"Gerry" wrote in message
...
Yes the fields are flooded, but only the part of the year that the
rice is actually growing. I have heard that in Viet Nam some
farmers
use blue-green algae to add nitrogen to the soil at this stage, but
I
can't confirm if that is true.

The time that the fields are fallow in the farms I am thinking of in
Thailand is during the dry season. It doesn't rain for months and
it
is really quite hot, especially in the sun as these fields are. It
is quite a different set of circumstances from when I plant hairy
vetch in my garden for the winter in New York!

In Malaysia, the most popular legume cover crop I think should be
Calopo(Calopogonium mucunoides) and
Butterfly Pea(Centrosema pubescens).

Both of them are drought and flood tolerance. Butterfly Pea are more
drought tolerance, Calopo are more flood tolerance. As legume they
are slow to start, and the organic matter they produce are not in long
lasting form. For what I notice, nearly all rice field are heavy clay
soils, since Butterfly Pea grow well in heavy clay soils, it may be
the better choice.

For fast growing and longer lasting organic matter, you have to look
for grass cover crop.

I suggest you try this:
After you harvest and drain, spread a four inches thick rice hull on
the rice field and till it in. Volunteer rice cover crop will grow
from the rice hull you till in. When the weather are getting dry,
till in the rice cover crop, wait for two weeks, seed the Butterfly
Pea and Calopo mixed, let the result to decide next time will goto
either Butterfly Pea or Calopo. Please put in mind that, you have to
seed before it's really dry, both legumes need rain to germinate and
grow their root to deeper part of soil in search of water.

The advantage a
Rice hull are free.
Rice hull do contain long lasting organic matter.
Rice hull will supress other weed but provide volunteer rice cover
crop from the rice that mixed in the rice hull.

BTW: The volunteer rice cover crop can grow without under flood or
irigation, but they will not produce good crop for harvest, this is my
personal experience.

--

Regards,
Wong

Latitude: 06.10N Longitude: 102.17E Altitude: 5m