Dan Kaiser

Dan Kaiser, Extension Specialist with the University of Minnesota.

ST. PAUL, Minn. – The nitrogen guidelines by the University of Minnesota have been updated and the new numbers are out. These recommendations can help growers find the most profitable use of their nitrogen fertilizer.

“We saw guidelines adjust by about 10 pounds of nitrogen, so we saw just a slight increase, which is still within the profitable range we had before,” said Dan Kaiser, Extension specialist with the University of Minnesota, during a recent phone interview.

Every year, the University is collecting information from on farm trials across the state. The data collected includes everything about that field, the location, soil conditions, cropping pattern, fertilizer used, hybrid planted, other inputs, and of course, yield.

Once the data is collected, analyzed and outlying data points removed, the information is added to the University’s Maximum Return to Nitrogen (MRTN) program.

“We have data in the database going back to 1990 for corn/soybean rotation and 1996 for corn on corn,” said Kaiser. “When we update the database, we go back and look at the older data to make sure it is still valid”

The advantage of using a data driven system like the MRTN approach is that it can be modified with current information. As hybrids change, weather patterns change and farming practices change, the MRTN system will stay updated with a starting point for growers’ nitrogen use.

The system allows corn producers to generate a custom guideline to allow them to adjust their rates based on the cost of nitrogen they are purchasing relative to the value of the crop, so growers can get the most return on investment. In most cases, a ratio of 0.10 is a good starting point.

Then farmers chose their crop rotation, corn on corn or corn/soybean rotation. They then have to input a price for nitrogen and an estimated crop value for their corn.

The current recommendation for a nitrogen cost-to-crop value ratio of 0.10 is 165 pounds of nitrogen, on a corn following corn rotation and 130 pounds of nitrogen for corn following soybean.

“The MRTN value for corn following soybean has been stable over the past 25 years. This has actually been the first change that I've seen since we went to the Maximum Return to Nitrogen in Minnesota,” he said.

“With the amount of denitrification we have had the last couple of years, with all the water sitting around, it doesn't really surprise me to see that one go up slightly,” he said. “In one of the last updates we looked at the yearly average MRTN values for the corn following corn rotation and noticed it has steadily increased from about 2000.”

“I would expect to see the corn following corn MRTN value to level off at this point, but it is hard to tell with increased rainfall in years like we have seen the past couple years,” said Kaiser. “Some of the yearly increase in the corn following corn MRTN value is likely a result of newer genetics.”

With better plant genetics, comes healthier plants, which means there is more growth and more plant residue at the end of the season. That residue can tie up the nitrogen in the field and this tie up is reflected in the MRTN guidelines.

The slight changes seen this year in the recommendations are not likely to impact growers much as the new MRTN values are likely within the range most growers are currently using for their nitrogen management programs. The recommendations have not exceeded the normal ranges. Every field is different, and growers know their fields and needs better than anyone.

“The major changes for anybody are going to be situations with manure, particularly manure management plans,” he said. “As the recommendations slowly creep up a little bit, there's going to be a little bit more of an allowance hopefully for those growers that have manure in terms of application rates.”

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