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  • Writer's pictureRachel

In-Season Nitrogen: Sidedress and Rescue Operations

Weather has posed a lot of different challenges for us this spring. From delayed planting and spraying, this year has been anything but easy. An additional challenge we are facing is reduced nitrogen supply from excessive spring rainfall. Normal climate data suggest that we receive around 14.94 inches of rain from March 1 to June 30th. This year we have received 20.76 inches of rain from March 1 to date. This extra rain in a shorter amount of time has resulted in loss of nitrogen through leaching and denitrification. This blog post will cover estimates of how much nitrogen we lost, rescue operations and sidedress methods, and useful tools for nitrogen management.

Nitrogen Loss

Nitrogen loss from excessive rainfall is quite common. This loss can be broken down into two categories: loss or transformations. Both effectively make the supply unavailable to the plant. The three modes of loss/transformation are leaching, denitrification, and volatilization.

Estimates by Iowa State suggest that 4-5% of Nitrate- N is lost by denitrification for each day the soil is saturated. Similarly, when soil temps are between 55-60 degrees, they expect a 10% total loss when saturated for 5 days and 25% loss when saturated for 10 days. These losses will increase with warmer soils. These losses will be worse with tile drainage. The more water flowing through the tile, the more nitrogen lost. Take special consideration for fields that you have a large amount of tile drainage in.

Losses of N will come from both the soil N that you have supplied to the field and the N in mineral forms in the soil. It is possible that coming off of two dry growing season that we have a larger amount of mineral N supply available. However, some of the mineral N will have been lost the same as fall or spring N applications. This makes calculations for residual N more complicated. Iowa state suggests using soil nitrate tests to calculated the amount of available N after a wet spring. Alternatively, computer models can provide insight into possible available N. Use of a chlorophyll meter or aerial images can also be very useful in determining available N.

A rough rule of thumb is this: if the total rainfall from April 1 to June 30th exceeds 15.5 inches, a sidedress application of Nitrogen is needed. That is the case this year. So what application method is right for you?

Rescue Operations and Sidedress Methods

Pioneer lists the following as the most desirable to least desirable sidedress sources:

1. Inject Anhydrous Ammonia or UAN between rows

2. Broadcast solid ammonium nitrate or ammonium sulfate

3. Broadcast urea

4. Dribble UAN between rows

5. Broadcast UAN

Honestly, one of the best methods of applying sidedress nitrogen is through irrigation. This can be applied when it is most convenient for you and at growth stages past when high clearance equipment can get through. However, since this is not an option for everyone, look over the previous list, talk with your agronomist about economical sources, and available equipment to pick out the source best for you.

There are some considerations as we start into sidedress. First, try to limit a single sidedress application to no more than 1/3 of the total crop supply. This will help reduce the amount of burn and damage to growing plants and root systems. Next, nitrogen stabilizers are recommended with any liquid application. We suggest using a volatilization inhibitor called Agrotain Plus.

We have several options for rescue operations if we don’t get nitrogen on in time, or don’t get enough on during one application. First, a study from Purdue suggests that rescue applications can still result in equal yields similar to a single spring application. While this may be surprising, remember when the majority of nitrogen uptake takes place. The majority of nitrogen supply is needed between V8 and VT. This may be a window of only 30 days. Another way of looking at it is this: 70% of nitrogen uptake happens up to and at silking. 30% happens after. If we are able to get nitrogen on during this critical period of uptake, then we are achieving one of our highest goals with nitrogen management: match the available N to when it is needed the most. While we have stated that the max uptake is up to silking, it is recommended to get the nitrogen on before V12. After this point the nitrogen use efficiency of the plant does begin to decrease.

In terms of sources of N for rescue operations, Pioneer recommends a UAN solution dribbled between rows if at all possible, but NOT broadcast. Another option recommended is granular nitrogen by airplane.

Tools for Nitrogen Management

One of the tools we have at our ready disposal is Encirca Nitrogen Management. This tool takes into account soil types, amount of nitrogen applied, when it was applied, growth stage of the crop and amount of rainfall to calculate the amount of surplus or deficit nitrogen for the crop. In years like this, that knowledge can be extremely useful. With increasing service levels also come variable rate nitrogen recommendations tailored to fit your field and hybrid. Check out this video to find out what Nitrogen services can do for you!


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