Tale of the Tape: Drip Irrigation Tests in Field Crops
Does subsurface drip irrigation save water in field crops? The answer, it turns out, is complicated.
By Claire Vath | Photos By Brett Deering
In the 1800s, settlers staked claim to land in the Texas High Plains in part because of its access to one of the world’s largest sources of fresh water. That underground lake—known as the Ogallala Aquifer—stretches beneath eight states, from South Dakota down to Texas, and has helped turn the land it irrigates into some of the world’s most agriculturally productive.
But recent studies have shown that this vast resource is being depleted faster than previously thought. Texas’ High Plains Underground Water Conservation District reports an 8.8-foot drop in underground water levels over the past decade, with several counties seeing declines of more than 15 feet. And a recent Kansas State University study projects, if irrigation continues at current rates, a 69% depletion in the aquifer by 2060.
So what can be done to conserve those reserves? Many approaches, both new and old, are being researched, but one method of particular interest is subsurface drip irrigation (SDI).
A comprehensive USDA-ARS study in the late 1990s, when SDI use became wider-spread in North America, found yields of some crops were at or slightly above yields compared to when other irrigation methods were used, and it concluded that SDI “generally … provides a more efficient delivery system [for fruit and vegetable crops], but the realization of this increased application efficiency will depend upon how well the application is matched to the [crop’s] water and nutrient requirements.”
But could drip replace center-pivot irrigation in field crops to improve water conservation and increase yields?
Putting Drip to the Test
That’s exactly what Texas researchers and producers set out to determine. Rick Kellison is project manager of the Texas Alliance for Water Conservation (TAWC), a group of farmers, researchers, and state and local agencies working to develop water conservation strategies. In 2012, the TAWC worked with Eddie Teeter, a Lockney, Texas, producer—65 miles north of Lubbock—to test drip irrigation versus LEPA (low-energy precision application) on 240 acres of his property.
Local drip installer Dusty Cornelius worked with Kellison and Teeter to design and install an SDI system from irrigation company Netafim on the 240 acres of flat crop ground. Cornelius ran dripline 12 to 14 inches subsurface on conventional-tilled grain sorghum, cotton and corn, and he spaced the dripline on 40-inch centers.
They divided the acreage into six different fields. “Each field was replicated twice,” notes Kellison, explaining the producer planted the same types of crops at the same planting dates. Soil moisture was monitored using capacitance probes.
Three fields utilized drip. The other three used LEPA center pivots, outfitted with bubbler nozzles, “a sprinkler that delivers water straight to the soil in a narrow band, reducing the propensity for wind drift or evaporation,” Kellison explains.
According to Kellison, the amount of water used in SDI and LEPA was the same. At the trial’s conclusion, the corn yield from SDI was slightly higher, but, Kellison says, it was only “a half-bushel of a … difference in yield.”
Still Teeter liked the technology so much, he installed drip on additional acreage. His clay loam soils allow the moisture to get where it needs to go, and he believes it’s the most efficient way to irrigate in West Texas. “If you compare the drip with LEPA, which concentrates the water in one area, you still have so much evaporation, and you don’t have that with the drip.
The balance of what Teeter farms is on LEPA, with the corners of those fields planted to CRP grasses. “A pivot still only irrigates a circle and leaves out the four corners,” explains Craig Jones, local Netafim representative. “Drip can fill any shape field and cover it 100%.
“I’m not really saving on the amount of water used,” Teeter continues, “but I’m using it when it’s most effective. Yes, we are conserving water because there’s no evaporation but, in general, I’m able to water more acres with the water I have.”
Growing Pains with SDI
Plainview producer Ricky James farms 2,600 acres. A little more than a decade ago, James decided to give SDI a try on 40 rented acres. Back then, most SDI was put on 80-inch spacings. “But then we hit the 2011 drought, with only 7 inches of rain that year, and those 80-inch centers wrecked us,” he says. So the producer, who also sits on the Texas State Soil and Water Conservation Board, was left scrambling to add in the tape necessary for 40-inch centers. “Then the cost of that thing ran way up,” he says.
Cornelius concedes that cost does intimidate some producers. He estimates $1,700 to $2,200 an acre for installation on 40-inch centers. By way of comparison, a half-mile pivot system generally runs $70,000, or about $218 an acre.
In addition to price, there are some barriers that make drip less effective. Rolling terrain may present a challenge to establishing equal water pressure, and fields often need to be subdivided, which ups the cost. Rodent damage can be problematic; and, since the soil surface stays dry, SDI can affect seed germination.
Soil types also plays a role in water-use efficiency. “In the area I cover, the soil media is almost pure sand,” says Keith Sides, a civil engineer with NRCS who helps area producers utilize EQIP funding for irrigation. “SDI doesn’t work as well in that.”
But the biggest issue, James believes, is water scarcity itself. “When we had more water, it was under pressure and flowed more freely,” he says. “Now we really have to work to get [water] out of there, and as we pull up dregs, we’re getting water that’s maybe not as clean as before. That doesn’t much matter with center pivot, but it causes clogs in driptape emitters, and so we were having to add chemicals to clean out the tape.”
James no longer farms that SDI rental acreage. He did, however, see modest yield increases, but he finds claims of actual conservation a bit dubious, particularly during that 2011 drought. “Yield increase was there as long as you had water,” he adds. “But to make those yields, our water had to run continuously and we ended up using more.”
Impetus for Change
The one thing every producer, researcher and installer in the Texas Panhandle can tell you for certain: Water must be efficiently used … before it’s all gone.
But can SDI be that savior? Well … it all depends whom you ask and a variety of other factors. “I haven’t really seen any data that has shown a true potential for overall water savings,” says Sides of SDI use in Texas High Plains field crops. “There are a lot of parts to the total water savings [that] contribute to the overall water savings an individual will see.
“Over the last few years, we’ve converted a lot of center pivots from MESA to LEPA, LESA and SDI,” he adds. Those latter three methods, Sides continues, “are the best ways to help conserve water in the Texas High Plains.”
“There’s not cut-and-dried best management practices for any kind of irrigation,” Kellison adds of field crop observations. “Regardless of technology, we’re trying to introduce producers to management technologies that help utilize whatever delivery system they have in place.”