Salt-affected soils in England and Wales

. Soils mainly in alluvial marine sediments around the coast of England and Wales, occupy about 6% of the agricultural land. The extent of salt‐affected soils within these parent materials is unknown, but is believed to be significant from the evidence of existing soil surveys. The principal salt is sodium chloride, and the degree of salinity depends on depth to saline groundwater, the intensity of leaching, and the frequency and severity of past marine flooding. Evidence suggests that while the effects of the flooding are obvious and immediate, long‐term salinity owes more to groundwater behaviour and chemistry. The amount of sodium in these soils, particularly the heavier‐textured ones, makes them structurally unstable, especially when wet. The instability in turn makes them difficult to drain. Ameliorative treatments are possible, but are expensive and slow to take effect. In their natural or semi‐natural state these soils form large areas of wetland or unimproved grassland, often of interest to conservationists. In spite of this, and their generally unfavourable properties for cultivation, extensive areas have become arable in recent years. Structural stability, salt content, and exchangeable sodium percentage are intimately linked and can be measured during soil survey, which then aids rational decisions about land use. Such a survey of the North Kent Marshes is presented as a case study.