CARY, N.C. — Many farmers looking to improve their nitrogen efficiency and their nutrient stewardship are turning to splitting their nitrogen (N) applications and following pre-plant N applications at lower rates with a sidedress or topdress application during the growing season.

“More farmers are adopting the 4Rs of Nutrient Stewardship, which includes good timing to put the N down when the plant needs it,” says Darin Lickfeldt, Ph.D., senior technical development manager for Verdesian Life Sciences. “Applying 100% of N prior to planting is not optimal in most cases, so split N applications are becoming more popular.”

Farmers in the Midwest, Northeast and North Central states interested in splitting their N applications should follow some best practices, including knowing what your soil type needs. Less than ideal soils, including sandy soils, soils with lower organic matter, lower cation exchange capacity or a shallow A horizon (meaning the top soil is not deep), should apply about 50% of their total N in a pre-plant application and the rest with an in-season application, says Lickfeldt.

If farmers have close to ideal soils that hold N better with less risk of N loss, they may be able to apply up to 75% of their N in a pre-plant application with the rest in an in-season application.

Timing your in-season applications is another factor to consider. Lickfeldt says the later you can apply a sidedress or topdress application, the better. For applications with a standard spray rig, the preferred timing is usually around the V6 to V8 growth stages, before the canopy closes. If you try to apply when the corn is taller, it would require a high-clearance sprayer to apply the N to avoid damaging stalks. 

Farmers should avoid applying N in wet conditions, which can lead to soil compaction. Another concern is that N applied under wet conditions is more susceptible to loss to the environment.

Another consideration when splitting N applications is minimizing risk of crop injury. One challenge with a topdress application broadcast over the top of the crop is that some of the fertilizer granules could get caught in the whorl, which can cause injury to the crop. At those vegetative stages, any injury to the crop will hurt your yield, says Lickfeldt. That’s why a lot of farmers sidedress the N application between rows.

“One of the 4Rs of Nutrient Stewardship is applying fertilizer at the right place, and it makes a lot more sense to place it right next to the corn plant rather than having a portion get caught in the whorl,” says Lickfeldt. “One trend is using a urea ammonium nitrate (UAN) liquid as a sidedress to avoid injury to the crop. There are also new technologies that can apply N directly on, or very near, the corn row rather than on the center.”

Following the 4Rs of Nutrient Stewardship and best management practices for N applications are critical, but conditions can still be conducive to N loss to the environment. Because weather is unpredictable and N that is lost to the environment does not help the crop, farmers should protect their N when possible.

The last tip to make the most out of your split N applications is to monitor the results. This will allow farmers to adjust their technique to avoid injury or possibly mirror successful results with variable rate applications the following year. Following these best management practices will help farmers realize both economic and environmental benefits by ensuring the plant takes more of their applied N up and less is available to be lost to the environment.