This year was dynamic regardless of where you grew corn. In the central Corn Belt, we received more rain than we had seen in decades (or ever). In the northern Corn Belt, there was some of the best environmental conditions we have ever seen.
As an agronomist, I can learn the most about systems and practices in a year like this – a year with a wide range of extremes. I have been scouring more than 100 field trials to find trends and facts about corn’s use of nitrogen in different environments. I can tell you, there are some definite trends emerging.
18.7 Inches of Rain – How Much N is Left?
It’s great when I can do a trial on my own farm – a farm where I know the soils and the history. The trial on my home farm centered on the amount and timing of nitrogen. You always learn something, even if it isn’t what you set out to learn. In this trial, we never anticipated the amount of rain we received from planting through mid-July. I assumed the large rain events that occurred from the day of pre-plant N application (April 28) impacted the amount of nitrogen we had left in early June, but I really didn’t know the degree of impact.
Measurement Reveals Answers
My wife and I took the samples on June 5th (at V7) across the 345-acre field and instantly ran the samples to test for nitrates using an in-field soil testing system, 360 SOILSCAN™. In the portion of the field that we had applied our full load of nitrogen (N) 3 days prior to planting (May 1), we measured about a 60% loss of nitrogen. In the strips where we applied a base rate – we measured about a 50% loss.
With the amount of nitrate left in the strips that had the full N load, my calculations showed that I would start showing nitrogen deficiency around V13, which occurred as expected. The strips with the base rate would start showing stress earlier if left untreated, but we already had a sidedress application planned and applied at V9 using 360 Y-DROP™ (prior to running out) By measuring and knowing how much N we had left in bank, I determined the rate needed to finish the crop strong, as well as adjust the timing of our sidedress application. The result: the base rate combined with measuring and supplying late season nitrogen added over 29 bushels per acre compared to the same amount of front-loaded pre-plant nitrogen.
I contrast this to other parts of the corn belt that didn’t experience these flushing rains. In Northern Iowa, fields were measured at V9 and found to have sufficient amounts of nitrate due to very active mineralization and no large rain events. Measuring in these fields allowed us to trim back – or even eliminate – our sidedress N rates, hit our yield potential, and increase our Nitrogen Use Efficiency (bushels per unit of N).
The Lesson from 2015
If we use a base rate (about 40-60% of our total estimated need), we feed the plant during the volatile planting and early spring weather events and we get to see what Mother Nature has in store for us. Then we can measure what nitrates we have in reserve to determine how much (if any) additional N we need to apply during the time the corn plant really starts taking up majority of its nitrogen (V9 and beyond).
Just a week ago, it was 55 degrees and we had record rains in central Illinois. For my friends that applied fall anhydrous, there are big questions about the ammonium to nitrate transition. How much has converted and moved? Based on what I learned this year, there is a big benefit to limiting the pre-season nitrogen that is subject to loss. There are tools like 360 SOILSCAN that let me measure what’s left and calculate the amount needed to reach my yield goal. And there are new tools like 360 Y-DROP, a nitrogen application attachment, that let me supply just the right amount at the right place at the right time.
(Source – http://www.agriculture.com/crops/corn/2015-lessons-in-nitrogen-magement_136-ar51815)