The scene of a center pivot irrigation system shooting water over a field of corn may be a thing of the past. Increasingly, irrigators faced with water shortages turn to subsurface drip systems. Today's question facing these irrigators is not if they can afford to upgrade to a drip system, but if they can afford not to adopt this water-saving technique.
Conserve 30 to 60%
Some growers in regions where water sources are shrinking fast are converting to subsurface drip irrigation (SDI). With the need to apply 20 in. or more of supplemental water to make a reasonable corn yield, SDI's ability to save 30 to 60% in water usage makes it an attractive alternative, even with a cost of $650 to $800/acre.
More than 12 years of SDI studies at the Kansas State University (KSU) Research & Extension Center in Colby have convinced irrigation engineer Freddie Lamm that SDI has its place in irrigated corn production, especially in areas of limited water. “We have seen excellent results in our field studies,” Lamm says, noting that drip-watered corn consistently yields in the 200-bu. range. “SDI can cut water usage by 25% over the next type of irrigation [low-pressure center pivot]. And some southwest Kansas growers have seen a 50% reduction in water usage when upgrading from furrow irrigation.”
How it works
In an SDI system, water from the irrigation pump flows through a backflow prevention device and flow meter and then through filtration tanks, which remove nearly all sediment, sand, biological materials and chemical precipitates. It then flows through the main line to submain lines. Systemwide pressure gauges and air vents monitor pressures and provide air venting at system shutdown.
Submains carry water to irrigation zones. Connected to submains are drip lines, also called laterals or tape. They are normally buried 12 to 18 in. deep using a special implement equipped to handle spools of tape. Shallower depths may be needed if soils are sandy or fields require watering-up for germination.
For corn or soybeans, drip lines are typically ⅝ to 1⅜ in. in diameter and are spaced in every other row, usually from 60 to 80 in. apart, depending on whether rows are 30 or 40 in. Each line has emitters, which evenly disperse water through small precision holes into the soil. Emitters are normally spaced 12 to 24 in. apart.
Drip lines stretch to the end of a row, where they are attached to a flush line and valve. A computerized control panel runs the operation, allowing for either manual or automatic irrigation.
Typically, an irrigation capacity of 3½ to 4 gal./min./acre is provided. A typical daily application is 1/5 to ¼ in. Most systems are also equipped with holding tanks for fertigation or chemigation via drip lines. “We can apply all or most of our nitrogen through the system,” Lamm says.
The number of SDI system manufacturers is growing. Two of the larger companies are Netafim USA and T-Systems International, commonly known as T-Tape. Netafim's Jim Phene expects the growth of SDI technology seen in southwestern cotton fields and the West's fruit and vegetable country to expand on to the High Plains and other irrigated areas facing dwindling water supplies. He suggests combining SDI with a minimum- or no-till cropping system to minimize erosion as well as field compaction.
“You have to put a value on the water in these irrigation-dependent areas,” he says. “There will continue to be less irrigation water available. Drip systems can reduce water usage by 30 to 60% and produce yields equal to or better than pivot-watered corn. That type of efficiency has to be considered by growers and communities that live by irrigated farming.”
Pluses and minuses
Along with better water use efficiency, lower energy costs, and reduced wear on pumps and other equipment, the advantages of SDI over other irrigation systems can include more uniform water application; less runoff; enhanced plant growth, crop yield and quality; improved fertilizer and pesticide management; fewer water quality hazards; less nutrient and chemical leaching and deep percolation; less disease pressure due to drier and less humid crop canopies; and overall improved cultural practices.
Some SDI downsides may include high initial investment cost ($650 to $800); more intense management; plugging if filtration is not properly managed; an operation that is mostly hidden from user observation; a wetting pattern that may be too small for light, sandy soil areas; and possible root intrusion in drip lines.
But KSU's Lamm sees many more pluses than minuses in the systems. “Our research station has had SDI systems in place for 12 years, and we have seen no degradation due to plugging,” he says.
For more information on drip irrigation systems, components, research results and other data, visit the Kansas State Research & Extension Web site at www.oznet.ksu.edu/sdi . A wealth of detailed information on drip irrigation equipment can be found at www.microirrigationforum.com/new/directory .
For more information about Natafim or T-Systems, contact Netafim USA, 5470 E. Home Ave., Fresno, CA 93727, 888/638-2346, www.Netafim-USA.com  or circle 200; or contact T-Systems International, 7545 Carroll Rd., San Diego, CA 92121, 800/765-1860, www.tsystemsinternational.com  or circle 201.