Imagine if your boss asked you to analyze the same report every day for years, without ever offering you a weekend or vacation. You could probably do the work, but how would the quality look after three years of non-stop production? Chances are good your desire to get the job done would be, well, a bit depleted. The same thing happens to soil when we ask our fields to be in constant one-crop production mode. Sure, you can still grow a wheat crop. But you’re going to have smaller, weaker plants with lower yields if you never give your soil a break. Crop rotation is one solution to soil depletion and a keystone of sustainable agriculture.
Crop rotation is the practice of planting different types of crops in your fields on a rotating basis. For example, one year a 1,500-acre plot might grow canola, and the next year it might be set aside for clover or chickpeas. Crop rotation is the opposite of monocropping, where farmers grow just one thing on the same land year after year.
Monocropping is the backbone of industrial agriculture. It’s founded on the need to produce large quantities of a single crop on a vast scale. The most common monocrops in North America include corn, soybeans, and wheat. Despite monocropping’s known consequences—nutrient depletion and increased vulnerability to diseases and pests—some commercial farms still practice it. In fact, according to the most recent study by the USDA, 16 percent of corn, 14 percent of spring wheat, and 6 percent of soybean acreage is continuously planted with one crop over three years.
The driving force behind monocropping? Profitability. Because they’re growing just one type of crop, industrial farms can invest in highly specialized material to plant, tend, and harvest efficiently. Considering the cost of equipment and technology—not to mention how unpredictable weather and political climates influence crop prices—it’s no wonder that the average farmer may elect to choose profitability over soil health.
Unfortunately, monocropping also tends to require more chemicals, pesticides, and fertilizers. For example, if you’re growing wheat in the same field, year after year, you’re depleting your soil of the nutrients wheat relies on. So, to help your wheat grow, you apply fertilizers. Monocrops are also more vulnerable to pests and disease because they can establish themselves for generations. Why would that family of grain weevils move out of your field when they know there’s going to be a fresh crop next year? You also can’t evict a fungus that survives on legume roots if you only ever grow chickpeas.
History of crop rotation
Current, widespread monocropping practices in America emerged during the Great Depression with the incentivization of staple crops provided by the Farm Bill. For centuries of human development, we intuitively practiced crop rotation. Some of the earliest observable instances of crop rotation were farming communities in ancient Greece and the Roman Empire. Even before we understood the science, we could observe that growing the same crops in the same fields year after year led to lower harvest yields and weaker plants.
Plus, early farmers grew different crops in different seasons to grow year-round and maximize their land’s output. During the formative years of North American agriculture, the majority of the labor force worked on homesteads and family farms. Most folks just needed to produce enough food for their families and communities. There was no need to grow massive monocrops for what many North Americans don’t realize are vital aspects of their modern lives—feedlots and ethanol.
Food, feed, fallow
One ancient practice involved splitting the land into three similarly-sized sections. The first grew food for human consumption like wheat or corn. The second grew feed for livestock. The third and final lot was left fallow, or unplanted. This crucial period of rejuvenation allowed the land to recover for the next food-growing season. Or so we thought. Scientific research and advances in data analysis have transformed the modern approach to fallow seasons. We’ve found that with proper management, continuously growing a variety of crops provides far more benefit to the soil than leaving it idle.
Principles behind crop rotation
A successful growing season starts long before we sink our seeds because everything we do depends on maintaining a healthy soil microbiome. A microbiome is an ecological community of organisms—living things—such as fungi and bacteria. Bacteria are by far the most plentiful microbes in soil. There can be billions of these single-celled organisms in just one gram of soil. There are many different types of bacteria, and each fills a crucial role in how well a plant can absorb water and nutrients. For example, bacteria are responsible for decomposition, which breaks down carbon-based cells into fuel that plant roots can use.
Crop rotation takes into account the various ways different crops replenish or deplete their soil microbiome. It also allows farmers to work with—rather than against—nature to grow stronger plants with higher yields.
Top benefits of crop rotation
Northerly’s crop rotation practice not only helps us grow better food. It also helps us minimize our environmental impact and conserve resources for future generations.
Increased soil fertility
We already know that crop rotation benefits the soil microbiome. But it also impacts soil nutrient levels and leads to healthier, more fertile soil. Each crop absorbs and releases varying levels of different nutrients. By strategically rotating crops, excess nutrients are absorbed, and depleted nutrients are restored.
Pest, weed, and disease control
With continuous cropping, or monocropping, pests establish themselves over several generations. Remember that family of grain weevils you can’t shake? Crop rotation breaks the reproductive cycle and helps control populations without pesticides and insecticides. Your grain weevils won’t be tempted to call your field home if you grow wheat one year and beans the next.
Crop rotation also helps to prevent disease and keep plants healthy. According to Farm Progress, “Continuously cropping the same crop builds up the population levels of any soil borne pathogen of that crop that may be present.” Eventually, pathogen levels get so high that you can’t grow that crop without heavy yield losses. By planting a crop that is not a host for that particular pathogen, you can essentially starve the pathogen out. “Most pest populations will decline in two to three years without a suitable host,” they assert. “Rotating to non-host crops prevents the buildup of large populations of pathogens.”
Nitrogen is a building block of all plants. It’s in their DNA, and even responsible for their ability to produce chlorophyll. Unfortunately, plants can’t absorb nitrogen from the air. They rely on the nitrogen cycle, during which nitrogen-fixing bacteria convert nitrogen gas into a compound they can use. Certain plants, such as clover, legumes, and soybeans, are called “nitrogen-fixing.” That means they have a symbiotic (or mutually beneficial) relationship with the bacteria that convert gaseous nitrogen into usable oxygen.
At Northerly, we practice crop rotation to manage soil nitrogen levels to minimize applying synthetic fertilizers. Synthetic, nitrogen-rich fertilizers, which enabled food production to feed an additional 3.25 billion people, can have negative environmental impacts if misused. Crop rotation is an easy solution that doesn’t endanger groundwater supplies or lead to toxic run-off. Moderation and good planning are key to preventing this.
“Green” manure (AKA cover crops)
Green manure, or cover crops, are plants specifically grown to be tilled back into the field. They work by drawing nutrients out of the soil and into their root systems. When the plants are dug back into the ground, they begin to decompose, releasing those nutrients in a form that future crops can use. Regularly growing cover crops improves the soil structure, can prevent erosion, and suppresses weed growth. While this can be an extremely beneficial tool for land that can produce several crops a year, like in Arizona or California, it can be detrimental to a farm’s profitability in locations that can only produce one crop per year, such as Canada. Without profitability, there’s no way a farm can stay in business.
Practicing purposeful crop rotation
With advances in agricultural software and technology, we have more information than we’ve ever had before. The Northerly team can monitor the most minute details of our soil health, which helps us practice strategic crop rotation. This modern twist on an ancient practice means fewer problems with insects, parasitic nematodes, weeds, and diseases caused by plant pathogens. It also means healthier soil and more nutrient-dense food. Crop rotation is sustainable agriculture’s win-win.