For those fortunate enough to have corn in the ground, it may be worthwhile to reevaluate your nitrogen management plans for the season.
Assessment of weather and field conditions following N application can help determine if supplemental nitrogen may be necessary.
For those who elected to plant first and sidedress N later, making a timely application by V4 will be crucial. Under either circumstance, it may make sense to tweak N rates to reflect expected yield potential.
Nitrogen is taken up by plants as nitrate (NO3-) or ammonium (NH4+). Understanding that soil is negatively charged, positively charged ammonium is held within the soil.
Ammonium is subject to nitrification, or the process by which it is converted to nitrite (NO2-) by Nitrosomonas bacteria and then to nitrate (NO3-) by nitrobacter.
Once negatively charged, nitrogen in the nitrate form is subject to loss via leaching.
Nitrogen stabilizers, such as N-Serve and Instinct II, work to halt the microorganisms’ activity, keeping nitrogen in the ammonium form.
Denitrification is the second-most way nitrogen is lost from the soil. Denitrification occurs when soils are saturated and oxygen deficient — the environment needed for microorganisms to convert nitrate into a gaseous form. Gaseous forms of N are able to escape the soil and be lost to the atmosphere.
Estimating N Loss
With so many factors — such as soil texture, temperature, use of a nitrogen stabilizer and tile drainage — influencing N loss, it’s difficult to get a grasp on how much nitrogen will be available to the growing corn crop this season. But one thing is for certain, the unprecedented rainfall this spring has done us no favors.
Research conducted at the University of Nebraska estimated nitrate loss of 2% to 2.5% per day under saturated soil conditions and soil temperatures of 55 to 60 degrees.
Illinois research studied loss with soil temperatures greater than 65 degrees, also under saturated conditions, and recorded nitrate losses from 4% to 5% per day.
Nitrogen In The Plant
Prior to nodal root development, young corn plants rely heavily on energy reserves stored in seeds. The first nodal roots appear by V1, the system is established by V6 and then the roots provide the plant with all the water and nutrients it needs.
The corn plant does not take up large amounts of nitrogen in early vegetative stages, VE-V4. However, nutrient availability is crucial from V5 to V8, the point when a plant determines the number of kernel rows an ear will have. Significant stress may result in a reduction of kernel rows and, therefore, yield loss.
Once the plant reaches V9, it begins a period of very rapid growth and nitrogen uptake until reaching reproductive stages. This makes it crucial to not delay sidedress N applications beyond V4 if no N was applied preplant, or if you believe a great deal of your fall N or early spring N has been lost.
Are the visual symptoms really N loss, or something else? Because visual symptomology of N deficiency is often similar to other crop afflictions, it can often be misdiagnosed.
Pale-yellow corn does not necessarily equate to N shortage. Rather, it may be function of wet, saturated soils and, therefore, oxygen deprived conditions.
Such an environment slows and restricts root growth. Plus, the majority of corn planted this year was more or less mudded in, resulting in sidewall compaction, which also restricts root growth.
Keeping these things in mind, it’s still good to be on the lookout for actual, not just induced, nitrogen deficiency. Younger plants may be stunted, spindly and pale green in color. Older plants will show the traditional V-shaped yellowing on older leaves.
Replenish N as needed for uptake later. Injecting UAN solution or anhydrous ammonia between the rows is considered the best option for in-season applications.
It keeps nitrogen at a safe distance from the plant. And because it is injected into the soil, the risk for loss through volatilization and for foliar burn of the plant is reduced.
If weather is not conducive to a timely application, a high-clearance rig with knives or drop hoses can be used, but care must be given as stalks may be brittle.
When a sidedress application is not possible later in the growing season due to corn height, a broadcast application of urea granules, UAN solution, ammonium nitrate or ammonium sulfate over the crop can be effective options.
Urea granules are the best broadcast option because they result in the least crop injury, but keep in mind that granules will need moisture — either rain or pivot irrigation — within three to four days of the application to minimize risk of loss due to volatilization.
However, a urease inhibitor can help buy some time until the next rain event.
Additional sources for information on nitrogen application are available at:
- Agry.purdue.edu/ext/corn/news/timeless/CornRespLateSeasonN.html; and
Several Midwest land-grant universities teamed up to develop an online calculator called Corn Nitrogen Rate Calculator. To access the calculator, visit cnrc.agron.iastate.edu.