Home » Canola Trials » Some thoughts on pre-plant nitrogen and a little outside the box thinking

Some thoughts on pre-plant nitrogen and a little outside the box thinking

It is that time of year, every Co-op I drove by the other day had a line of trucks pulling anhydrous tanks and the spinner spreaders were being loaded.  For those of you who haven’t applied your nitrogen yet lets discuss the options traditional and nontraditional.

Anhydrous Ammonia, 82-0-0: by far the most widely used N source is the southern Great Plains.  While it is not the most enjoyable to work with it is the cheapest per pound of N and that leads to its wide spread use without Oklahoma wheat production.  Just a few simple rules with NH3, get it in the ground and close the row behind you.  In conventional till this is usually easier unless the ground is too wet or too dry.  In no-till this may be a little more challenging but usually easily accomplished.  With the rise in low disturbance applicators I am seeing more and more acres of no-till receiving NH3.  Last year I was in a field of stripper stubble and I had a hard time finding where the rig had run, minus wheel tracks.

Urea, 46-0-0: is second on the hit list in nitrogen sales in our state.  It is a safe source that is easily handled and applied. In a conventional till system where the urea can be worked in shortly after application it is a very efficient and effective source.  Unfortunately when it is applied to the soil surface and rain is the method of incorporation we can experience between 5-60% N losses.  The losses come from how urea is converted to plant available ammonium (NH4).  For urea (NH2)2CO2, to be converted to plant available NH4 it needs the enzyme urease.  Urease is present everywhere but in the highest concentrations on plant residue.  The figure below shows the reaction, urease converts urea into NH3 as soon as the prill dissolves.  In the presence of moisture the NH3 (gas) is turned immediately to NH4 (solid) and is absorbed onto the soil particle.

Graphic of Urea's conversion to plant available ammonium.

Graphic of Urea’s conversion to plant available ammonium.

The problems come when there is no soil particle for the NH4 to bind with.  It usually takes 0.50 inches of rain or irrigation to fully dissolve and incorporate urea into the soil.  So if we only get a few tenths or hundredths, even heavy dews, some of the urea will dissolve, be converted to NH3 then NH4 and be left on the plant/residue.  When the moisture dries, some or all of the NH4 goes back to NH3 and will gas off into the atmosphere. I have even seen this happen when urea is applied on a wet/damp soil, not incorporated and it doesn’t rain for significant period of time.  If the temps are cooler the urease is slower so less of the urea is converted to NH4, but if the temps are warm 60+ degrees these little enzymes can act very quickly.

Urea placed on the surface of a wet soil under two temperature regimes. White text is the number of hours after application.

Urea placed on the surface of a wet soil under two temperature regimes. White text is the number of hours after application.

Urea placed on dry soil, Top row: dry soil no water added, Bottom left, moisture added from subsurface, Bottom right : simulated rain fall event of 1/2". White text is the number of hours after application.

Urea placed on dry soil, Top row: dry soil no water added, Bottom left, moisture added from subsurface, Bottom right : simulated rain fall event of 1/2″. White text is the number of hours after application.

 

 

 

 

 

 

 

 

 

 

Below is a short video on using urea fertilizer.

While the recent rains are a blessing and will surely help germination, it is not aiding our N use efficiency especially in no-till. That is why in some parts of the state you may see some grain drills running right now.  Some of those producers are not planting wheat they are actually applying there pre-plant urea.  I have even been told in the SW part of the start some producers are using air-seeders to apply their urea.  While this seems like a costly venture I have worked with the Ag Economist to create a calculator to figure up the break even for when it would pay to use an air-seeder over the traditional spinner spreader in no-till. We hope to put the finishing touches on it in the next few days.  When it is completed it will be shared on this blog.

Liquid Urea Ammonium Nitrate, 32-0-0 or 28-0-0: while this is one of the more expensive forms of N many producers are utilizing this source because the can pre buy and store on site and as sprayer get larger they can cover a significant amount of ground quickly.  For the most part UAN is used in no-till and is a great source.  I always recommend that applicators use streamer nozzle or streamer bars to apply UAN.  When UAN is applied via a flat fan nozzle it spreads the fertilizer across the residue allowing a significant portion to be tied up.  The streamers concentrate the fertilizer into streams/bands reducing contact with residue and increasing the amount of UAN that reaches the soil surface.

Timing and Rates

The cost of anhydrous, about $0.1 to 0.12 less per pound N less than urea is driving its use this year.  The lower price is also driving a significant about of producers to go with 100% of their N pre-plant.  While this makes for sound economics now having all of your N upfront is like putting all of your eggs in one basket.  If we do get that cold and wet winter as some are calling for this presents a great chance for the N to move down the soil profile and down the slope.  I have always recommended split application.  This allows a producer to judge the crop throughout fall, winter and even yearly spring and adjust his or her N plan accordingly.  For those who plan to graze there is still a need to get enough N down to produce fall forage, this may be 50 to 80 lbs of N, but for grain only production planted later in the fall a typical crop may only need 20-30 lbs of N before going into winter.  The old rules of thumb, 2 lbs N per bushel and 30 lbs N per 100 lbs of gain still work and are better than a guestimate but we have better ways. Right now is the time to plan to apply N-rich strip, a strip in the field with 40 to 50 lbs more than the rest of the field.  These strips can be applied with a variety of applicators, but as long as the N goes down in at least an area 10 ft wide by 300 ft long it is good to go.

Just a few of the applicators used for putting out N-Rich Strips. Not shown is NH3 applicator.

Just a few of the applicators used for putting out N-Rich Strips. ATV Sprayer, Receiver Hitch mounted Sprayer, Road sprayer with a rear boom, pull type spinner, large sprayer, push spreader.  Not shown is NH3 applicator.

Below is a N-Rich Strip 101 video.

If you have got the N-Rich strips out you can set back and watch to see when and if they develop.  If you can see the strip you know you need too fertilize.
While many are not ready to think about top-dressing yet, it is never too early.  Don’t be afraid to think outside the box.  Oklahoma’s springs tend to present the perfect conditions for N loss when urea is the primary N source.  This year in a 4R Top-dress Nitrogen Application Demo, at Lahoma and Chickasha, we are going to apply just about every available commercial source in about every possible manor.  Urea will be broadcast, coated with inhibitors, applied with a grain drill, NH3 will be knifed in, and UAN will be applied with flat fan nozzles, streamer nozzles and knifed in.  As technologies improve and the cost of N remains relatively high the options for top-dress N application will continue to improve. The economics of wheat production don’t look great right now so don’t be afraid to think outside the box, even if it does raise the eyebrows of your neighbors.  Fill free to contact myself or your local extension educator if you have any questions about N application.

 

John Deere double disk drill used to apply urea in-season.

John Deere double disk drill used to apply urea in-season.

WAKO NH3 applicator used for in-season application.

WAKO NH3 applicator used for in-season application.


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