Editing Soil (section)

===Studies of soil fertility===
{{Main|Soil fertility}}
The Greek historian [[Xenophon]] (450–355&nbsp;[[Before the Common Era|BCE]]) was the first to expound upon the merits of green-manuring crops: 'But then whatever weeds are upon the ground, being turned into earth, enrich the soil as much as dung.'{{sfn|Donahue|Miller|Shickluna|1977|p=4}}

[[Columella]]'s ''Of husbandry'', {{circa|60&nbsp;[[Common Era|CE]]}}, advocated the use of lime and that [[clover]] and [[alfalfa]] ([[green manure]]) should be turned under,<ref>{{cite book |last=Columella |first=Lucius Junius Moderatus |year=1745 |title=Of husbandry, in twelve books, and his book concerning trees, with several illustrations from Pliny, Cato, Varro, Palladius, and other antient and modern authors, translated into English |publisher=[[Andrew Millar]] |location=London, United Kingdom |url=https://catalog.hathitrust.org/Record/005783003 |access-date=19 September 2021}}</ref> and was used by 15 generations (450&nbsp;years) under the [[Roman Empire]] until its collapse.{{sfn|Donahue|Miller|Shickluna|1977|p=4}}{{sfn|Kellogg|1957|p=1}} From the [[fall of Rome]] to the [[French Revolution]], knowledge of soil and agriculture was passed on from parent to child and as a result, crop yields were low. During the European [[Middle Ages]], [[Ibn al-'Awwam|Yahya Ibn al-'Awwam]]'s handbook,<ref>{{cite book |language=fr |last=[[Ibn al-'Awwam]] |year=1864 |title=Le livre de l'agriculture, traduit de l'arabe par Jean Jacques Clément-Mullet |series=Filāḥah.French. |publisher=Librairie A. Franck |location=Paris, France |url=https://catalog.hathitrust.org/Record/009953450 |access-date=19 September 2021}}</ref> with its emphasis on irrigation, guided the people of North Africa, Spain and the [[Middle East]]; a translation of this work was finally carried to the southwest of the United States when under Spanish influence.<ref>{{cite book |last=Jelinek |first=Lawrence J. |year=1982 |title=Harvest empire: a history of California agriculture |publisher=Boyd and Fraser |location=San Francisco, California |isbn=978-0-87835-131-2}}</ref> [[Olivier de Serres]], considered the father of French [[agronomy]], was the first to suggest the abandonment of [[fallowing]] and its replacement by hay [[meadows]] within [[crop rotation]]s. He also highlighted the importance of soil (the French [[terroir]]) in the management of vineyards. His famous book {{Lang|fr|Le Théâtre d'Agriculture et mesnage des champs}}<ref>{{cite book |language=fr |last=de Serres |first=Olivier |year=1600 |title=Le Théâtre d'Agriculture et mesnage des champs |publisher=Jamet Métayer |location=Paris, France |url=https://gallica.bnf.fr/ark:/12148/bpt6k738381/f1.image |access-date=19 September 2021}}</ref> contributed to the rise of modern, [[sustainable agriculture]] and to the collapse of old [[agricultural practices]] such as [[soil amendment]] for crops by the lifting of [[forest litter]] and [[assarting]], which ruined the soils of western Europe during the Middle Ages and even later on according to regions.<ref>{{cite journal |last1=Virto |first1=Iñigo |last2=Imaz |first2=María José |last3=Fernández-Ugalde |first3=Oihane |last4=Gartzia-Bengoetxea |first4=Nahia |last5=Enrique |first5=Alberto |last6=Bescansa |first6=Paloma |journal=[[Sustainability (journal)|Sustainability]] |volume=7 |issue=1 |title=Soil degradation and soil quality in western Europe: current situation and future perspectives |year=2015 |pages=313–365 |doi=10.3390/su7010313 |doi-access=free}}</ref>

Experiments into what made plants grow first led to the idea that the ash left behind when plant matter was burned was the essential element but overlooked the role of nitrogen, which is not left on the ground after combustion, a belief which prevailed until the 19th century.<ref>{{cite journal |last1=Van der Ploeg |first1=Rienk R. |last2=Schweigert |first2=Peter |last3=Bachmann |first3=Joerg |journal=[[Scientific World Journal]] |volume=1 |issue=S2 |title=Use and misuse of nitrogen in agriculture: the German story |year=2001 |pages=737–744 |doi=10.1100/tsw.2001.263 |pmid=12805882 |pmc=6084271 |doi-access=free}}</ref> In about 1635, the Flemish chemist [[Jan Baptist van Helmont]] thought he had proved water to be the essential element from his famous five years' experiment with a willow tree grown with only the addition of rainwater. His conclusion came from the fact that the increase in the plant's weight had apparently been produced only by the addition of water, with no reduction in the soil's weight.<ref>{{cite web |url=https://www.bbc.co.uk/bitesize/clips/zpgb4wx |title=Van Helmont's experiments on plant growth |website=[[BBC World Service]] |access-date=19 September 2021}}</ref><ref name=Brady1984/>{{sfn|Kellogg|1957|p=3}} [[John Woodward (naturalist)|John Woodward]] ({{abbr|d.|died}}&nbsp;1728) experimented with various types of water ranging from clean to muddy and found muddy water the best, and so he concluded that earthy matter was the essential element. Others concluded it was humus in the soil that passed some essence to the growing plant. Still others held that the vital growth principal was something passed from dead plants or animals to the new plants. At the start of the 18th century, [[Jethro Tull (agriculturist)|Jethro Tull]] demonstrated that it was beneficial to cultivate (stir) the soil, but his opinion that the stirring made the fine parts of soil available for plant absorption was erroneous.<ref name=Brady1984/>{{sfn|Kellogg|1957|p=2}}

As chemistry developed, it was applied to the investigation of soil fertility. The French chemist [[Antoine Lavoisier]] showed in about 1778 that plants and animals must [[Combustion|combust]] oxygen internally to live. He was able to deduce that most of the {{convert|165|lb|adj=on}} weight of van Helmont's willow tree derived from air.<ref>{{cite journal |language=fr |last=de Lavoisier |first=Antoine-Laurent |journal=Mémoires de l'Académie Royale des Sciences |title=Mémoire sur la combustion en général |year=1777 |url=http://www.academie-sciences.fr/pdf/dossiers/Franklin/Franklin_pdf/Mem1777_p592.pdf |access-date=19 September 2021}}</ref> It was the French agriculturalist [[Jean-Baptiste Boussingault]] who by means of experimentation obtained evidence showing that the main sources of carbon, hydrogen and oxygen for plants were air and water, while nitrogen was taken from soil.<ref>{{cite book |language=fr |last=Boussingault |first=Jean-Baptiste |title=Agronomie, chimie agricole et physiologie, volumes 1–5 |year=1860–1874 |publisher=Mallet-Bachelier |location=Paris, France |url=https://archive.org/details/8TSUP364_1 |access-date=19 September 2021}}</ref> [[Justus von Liebig]] in his book ''Organic chemistry in its applications to agriculture and physiology'' (published 1840), asserted that the chemicals in plants must have come from the soil and air and that to maintain soil fertility, the used minerals must be replaced.<ref>{{cite book |last=von Liebig |first=Justus |title=Organic chemistry in its applications to agriculture and physiology |year=1840 |publisher=Taylor and Walton |location=London |url=https://archive.org/details/organicchemistry00liebrich |access-date=19 September 2021}}</ref> Liebig nevertheless believed the nitrogen was supplied from the air. The enrichment of soil with guano by the Incas was rediscovered in 1802, by [[Alexander von Humboldt]]. This led to its mining and that of Chilean nitrate and to its application to soil in the United States and Europe after 1840.<ref>{{cite journal |last=Way |first=J. Thomas |journal=Journal of the Royal Agricultural Society of England |title=On the composition and money value of the different varieties of guano |year=1849 |volume=10 |pages=196–230 |url=https://www.biodiversitylibrary.org/item/37078#page/220/mode/1up |access-date=19 September 2021}}</ref>

The work of Liebig was a revolution for agriculture, and so other investigators started experimentation based on it. In England [[John Bennet Lawes]] and [[Joseph Henry Gilbert]] worked in the [[Rothamsted Research|Rothamsted Experimental Station]], founded by the former, and {{Not a typo|(re)discovered}} that plants took nitrogen from the soil, and that salts needed to be in an available state to be absorbed by plants. Their investigations also produced the [[superphosphate]], consisting in the acid treatment of phosphate rock.{{sfn|Kellogg|1957|p=4}} This led to the invention and use of salts of potassium (K) and nitrogen (N) as fertilizers. Ammonia generated by the production of [[coke (fuel)|coke]] was recovered and used as fertiliser.<ref>{{cite web |last=Tandon |first=Hari L.S. |url=http://www.tandontech.net/fertilisers.html |title=A short history of fertilisers |website=Fertiliser Development and Consultation Organisation |access-date=17 December 2017 |archive-url=https://web.archive.org/web/20170123214241/http://www.tandontech.net/fertilisers.html |archive-date=23 January 2017 |url-status=dead}}</ref> Finally, the chemical basis of nutrients delivered to the soil in manure was understood and in the mid-19th century chemical fertilisers were applied. However, the dynamic interaction of soil and its life forms was still not understood.

In 1856, J. Thomas Way discovered that ammonia contained in fertilisers was transformed into nitrates,<ref>{{cite journal |last=Way |first=J. Thomas |journal=Journal of the Royal Agricultural Society of England |title=On the power of soils to absorb manure |year=1852 |volume=13 |pages=123–143 |url=https://biodiversitylibrary.org/page/45583402 |access-date=19 September 2021}}</ref> and twenty years later [[Robert Warington]] proved that this transformation was done by living organisms.<ref>{{cite book |last=Warington |first=Robert |title=Note on the appearance of nitrous acid during the evaporation of water: a report of experiments made in the Rothamsted laboratory |url=https://books.google.com/books?id=NlISAQAAMAAJ |year=1878 |publisher=[[Harrison and Sons]] |location=London, United Kingdom |access-date=19 September 2021}}</ref> In 1890 [[Sergei Winogradsky]] announced he had found the bacteria responsible for this transformation.<ref>{{cite journal |last=Winogradsky |first=Sergei |journal=[[Comptes Rendus de l'Académie des Sciences|Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences]] |title=Sur les organismes de la nitrification |language=fr |trans-title=On the organisms of nitrification |year=1890 |volume=110 |issue=1 |pages=1013–1016 |url=https://gallica.bnf.fr/ark:/12148/bpt6k30663/f1087?lang=EN |access-date=19 September 2021}}</ref>

It was known that certain [[legume]]s could take up nitrogen from the air and fix it to the soil but it took the development of bacteriology towards the end of the 19th century to lead to an understanding of the role played in nitrogen fixation by bacteria. The symbiosis of bacteria and leguminous roots, and the fixation of nitrogen by the bacteria, were simultaneously discovered by the German agronomist [[Hermann Hellriegel]] and the Dutch microbiologist [[Martinus Beijerinck]].{{sfn|Kellogg|1957|p=4}}

Crop rotation, mechanisation, chemical and natural fertilisers led to a doubling of wheat yields in western Europe between 1800 and 1900.{{sfn|Kellogg|1957|pp=1–4}}