RE: greenhouse-tomatoes: Want to automatically trigger irrigation cycles

["Eng, Doug MSER:EX" <Doug.Eng@gems3.gov.bc.ca>]

greenhouse-tomatoes - an email list for growers of greenhouse tomatoes.
Sent by "Eng, Doug MSER:EX" <Doug.Eng@gems3.gov.bc.ca>.
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Hello,

Thank you for your feedback.  The autopot system is very interesting however
the 
switchover for me would be too expensive because I would need enough for
4000 plants. 
Also, I have a system in place already. The lysimeter sounds like what I am
after.  

Here is bit of info on how I am doing irrigation. I have about 4000 tomato
plants in sawdust 
filled plastic bags.  2 per bag. The irrigation is delivered by a 115v pump
through 2" pvc 
pipe. The pipe sizes decrease until it eventually arrives at the bag as a
pair of .045 speggetti 
feeding tubes.  I have a pair of timers (intermatic electronic - max 4
cycles) that cycle on/off 
the irrigation pump. At this time of year each timer is programmed for 4
cycles ( 6 minutes = 1 feeding)
and together they feed 8 times a day.  On a cloudy day I disable one of the
timers to get 4 feedings.
 
This crude setup usually works okay. I try to give enough feedings to see
drainage on a sunny day. 
Unfortunately as the plant's needs increased, I did not increase the
feedings.  The result was 
the leachate stopped happening and thus salt builtup in the bag.  The top 1
foot of the plant looks 
wilted and the leaves are drying out.  In desparation, I am going around
with a garden hose and 
manually flushing each bag with plain water in hopes of correcting this
condition. 

I could have avoided all this if I had implemented something like a
lysimeter. 

Doug Eng,