Nitrogen On Corn For Success
How do growers plan nitrogen for spring after a wet fall & late harvest?
A: 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.
Should growers sidedress their corn to make sure nitrogen levels won’t limit yields?
A: 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.
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.
At what corn growth stage is nitrogen needed the most, and how do you determine deficiency?
A: 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 a nitrogen application.
How should growers fertilize prevent plant fields going into corn?
A: 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.
When is the best timing for nitrogen if corn needs a late-season application?
A: If you notice later season nitrogen 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 bushels per acre, but you may reach 225 bushels, which is better than 160 bushels if you didn’t make the application. Just make sure the nitrogen stress didn’t start early and you delay application to R3 because you’ve already lost too many bushels.
