Re: [compost_tea] Re: Fert, salt indexes

From: Brian Debasitis <bdebasitis_at_sustainablesoil.com>
Date: Tue, 19 Oct 2004 23:12:46 -0400

The formula's below seem to be more for determining how much salt could be =
added to soil. That would have to assume there was none there already if I'=
m understanding correctly. Is there a relatively easy way to determine the =
level of a particular salt concentration existing in the soil?
____________

Brian Debasitis
Sustainable Soil
Woodstock Vermont
(802) 457-6108
Brian_at_SustainableSoil.com
www.SustainableSoil.com


  ----- Original Message -----
  From: soilfoodweb_at_aol.com
  To: compost_tea_at_yahoogroups.com
  Sent: Tuesday, October 12, 2004 4:06 PM
  Subject: [compost_tea] Re: Fert, salt indexes


  I was asked the following -

  It would be handy to have the method of calculation so that if we get any=
 further salt indexes , we can work them out ourselves .

  Method of calculating salt index - This is a measure of osmosity, or the =
ability to hold water against the application of pressure. Plants apply pr=
essure to pull liquids into their roots. So if salts hold water more stron=
gly than the roots can apply pressure to remove it, the plant will die. Sa=
me for microorganisms.

  Sodium chloride is set as the standard, of 1.00, or in the scale of the d=
ata that was sent you, the relative unit for sodium chloride would be 100. =
 

  The easiest way to interpret that is that 100 pounds more or less of salt=
 per acre has no discernable effect on the biology in the soil. When the =
salt index is 100, and you apply less than 100lb/ac, we do not measure an e=
ffect. Probably there is one, but we can't detect it with current methods.=
  Let me point out that plate count methods won't show these negative effe=
cts, because plate count methods assess spores and other dormant stages. S=
o, ACTIVE organisms are being killed, and you'll miss it altogether if you =
rely on plate count methods.

  If more than 100 pounds per ac of NaCl is applied, a detextable number of=
 organisms will be killed. The higher the amount of salt applied, the more=
 organisms will be killed.

  The cause of the effect is holding water so organisms have no water avail=
able to use. Available water decreases below the threshold value needed by=
 the biology to survive. The higher the salt index, the more water that sa=
lt will hold against the pull of pressure, and so the less usable water for=
 the organisms, so more species die.

  So how to use the below salt index. If salt has an index value of 100, m=
eaning 100 lb/ac can be used without significant harm, then you can put tog=
ether a ratio to calculate the others.

  So, super phosphate has a value of 8, while sodium chloride has a value o=
f 100. Thus you could put on 100 divided by 8 times more super P than salt=
 beofre you would see a killing effect from the super P.

  NaCl index/Material of interest salt index =

  Multiply the 100 lb/ac amount by that ratio.

  100/8 times 100 = amount of material of intereat that can be put on bef=
ore damage to the microbes occurs.

  1250 lb/ac of super P before microbes will be harmed.

  Now, let me point out that this does not jive with what I've seen in the =
field. I think they gave you a value for rock phosphate, not super P. Or =
the value for super P was determined using coarsely ground super P, where m=
ost of the mineral did not react in their test. If they grind it finer, t=
he salt index would go way up.

  I also have a hard time believing the surpentine super value, whatever th=
at is. A value of 0 means the material does not dis-associate in water, so=
 it will never dissolve. Why would you put something into your soil that i=
s not capable of going into solution? Your plant will never be able to ta=
ke it up.

  Let's try another one

  Pot chloride
  100/114 times 100 = 87 lb/ac of potassium chloride could be used, not 1=
00 lb/ac. Or, if 100 lb/ac of KOH was used, organisms would be killed. Th=
e negative impact would be discernable.

  SALT INDEXES

  Surpentine super 0
  Super phosphate 8
  Pot. chloride 114
  Pot. sulphate 46
  CAN 82
  Nitrophoska 12/10/10 56
  Te Nitrophoska blue 60
  Urea 75
  Patent Kali 28

  The table of salt index values was supplied by Graeme Reid, an SFI adviso=
r in New Zealand, who obtained the data from Ravensdown, a government soil =
chemistry group in New Zealand.

  Hope this was clear. Any questions, please ask.

  --
  Elaine Ingham
  President, Soil Foodweb Inc.
  SFI Corvallis, OR
  SFI Port Jefferson, NY
  SFI Lismore, NSW, Australia
  SFI Cambridge, New Zealand
  SFI Culiacan, Mexico
  SFI Jerome, Idaho
  SFI South Africa
  http://www.soilfoodweb.com


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Received on Wed Oct 20 2004 - 01:05:15 EDT

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