A griculture is a major user of water in the United States. How the industry utilizes water resources through irrigation technologies and best management practices continues to be a focal point of agriculture policy. Recent droughts and water shortages have resulted in agricultural producers and conveyance institutions rethinking how water is delivered to and used on the farm to adjust to water shortages. Drought and water shortages affecting farmers' ability to irrigate, however, are not isolated to the western United States. Between 2008 and 2013, irrigation was discontinued on over 470,000 acres of farmland across the United States due to surface and groundwater shortages. Given the increasing demands on water supplies for other users and uses, especially for the urbanizing West, there are pressures for the agricultural industry to reduce its water footprint. At the same time, there are other forces (e.g., markets, policies, and droughts) that are encouraging increased interest in irrigation adoption and efficiency. Irrigation, generally defined, is the artificial application of water to plants to sustain or enhance plant growth. There are three primary sources of water for on-farm irrigation: groundwater from wells (55% of irrigation water applied in 2013), water delivered to farms (35%), and on-farm surface water (10%). The use and significance of irrigated agriculture varies widely across the United States. Five states (Nebraska, California, Arkansas, Texas, and Idaho) alone represent 52% of the total irrigated acres nationally. As shown in Figure 1 , irrigated farms in several western states (Arizona, California, Idaho, Nevada, New Mexico, Utah, and Wyoming) and two eastern states (Arkansas and Florida) produce over 89% of the market value of crops sold in those states. In 2012, farms with irrigated land accounted for 50% ($106.3 billion) of the market value of crops sold in the United States, with roughly 71% of irrigated farms residing in the 17 western states. Although the market share of many western states is high, most have seen a reduction in irrigated acres since 1997 (see Figure 2 ). At the same time, irrigation in the east is growing, with some states seeing a percent increase of more than 50% over this same time period. Figure 1. Percent of Market Value of Crops Sold from Irrigated Farms, 2012Source: CRS from USDA, National Agricultural Statistics Service (NASS), 2012 United States Census of Agriculture, AC 12-A-51, Washington, DC, May 2014, http://www.agcensus.usda.gov/Publications/2012/Full_Report/Volume_1,_Chapter_1_US/usv1.pdf. Figure 2. Percent Change in Irrigated Acres in the United States, 1997-2013Source: CRS from USDA, NASS, Quick Stats, http://quickstats.nass.usda.gov/. Many stakeholders are interested in policies associated with irrigation because of its significance to U.S. agriculture and water supplies. Drought and heat events, as well as agricultural market conditions, have raised agricultural producers' interest in investing in irrigation systems and improved irrigation practices; these producers often are weighing the benefits of irrigation-related investments with their costs. Many municipal interests and customers are concerned about irrigation's role in regional water demands and how agricultural water use may affect urban water supplies. These interests would often like to see more judicious use of water in agriculture. Environmental interests are concerned about irrigation's impact on water quality and water source depletion and resulting impacts on aquatic ecosystems and species. At the same time, agricultural producers are concerned about possible cuts to their right or access to water, the lack of which could alter their ability to farm or alter their current system, crop type, or yield. A report from 1996 by the National Research Council summarized the pressures affecting the changing nature of U.S. irrigation as follows: Water costs and demand for water are rising, which is likely to continue. Irrigated agriculture, as the largest and most economically marginal user of water in water-scarce areas, is vulnerable to changing water availability. The viability of irrigated farming may be threatened by problems, such as salinization of soils and dependence on nonrenewable water supplies. The quality of irrigation drainage or return flows is sometimes sufficiently impaired as to limit the future reuse of that water for other purposes, including environmental uses. Irrigation systems and management will likely continue to evolve, moving toward advanced technologies that provide better water control. The ability of states, Indian tribes, and individual water users to market water could be central to increasing the flexibility of water allocation, whether for irrigation or nonirrigation uses. Agricultural water use and irrigation practices raise a number of policy questions. For example: Are on-farm irrigation best management practices (BMPs), and the programs that support them, the most cost-effective use of federal funding? Are there other areas of the water supply chain or involving water users (e.g., irrigation districts, municipal, manufacturing, thermoelectric power, etc.) that could provide greater water conservation more economically and/or in greater quantities? How is the efficiency of irrigation BMPs at conserving water measured? Could these efficiencies be incorporated into federal conservation program implementation and funding allocations? Should new and emerging precision technologies, such as data analytics and drones, receive federal assistance similar to the more traditional irrigation BMPs? What level of priority should these technologies receive, and what level of water conservation do they provide? Should conditions be attached to federal funding for irrigation BMPs to limit agricultural consumption of conserved water (e.g., limiting new irrigated land from coming into production when federal funds are used to convert to efficient irrigation systems)? If consumption restrictions were required, what impact would this have on irrigation BMP adoption? What impact would this have on voluntary federal conservation program participation? What would the conserved water be used for, and who controls it? If the conserved water is diverted to another consumptive purpose (e.g., urban use), is it truly "conserved?" This report primarily addresses two U.S. on-farm irrigation topics: (1) the adoption of irrigation technologies and best management practices and (2) water use associated with irrigation. The report is intended to provide an overview of on-farm irrigation and does not cover storage and conveyance prior to the farm or how irrigation adoption may alter other farm practices, such as the use of fertilizers and pesticides or impacts off-farm (e.g., groundwater and surface water quality concerns). While these issues are significant to understanding the full system that supports irrigated agriculture and the potential environmental impacts of irrigation, they are beyond the purpose and scope of this report. Irrigation has played a significant role in the development and economy of the United States. It was critical in the settlement of the West and agricultural reinvention after the Dust Bowl. While irrigation has ancient roots, technological developments (e.g., pumps, plastics, computers, and sensors) have transformed modern irrigated agriculture. The benefits of irrigation for the nation's agricultural industry have been expansive; however, the application of irrigation technologies and the concomitant changes in the industry have not been without their costs. These costs include but are not limited to associated infrastructure (e.g., dams and conveyance facilities), programs supporting use (e.g., federal assistance for irrigation investments and efficiency improvements), and potential effects on other current and future water users and the environment. The two primary measurements of irrigation water use are water withdrawals and water consumption. While irrigation water withdrawals measure the amount of water applied to lands to assist in crop and pasture growth, water consumption from irrigation refers to the water that is taken in by a plant or evaporated without returning to water sources through runoff or percolation. Although irrigation is the second-largest source of water withdrawals in the United States behind thermoelectric power, irrigation withdrawals have decreased by 23% since their peak in 1980. From 2005 to 2010, irrigation withdrawals dropped 9% nationally. It is unclear, however, whether this decline in withdrawals has led to a decline in water consumption. This is because as irrigation efficiency improves, often less water returns to surface or groundwater supplies through runoff or percolation. As Figure 2 illustrates, changes in the amount of land irrigated across the United States over time vary by region. Since 2003, only four western states have seen an increase in irrigated acres, while the rest have seen a reduction. Several eastern states, on the other hand, have seen a significant increase in irrigated acres over this same time period; seven states increased irrigation by 50% (Delaware, Georgia, Illinois, Indiana, Mississippi, South Carolina, and Tennessee). Since the 1980s, farmers shifted from gravity irrigation to pressurized sprinklers and microirrigation. This shift has been especially pronounced in 17 western states, with gravity irrigation declining from almost 62% of irrigated acres in 1984 to 30% by 2013. As shown in Figure 3 , irrigated land in the West increased by 1.7 million acres during this same time period, while applied irrigation water declined by over 1.37 million acre-feet (AF). There have been fluctuations in the amount of irrigation water applied over time with the current trend of decline in water application beginning in 1998. Figure 4 shows that although irrigation withdrawals from on-farm surface water and water delivered to farms in the West has decreased by about 2.5 million and 1.2 million AF, respectively, since 2003, groundwater withdrawals have increased by over 740,000 AF. Even with this overall decline in irrigation withdrawals, irrigation withdrawals remain highest in the western-most portions of the United States ( Figure 5 ). Growth in irrigated acres in the West is small when compared to increases in the East. Since 1984, irrigated land in eastern states has grown by over 8.7 million acres.