Split application study continues its positive trend

Splitting up nitrogen application during the growing season is widely believed to benefit yield and water quality. A cost share project by the Mid-Atlantic 4R Stewardship Association aims to spread awareness of the practice and persuade growers to adopt it. (Photo courtesy University of Nebraska)

NORTH EAST Md. — As a project to encourage split application of nitrogen enters its fourth year, a second year of data shows the practice varies widely in yield response, but remains positive on average. Eric Rosenbaum, a crop consultant and executive director of Pennsylvania 4R Alliance, gave an update on the project during the Mid-Atlantic 4R Symposium held Aug. 31 at Cecil College. 
Funded through a grant from the National Fish and Wildlife Foundation Chesapeake Bay Stewardship Fund, farmers in Maryland, Delaware and Pennsylvania could access cost-share funding for adding an additional split in their overall nitrogen application on their corn crop. Participants agreed to provide a comparison check strip where all of the crop’s nitrogen is applied at or before planting and share production and yield data.
The alliance’s split nitrogen study began in 2021 allowing participants to enroll between 40 and 400 acres.
In the Pennsylvania side of the program, producers were asked to move from one pre-plant application of nitrogen to splitting out a second in-season application, such as side dress or fertigation. With split application already in wider practice in Delaware and Maryland growers there were asked to add an additional split to what they had already been doing. In some cases, Rosenbaum said growers increased from three to four splits. In all cases, total nitrogen application could not exceed their nutrient management plan amounts.
In the three states, 16 farms participated last year enrolling 3,595 acres in the program in the 2021 crop year. In 2022, 21 farms participated with 4,213 acres. Also in 2022, the Pennsylvania side of the program expanded to allow growers from beyond Adams County.
Maryland and Delaware farms participating in 2021 had an average yield increase of 19.2 bushels per acre and nitrogen use efficiency on average increased five percent, though in 2022, the average yield increase was 4.3 bushels per acre.
On the Pennsylvania farms for 2021, farmers saw an average yield increase of 17.6 bushels per acre and 12 percent better nitrogen use efficiency. In 2022, the average yield increase was 13 bushels per acre.
While the Pennsylvania yield data saw less of a change year-to-year, Rosenbaum offered a few possible explanations for larger drop in Delaware and Maryland yields. With longer dry spells in 2022, weather not surprisingly had the largest effect, he said. Some sites didn’t even warrant harvesting and were counted as zero for yield, he said.
New participants trying new practices on their farms was another suggestion. Rosenbaum said with all the options and nuance in fertilizer application, he doubts any of the farms participating in 2022 had the same nitrogen management program. Nitrogen applications could come from manure or commercial fertilizer and timing of the splits could be made at different stages in the season. Application methods included early, traditional and late-season sidedress, fertigation, strip-till pre-plant, at planting and pre-emergence.
“We’re herding cats here. We have so many different variables but it’s all under the umbrella of split nitrogen,” he said. “When you think of fertilizer BMPs, split nitrogen is probably one of the biggest BMP that a farmer can do.”
But that’s indicative of farmers in general, each with their own needs, preferences and limitations, so remaining broad in scope and still showing an average increase supports the practice’s use, Rosenbaum added.
“Maybe it doesn’t matter how they’re applying their nitrogen,” Rosenbaum said. “Maybe the important part is if you take nitrogen that your nutrient management plan is calling for and you divide it up over the course of the season, to spoon feed that crop, you’re going to see a response.”
Management remains key in having success. Rosenbaum said of two farms that saw no yield increase in the project, one had too much nitrogen tied up in a cover crop that a second application wasn’t enough to boost the crop yield and the other farm included boron in the starter fertilizer which became toxic to corn roots.
Rosenbaum said one thing that has been made clear to him in the project is how having sound agronomic practices in place in general make more precise practices like split application more effective. He cited planting depth, seed spacing, weed and pest control as some of the many things growers focus on as a foundation in their production.
To participate or get more information, contact Rosenbaum ericrosenbaum@rosetreeconsulting.com or 484-788-7263. Maryland and Delaware growers can contact Jenell Eck McHenry at 443-262-6969 or jenell.mdag@gmail.com.