Farm strip trials to aid in fine-tuning N rates

CHAMPAIGN, Ill. — New nitrogen rate verification trials were introduced last year and researchers believe pairing that data with the current database will help fine-tune the recommendations.

Emerson Nafziger, University of Illinois crops professor emeritus, said the new nitrogen rate verification trials can be done by farmers on their own farms to determine the optimum nitrogen rates for specific fields.

The nitrogen rate verification involves two rate strip trials. One strip would have the rate that is typically used on that field.

A second strip through the field would have 50 to 60 more pounds applied above the farmer’s rate if the farmer’s rate was near the Maximum Return to Nitrogen of 180 pounds or less in northern and central Illinois and 200 pounds or less in southern Illinois.

If the farmer’s rate was 225 pounds or higher, the comparison strip would receive 50 to 60 pounds less than the farmer’s rate.

The strips would be wide enough to allow yield data to be collected from two combine harvest passes.

“We think this is a good way to move nitrogen forward. We have a good basis right now with the Maximum Return to Nitrogen calculator. I think the N rate calculator is sound. We have hundreds of trials in that calculator. I think there are 290 corn-following-soybean trials in central Illinois that are going into that data base. So, this is a way to average those results, crunch them together,” Nafziger said.

He showed examples of six nitrogen rate verification trials conducted last year primarily in east-central Illinois.

Based on results from all 2022 nitrogen strip trials, adding an average of 57 pounds of nitrogen per acre increased yields by only 1.6 bushels per acre and lowered the net return by $43.41 and application costs were not included.

“The average medium rate was 186 pounds per acre, which would be a pretty good rate. That’s above the MRTN, but it’s not drastically above it,” said Nafziger at the Illinois Nutrient Research and Education Council’s “Investment Insight LIVE!” event.

“The N rate verification trials are something we hope will give some real visual evidence and yield monitor evidence to people that it works to do that.”

Future Data

Looking toward the future of managing nitrogen for corn, Nafziger believes “current Illinois N rate database is the sound basis for N rate recommendations for the next decade or more.”

“We expect the N rate verification (two-rate) trials to provide immediate assistance in helping to lower N rates where that is appropriate,” he said.

“We expect that two-rate trials, if they can spread widely in Illinois, will help fine-tune the N rate calculator MRTN. It may allow it to provide MRTN values for smaller regions and for different soil types/topographies.

“If paired with periodic sensing and modeling, existing data and N rate verification trials should make possible the ability to adjust N rates in-season based on crop and weather signals.”

Looking Back

Illinois had a record average corn yield of 214 bushels per acre and soybeans were slightly below the record at 63 bushels per acre in 2022 despite it being a relatively dry year.

“We had a little bit below normal rainfall here in July and August. It was much drier than normal in June. In this part of the state, we had barely an inch of rainfall in the whole month of June,” Nafziger said.

“That had some real benefits to it and we saw that this last year. One is that our stands were almost perfect. We had essentially no standing water damage anywhere in the state this year. That’s probably the first time in 41 years that I’ve can say that because we always have standing water somewhere.

“This year there might have been a little bit in southwestern Illinois. It came later in the season, but except for that dryness and some of those symptoms it was an excellent year from the soil standpoint.”

A common occurrence during the 2022 trials was that more nitrogen was applied to fields in trials than needed based on the MRTN calculator. Optimum nitrogen rates ranged from 100 to just under 200 pounds for corn following soybeans.

“Dry weather that preserves the nitrogen in the soil and gives the roots maximum ability to go and take that nitrogen up is the key to high nitrogen uptake and high efficiency of nitrogen use. That means that had we known that in advance we would certainly be able to have used that and lowered our rates,” Nafziger said.

“The real lesson we took from it is don’t go out and put more N on when it’s early in the season and crop looks really good. That’s what some people did in 2022 and it absolutely was a complete waste of money.

“If we have dry conditions, not too dry to wreck the yield of the crop, but dry enough to preserve the roots and to preserved the nitrogen that’s there, it’s highly beneficial.”

Nafziger and Dan Schafer, Illinois Fertilizer and Chemical Association director of nutrient stewardship, have conducted nitrogen timing trials the past four years. Those trials found the optimum nitrogen rate in 2022 was 111 pounds per acre.

“That’s all it took to maximize the yield. How can so little nitrogen maximize the yields at about 200 bushels per acre? It’s no big mystery. It has to come from the soil. It comes from the organic matter in the soil, and the crop probably took up all of the organic nitrogen that was made available,” Nafziger said.

Nitrogen ‘Rich’

Here are Nafziger’s takeaways from the last growing season:

• It was a nitrogen rich season this last year. There was a timely start to mineralization. The soils were warm at planting and there was very little nitrogen loss from the soil.

• There was less response than usual for like planter-applied nitrogen.

• In-season applications on the surface may have been delayed moving to the plant, but there was little or no nitrogen deficiency. It also meant that nitrogen probably didn’t do much good in many cases. That was unnecessary, though there was no way to know that, but even those who were using the proper rate and kept some of it back until the corn was taller very likely could have skipped that last application and would have been just fine.

• There was high leaf nitrogen content at maturity and slow dry-down. The high soil N and N concentration in water was taken up late. The signaling of maturity from the ears to the rest of the plant may have been “off.”

• There were relatively high yields with no or low N fertilizer this year and N rates needed to maximize dollar return were less than MRTN in most trials.

• There is no doubt that actual N amounts used in many Illinois corn fields in 2022 were higher, maybe much higher than the crop required.