Editing Crop rotation (section)

=== 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>