It sounds like you've been getting the chemical side of the story about
adding sawdust to your soil. May I offer my limited knowledge of the
biological side?
Without writing a tome, I'll try to explain why adding the sawdust is
not a good idea. I'm assuming that you want to grow vegetables or
pasture grass. These both require a bacterially dominated soil
ecosystem, as opposed to trees, grapes and blueberries which require a
fungally dominated soil.
To promote a bacterially dominated soil you need to add organic matter
that has more bacterial than fungal life- compost from a "hot" or
bacterial breakdown pile. (For fungal, use a "cold " pile that's higher
in lignin and has a higher C:N.
For more info on soil ecology, try this:
http://www.soilfoodweb.com/thesfw.html
The reason it's not a good idea to till uncomposted plant material into
the soil (other then green manure crops which break down rapidly if
plowed down while succualant) is what everyone's telling you about
"tying up the nitrogen". What happens is that you have a population
explosion in the soil life and these creatures can out compete plants
for N and you have an artificial N shortage. The N is there, but in the
cells of these animals (bacteria, etc.) and unavailable to the plants.
You need an explosion in the predator population to start releasing some
of this N, but mostly for the food source to be used up and the
population to start dying off and releasing N into the soil N cycle
(done by bacteria).
So, 2 problems with adding sawdust and raw manure to the soil- N
problems and possibility of a fungally dominated soil ecology. That's
why farmers say, from experience, that it's better to compost first.
Adding N fertilizer is an attempt to supply N to the plants while the N
from the soil foodweb is being used by soil animals. (By the way,
unpublished work has found that plants prefer nitrate from the natural
cycles in the soil over N from fertilizer- that is, they absorb the
natural nitrate first. So, the old saying by chemists that nitrate is
nitrate may not be true.)
There are multiple problems with adding N salt fertilizers to the soil-
mainly that only 25-30% is held in the soil. The rest winds up in
surface and ground water. The other main problem is the adverse effect
on the soil life, which cycles nutrients for plants and are plant
symbionts.
About manufacture of N fertilizer- It's an offshoot from war industries-
the manufacture of gunpowder and explosives. One of the reasons for
keeping these plants operating is so they can be quickly converted to
part of the war machine when needed. There's not much difference between
fertilizer and explosives; that's why people can easily make bombs from
fertilizer.
So, make your own judgment about the use of N fertilizer being
"environmentally responsible or effective." That's the kind of decisions
we all have to make every day. (Or, I should say, that we should be
making.)
Some of the "superstition of organic folks" is based on knowledge gained
from observation over years. It's enough to know that the application of
N fertilizer causes multiple problems to avoid the use of it. You don't
really have to know why it causes problems, unless you're in the
theoretical part of agriculture and not the practical part.
I hope this answers some of your questions. Keep asking and we'll keep
learning.
Alex McGregor
Walden Farm
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