Scientists promote strategies to keep nitrates out of water systems

Caitlin Deaver

ISU scientists have come together to pinpoint strategies to keep nitrates on fields and out of bodies of water.

The main problem focuses on corn and soybeans. Corn, especially, takes up nitrates for optimum growth, increasing the chance of nitrates entering a nearby body of water through various ways.

Matthew Helmers, associate professor agricultural and biosystems engineering, has been assisting scientists with research on effective ways of keeping nitrates in the fields and out of the water.

He said the research team — which includes other ISU scientists, the Iowa Department of Agriculture and Land Stewardship, the U.S. Department of Agriculture and the Iowa Department of Natural Resources — has seen many cases of high nitrate levels in Iowa waters.

Nitrates in water have harmful health and ecological effects. Before consumption, the water is treated to prevent those adverse effects.

According to the newsletter Reducing Nutrient Loss: Science Shows What Works, an assessment of effective nutrient reduction practices, there are three main categories for strategic reduction practices. They include nitrogen management, land use and edge-of-field.

Many of the strategies in the main categories do not only have the potential to reduce nitrate levels, but they also offer benefits like increasing wildlife habitats.

Management practices involve the application rate of nitrates, the timing of nitrate applications, methods of applying nitrates and the use of cover crops.

Some of these practices include applying fertilizers with nitrates during corn emergence, planting a late summer or early fall seeded cover crop, calculating the potential loss of nitrates and using a nitrification inhibitor to increase corn yields and decrease nitrate losses.

Land use practices include perennial, or returning, energy crops, extended crop rotations, grazed pastures and land retirement.

By extending crop rotations, not as much nitrogen needs to be applied, and therefore, less nitrogen will be lost. This would decrease the production of corn and soybeans while increasing the production of alfalfa, which supports an increase in livestock production. Soil quality would also be improved with extended crop rotations.

By replacing row crops with energy crops, the loss of nitrates can be reduced because of a decrease in erosion, surface runoff and leaching, otherwise known as drainage. Energy crops promote an increase in wildlife habitats, too, and have local and regional markets for perennial biomass crops that act as a source for energy or fuel production.

Edge-of-field practices involve drainage water management, wetlands, bioreactors, buffers and sediment control.

The creation of wetlands lowers the chance of nitrates entering water, as the nutrient is released as a gas to aid water quality. Wetlands also offer other benefits, such as providing habitats.

Subsurface drainage bioreactors help treat the outflow from subsurface drained landscapes, showing potential for nitrate reduction.

Buffers are designed to settle sediment and potential sediment nitrates, along with retain nitrates. They also help stabilize stream banks and reduce flood impacts.

Helmers said reducing the impact of nitrates is complex and will involve multiple strategies to be overall effective.

These practices may not be so easy to integrate for the average Iowan farmer, though.

“One of the main challenges is that, in almost all cases, there is a cost [to reducing nitrates in waterways],” Helmers said. “The extra cost is applied because water with nitrates present must be treated. Some places do not have nitrate removal facilities.”

Another challenge involves the change in management by implementing new research and reduction strategies to the average person. This includes programs like the Water Quality Initiative brought about by the National Resource Conservation Service that help farmers or the Iowa Department of Natural Resource’s platform called the Iowa Conservation Reserve Enhancement Program, which helps farmers develop wetlands.

“Nitrate exports certainly are a large concern,” Helmers said. “However, we have a lot of tools to utilize, like having more education about [nitrate reduction] practices and learning how to work with state-holders.”