Efficient irrigation systems crucial in water management

Efficient irrigation systems crucial in water management.

Long-term drought drives push for irrigation efficiency

Nothing drives home the importance of improving irrigation efficiency like a four-year drought.

“Farmers are just trying to keep up,” said Caddo County, Oklahoma, Cooperative Extension Educator David Nowlin at the inaugural Oklahoma Irrigation Conference held recently in Fort Cobb. “With new research on moisture sensors, drop nozzles, subsurface drip irrigation, new apps for smartphones and Mesonet data, it’s a whole new world.”

The issue has been even more pressing in the Southwest for the past four years during one of the worst stretches of drought on record.

Nowlin said technology will play a crucial role in helping farmers maintain yield goals with increased pressure on water resources. The conference focused on innovations currently available to Southwest farmers.

 The Oklahoma Mesonet, for instance, a network of environmental monitoring stations, offers farmers a tool to help them get “the most benefit from the water. It helps determine ‘when and how much,’” said Al Sutherland, OSU Mesonet Agricultural Coordinator.

Sutherland explained how the system functions and how farmers can use the data to make better use of irrigation water resources.

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“Often in hot, dry summers, farmers simply turn on irrigation systems and let them run,” Sutherland said. “But with subsurface drip irrigation systems and during years with more rain, producers need to make decisions on when to irrigate.”

The Mesonet system uses factors such as soil type, temperature, humidity, wind speed and solar radiation to determine evapotranspiration rate. The system website (http://www.mesonet.org) also includes an irrigation planner that helps farmers determine when and how much water to apply to growing crops.

Sutherland said the program works well with a tablet or laptop computer but not as well on a smartphone.

Mesonet analyzes a set of variables to determine plant moisture needs—water demand potential, Sutherland said. The irrigation planner “is simple to use,” Sutherland said. Farmers have to provide pertinent information about their crops, including the particular crop, planting date, estimated days to maturity and other factors.

The planner develops a number that shows plant need and irrigation application amount compared to rainfall to create a water balance number, which is the trigger for irrigation. “The irrigation planner shows how much water a farmer needs to apply to the crop,” Sutherland said.

Values vary

Values vary with different crops, planting date and maturity date. “The water balance also assumes producers apply what’s necessary for irrigation. The weakness in the system is that it assumes the crop is well-watered and not under drought stress.”

Even with that caveat, Sutherland says Mesonet data provides producers a starting point to show how much the crop needs.

He said soil type also makes a difference since soils vary in water holding capacity.

The Oklahoma Mesonet consists of 120 automated stations covering Oklahoma with at least one station in each of Oklahoma's 77 counties.

Stations also include moisture sensors, typically at depth intervals of 4 inches, 16 inches, 24 inches and with a few at 32 inches.

On-farm moisture sensors offer farmers another useful, inexpensive tool to gauge crop water needs, says Oklahoma State University Extension water resources specialist, Saleh Taghvaeian.

“Moisture sensors help farmers schedule irrigation,” Taghvaeian said.

Improving irrigation efficiency does not always mean maximizing yields. “But proper irrigation scheduling can reduce water waste and also assure that we apply adequate water to make yield goals. How much and when to apply are crucial decisions.”

Some soil moisture sensor packages include individual sensors, hand-held readers and technology to transfer data to a compact disk and a computer. “It’s easy to do,” Taghvaeian said.

Soil type

Soil type is also an important factor with moisture sensors. “Sand, clay, and loam soils have different water holding capacity,” he added. Gravity moves water and density of the soil affects how rapidly it moves.

Taghvaeian said irrigation should try to maintain a balance between field capacity and “wilting point.”

Sensors also show where water is located in the soil profile.

Several types of moisture sensors are available, including electrical resistance sensors, which Taghvaeian has used in field research. He says individual sensors are relatively inexpensive, about $35 each. Handheld readers run about $280. Some packages, including sensors, readers USB adapters and software, cost a little less than $800.

“Collecting the data, transferring it to a CD, and using it to schedule irrigation is easy,” Taghvaeian said.

Irrigation system innovations also help farmers improve water use efficiency. McLain Pool, Eco-Drip Irrigation in Altus, Okla., said subsurface drip irrigation arguably offers the most efficient irrigation option, providing uniform water distribution as well as precision application of water, nutrients and chemicals. “Drip irrigation helps maximize efficiency,” he said.

Pool said drip irrigation efficiency varies with design. Some systems are laid out with tape installed under or between every other row, typically 80 inches apart. That’s less expensive to install than systems with tape installed under every row. But the narrower spacing improves potential for pre-watering to increase germination and is also more adaptable to closely spaced or broadcast crops such as wheat or alfalfa. He said design also should adapt to fluctuating water tables and to different crops included in rotation.

“Drip irrigation loses virtually no water to evaporation, so we reduce potential for crop stress.” He says labor and energy expenses are lower and the system should last from 25 to 30 years.

Farmers can do a better job of managing center pivot systems, too, said Wayne Krehbiel, Krehbiels Southwest Center Pivots.

Pumps

Pumps, he said, make a difference. “We can pump surface water with just a 15 horsepower pump, but with deep wells we need 75 horsepower.” He said pumping cost may run from $1 per acre to $12 to $15 per acre, “depending on how much water we have to lift. It costs money to lift water and it cost even more to pump out of the bottom of the well. It’s better to have two smaller wells than one big one.”

Krehbiel said proper nozzle configuration also improves water use efficiency. He said wobblers are good options for center pivot systems because they “put more water into the ground. It has more ‘soaking time.’”

He said end guns “are a poor way to irrigate crops. But when we want to irrigate an entire field, we use them. Systems are available to turn end guns on and off; we just don’t want to use them.”

Don Mooring and Ben Herschfeld, Valley Irrigation, explained how the combination of GPS and smartphone technology helps farmers manage irrigation systems. Marrying irrigation control options with smartphones, they said, provides remote control and system monitoring options.

“Producers still have to check pivots,” Mooring said, “but they can set a plan of attack and be more efficient.”

Herschfeld discussed options on several systems that may include alarm notifications by email, cell phone or text. With certain units, “producers can manage all types of irrigation systems remotely. The can change and control a number of irrigation functions remotely. They can access any computer, anytime, anywhere and have access through smartphones, tablets or computers.”

Nowlin said farmers may have to avail themselves of tools such as Mesonet, soil moisture sensors, smart phones, more efficient pivot irrigation and other innovations to maintain yield goals or in some cases just to save a crop. And water may become even more precious in the near future as demand and competition for the resource increases.

He said Oklahoma landowners currently have the right to the water under the land they own, but wonders, “How will water rights change in the future?”

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