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Successful field day offers details on nutrient management, cover crops

Article cover photo
ISA field agronomists Brett McArtor and Anthony Martin share results from ISA on-farm trials as well as details on the Iowa Nutrient Reduction Strategy at the 4R field day held on Darin Stolte's farm near Olin. (Photo: Carol Brown/Iowa Soybean Association)

By Carol Brown, ISA communications specialist

The 4Rs of nutrient stewardship took center stage at a recent field day near Olin, in northeast Iowa.  The Iowa Soybean Association’s (ISA) On-Farm Network® sponsored the event where nearly 100 attendees learned about the 4Rs, cover crops, and conservation drainage systems.

Host farmer Darin Stolte, a fourth-generation farmer, shared how he has incorporated the 4Rs of nutrient stewardship — right source, right rate, right time and right place ­— since 2012 into his corn and soybean production. He received 4R Advocate Award from The Fertilizer Institute in 2016, the only Iowan to receive the honor so far, Stolte said. 

“An accurate soil sampling system is the basis of building a 4R program,” Stolte said. “We test our soils consistently and often to learn how it is responding. It also lets me know how and where to incorporate macro- and micro-nutrients.”

He provided the recipe for his fertilizer blend, which included sulfate of potash, ammonium sulfate, MAP (monoammonium phosphate), encapsulated urea, calcium sulfate and more. Stolte also walked through his in-season nutrient application methods.

Sulfur is an overlooked mineral for soil, Stolte said. He incorporates sulfur into his fertilizer application to reap the benefits including improved nitrogen utilization, soil structure as well as lowering the soil pH. Sulfur in the soil makes better humus, according to Stolte. “For every pound of sulfur available to the soil microbes, 100 pounds of humus is retained,” he said.

In addition to using best management practices for fertilizer application, Stolte made the switch to strip-tillage in 2016, starting with a demonstration plot then committed all his acres to the practice the following year. He has embraced cover crops and added contour strips, grassed waterways and streambank buffers to his farmland.

He recommended that farmers really get to know their fields, soil types and to address any drainage issues before investing in fertilizer. “Knowing your soils’ and plants’ needs affects the prescription fertilizer application and soil fertility,” he said.

On-farm field trials inform

ISA field agronomists Anthony Martin and Brett McArtor discussed results from the On-Farm Network’s replicated strip trials that focused on profitable nutrient management. The agronomists reminded attendees that although ISA conducts trials on both corn and soybeans, corn studies are not supported by the soybean checkoff, rather by other industry partners.

“Iowa soybean farmers are also corn farmers. We try to offer the same unbiased research for both crops,” Martin said.

“In our field trials, it is showing that variable rate nitrogen application can be profitable, especially when your fields aren’t uniform,” said Martin. “Nitrogen response is different for every field and within fields as well.”

Results from the trials conducted across the state showed when comparing variable-rate to consistent-rate application, yield differences were minimal, but the nitrogen usage lowered by as much as 40 pounds per acre. Because of the reduced nitrogen usage, profits ranged from nearly $8 per acre to more than $25 per acre.

“Best management practices for nutrient management, like variable rate application, will help a farmer’s bottom line and help to achieve the goals of the Iowa Nutrient Reduction Strategy,” McArtor said. “Proper nitrogen application form and placement saves the farmer money and helps keep nutrients out of rivers and streams.”

The Iowa Nutrient Reduction Strategy (NRS), in place since 2013, offers a suite of practices that can be implemented to help meet the strategy’s goal of a 45 percent reduction of nitrogen and phosphorus in Iowa’s waters and the Gulf of Mexico. In-field practices, including nutrient management and cover crops, as well as edge-of-field practices, such as a bioreactor or a wetland, all work together to reduce nutrient loss into waterways. 

A chronicle on cover crops

Dean Sponheim spoke with attendees about the benefits of using cover crops. The Nora Springs farmer has been using cereal rye since 2012. In addition to growing corn and soybeans, Sponheim runs a cover crop seed business. Sponheim also uses strip-tillage and is converting his acres to no-till.

“When I started with cover crops, I thought bigger was better. I planted a mix of five species of cover crops—expensive seed. I got nothing out of it,” Sponheim said. “My neighbors were raving about how well their cover crops were growing. I found out they were using only cereal rye, so I switched the next year.”

The discussions between Sponheim and attendees ranged from handling pests, termination tips and nitrogen management.

“A rule of thumb with cover crop termination: if you terminate after May 15, use an insecticide as well,” Sponheim offered. “If not, the armyworms will hatch and will look for other sources of food, including corn.” He noted that it doesn’t matter if the field will be going to corn or not, as there probably will be neighboring corn fields and the armyworms will find it.

Sponheim uses cereal rye mainly as a storage facility for nitrogen. “Why lose all my nitrogen in the spring due to leaching? When it’s in the cover crop, I can utilize it later as the rye decays and releases it back into the soil,” he said. “Cover crops are going to do more good than harm because of what they do to your soil, increasing soil biology and sequestering nitrogen.”

Improving water quality from tile drainage

Chris Hay, ISA senior environmental scientist, walked through several drainage management methods that farmers and landowners could adopt for nitrate reductions in tile water. Bioreactors and saturated buffers can be installed to intercept and reduce nitrate in tile-drained water before it enters a stream.

Woodchip-filled bioreactors are placed adjacent to a field and have a lifespan of approximately a decade or more. Saturated buffers consist of an additional tile line in between a row crop field and a streambank buffer, running parallel to the stream. This line diverts tile-drained water into the buffer area allowing the natural denitrification process to occur in the buffer before the tile water reaches the stream. These practices also contribute to the Iowa NRS goals.

Sponsors of the field day included The Fertilizer Institute, Mosiac, Iowa Learning Farms, Environmental Tillage Systems­ and Midwestern BioAg.

Contact Carol Brown at

For media inquiries, permission to republish articles or to request high-res photos, please contact Katie James, ISA Public Relations Manager at © 2020 Iowa Soybean Association. All rights reserved.

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