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Timely Surge Of Moisture

Friday, December 1, 1995
filed under: Irrigation/Water Use

Mile after mile of sage-pocked rangeland testify to Mother Nature’s typical stinginess when it comes to providing rainfall for western Wallace County, Kan. Be that as it may, Craig Sloan’s sunflower crop can count on at least two things in a dry year: (1) a “surge” of moisture during the bud stage and (2) another “surge” around the time of petal drop.

Sloan, who farms along the Kansas/Colorado border near Weskan, produces most of his sunflower on ridges under surface (furrow) irrigation employing a surge valve system. Surge irrigation is a method whereby water is applied to fields in alternate, automatically timed sets, as opposed to conventional continuous-flow application. A butterfly valve located in the center of two wings of gated pipe directs water to one side of center for a programmed period; then automatically switches over to water those rows on the other side for another programmed length of time. This back-and-forth process continues throughout the predetermined irrigation cycle.

Alternating the flow of water down field rows has several advantages, according to Sloan — all of them centering around improved watering efficiency.

Under conventional surface irrigation, getting sufficient water to the tail end of a field often means an excess of water at the upper end. That not only translates into higher pumping costs, but also more soil erosion near the upper end — particularly if it’s a fairly long field. Any surface irrigator can attest to the continual challenge of trying to achieve a happy medium.

With a surge system, watering cycles can be tailored to a particular field’s length, slope, shape and soils. Though he has the capacity to program for irrigation sets of up to 48 hours, a typical set for Sloan would be 12 hours. That set would encompass nine hours of “push” time (four and a half on each side of the valve) and three hours of “soak.” During the first cycle, water would likely flow for 40 minutes on each side; during the second, 55 minutes; and during the third cycle, for 75 minutes per side. “Then it cuts back for the last two or three cycles, shuts off and soaks,” Sloan explains. The cycles also can be customized on each side of the valve if the field has an irregular shape, with one side’s rows longer than the other’s.

While water is flowing down rows on one side of the valve, the soil surface in watered row portions on the other side becomes somewhat sealed. So later, when water is again flowing down those furrows, it flows faster over the already-watered portions, arrives more quickly at where it’s still dry — and then slows from that point onward.

By applying water more consistently across the field, Sloan simultaneously achieves a substantial reduction in the amount of tail water coming off the bottom of the field. He says the surge system also allows water to soak more effectively into the sides of furrows — a particularly important consideration for Sloan, since he waters only every other furrow.

So what are the water and dollar savings of surge versus conventional surface irrigation? Sloan believes that over the past five years, he’s probably averaged a 40-percent water savings on his surge-irrigated sunflower. In pumping costs alone, that savings translates into roughly $15 per acre per year (average of two waterings). Then there’s the savings in time. Sloan says his surge system allows him to basically double the number of acres he can irrigate per day compared to conventional “flood” irrigation — all the while being much more consistent in the amount of water applied across the entire field.

Usually rotating with corn, Sloan grows some sunflower under center-pivot irrigation and also fills in the corners of his center-pivot corn fields with dryland sunflower. All of his row crop ground is ridged — including the center-pivot fields.

When moving from corn into ’flowers, Sloan will leave the ridges as intact as possible prior to shredding the corn stalks in late winter or early spring. A burndown herbicide goes on about a month before planting sunflower. The northwestern Kansas producer seeds his ’flowers in 30-inch rows with a John Deere 7100 MaxEmerge equipped with Hawkins ridge cleaners which shave off the ridge top.

Ideally, says Sloan, the ridge cleaners are set at a depth where they “just clip off the crown of the corn root ball before the brace roots.” The actual shaving depth depends on how dry the ridge tops are, however, as well as weed populations on those tops. “We’ll go deeper in some years, pulling out more of the [corn] root balls and tossing them between the rows,” he explains.

Since Sloan doesn’t prewater his sunflower, those corn roots and other trash will lie between the rows until he “furrows up” when the ’flowers are about a foot tall. That process readies the corrugates for watering and rebuilds the ridges. An earlier cultivation with sweeps helps control late-spring weed flushes and also provides the opportunity to sidedress nitrogen as needed.

Sloan uses CornSol® attachments on his corn head to harvest his sunflower, leaving the stalks standing over winter. “Part of the ridge till formula for me is to catch that snow and let it percolate down, keeping the ridges as wet as possible,” he notes. A drag harrow breaks up the sunflower stalks the following spring, working the trash into the furrow. The ridges remain intact and, following a burndown herbicide treatment, are ready for the corn planter. “The sunflower ridges provide a beautiful mellow seedbed for the corn,” Sloan affirms.

Another advantage of the ridges, he points out, is the complete lack of equipment wheel tracks — hence compaction — within the seedbed. “We try to make the furrows and ridges in the same place every year,” he notes.

Sloan, who produced sugarbeets under surface irrigation before that industry vacated his area in the mid-1980s, says sunflower has evolved into an excellent rotational crop with his corn. A big reason why is its ability to produce competitive yields with less than half the moisture required by the corn crop.

“I’ve found that irrigated ’flowers — and dryland ones, too, if we get the right rainfall — have a lot less overhead than corn and often compete with the [irrigated] corn on a profit basis,” the western Kansas producer reports. And if sunflower yields are above average, “I can actually beat my net return on corn.”
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