In much of South East Australia, horticultural production is hampered by heavy clay soils and high water table. Which causes rootzone-waterlogging and soil salinisation. Much can be achieved by improved irrigation management and adequate surface drainage.

However there is still the necessity of some Subsurface drainage to manage water tables and prevent salinity.

Many people think water logging is the water they see lying on the ground surface although real water logging is often the unseen water or ground water below the surface.

It is therefore good to know what happens in soil.

We know that soils consist out of small particles of uneven size and shape. Leaving larger and smaller voids between the particles.

In these voids water is held in three ways:

• Water held by surface tension or adhesion called absorbed water.
• Water held in the very small spaces between the particles ( capillary water)
• Water in the larger voids, which is free draining and moves down by gravity.

When there is a point , that there is only absorbed water and capillary water, we talk about Field Capacity.

This means there is no free water and the larger pores are filled with oxygen. The soil will feel moist and the conditions are ideal for plant growth. If the larger pores are also filled with water and the soil can't take up any more water we talk about Saturation.

Normally this will happen for a short time until the water in the larger pores has drained by gravity to a fluctuating water table.

If for some reason more water is added to the soil than can drain away the water table will rise.

Above the water table we will have a capillary fringe after water has freely drained away. Salt stored in the soil will mix with the water and rise with the water table and pull into the capillary fringe.

If the process of adding water continues the roots will end up in this capillary fringe or worse in the water table.