Transpiration and evaporation

[Barry Supernaw]

       We have about 530 gallons total in our system, 370 g in two FTs and 160 in a 4x8 DWC with about 300 2" pots with wheat grass, a few tomatoes and even a couple volunteer cottonwood trees. We've been losing 6%-8% or 30-40 gallons a day. I'm not seeing any leaks unless there's a hole in the bottom of the grow bed but it seems to me I'd see evidence of that in the dirt around the bed. I've been researching transpiration but have been unable to find a definite amount that plants will transpire.The humidity has been lower than normal recently which I know will increase transpiration rates but losing 30-40 g a day seems like a lot! Have any of you had problems like this?

       Also I'm currently using 1.5" foam rafts and wonder if switching to 2" would help keep the coir from wicking as much water as it does (we use straight coir in our pots, finely ground). The coir on top of the pot is very moist which leads me to wonder if I'm losing a lot of water to evaporation.

[David - WI]

I think a field of planted corn loses something like 1 gallon per day for every 10 square feet... yours sounds like about 10x that much?

If it were mine, I would;

Cut the tops off of two 2-liter soda bottles (or use a milk jug or any other container, I guess).  Make a 2" thick "raft" that fits loosely into one soda bottle and a 1-1/2" raft that fits loosely into the other bottle.

Then put one of your already growing wheat grass net pots into each raft and mark the water level on each bottle.  Every day I would check the levels to see a) how much a single plant transpires and b) how much difference the 1-1/2" raft makes versus the 2" raft.

[Harold Sukhbir]

Hi Barry,

Had a system of similar size and lost about 40 gal per month and i live in the tropics, with daytimes in the high 80's!  You need to check for leaks.

[Alex Veidel]

I have a similar size system, and I lose nowhere near that amount of water

[Barry Supernaw]

I tried David's test and figure I'm losing 4-5 gal max per day to transpiration and probably some to evaporation so yea I have a significant leak somewhere.