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Considerations for sidedressing nitrogen

Jun 05, 2020

Corn utilizes an incredible amount of nitrogen per day. In fact at V6, the corn will uptake 25lbs N per day. This is why it is so critical to ensure that nutrient levels in the soil are adequate enough to get the corn plant through the season. With sidedressing either here or right around the corner, be sure to consider some factors before making that critical application.

1: What Did You Apply For Nitrogen Previously and Did You Use a Stabilizer?

This should be the first question you think about when deciding if you should sidedress or not. Did you apply enough nitrogen (N) or Sulfur (S) in the fall to make it through the summer? If not, the decision to sidedress is easy. If you did apply enough in the fall, there is a chance that weather (or other conditions) had an impact on the N and you need to apply more. Sometimes nitrogen stabilizers can help, but depending on the rainfall amount, they may not be as effective as you initally hoped.  Consider the next 3 questions when deciding if your fall application was truly enough.

2: Did You Have Above Average Rainfall?

More than likely your answer this year is yes! Weather, especially rain, negatively affects both nitrogen (N) and sulfur(S). N and S can be washed out of the soil as the water drains or runs off. In above average rainfall years, we see an increase in the sidedressing applications due to lower levels of nitrogen in the soil. Take a look at the rainfall in your area, was it above average? If so, you probably lost a good portion of your available N and S.

3: What Does Your Tissue Sample Say?

When your plants emerge, you now have the ability to take a tissue sample. Sampling can give you a little bit more insight into how much nitrogen or sulfur the plant is getting from the ground. If your tissue sample results comes back and your N level is less than 4.2%, your plants would greatly benefit from a N application.

4: Did You Take a Pre-Sidedressing Nitrate Soil Test?

A Pre-Sidedressing Nitrate Soil Test (PNST) is a 12-inch soil sample that give an in depth (no pun intended) look at your soil. As the plant grows, the roots dive deeper into the ground. A typical 4-6-inch soil test won't tell you what’s actually going on in the root zone. This is because the roots have grown below the 4-6 inch depth of your previous soil sample. If your PNST comes back with a score of 25 ppm or less, you should seriously consider applying more N through sidedressing. To learn more about the PNST, check out this article. It is also important to remember that sidedressing can be influenced by soil texture. For example, especially course textured soils may been multiple side dress applications to maximize yield. 

5: More Decisions to Be Made…

Now you may be asking, they want me to do this for every one of my fields?! In a perfect world, we would hope every field could have such an in-depth investigation. However, we know how busy this time of the year is, so we suggest selecting 10 of your “worst” fields to look at. Determine “worse” fields by looking at Response to Nitrogen Scores (RTN) and using a crop modeling tool like the Winfield United Field Forecasting Tool.

RTN scores can help you decide what varieties you need to pay special attention to. Varieties are rated by how well they will respond to a nitrogen application. If you are going to sidedress, be sure to apply fields planted with varieties that have a higher RTN. These will require more N and should be prioritized. Talk with your local Centra Sota Crop Advisor to find out the RTN score of your varieties.

Crop Modeling is another way to help you determine if your fields would benefit from a nitrogen application. Tools such as the Field Forecasting Tool and R7 imagery can help you get a different perspective of the state of your fields. Work with your Centra Sota Crop Advisor and have them show you how these tools can be utilized on your farm.

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