More than 1.5 million acres of orchards and fields are irrigated in Georgia, and a cornucopia of vegetable, fruit, nut, fiber, and animal feed crops are made possible by the surface runoff and groundwater stores that are replenished by Georgia's generous rainfall. A close look at the workings of the two most prevalent types of irrigation reveals how critical these processes are to sustaining Georgia's agricultural economy.
With its humming, grinding noise muffled by the thirty feet of water overhead, a well's submersible pump
At each joint, set 155 feet apart, a small steel triangular tower holds the pipe aloft. Two tractor-like tires at the base of each tower are driven by a small motor between them. At the end of the pipe, the last tower, known as the boss tower, moves in its regular rhythm: forward one minute, stop; forward one minute, stop. Each of the towers in between the boss tower and the well adjusts in turn, following the boss tower's lead. Their role is to keep the pipe in a straight line. All along the pipe carefully spaced openings lead water down drop tubes to sprinkler heads, which create a spray that trickles into the soil, replenishing the root zone with an inch of water.
For the next two and a half days the boss tower will travel over six miles as it traverses the circumference of a 125-acre field of peanuts. By the time it has finished, every portion of the field will have received a uniform helping of water to sustain plant growth for a few more days. As the farmer shuts down the system, he hopes that next week will bring some of Georgia's annual forty to fifty inches of rainfall instead.
Nearby, in a field of tomatoes, no superstructure of wheels and pipe can be seen. Growing out of holes in a plastic sheet covering the soil, each tomato plant is carefully staked and tied. The plastic cover and staking help to assure that nicely shaped, blemish-free tomatoes, which will be hand picked and boxed as vine ripe, will reach the stores. Beneath the plastic and under a few inches of soil, a one-inch-wide flat tube snakes for 500 feet. Every foot along the way, a tiny hole at the end of a remarkably well-engineered flow path built into the plastic wall emits a precise steady drip. After an hour, two quarts of water have been added right into the root zone of each tomato.
Three times each day, that drip will replace the water that sun and wind and heat pull from the tomato plants. Precisely controlled valves will open flow to the drip tapes and control the pressure of water flowing into each of hundreds of tapes. In response, a well located 100 feet below the ground pumps water through filters to remove any tiny grains of sand that could clog the tubes. As with center-pivot irrigation, the drip process provides not only water but also dollars. A 125-acre field of drip-irrigated tomatoes will pump $1.5 million into the local economy annually if conditions are right at harvest time. Drip irrigation, one of the fastest-growing methods of irrigation for high-value crops and orchards, is used on about 73,000 acres in Georgia. Because the water is placed directly at the roots, little is wasted in application.
A green industry has developed to meet this new demand and to establish and protect urban landscapes with a dependable water supply through irrigation. Municipal suppliers of water have responded by increasing infrastructure and impoundments to accommodate the surge of water needed for irrigation during the summer, when water usage typically increases by an extra 50 percent. Though periods of drought have often required that some types of irrigation be curbed, such new methods as Xeriscape gardening, which relies on efficient irrigation practices to conserve water, allow urban dwellers to maintain their landscapes. Irrigation systems will remain a key ingredient in our economy as we gather and distribute water to supplement the state's abundant rainfall.
James E. Hook, University of Georgia
A project of the Georgia Humanities Council, in partnership with the University of Georgia Press, the University System of Georgia/GALILEO, and the Office of the Governor.