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Corn+Soybean Digest

Every Drop Is Precious

It costs more to buy and install and is management-intensive. Still, an irrigation system that can produce 220-260-bu. corn with at least 25% less water than even an efficient center pivot makes the extra expense and effort worth it for Eldon and Dale Schmidt.

The southwest Kansas corn, soybean and wheat producers grow about 30% of their 1,000 acres of corn “over” subsurface drip irrigation (SDI). And SDI is catching on in many parts of Kansas, Nebraska and other areas the way it has in West Texas cotton country where there are at least 250,000 acres of SDI production.

Eldon Schmidt has farmed near Copeland, KS, since the late 1950s. His son Dale grew up in the system that has virtually always counted on irrigation. After they saw continued inefficiencies in their aged furrow irrigation program, they began converting to center pivots. And in the mid-'90s, weaker irrigation wells indicated it was time to improve their watering capabilities even more.

From the first SDI system on, they've noticed considerable improvements in their ability to get more out of their water. SDI delivers a good corn crop with much less water.

“In a normal year, we must apply about 20 in. of water from a pivot to produce a normal corn crop of 220 bu.,” says Eldon. “With drip, it requires only 12-15 in. (about 25% less).”

In a typical SDI system, a main line (about a 12-in. diameter PVC) leads to the pump station. Water then moves past a backflow-prevention device and through an elaborate filter system, which prevents even minute particles of sand or soil from entering drip tubing or tape.

Water then flows through a submain line, usually 6-in. PVC. The submain runs adjacent to the field and is buried about 3 ft. deep. Connectors and a 1-in. diameter PVC hose feed from the submain to drip tape, which can range from ⅝ in. to 1⅜ in. in diameter.

The tape is buried 12-18 in. deep down a furrow. Emitters, or tiny holes from which water flows, are positioned every 12-24 in., depending on engineer recommendations.

Submains feed various zones, each of which feeds a different portion of a field. The Schmidts have 12-in. mainlines buried 3 ft. deep. They connect to 10-in. lines at the filtering stations, which lead to 6-in. submains.

“Every five feet we have connectors leading from the submain to 13/8-in. T-Tape tubing,” says Eldon, noting that the larger diameter tape facilitates longer runs up to one-half mile. “Emitters are 12 in. apart. Overall, they'll emit .22 gal./minute per 100 ft. of tape.”

SDI zones are about 15 acres each. Since corn is planted in 30-in., strip-tilled rows, one line of tape waters two rows in the 60-in. spacing system. And that is adequate, even in a dry year like 2006.

The Ogallala Aquifer feeds the Schmidts' irrigation wells, along with eight Great Plains states. But many irrigators are seeing their water table sink. And in dry years, some pumps can't supply enough for thirsty corn, soybeans or cotton. Some even run dry.

Limited irrigation is where SDI shines the most. Research at Kansas State University (KSU) and Texas A&M show the benefits of SDI over pivots. “Our studies show that when you have limited irrigation, it looks like SDI can stabilize yields at a little higher level (than pivots),” says Freddie Lamm, KSU agricultural engineer in Colby with 17 years of SDI research in northwest Kansas.

“We feel comfortable in saying we see a 25% water savings from the net irrigation requirements because we reduce the amount of drainage, soil water evaporation and rainfall runoff from the soil surface.

“It's not uncommon to see 250-270-bu. corn with SDI, and we have seen 300 bu.,” Lamm says. “Those yields are possible with center pivots and good management, but it may be easier said than done.”

Excessively dry conditions can hurt SDI capabilities. For example, if drip tape is buried 18 in. deep, the water may not be accessible to seedlings at planting. Help is needed from Mother Nature.

“But if you don't have that problem, SDI often looks better than a pivot later in a drought season because of reduced water stress,” says Lamm. “In 2003, a bad drought year, a lot of center pivots had erratic performance. We didn't see that same effect with drip irrigation.”

The Schmidts average about 18 in. of rainfall per year. “We need 28-30 in. to make a good corn crop,” says Eldon, adding that soybeans are also grown under SDI in the farm's rotation program. “The maximum amount of water we can apply is 24 in. (due to state law), and that may be cut back to 18 in.

“Our drip systems really help us in dry years. For '06, we will probably put down 16-18 in. of drip water, well above the 12-13 in. in a normal year.”

That compares to probably the 24-in. maximum for some of the pivot-irrigated fields.

A drawback to SDI is its cost, about $1,000-1,200 for a turnkey purchase and installation. There is also more management involved, with consistent monitoring of filtration, etc.

“Corn under pivots provides the same yields as full irrigation programs, but usually cannot produce what the drip does in limited water,” Eldon says. “Also, water changing is easier. Two-hundred rows of water can be changed in 10 minutes.”

The Schmidts feel their ability and desire to enhance their irrigation through SDI or more efficient pivot systems is an illustration of their attitudes toward farming.

“Remember, our Lord has entrusted the stewardship of his good earth to us,” says Eldon.

SDI Advantages

For irrigators serious about water use efficiency, using up-to-date low-pressure spray center-pivot systems or subsurface drip irrigation (SDI) is a must if optimum yields for corn, soybeans or cotton are expected. Large yields from limited water availability have been seen for corn and cotton with SDI. And many such systems have proven their durability and continue to provide consistent water distribution for 10, 15 or more years.

Freddie Lamm, Kansas State University agricultural engineer with 17 years' experience in SDI studies, says there are several advantages of using SDI as opposed to center-pivot systems:

Less evaporation — Using SDI can reduce soil water evaporation by as much as 10% based on early season watering before the canopy forms.

Irrigation runoff — SDI systems do not experience irrigation runoff, while even an efficient pivot with a 3 slope can see a 30% runoff.

Smaller irrigation events — SDI can efficiently apply smaller irrigation amounts than pivots. Irrigation can often be applied more closely to when the crop needs watering the most.

Hitting the root zone — SDI targets application to the crop root zone rather than totally relying on soil-water redistribution forces needed by pivots or furrow irrigation.

Improved infiltration — SDI may be able to “mine” water better during the growing season without yield reduction and can provide drier soil profiles at harvest to facilitate more water storage over winter.

There are various other benefits of using SDI, although there can be some disadvantages, too. While some groundwater can be clean, others can contain contaminants that must be filtered or treated before they run through drip tape to crops, says Lamm.

For more information on the pros and cons of SDI, go to

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