Drip by Drip

October 28, 2009 07:00 PM

Subsurface drip irrigation is used on less than 1% of Kansas' irrigated land. Yet, it still holds plenty of promise, says Freddie Lamm, research ag engineer at Kansas State University's Northwest Research-Extension Center in Colby, Kan.
The first drip system Lamm began testing will mark its 20th year in the field in 2009, which he says is an
important milestone. "If the drip system can last that long in the field, we can amortize the cost and it actually looks pretty attractive,” Lamm says.
Subsurface drip irrigation can water small and odd-shaped fields and entire square or rectangular fields, not leaving out corners as center pivots do. Average installation cost for subsurface drip irrigation runs about $1,200 per acre, Lamm says. That compares to $588 per acre for center pivot systems.
Subsurface drip irrigation makes up economic ground by reducing pumping cost by 25% and not leaving dryland corners, Lamm says. However, it requires close management.
"They need consistent monitoring with flow rates and pressure gauges to make sure they're performing adequately. Clogging is the main failure problem. You need to provide filtration and water treatment for clogging. Rodents and tillage incidents can increase the possibility of leaks and decreased pressure,” Lamm says.
"By using high-quality groundwater and being consistent with maintenance, you can do well with subsurface drip. It does need good management. If pressure is decreasing and flow is increasing, you've got a leak,” Lamm says.
Rodent damage concerns mean few farmers so far use subsurface drip irrigation in conservation-tillage fields.
Lamm sinks most of his subsurface drip irrigation systems 16" to 18" into the soil to avoid problems with tillage implements. Many farmers choose to run their lines only about 12" deep to help with seed germination.
"At 16" to 18" deep, it's sometimes hard to consistently get water to come to the soil surface,” Lamm says.
Subsurface drip irrigation can reduce nonbeneficial water use (runoff, deep drainage and evaporation) and result in 25% less irrigation water use than center pivots to produce a corn crop, he says.
Drip Draws Attention
Beyond the Great Plains, subsurface drip irrigation continues to gain an increasing amount of interest. "It fits where land and water are the limiting factors, in odd-shaped fields, under power lines. Some farmers are even converting their fields with pivots to subsurface drip,” says Michael Dowgert, director of marketing for Netafim, based in Fresno, Calif.
Though the national percentage of acreage with subsurface drip irrigation is still tiny compared with center pivot irrigation, farmers in some areas, such as West Texas' cotton fields, are installing it fairly quickly.
"If you can put it on cotton, you can put it on corn. The economics are not a lot different,” Dowgert explains. "With corn, we're just beginning to learn how to fertilize subsurface drip irrigation fields right. It will help get the most out of water. That's why I think what's taking place in West Texas, where there's a water shortage problem, is so cool.”
That's the big reason for the growing interest in subsurface drip in the Great Plains, where groundwater gets more difficult and expensive to pull to the surface each year.
Oddly enough, some observers worry that more efficient systems might result in greater consumptive water use.
"There is some thinking that increased efficiency increases consumptive use. It's counterintuitive,” says Wayne Bossert, manager of Northwest Kansas Groundwater Management District No. 4. He monitors 3,540 irrigation wells in his district. Few new wells have been drilled since the mid-1980s.
"The danger is that we pump less water per acre but actually use more if everybody starts doing it. When we monitor the Ogallala, we see a subtle increase in consumptive use almost every time. If we promote reduced consumptive use, we've got to reduce the acres,” Bossert says.
Lamm understand the argument but still thinks drip has its place. "No irrigation system saves water. Management saves water. Within economic reason, it makes sense to get the most bang for your buck,” he says. 

You can e-mail Charles Johnson at cjohnson@farmjournal.com.

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