[permaculture] Growing algae in irrigation water?

Lawrence F. London, Jr. venaurafarm at bellsouth.net
Sun Nov 20 23:44:41 EST 2011

On 11/19/2011 11:14 PM, Lawrence F. London, Jr. wrote:
> On 11/19/2011 6:18 PM, Dieter Brand wrote:
>> Thanks Lawrence,
>> The shading from plants may reduce evaporation but that is probably
>> more than offset by transpiration via the leaves.
> Dieter, my impression is that it might be good to look into that
> further, transpiration figures for duckweed as opposed to direct loss
> through evaporation, ratios and comparison with water conservation
> figures for other schemes. Also the duckweed with reduce water
> temperature thus reducing loss through evaporation. Google it.
> "reduced evaporation in pond when surface is covered with duckweed"

>> I hit on the idea of trying to encourage algae growth in my
>> irrigation system because of something I read about high fertility in
>> some of the ancient cultures in which irrigation was used.  It was
>> assumed that part of the fertility was due to the algae that would
>> form in the extended network of irrigation channels.
> It sounds like a great idea. If you can grow azolla where you are then
> that would be the aquatic plant of choice for accomplishing
> nitrification of irrigation water.
> DUCKWEED: A tiny aquatic plant with enormous potential for agriculture
> and environment
> http://www.fao.org/ag/againfo/resources/documents/DW/Dw2.htm
> "Azolla, which is a member of the fern family grows extensively in
> association with nitrogen fixing bacteria, which allows it to produce on
> waters low in N but containing phosphorus. Azolla has been
> comprehensively discussed by van Hove (1989)."

Another suggestion:

Obtain some Reemay or translucent woven synthetic fabric row cover used 
for crop cold protection. Grow duckweed in your water impoundment or 
tank(s) for added nitrogen or azolla or throw a little manure or compost 
in there and watch the algae grow. Cover the tank(s) with or without 
aquatic plants with Reemay to prevent most evaporation or loss through 
plant transpiration. Build a frame out of wood or plastic pipe
a little bigger than the opening of your tank; attach a section of 
Reemay to it; the weight of the frame will hold the Reemay in place over 
the tank while providing easy access to the tank for maintance, i.e. 
harvesting duckweed for animal feed or compost/fertilizer (high in 
nitrogen). There's a big plus to growing duckweed, you shade your 
impoundment, purify the water and produce high quality fertilizer.


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