Controlled Drainage Practices Boost Yields, Stem Nutrient Runoff

Mother Nature always likes to have her own way but farmers can now have more say over how much water stays in or out of their fields, thanks to the use of controlled drainage technology.

The basic concept with controlled drainage is that a water-control structure attached to traditional tile can be used like a dam in farmers’ fields, says Crop-Tech agronomist Isaac Ferrie.

When gated with stacked baffles, the structures allow you to release water when you don’t want it in the field, like during planting or harvest, or to hold it back for a crop’s use when rainfall is scarce.

Crop-Tech’s ongoing research on two, 80-acre research fields in central Illinois, near Heyworth, for the past 17 years, has evaluated the effect tile spacing and depth have on yield as well as the number of days the field is fit and, therefore, available for planting, in-season nutrient applications and harvest. The study was expanded in 2013 to include controlled drainage. The two fields are managed and tiled identically, but one has water-control structures in it while the other does not.

Ferrie says that Crop-Tech found that using controlled drainage practices in the two fields contributed to corn yield increases.

University of Missouri Extension studies at the Greenly Research Center near Novelty, Mo., determined that a combination of controlled drainage and subirrigation boosts corn yields by 45% and soybean yields by 20% in claypan soils, reports Kelly Nelson, Extension agronomist, in a university-issued press release.

Addressing nutrient runoff. Beyond yield increases, one of the most significant benefits from water-control structures is they can help farmers stem the tide of nutrient runoff. Whenever water flows freely from fields, nitrogen (N) and phosphorus (P) naturally tend to go with it. Water-control structures help hold water back in the field, thereby keeping more nutrients in the field where they belong instead of contributing to pollution.

University of Missouri Extension found that the drainage water management system at its Novelty research center reduced nitrate losses by 70% and phosphorus losses by 80%.

Natural Resources Conservation Service (NRCS) funded demonstrations in several states last year showed that controlled drainage decreased nitrate losses by approximately 45% and the amount of water drained from fields by about 40%.

Ferrie says Crop-Tech also measured runoff reductions in 2016.

“From our 2016 data in the gated field, with tile spaced 120’ wide we saw close to a 40% reduction in the amount of N lost through a single large rain event,” Ferrie says.

The gate essentially held the water and nutrients in the field where corn plants could use them later in the season.

When heavy rains fall quickly on a field, Crop-Tech test results have shown that approximately 70% of the nutrient loss happened within the first 48 hours.  “Even though the gates allow water to flow over top in times of high flow to avoid saturating active root zones, the gates still significantly reduced the amount of water that left the field,” Ferrie says.

Keeping moisture available. During hot, parched periods of the growing season, large cracks can form in the ground. These large cracks can create paths of preferential flow, allowing rain water to move quickly through the soil and into ungated tile, providing less benefit to the growing plants. Gates can hold water back longer, giving it time to adequately soak into the soil profile.

“The idea with tile gates is to keep the water table root accessible, without saturating the root zone, retarding root growth and potentially causing nitrogen volatilization,” Ferrie notes.

“Keeping the water table too high early in the season will retard root growth as roots will not grow into saturated zones,” he adds. “This can be problematic later in the season if the water table lowers dramatically and the plant roots are confined to a shallow zone.”

There are a couple of ways to keep an eye on your water levels. One is you can buy soil moisture sensors that will tell you where the water level is and where root uptake is taking place.

Another, more low-tech option, is to estimate rooting depth based on crop height. Ferrie says corn roots can grow below the soil at a rate of 2” to 3” in depth, per leaf stage. As you estimate where the roots are located, you can then keep the water level just below them. As root growth progresses, gates can be pulled to match rooting depth throughout the season. 

Where to start. Ferrie says one of the most common questions farmers ask him is where and how to install the gate structures. “How is not a difficult undertaking; you just dig down to the tile and install the structure,” he notes.

The bigger challenge is determining whether your tile system can or should be gated, and where to install the gates. “For every 1’ to 2’ change in elevation you’ll need a water level control structure,” Ferrie says. “If you have a bunch of parallel runs that are all doing a 4’ drop, you may need a drainage control structure in each and every run and that could be cost prohibitive.”

On new tile installs, Ferrie recommends getting a professional involved to help design a plan that is tile-gate compatible, making it more practical to install gates later if warranted.

Prices can vary significantly for the gated structures and installation, as little as $500 and upwards to several thousand dollars.

As you evaluate making the investment, Ferrie says to consider that you may have services available that will help you cost-share the installation because of the environmental benefits they offer. He also encourages farmers to weigh the value of moisture availability to enhance crop growth during the summer.

“If you could hold back water that fell on your field in the winter, keep it through spring and early summer, and then use it in late June or July, that could result in a yield benefit as well as a reduction in lost nutrients. That could help cover the cost of the purchase and installment,” Ferrie says.