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Re: Strong or weak phosphoric acid?



Hi Klaas -

Please note that I was very CAREFUL to state that the acid had to be strong enough to kill the fungus.  I clearly made the case that low molarity acids were not being considered.  I stated that the acid had to be strong enough to kill the fungus on contact.  And it was not a wimp fungus that was under discussion.   

If the soil is alkaline, and please go back to my post and see that I CLEARLY stated that condition, then P will not become available to the plant, unless the necessary biology is present in the soil to solubilize the phosphorus.  In acidic conditions, things are different, as I said. 

Were you quoting the study where calcium phosphate was added to soil, and some of the calcium was later found in the plants?  That is not proof that the plant can, by itself, take up calcium phosphate. 

Biological processes in and around the root alter the availability of P.  The plant controls P availability only indirectly, by feeding the organisms in the root system.  Without the right set of organisms in the root system, plants are up a crick without any P. 

Please read the papers by V. Cole, D Coleman, Bill Hunt and others from NREL at Colorado State University about why tillage is so detrimental.  Bobby Brock has published more recent information, supporting the same work.  Doran's papers reach the same conclusions.  Tillage adds air to soil, but typically results in a huge burst of bacterial growth on the fresh organic matter surfaces opened up by that disturbance, resulting in a 60% loss of that organic matter which the bacteria grow on.  There's a clear relationship of too-much tillage with loss of organic matter and reduced fertility. 

Tillage needs to be carefully balanced to prevent compaction, to bring oxygen into the soil, but not so much that the biology (particularly the fungi and microarthropods) is sliced and diced, or the ratio of fungi to bacteria is altered outside the range the plant you are trying to grow requires.  The more tillage, the more organic matter is consumed, the greater selection for bacterial growth, which competes with and selects against fungi.  As fungi are lost, the larger size aggregates are lost, and soil structure suffers, leading to increased rates of compaction.  In soil in really bad condition, the first rain after tillage results in immediate collapse of whatever "fluff" was put into the soil by tillage.  The "cotton candy" relationship between fluffing versus building soil structure. 

Elaine Ingham
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In a message dated 12/29/2002 4:31:08 PM Pacific Standard Time, kandmhfarm@SPRINTMAIL.COM writes:


am concerned though, that the recent exchange has gotten a little careless
with the facts. For instance:
1) Yes, pure phosphoric acid would harm you if you drank it, but millions do
drink it everyday with few ill effects. (just read the label on a can of
pepsi cola - pepsi contains phosphoric acid)
2) Pure phosphoric acid would burn plants but diluted properly, it's a good
follier fertilizer and is an ingredient in virtually all of the follier
applied fish emulsions used by organic farmers.
3) Yes, soil applied phosphoric acid combines with calcium to form
tricalcium phosphate but no, tricalcium phosphate is not unavailable to
plants.  Legumes especially, are well known to make good use of tricalcium
phosphate even in high pH soil.
4) There is no question that plowing can reduce the population of some
organisms (this is especially true for anaerobes) but it adds the oxygen
needed to stimulate the areobic organisms and results in a huge net increase
in soil microbial activity.  That's why plowing is blamed for burning
organic matter.  The greatly increased microbial population needs some of
the OM for food.

Please remember that when a teacher gets "yes, buts...." it is actually a
great compliment.  It shows that the students are paying attention and
actually learning the material!

Happy New Year to everyone, and let's hope that more people take the chance
to post on SANET and less people on SANET flame them in the new year!

Klaas Martens