Where Did My Nitrogen Go?

Nitrogen is the 2nd most expensive input but the #1 yield-influencing input we apply every year to our corn crop. So how can we use it more efficiently?

According to Oklahoma State’s Nitrogen Use Efficiency (NUE) website, side-dress or top-dress practices see about 50% NUE. That means that when you apply 200 pounds/acre of nitrogen to achieve a 200- to 250-bushel yield, the corn crop only uses around 100 pounds per acre of nitrogen. That’s not easy to digest in these economic times, but it provides motivation to determine the best nitrogen rate to keep yields up while ensuring the corn plants use it. This is where precision ag software comes into play.

The Climate FieldView (CFV) Nitrogen Advisor (NA) is one of several nitrogen models that factors weather into the equation. During the 2018 growing season? We tested the CFV NA in a large plot at the Latham Farm in Alexander, Iowa. The test was replicated three times, using two nitrogen rates.

Using the NA, we applied a total 135 pounds per 3 212.9 acre. Using our previous Yield Goal approach (YG), we applied a total of 170 pounds/acre. We put down 25 pounds per acre with MAP before planting then an additional 70 pounds/acre UAN with our herbicide at planting. The last application of 32% UAN was applied June 13. This study also included a high and low seeding rate of 37,500 and 31,500 seeds per acre.

We planted LH 5245 VT2 PRO on May 18 for this study. After analyzing yield across the two different nitrogen rates and two seeding rates, there was not a significant difference in yield between the Nitrogen Advisor and our Yield Goal approach. Given that 31 inches of rain fell this growing season as compared to the 10-year average of 23.4 inches, I thought we’d see more difference between the two nitrogen rates. I flew my drone periodically throughout the growing season and noticed a few NA plots showed some yellowing. The yellowing wasn’t major and it didn’t last long.

I also pulled ear leaf samples at R1 and compared them to our yield results. There was a significant impact of the lower nitrogen rate by the Nitrogen Advisor but only at the higher populations, which follows the trend many researchers have found. As the population increases, nitrogen decreases in the ear leaf. It is difficult to apply enough nitrogen to make up for the extra demand that all those extra plants put on the supply in the soil. Therefore, if you are VR seeding, then VR apply nitrogen to apply more in the heavier seeded areas or consider applying higher blanket rates if you can’t VR apply nitrogen.

The biggest take away from the R1 ear leaf samples is that all were “deficient,” meaning we aren’t applying enough nitrogen overall with our YG approach to see the full potential. We must keep in mind 50% NUE and the role that the weather, especially this year’s heavy rain events, likely played on how much nitrogen was taken up and how much was lost due to leaching.

Look for Part 2 of our research findings in next month’s article. I will discuss the surprising impact that the different seeding rates had on this study.