Godsey Ag

Nitrogen Management


Nitrogen (N) management is often the largest expense of most grain crops. It is also perhaps the most important, whether you apply a flat rate across the field; variably apply it across the field; apply it all pre-plant; or make split applications. These decisions often significantly impact your ability to meet your yield goal and make money.

Research has shown that split applications and using variable rate technology will decrease N costs and has the potential to increase yield. Every producer will agree that yield is not the same over an entire field. This means that N requirement is not the same. This begs the question what can we do to increase N use efficiency and place N where it is needed? There are two main options for producers in regards to placing the N where it needs to go; sensor based N management or yield map based N management.

Figure 1. Variable rate N prescription based off of past yield history.

Sensor-based N management has been proven in winter wheat. On average producers using sensor-based N management saves $10/ac in N costs without sacrificing yield. This involves utilizing a N rich strip early in the growing season and using it to determine N requirement at top-dressing time. Using optical sensors does an excellent job of predicting N response within the growing season. N response varies from year to year based on precip. and soil temperature.

Over the last several years, we have fine-tuned several methods for successfully changing the N rate to match it with yield potential. The best method depends on the factors affecting yield differences. In most cases, basing N rates off of historic yield potential with several (3-4 years) years of yield data is the best method. This approach will work with any crop.

Some may view the N savings as minimal but the biggest potential to increase profits comes from targeting N to the high yielding areas of the field. In the past with uniform applications these areas have been under fertilized.Figure 1 is an example of N rate based off of historic yield. The different colors represent side-dress rate in irrigated corn from 5 to 25 gal UAN/ac. In this example the average N rate over the field is 20 gal/ac but as mentioned previously we variably applied it from 5 to 25 gal/ac. If the producer wanted to apply an N rate to meet his highest yield goal in the field he would apply the 25 gal/ac rate across the entire field. When comparing the variable rate application vs. the uniform rate the savings with variably applying is >$1500 for this 130 ac field assuming an N price of $0.75/lb.

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