Alkalinity
Alkalinity is usually an inherent characteristic of soils, although it can be increased by irrigation with alkaline or saline water . Soils made alkaline by calcium carbonate alone rarely have pH (water) values above 8.3 and are termed 'calcareous'. Alkaline soils with pH values higher than 8.3 usually have significant exchangeable sodium (sodic soils) and carbonates and bicarbonates of sodium. Extensive observations indicate that cereal root growth is very poor or non-existent in soils with pH (water) values exceeding 9.2. Alkaline soils are largely confined to areas with less than 400 mm annual rainfall.
Statistics on classes of alkaline soils - southern South Australia
| pH of topsoil * | pH of subsoil * | Area (ha) |
| Neutral to acidic | Non alkaline | 2,271,173 |
| Neutral to acidic | Alkaline | 3,478,113 |
| Neutral to acidic | Strongly alkaline | 1,403,013 |
| Alkaline | Alkaline | 2,413,230 |
| Alkaline | Strongly alkaline | 5,844,605 |
| Strongly alkaline (10-30cm) | Strongly alkaline | 71,855 |
| Strongly alkaline (0-10cm) | Strongly alkaline | 45,447 |
| Not applicable (includes urban, reservoirs, lakes, quarries, evaporation pans) | 220,702 | |
| Total | 15,748,137 | |
| *Topsoil is 0 – 10cm | Neutral to acid | pHwater < 8.0 |
| * Subsoil is 30 – 80cm | Alkaline | pHwater 8.0 – 9.2 |
| Strongly alkaline | pHwater > 9.2 |