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Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing
season A season is a division of the year based on changes in weather, ecology Ecology () is the study of the relationships between living organisms, including human Humans (''Homo sapiens'') are the most abundant and widespread speci ...
s. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant pests and weeds. Growing the same crop in the same place for many years in a row, known as monocropping, gradually depletes the
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume ...
of certain
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few ...
s and selects for a highly competitive pest and weed community. Without balancing nutrient use and diversifying pest and weed communities, the productivity of monocultures is highly dependent on external inputs. Conversely, a well-designed crop rotation can reduce the need for synthetic fertilizers and
herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page ...
s by better using
ecosystem services Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystem ...
from a diverse set of crops. Additionally, crop rotations can improve soil structure and
organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compound In chem ...
, which reduces erosion and increases farm system resilience.


History

Agriculturalists have long recognized that suitable rotations — such as planting spring crops for
livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool Wool is the textile fibre obtained from ...
in place of grains for human consumption — make it possible to restore or to maintain productive soils. Ancient Near Eastern farmers practiced crop rotation in 6000 BC without understanding the chemistry, alternately planting legumes and cereals.


Two-field systems

Under a two-field rotation, half the land was planted in a year, while the other half lay fallow. Then, in the next year, the two fields were reversed. In
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India India, officially the Republic of India ...
both the two-field and three-field system had been used since the
Eastern Zhou The Eastern Zhou (; zh, c=, p=Dōngzhōu, w=Tung1-chou1, t= ; 771–256 BC) was a royal dynasty of China and the second half of the Zhou dynasty The Zhou dynasty ( ; Old Chinese ( B&S): *''tiw'') was a royal dynasty of China that follo ...
period. From the times of
Charlemagne Charlemagne ( , ) or Charles the Great ( la, Carolus Magnus; german: Karl der Große; 2 April 747 – 28 January 814), a member of the Carolingian dynasty, was King of the Franks from 768, King of the Lombards The Kings of the Lombar ...
(died 814), farmers in Europe transitioned from a two-field crop rotation to a three-field crop rotation.


Three-field systems

From the end of the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
until the 20th century, Europe's farmers practiced a three-field rotation, where available lands were divided into three sections. One section was planted in the autumn with rye or winter
wheat Wheat is a grass widely cultivated for its seed, a cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit In botany, a fruit is the seed-bearing structure in flowering p ...
, followed by spring
oat The oat (''Avena sativa''), sometimes called the common oat, is a species In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a ...
s or
barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley ...
; the second section grew crops such as peas, lentils, or beans; and the third field was left fallow. The three fields were rotated in this manner so that every three years, one of the fields would rest and lie fallow. Under the two-field system, if one has a total of of fertile land, one would only plant 300 acres. Under the new three-field rotation system, one would plant (and therefore harvest) 400 acres. But the additional crops had a more significant effect than mere quantitative productivity. Since the spring crops were mostly legumes, they increased the overall nutrition of the people of Northern Europe.


Four-field rotations

Farmers in the region of
Waasland The Waasland is a Belgian region. It is part of the Belgian provinces of East Flanders and Antwerp Antwerp (; nl, Antwerpen ; french: Anvers ; es, Amberes) is the largest city in Belgium by area at and the capital of Antwerp Provinc ...
(in present-day northern Belgium) pioneered a four-field rotation in the early 16th century, and the British agriculturist Charles Townshend (1674–1738) popularised this system in the 18th century. The sequence of four crops (
wheat Wheat is a grass widely cultivated for its seed, a cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit In botany, a fruit is the seed-bearing structure in flowering p ...
, turnips,
barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley ...
and
clover Clover or trefoil are common names for plants of the genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as virus A virus is a submicroscopic infectious ...
), included a fodder crop and a grazing crop, allowing
livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool Wool is the textile fibre obtained from ...
to be bred year-round. The four-field crop rotation became a key development in the British Agricultural Revolution. The rotation between arable and ley is sometimes called ley farming.


Modern developments

George Washington Carver George Washington Carver ( 1864 – January 5, 1943) was an American agricultural scientist and inventor who promoted alternative crops to cotton and methods to prevent soil depletion. He was one of the most prominent black scientists of the ...
(1860s–1943) studied crop-rotation methods in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territor ...
, teaching southern farmers to rotate soil-depleting crops like cotton with soil-enriching crops like
peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume A legume () is a plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms ...
s and peas. In the Green Revolution of the mid-20th century the traditional practice of crop rotation gave way in some parts of the world to the practice of supplementing the chemical inputs to the soil through topdressing with
fertilizer A fertilizer (American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language English is a West Germanic language of the Indo-European language family ...
s, adding (for example) ammonium nitrate or
urea Urea, also known as carbamide, is an organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other ...
and restoring soil pH with lime. Such practices aimed to increase yields, to prepare soil for specialist crops, and to reduce waste and inefficiency by simplifying planting, harvesting, and
irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main ...
.


Crop choice

A preliminary assessment of crop interrelationships can be found in how each crop: #contributes to soil organic matter (SOM) content #provides for pest management #manages deficient or excess nutrients #how it contributes to or controls for
soil erosion Soil erosion is the denudation or wearing away of the upper layer of soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquid A liquid is a nearly incompressible fluid that ...
#interbreeds with other crops to produce hybrid offspring, and #impacts surrounding food webs and field ecosystems Crop choice is often related to the goal the farmer is looking to achieve with the rotation, which could be weed management, increasing available
nitrogen Nitrogen is the chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical element ...
in the soil, controlling for erosion, or increasing soil structure and biomass, to name a few. When discussing crop rotations, crops are classified in different ways depending on what quality is being assessed: by family, by nutrient needs/benefits, and/or by profitability (i.e.
cash crop A cash crop or profit crop is an agricultural crop which is grown to sell for profit. It is typically purchased by parties separate from a farm. The term is used to differentiate marketed crops from staple crop (or "subsistence crop") in subs ...
versus cover crop). For example, giving adequate attention to plant family is essential to mitigating pests and pathogens. However, many farmers have success managing rotations by planning sequencing and cover crops around desirable cash crops. The following is a simplified classification based on crop quality and purpose.


Row crops

Many crops which are critical for the market, like
vegetable Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the flowers, fruits, stem ...
s, are row crops (that is, grown in tight rows). While often the most profitable for farmers, these crops are more taxing on the soil. Row crops typically have low biomass and shallow roots: this means the plant contributes low residue to the surrounding soil and has limited effects on structure. With much of the soil around the plant exposed to disruption by rainfall and traffic, fields with row crops experience faster break down of organic matter by microbes, leaving fewer nutrients for future plants. In short, while these crops may be profitable for the farm, they are nutrient depleting. Crop rotation practices exist to strike a balance between short-term profitability and long-term productivity.


Legumes

A great advantage of crop rotation comes from the interrelationship of nitrogen-fixing crops with nitrogen-demanding crops. Legumes, like alfalfa and clover, collect available nitrogen from the atmosphere and store it in nodules on their root structure. When the plant is harvested, the biomass of uncollected roots breaks down, making the stored nitrogen available to future crops. In addition, legumes have heavy tap roots that burrow deep into the ground, lifting soil for better tilth and absorption of water.


Grasses and cereals

Cereal and grasses are frequent cover crops because of the many advantages they supply to soil quality and structure. The dense and far-reaching root systems give ample structure to surrounding soil and provide significant biomass for
soil organic matter Soil organic matter (SOM) is the organic matter component of soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquid A liquid is a nearly incompressible fluid that conforms t ...
. Grasses and cereals are key in weed management as they compete with undesired plants for soil space and nutrients.


Green manure

Green manure is a crop that is mixed into the soil. Both nitrogen-fixing legumes and nutrient scavengers, like grasses, can be used as green manure. Green manure of legumes is an excellent source of nitrogen, especially for organic systems, however, legume biomass does not contribute to lasting
soil organic matter Soil organic matter (SOM) is the organic matter component of soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquid A liquid is a nearly incompressible fluid that conforms t ...
like grasses do.


Planning a rotation

There are numerous factors that must be taken into consideration when planning a crop rotation. Planning an effective rotation requires weighing fixed and fluctuating production circumstances: market, farm size, labor supply, climate, soil type, growing practices, etc. Moreover, a crop rotation must consider in what condition one crop will leave the soil for the succeeding crop and how one crop can be seeded with another crop. For example, a nitrogen-fixing crop, like a legume, should always precede a nitrogen depleting one; similarly, a low residue crop (i.e. a crop with low biomass) should be offset with a high biomass cover crop, like a mixture of grasses and legumes. There is no limit to the number of crops that can be used in a rotation, or the amount of time a rotation takes to complete. Decisions about rotations are made years prior, seasons prior, or even at the last minute when an opportunity to increase profits or soil quality presents itself.


Implementation

Crop rotation systems may be enriched by the influences of other practices such as the addition of livestock and manure, intercropping or multiple cropping, and is common in organic cropping systems.


Incorporation of livestock

Introducing
livestock Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool Wool is the textile fibre obtained from ...
makes the most efficient use of critical sod and cover crops; livestock (through
manure Manure is organic matter that is used as organic fertilizer in agriculture Agriculture or farming is the practice of cultivating plants and livestock Livestock are the domesticated animals raised in an agricultural setting to ...
) are able to distribute the nutrients in these crops throughout the soil rather than removing nutrients from the farm through the sale of hay. Mixed farming or the practice of crop cultivation with the incorporation of livestock can help manage crops in a rotation and cycle nutrients. Crop residues provide animal feed, while the animals provide manure for replenishing crop nutrients and draft power. These processes promote internal nutrient cycling and minimize the need for synthetic fertilizers and large-scale machinery. As an additional benefit, the cattle, sheep and/or goat provide milk and can act as a cash crop in the times of economic hardship.


Intercropping

Multiple cropping systems, such as intercropping or companion planting, offer more diversity and complexity within the same season or rotation. An example of companion planting is the three sisters, the inter-planting of corn with pole beans and vining squash or pumpkins. In this system, the beans provide nitrogen; the corn provides support for the beans and a "screen" against squash vine borer; the vining squash provides a weed suppressive canopy and a discouragement for corn-hungry raccoons. Double-cropping is common where two crops, typically of different species, are grown sequentially in the same growing season, or where one crop (e.g. vegetable) is grown continuously with a cover crop (e.g. wheat). This is advantageous for small farms, which often cannot afford to leave cover crops to replenish the soil for extended periods of time, as larger farms can. When multiple cropping is implemented on small farms, these systems can maximize benefits of crop rotation on available land resources.


Organic farming

Crop rotation is a required practice, in the United States, for farm seeking organic certification. The “Crop Rotation Practice Standard” for the National Organic Program under the U.S. Code of Federal Regulations, section §205.205, states
Farmers are required to implement a crop rotation that maintains or builds soil organic matter, works to control pests, manages and conserves nutrients, and protects against erosion. Producers of perennial crops that aren’t rotated may utilize other practices, such as cover crops, to maintain soil health.
In addition to lowering the need for inputs (by controlling for pests and weeds and increasing available nutrients), crop rotation helps organic growers increase the amount of biodiversity their farms. Biodiversity is also a requirement of organic certification, however, there are no rules in place to regulate or reinforce this standard. Increasing the biodiversity of crops has beneficial effects on the surrounding ecosystem and can host a greater diversity of fauna, insects, and beneficial microorganisms in the soil as found by McDaniel et al 2014 and Lori et al 2017. Some studies point to increased nutrient availability from crop rotation under organic systems compared to conventional practices as organic practices are less likely to inhibit of beneficial microbes in soil organic matter. While multiple cropping and intercropping benefit from many of the same principals as crop rotation, they do not satisfy the requirement under the NOP.


Benefits

Agronomists describe the benefits to yield in rotated crops as "The Rotation Effect". There are many benefits of rotation systems. The factors related to the increase are broadly due to alleviation of the negative factors of monoculture cropping systems. Specifically, improved nutrition; pest, pathogen, and weed stress reduction; and improved soil structure have been found in some cases to be correlated to beneficial rotation effects. Other benefits of rotation cropping systems include production cost advantages. Overall financial risks are more widely distributed over more diverse production of crops and/or livestock. Less reliance is placed on purchased inputs and over time crops can maintain production goals with fewer inputs. This in tandem with greater short and long term yields makes rotation a powerful tool for improving agricultural systems.


Soil organic matter

The use of different species in rotation allows for increased soil organic matter (SOM), greater soil structure, and improvement of the chemical and biological soil environment for crops. With more SOM, water infiltration and retention improves, providing increased drought tolerance and decreased erosion. Soil organic matter is a mix of decaying material from biomass with active
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a ...
s. Crop rotation, by nature, increases exposure to biomass from sod, green manure, and various other plant debris. The reduced need for intensive
tillage Tillage is the agricultural preparation of soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shoveling, picking, mattock work, h ...
under crop rotation allows biomass aggregation to lead to greater nutrient retention and utilization, decreasing the need for added nutrients. With tillage, disruption and oxidation of soil creates a less conducive environment for diversity and proliferation of microorganisms in the soil. These microorganisms are what make nutrients available to plants. So, where "active" soil organic matter is a key to productive soil, soil with low microbial activity provides significantly fewer nutrients to plants; this is true even though the quantity of biomass left in the soil may be the same. Soil microorganisms also decrease
pathogen In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that pro ...
and pest activity through competition. In addition, plants produce root exudates and other chemicals which manipulate their soil environment as well as their weed environment. Thus rotation allows increased yields from nutrient availability but also alleviation of
allelopathy Allelopathy is a biological phenomenon by which an organism produces one or more biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemis ...
and competitive weed environments.


Carbon sequestration

Studies have shown that crop rotations greatly increase soil organic carbon (SOC) content, the main constituent of
soil organic matter Soil organic matter (SOM) is the organic matter component of soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquid A liquid is a nearly incompressible fluid that conforms t ...
. Carbon, along with hydrogen and oxygen, is a macronutrient for plants. Highly diverse rotations spanning long periods of time have shown to be even more effective in increasing SOC, while soil disturbances (e.g. from tillage) are responsible for exponential decline in SOC levels. In Brazil, conversion to no-till methods combined with intensive crop rotations has been shown an SOC sequestration rate of 0.41 tonnes per hectare per year. In addition to enhancing crop productivity, sequestration of atmospheric carbon has great implications in reducing rates of
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
by removing carbon dioxide from the air.


Nitrogen fixing

Rotating crops adds nutrients to the soil.
Legume A legume () is a plant Plants are predominantly photosynthetic eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the gro ...
s, plants of the family
Fabaceae The Fabaceae or Leguminosae,International Code of Nomenc ...
, for instance, have nodules on their
root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often b ...
s which contain nitrogen-fixing
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were a ...
called rhizobia. During a process called nodulation, the rhizobia bacteria use nutrients and water provided by the plant to convert atmospheric nitrogen into ammonia, which is then converted into an organic compound that the plant can use as its nitrogen source. It therefore makes good sense agriculturally to alternate them with cereals (family
Poaceae Poaceae () or Gramineae () is a large and nearly ubiquitous family Family (from la, familia) is a group of people related either by consanguinity Consanguinity ("blood relation", from Latin Latin (, or , ) is a classical langu ...
) and other plants that require
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an ins ...
s. How much nitrogen made available to the plants depends on factors such as the kind of legume, the effectiveness of rhizobia bacteria, soil conditions, and the availability of elements necessary for plant food.


Pathogen and pest control

Crop rotation is also used to control pests and diseases that can become established in the soil over time. The changing of crops in a sequence decreases the population level of pests by (1) interrupting pest life cycles and (2) interrupting pest habitat. Plants within the same taxonomic family tend to have similar pests and pathogens. By regularly changing crops and keeping the soil occupied by cover crops instead of lying fallow, pest cycles can be broken or limited, especially cycles that benefit from overwintering in residue. For example, root-knot nematode is a serious problem for some plants in warm climates and sandy soils, where it slowly builds up to high levels in the soil, and can severely damage plant productivity by cutting off circulation from the plant roots. Growing a crop that is not a host for root-knot nematode for one season greatly reduces the level of the nematode in the soil, thus making it possible to grow a susceptible crop the following season without needing soil fumigation. This principle is of particular use in
organic farming Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...
, where pest control must be achieved without synthetic pesticides.


Weed management

Integrating certain crops, especially cover crops, into crop rotations is of particular value to weed management. These crops crowd out weed through competition. In addition, the sod and compost from cover crops and green manure slows the growth of what weeds are still able to make it through the soil, giving the crops further competitive advantage. By slowing the growth and proliferation of weeds while cover crops are cultivated, farmers greatly reduce the presence of weeds for future crops, including shallow rooted and row crops, which are less resistant to weeds. Cover crops are, therefore, considered conservation crops because they protect otherwise fallow land from becoming overrun with weeds. This system has advantages over other common practices for weeds management, such as
tillage Tillage is the agricultural preparation of soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shoveling, picking, mattock work, h ...
. Tillage is meant to inhibit growth of weeds by overturning the soil; however, this has a countering effect of exposing weed seeds that may have gotten buried and burying valuable crop seeds. Under crop rotation, the number of viable seeds in the soil is reduced through the reduction of the weed population. In addition to their negative impact on crop quality and yield, weeds can slow down the harvesting process. Weeds make farmers less efficient when harvesting, because weeds like bindweeds, and knotgrass, can become tangled in the equipment, resulting in a stop-and-go type of harvest.


Preventing soil erosion

Crop rotation can significantly reduce the amount of soil lost from
erosion Erosion is the action of surface processes (such as water flow or wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minut ...
by water. In areas that are highly susceptible to erosion, farm management practices such as zero and reduced tillage can be supplemented with specific crop rotation methods to reduce raindrop impact, sediment detachment, sediment transport,
surface runoff Surface runoff (also known as overland flow) is the flow of water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosph ...
, and soil loss. Protection against soil loss is maximized with rotation methods that leave the greatest mass of crop stubble (plant residue left after harvest) on top of the soil. Stubble cover in contact with the soil minimizes erosion from water by reducing overland flow velocity, stream power, and thus the ability of the water to detach and transport sediment. Soil erosion and seal prevent the disruption and detachment of soil aggregates that cause macropores to block, infiltration to decline, and runoff to increase. This significantly improves the resilience of soils when subjected to periods of erosion and stress. When a forage crop breaks down, binding products are formed that act like an adhesive on the soil, which makes particles stick together, and form aggregates. The formation of soil aggregates is important for erosion control, as they are better able to resist raindrop impact, and water erosion. Soil aggregates also reduce wind erosion, because they are larger particles, and are more resistant to abrasion through tillage practices. The effect of crop rotation on erosion control varies by climate. In regions under relatively consistent climate conditions, where annual rainfall and temperature levels are assumed, rigid crop rotations can produce sufficient plant growth and soil cover. In regions where climate conditions are less predictable, and unexpected periods of rain and drought may occur, a more flexible approach for soil cover by crop rotation is necessary. An opportunity cropping system promotes adequate soil cover under these erratic climate conditions. In an opportunity cropping system, crops are grown when soil water is adequate and there is a reliable sowing window. This form of cropping system is likely to produce better soil cover than a rigid crop rotation because crops are only sown under optimal conditions, whereas rigid systems are not necessarily sown in the best conditions available. Crop rotations also affect the timing and length of when a field is subject to fallow. This is very important because depending on a particular region's climate, a field could be the most vulnerable to erosion when it is under fallow. Efficient fallow management is an essential part of reducing erosion in a crop rotation system. Zero tillage is a fundamental management practice that promotes crop stubble retention under longer unplanned fallows when crops cannot be planted. Such management practices that succeed in retaining suitable soil cover in areas under fallow will ultimately reduce soil loss. In a recent study that lasted a decade, it was found that a common winter cover crop after potato harvest such as fall rye can reduce soil run-off by as much as 43%, and this is typically the most nutritional soil.


Biodiversity

Increasing the biodiversity of crops has beneficial effects on the surrounding ecosystem and can host a greater diversity of fauna, insects, and beneficial microorganisms in the soil as found by McDaniel et al 2014 and Lori et al 2017. Some studies point to increased nutrient availability from crop rotation under organic systems compared to conventional practices as organic practices are less likely to inhibit of beneficial microbes in soil organic matter, such as arbuscular mycorrhizae, which increase nutrient uptake in plants. Increasing biodiversity also increases the resilience of agro-ecological systems.


Farm productivity

Crop rotation contributes to increased yields through improved soil nutrition. By requiring planting and harvesting of different crops at different times, more land can be farmed with the same amount of machinery and labour.


Risk management

Different crops in the rotation can reduce the risks of adverse weather for the individual farmer.


Challenges

While crop rotation requires a great deal of planning, crop choice must respond to a number of fixed conditions (soil type, topography, climate, and irrigation) in addition to conditions that may change dramatically from year to the next (weather, market, labor supply). In this way, it is unwise to plan crops years in advance. Improper implementation of a crop rotation plan may lead to imbalances in the soil nutrient composition or a buildup of pathogens affecting a critical crop. The consequences of faulty rotation may take years to become apparent even to experienced soil scientists and can take just as long to correct. Many challenges exist within the practices associated with crop rotation. For example, green manure from legumes can lead to an invasion of snails or slugs and the decay from green manure can occasionally suppress the growth of other crops.


See also

*
Agroecology Agroecology (US: a-grō-ē-ˈkä-lə-jē) is an academic discipline that studies ecological processes applied to agricultural Agriculture or farming is the practice of cultivating plants Plants are predominantly photosynthetic euka ...
*
Carbon cycle The carbon cycle is the biogeochemical cycle by which carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetal In chemistry, a nonmetal is a chemical element that generally lacks a predomina ...
* Convertible husbandry * Tillage erosion


Notes


References

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External links


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* {{Authority control Agricultural soil science Sustainable agriculture Agronomy Crops