As soon as the Red River crested last May, North Dakota farmer Steve Miller opened the drainage outlet on a 108-acre tiled field, to dry out the soil.

In late June, Miller closed the outlet to hold moisture in the field.

And in July and August, he pumped water from the aquifer beneath the field back into the tile lines to irrigate the growing corn crop from below.

Miller’s “double duty” drainage and sub-irrigation system lets him control the water table in this field year-round. “I thought, if you can suck water out of the field, you should be able to pump it back in!” says the Fairmount, N.D. farmer, who grows corn, soybeans, wheat and sugar beets with his daughters, Alicia Holubok and Amanda Fisher.

The yield results have been encouraging, Fisher says. In 2013, which began with flooding and turned to drought, the sub-irrigated field produced 172 bushels per acre of corn following sugar beets, compared to 146 bushels in a comparable field in the same rotation, but without sub-irrigation. “It was one of our best fields in 2013,” she says. The crop received 7.8 inches per acre of water through the tile lines.

In on-farm, side-by-side comparisons from 2008 to 2010 — all good rainfall years — subsurface drainage and sub-irrigation boosted corn and soybean yields by 8% compared to conventional production, Fisher says.

Combining controlled drainage and subsurface irrigation offers “the best water-management in a wet or a dry year,” says Xinhua Jia, a North Dakota Extension agricultural engineer, who leads sub-irrigation research.

How it works

The Millers’ field is pattern-tiled with 4-inch laterals on 30-foot centers, placed 3-4 feet deep. Sixty-foot spacings would be sufficient for drainage alone at this site, Jia says, but closer spacings are needed for efficient sub-irrigation.

Drainage water flow is controlled by a sump-pump outlet, which is turned on in early spring and late fall to lower the water table, and shut off in summer and winter. The same sump-pump system pushes water back into the pipes in mid-season for subsurface irrigation. Water seeps out of the tile, permeating the soil through capillary action. Two pumps and wells are needed to achieve uniform water distribution on the field, which slopes 0.14%. The entire system cost about $2,000 per acre, Miller says.