Keeping nitrogen fertilizer on farm fields, to support optimum crop growth, and out of streams and rivers is no simple formula. It's complex.
"Think 'writing a novel' versus 'writing a recipe,' " said Matthew Helmers, an 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, using a systems approach.
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 USDA-ARS, USDA-NRCS, 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 last May.
The Science Assessment highlighted that the state's nonpoint 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, said Helmers.
"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," said Helmers.
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 system." 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," said Helmers.
Other opportunities to reduce nitrate transport can be seen when studying what happens when water flows through and out of a cropping system.
"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," said Helmers.
To be successful and reduce unintended consequences, Helmers says 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 climate scientists.
"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."
