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Little River, TX | This I got by reading in the Library at Blackland research.
This is based on work they on bermudagrass using ammonium nitrate at high rates.
I found this rule of thumb works on my land, Little River. bottom land, WC Evans farms on all sides of me.
This what they had to say and it is just like they say but with me using anhydrous.
A rule of thumb.
Up to half the nitrogen applied in year one can be used by the crop. Year two, half the applied nitrogen can be available to the crop and up to half the accumulated nitrogen can be used by the crop.
In a few years the crop apparently uses 100% of the applied nitrogen.
Then they say if you stop applying nitrogen it will require 5 years to effectively eliminate the residual nitrogen.
One year I applied a little over 1500 lbs/A of anhydrous on a small patch of bermudagrass. Something I do not recommend but for different reasons.
Here is the poop. Our soils have a very high CEC value. Mine runs from 40 to over 50 meq/100g CEC.
Ammonia is just another cation and it will quickly attach to the clay particles. (Nitrates are on their own.)
Not only that but our clay has a high shrink swell ratio and the clay plantlets temporarily separate during drying. Then when wet again the plantlets close and trap many of the cations. This includes potash, magnesium calcium and most of the micronutrients.
This is why our soil can test above 300 ppm K, and our crops will show potash deficiency symptoms. This is why my soil must test above 350 ppm K (better if it test above 450 ppm K) to prevent potash deficiency.
Word of caution, no one at TAMU or Extension will confirm this little fact.
Ed Winkle, probably give you some ideas about tissue sampling small grains. I limit my exposure to bermudagrass for hay and alfalfa as a cash hay crop.
Through some reading I found the process of drying our clay soil samples causes the plantlet to separate and more K, Mg, & Ca is reported as available than the crop can find during any one season. They assure me their grinding of the sample into a fine power does not add to the problem.
I gave up on TAMU years and years ago. Poor DR Caffman tried to fined why TAMU's lab reported our soil had excessive phosphate even though the farmers knew our crops had a positive response to phosphate.
Rick Haney, at Blackland, does not give TAMU a high recommendation. Till Rick proves his extractant, designed to work in high pH soils we will have to keep on as we were.
Way past my bed time.
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Are we all guilty ??
