Alkaline soils are soils (mostly clay soils) with a high pH (> 9) and a poor soil structure and a low infiltration capacity. They are not saline, i.e. the total amount of soluble soils, especially sodium chlorides, is not excessive (ECe < 4 to 8 dS/m). Often they have a hard calcareous layer at 0.5 to 1 m depth.

The causes of soil alkalinity are natural or they can be man-made. The
natural development is due to the presence soil minerals producing sodium
carbonate upon whethering. The man-made development is due to the application of irrigation water (surface or ground water) containing a relatively high proportion of sodium bicarbonates.


Source: Oosterbaan, R.J. 2003. Soil Salinity. Water-Logging (Waterlogging), Soil Salinity, Plant Growth, Subsurface Drainage, Ground-Water (Groundwater) Flow, Surface Runoff, Irrigation, Land Reclamation and Improvement. Available at