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Narrow Nitrogen Use
Nitrogen is one of agriculture’s essential building blocks. However, N in the wrong place can wreak havoc. In the Gulf of Mexico, a large hypoxic zone has formed primarily due to excess nutrients. In that zone, the amount of dissolved oxygen is too low for many aquatic species to survive, which has led to environmental concerns. The EPA’s Mississippi River/Gulf of Mexico Task Force set goals to reduce N loss by 45% in addition to other goals by 2035. For now, participation is voluntary.
Consumers and the general public are going to start asking how farmers are managing nutrients and reducing losses, says Jean Payne, Illinois fertilizer and chemical association president. Being able to answer that question is key.
“My biggest concern is that unless we remain very proactive on this issue, we may end up with regulations on fertilizer rates that will be one size fits all,” says Payne. “If we want to avoid that future and keep flexible rates, we have to be cognizant that we can’t go out there and put on rates that are too high, and think that nobody is going to notice. They will.”
Challenges for N Management
Back in 2012, Iowa, like other states, had a major drought. The drought resulted in lower-than-normal crop yields and a large amount of unused N in the soil. The tile lines remained dry until heavy spring rains caused leaching of nitrates in 2013, says Matt Helmers, Iowa State University professor.
“What could farmers do to reduce the peak we saw in nitrate concentration with in-field N management? Not as much as we would like,” says Helmers.
Some of the highest nitrate concentrations throughout 2013 were in soybean plots.
“That shows the high nitrate concentration wasn’t just from applied N that year. Instead, what came off was the N that wasn’t utilized in 2012,” he says. “It illustrates the challenge we have in N management.”
Fall N applications are quickly becoming the scapegoat. But should they be taking all the blame?
“One of the things we often hear is the timing of fall vs. spring N applications,” says Helmers. “People say if we just ban fall fertilizer, then there wouldn’t be any nitrate problems.”
He wishes it were that simple.
“From the data in Iowa, when fall N applications are made after soils are 50°F. and cooling and then when N applications are made in the spring, we see very little impact on nitrate concentration,” says Helmers. “From a best-management practice, we want N applications made as close to crop uptake as possible. That’s not going to solve the problem, however.”
Payne wants farmers to continue to have options.
“Our goal in the fertilizer industry is to keep the marketplace flexible, viable, and sustainable because we have to prove to the food companies that we are doing this the right way,” she says. “We want our U.S. farmers to have the first shot at the best forms of N for their crops.”
Do the Math
When Iowa’s nutrient-reduction strategy was formed, scientists examined different nitrate concentrations in field tile. Unfortunately, it’s not as straightforward as simply cutting N applications by 45%.
“As we increase N application rates, we see higher nitrate concentrations coming out of the tile,” explains Helmers.
But the elimination of N applications doesn’t equal zero.
For example, say a farmer starts with 150 pounds of N per acre. That’s ISU’s average N rate estimate for corn in a corn-bean rotation in Iowa based on sales data and manure numbers, says Helmers. This estimate could then be transferred to ISU’s Corn Nitrogen Rate Calculator. The calculator pegs the maximum return to N (MRTN) recommendation, which is about 135 pounds of N per acre. That results in only a 10% reduction in nitrate concentrations, says Helmers. However, savings would quickly rise in other situations.
If a producer is significantly overapplying N then adopts a lower rate, there would be a bigger impact on water quality and an increase in profitability for the farmer, says Helmers.
While you might expect there to be no N loss if no N application is made, that’s not the case. Data shows an N application rate of 0 pounds of N per acre in a corn-soybean rotation only has a 40% to 50% reduction in nitrates over an average application rate of 150 pounds of N.
Payne knows there’s always going to be a certain level of loss since nutrients are naturally present in soil, and additional N is added to get optimum yields. “I tell farmers that part of the 4R’s (right source, right rate, right time, right place) is social responsibility.”
“When there’s loss, it needs to be an acceptable level of loss,” she explains. “We have to prove that it’s something we can manage. We’ve been given a lot of leeway to determine these levels on our own. The protection of N is important.”
It will take a combination of practices. Those practices will include N management tools, accurate N rates, and both in-field and edge-of-field practices.
“One example scenario to reach the nitrate-N reduction targets of the Iowa Nutrient Reduction Strategy includes 60% of corn-soybean and continuous corn acres having cover crops (about 12.5 million acres), 27% of all agricultural land being treated with a wetland, and 60% of the tile-drained acres being treated with a bioreactor,” Helmers says.
That needs to happen throughout the Midwest to meet the goals of the task force.