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

["Michael Pierce" <michael@mrhydro.com>]

greenhouse-tomatoes - an email list for growers of greenhouse tomatoes.
Sent by "Michael Pierce" <michael@mrhydro.com>.
-

I'm going to have to chime in here! DO you want to grow tomatoes or go into
computer programming?

First of all, good for you; you have a system that you have invested in so
as long as it works to a good degree, keep it. It does sound like it needs a
little help.

If I understand, your timers are feeding 4 times per day for each timer (a
total of 8 times a day for both timers). If this is correct, you are feeding
6 minutes of water 4 times a day for one timer. THIS IS NOT GOOD!! On top of
that, you are watering out of a PVC pipe reduced to a spaghetti tube. I
don't have my flow calculator in front of me but running water out of a
spaghetti tube for 6 minutes (without a pressure compensated dripper) is
going to dump a bunch of water. All of this water must be running to waste.
You need more control of the flow even if you don't add drippers.

If you have the two timers wired to water the whole range 8 times a day for
6 minutes each feeding, THIS IS NOT GOOD!!

If the sun comes up at 6:00 AM and you begin to water at 8:00 AM then you
will only water until 4:00 PM (that is 8 feedings). You still have 3.5 hours
of light left in the day. I'm not sure where you are and I'm not sure about
saw dust but I would not stop watering at 4:00 PM in Houston, Tx.

I'll go back to something much simpler than diodes, relays, and other
electronic wizardry. What do you mean by "the plants needs"? I say get a
controller that waters what you want; something per second per minute. This
will allow you to water so many seconds every few minutes for any duration
through out the day or night. (BTW - you should not have to water at night!)


I'm going to see if I can get some saw dust to see what water holding
properties it has. My first reaction is to ditch that stuff and go with
perlite.

As a general rule, water cycle timers and individual thermostats will not
suffice for commercial tomato greenhouses. They are very limiting and do not
allow for the flexibility that is needed to manage proper environmental
needs.

BTW - flushing with non-pH corrected water is going to exacerbate your
wilting problem because it's going to knock the pH to hell and back and then
your anions are going to be defibrillating with the cations.

In other words, there will be a fluctuation in the eddy currents that will
incapacitate the flux capacitor!
 
Michael Pierce
M & R Hydroponic Farms


-----Original Message-----
From: owner-greenhouse-tomatoes@Lists.MsState.Edu
[mailto:owner-greenhouse-tomatoes@Lists.MsState.Edu] On Behalf Of Eng, Doug
MSER:EX
Sent: Thursday, June 10, 2004 11:59 AM
To: 'greenhouse-tomatoes@Lists.MsState.Edu'
Subject: RE: greenhouse-tomatoes: Want to automatically trigger irrigation
cycles

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

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,