Water from Drainage Ditch Bolsters Crop When Rain Lags in July/August
With just a small percentage of Red River Valley sugarbeet acreage being grown under any type of irrigation, Gerry Zimmerman already falls within a distinct minority. But it’s the irrigation method he employs that places the western Clay County, Minn., beet, corn and soybean producer in an even smaller group — a very, very small group.
Zimmerman, who farms northwest of Glyndon with his son, Ryan, has developed a subsurface irrigation system on four tile-drained fields as of 2015. While the primary purpose of tile drainage for the Zimmermans is similar to that of other producers — i.e., to drain excess water off their fields — they use those same tile lines to also pump water back into these fields later in the season when the crop can use it due to drier soil moisture conditions.
The water is pumped out of a large nearby drainage ditch (with a permit from the Minnesota Department of Natural Resources) that eventually discharges into the Buffalo River. Sandbags placed into the ditch bottom (with permission from the local watershed board) form a static dam about 4.5 feet high. The dam is built in May and removed in October each year.
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For one field, an old grain auger (with flighting removed) is set atop the ditch bank, with the water then pumped up through the auger and into a 10,000-gallon storage tank at the field head. The tank is never filled; a variable frequency drive and pressure transducer maintain its water level at between six and seven feet. “We don’t need that big a tank, but we need elevation to give us head. That’s what allows us to push water a half mile away,” Zimmerman explains. “The pump is rated at 780 gallons a minute, but we’ve always been down around 150 to 300 just because that’s the capacity of the ditch.”
At another site, further “upstream” on the ditch, a second auger empties directly into the line manifold at the top of that field, since not as much head pressure is required to push the water through those lines.
At both sites, control structures — each servicing 70-75 acres on three quarters and then three structures servicing the other quarter — help Zimmerman gauge and maintain the water table for those fields. As with any irrigated field, the “when to” of irrigating is when the crop shows signs of needing it. “We have to be the judge of what’s in the water table, and then irrigate or not irrigate accordingly,” Zimmerman relates. The control structures, as well as the crop’s visual appearance, help with the “when to” decision. (He may eventually replace the control structures with remote controlled valves that can be buried and farmed over. With the feeder pipes located in the field center, the valves will divert the water from one quarter to another as needed.)
“As to the ‘how much’ part, we’re sticking with about two inches. We pump two inches of water equivalent,” he says. That’s assuming Mother Nature has been sparse with rainfall in those key row-crop growth months of July and August and that there is available water to accomplish that amount of irrigation.
About 1,100 of the farm’s 2,000 acres are presently tiled, “and our intentions are to keep moving forward,” says Zimmerman, who owns (with a neighbor) and operates his own tile plow. Of the 1,100 tiled acres, 570 are set up for subirrigation as of 2015. “We’re grid tiling, so we’re on half-mile laterals,” he explains. Given their field grade, they may start out with a tile depth of two and a half to three feet, but end up being five to almost six feet by the time they get to the other end of the field. “That’s one question that remains: Will this still work for the deepest part? If we had a field with a natural grade of around 0.1%, that would be the ideal, because then we could put the tile in at about three feet the whole way,” Zimmerman says. “Owning my own equipment allows for continued modification of the systems as we learn what works and what does not work. For instance, we replaced a header pipe in the first field because the initial installation did not work as we thought it would.”
Had he been installing the tile for drainage only, Zimmerman says he would have used four-inch lines at a 55-foot spacing. However, to accommodate the addition of subirrigation capability, he went with three-inch-diameter lateral lines on a 40-foot spacing. (He narrowed it to 35 feet on their most recently tiled field.) The predominant soil type of the subirrigated fields is a Bearden silt loam.
Two of the four Zimmerman subirrigated fields are in sugarbeets as of 2015, with the other two in soybeans. Since the lines are quite deep, the crops wouldn’t benefit from early season irrigation; July and August are the months the system is used — unless it’s a year like 2011, which was so abnormally wet for most of the season that they didn’t pump on any water.
So has the subirrigation system, which the Zimmermans initially installed in 2010, paid off in terms of increased crop yields? Gerry certainly believes so, though results obviously vary from year to year. In 2012, for example, subirrigated corn yielded about 40 bushels more per acre than nearby non-irrigated corn. The next year, though, the advantage was just eight bushels an acre. With sugarbeets, “we have seen 35-ton beets when the rest (of the beet acreage) came in at about 24 tons,” he notes. However, that was not a good apples-to-apples comparison, he emphasizes, since the subirrigated field portion was planted a couple days earlier into better moisture and had a better plant stand.
From 2012 through 2014, researchers from North Dakota State University recorded data from one of the Zimmermans’ Morken Township fields under a SARE (Sustainable Agriculture Research & Education) grant. (Though the SARE project has ended, the NDSU group is continuing its data collection in 2015.) The project evaluated crop yield, water quality and water balance under undrained (UD), subsurface drained with free outlet (FD), subsurface drainage with controlled drainage structure (CD), and CD plus subsurface irrigation (SI). They found that the crop yields showed some promising improvement with the dual CD (controlled drainage structure) and SI (subirrigation) system setup, despite the extreme wet and drought conditions encountered during the three-year study period. Project coordinator Xinhua Jia, an associate professor in the NDSU Agricultural and Biosystems Engineering Department, reported that the crop yields with SI were in general 10% higher than those of the CD acreage.
For his part, Gerry Zimmerman knows there’s still a lot to learn about subsurface irrigation and its benefits for his historically dryland farm. But he believes the effort is paying off — and will do so even more as he refines his system. “It’s all about risk management,” he affirms. “This allows us to make use of a water resource, when needed due to lack of rainfall, that would otherwise go unused and just end up back in the river.”
— Don Lilleboe
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