[permaculture-oceania] No till methods

[Terry Leahy]

Dear Permies,  

I note the recent discussion on glyphosate and it reminded me of
something I wanted to ask this chatline about.  I recently presented
some stuff on agriculture in my broader course on environment and
society.  In this I showed some of the video Global Gardener where it
starts with Bill talking about how plough agriculture is not suitable
for the humid tropics because the nutrients get washed away and
dissolved and also because of hard pan.  Earlier in the lecture I talked
about problems with cereal crops that include soil erosion following
ploughing and figures on this - now many kilos of topsoil we lose for
every kilo of wheat.  In the class, one of my students said he found
this a bit out of date really;  most Australian farmers now use
"No-Till" or "Conservation" farming.  This means that the stubble is
left rather than burned,  they let the weeds grow and knock them out
with round up before sowing.  They do not turn the soil with a "plough"
but rather use a disc  (?) which just puts in a small knife like slit in
the soil to drop the seed in.  He also said that if they get a hard pan
they use lime to break it up.  

None of this is entirely new to me; I have of course read about all
this but I thought afterwards that the student is maybe right to an
extent and I am unfairly bagging cereal crop production on the modern
Australian farm.  

There are a number of issues that I would be interested in hearing
about:

Firstly, my understanding is that frog friendly round up is only used
by home gardeners - commercial farmers just think the extra cost is not
doing anything for their bottom line.  So this no-till tech actually
intensifies environmental problems for frogs.

Secondly, my understanding is that topsoil is usually the result of
centuries of humus deposition by various kinds of trees and bushes.  No
- till may prevent further erosion of this topsoil but it cannot build
the topsoil very readily.  But again I know that with maize they can
achieve a mimic of a forest humus production by putting in a cover crop
and slashing it - for example velvet beans are very popular in Latin
America.  Do no-till farmers in Australia do anything like this or are
they essentially mining soils when they plant cereals?

Thirdly, do these new "ploughing" techniques - it seems they do not
like them referred to as "ploughing" which conveys the concept of
turning over the soil - really stop soil erosion or not?   

What about hard pan?  Are there any problems with repeated applications
of lime?  Does it actually work?  Doesn't the weight of agricultural
machinery pack down the soil regardless?  This liming solution is
probably too expensive for some cereal farmers, especially in developing
countries.  Again, I would have thought that in the context of grain
agriculture some kind of rotations and cover crops that were reasonably
deep rooted combined with minimal ploughing would have solved these
problems better than applications of lime but maybe I am wrong?   

What about the problems of dissolving soil minerals that Mollison talks
about and which is often referred to especially in relation to former
rainforest soils?  Does no-till stop this mineral leaching?   

Would be interested in any comments on this,

Terry