By Tanner Ehmke
September 3, 2013 -- In the Upper Midwest, hundreds of thousands of additional acres have been placed into tile drainage over the past couple of years as the Corn Belt continues to expand. Unmanaged tile systems, though, have virtually no control over when and how much water and nutrients are removed. A smarter system using drainage water management puts farmers in the driver seat with better management over their water and nutrients.
Subsurface tile drainage is getting smarter as farmers continually seek out better ways to get more out of their most valuable inputs like nitrogen. But the investment isn’t just paying off with higher yields. Improved drainage systems are also reducing the amount of nitrogen leaking into rivers, streams, and groundwater.
For years, the purpose of burying drainage tiles below the soil surface was to shed water from the field as quickly as possible to expedite planting during a wet spring. Unmanaged tile systems, though, have virtually no control over when and how much water and nutrient is removed. A smarter system using drainage water management puts farmers in the driver seat with better management over their water and nutrients.
In a managed drainage system, a farmer can raise or lower the outlet level with adjustable riser boards in a water control structure located at the edge of the field.
“The farmer isn’t plugging the tile. He’s just forcing that water table closer to the surface with a control structure before the drainage exits from the system,” explains Matt Helmers, associate professor of agricultural engineering at Iowa State University.
The outlet in the structure typically is raised after harvest to reduce the amount of water delivered to a drainage ditch, then lowered a few weeks prior to planting to allow the field to drain, and then raised again after planting to store water through the growing season.
With this controlled system that limits the amount of water drained from the field, nutrient loads can also be reduced by as much as 45% or more, according to USDA’s Natural Resources Conservation Service (NRCS), which is promoting managed drainage as a way to improve water quality in the U.S.
This new approach to managing drainage is a significant break from the old way of draining excess water from fields, specifically in the Upper Midwest where tile drainage systems are most common, says Leonard Binstock, drainage consultant and executive director of the Agriculture Drainage Management Coalition.
“It’s not necessary to drain 24/7,” Binstock says in reference to the old tile drainage systems that lack a control structure. “That’s one thing that’s been going on for the last 100 years. You put the system in, and it basically drains 24/7.”
With a managed system that controls the water level in the field, drainage happens largely at the farmer’s discretion, he explains. That gives the farmer another tool to control water and nutrient use efficiency with bigger payoffs in higher crop yields.
“If you’re using a tile system and doing drainage water management with it—which means you’re not only shutting it off during the off-season, but you’re also controlling the water during the growing season—there can be a yield advantage,” Binstock explains. “We’ve seen some producers in any given year that will have maybe a 10 to 20% yield increase. Now, it’s not going to be constant, and it’s not going to happen every year. But, in a case like last year where we had dry conditions all across the Corn Belt, it made a huge difference in your yields.”
A field can see a one to two-inch increase of additional water to the soil’s profile with a managed system, which can be a significant yield enhancer in years of drought, Helmers says.
“Some people think that when we drain the soil, we’re taking all of the water out. Really, we’re only taking a very small portion of the water out of the soil. Maybe only about 5% is what we would call drainable porosity,” Helmers explains. “So most of the water is still in the soil and is plant-available water.”
Farmers also achieve better utilization of the nitrogen that the tile system otherwise would have carried off the field, Binstock adds. The increase in efficiency can lower the farmers’ overall fertility cost. If water outflows are reduced by 25 to 50%, he explains, nutrient outflows are going to drop that same percentage.
For that reason, NRCS has recently promoted drainage water management as a way to improve water quality, with specific focus on the Upper Midwest states where tile drainage and nitrogen loss are most extensive in the U.S. NRCS also points out other benefits that can result from farmers managing their drainage with a smarter tile system, such as reduced organic matter oxidation to retain soil productivity, reduced wind erosion, and more seasonal soil saturation or shallow flooding habitat for wildlife.