Soils with paleosol features occur at the surface on the Chalky Boulder Clay in the Chelmsford area, &sex Their particle size distribution, micromorphology and a d , silt and clay mineralogy indicate periods of weathering, clay illuviation and hyQromorphism before deposition of loem in the Late Devenaian. These periods are provisionally related to the Ipswichian and/or Hoxnian Interglacials.
Abstract. 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.
SummarySoil instability, as measured by the dispersion ratios of the reclaimed salt-marsh soils of ca. 70 km2 of north Kent, was assessed on samples taken from 0–15, 35–50 and 70–85 cm depths from sites at the intersects of a 250 m square grid or along transects. The dispersion ratios were related to other soil properties including exchangeable sodium, potassium and magnesium percentages, organic carbon content, calcium carbonate content and electrical conductivity. The dispersion ratio correlates most closely with exchangeable sodium percentage and organic carbon content; weaker correlations exist with exchangeable potassium and calcium carbonate contents. Dispersion ratios rise sharply, i.e. reflect a marked increase in soil instability, when organic carbon content is less than 2·5% and calcium carbonate content is less than 2%. Magnesium has little effect on the dispersion ratio. The soil solution salt concentration (as expressed by electrical conductivity) is too low over much of the area to promote flocculation, and hence stability, of the soil clays.
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