Quote:
Originally Posted by arvin555
I imagine one big contribution with burned earth (if it is clay based) is that it will give the plants some Iron. A native plant enthusiast that I got to know and chatted with, told me that he has seen local nepenthes on Red Clay, the leaves and pitchers he said had really great coloration.
TTFN
Arvin
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Iron in lateritic soil is in the Fe3+ state. Unless it is reduced to Fe2+ or organic acids leaches it out, there would be minimal contribution of iron to plants. I am aware of only graminaceous monocots possessing the Strategy II iron (Fe)-uptake system in which Fe is absorbed by roots as an Fe3+-phytosiderophore. Plus it takes a small amount of iron to color the soil red (else everyone would be mining their garden for iron) and upon baking (the burning process), the alumina becomes partially fused, thereby locking the iron away.
Therefore, it would be tempting to postulate that burnt soil works best because it is inert and undergoes minimal change (physically and chemically). Anecdoctal evidence suggests that it works. Personally, my sibuyanensis, sanguinea, hirsuta performs much more consistently in burnt soil. The only drawback is frequent watering.
The baking leaves a certain amount of hydroxides (from oxides) of group I and II elements. They are water soluble to slightly soluble. For me, I always wash and soak the soil to allow these salts (as well as any mobile phosphates & sulphates) to be leached out. Else there will be salt built-up. It is noticeable either on the surface (capillary draw followed by evaporation), or at the bottom of the pot (from leaching through watering and then evaporation). I also sieve burnt soil to get a minimal size. Prevents clogging and makes the soil open. Messy, but if you have an area to work with, gives you inert, almost salt free (you can test the conductivity) media.