ABSTRACT
The soil profile characteristics in the various major climatic regions were the initial stimulus to the study of penology and to the development of systems of soil classification. Thus liming reverses the natural trend towards soil acidity whereas conifer plantations may increase the rate of acidification. Irrigation of soils in may if carefully managed reduces the tendency to alkalinity, but history shows that this has often not been the case. The management of alkalinity in sodic soils is discussed. Exchangeable H+ is held on permanent charge sites of clay minerals. Similarly, some aluminium bound to humus is also released and neutralized. Together these are known as non-exchangeable acidity. As soils become more alkaline, the concentration of OH increases with associated increases in bicarbonate which becomes the dominant anion. Carbonate also increases but its concentration is much lower than bicarbonate. There are no significant changes in the exchangeable cations present because the soil is already base saturated at pH.
