Soils pH and moisture...

[Externet]

Hi.   These gadgets for reading pH; how they read on same soil samples with different contents of moisture ?

Is there any compensating to ignore changes of conductivity by soil wetness ?  How dry or wet can soil be for accurate reading ?

[Sensei]

Good timing. I bought today YL-96 moisture sensor for Arduino. Similar to this one:

You connect it to analog pin on Arduino e.g. A0.

This code can be used to read sensor, and send data directly to the computer:

static const int pinHumidity = A0;

void setup() {
  // put your setup code here, to run once:
  while( !Serial )
  {
    delay( 100 );
  }
  pinMode( pinHumidity, INPUT );
  Serial.begin( 9600 );
  Serial.println( "setup ok!" );
}

void loop() {
  // put your main code here, to run repeatedly:
  int state = analogRead( pinHumidity );
  Serial.println( state );
  delay( 1000 );
}

It's returning 1023 when sensor is in the air, and lower, and lower values, when it's put deeper and deeper in water container (that's what I checked). Fully immersed in the water was returning ~240.

Notice that your pH and moisture sensor (unlike mine), has two different metals used for two different electrodes. Their tips is yet another metal.

 

 

Edited November 28, 2018 by Sensei

[tinkerer]

I have and use such devices, and have forever and a day wondered about "Soil Ph". Rather still "up in the air", though.

[StringJunky]

41 minutes ago, tinkerer said:

I have and use such devices, and have forever and a day wondered about "Soil Ph". Rather still "up in the air", though.

Soil pH is quite dynamic and rather chasing a moving target with the crop and conditions changing it constantly. The main thing is to keep it in the range that keeps the nutrients bio-available; generally between 5.5 - 6.5, This graph gives the plant uptake of various nutrients at different pH ranges. Fatter parts of the bars show greater uptake, so you need to find the position that optimises for all nutrients. Different plant  types will want slightly different biases but 6.2 would probably be the best starting position in the absence any information..

 

Edited December 12, 2018 by StringJunky

[studiot]

Surely the pH is a measure of the acidity of the water in the soil, not the soil itself?

So a pH meter will not give any sensible reading when placed in kiln dried sand.

I think that some pH meters are actually a form of conductivity meter. These could obviously be confused by the presence of conductive minerals in the soil.

[StringJunky]

3 minutes ago, studiot said:

Surely the pH is a measure of the acidity of the water in the soil, not the soil itself?

So a pH meter will not give any sensible reading when placed in kiln dried sand.

I think that some pH meters are actually a form of conductivity meter. These could obviously be confused by the presence of conductive minerals in the soil.

From what I've read, they are. I think the best way is to standardize a sample size, mix with a standard volume and then litmus it. Would you think so?

[studiot]

13 minutes ago, StringJunky said:

From what I've read, they are. I think the best way is to standardize a sample size, mix with a standard volume and then litmus it. Would you think so?

So long as the mud doesn't discolour the litmus.

Also that won't give you much of a range.
Soil is rarely neutral.

 

https://www.google.co.uk/search?q=range+of+pH+indicators&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjn2ufym5rfAhWM26QKHbYxCRsQ_AUIDigB&biw=1366&bih=622

[StringJunky]

9 minutes ago, studiot said:

So long as the mud doesn't discolour the litmus.

Also that won't give you much of a range.
Soil is rarely neutral.

 

https://www.google.co.uk/search?q=range+of+pH+indicators&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjn2ufym5rfAhWM26QKHbYxCRsQ_AUIDigB&biw=1366&bih=622

You let it settle a bit.  Have I suggested the wrong test paper?

[studiot]

14 minutes ago, StringJunky said:

You let it settle a bit.  Have I suggested the wrong test paper?

Compare the pics of ranges I linked to and ask what will tell you the difference between say pH = 6 and pH = 6.5

Here is a good link to soil PH, where this pic comes from.

http://soilquality.org.au/factsheets/soil-ph-south-austral

 

[StringJunky]

11 minutes ago, studiot said:

Compare the pics of ranges I linked to and ask what will tell you the difference between say pH = 6 and pH = 6.5

Here is a good link to soil PH, where this pic comes from.

http://soilquality.org.au/factsheets/soil-ph-south-austral

 

The one I've used has a chart that shows a gradation of tone from yellow to red  in half pH units and you check the result against that.

[John Cuthber]

8 hours ago, studiot said:

I think that some pH meters are actually a form of conductivity meter.

I don't.

Or, at least, they shouldn't be.
It may be simply that, if the soil is too dry for the pH meter to work, the plant dies anyway.

[tinkerer]

On 12/12/2018 at 12:31 PM, John Cuthber said:

I don't.

Or, at least, they shouldn't be.
It may be simply that, if the soil is too dry for the pH meter to work, the plant dies anyway.

What might you imagine such meters to be then? Off the shelf ten-dollar priced devices capable of measuring H+ ion content?

[John Cuthber]

7 hours ago, tinkerer said:

What might you imagine such meters to be then? Off the shelf ten-dollar priced devices capable of measuring H+ ion content?

My first guess would be a piece of aluminium and a piece of copper connected to a meter.

Working like a cheap + shoddy variant of this

http://jes.ecsdl.org/content/72/1/139.abstract