January 28, 2025

Plant-available nitrogen is constantly being supplied through mineralization, fixation and fertilization, lost through volatilization, denitrification and leaching, or becoming unavailable through immobilization. These factors are highly difficult to predict and often are environmentally controlled. Therefore, accurately predicting the “when,” “what” and “how much” when it comes to in-season nitrogen losses and contributions is almost impossible.
Weather conditions also affect corn nitrogen uptake and use efficiency. Accurately predicting the total nitrogen fertilizer rate required for corn from year to year and field to field is difficult. However, by understanding field characteristics and evaluating yield responses with different nitrogen fertilizer rates applied each year, you can at least get in the ballpark of the correct nitrogen rate needed.
Nitrogen supply varies
One of the most eye-opening and challenging factors when understanding corn response to nitrogen fertilizer is the soil’s ability to supply available nitrogen to the corn plant during the season. Many people often assume that if they don’t apply any nitrogen fertilizer, their yield will be terrible. That often isn’t the case.
Figure 1 shows yield data from replicated research plots performed across multiple Indiana locations in 2023 and 2024. It 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 shows the drastic differences in soil nitrogen supply and yield potential just based on location.
The field location in Farmland, Ind., is lower in soil organic matter, more poorly drained and less productive than the field in West Lafayette, Ind. The optimum nitrogen rates required follow a similar pattern to these results. The field in Farmland requires a higher optimum nitrogen rate of 240-plus pounds of nitrogen per acre, while the West Lafayette field requires 180 pounds of nitrogen per acre to reach maximum yield. Furthermore, yields at the optimum nitrogen rate for the field in Farmland were about 230 bushels per acre, whereas in 2024 in West Lafayette, yields at the optimum nitrogen rate were about 295 bushels per acre.
No clear answer
I still often get asked: “What is the target amount of yield I should get per pound of nitrogen fertilizer applied?” That number can change and differ based on year and location. In addition, yield and nitrogen fertilizer rate applied typically do not have a linear relationship.
Overall, I share this data to further highlight the complexities of managing and determining optimum nitrogen fertilizer rates. In some locations and years, strong yields can be achieved with no nitrogen fertilizer applied.
Many aspects about managing nitrogen fertilizer in corn are almost impossible to predict due to our inability to accurately predict weather over an extended time, but that doesn’t mean we can’t keep getting better. Try placing a couple of small blocks within a field with no nitrogen fertilizer applied to get an idea of the soil-nitrogen supply capacity. Varying multiple nitrogen rates within a field or two to further refine and assess optimum nitrogen rates in your own fields can help you be more efficient and cost-effective.
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