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Tale of the (Buried) Tape

Tuesday, February 15, 2005
filed under: Irrigation/Water Use

Were there a contest to determine the nation¹s most beautiful sunflower field in 2004, Mike Harkness’ southwestern Kansas entry would be at least a finalist, and perhaps the winner. Motorists traveling along U.S. Highway 83 in early September were treated to a memorable view at the hamlet of Friend, located midway between Scott City and Garden City. There, with concrete elevator bins looming in the background, posed an 88-acre blooming sunflower field made to order for a postcard.

Its uniform beauty notwithstanding, what made this field so special was the fact that it was grown under subsurface drip irrigation (SDI). SDI acreage in the High Plains is very small compared to sprinkler and surface (flood) irrigation. Likewise, the acreage of High Plains SDI sunflower is miniscule compared to other regional crops (mainly corn) grown under subsurface drip.

As the accompanying article explains, subsurface drip irrigation systems utilize buried polyethlene tubes (driplines) to carry water and nutrients directly to the plant root zone. Properly designed and managed, SDI systems commonly maintain (or improve) crop yields compared to other irrigation methods while simultaneously saving on water, energy, fertilizer and even herbicides.

All that proved true for Mike Harkness’ 2004 SDI sunflower field. Those 88 acres averaged 2,192 pounds, with 41% oil and a test weight of 30.1 pounds. Not bad for low-input double-cropped Oflowers planted after wheat on July 12 and harvested in early December.

Harkness - a predominantly dryland no-till producer - didn¹t have sunflower in mind when deciding to install a subsurface drip system in this field in the fall of 1999. It had been under flood irrigation; but with a well capacity of just 200 gallons per minute, that was not an efficient or cost-effective approach. Installing a sprinkler system wasn’t a good option, either, since Harkness’ legal water rights were restricted to that 88-acre rectangular parcel - hardly the optimal use of a 120-acre center pivot.

“So it was either subsurface drip or no irrigation at all,” he recounts. This extremely flat northwestern Finney County field was ideally suited for SDI. Elevation differences along the quarter-mile dripline run total a mere four inches, meaning Harkness did not need to install higher-cost pressure-compensating lines. He spent less than $725 per acre to install his SDI system, which would be on the low end of the cost spectrum. That’s less than what it would have cost to go with a center pivot that could have watered only about half its 120-acre range due to his restricted water rights situation and field shape.

Like any properly designed SDI system, Harkness’ package includes a pump station (he draws from his well with an electric submersible pump), a flow meter, backflow prevention device, chemical injector (for fertilizers and pesticides) and filtration system. The water flows through the main line into submains; then into the dripline laterals and finally to flushlines at the tail end of the system.

Filtration is extremely important - the ‘heart of the system,’ Harkness emphasizes. The filters remove suspended particles from the water to prevent clogging of emitters (the small holes in the driplines through which water moves out into the soil). His filters are very fine, with an opening size of 400 mesh (0.0015 inch). He wouldn’t need that fine a mesh if sand was his only concern; but the presence of iron bacteria in his water

requires the more-intense filtration.

The driplines in Harkness’ field - spaced 60 inches apart - lie at a 15-inch depth. Typical life-span of buried driplines is 12-15 years, depending on water quality and the filtration system’s efficiency. And, there are a couple additional threats to the lines as well.

One is rodents and other burrowing animals. Ground squirrels like to nest next to the driplines, and Harkness has on several occasions replaced short sections of line that had been chewed on by the squirrels. Mice and other small rodents can be troublesome as well.

The other threat is crop root hairs entering emitters and causing clogging. That hasn’t been a common problem with adequately watered seasonal crops like wheat or corn; but it is more worrisome with a perennial like alfalfa. Keeping the ground well watered so the plants aren’t rooting deeply in search of moisture certainly helps, as do the use of acidic fertilizers and/or preventive acid treatments.

Though he hasn’t encountered the problem with other crops, concern over root intrusion made Harkness hesitate over planting sunflower in his SDI field. Given its reputation as an aggressive, deep-rooting crop, he worried about sunflower root hairs getting into and plugging emitters. But he felt he could minimize the threat by filling the subsoil moisture profile before planting the sunflower.

Complicating the issue was his planting direction. Though Harkness’ driplines run north-south, he plants east-west; so the sunflower rows ran perpendicular to, rather than parallel with, the lines. The main reason for his planting direction is logistical: 11 sets of above-ground zone valves line the north side of the field, with protruding flush valves spaced along the south side. So it’s much easier to plant and harvest in an east-west direction.

Until 2004, Harkness had never grown anything but corn and winter wheat on his SDI field. He’d originally intended to plant corn following the wheat this past year, but rains delayed the wheat harvest. By the time the wheat was finally combined it was too late for corn.

On July 12, a day after applying a burndown herbicide (Roundup at the one-quart rate), Harkness planted sunflower (Mycogen 8377NS) no-till into the wheat stubble in 30-inch rows. Seed drop was 23,000 per acre, and he also put down about 40 pounds of nitrogen at planting. (He’s able to inject nitrogen through his driplines but opted not to do so with the sunflower.)

On August 13 Harkness applied six ounces of Select for control of volunteer wheat and other grassy weeds. Other than irrigation water, those were his total crop inputs until harvest.

He had watered the wheat up to the stiff dough stage and also received nearly three inches of rain during wheat harvest. So Harkness was confident he had plenty of topsoil moisture to get the ‘flowers off and running. That proved to be the case, as germination and emergence were excellent. He restarted the irrigation system around August 1 and kept it running through seed fill (latter September).

Harkness left the sunflower stalks standing following his early December harvest in the hope of trapping winter snows. As of mid-January, however, snowfall in the area had totaled less than three inches. He’ll plant corn on the field this spring, so will either plant the corn between the old sunflower rows or shred the stalks prior to seeding.

Mike Harkness is very high on subsurface drip irrigation’s watering efficiency (90% or greater) and the concurrent savings in water use and pumping costs compared to other forms of irrigation. One drawback to SDI, though, is the inability to ‘water up’ a field to aid germination and early crop growth. Since SDI is focused on the root zone, water from driplines buried 15 inches deep will not reach the top several inches of soil.

For that, Harkness must rely upon natural precipitation. As long as the crop gets off and running, though, there’s a plus side to dry topsoil: fewer weeds. Harkness has noticed a definite decline in weed pressure on his SDI fields during recent drought years due to fewer weed seeds germinating in that dry topsoil layer.

Will he plant sunflower again on his subsurface drip irrigation field, given his very positive experience in 2004?

Assuming he doesn’t notice any emitter-plugging problems from this past year’s ‘flowers, the odds are quite good. He may go with double cropping again; or, if he has a late spring where he can’t plant no-till corn, he would go with a full-season sunflower crop. Soybeans are not feasible, due to the highly chlorotic nature of his SDI field. “So my options are corn, wheat, and sunflower.”

But while he anticipates at least a three-year rotation with sunflower on his own SDI field, that doesn¹t mean Mike Harkness will step away entirely from the crop those other two years. His father, Bob, has three small fields totaling 110 acres under subsurface drip irrigation. “Dad has enough water where sunflower on a regular basis shouldn¹t be a problem (in terms of emitter-clogging roots),” Harkness notes.

So even if travelers on Highway 83 don’t see a beautiful blooming field near Friend in 2005, that doesn¹t mean there won¹t be one nearby! -- Don Lilleboe

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