AMES, Iowa — Keeping nitrogen fertilizer on farm fields to
support optimum crop growth and out of streams and rivers is no simple formula.
“Think ‘writing a novel’ versus ‘writing a recipe,’” said
Matthew Helmers, associate professor of agricultural and biosystems engineering
at Iowa State University, where he is working with teams of scientists who are
field-testing promising strategies.
Whether present naturally in the soil or added during
chemical fertilizer application, nitrogen not taken up by crops can move with
water flowing through soil during rains and snow melt and into streams and
rivers where excess nitrogen can cause adverse health and ecological effects.
To address the issue of nitrogen and other farm nutrients
leaving farm fields, ISU scientists, including Helmers, worked with scientists
from the U.S. Department of Agriculture’s Agricultural Research Service and
Natural Resources Conservation Service, the Iowa Department of Agriculture and
Land Stewardship and the Iowa Department of Natural Resources on the Iowa
Nutrient Reduction Strategy Science Assessment, which was finalized in
The assessment highlighted that the state’s non-point source
nitrate reduction goal of 41 percent becomes attainable only when the problem
and the solutions are seen through a wide lens of interconnected ecological and
social systems, which present a multitude of opportunities to minimize loss,
“When we look at in-field and edge-of-field opportunities,
for example, we can start by doing the best job we can, putting the right amount
of nitrogen on as close as possible to when the crop needs it,” he said.
Helmers leads ISU’s Ag Water Management Research Group,
which is a multi-tiered effort to study and analyze the impact of agricultural
management practices on surface and subsurface drainage.
He also is a principal investigator on the field research
team of the Climate and Corn-based Cropping Systems Coordinated Agricultural
Project, also known as the Sustainable Corn Project.
It’s a 10-university research project in the Midwest, funded
by the USDA and led by Iowa State.
Team members are gathering and analyzing field trial data
from 35 field sites and thousands of farmers in eight Midwestern states in an
effort to create a suite of practices that make corn-based cropping systems more
resilient in response to climate change.
The project includes field trials of practices, such as
cover crops, which have the potential to reduce soil and nutrient losses under
saturated soil conditions.
Some of his colleagues on the Sustainable Corn team are
testing fertilizer application done with equipment that senses the nitrogen
needs of each plant and adjusts the rate of application accordingly.
Applying nitrogen fertilizer in the “right amount and at the
right time” is an essential step, but not enough, said Helmers, who sees
opportunities for reduction “with every input and output of the cropping
Results from field trials have made him a staunch supporter
of cover crops, which can hold nitrogen in the soil.
“The Science Assessment showed that cover crops can reduce
nitrate transport by approximately 31 percent. They are going to have to be a
major player, if we want to reduce nutrient loading to water bodies downstream
of row crops,” Helmers said.
Other opportunities to reduce nitrate transport can be seen
when studying what happens when water flows through and out of a cropping
“In some areas we may be able to manage or treat the outflow
from the subsurface drained landscape with practices like drainage water
management, subsurface drainage bioreactors, wetlands or the emerging practice
of saturated buffers,” the professor said.
To be successful and reduce unintended consequences, Helmers
said related social and economic systems also need to be included. The
Sustainable Corn research teams include social scientists, rural economists,
extension specialists, farmers and farm advisors in addition to crop, soil and
“We need to understand the agronomic side, the impacts of
climate change, pests and pathogens and all of the economics of the practices
we’re testing,” Helmers said.
“The cropping system has to be profitable, and we have to
help farmers understand how to manage it and work with them to implement and
figure out what works on their farm. Only this broad systems approach is going
to be effective in helping us solve our water quality problems.”