Library Categories


Reality check needed on N loss

It’s been another wet year, and many Iowa cornfields have shown the tell-tale yellow cast this growing season, instead of the desired deep-green color. Yellow corn plants during summer are usually a sign they’re running out of nitrogen, which washed or leached away, or otherwise escaped. Many farmers are wondering, “Should I just go ahead and apply a nitrogen stabilizer product with my nitrogen fertilizer?”

Key Points

• 2010 was another wet year, with more fields showing N deficiency symptoms.

• Iowa farmers are interested in preventing losses of this valuable crop nutrient.

• More farmers are asking questions about the use of nitrogen stabilizer products.

Even though there is finally consensus among Iowa State University agronomists on dropping yield-goal-based N recommendations, this decision has added to confusion on how much nitrogen is really needed. “Clearly, it takes more N to produce higher corn yields,” notes Tracy Blackmer, research director for the Iowa Soybean Association’s On-Farm Network. “However, the reason the recommendations have changed in most of the Midwest is because N losses and the availability of N from soil reserves are so much more important than differences in yield levels when it comes to determining how much N to apply.”

The amount of N apparently being lost from the system has many parties — agencies, environmental groups, ag groups and private industry — looking for solutions. As with most agronomic decisions, there are few universally accurate guidelines for using nitrogen stabilizers. That leaves growers with the challenge of sorting out the best information on which to base their decisions. Some of these products have been tested by growers on their fields.

Some industry reports say using nitrification inhibitors can produce an average yield increase of 8 bushels per acre. This is inconsistent with ISU and On-Farm Network data, notes Blackmer. For this to be true, it would mean that growers on average are grossly underapplying N. While it’s likely there are specific cases where this has occurred, it’s doubtful these results could be repeated under average Iowa conditions.

Need better guidelines

Nitrogen stabilizers used properly could be a good fit. However, guidelines on how to use them and when they may be appropriate have not been defined. Nitrification inhibitors have been a recommended practice in a number of watershed projects meant to reduce nitrate content in leaching water. But Blackmer says he hasn’t been able to find a single example showing a reduction in nitrate in water leaving the watershed from the use of a nitrification inhibitor.

He notes there is an increasing trend for companies, co-ops and agencies to use N stabilizers as a solution to environmental problems. While there are places where they fit in, there may be more misuse of these products than clear targeting with data to prove the claims. Some co-ops and fertilizer dealers have positioned N-Serve applied with anhydrous ammonia when soil temperatures are still at 60 degrees F as a best management practice, or BMP. “This isn’t supported by our data or that from any university, and does not benefit the individual grower,” says Blackmer.

Last year in Iowa, the majority of the nitrogen stabilizer product studies done by the On-Farm Network did not show an economic benefit to the grower or a difference in N available to the plant. These tests were largely done by growers, with their own equipment, the way they would apply nitrogen. There is a huge need to better define when and how to use nitrogen stabilizer. A report about these products and how they’ve performed in Iowa trials is at www.isa

Lane is research communications manager for ISA’s On-Farm Network.

This article published in the September, 2010 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.