Topic: soil temperature

[Aardvark]

Now here is a new twist..  I have a fully populated soil/moisture/leaf station on my VP2 setup.   I have  the moisture probe and the temperature probe at the same depth, I used a plastic cable tie to get it that way, so when I planted it at the right depth, they were mated (oooh.. sounds dirty).

The depths were done with a soil auger to the depths of 4, 12, 24 and 36 inches  all about in the same location (  probably a 2 foot diameter plot) so I could get all the data in the same soil area.   The soil  much beyond six inches becomes clay and sand, mostly on the clay side.   The top soil is pretty good with the last 28 years of me putting back into the soil.

Ok.. so I have the station working fine and I am noticing that the soil temperature at the 4 inch depth cooler than it should be.  Each other probe is doing fine, but this one seems as the soil dries out the temperature gets cooler rather than hotter.


http://www.weatheraardvark.com/Soil.htm    I am not sure if it is the station or not.  The soil around it is top soil, it is drying out 4 inches down, so it seems possible that the water molecules that would be transferring temperature down to the probe are less and the soil could be insulating at this time.

However, that sounds also like a lot of hooey ( that is a Iowa term to replace references to cow dung).   

I did send an email over to Davis, but they often take time to respond.   I suppose I could move the probe wire to a new terminal, but I am pulling data from all 4 locations.

A while back,  I was getting  an odd thing with the moisture probe at that depth  , when it would rain the readings would go to the dry side for a while.  I wrote Watermark about their probe and found that sometimes the soil will pull away from the surrounding soils and give the probe a drier reading. So I removed the probes and filled them with garden black soil and it was fine for almost 2 years now.

This temperature thing has me curious.    I really am not sure what is going on.

[Downlinerz2]

    I remember back in Jr. High School I did a soil temp project.  For the whole school year I had holes that were 2", 4", 8", 12", and 16".  I then had one at 2 feet. I had 2 sites where I took measurements.  One in a sunny area and one in shade most of the time.  I wish I had had a Davis set-up back then.  All I had was the regular long glass liquid thermometers.  I would put the thermometer into the hole every morning, and every evening for 5 minutes.  The holes were covered to keep any sunlight off at reading time.
I cannot remember specifics of the results and they may be up in the attic someplace but I remember being very surprised by some of the results.  The resulting graphs were very cool even before the computer age.  That was fun.  Wouldn't mind doing it again.

[Heirphoto]

Just wonder if at the shallow depth the drying of the soil by evaporation is working the same as a wet bulb thermometer and lowering the temperature of the probe just as it does in a wet/dry bulb setup.

Tony

[wxtech]

Just wonder if at the shallow depth the drying of the soil by evaporation is working the same as a wet bulb thermometer and lowering the temperature of the probe just as it does in a wet/dry bulb setup.

Tony

evaporative cooling.  Sounds right.
I have the Davis soil temperature transmitter and 4 sensors.  I moved my station and left the sensors buried and no longer connected. 
I dug a hole with a post hole digger.  Then I attached the 4 sensors to a plastic pipe arranging the sensors horizontally to get the depth accurate.  I replaced the soil that came out of the hole, packing it tightly.  I attached the cables to the plastic pipe so that I could dig them out if needed. 
I never noticed any unusual temperatures with the 4 sensors.

[Aardvark]

Right now it is really hot and humid,  I am thinking of going out and shift the leads  to another station and see if that makes a difference at the 4 and 36 inch levels.    I have a hell of a dental appointment on Wednesday, so I might be in the right frame of mind to go out and do that later this week.

However.....

[Aardvark]

I went out and stomped on the ground around where the sensor is, opened the transmitter box, it looks dirty in there, but no critters so far.  I wiggled wires around and saw nothing was  shorting over.

So the graphs today are mirror images between moisture and temperature.   I am wondering if the unit is crapping out.  I keep it outside 24/7 all year.  Here are the images 

[d_l]

Are all your probe's leads directly connected to the leaf/soil station or do you have extension wires between them and the station on some or all of the probes?  Just checking if there may be a failed (wet) wire splice causing your temperature/moisture problems.

[Aardvark]

direct connect, no splice

[Aardvark]

disagree  with the "evaporative cooling " theory.

I unplugged the soil moisture sensor for the 4 inch depth and the temperature rose to 90F.   Tomorrow, when I feel better, I am going to plug it into another soil moisture pair and see if it affects that temperature sensor as well.

If it doesn't then the problem is with the circuit for the 4 inch and it is call Davis time.  IF it does, then it is the sensor.     

[Skywatch]

Just wonder if at the shallow depth the drying of the soil by evaporation is working the same as a wet bulb thermometer and lowering the temperature of the probe just as it does in a wet/dry bulb setup.

Tony

evaporative cooling.  Sounds right.
I have the Davis soil temperature transmitter and 4 sensors.  I moved my station and left the sensors buried and no longer connected. 

You would happen to be giving those sensors away? I need 2 of those things right now. LOL.

[Aardvark]

no,  but I did some price cheching.

Irrometer makes the watermark sensors for the soil moisture  if that helps.
Ambient charges 52 for the moisture where as provantage charges 33 and scienftific sales.
Ambient chares 48 for the temperature and the moisture from provantage is 43.  i gave up on sales.

I did get a memo back from Davis, it was I should dig out the sensors  and place them inwater to condition them.  Of course they have been in the ground for 4 years now, so they must be already damp and then the rest of the message was about  conditioning soil sensors.  I did write them back, re explained it but came to the revelation that they must work for the government.  with their adeptness and accessing the wrong solution .