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Irrigation in agriculture is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns.

Irrigation has been a key aspect of agriculture for over 5,000 years and has been developed by many cultures worldwide. Irrigation helps to grow crops, maintain landscapes, and revegetate disturbed soils in dry areas and during times of below-average rainfall. Several irrigation methods differ in how water is supplied to plants. Surface irrigation, also known as gravity irrigation, is the oldest form of irrigation and has been in use for thousands of years. In sprinkler irrigation, water is piped to one or more central locations within the field and distributed by overhead high-pressure water devices. Micro-irrigation uses less pressure and water flow than sprinkler irrigation. Drip irrigation delivers water directly to the root zone of plants. Subirrigation has been used in field crops in areas with high water tables for many years. Irrigation water can come from groundwater (extracted from springs or by using wells), from surface water (withdrawn from rivers, lakes or reservoirs) or from non-conventional sources like treated wastewater, desalinated water, drainage water, or fog collection. Irrigation can be supplementary to rainfall, which is common in many parts of the world as rainfed agriculture, or it can be full irrigation, where crops rarely rely on any contribution from rainfall. Full irrigation is less common and occurs only in arid landscapes with very low rainfall or when crops are grown in semi-arid areas outside the rainy season. The environmental effects of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the subsequent effects on natural and social conditions in river basins and downstream of an irrigation scheme. Over-irrigation can cause deep drainage from rising water tables, which can lead to irrigation salinity problems, requiring watertable control through some form of subsurface land drainage.

The global land area equipped for irrigation reached 355 million ha in 2023, an increase of 23% from the 289 million ha of 2000 and more than twice the land area equipped for irrigation in the 1960s.

The water application efficiency of surface irrigation is typically lower than that of other irrigation methods, due in part to limited control over applied depths. A special form of irrigation using surface water is spate irrigation, also called floodwater harvesting.

Micro-irrigation, sometimes called localized irrigation, low volume irrigation, or trickle irrigation, is a system where water is distributed under low pressure through a piped network, in a pre-determined pattern, and applied as a small discharge to each plant or adjacent to it. Traditional drip irrigation uses individual emitters, subsurface drip irrigation (SDI), micro-spray or micro-sprinklers, and mini-bubbler irrigation, all of which belong to this category of irrigation methods.

This type of system is known to most people as a "water reel" travelling irrigation sprinkler, and it is used extensively for dust suppression, irrigation, and the land application of wastewater.

The Indus Valley Civilization developed sophisticated irrigation and water-storage systems, including artificial reservoirs at Girnar dated to 3000 BCE, and an early canal irrigation system from c.

In North America, the Hohokam were the only culture known to rely on irrigation canals to water their crops, and their irrigation systems supported the largest population in the Southwest by CE 1300.

Irrigation techniques across the globe include canals redirecting surface water, groundwater pumping, and diverting water from dams. In the 20th century, global anxiety, specifically about the American cotton monopoly, fueled many empirical irrigation projects: Britain began developing irrigation in India, the Ottomans in Egypt, the French in Algeria, the Portuguese in Angola, the Germans in Togo, and Soviets in Central Asia. Salinization of irrigation water damaged the crops and seeped into drinking water.

Quick Facts

• Surface irrigation, also known as gravity irrigation, is the oldest form of irrigation and has been in use for thousands of years.
• The environmental effects of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the subsequent effects on natural and social conditions in river basins and downstream of an irrigation scheme.
• Irrigation can be supplementary to rainfall, which is common in many parts of the world as rainfed agriculture, or it can be full irrigation, where crops rarely rely on any contribution from rainfall.
• Micro-irrigation uses less pressure and water flow than sprinkler irrigation.
• Irrigation water can come from groundwater (extracted from springs or by using wells), from surface water (withdrawn from rivers, lakes or reservoirs) or from non-conventional sources like treated wastewater, desalinated water, drainage water, or fog collection.

Source material: Wikipedia - "Irrigation". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.