Making the Most of Your Water
There are two components to irrigation efficiency, says Dr. David Zoldoske, director of the Center for Irrigation Technology (CIT) in Fresno, Calif.: uniformity and timing/amount of water. Manufacturers are improving both, from drip lines that resist clogging to a software program that text messages growers when the system has a problem to a soil moisture sensor that’s been to Mars.
Drip irrigation is ideal for irrigating hedgerows and high-cash-value row crops, such as tomatoes, peppers and strawberries.
“Farmers are requesting very low flow emitters spaced 4 to 6 inches apart on drip tape,” says Zoldoske. “Permanently installed buried drip is probably preferred [in California], except along the coast, where strawberry and other small growers rent or lease land and have to remove it. The tomato processing industry is adopting SDI [subsurface drip] almost across the board. They don’t want tomatoes sitting on wet ground.”
Because water is applied slowly and evenly in a narrow strip near the plant, drip irrigation can better target applied water and use less energy than traditional sprinklers. There’s potentially less plant stress, less water wasted due to evaporation and less runoff and erosion, and therefore less leaching of nutrients into the water supply. There can also be fewer weeds.
Water doesn’t touch leaf surfaces or oversaturate the soil surface, so diseases are less of a problem and salts can be more easily managed in the soil. Fertilizer and chemicals can be applied efficiently because they are delivered directly to the plant roots. More field operations can continue during irrigation, especially with SDI. It can be used in windy and freezing weather, but not for cooling or frost control.
“Drip irrigation needs to be properly designed,” Zoldoske says. “Few farmers design their own equipment for installation. It’s usually better to purchase a tool that is commercially built.” Subsurface drip irrigation systems should be professionally designed and can cost $1,500 per acre or more, depending on the system. GPS should be used to install the pipes and tubing precisely.
Surface drip tape can be removed and reused, but care must be taken to not damage the product during the process. Specialized equipment, much of it made by Andros Engineering in Paso Robles, Calif., installs it, retrieves it and rewinds it into compact rolls to be used again.
Both aboveground and belowground drip are easily automated. They also can be used with tensiometers such as Irrometer by Irrometer Company in Riverside, Calif., and electrical resistance blocks and meters. These measure soil moisture in the rootzone and allow growers to apply water only when and where it’s needed. PureSense, in Oakland, Calif., manufactures Irrigation Manager, which monitors growing conditions both aboveground and belowground.
Decagon Devices in Pullman, Wash., manufactures a sensor that is part of the robotic arm on the landing craft “Phoenix,” which found traces of ice on Mars. Netafim USA, based in Israel, will be incorporating the sensor in its IrriWise soil moisture monitoring system.
Although drip irrigation has fewer mechanized parts than other systems, and leaks are less of a problem due to low flow rates, problems are harder to find, especially with SDI, which is also especially hard to repair.
Even clean water can contain enough soil particles and minerals to clog the openings in the tubing. Depending on the quality of the water, they can be managed with filters, periodic flushing and injections of chlorine and acid solutions. Drip systems have been susceptible to damage by animals, especially rodents, but it is less of a problem with tubing made of stronger polymers.
SDI is also susceptible to root intrusion and the backflow of dirt into the drip line when the system shuts off. Netafim is one of many companies with drip lines that resist clogging, maintain uniform flow rates at different inlet working pressures and have an anti-siphon system to prevent dirt backflow.
Sprinklers are designed so the water flow rates, which are controlled by the operating pressure and the size and shape of the nozzle, suit the type of soil and the slope of the field.
Micro-sprinklers are best suited for widely spaced plants, such as those in orchards and vineyards. Emitters are connected to lateral pipes that usually use tubing .25 to 1/8 inch in diameter and are mounted on a support stake or connected to supply pipe, according to the North Dakota State University Extension Service Web site. They throw water into the air 3 to 20 feet in diameter, usually in predetermined patterns. Rain Bird in Azusa, Calif., has a micro-quick spray, for example, that includes “star bird” and “proportional butterfly,” as well as “fan spray” patterns.
Micro-sprinklers use less energy and water than traditional sprinklers. They leave larger dry areas, create fewer weed problems and make it easier to work in the field during irrigation. Flow rates vary from 3 to 30 GPH (gallons per hour), according to the university’s Web site. In sandy soils, emitters should be placed closer to the plants and the flow rate set higher than in less porous loam or clay. In clay soils, the least porous, the flow rate should be the lowest, to avoid evaporation and standing water on flat land and runoff on slopes.
Micro-sprinklers can be automated and used for fertigation. They can be used for frost protection, but not in windy conditions. They’re less prone to clogging, and it’s easier to detect problems.
Manufacturers make deflectors to prevent water from spraying into unwanted areas as well as devices to prevent branches and foliage from distorting the spray patterns. Distortion usually isn’t a serious problem, though, Zoldoske says, as long as each tree gets the same amount of water.
“Trees are pretty adaptive,” he says. “Their roots will go where the water is.”
Sprinkler heads can be mounted on risers above the canopy to avoid distortion. Shaping vanes, or spokes, create streams of water that are less susceptible to distortion, but on sandy soils this can result in unwatered areas. Sprinklers with spinners offer more uniform coverage.
Rain Bird has a software program, Uniformity Pro, that helps growers pick the best nozzle and deflector combination for their needs.
The Irrigation Technology Center’s software program, SPACE (Sprinkler Profile and Coverage Evaluation), allows designers and growers to place sprinkler heads in almost any configuration and combination, calculate the uniformity and display the results using sprinkler test data.
“It’s a visual way to show how water is distributed with their products,” Zoldoske says.
Center pivot and linear irrigation
“You’ll see more center pivots than ever before,” he predicts. First, he says, they work, and not irrigating the corners of fields is less important because of water supply issues, they can require less labor to operate than other irrigation systems.
With center pivot systems, one long arm rotates around a central pivot point, usually propelled by electric power. The amount of water being applied determines the amount of time it takes for one rotation. Although the outer end of the arm covers a larger area than the end closest to the pivot, with proper design and installation these systems deliver a constant flow of water to all cropping areas. They’re best suited to porous soils, and are easily adapted to slopes that may need pressure regulators to stabilize the flow rate. They also can deliver fertilizer.
They’re most efficient on round fields, although most systems have end guns or part-circle attachments that spray into corners and irregular areas. FieldPLUS, from Lindsay Corp. in Omaha, Neb., has a pivoting joint that can be placed at nearly any pivot tower, and acts as a new pivot point. This allows the outer spans to wrap another 165 degrees in either direction. If it reaches a barrier, the tower automatically stops.
Linear irrigation systems are similar to center pivot systems, but the towers move in a line, at the same speed and in the same direction. They’re usually powered by a diesel motor with a generator on the main drive tower. They’re especially useful on vegetable crops on rectangular fields up to 1.5 miles long.
Valley Irrigation, in Valley, Neb., manufactures the AutoPilot, the first computerized control panel with the ability to perform GPS calculations for linear irrigation. With the AutoPilot, growers can automate functions such as changing direction, stopping the machine and starting and stopping chemigation. The AutoPilot won the Irrigation Association’s New Product Contest in 2008.
The original, high-pressure sprinklers require more energy than other center pivot systems. They irrigate a wider radius and are effective on relatively uneven and sloping land. Medium, low-pressure and LEPA (low- energy precision application) sprinklers irrigate smaller areas, but are more efficient in terms of application uniformity, energy use and water loss through runoff, evaporation and wind drift. Medium and low-pressure sprinklers perform best on relatively flat land smaller than 100 acres.
LEPA systems use attachments, usually drop tubes, hanging a few feet above the ground to apply water directly, usually to alternate furrows. Most often, crops are planted in circular rows, with furrow diking to contain the water. LEPA systems minimize leaf wetting, are the most energy efficient, have the lowest evaporation rates and are the least affected by wind drift of these four systems. Because a relatively large amount of water is applied to relatively small surface areas, slopes should be less than 1 percent on most of the field and the land should be level. GPS can be used for land leveling.
These systems need to be monitored. A software monitoring program, FieldNET by Lindsay, was the top new agricultural product at the 2007 International Irrigation Show. It also won the 2007 AE50 Award from the American Society of Agricultural and Biological Engineers (ASABE). With FieldNET, growers can check the location, status and water usage of their system, view the pivot positions and make changes from any Internet connection or cell phone. They can also receive real-time text messages if there’s a problem. The program also keeps track of the system’s water usage.
“We have the technology to manage our water resources in agriculture,” Zoldoske says. “The bigger question in the future will be dependable supplies and water quality.”
The author is a freelance writer based in Altadena, Calif. Visit www.FarmingForumSite.com to discuss this article!