Editing Crop rotation (section)

== History ==

[[File:Robinia pseudoacacia root nodules.JPG|thumb|[[Legume]]s such as [[alfalfa]], [[bean]]s, and [[clover]] have long been used in crop rotations. They have bacteria in their root nodules which take nitrogen from the air and fix it into the soil as [[nitrate]]s that crops can use.]]

Farmers have long recognized that suitable rotations such as planting spring crops for [[livestock]] 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, alternately planting [[legumes]] and [[cereals]].<ref>{{Cite web |url=https://time.graphics/event/2281456 |title=Jan 1, 6000 BC – Crop Rotation (Timeline) |website=time.graphics |access-date=23 September 2019 |archive-url=https://web.archive.org/web/20190923164709/https://time.graphics/event/2281456 |archive-date=23 September 2019 |url-status=dead}}</ref><ref>{{Cite web |url=https://www.worldatlas.com/articles/what-is-crop-rotation.html |title=What Is Crop Rotation? |website=WorldAtlas |date=25 April 2017 |access-date=25 January 2019}}</ref>{{better source needed |date=December 2021}}

=== 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]] both the two- and three-field systems had been used since the [[Eastern Zhou]] period.<ref>{{cite book |last=Needham |first=Joseph |year=1984 |title=Science and Civilization in China 6-2 |page=150}}</ref>

=== Three-field systems ===

{{main|Three-field system}}

From the 9th century to the 11th century, farmers in Europe transitioned from a two-field system to a [[three-field system]]. This system persisted until the 20th century. Available land was divided into three sections. One section was planted in the autumn with [[rye]] or winter [[wheat]], followed by spring [[oat]]s or [[barley]]; the second section grew crops such as one of the [[legume]]s, namely 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, only half the land was planted in any year. Under the new three-field rotation system, two thirds of the land was planted, potentially yielding a larger harvest. But the additional crops had a more significant effect than mere quantitative productivity. Since the spring crops were mostly legumes, which [[Nitrogen fixation|fix nitrogen]] needed for plants to make [[protein]]s, they increased the overall nutrition of the people of Europe.<ref name="Lienhard 2023">{{cite web |last=Lienhard |first=John |title=No. 26: Three-Field Crop Rotation |publisher=[[University of Houston]] |url=https://www.uh.edu/engines/epi26.htm |series=The Engines of Our Ingenuity |date=2023 |access-date=31 December 2023}}</ref>

=== Four-field rotations ===

{{main|Norfolk four-course system}}
{{further|Convertible husbandry}}

Farmers in the region of [[Waasland]] (in present-day northern Belgium) pioneered a four-field rotation in the early 16th century, and the [[United Kingdom|British]] agriculturist [[Charles Townshend, 2nd Viscount Townshend|Charles Townshend]] (1674–1738) popularised this system in the 18th century. The sequence of four crops ([[wheat]], [[turnip]]s, [[barley]] and [[clover]]), included a [[fodder crop]] and a grazing crop, allowing [[livestock]] to be bred year-round. The four-field crop rotation became a key development in the [[British Agricultural Revolution]].<ref>{{cite web |url=https://www.britannica.com/topic/Norfolk-four-course-system |title=Norfolk four-course system |website=Encyclopædia Britannica |accessdate=31 May 2017}}</ref>

=== Modern developments ===

In the [[Green Revolution]] of the mid-20th century, crop rotation gave way in the developed world to the practice of supplementing the chemical inputs to the soil through [[topdressing]] with [[fertilizer]]s, adding (for example) [[ammonium nitrate]] or [[urea]] and restoring [[soil pH]] with [[Lime (mineral)|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]].