Soil Aeration

Soil Aeration

Soil aeration is the circulation or movement of air with in the soil. Soil living organisms require gaseous exchange for survival.

The factors that influence the rate of gaseous exchange are:

Soil pore space sizes

Soil temperature.

Soil depth

Amount of moisture in the soil

Mulching / covering of the soil

Causes of poor aeration

Water logging.

Presence of clay

Compaction of the soil by use of heavy machines.

Deep soils.


Soil capillarity is the ability of water to rise through the small pores of the soil.

The rise of water is brought about by the forces of adhesion and cohesion.

Importance of soil capillarity

It helps to make water available to plants.

It enables the plant to have access to plant nutrients the dissolve in water.

Experiment to investigate soil capillarity


Get a tube that is open on both ends ( capillary tube)

Plug the bottom end of the tube with cork or cotton wool as shown below.

Fill the tube with dry soil samples

Place the plugged end of the tube in a water bath and leave it to stand for some time.

Note the speed of water movement in the soil. That represents the capillarity of the soil.


Note :

Water rises fastest in sand and highest in clay

This is because sand has bigger particles with larger pore spaces that allow easy movement of water.


Clay has the highest capillarity

Sandy has the lowest capillarity

Drainage and water retention

Experiment to determine porosity/ drainage/water retention capacity of the soil

Set a measuring cylinder and place a funnel at the mouth of the cylinder.

Plug the funnel with cotton wool or filter paper.

Measure a given quantity of dry soil and place it in a funnel.

Allow the water to drip through the funnel into the measuring cylinder until it stops dropping,


The amount of water collected in a measuring cylinder is the water that drained through the soil.

Amount of water retained

= Amount of water added to the soil – volume of water collected in the cylinder

Percentage of water retained

= Amount of water retained   X 100

    Amount of water added

Percentage of water drained

= Amount of water collected X 100

Amount of water added

Drainage and water retention are inversely proportional i.e. a soil with good drainage has poor water holding capacity/ retention.

Arrangement of the experiment


Soil typesVolume of water usedVolume of water drainedVolume of water retained
Loam100 40

Fill in the blank spaces in the table

Calculate the percentage of water drained and retained in each sample

b)      Chemical properties of the soil

The chemical properties of the soil deal mainly with the chemical composition of the soil. They include:

Soil pH

Cation Exchange Capacity

Anion Exchange Capacity

Mineral content.