Does Every Acre Require the Same Nitrogen Application?

Traditionally, Nitrogen fertilizer (N) rates have been linked primarily to expected yield goals.  However, with recent high N fertilizer costs, above average commodity prices, and unpredictable rainfall patterns, the focus on improved nitrogen management, reduced environmental risk, and maximizing yield potential has become more important than ever. For corn following soybeans, the traditional guidelines have been a N rate equal to approximately 1 lb of N per bushel of expected yield. For corn following corn or wheat, the recommendation has been equal to approximately 1.2 lbs of N per bushel.

Additionally, general rules implied that there was a straight-line relationship between yield and N rate; meaning that the more N you apply, the more grain you would harvest.  However, according to research conducted at Purdue University, the relationship is not a straight line.  Purdue’s research indicates that as the amount of applied N fertilizer nears the optimum rate or beyond optimum, the magnitude of the yield response decreases dramatically. Consequently, applying more N than is required by the crop is rarely cost effective and bears environmental risk.

While similar research has been conducted on this topic, much of the research would assume an average yield goal for a particular farm or field.  However, we believe it’s important to step back and ask the question, “Does every acre in the field require the same N rate, specifically when yield varies across a single harvest pass and with knowledge that mineralization from soil-supplied organic matter also varies?”

For example, if our average N rate is 210 lbs and we’re applying the same rate across the entire field, then we’re more than likely over-applying N on some acres and under applying N on other acres.   With nitrogen at nearly $1.00 per pound, we could be spending $25 to $30 more an acre than is necessary on some acres and potentially leaving $75 to $100 dollars an acre on the table where under applying N.

However, what if we could be more efficient with our N investment dollars by appropriately reallocating N within a given field to reduce risk and increase productivity?  By understanding landscape position and spatial variability as well as the influence that organic matter and water availability have on N contribution, we can more accurately predict N requirement and improve N use efficiency down to the acre or sub-acre.

As we enter the late vegetative growth and early reproductive stages of corn growth and development, it’s critical to have sufficient nitrogen on every acre. There’s an old saying that a healthy plant is a happy plant.  With fungicide and plant health applications around the corner, sufficient N management can have a significant impact on the plant’s ability to fight off disease and protect itself under stressful conditions. The combination of a Plant Health application and a healthy plant can have synergistic benefits from a disease perspective as well as the ability to reduce stress and lower respiration rates.  However, when N is a limiting factor, the fungicide and Plant Health application is often at risk of being trumped, leaving one disappointed in the results.

I’ve always said that 1 + 1 can equal 3.  Let’s make sure our N management program isn’t the limiting factor which trumps all other pieces of the agronomic production puzzle.  We have an opportunity to get N right on every acre and take advantage of mid-late season agronomic strategies that work together and allow us to finish strong. With current input costs and commodity prices, it’s imperative that we mitigate risk and maximize additional opportunity.

Jeremy Hogan

Lead Agronomist – Illinois & Agronomy Training Lead

Last Updated on July 26, 2024