Friday, March 1, 1996
filed under: Irrigation/Water Use
Steve Scott chuckles as he relates the story of how, on a bitterly cold winter morning, he walked into a local irrigation supply shop and heard another customer exclaim, “There’s some guy south of here who’s got his sprinkler running today! What the hell is he doing?”
“First of all, I thought, ‘Now what idiot would do that?,’ “ Scott quips. “And then I realized I was thinking of myself!”
The Burlington, Colo., sunflower, wheat, edible bean and corn producer concedes that more than one neighbor probably thought he’d been afflicted by dehydration of the brain when they saw water coming out of his LEPA drop-equipped center pivot in midwinter. But by applying water at that time of year, and coupling it with an extremely slow rate of application, Scott says he is maximizing not only the number of acres he can irrigate with his wells, but also the efficiency with which the water is applied.
“I don’t have what I’d call ‘irrigated’ ground,” relates the Kit Carson County producer. “Because all my wells are so small, I have ‘semi-irrigated’ ground.” By that, Scott means he utilizes towable sprinklers, each of which service a minimum of two center-pivot systems. “After I take off a crop, I’ll build up the moisture profile on that field,” he explains. “Then I’ll tow it to another field and build up that profile.”
The water-holding capacity of Scott’s silty clay loam soils is between 2.2 to 2.4 inches per foot. Gypsum blocks are installed in his fields to a four-foot depth as a moisture-measurement tool. “I’ll read my gyp blocks in the fall, compute how much water is there — which generally is not very much — and then decide on my watering plan,” he says.
Scott hit upon the idea of winter watering in the fall of 1992. Because of the limited pumping capacity of his wells, he wanted to build up the moisture profile on a harvested 130-acre wheat field which would be planted to corn the following spring. How could he make the most timely use of that well — and simultaneously maximize the percentage of applied water actually moving into the soil profile?
That’s when he hit upon the idea of turning on the sprinkler during winter — a time when evapotranspiration rates would be at their lowest level.
Then came the logistical questions: Can it work? What’s the best way to go about it?
Scott switched on the center pivot one day in January. It made a single circle — and became stuck. The alternating nighttime-freeze/ daytime-thaw nature of winter in eastern Colorado allowed the sprinkler to move around the field without difficulty at night, but it then would bog down during the day as the top few inches of wet soil unthawed.
Scott wanted to apply 7.5 inches of water across the field. To skirt the stuck-sprinkler dilemma, he decided to do it in a single pass, not in two or three. That meant reducing the sprinkler’s travel speed to an excruciatingly slow pace, which in turn required the installation of a customized secondary timer. (The dual timers since have been replaced by a new, more-accurate digital timer.)
The result? The end tower on Steve Scott’s sprinkler moves for a grand total of three seconds every three minutes. To make one circle while applying the 7.5 inches of water takes nearly 43 days. The formula looks like this: 430 gallons per minute x 60 minutes x 24 hours ÷ 27,154 (the number of gallons in an acre inch of water) = 22.8 acre inches pumped every 24 hours. Applying 7.5 inches across a 130-acre field calls for pumping a total of 975 inches of water. Divide that by 22.8, and the result is a time span of just under 43 days.
A center pivot that’s putting out water during a snowstorm is bound to draw attention, Scott concedes. “When a sprinkler is moving that slowly, especially when the temperature is below zero, you get all kinds of comments,” he muses. But the bottom line is that it works. “There’s little or no evaporation. I know there are days when I’m getting virtually 100-percent efficiency,” Scott states.
The Colorado grower’s sprinkler is equipped with bubble-mode nozzles, dropping the water from a height of 16 inches above the soil surface. As along as the water keeps running, he says, there’s no danger of freezeup — even at the very low rate of application. “And I’ve run it in sub-zero weather.”
One of the initial questions he had, Scott says, is whether water the would run off the frozen ground. That has not been the case, however. “The reason I don’t have runoff, I believe, is because our water temperature here typically is around 43 or 44 degrees,” he explains. “When the water comes out at that temperature and hits the ground, it warms up the soil enough to where it thaws slightly and the water can move into the profile.”
The only significant risk with winter-time irrigation, says Scott, would be a electrical power loss resulting in water freezing inside the center pivot. To date, however, that has not occurred.
While there’s no doubt in Steve Scott’s mind that his unorthodox watering program has allowed him to irrigate additional acres with maximum efficiency, perhaps the most-telling testimonial is the fact that additional irrigators in the Burlington area have adopted the practice as well. Somehow, when a series of center pivot in an area are creeping over one- or two-foot high snowdrifts, the concept becomes more acceptable to those who, a few years ago, may have wondered what kind of “idiot” would do something like that.