Re: [compost_tea] low phosphate?
Hi Thomas,
That's really interesting, espescially along with what Elaine just wrote
(sorry my message was a bit brief, Elaine, but you got the drift ok).
So, as for the P figures you mention Thomas would they all be considered
"available" in the sense of Bray-2 or Reams style extractions?
And when talking of applying P, surely it wouldn't all be available
immediately?
If it were, it would upset the soil mineral balance very greatly?
Oh, and would it be ok for me to post the BDnow! list with developments in
this thread? Elaine, Thomas?
Lynton
----- Original Message -----
From: Thomas Giannou <thomas_at_tandjenterprises.com>
To: <compost_tea_at_yahoogroups.com>
Sent: Friday, September 17, 2004 2:06 PM
Subject: Re: [compost_tea] low phosphate?
Hi Elaine,
Bray-2 can be defined as: "This test sets out a method for the
determination of available phosphorus in soils. Bray No 2 solution is
designed to extract adsorbed forms of phosphate only and is for use with
soils with a pH =>7.5." See:
http://www.dlwc.nsw.gov.au/care/soil/soil_pubs/soil_tests/pdfs/bp2.pdf .
The original message didn't specify what the value was for the soil pH.
And, as you have stated, the Bray-2 doesn't account for the phosphorous that
can be made available by microbes and fungi although it might pick up some
of it. I noticed the Bray 2 solution was using ammonium fluoride and
concentrated hydrochloric acid. Would the combination of those two
chemicals free up the phosphorous from organic material or minerals? The
above link talks about removing "absorbed" phosphorous... what does that
mean exactly? If the Bray 2 solution was extracting P from organic material
and minerals as well as the rather low amounts of any P that was already
free, then 77 kg / ha is 170 lbs (rounded up to the nearest pound) per ha or
68.82 lbs of available P per acre. 64 lbs of P per acre is just fine when
using mycorrhizal fungi on plant roots. The 620 kg / ha equates to 1367 lbs
/ ha or 553.4 lbs of P per acre. 553.4 / 64 = 8.64 years of P if 64 lbs of
P were applied each year. And they are calling that normal? That's
ridiculous! 64 lbs of "total" P is fine when using endomycorrhizal fungi on
plant roots.
If you put down 3 tons of compost per acre and the compost was 2% total P,
that would be 120 lbs of P per acre and would bring that 68 lbs up to 188
lbs of P per acre, which is about three times what's needed when using
mycorrhizal fungi. (UC Davis advises having 64 lbs total P per acre as
optimal when using mycorrhizal fungi.) Don't ask me "who at UC Davis" ...
or how they made their determination, but they were coming up with 37 ppm P
as a figure to shoot for. That does bear out with quite a few experiments I
read about P and mycorrhiza fungi.
In fact, there was an interesting experiment with mycorrhizal plants and
weeds. As the P was increased, the ppm got too high and the weeds started
encroaching upon the plants colonized with mycorrhiza fungi. As the P was
decreased below 50 ppm, the weeds started retreating. P above 50 ppm will
start to shut down the flow of all nutrients through the mycorrhizal fungi
into the plants. Get the P below 50 ppm, like our 37 ppm target, and the
hyphae of the mycorrhiza fungi are carrying all kinds of nutrients into the
plants. The weeds retreated, because they are non-mycorrhizal and simply
could not live in the soils where the mycorrhizal fungi hyphae were
plentiful and active. The` fungi takes the nutrients away from the weeds
and so the weeds will starve near plants treated with mycorrhizal fungi.
The study didn't make that conclusion... they just noticed weeds encroaching
at high P and retreating at lower P levels.
Anyway, if a farmer added 553 lb of P per acre every year, it wouldn't be
long before there would be enough P to last for quite a number of years...
especially if one switched over to using soil biology to make nutrients
available. This is what you were talking about earlier right?
--Thomas Giannou
http://www.tandjenterprises.com
----- Original Message -----
From: soilfoodweb_at_aol.com
To: compost_tea_at_yahoogroups.com
Sent: Thursday, September 16, 2004 5:40 PM
Subject: Re: [compost_tea] low phosphate?
Hi Lynton -
I'm not really clear on what the reply from the person was, because the
following is not a reply that makes any sense.
Also total P (Bray-2, as done by agri-energy www.agrienergy.net) is
very low (77kg/ha - compared to 620 kg/ha 'desired').--->
Do they understand what a Bray -2 extraction actually measures? It does
NOT give total P. Not by a long shot.
Total P has to be extracted using a strong acid, like sulfuric, or
hydrochloric. A Bray 2 only gives tiny proportion of the P that is actually
present in the soil.
A huge number of species of bacteria and fungi can extract P from the
soil. All those mycorrhizal fungi are great at doing this in addition.
They can access literally thousands of micrograms of P that a Bray 2 will
not even begin to extract, if you give the organisms the chance. Just like
people, however, soil organisms need air, water, food and housing.
Supply these things, and what is extractable by a Bray 2 will suddenly
increase by many fold.
Elaine R. Ingham
Soil Foodweb Inc., Corvallis, Oregon
Soil Foodweb Inc., Port Jefferson, New York
Soil Foodweb Institute, Lismore Australia
Soil Foodweb Institue Cambridge, New Zealand
Soil Foodweb Inc., Hilversum, The Netherlands
Laboratorios de Soil Foodweb, Culiacan, Mexico
Soil Foodweb Inc., Jerome, Idaho
Yahoo! Groups Sponsor |
ADVERTISEMENT
 | |
 |
Yahoo! Groups Links
Received on Fri Sep 17 2004 - 01:15:46 EDT
This archive was generated by hypermail 2.3.0
: Tue Feb 07 2012 - 14:15:29 EST