Topic: Wacky soil moisture levels

[Aardvark]

Last year we had a drought, it was dry 3 feet down. Now we have had a lot of rain and I am noticing my sensors are a little strange.   I am thinking I need to dig out the 4 and 12 inch sensors, clean them off, resoak and replant them.   The 24 inch could be that, but the 36 inch is way off .    The unit works, but I am wondering if because of the dryness of last year,  the soil has caked around the sensor making a barrier.  I'd hate to have to drill down the 3 feet to get it.

My big worry is that at 3 feet and pulling the unit up out of the soil , could tear the leads.  I can solder them, but what I hate is the terminal block in the soil station. it is those pinch clamps that you have to take a tiny flat blade screwdriver and push the plastic straight back to make the jaws open. push a tad either direction off and it breaks and you are screwed.

anyway here is my readings and it would be live.   Tomorrow it is supposed to hit 92 then storm...   what a day to live for.


the second non solar is just to measure soil surface temperature.  I am thinking of repairing my old ISS finally and changing it out for that unit, making it solar, but the jury is out on it.

[dalecoy]

I'm totally clueless about soil moisture measurements, so perhaps you would explain why those are (necessarily) "strange"?

Thanks.

[floodcaster]

My second soil moisture sensor at 12 inches appears to be dead. It's been reading 200 since winter, even with abundant moisture. Not sure what the average life of the sensor is but mine was installed in 2008.

[Aardvark]

I thought 5 years .   Today I am going out before it gets hot and dig up the 12 and 4 inch and see what is going on.   These are so dang expensive.  By rights I should replace all 4 but, that is 200 easily.

[moehoward4]

You must be buying the expensive ones.......www.archertradingpost.com/atp       $41/ea plus s/h

[Aardvark]

I can get from Ben Meadows for 35.

Anyway, I hoofed out to the garden store and got a Ross Root feeder.   I am pumping water down to the 3 foot sensor  and I am getting a wetter reading but it is real muddy still.  not sure what the deal is as I it is slowly doing an up hill climb.  The station sends a signal every 90 seconds so there is some lag time.  I think the transmitter is fine, and I will even go with the 24 inch sensor as being the honest one.   with the water  that is out there, I should see a sharper decline.
here is the last auto plot showing the sensors

[Skywatch]

Got my soil moisture sensors from Ryan for 36$ after emailing him a link to Hobby Boards moisture sensors which is the same Watermark sensor. He matched the price. Try finding the link to moisture sensor on Hobby Boards web site and email that to Ryan.

[dalecoy]

I'm totally clueless about soil moisture measurements, so perhaps you would explain why those are (necessarily) "strange"?

Just curiosity, but I'm still wondering how you determine that those readings might be strange.

[dendrite]

For those who think their readings are too dry, I'd recommend pulling all of them up in the Spring and repeating the installation procedures. This has fixed my problems in the past. I've wondered if it's a freeze/thaw issue where maybe after a thaw the soil recedes a bit from the sensor. Good luck.

[Aardvark]

I did that , pulled up the 4 and 12 sensors as they are easier than the 24 and 36  , cleaned and soaked them and it didn't do anything except show a very slight change.

Then on the 24 and 36,  I put in my Ross Root feeder and saturated the soil at sensor level  and not a change.   So  I am going to relocate the station a bit when the replacements come, soak and condition the sensors and back fill after planting.   

[Aardvark]

I'm totally clueless about soil moisture measurements, so perhaps you would explain why those are (necessarily) "strange"?

Just curiosity, but I'm still wondering how you determine that those readings might be strange.

the values are not what they should be for saturated .  If the values were between 0-10, I would be happy.  By saturated,  two tests.. one removed the sensor, cleaned it off with clean water, taking care not to break the membrane, then leaving the sensor submerged in clean water for 2 hours and noticing that the values remained in the double digits.

The second test was to let the sensor dry out and it remained near the wet level.   I then took out my Ross Root feeder and by each soil sensor  Saturated the ground in all directions around the sensor, then watched the values.   The only one that changed was the 24 inch sensor.  So as McCoy says " He's dead, Jim."

[dalecoy]

Thanks.  Of course, those tests were "after the fact".

I'm guessing you were expecting readings from all four sensors to be less than 10 cb - based on experience and also the normal range of measurements.  So, three of the readings were "wacky".

...which caused you to perform further tests on the sensors.

Thanks again.

[floodcaster]

For those who think their readings are too dry, I'd recommend pulling all of them up in the Spring and repeating the installation procedures. This has fixed my problems in the past. I've wondered if it's a freeze/thaw issue where maybe after a thaw the soil recedes a bit from the sensor. Good luck.

For me I think it is an issue of our clay soil. When it shrinks I think you lose the sensor/soil contact. I did my best to bury it correctly, following the sequence of soil horizons I took out and making a slurry to help make good contact but I'm sure there were some gaps at the time of installation. I plan on replacing mine soon.

[Aardvark]

Thanks.  Of course, those tests were "after the fact".

I'm guessing you were expecting readings from all four sensors to be less than 10 cb - based on experience and also the normal range of measurements.  So, three of the readings were "wacky".

...which caused you to perform further tests on the sensors.

Thanks again.

No,  I noticed these trends for the last 60 days,  we've had sufficient rain so far this year that the 4 and 12 inch sensors should have had a greater  range, The 24 inch sensor  was reading fine and I had "guessed " that the 36 inch had a coating of dry clay from the drought, in fact I watched that sensor dry out as it was dry at least 3 feet down.  A lot of folk around here are having their sewer lines dug and replaced because the clay pipe that was used has tree roots or collapsed, so I went over and looked. 

Anyway,  I never expect to see anything, man.. I am a scientist, been doing this gig for 30 years now.  I look for trends and try to figure what is happening and to conclude this , I don't want to get into a pissing match with an engineer.  So lets see how these 8 dollar sensors work out.

I have to solder on 10 feet of lead to the 5 foot that comes with it, cut the PVC pipe and so forth  and bore the holes.  Connect it up and then wait.   6 years is beyond the life time of the sensors.  I am replacing all 4.  The temperatures look fine, but again   those sensors have to come up as well,  unless I want 8 pvc pipes instead of 4.

[dalecoy]

No contest intended.  I know next-to-nothing about soil moisture or its measurement.  Just trying to learn.

Although I do remember once observing - in the midst of a Vietnamese monsoon - a truck driving through my salvage yard, kicking up a lot of dust.

[Aardvark]

I have been tracking the sensors being shipped and it looks like they will arrive tomorrow.  It is a risk  buying a 41 dollar sensor for 8, we'll see .

Soil structure has a lot to do with how wet things are.   we just had a good rain in a hurry, the 4 inch sensor should be between 0 and 10 , it is at 87. anyway,  my plan is to move the station to near the ISS and see how things work there.  The wife might have a cow, but she is out of town and besides, once it is in the ground, I am not moving it.

I'll let you know how things go.

[Aardvark]

the sensors arrived today. new and in the packages.  they come with a screw lug that I will remove and tin the ends.  and use a duraseal heat shrink for additional whatever.   They have a five foot lead, so I am going to solder an extention on the wires before I condition them.   

The downside is it really rained this morning 0.75 inches and it is too muddy to go out and pull the sensors.   although I am really temped to do so .  This time I think with the temperature lead, I am sending it down on its own pvc pipe. that I can do with 1/4 inch pipe as it is a single lead.   Next time I have to pull  up a sensor, it will just be one and not the temperature/moisture pair.

Dalecoy:  if you are interested in this http://www.irrometer.com/sensors.html   gives a lot of good information on their site.

[dalecoy]

Dalecoy:  if you are interested in this http://www.irrometer.com/sensors.html   gives a lot of good information on their site.

Thanks.  That's quite informative.

[Aardvark]

I have 3 of the 4 sensors in the ground and of course the readings are not right.   The sensors are planted saturated after a good 2 day process so that is going to take time before the sensors read right.  It has been hot

It is hot, and the 3 foot hole is going to be a bear to drill.  My cordless drill with the 24 inch auger has worn down its battery and the hand one , well using a soil auger isn't a lot of fun.

So I am going out in a bit and try to see if I have enough charge on the battery to drill the hole, plan it.

One thing about the Davis soil station, they have these evil little plastic tabs you have to push to open the jaws on the wire clamp.  if the angle is off a bit, they break and you are screwed. I did manage to get the wire in before it broke.

I have a 2nd station with problems but I am planning on sending that in to Davis to be fixed and when it returns put in a terminal screw block instead of that wire gig.   I have a plan ...