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Old 09-13-2012, 12:35 PM
Skipster Skipster is offline
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Join Date: Dec 2010
Location: Billings, MT
Posts: 778
Quote:
Originally Posted by Smallaxe View Post
That would be interesting to know... They've recently shifted the the idea that P doesn't leach,,, yet now they are highlighting the conditions in which there may be some leaching...
This was your quote the other day. As far as I know, P has never been thought to leach at all, so I don't think that anyone is highlighting conditions under which P may leach.

You are right to recognize that K is not as tightly held on cation exchange sites as P. But, soil K is a different animal.

K usually hangs out in four places in soils.:

1) Unexchangeable K is held in K-bearing minerals, like micas and
feldspars (90-98% of soil K). This is NOT leachable and NOT plant
available.

2) Unexchangeable K can be held inisde layers of 2:1 clays (1-10% of soil
K). This is NOT leachable and NOT plant available.

3) Exchangeable K can be adsorbed to soil particles on CE sites and in soil
solution (1-2% of soil K). This is somewhat leachable and is totally plant
available.

4) Exchangeable K can be bound in OM (<1% of soil K).

A study by Jerry Sartain on sandy soils at University of FL in 1998 showed K source to be an important factor in leaching loss from turf. K2SO4 required 50 inches of water to move any K below the rootzone, while K3PO4 required 100 inches of water to move any K below the rootzone. Maximum leaching depth was 10 inches.

So, K can be leached, but it doesn't move far.
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