[APWG] Allelopathic straw keeping weeds out & moisture in during drought

[Craig Dremann - Redwood City Seed Company]

Dear Wayne and All,

Thanks for your email.  I will comment below your email:

Wayne--The grass-straw mulch is an interesting idea, and I certainly don't
doubt
that such a practice might have some utility in suppressing weeds, but I am
concerned about suppression of indigenous species as well.

Craig--Native grass and wild oats straw are being used on a site that has
been 100%  devoid of any natives for the last 12 years of monitoring, and
you can see a painting of the site at http://www.ecoseeds.com/art3.html. 
Since the straw is 100% effective against annual weed grasses like cereal
rye, Medusahead or cheatgrass, plus annual thistles like Italian and
Yellow Star, I do not recommend straw to be used in areas where native
seeds might still be in the soil seedbank.

I wonder just which "allelopathogens" are responsible for the observed
effects? What is their mechanism of action?

There are many  Journal of Chemical Ecology articles an allelochemicals,
that you can access through http://scholar.google.com and Dr. Liu and his
team have been important authors since the early 1990s studying the
allelochemicals involved.  His work was the first to sort out the
allelochemical effects from the other plant suppression effects, like
roots robbing water, or stealing nutrients, or shading of one plant by
another, etc.

Since most of the USA is in severe drought mode again, that you can see at
 http://droughtmonitor.unl.edu/ the straw mulch is keeping the soil
surface moisture in place for much longer, perhaps twice as much moisture
today--while we have a dry 40% relative humidity, barometer reading 30.20
inches (no rain for a while),  and no dewfall at night--than in areas that
do not have any mulch.

Sincerely,  Craig Dremann (650) 325-7333