Editing Crop rotation (section)

== 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 include reduced production cost. 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]]s. Crop rotation, by nature, increases exposure to biomass from sod, green manure, and various other plant debris. The reduced need for intensive [[tillage]] under crop rotation allows biomass aggregation to lead to greater nutrient retention and utilization, decreasing the need for added nutrients.<ref name=baldwinCEFS/> 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]] and [[pest (agriculture)|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]] and competitive weed environments.<ref name="One Earth 2020 pp. 284–293">{{cite journal |title=Long-Term Evidence Shows that Crop-Rotation Diversification Increases Agricultural Resilience to Adverse Growing Conditions in North America |journal=One Earth |volume=2 |issue=3 |date=20 March 2020 |issn=2590-3322 |doi=10.1016/j.oneear.2020.02.007 |pages=284–293 |last1=Bowles |first1=Timothy M. |last2=Mooshammer |first2=Maria |last3=Socolar |first3=Yvonne |last4=Calderón |first4=Francisco |last5=Cavigelli |first5=Michel A. |last6=Culman |first6=Steve W. |last7=Deen |first7=William |last8=Drury |first8=Craig F. |last9=Garcia y Garcia |first9=Axel |last10=Gaudin |first10=Amélie C.M. |last11=Harkcom |first11=W. Scott |last12=Lehman |first12=R. Michael |last13=Osborne |first13=Shannon L. |last14=Robertson |first14=G. Philip |last15=Salerno |first15=Jonathan |last16=Schmer |first16=Marty R. |last17=Strock |first17=Jeffrey |last18=Grandy |first18=A. Stuart |display-authors=5 |bibcode=2020OEart...2..284B |s2cid=212745944 |doi-access=free |hdl=10214/21229 |hdl-access=free }}</ref>

=== Carbon sequestration ===

Crop rotations greatly increase [[soil carbon|soil organic carbon (SOC)]] content, the main constituent of [[soil organic matter]].<ref name="triberti2016">{{cite journal |last1=Triberti |first1=Loretta |author2=Anna Nastri |author3=Guido Baldoni |title=Long-term effects of crop rotation, manure fertilization on carbon sequestration and soil fertility |journal=European Journal of Agronomy |volume=74 |pages=47–55 |year=2016 |doi=10.1016/j.eja.2015.11.024}}</ref> 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.<ref name=triberti2016/> 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.<ref name="victoria2012">{{Cite report |author= Victoria, Reynaldo |date= 2012 |chapter=The Benefits of Soil Carbon |title=Risk Management Guide for Organic Producers |publisher=[[United Nations Environment Programme]] }}</ref>

In addition to enhancing crop productivity, sequestration of atmospheric carbon has great implications in reducing rates of [[climate change]] by removing carbon dioxide from the air.

=== Nitrogen fixing===

Rotations can add nutrients to the soil. [[Legume]]s, plants of the family [[Fabaceae]], have nodules on their [[root]]s which contain [[nitrogen fixation|nitrogen-fixing]] [[bacterium|bacteria]] called [[rhizobium|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.<ref>{{Cite web |url=http://www.public.iastate.edu/~teloynac/354n2fix.pdf |title=Nitrogen Fixation by Forage Legumes |last=Loynachan |first=Tom |date=1 December 2016 |website=Iowa State University |publisher=Department of Agrology |access-date=1 December 2016 |archive-url=https://web.archive.org/web/20130503221208/http://www.public.iastate.edu/~teloynac/354n2fix.pdf |archive-date=3 May 2013 |url-status=dead}}</ref> It therefore makes good sense agriculturally to alternate them with cereals (family [[Poaceae]]) and other plants that require [[nitrate]]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.<ref>{{Cite web |url=http://www1.foragebeef.ca/$Foragebeef/frgebeef.nsf/all/frg90/$FILE/fertilitylegumefixation.pdf |title=Nitrogen Fixation and Inoculation of Forage Legumes |last=Adjei |display-authors=etal |first=M. B. |date=1 December 2016 |website=Forage Beef |publisher=University of Florida |access-date=1 December 2016 |archive-url=https://web.archive.org/web/20161202170130/http://www1.foragebeef.ca/$Foragebeef/frgebeef.nsf/all/frg90/$FILE/fertilitylegumefixation.pdf |archive-date=2 December 2016 |url-status=dead}}</ref>

=== Pathogen and pest control ===

{{Main |Plant–soil feedback}}

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.<ref name="johnson2009"/> 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.<ref name=moncada2010/> 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]], where [[biological pest control|pest control]] must be achieved without synthetic pesticides.<ref name="NCATweb"/>

=== Weed management ===

Integrating certain crops, especially [[cover crops]], into crop rotations is of particular value to [[weed control|weed management]]. These crops crowd out weeds 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.<ref name="moncada2010">{{Cite report |author1=Moncada, Kristine  |author2=Craig Sheaffer |date= 2010 |chapter=Chapter 2 Rotation |title=Risk Management Guide for Organic Producers |publisher=[[University of Minnesota]] }}</ref>

This system has advantages over other common practices for weeds management, such as [[tillage]]. 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.<ref>{{Cite web |url=http://potatoes.ahdb.org.uk/sites/default/files/publication_upload/Weed%20Control%20in%20Potatoes.pdf |archive-url=https://web.archive.org/web/20161019200703/http://potatoes.ahdb.org.uk/sites/default/files/publication_upload/Weed%20Control%20in%20Potatoes.pdf |archive-date=19 October 2016 |url-status=live |title=Weed Control in Potatoes |last=Davies |first=Ken |date=March 2007 |publisher=British Potato Council |access-date=1 December 2016}}</ref>

=== Reducing soil erosion ===

Crop rotation can significantly reduce the amount of soil lost from [[erosion]] 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]], and soil loss.<ref>{{cite journal |last1=Unger |first1=P. W. |last2=McCalla |first2=T. M. |title=Conservation Tillage Systems |journal=Advances in Agronomy |volume=33 |pages=2–53 |year=1980 |doi=10.1016/s0065-2113(08)60163-7 |isbn=9780120007332 }}</ref>

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.<ref>Rose CW, Freebairn DM. "A mathematical model of soil erosion and deposition processes with application to field data".</ref> Soil erosion and seal prevent the disruption and detachment of soil aggregates that cause macropores to block, infiltration to decline, and runoff to increase.<ref>{{cite journal |last1=Loch |first1=R. J. |last2=Foley |first2=J. L. |title=Measurement of Aggregate Breakdown under rain: comparison with tests of water stability and relationships with field measurements of infiltration |journal=Australian Journal of Soil Research |volume=32 |issue=4 |pages=701–720 |year=1994 |doi=10.1071/sr9940701}}</ref> 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.<ref>{{Cite web |url=http://www.soilcc.ca/ggmp_fact_sheets/pdf/Forages%20in%20rotation.pdf |archive-url=https://web.archive.org/web/20161202101131/http://www.soilcc.ca/ggmp_fact_sheets/pdf/Forages%20in%20rotation.pdf |archive-date=2 December 2016 |url-status=live |title=Forages in Rotation |date=2016 |publisher=Saskatchewan Soil Conservation Association |access-date=1 December 2016}}</ref> 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.<ref>{{Cite web |url=http://soilquality.org/indicators/aggregate_stability.html |title=Aggregate Stability |date=2011 |publisher=Natural Resources Conservation Centre |access-date=1 December 2016}}</ref>

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.<ref name="Carroll Halpin Burger Bell 1997">{{cite journal |last1=Carroll |first1=C. |last2=Halpin |first2=M |last3=Burger |first3=P. |last4=Bell |first4=K. |last5=Sallaway |first5=M. M. |last6=Yule |first6=D. F. |title=The effect of crop type, crop rotation, and tillage practice on runoff and soil loss on a Vertisol in central Queensland |journal=Soil Research |volume=35 |issue=4 |date=1997 |issn=1838-675X |doi=10.1071/S96017 |page=925}}</ref> 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.<ref>{{cite journal |last1=Littleboy |first1=M. |author2=Silburn, D. M. |author3=Freebairn, D. M. |author4=Woodruff, D. R. |author5=Hammer, G. L. |title=PERFECT. A computer simulation model of Productive Erosion Runoff Functions to Evaluate Conservation Techniques |journal=Queensland Department of Primary Industries. Bulletin QB89005 |year=1989}}</ref>

Crop rotations also affect the timing and length of when a field is subject to fallow.<ref name="Huang Shao Zhang Li 2003">{{cite journal |last1=Huang |first1=Mingbin |last2=Shao |first2=Mingan |last3=Zhang |first3=Lu |last4=Li |first4=Yushan |title=Water use efficiency and sustainability of different long-term crop rotation systems in the Loess Plateau of China |journal=Soil and Tillage Research |volume=72 |issue=1 |date=2003 |doi=10.1016/S0167-1987(03)00065-5 |pages=95–104|bibcode=2003STilR..72...95H }}</ref> 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.<ref name="Carroll Halpin Burger Bell 1997"/> 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.<ref>{{Cite news |last=Walker |first=Andy |url=http://www.peicanada.com/island_farmer/article_1f8f774a-ea1d-11e5-b9b4-2314cedac479.html |title=Cover crops have major role to play in soil health |newspaper=peicanada.com |access-date=1 December 2016}}</ref>

=== Biodiversity ===

Increasing the biodiversity of crops has beneficial effects on the surrounding ecosystem and can host a greater diversity of fauna, insects,<ref name=coleman2012/> and beneficial microorganisms in the soil<ref name=coleman2012/> as found by McDaniel et al 2014 and Lori et al 2017.<ref name="Saleem-et-al-2019" /> 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.<ref name="mader2000"/> Increasing biodiversity also increases the resilience of agro-ecological systems.<ref name=baldwinCEFS/>

=== 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.<ref>{{Cite web |url=http://permaculturenews.org/2016/06/15/crop-rotation-a-vital-component-of-organic-farming/ |title = Crop Rotation – A Vital Component of Organic Farming |date = 15 June 2016}}</ref><ref>{{cite journal |last1=Yamoah |first1=Charles F. |last2=Francis |first2=Charles A. |last3=Varvel |first3=Gary E. |last4=Waltman |first4=William J. |title=Weather and Management Impact on Crop Yield Variability in Rotations |journal=Journal of Production Agriculture |date=April 1998 |volume=11 |issue=2 |pages=219–225 |doi=10.2134/jpa1998.0219 |s2cid=54785967 |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1334&context=agronomyfacpub |access-date=9 November 2022 |language=en|url-access=subscription }}</ref>