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Fall Fertilizer Applications (08/29/19)

With the problems applying fertilizer in fall 2018 and fertilizer application delays spring 2019, I anticipate much more interest in fall fertilization this year than in most years.

With the problems applying fertilizer in fall 2018 and fertilizer application delays spring 2019, I anticipate much more interest in fall fertilization this year than in most years. The following are guidelines to consider.

Fall strip-till

  The best plan to make sure that the strip-till strips are made is to run the strip-till implement directly after harvest of early crops. Fertilizer P and K, if needed, can be applied in an August/September strip-till pass, but fertilizer N should be delayed as detailed in the ‘Fall N application’ guidelines later in the article.

Fall P and K application

  Fertilizer P and K can be applied anytime in the fall that field conditions permit. For no-till fields, surface application is possible, but not when fields are frozen. Application with an air-seeder or similar implement can help prevent movement of recent surface-applied fertilizer should a heavy rain fall shortly after the application.

Fall N application

The guidelines for fall N application are as follows for ND:

-No fertilizer N (except the small amount in MAP or other P products) before October 1.

-After October 1, wait until soil temperature measured at 4 inch depth between 6AM and 8AM reaches 50oF or lower. At that date it would be reasonably safe to begin anhydrous ammonia application.

-Wait another week to begin banded urea application.

-Wait 2 weeks after the anhydrous safe date to begin broadcast urea application.

These guidelines are no guarantee that some ammonium-N will not transform to nitrate should we experience a long fall period before soil freeze-up, but these guidelines are practical compromises to allow semi-protected ammonia stability in most fall seasons.

The two chemistries that have nitrification inhibited are nitrapyrin (N-Serve™, Instinct II™, others) and DCD products. In research studies the formulation with greatest effectiveness tends to be the N-Serve for anhydrous ammonia. The urea products show effectiveness, but not to the same degree. For best effectiveness, use a DCD rate on urea which is similar to the concentration in SuperU™ (Koch product).

See the circular Nitrogen Extenders and Additives for more detailed information -https://www.ndsu.edu/fileadmin/soils/pdfs/Nitrogen_Extenders_and_Additive_for_Field_Crops_2017.pdf  (Reference to specific products are not endorsements of these products).

A nitrification inhibitor should not be used to push application date of N fertilizers earlier. The nitrification inhibitors can best be used to provide protection against a warmer-than-normal fall, or a longer fall period than anticipated.

Fall Sulfur?

Sulfur is not a fall fertilizer. Sulfate-S can leach in the spring, so fall application is unreasonable. It can only work if there is a drought. The proposed strategy of using elemental-S in the fall is flawed, because any sulfate produced from this application in the fall is susceptible to leaching in the spring. The remaining S is elemental-S so release of any available S would be very slow and probably not enough to sustain any crop that requires S. So spring applied sulfate-thiosulfate fertilizers are the rule.

Lime application

I realize that limestone application/sugarbeet waste lime/municipal water treatment lime application has not been common in North Dakota, but that history is changing rapidly. In the west particularly, as I tried to convey in a previous C&P report, there are great expanses that have pH as low as the high 4’s. In no-till fields, recent research from the North Central and Dickinson R&E Centers indicate that great improvements can be made with surface application. Sample the 0-2 inch and 2-6 inch depths in a zone pattern within fields and lime accordingly.

One to 2 tons per acre of sugarbeet/municipal lime sources should be sufficient to correct a low pH, Al toxicity problem for several years. Fall is the ideal time to apply lime. Time is too short in the spring for practical application.

 

Dave Franzen

Extension Soil Specialist

701-799-2565

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