For the Instructor

These student materials complement the Future of Food Instructor Materials. If you would like your students to have access to the student materials, we suggest you either point them at the Student Version which omits the framing pages with information designed for faculty (and this box). Or you can download these pages in several formats that you can include in your course website or local Learning Managment System. Learn more about using, modifying, and sharing InTeGrate teaching materials.

Irrigation Efficiency

The amount of water used for irrigation varies depending on the climate and on the crop being grown, and it also depends on the irrigation technique used. Just like in your garden or home landscaping there are more or less efficient sprinklers. In many parts of the world flood or surface, irrigation is still used where water flows across a field and soaks into the soil.

Surface or flood irrigation is the least efficient manner of irrigation. When a field is flooded, more water than is needed by the plant is applied to the field and water evaporates, seeps into the ground and percolates down to the groundwater, where it can be out of reach of the plant's roots. Another problem with flood irrigation is that the water is not always applied evenly to all plants. Some plants might get too much water, and others get too little. On the other hand, flood irrigation tends to use the least energy of any irrigation system.

Furrow irrigation (Figure 4.1.8) is another type of surface irrigation in which water is directed through gated pipe or siphon tubes into furrows between rows of plants. When using furrow irrigation, water is lost to surface runoff, groundwater, and evaporation, and it can be challenging to get water evenly to an entire field.

More efficient methods of irrigation include drip irrigation (Figure 4.1.9) sprinklers (such as center pivots, Figure 4.1.10), and micro-spray (Figure 4.1.11) irrigation. All of these methods, while more efficient, also require significant investments in equipment, pipes, infrastructure (e.g., pumps Figure 4.1.9) and energy. In addition to the high cost, some soil types, irrigation networks, field sizes and crops pose greater challenges to implementation of more efficient methods of irrigation. For example, in the Grand Valley of western Colorado, the irrigation network is entirely gravity-fed, meaning that farmers can easily flood and furrow irrigate without the use of pumps. In addition, the fields are small and the soils are very clayey, all of which make using center pivots for row crops particularly challenging and expensive. But, in the same valley, the peach orchards have successfully used micro-spray and drip systems. A major advantage of more efficient irrigation in addition to reduced water consumption is that crop yields are often higher because the water can be applied more directly to the plant when water is needed.

Activate Your Learning

Table 4.1.1 below presents data on the top 15 irrigated states in the United States. You can see how many acres of land are irrigated in each state, and how much water is used for irrigation of both surface water and groundwater. Consider the relationship between the amount of irrigated land in a state, the type of irrigation used and the amount of water used. Answer the questions below.

An acre-foot is a unit of measure for large volumes of water and is the volume of water required to cover one acre of land to a depth of one foot (325,851 gallons). Imagine a football field, including the end zones, one foot deep in water.

Table 4.1.1. Top 15 Irrigated States, 2010
Data from U.S. Geological Survey, 2014, Estimated Use of Water in the United States in 2010, Circular 1405, Washington, D.C., U.S. Department of Interior
State	Irrigated Land (in thousand acres) by type of irrigation	Surface Water Withdrawals	Groundwater Withdrawals	Total Irrigation Withdrawals
	Sprinkler	Micro-irrigation	Surface	Total	Thousand acre-feet per year	% of irrigation water from surface water	Thousand acre-feet per year	% of irrigation water from groundwater	Thousand acre-feet per year	Percent of total water withdrawals used for irrigation
California	1790	2890	5670	10400	16100	62%	9740	38%	25840	61%
Idaho	2420	4.57	1180	3600	11500	73%	4280	27%	15780	82%
Colorado	1410	0.2	1930	3340	9440	87%	1450	13%	10890	88%
Arkansas	518	0	4150	4670	1500	15%	8270	85%	9770	77%
Montana	753	0.64	886	1640	7880	98%	142	2%	8022	94%
Texas	3770	244	1910	5920	1940	25%	5710	75%	7650	27%
Nebraska	6370	0.57	2360	8730	1520	24%	4820	76%	6340	70%
Oregon	1210	97	594	1900	3750	64%	2140	36%	5890	78%
Arizona	195	28.1	770	993	3220	63%	1900	37%	5120	75%
Wyoming	184	4.12	892	1080	4410	90%	490	10%	4900	93%
Utah	625	1.45	710	1340	3060	85%	554	15%	3614	72%
Washington	1270	86.1	221	1580	2630	75%	894	25%	3524	63%
Kansas	2840	18.1	217	3080	179	5%	3230	95%	3409	76%
Florida	548	712	731	1990	1500	46%	1770	54%	3270	20%
New Mexico	461	19.6	397	878	1640	54%	1390	46%	3030	86%

Do the states that use the most water also irrigate the most land? Which states are an exception?

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Compare the data for Nebraska with Idaho. Nebraska's water withdrawals are much lower for a larger acreage of land than Idaho. What is the major source of Nebraska's irrigation water? Surface or ground water? And, which type of irrigation is used?

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What are two reasons, in addition to differences in irrigation efficiencies, that a state might use more water to irrigate less land?

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