March 27, 2018 Sustainable Farming Written by Sara Slavikova
Benefits of crop rotation
Crop rotation is a farming technique

dating as far back as the Roman Empire or Ancient Greece. Although ancient farmers didn’t fully understand the science behind the crop rotation, they observed that growing the same crop at the same plot for several years depletes soils of nutrients and decreases crop yield.

To tackle the problem, the Romans came up with a simple system called “food, feed, fallow.” During this practice, farmers divided the land into three sections. In one section, food crops such as wheat were planted; in the next section, livestock feed like oats was grown, and the last section was left fallow to recover. Every growing season, sections were rotated to ensure the highest land productivity in the long-term [1].

Once farmers applied this system, the soil quality improved and losses of crops due to the pests or diseases dropped. Simple and effective.

To understand why such a simple practice makes difference, we have to look first at the basic principles of crop rotation.
 

The principles of crop rotation

Crop rotation is based on growing a series of different types of crops in the same area in sequential seasons. The planned rotation may vary from a growing season to a few years or even longer periods. Farmers usually do not follow one specific plan. They choose to alternate crops based on their individual requirements, possibilities, environmental conditions and budget.

For example, one farmer might follow a seven-year rotation scheme as follows:

  • First year: Corn
  • Second year: Oats
  • Third to fifth year: Alfalfa or clover
  • Sixth to seventh year: Fallow or use as a pasture for livestock

 
Another farmer might choose a simpler scheme:

  • First year: Carrots
  • Second year: Wheat
  • Third to seventh year: Bluegrass

 
Even though these two plans differ, they both stick to the general rule of crop rotation. The basic principle is to plant leguminous crops (e.g. pulses, alfalfa, bluegrass, clover) after the cereal crops (e.g. wheat, oats, maize, rice), and then leave the land undisturbed for at least one season.

A carrot field

A carrot field

Following this rotation sequence helps prevent three main problems we see when planting only one crop year after year. These problems are:

    • Loss of soil fertility: If the same crop is grown continuously, the plant drains always the same nutrients from the soil. This eventually leads to nutrient depletion and soil infertility.

    • Pest infestations: Many pests specialize in a certain kind of crops. When we plant repeatedly their crop of choice, we are providing them favorable conditions to strive.

    • Erosion: Repeated planting of the same crop makes soils more susceptible to erosion. Each crop species has a specific shape of the root system, water requirements, spacing between plants and canopy. When growing only one kind of crop over prolonged periods of time, soil will start eroding in places where plants leave it uncovered and weakened.

The practice of crop rotation is, therefore, one of the most effective agricultural control strategies, as it comes with numerous advantages that are very important for reducing the use of chemicals on farms and supporting long-term soil fertility.
 

 
 

Top 10 benefits of crop rotation in farming

 

#1 Better nitrogen management

Nitrogen is one of the crucial nutrients for plant development. It is an indispensable part of DNA, the building block of proteins, and even chlorophyll.

Although the atmosphere contains 78 percent nitrogen, plants are not capable of using the atmospheric form. They need a “fixed” type of nitrogen from the soil either in the form of ammonia, nitrate or nitrite.

One way nitrogen is drawn into soils is through the activity of symbiotic bacteria (Rhizobium spp.) living on the roots of legumes, such as soybean, peas, lentils or other previously mentioned examples.

When a farmer plants leguminous crops, legumes together with these nitrogen-fixing bacteria enrich soils with the “fixed” type of nitrogen.

For example: Soybeans can fix up to 200 kg of nitrogen per hectare in one year. Although a part of this nitrogen is used by the plant itself to produce protein-rich beans, the rest of nitrogen remains in the soil [3].

This ensures that the following cereal crop or grass species cultivated on the same land will have a sufficient amount of this important nutrient for its healthy growth. So, planting a leguminous crops results in nitrogen enriched soils and higher yields of subsequent rotational crops.
 

#2 Reduced land and water pollution

With the intensification of the agricultural system, we have learned how to artificially boost the nitrogen content in the soil with the use of fertilizers. But the alteration of the natural nitrogen cycle combined with the excessive and inefficient use of fertilizers has led to releasing too much of this nutrient into the environment, disrupting the balance of ecosystems (especially aquatic ecosystems).

Some studies estimate that around 80 percent of the nitrogen used as agricultural fertilizers end up released freely in the environment, contaminating water resources.

The most serious effect of nitrogen pollution is eutrophication of water bodies, which is dangerous for our drinking water supply and results in severe health problems. For example, a nitrate-rich water restricts oxygen transport in the bloodstream of babies and causes a serious condition known as Blue Baby Syndrome.

Cotton monoculture plantation

Cotton monoculture plantation

If you think this problem does not affect you directly, think twice. In 2010, U.S. Geological Survey found that 64 percent of shallow wells in agricultural areas of the United States had above normal levels of nitrates [4]. The nitrogen contamination is more widespread than expected.

Unlike intensive fertilizer agriculture, crop rotation systems work by naturally replenishing nitrogen levels in soils through switching leguminous crops with other crops.

According to research, nitrogen fixed by legumes even remains longer in the soil than the synthetically provided form [5]. Rotation crops do not leach nitrogen into the environment. Instead, the nutrient remains stored in the soil for the plant uptake.

The practice of crop rotation reduces the need for the application of fertilizers and minimizes the risk of land and water pollution.


“Diversifying crop rotations is a win-win-win solution for farmer profits, the long-term health of their soil, and clean water for communities.”  

Kranti Mulik


 

#3 Improved soil structure

Soil structure is an important factor of a healthy crop growth. It affects how much space roots have to expand through the soil and how easy water, air and nutrients reach them.

If soil structure is poor, plants will not develop a healthy root system and will not grow well. This triggers a set of negative consequences for farmers, as they will not only lose crop yield, but their farmlands become much more vulnerable to erosion and surface runoff, leaking away nutrients and further decreasing fertility.

When rotating crops on the same land, soil structure improves because we alternate between deep and shallow rooted plants. For example, oats have large and deep reaching root system, while red clover has small and shallow roots [6]. By planting these plants subsequently, their different root systems boost soil structure by:

  • Increasing soil porosity
  • Stabilizing soil particle aggregates
  • Improving nutrient management by plants – e.g. oats reach for nutrients from the deeper soil layers, while clover draws nutrients from the upper layer.
  • Increasing water retention in soils
  • Providing habitat for more diverse soil organisms
  • Supplying higher content of organic matter

 
An additional benefit of crop rotation systems is that farmers can intentionally select the rotation sequence that enhances soil structure when needed. For example: A leguminous plant, lupin, has a deep root system that enables the plant to grow well in exhausted soils. And what’s more, lupin replenishes nitrogen levels in soils as well, preparing them once again for nutrient-demanding cereal crops [7].
 

#4 Water conservation

In combination with improved soil structure, crop rotation enhances water holding capacity of soils. Soils with good structure allow fast and thorough absorption of water. Some of this water is readily taken by crops, while the additional water is retained deeper in pores to be drawn by plants during a drier season.

In this situation, crop rotation helps conserve water on farms, because the need of irrigation is decreased.

Some additional benefits of better water holding capacity are:

  • Reduction of runoff and loss of nutrients from soils
  • Lower risk of flooding because soils act as a sponge
  • Prevention of erosion
  • Groundwater reservoir replenishment
  • Striving crops

Irrigation

Irrigation


 

#5 Prevention of soil erosion

Soil erosion has become a widespread problem around the world today. Extensive erosion causes many problems in modern agriculture, including the loss of topsoil, harmful agricultural runoff, and an increased risk of flooding and landslides due to restricted capacity of soils to retain water.

While soil erosion wreaks a havoc on intensively-cultivated farmlands, rotation planting helps to prevent all these negative impacts. According to a 13-year period research of a crop rotation system in Iowa, crop rotation reduces erosion by almost 90 percent compared to traditional maize and soy monoculture farming.

Amongst the reasons why crop rotation reduces erosion are:

    • Reduced soil disturbance: Longer periods of reduced disturbance to soils. When the land is left fallow, the soil is not tilled at all. This is the complete opposite to intensive monoculture farming, where the land is often tilled every year.

    • Cover crops: Cover crops are planted on the land for most of the rotation cycle. Plants hold soil in place and minimize its direct exposure to rain and wind – the main factors causing erosion.

    • Diverse root systems: Combination of crops with different length and shapes of root systems ensures that soil particles hold better together.

    • Spacing: Each crop has different space demands. Some crops grow when rows have larger spaces in between; other crops require smaller or no rows at all. The period of leaving some parts of soil directly exposed is shorter in crop rotation planting, because the subsequent crop will most likely need shorter spacing or none at all.

    • Healthy soils: Improved soil structure and water holding capacity prevents the damage done by heavy rainfall or flooding – the common triggers of erosion.

You can read more information about tackling erosion in How Can We Prevent Erosion.

 

#6 Easier pest, weed control and resistance to diseases

One of the main reasons why ancient civilizations applied crop rotation was to prevent the spread of pests, weeds and diseases. With the introduction of chemicals into the agriculture, the need to rotate crops disappeared. However, the widespread application of these chemicals has led to some serious cases of poisoning, contamination of the environment and even the increased resistance of pests to the active substances.

Luckily, just a simple step such as rotation of crops can prevent an outbreak of pests or diseases. This method is effective because many harmful insects and bacteria winter in soil. If we cultivate the same crop in the same place every growing season, we are creating perfect conditions for their colonies to spread more every year.

Many pests or diseases prefer only a certain host. By moving the crops and diversifying the cropping sequence, we take away their preferred host and cause a disruption in the annual life cycle of these pests or diseases.

For example, rice stem borer feeds mostly on rice. If we do not rotate rice with other crops belonging to a different family, the problem continues as food is always available to the pest. However, if we plant legume as the next crop, the insect pest will likely die due to absence of food.
 
Integrated Pest Management
Food and Agriculture Organization (FAO) recognizes crop rotation as one of the methods of Integrated Pest Management (IPM) – an ecologically-friendly method of crop production that aims to reduce the use of chemical pesticides and herbicides in agriculture.

Crop rotation is one of the recommended IPM strategies to prevent and suppress harmful organisms.

Further reading on the FAO site: How to practice Integrated Pest Management?

Colorado potato beetle

Colorado potato beetle


 

#7 Climate change mitigation

Crop rotation helps mitigate climate change in two important ways:

  1. Reduction of greenhouse gas emissions;
  2. Increased ability of soils to store carbon.

 
Intensive agriculture has become one of the main emitters of a potent greenhouse gas called nitrous oxide. The global warming potential of this gas is 300 times greater than carbon dioxide. Since our excessive use of nitrogen fertilizers in agriculture, its emissions have increased by almost 50 percent [8].

By implementing crop rotation, the use of nitrogen fertilizer can be reduced by up to 100 kilograms per hectare each year [9]. This in turn considerably lowers emissions of nitrous oxide and helps prevent further changes in greenhouse gas concentrations stemming from our activities.

Soil has a great capacity to capture and store atmospheric carbon. By improving the soil structure, leaving soils undisturbed and practicing cover cropping, crop rotation farming boosts the ability of soil to store more carbon, and therefore, helps to offset carbon emissions associated with agricultural production.

A study showing the great capability of crop rotation in mitigating climate change compared a monoculture wheat crops with a rotation cropping of lentil and wheat. Here is what the scientists found out:

    • Both systems produced nearly the same amount of wheat – around 1,800 kilograms per hectare.

    • Crop rotation fields used nearly 30 percent less fertilizer.

    • Nitrous oxide emissions were 16 percent lower at the rotation crop.

    • The carbon footprint was 150 percent lower at the rotation system [10].

These results clearly demonstrate overall the positive effects of rotation cropping over the standardized wheat planting.
 

#8 Production of green manure cover crops

Green manure are fast-growing crops sown to cover bare soil, add organic matter and enrich soils with minerals. They are often used in vegetable gardens or as winter crops as their foliage smothers early-growing spring weeds and their roots hold soil in place during harsh winters. These crops are normally tilled into the soil before they reach maturity. When dug into the ground while still green, they return most nutrients to the soil and improve soil structure.

Clover crop

Clover crop

Commonly used green manure crops are red clover, alfalfa, rye grass, peas, lentils, vetch, hay or pasture grasses. Most farmers select their green manure cover crops based on some of their functions, such as:

  • Soil protection from erosion
  • Nutrient conservation
  • Pests and disease lifecycle interruption
  • Nitrogen fixation
  • Weed suppression
  • Biomass provision [11]

 
The cultivation of green manure cover crops is an effective strategy of reviving soil fertility on a farm. Crop rotation farming benefits from this method by achieving stabilized long-term productivity of farmlands.


 

#9 Higher crop yields

The list of positive effects of crop rotation would not be complete without mentioning increased yields. All the previous benefits combined together create a perfect environment to grow healthy and abundant crops.

Numerous studies have confirmed that crop rotation as a sustainable farming method increases harvest. For example, a study carried out by the Washington State University investigated the change of maize yield in a crop rotation system in Malawi. Compared to no-till maize cultivation, crop rotation yielded 11 to 58 percent more.

A similar study from other developing countries confirms that harvests of maize, potatoes and beans nearly doubled on sustainably managed lands [12]. Such positive results happen most likely due to the weed and pest suppression, maintenance of healthy soils and smarter use of nutrients in crop rotation.
 

#10 Creates a healthier environment for life

More than 200,000 people die each year due to pesticide poisoning and at least two million cases of pesticide related health issues are reported annually [13].

Over two billion kilograms of pesticides are applied every year on crops all over the world, even though, only 0.1 percent of this amount reaches the targeted pests. The remaining 99.9 percent is recklessly released into the environment, where it silently ravages ecosystems and our health [14].

Crop rotation is a very effective way of growing a sufficient amount of food at the lowest environmental cost.

The practice itself significantly reduces the need to apply many aggressive agricultural chemicals, including pesticides and herbicides.

A beautiful poppy field

A beautiful poppy field

Scientists have ran a series of tests with a pest called rootworm. This pest often causes problems to continuously-grown maize fields. In their test plot, over 60 percent of the field had to be treated with an insecticide to tackle the rootworm infestation. However, they found out that when maize is alternated with other crops, only 8 to 26 percent had to be sprayed with the insecticide [15].

The same result was confirmed with cotton. Continuously-grown cotton had to receive 50 percent more pesticide than cotton from a crop rotation system [15].

Based on these results, it is clear that crop rotation could help tackle the widespread chemical contamination of the environment we live in. The practice is, therefore, beneficial to our health and could be one of the ways to maintain our food security, while minimizing negative effects of agriculture on ecosystems.  

 


References

[1] http://oregonstate.edu/dept/coarc/sites/default/files/may_2013_article.pdf
[2] https://goo.gl/Y1BK5Q
[3] https://goo.gl/z7X74Q
[4] https://www.epa.gov/nutrientpollution/effects-human-health
[5] https://www.ncbi.nlm.nih.gov/pubmed/20014586
[6] http://www.yara.co.uk/crop-nutrition/crops/oats/yield/
[7] http://www.nrcresearchpress.com/doi/pdf/10.4141/S04-078
[8] https://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-frontmatter.pdf
[9] https://goo.gl/7Rs1PV
[10] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4243251/
[11] http://eap.mcgill.ca/MagRack/COG/COGHandbook/COGHandbook_1_5.htm
[12] https://www.sciencedaily.com/releases/2006/01/060123163315.htm
[13] https://goo.gl/RSb7nH
[14] https://goo.gl/9Ad06A
[15] https://goo.gl/EmmXyw