Crop Rotation: Why It Matters So Much
What exactly is crop rotation, and why does it matter? We explain the science behind crop rotation and why it's so beneficial.
Do you find yourself growing the same thing in your garden beds every year? Maybe consider incorporating a diverse crop rotation to better your garden ecosystem. Because after all, that’s the best thing to do: build an ecosystem. Crop rotation is an opportunity to increase the diversity within your garden.
In this article, I will discuss the role crop rotations play in large-scale agriculture and how we can scale this down to the small homestead. While not all the benefits apply to small homesteads, crop rotation still has many benefits, like improved soil health and a more diverse garden ecosystem.
Crop rotation gives us as gardeners time to try different crops in the garden. Growing new things helps us gain a better understanding of new kinds of crops and techniques which ultimately makes us better gardeners.
What is a Monoculture?
Before getting into what crop rotations are, we first need to think about what a monoculture is. Monocultures are farming systems where one crop is planted every single year in the same place. The stereotypical monocropped system involves the continuous cropping of corn. These multi-step systems are intensive processes that occur in large-scale production.
These use frequent tillage, before planting and after harvesting. If you’re curious about tillage in detail, consider reading this other article on the Epic Gardening site. Tillage is especially destructive to the soil as a whole. Yearly tillage prevents stable organic matter from accumulating. Tillage is a damaging process for many reasons, but reducing water infiltration and soil erosion are two. Tillage leaves the soil bare which can lead to runoff. Depending on the farmer this may happen several times annually.
In many large-scale farms in the Grain Belt, farmers till at the end of the season and fertilize. Fertilizer prices are lower then, so farmers will buy and apply the fertilizers in the off-season. By the time farmers plant the cash crop in the spring, excess nutrients like nitrogen (and some phosphorus) have already leached out of the soil. Others in the row crop become unavailable to the plant roots in that time. To make up for unavailable nutrients, more fertilizer will be applied.
This row crop system, while still productive, is ultimately destructive to the soil and the environment. This study published in PeerJ outlines a study investigating the continuous cropping of peanuts. They found that the surrounding soil bacteria were less diverse and the beneficial ones were reduced. While this study focuses on peanuts, other crops have a similar effect on soil microbe communities and soil structure overall.
Monocropping is the process of continually cropping the same thing every single year, without crop rotations. The most common examples are corn or soybean. These two represent the largest crops in the United States. Monocoropping is a heavily intensive process generally requiring more fertilizers, tillage, and chemicals like herbicides and pesticides to mitigate plant diseases.
What is Crop Rotation?
Crop rotation is the opposite of a monoculture. It is the planned sequence of different crops over the course of a year or more. Crop rotation is different from polyculture and intercropping. These describe the practice of planting multiple crops at one time in the same place, which can also be beneficial for the garden. Often the more diverse a crop rotation is, the better it will be. Rotations can last for several years. Typically these systems try to keep the soil ‘green’ meaning that there are always living plants in the ground.
Conventional systems rely on herbicides to terminate cover crops in the rotation, leaving residues on the surface. In organics, it is challenging to avoid tillage altogether on a large scale. Limited options of chemicals make it difficult to control weeds at planting and harvesting times. Even if tillage has to happen, employing a rotation of crops is still beneficial. Crop rotations can be beneficial for the soil, pests, pathogens, and productivity.
Cover crops are a critical part of any rotation. These crops are there to cover the soil and improve soil health. They are often planted in the non-growing season but can be planted in fields not in use. This section will cover major types and the importance of mixing them together.
There is a wide variety of crops that fit into this category. They all have something in common: relationships with nitrogen-fixing rhizobia bacteria in the soil. Nitrogen fixation is the process by which atmospheric nitrogen is taken in and converted to plant-available compounds. This process is done by these specialized bacteria and by humans during the Haber-Bosch process to make inorganic nitrogen fertilizers. These crops develop nodules on the roots as shown below. The nodules form as the soil bacteria enter the roots of the plant. The insides of active nodules have a reddish appearance due to a compound, leghemoglobin, which is similar to that of human hemoglobin but found in bacteria. Examples of legume crops include clover, beans, peas, alfalfa, and vetch. Some tend to have more nodules than others.
Something important to consider with legumes is that if you fertilize them, they will not form these nodules. Rhizobia bacteria provide the plant with usable nitrogen sources in exchange for sugars from the plant. Without a need for nitrogen (because it is provided by the fertilizer), the plants will not accept the bacteria. So, avoid nitrogen fertilizers while these legumes are planted.
Planting legumes before planting a cash crop that is a heavy feeder and uses a lot of nitrogen is one way to approach rotation. This allows the following crop to access some of the nitrogen provided by the legume. It is critical to plant a crop following the legume, because nitrogen can easily leach down the soil profile.
Brassicas are a group of plants that include radishes, turnips, mustard, rapeseed, and others in the cabbage family. Radish and rapeseed are two of the more common brassicas used as cover crops. These crops have large taproots which can scavenge excess nutrients and improve compacted soils. They also have good above-ground biomass to help cover soil with better erosion control. Forage radishes (a type of daikon radish) are particularly good at this. Pictured below is the forage/tillage radish. These grow large roots and are much bigger than typical root crops you see in the garden.
These are good at breaking up compacted soils with their impressive taproot that penetrates into the soil and scavenges nutrients deep in the profile. These nutrients are then available to the following crops as the plant decomposes. Rapeseed also has strong root systems that are capable of doing similar things. These crops are performing tillage without causing the soil disturbance and negative effects of tillage.
Oats, rye, sudangrass, sunn hemp, triticale, wheat, and other small grains can be used as cover crops. This vein of crops has fibrous roots and often have high biomass. They are especially good at adding carbon into the soil and provide better erosion control. The fibrous roots do a good job at holding together the soil and the high biomass provides cover for the soil. Once the next crop is planted this crop can serve as a mulch to suppress weeds and protect the soil.
Rye, wheat, and triticale are cold hearty cereals that you can plant in the late summer. They’ll grow a bit in summer and fall, and overwinter into the spring. Oats are less hearty and will die in cold weather. This provides a natural way to terminate the crop in the fall. Sudangrass and sunn hemp are warm-weather crops that can serve as cover crops in warmer months, after spring crops. This is all depending on climate as some places have much warmer climates than others. Consider what climate you are in to figure out when and what crops to use.
Importance of Mixing Cover Crops
Cover crops are great, with each type serving a specific purpose. But they all have drawbacks which is why mixing them gives you the best of each. Legumes add more nitrogen into the soil but are a low residue crop. Increased crop residue helps reduce weed pressure and soil erosion. Brassicas can help compacted soil and bring nutrients to the surface. Grasses have better erosion control and add carbon to the soil. Remember that higher carbon content causes a reduction of nitrogen. Combining these crops into a singular mix provides the benefits of each while eliminating their shortcomings. Often cover crops are already sold in mixes which makes it easy for home gardeners to use.
Rotations vary in their timing and diversity. Here are a couple of possible rotations used by farmers. A classic rotation is a two-year rotation of corn and soybeans. This rotation is better than a monoculture of just corn but still lacks diversity. Another rotation could be soybean, corn, and wheat. Yet, another rotation could include a tomato crop, cover crop mix, and alfalfa. There are endless possibilities in what a rotation could be. Additional years can be added to include other crops so that it is a five or seven-year rotation. The general rule of thumb is to have the nitrogen-fixing crops (legumes) before heavy feeders that utilize a lot of nitrogen. These include vegetable and cash crops. Including legumes reduces inputs needed and ultimately improves future crops.
In larger-scale farms, livestock is also an option. Grazing lands in addition to producing row crops increases diversity and nutrients added to the field. Row crops may be crown for several years. Then the existing hay stand could be used for grazing sheep or cattle the following years. Then back again to row crops in the vegetable family.
Goals of Crop Rotation
This section details the benefits and goals of implementing a crop rotation in large-scale production.
Soil fertility and overall soil health are two things improved with crop rotations. Good soil health and a lack of soil erosion is critical for the success of farmers and home gardeners. Including crops in the ground at all times allows organic matter to build up, especially when tillage is limited. Rotating crops and leaving the crop residue on the field allows most of the same nutrients to stay in the system. This results in a reduction in synthetic as well as organic inputs. Reducing erosion and increasing soil organic matter through crop residues and constant plant cover prevents nutrient pollution and improves the water quality of nearby water sources.
Pests and Diseases
Another benefit to rotating crops, especially on large-scale farms is managing pests and diseases. This is helpful when planting many crops across several different fields. Pest management requires looking at the farming system as a whole. Integrated pest management is key to understanding what to do about pests. It’s an all-encompassing approach that aims to reduce the need for pesticides. Crop rotations are a part of this method. By rotating crops across several fields, the pests’ ability to cause damage is reduced. The distance the pest has to travel for the host plant increases and for many pests this distance is too far. They cannot live and thus struggle to reproduce. The amount of time between rotation helps diminish the pest population. Reducing pests reduces pathogens because there are fewer vector insects present to spread disease.
The benefit of pathogen management through crop rotation is similar to pests. Some are spread by vectors and some are soil-borne. Just like diseases between humans and animals, not all diseases impact the same plants. There are certain diseases that impact a wide variety of plants, but there are also many that impact a small group of plants. To reduce pathogen loads, rotate crops in the system that are not impacted by the particular pathogen.
Organic farming attempts to reduce or eliminate the usage of synthetic inputs: pesticides, herbicides, and fungicides. Rotating crops into the field helps reduce pests and pathogens, therefore requiring less of these chemicals. Less pesticides means better soil content and improved water quality in nearby sources.
The goal of farming that is missed by many farmers is to build an ecosystem in the process of producing food. Diversifying the crops in the rotation increases beneficial organisms in the ecosystem. As mentioned before adding several crops into a rotation increases the diversity in microbial communities, which benefits other plants over time. Many beneficial insects have particular crops they are attracted to. Increasing the different plants allows more insects to find the farm or garden. Attracting more insects means the possibility of attracting predators to cut down pest populations. By building the ecosystem, the farm has increased resilience. This means the farm is more self-sustaining and can better handle problems.
Application to Home Gardeners
The goal of this article is to help you know how crop rotation can be adapted to your needs. Specific rotation methods have different applications, but how to implement them remain the same.
Crop rotation is an extremely beneficial way to farm, especially in large-scale operations. Pest control may be less effective in small-scale gardens because of the size of the operation. In many cases, the same general crops are planted on the same land. The space is not big so pests find the targeted crop easier. Increasing diversity can attract pest predators which helps reduce the pest population.
Crop rotation cycles nutrients by using other crops to keep nutrients in the system. Including compost in the system can increase plant growth and productivity. Combining the rotation with limited tillage can be extremely beneficial to soil health. In this case the soil structure remains intact which improves water quality, even on a small scale.
There are many different ways to include crop rotation in the home garden. A good rule is to plant crops from a different plant family the next year in the same place.
Frequently Asked Questions
Q: What is the 4 crop rotation?
A: The four crop rotation refers to the inclusion of livestock grazing in a system commonly used in the UK.
Q: What is a good crop rotation?
A: There is not one specific rotation that should be used by everyone. Crop rotation practices differ in length and diversity. A general rule: heavy feeders are planted after nitrogen-fixing crops.
Q: What is a 2 year crop rotation?
A: A two-year crop rotation is one that lasts two years. The most common one involves a process where corn is planted one year and soybeans are planted the next.
Q: Is crop rotation still used today?
A: Yes! Crop rotation is found on many farms. The methods used vary greatly in the type of rotation and crops used. Corn-soybean two-year rotations are most common in the United States. Different crops and livestock are used in rotations lasting five or more additional years.