Irrigation

Throughout human history, agricultural societies in semiarid and arid regions have relied on irrigation to sustain food cultivation. Widespread application of irrigation technologies, particularly after the green revolution, resulted in environmental problems including waterlogging, salinization, and land subsidence. Research and development efforts aim at [Page 265]increasing irrigation efficiency while promoting greater socioeconomic equity and ecological sustainability.

In his highly controversial 1957 volume Oriental Despotism, historian Karl Wittfogel argued that rulers who controlled expansive hydraulic networks were uniquely able to wield political power. Wittfogel theorized that large-scale irrigation required a form of highly organized and centralized control that led to an absolutist managerial state.

This fertilizer and irrigation, or fertigation, system mixes water with chemical fertilizers that are injected into the pipe at several locations. It then delivers the mixture to individual furrows of this romaine lettuce crop in California's Coachella Valley.

Source: U.S. Department of Agriculture Agricultural Research Service/Floyd Adamsen

Although many have noted the shortcomings of Wittfogel's “hydraulic society,” his writings have spurred many ecological anthropologists and historians to more closely examine the relationship between irrigation control and sociopolitical development. Revising Wittfogel's original thesis, environmental historian Donald Worster has argued that the modes of water control that gave rise to settlement of the American West were based less on self-governed agrarian democracy than on the federal government's vast appetite for public subsidization of large-scale irrigation.

Irrigation is no less important today than it was at the turn of the 19th century. Irrigation can be sourced from surface water, groundwater, or wells that tap deep aquifers. Surface water for irrigation is usually withdrawn from rivers, lakes, or reservoirs created by dams. Large-scale canal systems carry water hundreds of miles from reservoirs to fields through a combination of water-pumping and gravity-fed systems.

Modern irrigation systems rely on several different kinds of technologies to deliver water to fields. The main systems for delivering irrigation are:

• Flood: a system of applying water in which the entire surface of the soil is covered by ponded water
• Furrow: a system of partial surface flooding in which water is applied in furrows or rows
• Sprinkler: an automated system in which water is applied at a uniform rate and fixed pattern through small droplets emanating from pressurized pipes; sprinkler irrigation can include center pivots or traveling guns
• Drip or trickle: a system in which water is applied directly to the root zone of plants through low-pressure hoses that are placed either on or right below the surface of the ground