Corn nitrogen management headaches and the soil nitrogen supply conundrum 

By Dan Quinn, Ph.D. Purdue University Extension Corn Specialist 

Nitrogen fertilizer is a hot topic each year in corn management due to its high cost, necessity for adequate yield production and environmental impacts. However, nitrogen fertilizer is and will continue to be a very challenging nutrient to manage due to its unpredictability and connection with weather conditions. 

For example, in an agronomic system, plant available nitrogen is constantly being supplied (mineralization, fixation, fertilization), lost (volatilization, denitrification, leaching) or becoming unavailable (immobilization). And to add to the complexity, all of these factors are highly difficult to predict and are often environmentally controlled. 

Therefore, accurately predicting the “when, what and how much” when it comes to in-season nitrogen losses and contributions is nearly impossible. In addition, weather conditions also impact corn nitrogen uptake and use efficiency. This is why accurately predicting the total nitrogen fertilizer rate required for corn from year to year and field to field is so hard. 

However, by understanding various aspects such as field characteristics (rotation, soil type, drainage class, etc.) and evaluating yield responses with different nitrogen fertilizer rates applied each year, farmers can at least get in the ballpark of the correct nitrogen rate needed. 

Corn response to nitrogen 

One of the most eye-opening – and also challenging – factors when understanding corn response to nitrogen fertilizer is the ability (or lack of ability) of the soil to supply available nitrogen to the corn plant during the season. One interesting aspect from doing a lot of nitrogen rate research trials, each of which contain replicated treatments across different fields, is observing how much grain yield can actually be produced when no nitrogen fertilizer is applied, and how this differs based on year and location. 

Many people often assume if they don’t apply any nitrogen fertilizer, then their yield will be terrible, which often isn’t always the case. Figure 1 shows corn grain yield data from replicated research plots performed across multiple Indiana locations in 2023 and 2024 and highlights both the level and distribution of yields when no nitrogen fertilizer is applied. 

In just these four locations in 2023 and 2024, corn yields when no nitrogen fertilizer was applied ranged from 20 bushels per acre to 210 bushels per acre. Therefore, this data showcases the drastic differences in soil nitrogen supply and yield potential with no nitrogen fertilizer just based on location. 

The field located in Farmland, Ind., was lower in soil organic matter, more poorly drained and less productive than the field in West Lafayette, Ind. In addition, the optimum nitrogen rate required follow a similar pattern to these results with the field in Farmland requiring a higher optimum nitrogen rate (more than 240 pounds N/acre) vs 2024 West Lafayette (180 pounds N/acre) to reach maximum yield. 

Furthermore, yields at the optimum nitrogen rate for the field in Farmland were approximately 230 bushels per acre, whereas at 2024 West Lafayette, yields at the optimum nitrogen rate were about 295 bushels per acre. 

What is the target amount? 

I still often get asked the question “What is the target amount of yield I should get per pound of nitrogen fertilizer applied?” 

Just from looking at this data shows how much that number can change and differ based on year and location. In addition, yield and nitrogen fertilizer rates applied are not linear relationships. 

Overall, I share this data to further highlight the complexities of managing and determining optimum nitrogen fertilizer rates in corn, the fact that in some locations and years strong yields can be achieved with no nitrogen fertilizer applied, and where further research and examination is still needed. 

There are many aspects about managing nitrogen fertilizer in corn that are nearly impossible to predict due to our inability to accurately predict weather over an extended time period, yet that doesn’t mean we can’t keep getting better. 

Also, don’t be afraid to try placing a couple small blocks within a field with no nitrogen fertilizer applied to get an idea of what the soil nitrogen supply capacity is. In addition, varying multiple nitrogen rates within a field or two to further refine and assess optimum nitrogen rates in your own fields and locations can help you be more efficient and cost effective with your nitrogen fertilizer applications.