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How To Measure Air Filled Porosity

T

tilopa

Member
How can I measure the actual afp of a medium? In other words, if I take two different media, and I want to see which one is more airy, how can I do that scientifically?
 
Creeperpark

Creeperpark

Well-known member
Mentor
Veteran
By water volume. Use the exact weight of two different soils then add water. The one one that takes the most water has the most porosity/
 
brickweeder

brickweeder

Well-known member
Creeperpark said:
By water volume. Use the exact weight of two different soils then add water. The one one that takes the most water has the most porosity/
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So add the same amount of water to the the two diff materials of the same weight, then separate and measure the volume of the non-retained water, and the material with less non-retained water has more porosity?
 
T

tilopa

Member
Mist said:
Why bother? If your plants are healthy and growing well you are doing it right..
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Why bother, to take the time to post a response that has nothing to do with answering the posted question. Nor does it even consider other reasons for the question beyond your narrow view.
 
T

tilopa

Member
brickweeder said:
So add the same amount of water to the the two diff materials of the same weight, then separate and measure the volume of the non-retained water, and the material with less non-retained water has more porosity?
Click to expand...

Its not quite correct. Porosity is the amount of air in a medium. If you add water to a medium in a container that has no drainage then the amount of water that it takes to saturate the medium can tell you how porous it is. The more water the medium holds the more porous it is.
 
I

Ichabod Crane

Well-known member
Veteran
Mist said:
Why bother? If your plants are healthy and growing well you are doing it right..
Click to expand...

Wouldn't it be nice to know if your plants will grow well before you put them into a non breathing media?

It is simple to check your media to see how much air it holds. Take two containers of the same size. Fill one with the media you want to check. Then pour as much water into it as you can.



Once you have filled up a jar with the media and the water drain off the water into the second container. I used the quart jars because I had a nice screen for them. You could use cheese cloth or even a coffee filter. If you do leave the band a little loose because the screen material will swell slightly.

Here you can see I used a funnel to get the water into the second jar. I just stood it up in the filter till it stopped draining.



When you are done just measure how high the water is in the second container. If you used the same size container you can get a accurate measurement. In my case it was about 32-34%. The amount of water you get will be how much air your media will hold.

 
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