As we entered June many farmers were preparing to side-dress their corn fields. They might be considering how much nitrogen to apply.

A common question we receive from the participants of the Nitrogen Use Efficiency project at University of Wisconsin-Discovery Farms is “Can a split application in nitrogen help improve my efficiency?” Four years of monitoring our data indicates that corn-grain production is transitioning away from nitrogen-management systems that apply all nitrogen at the beginning of the season. Instead producers are shifting toward systems with more in-season applications.

But so far our Nitrogen Use Efficiency project data set doesn’t show a correlation between split applications and better nitrogen-use efficiency. From 2015 to 2018 almost 80 percent of monitored corn-grain fields – 157 fields total – had either one or two applications of fertilizer, not including starter. While that remained the most common practice, we observed an increase in nitrogen applications in-season. With each year we monitored, the percentage decreased of nitrogen being applied to fields before or at planting. Increasing was the percentage of fields where nitrogen was split-applied – nitrogen applied at planting and in season – or nitrogen applied only in-season. Also increasing was the percentage of fields nitrogen was applied to three or more times throughout the season, often with more than one in-season nitrogen application.

For those planning to split-apply nitrogen this year, great. Applying nitrogen closer to when the crop needs it can be an environmental and economic benefit. But keep in mind that increasing the nitrogen rate without a proportionate gain in yield will make the nitrogen-use-efficiency value suffer, and can negate environmental and economic gains.

Split-applying nitrogen allows for the flexibility to adjust nitrogen rates given spring conditions and the weather’s impact on available nitrogen. That could help improve nitrogen-use efficiency. In our data set as the number of fertilizer applications increases, so does the total nitrogen applied as fertilizer. As a result fields that had nitrogen split-applied, on average, had greater fertilizer-nitrogen rates than fields that had all nitrogen applied at planting or those that had all nitrogen applied in-season. As nitrogen rates increase, yield must also increase proportionately in order to maintain an average nitrogen-use efficiency.

While the data set doesn’t demonstrate that split applications can improve efficiency on a large scale, for certain field conditions or farm systems there is potential to improve nitrogen-use efficiency. Consider monitoring fields for nitrogen-use efficiency if interested in assessing how efficient side-dress application is. Visit bit.ly/2V4s8Yk for a guide to monitoring fields.

Visit www.uwdiscoveryfarms.org for more information.

Abby Augarten, Nitrogen Use Efficiency Project coordinator at University of Wisconsin-Discovery Farms, records on-farm agronomic information, collects soil and plant samples, analyzes data and organizes project outreach. Visit www.uwdiscoveryfarms.org for more information.