What probe to use to test soil nutrients


I have created a Lora node and connected to TTN. I am able to read humidity and temperature and all seems nice for now. For the end product:

I am planning to install probes in agricultural fields to measure moisture, ph, temperature and humidity. For temperature and humidity, I have DHT11 sensor. However, for checking moisture and ph value of soil, I am not sure what material to use to probe the soil. Attached an image of a probe available online. probe probe

Someone who is aware of soil testing, can you please confirm the type of metal used to test ph and moisture. Also, as per the image, there is only one metal rod. How would it and what would it test? Resistivity, or capacitivity?


Have you asked the manufacturer/supplier? :thinking:

These are available in China and on Aliexpress. I sent them about electrodes and they replied saying that they are ready to source upto 1000 units per day. Not sure they would tell about electrodes. Written to them again about the electrodes used.

For this kind of measurements I would use more “professional” sensors, not the DHT 11 and not this kind of soil moisture sensor. https://dl.sciencesocieties.org/publications/vzj/abstracts/12/2/vzj2012.0160 or https://www.mdpi.com/1424-8220/11/1/1192/htm. success.

Thanks for the info. DHT11 is just for testing and will replace with a better sensor. Regarding the links you have suggested, the second link does not provide any info on probes or further details. Reading the first paper…

How are things going for you? I worked with the stevens hydraprobe, but there are more soil probes ( Spectrum, etc).

There was a gentlemen that was working a somewhat similar project for his winery. One the thing he did for soil moisture monitoring was make his own. His capacitive sensors using a couple of stainless steel bolts embedded in gypsum(plaster of Paris) he put several at different depth to measure upper lower root zone and to measure when the water was passed the root zone.

Just focusing on soil moisture, if you want a sensor that produces reliable, validated data long-term (ie rather than a proof of concept or basic demonstrator), then maybe you need to be looking at established sensor makes. After all, measuring soil moisture is a well-established and widely-used technique in agronomy.

Probably the most familiar gypsum block sensor is the Irrometer make. For a better approach then Decagon is another well-known make and some Decagon sensors will also measure salinity and (IIRC) pH.

Serious agonomists are starting to recommend sensors like ‘Sentek Drill and Drop’ which can measure soil parameters like moisture & salinity at up to 12 depths simultaneously with a single sensor assembly (they’re available in different lengths from 30cm to 120cm with individual sensors spaced at 10cm intervals). These sensors are very clever and great for ‘Smart Farming’ but are also seriously expensive.