[APD] Complexation with metals, peat and organic matter ramblings

["Thomas Barr" <tcbiii at earthlink_net>]

Some folks have wanted to know a bit more about humic and fulvic substances
and why Amano, myself, Steve Dixon and others add peat to a substrates.
>From some of Reddy's work and (Brady & Weil 1999, Stevenson 1982):

Humics(and fulvics) have an abilty to form a chelated compund with metal
ions, a chelated compound is a type of compound where a a metal ion is
firmly attached within an organic molecule by multiple chemical bonds.
Many of these bonds contain Oxygen groups, like -COOH, phenolic OH's, C=O.
Generally the max amount of metal ions that can be bound to these acids is
about equal to the content of acidic functional groups as measured via base
titration  

The other issue with peat is the organic matter content and the reductive
environment it provides which also allows for more metals to become
bioavailable.
OM has a a net negative charge on the surface and has a greater affinity
for cations like NH4+, K+, CA++, Fe and most metals etc.

This can an enhance over time a substrate's "richness".
This depends on the amount of material being added(eg if you dose a fair
amount of NO3/PO4 etc, have high plant biomass, don't remove your dead
leaves etc) 

Harder waters buffer the affects but also provide less enzyme inhibition
from humics/fulvics in terms of productivity.
 
Sources of OM(organic matter): detritus, dead plant leaves(even those dead
ones still on the plant), algae  bacteria, fish waste, food, dead
fish/critters.
Plant and algae OM is very labile and is recycled quickly. 
Generally sugars and other souble substances are leached out before the
plant loses the leaf.

This is one reason to prune and plant only the tops decarding the lower
ratty portions. This can and does cause issues for folks if they stop
adding CO2 or something is wrong with the CO2 delivery system. You'll see
the plant lose many leaves, and this allows for algal growth very often and
perhaps importantly: not just the slower plant growth/less O2 from plants.

It should be noted that this decompsition creates an O2 demand. The rates
of decompsoition and hence cycling of these materials/compunds in the water
column can be be greatly enhanced at HIGHER O2 levels vs lower O2 levels.

Often when you pull up a good deal of material from the substrate, this
lowers the O2 levels rapidly.
I've suggested to folks to do a water change after you do any large pruning
for this reasoning. Gets the dirt out also.

I also want to add that although the bacteria in substrate represents a
small fraction (1-5% of the total C), they are very dynamic with rapid
turnover rates and aid in decompsing the matter into plant nutrients(CO2, N
etc ).

Plant and soil OM:
water sulble fraction ,10%, amino acids, sugars, fatty acids
Cellulose 15-60%
Hemicellulose 10-30%
Lignin 5-30%
Proteins 2-15%
Lipids and waxes 1-8%
Ash 1-13%

Generally the chemical constituents are groups into:
Non humic substances: carb's protiens and fats
Phenolics lignins/tannins
Humics 

Regards, 
Tom Barr
  


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