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Plenum and resolubalization of Fe
I wrote that I thought a plenum below the substrate would
interfere with the reduction processes which resolubalize
ferric oxide precipitates and Karen asked why I thought this.
I expect you are correct that a plenum may not introduce
oxygen into the overlying substrate. Within the substrate
the anaerobic bacteria would continue to metabolize the
ferric oxide. Paul Krombholz has made observations that a
brown iron oxide coating appears on the glass surfaces where
there is oxygen being supplied by the roots as well as
precipitates forming wherever there is not soil contact.
I expect there would be a buildup of rust in the plenum.
Although it might be anaerobic, I think the bacteria
require the humic compounds to complete the process and
the root hairs won't penetrate to that area. Paul has
suggested that a "continuous" substrate (right down to the
bottom) is much better suited to this process.
Please correct any inaccuracies in my description and feel
free to expand upon the process folks!
Steve Vancouver BC