Agronomy Talk

Agronomy Talk: Economic Optimum Nitrogen Rate - Corn

Published on Tuesday, March 10, 2020

Nitrogen (N) is a critical input for a corn crop’s success. It is also one of the more challenging inputs to manage as every year brings a different set of environmental conditions that can change the response to different forms, timing, and placement of N on your farm. Researching N is equally challenging because so many external factors can impact the results. That’s why multi-year and multi-location data are key components to gaining a deeper understanding of N results. Through Beck’s PFR, we will continue to evaluate different timing and placement methods as we strive to help solve the puzzle that is N management.


We have learned over time that some hybrids and hybrid families tend to have a higher likelihood of response to fullseason N availability while others may have a lower level of response. It is important to know which category the hybrids you're planting fall into so they can be placed in fields and situations that may provide the best opportunity for fullseason N availability. The Beck's Product and Program Guide contains ratings and information on all Beck's hybrids in regards to N response. 


Stalk nitrate samples illustrate the genetic differences between hybrids in a given year. Below are stalk nitrate samples taken at black layer from the 2017 Indiana N Rate Corn after Soybeans study. Genetic differences are apparent as the more efficient N user consistently has greater nitrate content in the stalk compared to the higher N user. It’s clear that at this point, when the N has moved from the stalk to the ear for grain fill, more N is required with the higher N users when compared to the efficient N users. 


For nine years, Beck's PFR has worked to determine what the Economic Optimum Nitrogen Rate (EONR) is in a corn after soybean rotation. As a mobile nutrient, the amount of N that is necessary in a given year varies due to environmental conditions. However, our EONR consistently comes in around 190 to 195 units of N /A. In a given year, we typically see a 25 to 50 unit difference in the EONR between the N efficient hybrid and the higher N user at a given site. For the corn after soybean rotation, this is traditionally 175 units for the N efficient user and 200 units for the higher N user. This has resulted in a long-term average EONR of 190 to 195 units nitrogen/A. 


In nine years of corn after corn N data, we have observed similar trends to those in corn after soybean rotations. The higher N user typically requires more N than the N efficient hybrid. However, the overall EONR is typically higher for the corn after corn system. This greater rate results from the previous corn crop residue tying up N from the current season in what is called the “carbon penalty.” This results from the fact that a specific C:N ratio is ideal for promoting microbial activity and the breakdown of stalks from the previous season. By adding more N, we feed the soil microbes that can help with stalk degradation and ultimately, promote yields. 


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Author: Jim Schwartz

Categories: Agronomy, Agronomy Talk


Jim Schwartz

Jim Schwartz

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