Editing Irrigation (section)

=== Technical challenges ===
[[File:Сток воды при орошении.png|thumb|Overirrigation because of poor distribution uniformity in the furrows. Potato plants were oppressed and turned yellow]]
Irrigation schemes involve solving numerous engineering and economic problems while minimizing negative environmental consequences.<ref name=":0">ILRI, 1989, Effectiveness and Social/Environmental Impacts of Irrigation Projects: a Review. In: Annual Report 1988, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands, pp. 18 – 34 . On line: [http://www.waterlog.info/pdf/irreff.pdf]</ref> Such problems include:
* Ground [[subsidence]] (e.g. [[New Orleans, Louisiana]])
* Underirrigation or irrigation giving only just enough water for the plant (e.g. in drip line irrigation) gives poor [[soil salinity control]] which leads to increased [[soil salinity]] with consequent buildup of toxic salts on soil surface in areas with high evaporation. This requires either [[leaching (agriculture)|leaching]] to remove these salts and a method of [[drainage]] to carry the salts away. When using drip lines, the leaching is best done regularly at certain intervals (with only a slight excess of water), so that the salt is flushed back under the plant's roots.<ref>EOS magazine, September 2009</ref>
* [[wikt:Overirrigation|Overirrigation]] because of poor [[distribution uniformity]] or [[irrigation scheduling|management]] wastes water, chemicals, and may lead to [[water pollution]].<ref>Hukkinen, Janne, Emery Roe, and Gene I. Rochlin. "A salt on the land: A narrative analysis of the controversy over irrigation-related salinity and toxicity in California's San Joaquin Valley." ''Policy Sciences'' 23.4 (1990): 307–329. [http://blogs.helsinki.fi/jahukkin/files/2012/02/PolSci1990.pdf online] {{webarchive|url=https://web.archive.org/web/20150102191753/http://blogs.helsinki.fi/jahukkin/files/2012/02/PolSci1990.pdf |date=2015-01-02 }}</ref>
* Deep drainage (from over-irrigation) may result in rising water tables which in some instances will lead to problems of irrigation [[Soil salinity|salinity]] requiring [[watertable control]] by some form of [[Drainage system (agriculture)|subsurface land drainage]].<ref>{{cite book | title = Drainage Manual: A Guide to Integrating Plant, Soil, and Water Relationships for Drainage of Irrigated Lands | year = 1993 | publisher = Interior Dept., Bureau of Reclamation | isbn = 978-0-16-061623-5 }}</ref><ref name="Waterlog">{{cite web |url=http://www.waterlog.info |title=Free articles and software on drainage of waterlogged land and soil salinity control in irrigated land |access-date=2010-07-28 }}</ref> For example in [[Australia]], over-abstraction of fresh water for intensive irrigation activities has caused 33% of the land area to be at risk of [[Soil salinity|salination]].<ref name="Gordon">{{cite journal |author=Gordon L., D. M. |year=2003 |title=Land cover change and water vapour flows: learning from Australia |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=358 |issue=1440 |pages=1973–1984 |doi=10.1098/rstb.2003.1381 |jstor=3558315 |pmc=1693281 |pmid=14728792}}</ref>
* [[Saffman–Taylor instability|Drainage front instability]], also known as viscous fingering, where an unstable drainage front results in a pattern of fingers and viscous entrapped saturated zones.
* Irrigation with [[saline water|saline]] or [[sodium adsorption ratio|high-sodium]] water may damage soil structure owing to the formation of [[alkaline soil]].
* Clogging of filters: algae can clog filters, drip installations, and nozzles. Chlorination, algaecide, UV and ultrasonic methods can be used for algae control in irrigation systems.
* Complications in accurately measuring irrigation performance which changes over time and space using measures such as productivity, efficiency, equity and adequacy.<ref>{{Cite journal|date=2020-11-01|title=A scale-based framework to understand the promises, pitfalls and paradoxes of irrigation efficiency to meet major water challenges|journal=Global Environmental Change|language=en|volume=65|pages=102182|doi=10.1016/j.gloenvcha.2020.102182|issn=0959-3780|doi-access=free|last1=Lankford|first1=Bruce|last2=Closas|first2=Alvar|last3=Dalton|first3=James|last4=López Gunn|first4=Elena|last5=Hess|first5=Tim|last6=Knox|first6=Jerry W.|last7=Van Der Kooij|first7=Saskia|last8=Lautze|first8=Jonathan|last9=Molden|first9=David|last10=Orr|first10=Stuart|last11=Pittock|first11=Jamie|last12=Richter|first12=Brian|last13=Riddell|first13=Philip J.|last14=Scott|first14=Christopher A.|last15=Venot|first15=Jean-Philippe|last16=Vos|first16=Jeroen|last17=Zwarteveen|first17=Margreet|bibcode=2020GEC....6502182L |hdl=1885/224453|hdl-access=free}}</ref>
* Macro-irrigation, typical in [[intensive agriculture]], where also are used agrochemicals, often causes [[eutrophication]].