Available and Non-available Water
You have seen above that water is present even in the apparently dry soils but it is of not much use as far as the plants are concerned. They cannot utilise the water that remains tightly adhered on to the surface of soil colloids. Therefore, water remaining in the soil at the time of permanent wilting is non-available to plants. For plant growth, only available water is important and not the total amount of soil moisture. The amount of available water varies in different soils. For example, a sandy soil may have a field capacity of 12 per cent, of which only one per cent is non-available. A clay loam has a field capacity of 35 per cent, and it may have about 10 per cent non-available water.