"Billy Rose" wrote in message
...
In article ,
"David E. Ross" wrote:

George.com wrote:
A question for people in the know. What is the best time to apply P &
K
during a plants growing cycle?

especially in relation to seeding plants like cucumbers & tomatos or
root
vegetables like potatos etc.

Many thanks.
rob



Phosphorus does not dissolve and leach through the soil. Instead, it
needs to be dug into the soil to where plant roots will find it. Thus,
phosphorus should be applied before planting.

PO4 3- doesn't dissolve?

Pure anhydrous phosphoric acid is a white solid that melts at 42.35°C
to form a viscous liquid. In solution, phosphoric acid behaves as a
triprotic acid, having three ionizable hydrogen atoms. The hydrogen ions
are lost sequentially.
H3PO4(aq) H+(aq) + H2PO4¯(aq) Ka1 = 7.5 Å~ 10¯ 3
H2PO4¯(aq) H+(aq) + HPO42 ¯(aq) Ka2 = 6.2 Å~ 10¯ 8
HPO42 ¯(aq) H+(aq) + PO43¯(aq) Ka3 = 1.7 Å~ 10¯ 12

Phosphoric acid is not a particularly strong acid as indicated by its
first dissociation constant. It is a stronger acid than acetic acid but
weaker than sulfuric acid and hydrochloric acid. Each successive
dissociation step occurs with decreasing ease. Thus, the ion H2PO4¯ is a
very weak acid and HPO42 ¯ is an extremely weak acid.

Replace the hydronium (H+) with a Na+ and you have essentially the same
thing, only it is in the east.

Phosphoric acid is used primarily in the manufacture of fertilizers,
detergents, and pharmaceuticals. In the steel industry, it is used to
clean and rust-proof the product. It is also used as a flavoring agent
in carbonated beverages (read the ingredients list on a can of
Coca-Cola), beer, jams and jellies, and cheeses. In foods, phosphoric
acid provides a tart, acidic flavor.

In the manufacture of detergents, phosphoric acid is used to produce
water softeners. Water softeners remove Ca2+ and Mg2+ ions from "hard"
water. If not removed, these hard-water ions react with soap and form
insoluble deposits that cling to laundry and the washing machine.
Phosphates produced from phosphoric acid are used extensively as water
softeners (builders) in detergents. The most widely used phosphorus
compound in solid detergent mixtures is sodium tripolyphosphate,
Na5P3O10. As a water softener, sodium tripolyphosphate binds to Ca2+ and
Mg2+, forming soluble chemical species, called complexes or chelates.
These complexes prevent the Ca2+ and Mg2+ from reacting with soap and
forming deposits.

Most phosphoric acid is used in the production of fertilizers.
Phosphorus is one of the elements essential for plant growth. Organic
phosphates are the compounds which provide the energy for most of the
chemical reactions that occur in living cells. Therefore, enriching
soils with phosphate fertilizers enhances plant growth.

Increasing the phosphate concentration in surface waters also enhances
the growth of aquatic plant life. Run-off from fertilized farm lands can
stimulate plant growth in lakes and streams. Waste water that contains
phosphates from detergents can have the same effect. Lakes that are rich
in plant nutrients suffer from accelerated eutrophication. When the lush
aquatic plant growth in a nutrient-rich lake dies, the decomposition of
the dead plant material consumes dissolved oxygen. This consumption
reduces the level of dissolved oxygen to a point where it is
insufficient to support animal life. To reduce the threat of lake
eutrophication, many localities have banned the use of phosphates in
detergents. In some cases, the phosphates have been replaced by
carbonates. In others, new detergents have been developed that do not
react with the Ca2+ and Mg2+ ions of hard water.

Bone meal (an organic source of phosphates), on the other hand, is not
very soluable a should be worked lightly into the soil so as not to
damage the roots.

Bill. When you say bone meal is not very soluable, are we talking here
about:

1. Something that time will resolve, ie is it is slow release?
2. Or are we talking about something that is distance related, ie it will
not work down into the soil & plants root systems if used as a top dressing
(unless dragged down by worms maybe)?

Thanks
rob