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Coldwater, Michigan | Bill,
You bring up a point that isn't addressed very often, but still a factor to consider. Liming, or additions of Calcium, or Magnesium, or both tends to dominate the CEC exchange sights. First we "lime" to remove the Hydrogen element. By flooding the soil with similarly charged elements of Calcium and Magnesium (which have a stronger charge), we can knock the hydrogen off the soil particle. Similarly, with either Calcium, or Magnesium, we can knock potash off, if enough Ca and Mg are applied. That's not all bad! That makes potash more available.
That's part of the reason Ag Spectrum gets away without potash application for years. The gypsum application can help knock that loose, just as a liming program of any type can. The issue that runs thru my mind is: If we apply gypsum, what tells the sulfur that has been split out from the gypsum (Ca and Su) to attach to the Mg, instead of the Potash. Probably the stronger bond of the Mg dominates that reaction also. That being water soluable tends to possibly wash down the tile.
Still with me? Here it is: so we have Mg maybe taken care of! We still need to address the potash that was knocked off. Remember knocking it off wasn't all bad, it made it more available, therefore, possibly some good things. The rub comes in particularly in a lighter soil. Sometimes in S. Michigan we can't hold even potash in the soils w/o leaching. Deliberately knocking more loose isn't necessarily good! Even more to leach, and with that more possibility for potash shortages in a growing crop.
In our Eastern Indiana, NW Ohio soils, many people on the Ag Spectrum program have not applied potash for years, possibly due to this effect. These are heavy soils with lots of potash, many times the pH is very high as well (7.4-8.2). Adding gypsum may indeed knock potash off for years. One day the piper showed up for some of them, and they were found with low potash levels. One after another with low potash levels.
That was "Never" supposed to happen! But it did! What's the answer? Common sense!
I think some of the traditional programs I sold when I was with Sohigro, and later Terra, were in many cases wasteful. Maybe more fertilizer than was necessary with our current understandings of what it takes to make a crop. It certainly never really considered what was in the soil. For the most part, comercial recommendations don't really care what the soil test reads, so much as what it takes to maintain the levels (keep the doors open).
You guys have in many cases been sold the bill of goods "you don't want to rob your soil" or "you don't want to deplete your soil". When my father died, his soil test levels were for "P" approximately 7&8 times what is generally accepted to be enough to raise the fields yield potential. His potash reading were approximately 3-4 times what would have been considered enough for that same potential. Don't cry for him very long because he wasn't the one farming it for the last 14 years of his life. The tenent stated "that's what they told me I needed".
Assume for the sake of arguement, that the soil levels vs. yield potential is true. If that be true: why would you want to maintain those levels? Why would you NOT want to rob your soil?
Our universities tell us that of every 100# of "P" we apply to a row crop (corn in particular) we only get the use out of 20# at best in the year of application (if it is banded beside the row). If it is broadcast they tell us we are lucky to get 5# in the year of application. The rest they tell us (80-90%), is tied up by the soil and becomes available in later years at the rate of approximately 1% per year. Even though it never shows up on a soil test, that build up is there. Man there are better ways to get bushels for lesser applications of "P". Some soils will tie the "P" up to the point of reading low on the soil test in just a few years, if you never grew a crop on it. They have that ability to fix "P". By making annual applications of "P" we can keep the soil test reading high. It may not be more productive, but it reads "HIGH" and that is what the experts say you have to have.
Soils have the same ability to do that with Potash depending on what is going on out there. Bill "HAY" Wilson keeps making the point that his is different than the rest of ours. Not really Bill! Yours is different in that it is "there", and you have discovered that what you have going on isn't the way it was always (maybe still is) taught. That is no different than what many others are beginning to find in their area. That's why your soils aren't necessarily different than the others are "Different". Maybe they never were the way we were taught either, except in the "ideal" sense.
Ag Spectrums potash situation wasn't all bad, they just didn't adjust to a changing situation. Actually, they couldn't! They had told people that they would never need potash, they had enough. They had told people they didn't need any more phosphorous than just enough to get the plant started. Their products would do the job from there. Those ideas were in many cases true, at least for a time. But they don't dare to change, because it then makes their absolutes to be untrue. If those aren't "true", then how much of the rest is also untrue? They are in a box.
I personally believe, and have believed, a more common sense approach needs to be taken to soil fertility. One that lands in the middle. I believe we have used too much in some cases, in the past. I also believe the weaning of the soils from those extremely high numbers needs to be done with caution. Yes the AS approach can work for a while, but let us use some common sense while we are doing that.
Sorry, I didn't mean to get that far on the rant!
Edited by Bill Moyer 9/30/2007 17:10
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¿ High Mg soils treated with gypsum?
