Re: [compost_tea] low phosphate?

From: Thomas Giannou <thomas_at_tandjenterprises.com>
Date: Thu, 16 Sep 2004 19:06:31 -0700

Hi Elaine,

Bray-2 can be defined as: "This test sets out a method for the determinati=
on of available phosphorus in soils. Bray No 2 solution is designed to extr=
act 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/p=
dfs/bp2.pdf .

The original message didn't specify what the value was for the soil pH. An=
d, 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 conce=
ntrated hydrochloric acid. Would the combination of those two chemicals fr=
ee up the phosphorous from organic material or minerals? The above link ta=
lks 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 k=
g / 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 mycorrh=
izal 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 a=
pplied each year. And they are calling that normal? That's ridiculous! 6=
4 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 l=
bs of P per acre, which is about three times what's needed when using mycor=
rhizal 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 t=
hey made their determination, but they were coming up with 37 ppm P as a fi=
gure 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 we=
eds. As the P was increased, the ppm got too high and the weeds started en=
croaching upon the plants colonized with mycorrhiza fungi. As the P was de=
creased below 50 ppm, the weeds started retreating. P above 50 ppm will st=
art to shut down the flow of all nutrients through the mycorrhizal fungi in=
to the plants. Get the P below 50 ppm, like our 37 ppm target, and the hy=
phae of the mycorrhiza fungi are carrying all kinds of nutrients into the p=
lants. The weeds retreated, because they are non-mycorrhizal and simply co=
uld 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 d=
idn'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 l=
ong before there would be enough P to last for quite a number of years... e=
specially if one switched over to using soil biology to make nutrients avai=
lable. 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 f=
ollowing 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 hydroc=
hloric. A Bray 2 only gives tiny proportion of the P that is actually pres=
ent in the soil.

  A huge number of species of bacteria and fungi can extract P from the soi=
l. 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 ev=
en begin to extract, if you give the organisms the chance. Just like peopl=
e, however, soil organisms need air, water, food and housing.

  Supply these things, and what is extractable by a Bray 2 will suddenly in=
crease 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




Received on Thu Sep 16 2004 - 23:02:16 EDT

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