When waterlogged soils dry out later in the season, the crop's root system is still confined to the surface soil because of the earlier damage. These shallow roots cannot take up nutrients from drying soil near the surface, nor reach nutrients and water deeper in the profile. Waterlogging also kills crops rapidly if the soil contains any salt. Waterlogging is most damaging to crops in soils with a shallow, sandy topsoil over a clayey subsoil. The clayey subsoil is usually within 50 cm of the soil surface.
Water lies on top of the subsoil and kills the deeper roots.
Most damage occurs when the water is within 30 cm of the soil surface and when the crop is growing rapidly. About two-thirds of the soils in the Upper Great Southern have perched water within 30 cm of the soil surface in years with average rainfall. In most cases, drainage is the best way to overcome waterlogging and inundation in most areas. Drains in cropped areas pay for themselves within a few years. Where drains can only partially overcome the problem, changes to crop species, varieties and management may be necessary.