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  • From: "Lawrence F. London, Jr." <lflj@intrex.net>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: [permaculture] Dry farming [Fwd: [SANET-MG] soil's influence on transpiration]
  • Date: Sat, 12 Jan 2008 23:55:23 -0500

-------- Original Message --------
Subject: [SANET-MG] soil's influence on transpiration
Date: Sat, 12 Jan 2008 17:05:03 -0700
From: Edna Weigel <eweigel@CABLEONE.NET>
To: SANET-MG@LISTS.IFAS.UFL.EDU

A friend convinced me to read John Jeavon's "How to Grow More
Vegetables..." It's extensive bibliography includes John A. Widtsoe's 1919
"Dry Farming." On http://books.google.com/books I found Widtsoe's 1910
"Dry Farming: a System of Agricultures Under a Low Rainfall" in free
downloadable .pdf format which I found very interesting.
I had always regarded transpired water as something over which I had no
control if I wanted to grow a particular crop. However, Widtsoe quotes
study after study in which fertilized soils or well-cultivated soils or
previously summer fallowed soils produce on the order of twice as much dry
matter per unit of water transpired as controls. That's impressive and
especially important for growers like me in arid lands with falling water
tables! There are brief hints that the addition of (as sodium nitrate) or
formation of nitrates (enhanced by cultivation) makes the difference.
These questions come to mind:
1) Have these observations from a century ago stood the test of time?
(Enough studies were quoted to convince me the effects were real.)
2) If the answer to #1 is affirmative, why, in these days of global warming
and drought and overdrafted aquifers and no-till methods is this information
not more widely known? (I can't believe I'm the last person to learn this.)
Could this relate to the cheapness of chemical fertilizers?
3) Could the numerous anecdotal stories (plus some careful experiments)
showing the value--especially in drought conditions--of compost and other
soil organic matter relate to the form (nitrate vs. ammonium) of nitrogen in
the soil with or without added compost?
My understanding of the chemistry of nitrogen compounds in the soil is
sketchy, but it passes my common sense test that an aerated soil would tend
to have more nitrate relative to ammonium ions when compared to a compact or
water-logged soil. I don't have a feel for the effect of organic matter on
the nitrate/ammonium balance. It also passes my common sense test that
plants will transpire more water (until they get enough nutrients to carry
on their life processes) if the water they take up from the soil doesn't
contain adequate amounts of nutrients.
I hope one or more SANETer(s) can enlighten me on transpiration and ways
of maximizing crops while minimizing water loss.
Regards,
Edna






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