Kevin Larson is going underground to make better use of water. He's testing a subsurface drip irrigation system on row crops at the Plainsman Research Center in Walsh. "I've never seen such consistency and high yields in the plots," he says, "and it's with less water." Larson is testing this irrigation method on corn, grain sorghum, sunflowers, and, in the future, soybeans. Drip irrigation isn't just a pipe dream, either, since a new government aid program makes it attractive for farmers to invest in the water-efficient system.
"Subsurface drip irrigation is the next quantum leap in irrigation efficiency," says Larson. Since water never reaches the soil surface in a subsurface drip irrigation system, there is almost no evaporation loss. This compares to 50 percent efficiency for furrow irrigation, 75 percent for sprinkler, and a maximum of 90 percent for a "low-energy precision application" sprinkler systems.
Subsurface drip irrigation has a network of perforated tubing, called drip lines, buried one foot deep and fi ve feet apart. Each drip line runs between two rows of crop. The drip lines are divided into zones that are supplied well water. Similar to a home sprinkler system, a controller and a system of valves turns the supply of water on and off to each zone on a programmed schedule.
For more than a decade, Larson has been experimenting with limited irrigation methods with furrow and sprinkler systems to make even better use of water. Limited irrigation is used to create an economic balance between the costs of irrigating versus the reduction of crop yield if less water is applied. Farmers have a pretty good idea of how much water is necessary to get maximum yield from their fields. However, with high energy costs, Larson has found it may be more profitable to pump less water than required on a field. The loss in crop yield is offset by the cost of the water. Now Larson is applying limited irrigation with drip as well. So far, he thinks the crops respond well with limited irrigation applied with drip.
Besides efficient use of water, drip offers several other benefits. With subsurface drip irrigation the entire field is irrigated. Center pivot irrigation systems do not water the corners of the field–about 20 percent of the crop area. Also, because subsurface drip irrigation waters the plants up to four times per day, they are less stressed. Crops under a center pivot only may be irrigated once a week. Less surface water also means potentially less weed germination. It's also easier to deal with any weeds, since the farmer can run equipment in the field at any time because it never gets muddy from watering.
An additional benefit is that drip systems promote uniform yield. "Last year, my grain sorghum was as uniform as I have ever seen any crop," Larson says. "I have a yield monitor on my combine, and from one end of the field to the other, it didn't vary more than two bushels, whereas normally the yield could vary by 10 to 15 bushels. Yield uniformity suggests that a probable limiting factor, even water distribution, was overcome."
Typically, the advantage of drip irrigation is only economically viable for cash crops, such as vegetables, and is unaffordable for row crop farmers. However, the federal government is digging deep to help farmers go underground and make better use of water. A USDA aid program covers up to 75 percent of the cost of a subsurface drip irrigation system. "With this funding, it's cheaper to put in subsurface drip than to convert from furrow to center pivot irrigation system.," says Larson. The Plainsman Research Center system was purchased with funds from the Colorado Agricultural Experiment Station.
Subsurface drip irrigation isn't without its challenges, though. A good filtration system is a key component of a drip irrigation system. Any particulates in the water will clog the emitters, the small holes in the drip line. Draining the system for winter is important to prevent freezing. Larson also has had rodents gnawing at his drip line, causing leaks. Fortunately, leaks are easy to detect, locate, and repair.
This year's drought made subsurface irrigation unusually challenging for Larson. There wasn't enough moisture in the soil to germinate his seeds. The drip irrigation system isn't designed to reach all the way to the surface where the seeds are located. Larson was able to get his crops started since he still had the capacity to flood irrigate with gated pipe to get the crops started. In normal years, this wouldn't be necessary; however, in exceptionally dry years, some redundancy is in order.
The final hazard to subsurface drip irrigation is boredom, Larson jokes. "It's the most boring technology ever conceived. You can't even tell you're irrigating. I suppose if one of the trade-offs for high economic yield is boredom, then that's a small price to pay."