When phosphate loads
are rapidly complexed or not made available, fundamental sugar formation
continues to function. Symptoms wave a warning flag that can be seen from great
distances. Leaves often become reddish and purplish – a lack of chlorophyll –
and tips die off. Seeds, tubers, grains, all suffer since all require
phosphorus for adequate metabolism. Growth is slowed accordingly. The corn
plant has a sign all its own. When there is a phosphorus deficiency, the
kernels drop off about an inch or two from the cob’s end, or they may fail to
develop in the first place.
In short, there is a
chemistry involved whenever anything is put into the soil, inorganic, organic,
salt form, whatever. Rock phosphate is called tricalcium phosphate, and this
means it has three calciums, or three negative charges for bonding. This makes
it more difficult to disattach from fixation than would be the case with
dicalcium phosphate, which has only two charges – thus tri, di! Last, there is
the water soluble monocalcium phosphate, which means that as a consequence of
acid treatment this form has only one remaining bond.
So if you’re over 6.5
pH, and you want to farm organically for good and obvious reasons, you’re in
trouble. You probably shouldn’t be using nonwater soluble phosphorus because
the soil does not have enough acid to free it up. If a soil system has a pH of
7.5 the farmer probably shouldn’t be using the di forms. He should go to
strictly mono forms of phosphate. Any farmer who doesn’t take into
consideration the importance of the active hydrogen ion as being the most
important thing to work with thereby authors his own failure.
Acid treatment merely
means rock phosphate is being converted from tricalcium phosphate to
monocalcium phosphate, and that this highly unstable form is subject to natural
reversion back to the stable tricalcium form. The rate of reversion differs.
The pH, the free calcium in the soil, the organic matter – all figure in this
rate of reversion. But it is safe to say that 75% of the monocalcium phosphate
reverts back to stable tricalcium phosphate within 90 days. In some soils the
reversion takes place within hours. As soil conditions worsen, release of
nutrients from rock phosphate worsens, and the chemical amateur becomes married
to buying salt fertilizers, each go-round worsening still further the structure
of that soil.
The water soluble
phosphates are simply water soluble, not acid. But they are a poor substitute
for having the proper pH with calcium, potassium, magnesium and sodium in
equilibrium, and form an economic point of view they take on ripoff dimensions.
First, the soluble
phosphates come from rock phosphate in any case. By treating, say, 1,400 pounds
of rock phosphate with 1,200 pounds of sulfuric acid, the fertilizer industry
gets 20% superphosphate – the tricalcium phosphate form being converted into
water soluble monocalcium form. This chemical reaction causes 20%
superphosphate to be represented by about 45% monocalcium phosphate, and 55%
calcium sulfate, or gypsum. This means the bag of 0-20-0 contains about 45
pounds of water soluble monocalcium phosphate, which is presumably desired, and
about 55 pounds of calcium sulfate, which may or may not be desired, but which
farmers are frequently not aware of.
The fertilizer rating
0-45-0 is quite different material. Farmers who see symptoms of phosphorus
deficiency sometimes think a higher rating is the answer, and this one comes
styled triple superphosphate. Here the acid used to do the etching is
phosphoric. This eliminates the calcium sulfate in the bag, calcium frequently
needed to kick up to calcium reserve, sulfate needed to complex an excess of
magnesium. By invoking the hotdog concept of plant nutrition a much needed
nutrient might be eliminated exactly when it is needed.
Ammonium phosphate such
as 8-32-0, 11-48-0, and 80 on, also involve concentrated phosphoric acid in the
processing, and this provides a handy outlet for otherwise unsalable fossil
fuel company byproducts.
- Excerpted from Eco-Farm An Acres U.S.A. Primer
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