Crop Rotation Strategies
Copyright © September 1, 2014 by Robert Wayne Atkins, P.E.
All Rights Reserved.
In several of my articles I have mentioned that the same vegetable crop should not be planted in the same place every year. Instead I have consistently recommended that each vegetable crop be planted in a different spot than where it was planted the previous year.
The purpose of this article is to explain why I have consistently recommended a crop rotation strategy.
The Benefits of Crop Rotation
Crop rotation has all the following benefits:
- Disease Control: Some crops are subject to attack by specific types of microbial pathogens. If the same crop is planted in the same soil year after year then specific microbial pathogens have a chance to multiply and they can more easily infect the new crop the following year. But if a different type of crop is planted that is not attractive to a specific type of pathogen then the pathogen will not attack that crop and the pathogen will decrease in the soil instead of multiplying in the soil. This minimizes and sometimes eliminates the need to add special chemicals to the soil to kill the pathogens.
- Insect Control: Some crops attract a specific type of insect. Some of those insects can survive in the soil during the winter months. If the same crop is planted in the same soil every year, then when the new inspects reappear in the spring they will find the type of food they prefer growing directly above them. This allows them to multiply and increase in number year after year. But if a different type of crop is planted in the soil, and if it is a crop that the insects do not eat, then the insects will be forced to search elsewhere for their food. This minimizes and sometimes eliminates the need to spray special insecticide chemicals on the plants to kill the insects.
- Nutrient Balance: Different types of crops consume different nutrients from the soil. If the same crop is planted in the same spot year after year then the soil will become depleted of a specific nutrient and the crop will become less and less productive each year. Other crops require different nutrients and by rotating the crops the new crops will absorb different nutrients from the soil and this will help to balance the nutrient depletion from the soil over time. In addition, depending on the type of root system, some crops remove nutrients close to the surface of the soil, and other crops remove nutrients from deeper down in the soil. Crop rotation allows for the depletion and the replenishment of nutrients at different depths in the soil. This minimizes the need for commercial fertilizers and it sometimes allows ordinary garden compost to be adequate for the successful growth of a different crop the following year.
- Nutrient Replenishment: Some crops actually add specific nutrients into the soil while they are growing. In addition, after some crops have been harvested they leave behind inedible stalks, vines, and roots. If these items are plowed into the soil then they will further increase the nutrients in the soil as they gradually decay. This minimizes the need for commercial fertilizers and it sometimes allows ordinary garden compost to be adequate for the successful growth of a different crop the following year.
- Increased Harvests: Crop rotation allows for more food and for a better quality of food to be harvested from the same amount of garden space.
Crop Rotation Strategies
There is no single crop rotation plan that is used by everyone. Each farmer will implement a crop rotation schedule that is best suited to the types of crops that the farmer wishes to grow.
Depending on the number and types of crops involved, crop rotation plans vary from two years to six years before a crop is planted in the same space that it previously occupied. The most common strategy is a four year plan because it takes between three to four years for most microbial pathogens and for insects to die off to insignificant levels.
You will need to create a crop rotation plan based on the types of vegetables you enjoy eating and that also grow well in your geographical area.
Beans: As legumes (or beans) grow they absorb nitrogen from the air and then release that nitrogen through nodules on their roots into the soil. After the beans have been harvested from the plants, the vines should be plowed into the soil and allowed to decay in the soil to add an additional nitrogen rich organic material into the soil. Therefore beans are a good crop to plant the year before you plant a crop that absorbs a lot of nitrogen from the soil.
Root Crops: Root crops help to break up the soil and they are best followed by legumes that prefer loose soil. Root crops also do better in soils that are not rich in nutrients because a nutrient rich soil will usually result in more above ground leaf growth and less below ground root (vegetable) growth. Therefore root crops are usually planted the year before legumes because legumes significantly enhance the nutrients in the soil.
There are sophisticated crop rotation plans that divide crops into seven or more groups based on color (or other variables) and these more advanced plans do have specific advantages. However, for the average home gardener the following four year plan usually produces very good results:
Group 1 (Legumes): Beans, peas, peanuts.
Group 2 (Leafy Vegetables): Broccoli, Brussels sprouts, cabbage, cauliflower, lettuce, spinach.
Group 3 (Fruit Bearing): Corn, cucumber, eggplant, melons, peppers, potatoes, pumpkins, tomatoes, squash.
Group 4 (Root Vegetables): Beets, carrots, radish, onions, shallots, turnips.
Divide your garden area into four sections or areas. The first year plant one of the above groups of vegetables in each of the four sections. The first year you plant a garden you may plant anything anywhere you wish but keep track of where each group of vegetables was planted. Then the following year rotate the vegetables into the next section. In other words, plant group 2 in the area where group 1 was planted the previous year. Plant group 3 in the area where group 2 was planted the previous year. Plant group 4 in the area where group 3 was planted the previous year. And plant group 1 in the area where group 4 was planted the previous year.
You do not have to reserve an entire area for a single type of vegetable. It is usually okay to plant more than one type of vegetable within a specific group in the same area. For example, it would be okay to plant corn and squash in the same general area because they are both in group 3. In fact, some North American Indian tribes planted corn, beans, and squash together every year and it was called the "three sisters garden." After the corn was about two feet tall then pole beans were planted and they climbed the corn stalks and they helped to anchor the corn stalks in the ground during windy weather. The beans also released nitrogen into the soil to feed the corn. After the pole beans started growing then squash was planted because it would cover the ground and provide shade for the roots and the squash would also help to minimize the growth of weeds.
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