Topic: Soil Moisture Sensors reading zero

[zachelliottwx]

I installed 4 soil moisture sensors on Saturday. I soaked them overnight and then set them in the ground. I wired them all up with the temperature sensors. Temp sensors are working great. However all 4 soil moisture sensors are reading "L" on the VP2 Console, and in wView, they're reading "0" two days later. I understand they should read zero if they are soaking wet, but over 2 days they certainly should have dried out, especially the 2" sensor. I've attached an image below of the VP2 console.

I've contacted Davis but no response yet. Any ideas? Are all 4 of my sensors somehow hosed? That seems really unlikely. I can't find any documentation on what the "L" means.

[Aardvark]

I have never had the display reading, but it is possible that the sensors can read zero for longer than you think.
Couple of sensor questions. SOil type, does it have clay?  clay hold the water in.   Did you pack the soil down around the sensors and wet it, or did you use a slurry of soil and/or bentonite.   I would be more worried if I had planted my sensors and it was a month at a 4 -12 inch depth.   Attached is my sensors right now. 

How are the soil temps going?  for me,  I have clay at 24 inches so water at 36  pretty much stays saturated unless we have a drought.   A good source to contact directly about the sensors : http://www.irrometer.com/    They make the sensor that Davis uses.  They have always responded quickly to me regarding any question about the sensor and I recommend contacting them .   If the sensor is working you have a zero to 200 reading. if the wire is broken, you get  ------ 

[zachelliottwx]

We dug the hole, then placed the sensor apparatus in it. (I made a PVC pipe conduit system) then we shoveled the soil back in, pouring water over the soil over the sensors so it was nice and wet. Then we finished shoveling it in, and packed it down up top.

I contacted Davis and they mentioned restarting the console. I'd prefer not to do that since my station is 300 miles away so there's always a pucker factor involved. Given the leaf wetness and soil temp sensors are working, I have a had time believing all 4 soil moisture sensors wouldn't work.

I should have tested it out before I wet them, just to see if I would get a 200 reading.

Soil temps are good. 24" is pretty consistent with 10" and 4" moving a tad, and 2" being the most variable obviously.

[Aardvark]

I think you answered it.  the water over the soil. It did a good job of grouting it in, but I would wait a while and see if the readings fluctuate up and down.  Again, contact irronmate and they have a lot of good stuff on their site about sensors and will promptly answe questions.

24 inches will take a while 2 inches again depends on the soil around the area.   Soil moisture is a weird thing changes slowly.  I have had a sensor at 4 inches reading 13 cb and it is raining all the heck out there and it it drops to 12 and then four hours later to  3.     

Irronmate also told me that there is a phenomen  where the soil contracts around the sensor giving it a higher reading.  The solution is either dig it out or pour that bucket of water.

[zachelliottwx]

I've reached out to Irrometer to see what they have to say.

[zachelliottwx]

They got back to me, and they said that it can take some time, but also that the horizontal mounting that I did (i did not place them vertically) may be part of the problem and water may be pooling on top of the sensor. I guess when I make a trip back up in July I may dig it up and remount the soil moisture sensors. I was not aware of the vertical requirement and saw other photos of people mounting them horizontally. But if moisture is pooling and not drying that makes sense that it may take some more time to dry out. I'll just give it some time, then work with it in July.

[Aardvark]

They got back to me, and they said that it can take some time, but also that the horizontal mounting that I did (i did not place them vertically) may be part of the problem and water may be pooling on top of the sensor. I guess when I make a trip back up in July I may dig it up and remount the soil moisture sensors. I was not aware of the vertical requirement and saw other photos of people mounting them horizontally. But if moisture is pooling and not drying that makes sense that it may take some more time to dry out. I'll just give it some time, then work with it in July.

I am glad they got right back to you. They are a good company.

[zachelliottwx]

So my 2" and 4" sensors are flipping between 1 and 0. So it seems like they're at least getting values. Appears i'll have to recompile wView though since it doesn't put the 3rd and 4th sensors in HTML files. That's another task for another day though.

[Aardvark]

I had to do a quick sensor replacement.my 4 inch was all over the place, so I had a spare one  and put it in.  When I get time , I  will make it permanent.  Always something

[zachelliottwx]

So I just wanted to post an update. After some time, the sensors are finally working properly. I believe the issue was the wet season KS has been having so far. The past 2 weeks the rain has been a lot less and sure enough, the sensors are reacting properly. The 2" sensor started drying out fast this past week and is almost up to 100Cbar. 4" is not quite as low, around 40cbar but it is steadily increasing. 10" is very slowly going up, and 24" has not moved. That's not shocking though, it's gonna take a long hot summer with little rain to get the 24" to dry out.

[Aardvark]

The conditions are similar in Iowa...  Soil moisture values change slowly, but the do change.   I learned a while ago that sometimes the soil can pull away from the sensor just so much that it gives a higher reading than it should.  THe solution is to bring up the sensor, back fill the hole. wash the sensor and replant in a different spot.  Irronmate will answer a lot of questions  about their sensors.   Good luck,  you are now getting readings.


My soil is odd,  about the top 12 inches is soil then it goes down to clay and thick.

[zachelliottwx]

The soil here was pretty much all soil. There was a little bit of clay towards the 24" mark but not much. As of this morning, 2" is maxed out at 200cbar. 4" has definitely cranked up and sitting at 40cbar and drying out quickly. I'm actually seeing a lot of change on the 10" as well, up to 10cbar from zero just a day or two ago. 24" has not changed which is no shock. Just today I had someone from the area tell me they needed rain, so it's definitely drying out.