[Prev][Next][Index][Thread]
Re: Organic matter's effect on soil bulk?
> Imagine I had a plot of land on which I dumped six inches of wood
> chips every year. Obviously this would cause the level of the plot
> to rise over the first few years. The question is, after, say, ten
> years, would the level continue to rise, or would it stay constant?
> In other words, when the wood chips deteriorate, do the elements go
> into the air and water?
It would continue to rise...you are, after all, bringing in material
>from the outside. Decay releases some of that material into the
atmosphere or leaves it in a form that can be carried away by water,
but plenty of the original mass will remain in the soil. Of course,
as the ground level in a particular spot rises, it becomes more
susceptible to erosion. Eventually, I guess you'd get a nice little
hill where erosion was in equilibrium with the amount of matter
being added.
>
> What got me thinking about this was the realization that trees
> don't seem to form the bulk of their substance from what they get
> from the soil. If they did, you'd expect them to be sitting in
> depressions. Instead, the soil around them actually seems to rise
> up a little. Then I realized that they could do quite a bit of
> building with just the elements found in air and water.
Yes, that's true. Trees, people, and most living things are mostly
water. A tree takes water that would otherwise have drained away
and builds its own bulk from the water. Some minerals are drawn
>from the soil, too, but the process is pretty gradual. I doubt if
you could see too much evidence of it, considering all the other
factors that change topography over time.
> If that's
> true then it's natural to ask whether decay reverses the process.
> Thinking about it, I guess that pretty much has to be what happens,
> but I never hear anyone phrase it quite like that.
>
My guess is that there is a net increase in soil mass in an area
that is heavily vegetated. Even after decay, some of the matter that
the plants have gotten from air and water remains trapped in solid
form. But I've never seen a thorough analysis of the subject.
Interesting thoughts!
--
===============================================================
Tom Tadfor Little tlittle@lanl.gov -or- telp@Rt66.com
technical writer/editor Los Alamos National Laboratory
---------------------------------------------------------------
Telperion Productions http://www.rt66.com/~telp/
===============================================================
References: