By: Chase Gingerich, ProVantage Specialist and Agronomy Sales
Managing nitrogen is the most important nutrient for optimizing corn yields. Mismanaged nitrogen is the most expensive nutrient program for a grower to get wrong. Too little nitrogen and you have shorted your corn yield. Too much nitrogen and you have wasted your money and a nutrient that has potential to cause environmental issues. How can we be sure that we are the most efficient with our applied nitrogen? Timing and placement.
From a timing perspective, in an ideal world, we would apply nitrogen as close to plant uptake as possible, which would be one to three pounds per acre per day. In the real world, this isn’t practical as we must manage field workload, weather, applications, and optimizing equipment without excessive field traffic. Fall nitrogen with a stabilizer is very effective at minimizing compaction and workload, even though it is the furthest from plant uptake. On the other end of the timing spectrum, sidedress applications are the closest to plant uptake but may not be the best choice for workload or field operations because of erratic weather patterns.
To optimize corn yields, in most cases, a good base rate of nitrogen should be applied before or at planting. This will allow plants to begin their normal uptake patterns without paying a timing penalty caused by dry weather during peak nitrogen uptake (between V8 and R2). In 2021, parts of southeast Iowa went through a three-week period in June with no rain. If your only source of nitrogen was a sidedress application that occurred before this dry spell, very little applied nitrogen was available in soil solution during this three-week period.
Preplant applications allow enough time for nitrogen to move throughout the soil where it can be captured by roots. The small roots of corn seedlings may not be in the direct zone of application, but nitrogen will eventually find its way to these small plants since it is a mobile nutrient. Traditional sidedress equipment places nitrogen 15 inches away, which is as far away as you can apply nitrogen from a 30-inch row of corn if you think about it. Will the roots ever get to this application?
We went out to the fields with a shovel to find the answer to this question in June 2021. We walked into a V8 corn field that was 24” tall and not canopied (Figure 1). This field had been sidedressed with a traditional rolling coulter and nozzle injector two weeks prior when the plants were at V4 or six inches tall. Because the weather had been dry immediately after the application, we were able to observe cracks from where the rolling coulter made its injection. Using a small pocketknife as a pick, we could delicately remove soil from the trench to uncover roots. This meant that the plants were able to access nitrogen from the sidedress application that occurred 15” away from the base of the plant.
At four inches deep we could find the bottom mark of the rolling coulter with roots proliferating through the sidewall of the sidedress trench (Figure 2). All fertilizer sources applied to a field will require some degree of moisture to dissolve the plant nutrients into soil solution. While there wasn’t a lot of extra water available at the three-to-four-inch depth, the roots had fully proliferated to the center of the row and grew all the way to the trench. In our field, any nitrogen that would have been injected into that band below the soil surface that was fortunate to be in soil solution would have been able to be taken up by these roots. Any measurable rain would activate the nitrogen in soil solution and be immediately available for plant uptake which was at the onset of peak nitrogen usage in this particular field.
What can go wrong with a sidedress nitrogen strategy? Managing soil compaction is critical to allow roots to proliferate through the soil profile. If something is restricting root growth, the ability of the plants to uptake all nutrients and water is diminished exponentially. The dry weather during June showed just how important a solid base rate of nitrogen is to a successful sidedress management strategy. The field was not suffering from nitrogen deficiency because of the ample base rate of nitrogen that was applied before planting, buying enough time for the roots to grow to the center of the row. If this grower had been relying on his sidedress application for 90% or more of his fertility program, this field could have suffered a yield penalty from not having the proper moisture to get the nitrogen into a soil solution.
There is always going to be a delay from nitrogen application until crop utilization. The goal with an effective nitrogen management strategy is to not suffer a yield penalty while waiting for this delay. By split applying your nitrogen applications, we can achieve this goal. Pre-season applications will give you available nitrogen from the start, while still applying nitrogen as close to uptake as possible with sidedressing. By implementing these strategies and managing your fields, you can be confident that you have optimized your in-crop application of nitrogen.