Colorado Ag. Science Curriculum Section: Plant and Soil Science Unit: 5 - Environmental Factors Lesson: 6 Managing Water – Irrigation

OBJECTIVES TO BE COVERED 1)To learn what irrigation is. 2)To learn how much water is used during irrigation practices. 3)To learn what type of irrigation methods are used.

How did ancient man water his/her crops? Can you guess? –A bucket! Ancient people must have been strong from having to haul buckets full of water to pour on their first plants.

What is irrigation? Irrigation is the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall.

Where do the farmers get the water? Rivers Lakes Streams Reservoirs Wells

How much water is used in irrigation? Almost 60 percent of all the world's freshwater withdrawals go towards irrigation uses. California, Idaho, Colorado, and Nebraska combined accounted for one-half of the total irrigation withdrawals in 2000.

Agriculture is the largest user of water due to irrigation. It takes over 1 million gallons of water a year to irrigate one acre of farmland in arid conditions. Most of the water used by irrigation re-enters the hydrologic cycle through evapotranspiration. Although it has only 28% of the U.S. population, the arid West accounts for 80% of the average water consumed daily due to extensive irrigation.

Irrigation withdrawals For 2000, withdrawals were an estimated 137,000 million gallons per day (Mgal/d), or 153,000 thousand acre-feet per year.Mgal/d Irrigation withdrawals were 40 percent of total freshwater withdrawals and, when excluding thermo-electric power, 65 percent of total freshwater withdrawals. Surface water accounted for 58 percent of the total irrigation withdrawals and ground water was 42 percent. About 61,900,000 acres were irrigated in Of this total acreage, about 29,400,000, acres were irrigated with surface (flood) systems; 28,300,000 acres with sprinkler systems; and 4,180,000 acres with micro-irrigation systems. Application rates were calculated by dividing total withdrawals by irrigated acres. The average application rate was 2.48 acre-feet per acre for the United States.

Flood (furrow) Irrigation This is sometimes referred to as “Surface Irrigation”. Surface irrigation is still used today throughout the world, especially in less-developed areas where mechanical techniques are not available. Farmers flow water down small trenches running through their crops. About one-half of the water used ends up not getting to the crops.

How much water is used? In the United States in 2000, about 29.4 million acres were irrigated by flood irrigation as compared to about 28.3 million acres irrigated by spray irrigation.

Sprinkler Irrigation Also called center pivot, center line or wheel line. This method is more expensive than “Flood Irrigation”. More efficient at using water, however, water is lost in evaporation. Problems due to foliar moisture-loving diseases can arise if over watering occurs.

Drip or Trickle Irrigation A planned irrigation system in which water is applied directly to the Root Zone of plants. This is the most expensive, but most water-efficient, method. Low-quality water (high in salts) should not be used, unless filtered, due to potentially devastating effects of clogged emitters. Drip irrigation is an ineffective leaching method.