Plan. Watch. Act.
Those are my key recommendations to avoid losing your shirt to nitrogen deficiency in this year’s corn crop.
Drenching rains since April 1 have endangered fertilizer nitrogen applied before that time, as well as nitrogen contributed by the soil. Over 58 million acres in the midwest received more than 16 inches of rain from April 1 to June 9. Iowa and Missouri lead the charge, with more than 15 million acres each, with Illinois close behind at 12 million acres. These areas are shown in cross-hatch in the map on the left.
Snow and rain in February and March also contributed greatly to re-wetting dry soil and beginning the processes leading to N loss.
In Missouri, more fall anhydrous ammonia was applied last fall than in any of the five previous years. This N has now been in the field for about 7 months. I would say that much of it has already been lost, or is in serious danger of being lost in coming weeks. N-Serve will not provide adequate protection to many of these fields.
I am also guessing that more N has been lost from well-drained soils than from poorly-drained soils to date. This is, if I’m correct (and I’m far from sure that I am), unusual. I’ve seen many more acres of yellow corn in areas with poorly-drained soils than in areas with well-drained soils over the years. But this year’s heaviest rains were in April, when well-drained soils are vulnerable to loss and poorly-drained soils are less vulnerable.
I believe that every farmer who applied all of their N before planting should have a plan for how they will apply more N fertilizer to the growing corn crop if it appears to need it. Further, every fertilizer retailer should have a plan for how they will help customers apply N to their growing corn. Tractor-drawn injection equipment, tractor-drawn dry N buggies, sprayers equipped with drop nozzles, high-clearance self-propelled spinners, airplanes....all are excellent options for how to apply more N if needed. Now is the time to develop a plan for how to apply more N, if you don’t already have one. Developing a backup plan as well would be even better. Fertilizer source should be planned and verified along with application equipment.
You may not need this plan. But if you don’t have one, your odds of getting more N applied if you need it are greatly reduced.
Watching the crop is the most reliable way to tell whether it needs more N or not. If the corn is lighter green than it should be, it probably needs more N, especially if it stays light once the soil is no longer waterlogged. This is reliable mainly for corn that is at least a foot tall.
Watching many fields from ground level is difficult and not very accurate. Getting up in an airplane with a camera is much better. Many local airfields have a pilot who can be hired.
I can predict how much yield will be lost from a straight-down aerial photo of corn that is at least hip-high. If you’re interested in trying this, call me. We can process a limited number of fields this year. Obviously the problem with this is that a limited number of machines are available that can apply N to corn this tall. The corn itself won’t mind at all.
Watching the corn is the most reliable indicator of whether additional N is needed, but requires waiting. Plans to get N applied may require quicker action on at least some fields to accomodate equipment limitations. Watching weather may need to be the basis for at least some decisions. The map above comes from my Nitrogen Watch page, which is based on cumulative precipitation maps and is updated weekly. You can find these maps at: https://plantsciencesweb.missouri.edu/nutrientmanagement/nitrogen/Nitrogen%20watch%202013/nitrogen%20watch%202013.htm
This is the most important part. If you need to act and don’t, you will lose a lot of yield and a lot of money.
I think that most producers in the cross-hatched area of the map who applied all their N before planting will profit from applying additional N even if it is not targeted. This is especially true for fields fertilized in the fall.
Fields that received anhydrous ammonia this spring, or that received the bulk of their N after planting, are least likely to need additional N.
Watching fields and targeting additional N to those fields that need it most, or putting higher rates on the fields that need it most, will increase the odds of profitability.
Targeting N within fields would be even better. My research shows the best return on rescue N applications in the areas with the greatest N stress. And my observations show that there is usually a wide range of N stress in fields that have lost N. You can see this in the N loss aerial photo galleries on my website: https://plantsciencesweb.missouri.edu/nutrientmanagement/nitrogen/loss.htm
Crop canopy sensors are the most widely available way to target N applications within fields, applying higher rates to more stressed corn and lower rates to less stressed corn. However, not all sensor interpretations follow this logic so look for those that do.
REVISED: October 1, 2015