Dieter, you can always edit the wikipedia page. ;)
One thing that humus does for a soil is increase cation exchange capacity.
This provides sites for mineral nutrients (such as ammonium released by the
breakdown of new organic material) to bind to so that it doesn't get washed
out of the soil. It also makes the soil a better buffer, keeping mineral
and pH levels more stable, and helps the soil clump into nice, water
holding, microbe sheltering aggregates. These effects are a big part of how
humus boosts soil fertility.
John, speaking of hormone-like chemicals, a lot of microbes excrete plant
hormones. I'd bet the increased microbial activity in high organic matter
soils means there are some bacterial or fungal hormones boosting plant
growth too. Or maybe these hormones even become part of the humus.
And good point about burning - think about how much carbon they're losing
in that smoke! They're starving their microbes...
And just a little trivia for you, the structure of humic acid and fulvic
acid (two components of humus) aren't defined by a chemical formula,
they're "operationally defined" by how they're separated out of the humus.
Humus is treated with NaOH (lye, or another strong base) and they separate
the what's in the resulting liquid by acidifying it. Everything that
dissolves in the NaOH and stays dissolved when it's acidified is fulvic
acid, everything that was dissolved but falls out of solution when it's
acidified is humic acid. The actual chemical components of all this are
still being explored.
Alia
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