How to Measure Soil Porosity

Knowing soil porosity is an important part of gardening and architecture. Porosity refers to the amount of water that different kinds of soil can hold. The more water the soil can hold, the more porous it is. Damp, porous soil works well for plants that love wet feet, but provides poor conditions for plants that like drier conditions. Porous soil also makes a poor foundation. If soil is damp and soft, buildings placed on top of it will sink. Fortunately, measuring porosity is so simple that your kids can help.

2, 400 ml beakers
Soil sample
Water
Pen and paper
Calculator

Instructions

- 1
  Set two 400 ml beakers side by side. Fill one to the 200 ml mark with soil. Fill the other to the 200 ml mark with water. The water temperature doesn't matter.
- 2
  Pour the water, a little at a time, into the soil. Wait about 30 seconds after each pour to add more water. This gives the soil time to absorb the water and fill up all available pore space.
- 3
  Stop pouring when the water covers the top surface of the soil. This means the soil has absorbed all the water it can. Carefully pour the water on top of the soil back into the water beaker.
- 4
  Write down how much water you have left in the water beaker and subtract that amount from the original 200 ml of water. This is the pore space.
- 5
  Divide the pore space number by 200, then multiply that product by 100 to get the percentage of pore space in your soil. For instance, if your soil sample held 100 ml of water, divide that by 200 to get .5. Multiply .5 by 100 to get 50. In this case, your soil sample has 50% porosity.

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