By Tom Dodge
Contributing Editor

Corn growers see up to 5 percent more yield in fields that have a controlled drainage system. (Progressive Farmer image by Rob Lagerstrom)

Farmers who push to break through yield barriers also are searching for ways to reduce nitrate and phosphorus loads in groundwater without inhibiting their drainage capacity. Some call this practice controlled drainage.

"Controlled drainage allows you to store water in the field, right where you need it," says Windom, Minn., producer Tony Thompson. "There's also the huge water-quality benefit. We can have a major impact on the amount of nutrients flowing downstream."

Thompson attended a seminar two years ago where he heard University of Minnesota scientist Gary Sands describe controlled drainage. He realized one of his quarter-sections was a perfect candidate for such a project.

The untiled quarter has heavy, rich loams. The piece, he says, holds a uniform 0.1 percent grade from end to end. Sands and his research colleagues at several Midwest universities say controlled drainage works best in fields with less than a 0.5 percent slope. That allows each control structure to manage the water table to within 1 or 2 feet of the surface for as many acres as possible -- 10 to 20 acres, depending on the field.

Thompson's field has no wetlands. But because the heavy soils retained moisture, they were damp and cold late into last spring, and most years it was the last land Thompson could plant, which hurt yield potential. He adds, "There were compaction problems and the crops often had poor utilization of nitrogen. Denitrification was evident in yellowed crops."

He knew if a controlled system could slow spring drainage, nitrate loading also would be reduced, enabling the crops to use more nitrogen. And if the new technology could hold more water in reserve during the season, his crops would have moisture to thrive through a dozen or so drought days later in the summer.

In the fall of 2007, per researchers' recommendations, a pattern tile was designed and installed at a 3.5-foot depth, with main lines running on the field grade and lateral lines running on the contour. Tiling contractor Andy Nickel of Mountain Lake, Minn., surveyed every 30 feet, instead of his typical 50 feet, due to lines adhering so closely to slope and contour.

The ridge-tilled field, on a corn/soybean rotation (with corn in 2009), was divided into three sections -- west, central and east -- for comparison purposes. The west section uses manual valves in the control units; the middle uses conventional corrugated rubber tile with no control units; and automated control units were installed in the east section.

While automated control units may cost more at the outset, Thompson points out the savings in time, labor and convenience over the manual-gate units. "The manual gates take significant time to manipulate, and that usually happens in the spring when the soil is very muddy and you must walk out to the gates. I have only one year of experience in management of the gates, but I anticipate that someday all of my gates will be automated."

While full-season results comparing automatic and manual control units versus the conventionally tiled middle section aren't yet available, the 2009 (March into August) results on Thompson's farm show impressive potential for the controlled systems. As of Aug. 1, the field had received 16.3 inches of rainfall. So far, 2.25 inches of rain have come through the control units, compared to 3.6 inches through the conventional tile.

As for the nitrogen loading, Thompson says, "From March to August, the controlled units have seen a loss of 3.75 to 4 pounds of nitrogen -- about half the amount that was lost in the conventionally tiled section."

Studies from other controlled-drainage sites around the United States have found reductions in annual nitrate load in drain flow to range from 15 to 75 percent, depending on location, soils, climate and cropping practices. Researchers do not recommend farmers use less nitrogen fertilizer with a controlled drainage system because the excess soluble nitrate still leaves the field by some route.

Researchers have seen average yield increases in North Carolina of 5 percent with controlled drainage. Computer modeling studies for Midwest conditions also indicate a benefit of up to 5 percent.

While Thompson has yet to determine his yield advantage with the controlled system, he fully expects one. "We'll know what we have when the combines roll."

Leonard Binstock of the Agricultural Drainage Management Coalition, one of the partnering groups on the Thompson project, offers a general cost/income analysis for drainage water management (DWM) systems.

• Additional cost for design and tile: $50 per acre

• DWM structure and installation: $1,100 each

• Total additional costs: $15,700, or $98.13 per acre

• 15-year amortized cost: $1,608.28 annually, or $10.05 per acre

(Does not take into account tax credits. Meanwhile, cost-share programs are being examined.)

• 3 percent yield increase = 4.8 bushels per acre x $4 = $19.20 minus cost ($10.05), net $9.15 per acre. Net payback on 160 acres = $1,464

• 5 percent yield increase = 8 bushels per acre x $4 = $32.00 minus cost ($10.05), net $21.95 per acre. Net payback on 160 acres = $3,512

(SK)

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