Iowa Farmer Today
08-19-06
High nutrient levels produce scramble to improve system
By Hannah Fletcher, Iowa Farmer Today
Drainage techniques were demonstrated July 12 at the Iowa State University
Southeast Iowa Research Farm. A volunteer installs a system at the field day.
CRAWFORDSVILLE -- Drainage tiles are an inevitable part of many Iowa farms,
but high nutrient concentrations in the state’s waterways has experts scrambling
to improve the system.
Despite improved nutrient-management efforts, nitrate concentration in many
water supplies remain high, says Greg McIsaac, University of Illinois ag engineer.
“In the past 5 to 10 years, farmers have been a lot more efficient in nitrogen
fertilizer application,” he says.
“You would expect less nitrogen fertilizer concentration (in the water), but we
actually haven’t seen that yet. That’s one of the things we are scratching our
heads about.”
Many researchers have looked to improved drainage to help the nitrate situation,
he says.
Researchers are trying to find a balance between improving crop production and
water quality.
A July field day at the Iowa State University Southeast Iowa Research Farm
demonstrated two techniques that showcase alternatives to conventional drainage.
They installed a shallow, close-spaced drainage system to compare with more
conventional deeper, wider drainage. The tile is installed at about 2.5 feet as
opposed to the more standard 4 feet.
Also, they will be monitoring a controlled-drainage system.
Both systems will flow into a constructed wetland, and nitrate flow will be
monitored for several years, says Greg Brenneman, Iowa State University
Extension field engineer in Southeast Iowa.
The goal of both systems is to see if nitrates can be reduced while maintaining
soil moisture ,which may be beneficial during dry times, he says.
“The concern with drainage flow is we do not really want to lose that water,”
Brenneman says.
The hope with shallow drainage is it will keep moisture longer in the soil profile.
The controlled drainage is made possible by a water-level control device installed
in the tile lines. The box-like structure contains 5- or 7-inch adjustable plates or
stop logs that dam the water and allow farmers to control the flow rate.
Farmers may take out the stop logs during harvest but put them back in after
harvest when they apply fertilizer and want to retain moisture.
“(The control device) is not going to change the nitrate concentration, but we are
looking to change the flow off the plot,” Brenneman says.
Regular tiles allow uncontrolled flow and heavy rainfall causes intense nitrate
saturation in the water source.
Agri Drain supplied the device for the Southeast Iowa project and has four test
sites in Iowa, says Charlie Schafer, president of Agri Drain, an Adair company in
Southwest Iowa.
The control device was developed in 1984 with yield and sub-surface irrigation
concerns in mind, he says.
“We recognized there was a yield benefit if you could manage outflow and hold
water. At that time, there was no talk about hypoxia in the Gulf,” Schafer says.
Later, Schafer realized the structure may benefit water quality and aid concerns
about nitrate levels and their contribution to the Gulf of Mexico’s hypoxia or loss
of oxygen that is harming aquatic life there.
“We all want to be responsible stewards for agriculture and the environment,”
Schafer says.
Brenneman said these practices are most suitable for flat land and can be
retrofitted to some existing drainage systems.
While researchers wait on data from Southeast Iowa’s project, other options
provide proven benefits to water in drainage areas.
Wetlands purify water leaving drainage tile outlets, says Matt Helmers, ISU
Extension ag engineer.
If 1 percent of the drainage area is wetland, there is a 40 percent reduction in
nitrates the wetland’s water. Within the wetland, grass borders perform
denitrification, Helmers says.
“That’s really what we are trying to do with this wetland, but it will certainly
provide some habitat and aesthetic value too,” Helmers told guests at the field
day.
Bioreactors are another denitrification option for drainage. A bioreactor is an
underground trench that runs water through a carbon source, such as wood
chips or corn cobs, to purify the water before releasing it.
Year-round practices, such as these, have the potential to make a bigger impact
on water quality, Helmers says.
A problem with drainages tiles is they drain water 12 months per year, but the
land is bare for a large portion of that time, he says.
“At least until the first part of June, we do not have much of a crop. Cover crops
could tie up some of the nitrates and control drainage,” he says.
Cover crops also may alleviate some of the nitrate infiltration in the water supply
because the later bare months are also heavy rainfall months, Helmers says.