Ask the Agronomist

Nitrogen on Corn for 2020 Success

Ask The Agronomist (Progressive Farmer image by eKonomics)

Optimizing returns on every dollar spent on fertilizer and crop nutrition holds the key to profitable crop production. Ask The Agronomist, brought to you by eKonomics, provides crucial nutrient management answers as you prepare for the 2020 growing season.

Q: Given a wet fall and late harvest with less anhydrous applied, how do growers rethink nitrogen applications for spring?

Robert Mullen: For those areas that missed fall application, the change is just a shift to spring nitrogen applications. Anhydrous ammonia is still a good option for those applications, just be mindful of depth, direction of travel, and timing. The biggest concern is exposing germinating seeds to ammonia which can cause dramatic stand loss. This also presents an opportunity to split apply nitrogen, if farmers have the equipment to do so.

Q: To make sure nitrogen levels won't limit yields in 2020, should growers plan to sidedress all their corn acres, and why?

Mullen: In the Eastern Corn Belt, many farmers have recognized the risk of nitrate-nitrogen loss from fall applications of ammonia, so they split apply much of their nitrogen. Some nitrogen goes down with the planter or a weed and feed, then the rest of the nitrogen budget is applied as a sidedress. I'm talking very early sidedress, as soon as you can see the corn rows.

For the rest of the Corn Belt, sidedress is an option, but not necessarily a practice that everyone has to follow. Areas that have a history of higher rainfall amounts and coarser textured (sandy) soils should seriously consider sidedress, but for many areas early anhydrous ammonia can be just as effective. One thing to note is that early spring applications should avoid nitrate containing fertilizer sources due to their loss potential.

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Spring applications of nitrogen open opportunities for other nitrogen sources as well. Early applications (well before the intended planting date) would ideally still be ammonia, but applications closer to planting can be urea-based materials. This includes controlled-release and inhibitor containing products.

If manure is a source of nitrogen in the nutrient budget, farmers can use a pre-sidedress or late-spring nitrate test to determine if additional nitrogen is warranted or not. These soil-based tests do not necessarily do a great job of indicating how much additional nitrogen is needed, but they do a decent job of indicating if more nitrogen is needed.

Q: At what corn growth stage is nitrogen needed the most, and how do you determine deficiency?

Mullen: Up until about growth stage V6 to V8, there is very little nutrient accumulation from the soil. From that point on, the crop accumulates nitrogen from the soil as well as phosphorus, potassium and sulfur. Early scouting helps determine nitrogen deficiency (yellowing begins on lower leaves at the tip, with the V pointing toward the stalk, not pointing away, which is potassium deficiency). You never want to stress the crop for nitrogen, so if lower leaves are firing at V8, you need an N application.

Q: How should growers fertilize Prevent Plant fields going into corn?

Mullen: If going to corn, and the ground was bare except for weeds, you want to prevent fallow field syndrome by considering a spring banded application of phosphorus, especially if soil test phosphorus levels are near or below the critical level. If cover crops were planted, you are less likely to suffer from fallow field syndrome, but I would not expect huge nitrogen benefits unless the cover was a legume. In the case of a legume cover, the nitrogen credit would likely be around 30-40 pounds.

Q: When is the best timing for nitrogen if corn needs a late-season application?

Mullen: If you notice later season N stress, like around V8, you can still make an application as late as R3 and save some yield. You won't recover to achieve your yield goal of 240 bu./acre, but you may reach 225 bushels, which is better than 160 bushels if you didn't make the application. Just make sure the N stress didn't start early and you delay application to R3 because you've already lost too many bushels.

In upcoming columns, Dr. Robert Mullen, Director of Agronomy for Nutrien, will focus on potassium and sulfur.

For More Information:

Visit Nutrien-eKonomics.comfor news and fertility management information. It also contains valuable tools like a rainfall tracker and Growing Degree Day calculator to help farmers assess possible fertility loss and plant development needs.

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