Peat has 75% air porosity?!!!

Hey JAG2,

Yup it does according to that thread I referenced and other materials I've read. But note that the peat was not tested when pre-moistened.

I have some peat here and I can do a test tomorrow. I think it's important to test dry and pre-mositened to get a better picture of it's structure. If the peat was pre-moistend then the air-porosity would be a good deal lower.

I attached a link for a how-to of the test I use

;-)

Here is a link that might be useful: Calculating total porosity, aeration porosity, and water retention of growing media or soil.

HI again.,

for an example of how dry and pre-moistened substrate show different properties I did two tests when I tested vermiculite:

Test 1: Dry vermiculite horitcultural course grade
(this is the result that matters and would be placed upon a bag)

Air porosity = 70%

Water capacity = 28%

Water saturation = 45%

Test 2: Pre-moistened vermiculite horitcultural course grade
(this is just for comparision and to see how the structure changes)

Air porosity = 45%

Water capacity = 3%

Water saturation = 42%

A great post by "shurbs and bulbs" which describes what I'm trying describing:

[begin quote]
They don't describe peat as "fluffy" for nothing ;) One of the problems with peat is the very large difference between the amount of water retained from a dynamic watering, and the maximum amount of water which can be soaked up, for example from standing in a saucer. This is what you referred to as wettability in another thread. Although peat retains air from a simple watering, it can become almost fully saturated from being allowed t soak up water. You can measure this by a third experiment where the cup is allowed to stand in water for a few hours.
[end quote]

Hey again,

Also another test would be to use dry substrate and add yucaa extract as surfactant to the water and see what the results are...they should be very similar to the pre-mositened test results.

Yup it does according to that thread I referenced and other materials I've read. But note that the peat was not tested when pre-moistened.

I have some peat here and I can do a test tomorrow. I think it's important to test dry and pre-mositened to get a better picture of it's structure. If the peat was pre-moistend then the air-porosity would be a good deal lower.

I attached a link for a how-to of the test I use

I don't get it. There is no way peat has an air porosity of 70% in any meaningful sense of the term.

It is more around 15-20% depending on the grade/freshness. Here is how I calculate porosity.

It may well be true that 100% dried out peat has an air porosity of 70%, but who uses 100% dried out peat? Normally wet/moist peat will have an air porosity of 20% or less and it falls quickly throughout the season due to particle size reduction as it breaks down.

Hey,

That's my point...moistened peat has much lower air porosity vs. dry peat (as it is with most any substrate). That's also the point of "shurbs and bulbs" when he/she was stating the flaw in "xerophite_nyc" experiment (the one I linked to, he/she tested the peat).

I think when xerophite_nyc did his/her tests he/she didn't let the peat absorb the water long enough...as in a couple of hours or overnight.

The link I posted showing how I calculate porosity is the same method you posted in your link...the same exact methodology except your link is better written...

I should have edited xerophite_nyc's info but I forgot to do so before I posted...this site needs an "Edit" button!