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user picture Paul Carter

How much soil N is available for the crop so far in 2021?

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Many growers and agronomists check GDUs weekly to track crop growth compared to long term averages. Now, you can also check weekly estimates of soil N mineralization compared to long term average to assess the pace at which soil organic N is becoming available to the crop in mineral forms.

The tool is available and described at this site developed by Drs. Sotirios Archontoulis, Mark Licht, and Michael Castellano at Iowa State University.

Note from the graphs below that the pace of soil N mineralization is slow so far for 2021, but will speed up as the soil warms if there is sufficient soil moisture for the soil microbes that facilitate conversion of N in soil organic matter to plant available N forms.

Note the wide variation from year to year in soil N mineralization during the growing season (see gray lines).  This variation along with variations in N losses is one reason the optimum N rate varies from year to year for corn. Use of 4R stewardship tools such as in-season and variable rate N application can help adjust N rates to match seasonal and soil type variations in soil N mineralization.  

For a larger view, you can click on the graph. 



  • Corn
  • Crop Management
  • Nitrogen, Phosphorus, Potassium
  • Nutrient Management

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Granular has an excellent tool that accounts for temperatures, application of units, source of n and the biggy, rainfall. Ton of history and data that built this model. I have a ton of faith in it. 

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This is really great information, Paul! Dr. Castellano is now on TopYeld, so I hope that he will poste a response to this thread directly. I asked Mike earlier this week whether the cold, dry weather earlier this spring would have caused below-average mineralization. I was surprised to learn that #Plant21 in Iowa has had close to average nitrogen mineralization so far. In addition, apparently there is still a lot of nitrate in the soil from last Fall (both from applied and mineralization). If we get a major rain event in Iowa, we're likely to have a major flush of nitrate which will pose big challenges to Des Moines Water Works and other municipal source water utilities charged with ensuring that the nitrate concentrations in drinking water fall below the Safe Drinking Water Act Standard of 10 parts per million. You've inspired me to do a post on that in the near future.  

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Billie, were you using Encirca prior to this year? I’m curious to hear how the Granular platform may or may not be an improvement over Corteva’s previous precision Ag platform after Corteva acquired Granular. I’m assuming the integration between Encirca and Granular has happened by now, but I’d enjoy hearing your take on that. Thanks.

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The integration with granular is a huge improvement. So many more options, tracking , and much more user friendly. Much more informative to a grower.

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It's great that Granular has been valuable to track and manage N on your farm. Do you use the Granular prescriptions for VRN?

I wanted the TopYield.Ag network to know about the useful and readily available N mineralization tracking information and tools from the Iowa State University team, but for those ready to get deeper with the same and more information for their specific fields as tools to manage N --- Granular is a consideration. (Since you brought Granular up, Billie, will mention here that from 2013-2018 I was on team developing the Encirca N tool version and it's great to hear that this is even better now as Granular.   

One of the team members then and now leading the Granular agronomy effort now is Bob Gunzenhauser.... and for those on the TopYield Ag network who want more information, below are links to his blog plus an audio interview. 

Those on the TopYield.Ag Network with experience with other tools can chime in with there observations too.


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