[RWG] Some weeds may just be there, because of low potassium

[Wayne Tyson]

Anything this earth-shaking should be published, showing the detail with 
respect to methods and procedures. Presuming that the information regarding 
K-deficiency = weeds because the weeds absorbed all or most of it, leading 
to K-deficiency in indigenous species was gleaned from published research, 
it would be nice to have some references and links.

Most cheap soil test kits are not accurate enough to give the whole relevant 
picture. Samples should be taken from near the surface, in the top half to 
one-third of the root zone, and as near to the bottom of the root zone as 
possible. I have seen wild differences among these three sampling regions.

Of course, checking the plants for K is even more important. If the weeds in 
question or weeds in general sequester more K than indigenous species, 
particularly if they create K-deficient soils that kind of evidence should 
be verified and the methods replicated before sending everybody off on a 
K-fertilizing binge. It might also help to check the K pathways and 
conditions of availability. P availability is restricted by a number of 
mechanisms, but there is usually so much K present in most soils that it can 
safely be left entirely out of any nutrient-adding "programs."

In fact, one way of restricting weed growth is the concept of 
"anti-fertilization," as in using iron to interfere with P absorption by 
non-mycorrhizal weeds.

Dremman has posed an interesting possibility, but one which I hope he will 
share more details.

WT


----- Original Message ----- 
From: "Craig Dremann - Redwood City Seed Company" <Craig at astreet.com>
To: <rwg at lists.plantconservation.org>
Sent: Thursday, November 10, 2011 5:12 PM
Subject: [RWG] Some weeds may just be there, because of low potassium


> Dear All,
>
> Tests done in California this year on solid Italian thistle and Medusahead
> grass infested area, point to their infestations are largely due to lack
> of potassium in the soil.
>
> When California's understory was converted from a perennial bunchgrass
> community to annual exotic weeds 100+ years ago, these exotic plants are
> very efficient soil nutrient scavengers.
>
> A lot of work has been done to manage two weeds in our State, the
> Medusahead grass and Italian thistle, without much luck, because the
> causes of the infestations were unknown until now.
>
> Using a $5 soil test kit that you can buy for your garden at most hardware
> store, you can test the top inch of soil in a Italian thistle or a
> medsuahead grass area, and see that it the potassium has been removed by
> decades of grazing, and might be bouncing right around zero.
>
> In the experiments I did this last year, I used cheap and easily available
> bulk Potassium sulfate that is commonly used by farmers, plus some local
> native seeds.  This may be an easy solution for annual and biennial weeds
> that seem to resist other methods, like cheatgrass, yellow star thistle,
> etc.
>
> By adding local native seeds at the correct pounds per acre, and adding
> the right amount of potassium, you can get a nice stand of natives in the
> place of either of these two weeds within six month.
>
> So instead of these two plants being considered bad weeds, we should now
> look at them as soil potassium indicators, and that they are trying to
> tell us that our potassium soil level is on empty, in the areas that they
> colonize.
>
> I hope that this information is useful to others working on weeds that
> look like they are invasives--but when we test the soil, these plants
> might just be indicators that our cows and sheep ran away with too much of
> a key nutrient--and we now need to make a deposit in the soil nutrient
> bank, instead of fighting the weed.
>
> Sincerely,  Craig Dremann (650) 325-7333
>
>
>
>
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