"Seeding" mineralized soil with KH2PO4, phosphorus mobility/bioavailability - The Planted Tank Forum
 
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post #1 of 3 (permalink) Old 02-17-2009, 11:20 AM Thread Starter
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"Seeding" mineralized soil with KH2PO4, phosphorus mobility/bioavailability

I've asked this in tandem with several questions on another thread, but hoped by dedicating a thread to the subject, it might be useful to others thinking to do the same thing.

I am preparing a mineralized soil and had a question on seeding it with phosphate. Many lay in dolomite and potash, but I have seen few** talk about laying in a phosphorus component; I've only seen Diana Walstad discuss it - she advocates the use of 0-11-0 (ideally, or at least something with very little N to P ratio) bone meal. I cannot locate anything other than 6-9-0 bone meal, and so was thinking of laying in a sprinkling of KH2PO4 on the glass, prior to overlaying with mud.

Since my understanding is that phosphorus is only taken up via root uptake, I'm a bit confused as to why there is a dearth of discussion on this notion.

In thinking of laying in the KH2PO4, I was doing some looking around the web this morning, and came across a couple of sites that described the unavailability of particulate phosphorus (both inorganic and organic) to plant life (one site), and another site, a wetlands study center, that described the absence of mobility of phosphorus within soil.

I'm many years outside of chemistry, so please forgive my naivete or misconstrual:

I presume that if I lay in KH2PO4, the particulate will eventually be dissolved under the soil - water and bacteria, solubilizing the inorganic particulate, and making it available. Given this, is there any reason not to lay it in as a first light layer in a mineralized topsoil tank, with the aim of providing an early "seed" for robust root and plant health?

Is it because inorganic phosphate is readily solubilized, and is therefore perhaps too readily available - it would represent something like a massive upfront overdose of phosphorus, and this is why an organic variant (like 0-11-0 bone meal) is advocated, because it is bound and must first undergo phosphatase transformation?

If by the above paragraph, bone meal is the only way to go, and if I followed Tom Barr's suggestion on boiling the mud (I don't have several weeks to mineralize the soil, so went this way), would boiling the meal also be recommended, prior to laying in, to oxidise organics, or would this somehow denature the phosphorus?

Finally, if KH2PO4 is possible to use, anyone have any thoughts as to how much?

**
Note: "Errors and omissions" - all mine, from a rather hazy recollection of chem, as I said. And I equally admit, this might have been discussed a good deal, and I've just missed it, though I've dug around a bit. Apologies, if so.
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post #2 of 3 (permalink) Old 02-17-2009, 10:48 PM
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been reading walstad huh?

I'm mineralizing now and added some KH2PO4. I'm not an expert but I'd think that would be beneficial. The PO4 salt will dissolve but might bind with other elements in the soil and possibly make it not soluble. Acids from the soil will make insoluble elements available for plants.

and I wouldn't add too much.. It's just a starter to give plant roots a boost.


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post #3 of 3 (permalink) Old 02-17-2009, 11:09 PM Thread Starter
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Originally Posted by mistergreen View Post
been reading walstad huh?

I'm mineralizing now and added some KH2PO4. I'm not an expert but I'd think that would be beneficial. The PO4 salt will dissolve but might bind with other elements in the soil and possibly make it not soluble. Acids from the soil will make insoluble elements available for plants.

and I wouldn't add too much.. It's just a starter to give plant roots a boost.
Yep - really intrigued by her idea, if it can be accomplished with what I have.

Uh, and if I don't change my mind a million times midstream, seems to be a problem - already thinking of setting up a "Japanese sea" kind of nano-environment, utilizing principles of Ikebana and relative sizing - 3 "mountains" - 1:.75:.5625 and two over-arching thin branches of driftwood, inspired by Takashi Amano's "Suikei"....anyway....

My only concern, if I have it right, is that organic phosphorus is bound, and not readily available for plant uptake - so it requires bacteria, phosphatase activity, to convert to inorganic form, and additionally aid in solubilizing, making it ready for plant uptake. In other words - and I am likely completely wrong on this, been a long time - organic phosphorus would act as a kind of time released supply, whereas inorganic is immediately available, hence my worry about overdosing up front, followed by no nutrient at all.

Of course, it seems the principle of high CEC substrate is precisely to bind ferts for later use, so I'm probably completely wrong, and very hopeful I'll be told I'm completely off on this - do you happen to know? Tom, anyone else?
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