as clover with high-N demanding crops.
- Grow winter-killed cover crops before early-season crops.
- Never grow any crop after itself.
- Use crop sequences that promote healthier crops such as cabbage family crops following onions or potatoes following corn.
- Avoid growing one heavy feeder after another heavy feeder.
- Grow tomatoes after peas, lettuce or spinach, because tomatoes take a lot out of the soil.
- Grow beans after sweet corn to rebuild nitrogen levels.
- Use a cover crop’s residue to help build organic matter levels.
- When growing a wide mix of crops, try grouping into units according to plant family, timing of crops planting dates and harvesting dates.
- A minimum return time of a crop should be in the four-to-five year range, which often prevents most soil-borne diseases.
- Attempt to keep something growing throughout the year, which keeps the ground covered, protecting the soil and at the same time will supply organic material for earthworms and beneficial organisms living within the soils. Incorporating cover crops into a rotation makes this possible.
Rotations are an important part of any gardening system. Yields of crops grown in rotations are typically 10 percent higher than those of crops grown in monoculture in normal growing seasons and as much as 25 percent higher in droughty growing seasons.
Adding cover crops to a rotation can add organic matter, enhance mycorrhizal numbers, add nitrogen, suppress weeds and nematodes, reduce soil erosion, increases infiltration of water, decreases nutrient loss and attracts beneficial insects.
Planning Crop Rotation in Vegetable Gardens
There is a growing consciousness around growing one’s own food and the reasons for doing so vary from person to person. Tough economic times, high unemployment, rising food costs and a desire to provide one’s family with fresh, super nutritious food are just a few examples.
One fact that remains the same is that gardener’s put a great amount of care, hard work and time into their gardens only to sometimes achieve mediocre results.
The one factor that we have no control over is Mother Nature. Gardening is inherently risky and pests, drought, flooding and wind along with other weather extremes can all destroy a year’s work. A good example of an extreme weather event would be the severe drought of 2012 that stretched across more than half of the United States and the record number of 90-plus days. With many of those days reaching up into the triple digits. The result was scorched crop fields, pastures and gardens. The drought was so extensive that it also created problems concerning producers’ water supplies. Creeks, rivers, ponds, lakes and aquifers had dangerously low water levels, while others completely dried up.
The number of farmers, livestock producers and gardeners who experienced crop and animal losses in 2012 will not only be felt by them, but will be felt by most American consumers. A large portion of our economy depends on agriculture.
Irrigation was a lifesaver in 2012 for those who had systems in place, but even then some farmers and gardeners were still unable to keep up with demand and eventually had to give up in the face of low water supplies and high fuel bills.
Many gardeners who utilized drip irrigation with mulch or a plastic layer had good results and were able to produce an abundant crop within their gardens.
There are many tools and techniques that growers use to grow their food, somethings they have control over, and others not, but one technique often misunderstood and under valued is crop rotations within a garden.
The smaller a garden is and when a gardener is only growing two or three different crops, it then becomes more difficult for a crop rotation to be effective. There are ways in which a gardener can increase his success rates and be extremely efficient and they include using mulch, compost, manure and short-term cover crops.
In the world of gardening there are so many names that it can be confusing and intimidating, but a new gardener who does not understand those horticulture names could make the wrong choice of plants for their garden and the crop rotation plan. To become more knowledgeable with these horticulture names stop by your local library and check out a few books on vegetable gardening, use the Internet, ask your local garden center staff or an experienced gardener. Understanding the vocabulary that comes along with gardening and a crop rotation can make the planning easier and gardening in general a lot more enjoyable, productive and successful.