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.
Figure 4.1.8.: Furrow irrigation of an onion field in the Uncompahgre Valley, CO. Credits: Perry Cabot
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 the 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.
Figure 4.1.9.: Filtration and pumps for a drip irrigation system for onion and bean crops in the Uncompahgre Valley, CO. Credit: Gigi Richard
Figure 4.1.10: a) Center pivot sprinkler irrigation on an alfalfa crop in the San Luis Valley, CO and b) a hay crop for cattle feed in the Uncompahgre Valley, CO. Credit: Gigi Richard
Figure 4.1.11.: Micro-spray irrigation at a peach orchard in the Grand Valley, CO. Credit: Gigi Richard
Activate Your Learning
Table 4.1.1 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.
|State||Irrigated Land (in thousand acres)
by type of irrigation
|Surface Water Withdrawals||Groundwater Withdrawals||Total Irrigation Withdrawal|
|-||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||% of total water withdrawals
used for irrigation
Knowledge Check (flashcards)
Based on the information in Table 4.1.1, consider how you would answer the questions on the cards below. Click "Turn" to see the correct answer on the reverse side of each card.
Front: Do the states that use the most water also irrigate the most land? Which states are an exception?
Back: Idaho and Colorado use the second and third most water, but irrigate considerably less land than four other states. Nebraska irrigates more than twice as much land with less than half of the water that Idaho uses and about 2/3 of the water the Colorado uses.
Front: 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?
Back: Groundwater and center pivot sprinklers are common in Nebraska. In Idaho, by contrast, gravity-driven, surface-water irrigation is more common. Differences in application efficiencies account for wide variation in irrigation water withdrawals between regions.
Front: What are two reasons, in addition to differences in irrigation efficiencies, that a state might use more water to irrigate less land?
Back: Difference in climate, that is temperature and humidity, can influence evaporation rates, and therefore affect crop consumption. Also, different plants consume different quantities of water, so irrigation needs vary depending on which crops are grown.