NPK ratios?
JamieV. (Thu, 31 Jan 2008 03:06:33 PST)
Jim,
this is an important point you mentioned with Ca, Mg and K competing for
free ions to combine. They do, but, as you wrote, the reaction is
largely governed by pH. Applying these elements at different times
would be the wisest solution, otherwise they may not be effective.
The same can be said of phosphates, but they will precipitate with Ca+
at higher pH, say around 7.2 or higher. I do not know at which pH it
combines with other elements.
Again, with phosphor compounds, they have a wide range of 'users' in
bio-systems. All plants require them, which may mean that in a pot
there are more takers to consider than the main plant. Algaes are huge
absorbers of PO4. Perhaps we have a situation similar to nitrogen in
orchid bark?
Just some more thoughts,
Mg (magnesium), Ca (calcium) and K (potassium) are similar in ionic charge
(Mg and Ca) and in size (Ca and K) and are said to be able to interfere
with each other's absorption. This alone might indicate that applying
calcium at a different time than magnesium would increase the effectiveness
of the applied nutrients.
Loading the fertilizer up with phosphate is relatively harmless in soilless
growth medium. In soil, excess phosphate can tie up iron, calcium, and
probably a couple of the trace elements, depending on the ambient soil
pH. Phosphate is of course essential for plant growth, but in
significantly smaller amounts that N and K. I've never understood where
people are coming from when they recommend high phosphate fertilizers; this
just does not make physiological sense to me.
Jim Shields
in cold central Indiana (USA)
--
Jamie V.
_______________________
Köln (Cologne)
Germany
Zone 8
jamievande@freenet.de