MGRox
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Well, no. I wasn't intending to refer to a lockout; though in a technical sense, P often must be acquired from precipitated compounds vs its' elemental state.
The statement I made there was, I guess, several areas of investigation condensed into one.......
Here. There has been research into various soil conditions. Quite simply. If you take a plant in a pot (or ground) and put 1/2 of the soil with No calcium and one half of the soil With calcium; then most plants will root much quicker and greater into the Ca containing sections.
The conclusion of the research, more or less, presumed that this was an evolved response as soils with Calcium can offer a higher degree of pH stabilization and acid neutralization that soils without Ca. I.e. plant genotypes that did not evolve this characteristic died off long ago lol.
Here. quite simply also; P, Ca, Fe and most metals, are most efficiently taken up at root tips or fine root hair surfaces. So from the perspective of a plant rooting into new soil. There will be XX time required in order for the plants to grow new tips and hairs (in the new medium); so that relative potential availability is high enough to support plant growth.
Prior to this, nutrient demands must come from either; nutrients in old medium section or energy / nutrients stored in leaves and roots.
(It is during this period and understandably so, that many plants will exhibit anthocyanic glycosylation or even acylation.......Urrr, Uhmmm.....Red / Purple stems and/or petioles)
Here. there are more elements that require time for efficient uptake; however P and Fe were just chosen as of note.
Again, lets look a this plant recently up-potted and after enough time has passed for some root growth into the new medium. Let's assume that this medium is already base saturated (say albrecht ratio) and that also, since time has passed for roots to grow; that the medium has been dried and new moisture added (at least once).
Specifically with Phosphorus;
it is pretty commonly known that the form of phosphate is dependent on pH. As well, it is commonly known that only small percentages of P are considered "active"ly available. When looking at the "Phosphorous Pool"; it includes Active, Available and Inactive forms of P. Active P, which represents ortho-phosphate forms; is often less than 5% of total P. Available P is phosphate that HAS been bound to another element, but IS easily recoverable; most often P is bound with Ca here (wide ranging 35-85% of P). Inactive P, would be a compound that also HAS been bound to another element; but is NOT easily recoverable; quite often P is bound with Fe here (wide ranging 10-50%).
Of note to point out also is that the forming of Available and Inactive forms of P are related to pH, but more specifically to the combined concentration (in localized areas) of said elements. I.e. if the combined concentration of P and Ca exceed 2.2 mol / 100gm of soil; then Calcium Phosphate will be precipitated. This occurs quite often an normally in wet /dry cycles of soils and tends to be the main reason that Available P is the largest total Pool Fraction
Of note to point out also is that the forming of Available and Inactive forms of P are related to pH, but more specifically to the combined concentration (in localized areas) of said elements. I.e. if the combined concentration of P and Ca exceed 2.2 mol / 100gm of soil; then Calcium Phosphate will be precipitated. This occurs quite often an normally in wet /dry cycles of soils and tends to be the main reason that Available P is the largest total Pool Fraction
At this point then, the limiting factor becomes the efficiency or productivity of said plant; at producing exudates that are effective in reducing Calcium Phosphate and or control of the local pH. Again during this period, energy required for this process must be derived from elements in the old soil fraction and / or stored nutrients / energy in plant tissues.
The productivity of the plant then at producing these exudates relates to is nature as a Califuge or Calcicole. IMHO I'm firmly decided that MJ is a Calcifuge.
Finally then, once enough new roots have grown into a medium and proper exudates have been produced; then a plant can uptake sufficient nutrients for both survival and new growth. So the time required from up-potting until sufficient uptake are dependent on: the health of the plant prior to up-potting, the reserves of nutrients in old medium, the rate at which new roots grow into the new medium, the strength and volume of exudates from roots and the fraction of P forms in the P pool of the new medium (of course along with common; moisture, pH and EC).
During this whole process, the plant has the "choice" to continue to draw elements from the old soil; or to remobilize stored nutrients in existing tissues. Quite often plants will choose to, at least in part, remobilize nutrients out of existing tissues; primarily as it costs less energy. A good analogy here is if you get thrust into some sort of outdoor survival situation. You came from a situation with plenty of food and if / when you find your way out; you will have plenty of food also. Is it more wise (From a survival perspective) to try and find all the food energy you will need to escape, before leaving? Or would it be more wise to try and escape first, relying on your stored fat / energy?
This is why we commonly see some mobilization and anthocyanin development shortly after up-potting, first potting rooted cuts, etc. As well it has been shown that certain plants will also show anthocyanin development as a response to rapid and robust rooting. Again here the plant is choosing to mobilize current reserves in favor of future uptake potential.
Ultimately then, since this "process" is unavoidable; IMHO, I try to do what I can to reduce this time // energy required by the plant. So the suggestion of starting with nutes, is in effort to get the macro elements to saturation faster (since a peat-lite mix). As well lowering the Ca of the first few feedings is to help possibly reduce the percentage of P converted to available; from active. Last, by slightly lowering the pH of the first few waterings can possibly reduce the required exudates during the optimization of uptake.
Sorry to be long and I hope it's not TMI for everyone. One of those areas that quick to say simply but hard to explain I guess, lol.