What is Crop Rotation?
Crop rotation is a planned sequence of growing different crops in the same field. Rotations are the opposite of continuous cropping, which is growing the same crop in the same field year after year. Ideally, these crops are not of the same family.
Why Do We Rotate Crops?
Crop rotation is a common practice on sloping soils because of its potential for soil saving. Crop rotations can be used to improve or maintain good physical, chemical, and biological conditions of the soil. They can be used to reduce the average rate of erosion from a field. Including a grass or legume in a rotation can be very effective for reducing erosion and improving soil structure. When a legume is used in the rotation, it may eliminate the need for nitrogen fertilizer. Other crops accumulate phosphorus or potassium. In addition crop rotation can be an important part of an integrated pest management (IPM) program.
The Value of Crop Rotation:
Plant Nutrition: Each crop uses different types and amounts of minerals from the soil. If the same crop is planted each and every year, over time the soil is depleted of the minerals essential for plant growth and health. In reverse, a different crop will sometimes return missing minerals to the soil as the plant dies and composts or is turned into the soil.
Soil Structure: Rotation preserves and improves soil structure. Crops have different root structures and grow to various depths. By rotating, the soil is not submitted to just shallow depth crops, but deep diggers that will slowly deepen the topsoil.
Insect Control: Insects can over winter in your soil. They enter the leaves and vines of your plants ready to reawaken in the spring to find their favorite meal. When you rotate, these insects are faced with a plant they don’t feed on.
Disease Prevention: Just like insects, plant diseases can over winter in plant leaves, roots and vines under your soil. Rotating crops helps to guard against these diseases returning the following year.
Water Quality: Surface water quality can be improved by reducing sediment loss, and losses of dissolved and sediment-attached nutrients and pesticides. Nitrogen losses to ground water can be reduced by deep rooted sod crops which may use nutrients from deep in the soil profile. In addition, legume crops fix atmospheric nitrogen that can reduce or eliminate the need for commercial nitrogen fertilizer for the subsequent crops. Crop rotations also tend to encourage healthy root systems which are effective at retrieving nutrients from the soil, thus minimizing leaching to ground water.
How to Rotate Crops:
Crops should be rotated on at least a three to four year cycle. They should be rotated every year. So a crop of corn planted this year is not planted in the same field for the next two or three years. Ideally, altogether different crops should be used each year as insects and disease that affects one crop will also likely affect similar crops, i.e. cabbage and broccoli are of the same family and should not follow each other. Crops are changed year by year in a planned sequence.
Patterns, though not agreed upon by all, emerge when deciding the best rotation plan. Legumes are generally a beneficial preceding crop. Potatoes yield best after corn. Some preceding crops (peas, oats, barley) increase the incidence of scab on potatoes. Corn and beans are not greatly influenced by the preceding crop. Carrots, beets and cabbages are generally detrimental to subsequent crops.
When legumes are used in a crop rotation, the nitrogen formed by fixation should be taken into account when determining the nutrients needed for future crops, thus preventing over application of nitrogen. Soil fertility levels should be regularly monitored and fertility maintained within the acceptable range for all crops in the rotation.
When planning out a rotation, divide the crops into their families. This follows the principle of not growing out the same crop or one in the same family. Beets, chard and spinach are in the same family for example. Also look at how much space the crop will require. Radish requires much less than corn.
In addition to rotating crops, many farmers rotate their livestock among different sections of pasture. This facilitates the dispersal of manure in the fields as well as prevents over-grazing of any one section. Overgrazing of pasture can lead to a depletion of vegetation and consequent soil erosion.
A few notes:
- Crops must be suited to your soils.
- Rotations that include small grains or meadow provide better erosion control.
- Small grains and meadow can always be used to replace any row crop or low residue crop to gain better erosion control.
- Corn (grains) can always be used to replace soybeans or any other low residue crop in the rotation to gain better erosion control.
- For crop rotations, which include hay (meadow), the rotation can be lengthened by maintaining the existing hay stand for additional years.
- Avoid planting a grass after a grass if possible.
Sample 8 year rotation:
Potatoes, corn, the cabbage family, peas, tomatoes, beans, root crops, squash. The rotation moves to the right, potatoes follow corn, corn follows cabbage family, etc.