High levels of potassium in lawn soil

I tested a few places front and back and all were pretty much the same. pH was 6.5-7.0 everywhere. Nitrogen was non-existent as I expected, phosphorus was the good range. (Sorry I don't have the values here with me right now.)
But potassium was way high off the scale. I checked again using half the amount of soil, and still came out in the low end of the high range.
The only fertilizing I have done is once a year or less with 15-15-15 and a drop spreader.
What I'm wondering is where that high level could have come from? And if this level is high enough to do damage? Have grass, avocado & lemon tree in this area.
This was the best test kit I have ever used -- will post the info & values I got later.
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On 6/23/2014 12:50 PM, Guv Bob wrote:

expected, phosphorus was the good range. (Sorry I don't have the values here with me right now.)

tree in this area.

One source of potassium is in the ash falling out from a wild fire. Also, there are soils that are naturally high in potassium, generally mineralized soils. In the latter case, however, most of the potassium is not available to plant roots; instead, it slowly dissolves, which provides just enough for plant growth.
The books I have only discuss potassium deficiencies, not excesses. You might try a Web search.
Since phosphorus does not readily dissolve and you already have abundant potassium, you are wasting money on a 15-15-15 fertilizer. You should concentrate only on nitrogen. Just be careful that you do not use something like ammonium sulfate (27-0-0) or urea (50-0-0) on grass; it will burn.
You should clear the grass from the drip zones of the lemon and avocado. Not only do they suffer when grass grows there, but also they have very similar fertilizer needs that differ from grass. Citrus and avocado require an acidic fertilizer that contains iron and zinc.
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David E. Ross
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Thanks for the info, David. We are downwind from a camping area and get a little smoke, especially in the summer.
Avoc trees are in the middle of the yard, 25+ feet canopy each and cover most of the yard. Is is OK to put down the N-rich fertilizer inside the drip line?
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On 6/23/2014 3:19 PM, Guv Bob wrote:

Use commercial citrus food on the avocado, after making sure it contains zinc. This should not harm the grass. Just make sure the grass was irrigated within the past two days, but not on the day you apply the fertilizer. NEVER apply fertilizer when the soil is dry; NEVER broadcast ferilizer when foliage is wet.
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inside the drip line?

Thanks, David. Any way to home test for iron and sulfur?
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On 6/25/2014 9:53 AM, Guv Bob wrote:

I do not test, so I am not familiar with testing methods. Instead, I rely on the appearance of growing plants. I can recognize mineral deficiencies from the appearance of leaves.
As for sulfur, the amount is generally irrelevant. Soil bacteria slowly convert it into sufuric acid, so slowly that it does not burn plant roots but quickly enough to lower the pH of alkaline soils. The process is so slow that I use only a small amount at a time; I do not want to waste it. I use it only on certain acid-loving plants: gardenia, camellia, azalea, liquidambar, and rose. I definitely keep sulfur away from dianthus and iris, both of which prefer an alkaline soil.
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