Measuring Porosity

More porous media will

Less porous media will

Volume of growing media in a container contains

• growing media

• Water

• Air space

• Roots

Total porosity is

The total amount of poor space in a soil growing media

Saturation point

The point at which all of the poor space in a soil growing media is filled with water

Gravitational water is

Drainage water that exceeds the growing medias ability to retain it

Field capacity

The point at which the growing medias ability to retain water is at a maximum

Aeration porosity

Is the amount of airspace in the growing media at field capacity

Permanent wilting point

The point at which the small amount of water in the growing media is so tightly held that it is unavailable to plants resulting in death

Hygroscopic water

At permanent wilting point this is the water that is too tightly held to be available to plant roots

Available water

The amount of water between permanent wilting point and field capacity

The formula for aeration porosity PERCENTAGE

Aeration porosity expressed as a percentage

gravitational water (aka water out)/sample volume x100=%

Formula for water holding porosity PERCENTAGE

Water holding porosity =

total porosity(water in)-aeration porosity(water out)= water holding porosity VOLUME

Water holding VOLUME /sample volume =

For percentage X100= %

total porosity is the amount of water you put in before anything drained out.

Formulas for figuring out volume and percentages for aeration and water HOLDING porosity