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Little River, TX | Brian,
The local official average rainfall is in the 35" area, while over 32 years of records I show a 37" average rainfall.
In my own use I use 28" as our average USEFUL rainfall.
Gerald J. is very astute in his observations! We tend to get our rains in Bunches. The Brian / College Station receives more rain than Seattle Washington but has way fewer days with rain.
Add to that here we have evaporation transpiration in all 12 months. It is a rare year that we see an average rainfall. Some years we may have 22" the next year we have 64".
One thing about a CEC is it is a function of the clay type and percentage and that does not change. True Organic matter also effects CEC BUT organic matter seldom goes above 6% in continuous sod. Three percent organic matter is more typical. Not much CEC associated with 3% OM.
For this reason I paid the extra money and ran a series of measured CEC analysis with Midwest Labs. ($40 each)
That data will still be good when my Great Great Grandchildren are in a nursing home.
The university types and learned authorities hint at the idea that the higher the CEC value th e higher the soil test for any and all cations has to be for the crop to benefit. There are a number of ways to compute this but roughly we can take our CEC times 11 and that is what we should have for a potassium soil test result. This is to have a reasonably good percentage of potassium in our crop. I have about given up on soil testing for potassium levels. Plant analysis is more costly, takes more effort, and forces us to plan at least a year in advance, but it still is better than soil analysis, HERE !
Something that is known by our university types is calcium tied up phosphate. In theory it requires 17 lbs of phosphate to change a soil test by 1 ppm P. PLUS another 10 lbs for each percentage of calcium carbonate (free lime) in the soil. Again Here, I need 70 lbs of phosphate to change a soil test 1 ppm P.
This is not a lost for ever phosphate, I expect I am using some of the phsophates my father applied in the 1950's ! I say this because of what I think I see in the plant analysis. Until the 1980's more phosphate was applied than removed. Starting in the 1990's less has been applied than removed.
From 1900 to 1950 little or no fertilizer, of any kind, was applied on this farm.
For now I see a positive crop response to P & K, though more is removed with the crop than applied each year.
Now to ammonia, & CEC. Here we can use this as a rule of thumb.
Only half of the Nitrogen we apply in a season is available to the crop that season. The other half becomes tied to the clay. Of this residual pool up to HALF is available to a crop each season. This residual can still be noticeable 20 years after a fertilizer spill.
We just do not see a luxurious consumption effect from over fertilization, because of the buffering effect of our high CEC soil. | |
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Gerald J you are addressing my greatest fear.
