"Ray" wrote in message
...
Doesn't that raise the question about what the red pigmentation does
(assuming all other mulch properties are identical)? Is it the reflected
red light back to the plant that makes a difference or is it a change in
the ground temperature under it?

Yes. ;-)

Both are likely to be happening. Any red light reflected onto a leaf will
likely contribute to photosynthesis, and possibly other processes. It is
certain that any light absorbed by the ground will be converted into heat,
producing nonlinear changes in soil temperature with depth. Now
understanding that process is considerably more complicated, involving
conduction and transport of heat, but the salient point is that light
hitting the soil will raise the temperature of the top layers of the soil,
and that will have the usual effect on reaction rates in the plant's roots.

How significant each process is is a different matter that can really only
be determined experimentally. I know the agriculturalists I know talkof the
importance of soil temperature, but I personally have not heard them discuss
the colour of the ground.

Cheers,

Ted