Many tools needed to reduce nitrate loss
By KRISS NELSON
AMES – Iowa State University Extension and Outreach continued its annual Crop Advantage series of meetings being held across the state with an all-day event in Ames last week.
Matt Helmers, professor and ISU Extension agricultural engineer, presented on the impacts of 4R nutrient management on drainage water quality. Helmers focused his presentation on some findings of the university’s 30-year study on drainage water quality of nitrogen management as well as some tips to help possibly reduce nitrate loss.
The 4R nutrient management approach, according to information provided by ISU, is “Right source, Right rate, Right time and Right place – for managing nutrient additions from commercial fertilizer and organic materials.”
Helmers said there has been an increased interest in drainage water quality just within the last decade.
“Ten years ago, was there much interest or concern in drainage water quality issues form a nitrate standpoint?” he asked. “At least not as much. So why as the interest or concern risen?”
According to Helmers, the Des Moines Water Works lawsuit certainly enhanced the urgency those involved in ag look at drainage water quality, but there is something else that has brought that issue to the forefront of agricultural nutrient usage.
“Two years before that lawsuit, the state of Iowa released the Nutrient Reduction Strategy, which was in response to the Gulf of Mexico Hypoxia Task Force, which is calling for a 45 percent reduction in nitrogen and phosphorus floating down the Mississippi River,” he said.
Oftentimes, it is believed the reason we have nitrate problems is due to over-fertilization.
“I think there is still sometimes a misconception that the reason we have high nitrates is just because of excess fertilizer,” he said. “I tell the story a number of years ago; I was at a meeting in Washington, D.C., talking about some of this, and there was a soil scientist from a university on the east coast. His comment to me was, ‘If farmers in Iowa would put on the right amount of nitrogen at the right time, there would be no nitrate coming out of the tile line.’ This person was a fairly well-educated individual and still has the misunderstanding.”
“There are things we can do about it, but we have to understand some of the reasons we have the problem.”
Helmers said nitrates are produced through native soil organic matter.
“When soils warm up and are moist in the spring of the year, we get a portion that converts from the organic nitrogen pool into the nitrate form,” he said. “The rate of corn and soybean uptake doesn’t time up right with the organic nitrogen. The rain moves through the soil profile and takes the nitrates with it. Even without inputs we would have this problem.”
What could be a way to handle losing nitrates through the soil’s organic matter?
“Maybe if we had some land use changes – a little bit more living vegetation, living roots on the land a greater percentage of the year – we could reduce some of that,” he said.
Drainage water quality research
“Iowa’s the leader in many things related to agriculture and I believe we are also a leader in drainage water quality research and the amount of data we have been able to collect,” Helmers said. “We have been very fortunate with that.”
He added there are five drainage water quality research facilities throughout the state and 172 plots collecting about 4,000 water samples a year.
For example, a facility in Gilmore City was started in the late 1980s as part of the Groundwater Protection Act, looking at ag drainage well conditions.
The site in Gilmore City provides for an opportunity to see a lengthy time record. When they look at in-field nitrogen management, the biggest factor they have seen causing some of the biggest variations from year to year is weather.
“If you’re a farmer and you’re managing your field, what can you do to minimize the risk of those peaks of nitrate losses occurring?” asked Helmers.
One potential way would be through the use of cover crops.
Helmers said the growth producers get from cover crops might vary and the nitrate reduction will be closely related to how much cover crop biomass they can get.
“Through studies using winter cereal rye, as we look at cover crops, we have to look at where can we get the greatest growth. How do we seed it so we get good germination and growth?” asked Helmers. “Any way we give ourselves the best chance to get cover crop growth the better it is from a nitrate reduction standpoint.”
“You want to get enough cover crop growth to take up nitrates, but not enough to be detrimental to your cash crop,” he added. “So I think there is still a learning process we are looking at.”
Cover crops, Helmers said, could potentially also help with losing nitrates after fall-applied manure.
“We did an early fall manure application and went in shortly after injection of manure and drilled in cover crops,” he said. “We did see a risk of nitrate loss with an early fall application, but we certainly mitigated that and then some with the use of cover crops.”
Helmers gave an example of looking at the highest concentration of nitrates in the drainage water was in 2013. He said there were plots that were soybeans in 2013 and were corn the previous year in 2012.
“It had nothing to do with management of nitrogen in the 2013 crop year,” he said. “It had more to do with the carryover from the previous year.”
Possibly by using cover crops, Helmers said they may have been able to utilize some of the nitrogen carryover, keeping it from making its way to the water.
What about reducing nitrogen applications? Would that be enough to help meet the 45 percent reductions being called for?
Helmers said when you look at the maximum return to nitrogen (MRTN) and use the MRTN’s 135 pounds per acre of nitrogen, on average recommendation it would be about a 9 percent reduction in nitrate concentration statewide.
“So we do the best job we can. On average, it gets us a part of the way there – 9 percent – but not the whole way,” he said. “That’s where, even if we do the best job we can, we still have some nitrate problems.”
He added there could be some fields that are maybe using 190 to 200 pounds of nitrogen per acre moving back to 160 or even 150 pounds of nitrogen per acre. Could that not only help with potential nitrate loss, but also help improve profitability?
“If we don’t get much yield benefit going from 150 to 160, if we move that back, if we went backwards and we didn’t see much yield decline, or very little, it could improve profitability,” he said. “You could reduce your input costs maybe $30-$40 (an acre) in nitrogen application.”
What happens when there is no nitrogen put down?
“Nitrate concentration is still about 7 parts per million if we went from a 150 pounds per acre statewide average to no nitrogen application, it’s about a 40-50 percent reduction,” said Helmers. “So if we wanted to just solve it with nitrogen management we would have to go to no nitrogen application in the state of Iowa. That is the wrong way to solve the problem.”
Helmers thinks of it from a soil standpoint.
“Because if we are trying to grow corn and beans with no nitrogen inputs, overtime, we are going to export nitrogen in the grain out of the system and we’re not putting it back in the soil and, overtime, we will deplete our organic nitrogen pool, organic matter in the soil profile,” he said. “So to me, that would be a detrimental way to solve this problem. Rate is critical and we need to continue to look at that on individual operations.”
Rate and possibly different sources of nitrogen that are becoming available could also be options for reducing nitrogen losses.
“There are discussions about different sources of nitrogen,” he said. “We have looked at some of the poly-coated urea products – a time release fertilizer – to have that fertilizer available for uptake when the crop needs it.”
From a five year study at the Gilmore City research site, there were studies using the poly-coated urea as a broadcast preplant and incorporated into the soil.
“We do see it trending in the right direction with lower nitrate concentrations with the poly-coated urea product,” he said.
The best management practice, according to Helmers, would be to apply nitrogen as close to when the crop needs it, if at all possible,
But it is also important to know what the impacts might be.
“We studied this for eight years; fall nitrogen to corn to spring nitrogen to corn,” he said. “We did see a slightly higher nitrate concentration on the corn crop where there was fall nitrogen-applied.”
“But what we saw was that the subsequent soybean year, we saw higher nitrates when we applied nitrogen to the proceeding corn crop in the spring,” Helmers added. “So when you averaged over both phases, there really wasn’t much difference between the fall and the spring.”
He noted that this study was using the same nitrogen application rate in the fall as in the spring.
“Most likely, you put on a little higher rate in the fall,” he said. “If we went a little higher in the fall to lower in the spring, you would have some positive reduction in part of the rate effect.”
Edge of field practices
Nitrogen rate management, cover crops, timely applications and using different forms of nitrogen can be helpful, but Helmers said, those are not enough.
“All of these things get us part of the way there, but it can be a challenge to get us a 45 percent reduction,” he said. “In tiled-drained areas we are fortunate we have other practices we can use; edge of field practices.”
“We are doing the best job we are doing with nitrogen management in the field, but let’s intercept that tile line and remove a portion of the nitrates.”
Subsurface bioreactors could be beneficial in helping to control nitrates making their way downstream. Statewide, he added, to meet nitrogen reduction goals, 120,000 would be needed.
Currently, there are only about 50.
Saturated buffers, watersheds, wetlands and combination of those tools are other options.
“Both saturated buffers and bioreactors are on a field scale,” he said. “It’s important if we think of another edge of field practice, or edge of watershed, is a wetland. Maybe there’s a buffer around there so 3 to 4 percent of the whole watershed we are taking out of production that we put into a practice to remove nitrates.”
Several could benefit from this practice, he said.
“The landowners benefit. It is treating the water from their land,” he said. “I think everybody benefits. Upstream landowners benefit because the water from their land is being cleaned. Downstream citizens benefit because the water is cleaner. The waterfowl and wildlife can benefit as well. When we think of practices that have multiple benefits, I think things like these wetlands are very effective for that.”
“If we want to reach our nitrate reduction goals, we need all available practices,” Helmers added. “I think the science is pretty clear – we aren’t going to get our goals with just nitrogen management, but it has to start there and do the best job we can. We are still going to have to look at cropping practices and some of our edge of field practices like bioreactors, saturated buffers and wetlands.”
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