Can grass revive dead zone in Gulf of Mexico?

More perennial bioenergy grasses throughout the Corn Belt would lead to a significant reduction in nitrogen moving down the Mississippi River and into the Gulf of Mexico, a new study shows.

Researchers used computer models to simulate how various levels of perennial grasses might affect the level of nutrient runoff from Midwestern farmland. The findings largely corroborate those of the Iowa Nutrient Reduction Strategy, a state plan designed to reduce nitrogen and phosphorus levels that contribute to the Gulf of Mexico’s hypoxic zone.

“This study adds to the portfolio of evidence that perennials can be a major part of the solution to nutrient runoff,” says Andy VanLoocke, assistant professor of agronomy at Iowa State University and coauthor of the study in the journal Global Change Biology Bioenergy. “This is a process that we’ll continue to refine, but it adds to the conversation.”

Nutrient runoff from the Mississippi River has contributed to a hypoxic zone in the Gulf of Mexico, or an area of water with low levels of dissolved oxygen. The low oxygen levels in the gulf “dead zone” make poor habitat for aquatic organisms, prompting scientists to look for ways to reduce nutrient runoff upstream.

Could tree microbiomes cut fertilizer on crops?

The study shows that perennials could reduce nitrogen runoff by more than 70 percent on farmland where they’re planted, a figure that closely mirrors the conclusions of the Nutrient Reduction Strategy which identified the planting of perennial crops, or plants that grow back every year, as a way to significantly reduce nitrogen runoff. Miscanthus and switchgrass are promising perennial options.

Researchers used computer models to account for climate and soils data across the Midwest, as well as historical maps of where corn and soybeans have been planted. The study analyzed different thresholds of crop replacement of current farmland between 5 percent and 40 percent. The study also examined different levels of fertilizer use for perennial grasses, since researchers are still experimenting with how best to fertilize perennials.

Perennial crops tend to start growing earlier in the spring than corn and soybeans. That longer growing season means they soak up more nitrogen, which keeps the nutrients from washing downstream, he said.

“The new research shows that a perennial market would have positive effects on water quality,” VanLoocke says. “With this model in place, we’ll be able to play with more scenarios and land-use practices. Our goal is to give as much information as possible about what’s possible with the landscape.”

Source: Iowa State University