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permaculture - Re: [permaculture] walking away/mulching

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  • From: Toby Hemenway <hemenway@jeffnet.org>
  • To: <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] walking away/mulching
  • Date: Sun, 21 Apr 2002 20:09:36 -0700

on 4/18/02, bmn@iglou.com wrote:

> This mulching will inhibit a lot of what is already on the site, but
> typically the soil dies underneath.

That's never been my experience. All the soils that I've deep mulched,
whether clay, sandy, or what have you, show an immense increase in soil
life, organic matter, and general tilth, down to a foot or more below the
mulch. It's how I renovate poor soils without tilling, and I've examined and
tested them to a good depth below the mulch. Far from dying, they become
much more alive. I'm puzzled as to what kind of mulching kills soil as bmn
says (as I type I'm looking out my window at a foot of mulch on top of what
a year ago was hard red clay and is now brown, wormy earth at least a foot
below the mulch, soft enough to shove my fist into).

> Add to that the fact that you
> basically install above ground what simulates disturbed ground. Most
> invasive exotics and unwanted invaders specialize in colonizing disturbed
> areas.

Again, that's not been my experience. I see completely different kinds of
"weed" species colonizing tilled or otherwise disturbed ground than what
colonizes bare mulch (if I'm foolish enough to leave it bare; you've got to
plant it!). Generally the weed seeds that prefer disturbed ground rot and
die in mulch. In tilled ground I see plantain, dandelion, wild lettuce,
chickweed, and other disturbance-loving weeds; in mulch I get mostly grasses
and other large-seeded or tillering species that are a later successionary
phase.

Mulching is not at all the same as disturbing soil. Mulching creates a
layer of nearly pure organic matter on top of (mostly mineral) soil. Over a
few days to weeks, micro- and macro-organism populations build up, slowly
using up the oxygen in the mulch. The mulch compacts as it decomposes,
slowing oxygen transfer. Decomposed organic matter is slowly carried into
the soil by rainfall and various fauna like worms, and aeration of the
deeper soil is a slow process, taking weeks and happening mainly through
worm and other burrows.

In contrast, tilling rapidly and thoroughly mixes organic matter and air
into soil, blasting the large existing population of soil life into rapid
action, quickly burning up organic matter. It also brings buried weed seeds
to the surface, or at least exposes them to the light and air they need to
germinate. The two treatments yield very different biota, decomposition
rates, gas transfer rates, water content and absorbance, and many other
parameters.

Of course, mulch is not a magic bullet; it requires maintenance like any
other technique. I use deep mulches primarily in the outer margins of Zone
1, or mulched circles in Zone 2. Close to my doorstep and paths, to quickly
build soil and get intensive production, I till in lots of compost, followed
in succeeding years by deep mulching. And further out from the mulched
areas, I use cover crops. Each method has its place.

Toby





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