Soil Associations

1024c ADVENTURERS' 3

Soil and site characteristics

Deep peat soils with associated extremely calcareous mineral soils. Some deep stoneless silty and clayey soils with a humose surface horizon in places. High groundwater levels.

Geology

Fen peat, tufa and river alluvium

Cropping and Land Use

Permanent grassland and rough grazing; some arable; species-rich wetland and grassland habitats.

Component soil series

Subgroup	Series name	Percentage	WRB 2006 link
10.24	ADVENTURERS'	45%	Drainic Rheic Sapric Histosols
3.72	COLTHROP	20%	Limnic Calcaric Gleyic Mollic Fluvisols
8.13	MIDELNEY	10%	Clayic Fluvic Eutric Gleysols
8.12	WITTERING	10%	Siltic Fluvic Calcaric Gleysols

Covers 42 km² in England and Wales

Soilscapes Classification

27	Fen peat soils

1024c ADVENTURERS' 3

Detailed Description

This association occurs in the floodplains of the Test, Itchen and Loddon in Hampshire, and in the Lydden Valley in east Kent. The streams are fed by groundwater from the Chalk so they carry little suspended sediment. Earthy peat soils predominate together with soils in calcareous tufa or marl, a pale coloured material precipated by freshwater algae and containing many mollusc shells. Other less calcareous silty and clayey soils in river alluvium, often with humose or peaty topsoils, also occur. These usually over overlie fen peat at some depth.

Adventurers' series, earthy eutro-amorphous peat soils, is developed in black, often calcareous, humified peat with a neutral or alkaline pH. Colthrop series, gleyic rendzina-like alluvial soils, has characteristic marly subsoil horizons developed in calcareous tufa with ochreous mottles indicative of periodic waterlogging. Associated soils include: Midelney series, pelo-alluvial gley soils, where the peat is overlain by non-calcareous clayey alluvium; Wittering series, calcareous alluvial gley soils, in thick silty alluvium; Willingham and Brimpton soils in calcareous tufa over peat; and Hatford soils in fine loamy calcareous alluvium over peat.

The frequency and distribution of the constituent soils varies markedly between the valleys. The soil pattern is influenced by water meadows constructed between the 17th and 19th centuries. Today the meadows are disused and the channels and ditches are partly infilled. Old ditches contain humose or thin peaty soils in contrast to the more freely draining mineral soils of the ridges.

In the Test valley, peaty Adventurers' soils cover two-thirds of the land, but are more common locally. Mendham soils also occur in places. The peat is generally well humified and contains abundant remains of reeds and sedges and often includes woody fragments. Thin seams of pale-coloured shelly marl occur within the peat, which either rests directly on gravels at depth or on a thin intervening layer of silty alluvium. Sinuous interweaving strips of pale chalky or nodular shelly material (tufa) carrying Colthrop soils are common especially between Stockbridge and Romsey. In places, on cultivated land, peat shrinkage has left these strips as upstanding ridges. Willingham and Brimpton soils occur where peat is covered by thin tufa deposits, the latter having peaty or humose topsoils. Shallow silty or peaty soils occur locally where the underlying gravels occur near the surface, especially towards the margins of the floodplain.

In the Itchen valley north of Winchester, Adventurers' series is dominant but Gade and Hatford soils are found where there are gravels at shallow depth, Brimpton soils where marl overlies peat, and Colthrop soils where the marl is thicker. In the lower reaches, where the valley crosses the Tertiary outcrop, much of the peat is covered by clayey and silty alluvium giving Midelney, Fladbury, Wittering and Bressington soils.

Near Basingstoke, the Loddon valley drains the chalk northwards across Tertiary strata. Here, strips of narrow clayey alluvial Fladbury and Midelney soils link broader peaty basins with Adventurers' and Colthrop soils along the valley. Colthrop soils occur as in the Test valley on shelly tufa. In the Lydden Valley between Deal and Sandwich in east Kent there are Adventurers' soils with a thickness of up to 3.9 metres of eutrophic fen peat. The peat is divided into two beds, separated by a seam of clay, and consists mainly of common reed with saw sedge (Cladium mariscus) at lower levels.

Soil Water Regime

The steady supply of groundwater from the chalk keeps the water level high throughout the year in the soils of the Test and Itchen floodplain. Winter rain is absorbed by the chalk but discharge to the rivers is delayed by up to three months. The spring water is alkaline with a typical pH of 7.2 to 7.7, although values of 8 or more occur locally. Adventurers' and Mendham soils are severely waterlogged throughout the year (Wetness Class V and VI), but Colthrop soils are better drained. The Lydden Valley in Kent suffers from mining subsidence so pumping is needed to control soil water levels and improve drainage.

Reclamation for arable cultivation is rare since the groundwater is difficult to control and there is conflict with sporting and wildlife conservation interests. Between Romsey and Stockbridge, Hampshire, a pump drainage scheme combined with underdrainage is proving successful, but elsewhere water levels are kept high for the fisheries.

Cropping and Land Use

In the Test Valley some cereals are grown but the high water-tables restrict most land to permanent grass. Manganese and copper deficiency are common in crops on arable land. The soils poach easily and in wetter areas on peat, grazing is restricted to the summer months.

The Itchen and Test floodplains provide a mosaic of habitats with the most extensive species-rich neutral grassland in England (Tubbs 1978). Fens, fen woodland, herb-rich grassland and unimproved but species-poor grassland also occurs. Though most of the grassland is neutral, some soils, in the Test and Loddon valleys in particular, are markedly alkaline.

Fen is associated with the wettest and more or less peaty soils. Here tall grass and herb communities typify these areas with reed (Phragmites australis), reed-grass (Phalaris arundinacea), bur-reed (Sparganium erectum) and great reedmace (Typha latifolia). Fen woodland is dominated by alder and/or willow, or on dry ground by oak with ash, hawthorn and blackthorn.

The swards with most species are found on land which has never been water-meadow. Flooding favoured grasses at the expense of herbs, and in general, the longer a water-meadow has been abandoned, the more diverse is its flora. Herb-rich grassland consists mainly of red fescue (Festuca rubra), rough-stalked meadow-grass (Poa trivialis), Yorkshire fog (Holcus lanatus) and reed-grass (Glyceria maxima). Sedges include hammer sedge (Carex hirta) and panicled sedge (C. paniculata). Characteristic herbs are water avens (Geum rivale), meadow-sweet (Filipendula ulmaria), marsh thistle (Cirsium palustre), bugle (Ajuga reptans), marsh marigold (Caltha palustris) and yellow flag (Iris pseudacorus). Meadows with more calcareous soils often have cotton-grass (Eriophorum angustifolium), common butterwort (Pinguicula vulgaris), bogbean (Menyanthes trifoliata) and marsh valerian (Valerians dioica) with a number of orchids including the marsh orchid (Dactylorhiza incarnata).

Unimproved species-poor grassland includes former water-meadows affected by heavy grazing and land with acid soils. Dominant grass species are red fescue, rough-stalked meadow-grass, Yorkshire fog, oat-grass (Arrhenatherum elatius) and sometimes rye-grass (Lolium perenne). Herbs include thistles (Cirsium spp), buttercups (Ranunculus spp) and ragwort (Senecio jacobaea), all of which tolerate grazing.

Fen vegetation including damp woodland, open fen and grassland communities occur on Adventurers' soils in the Lydden Valley, particularly in the area of Ham Fen and Hacklinge Marshes, although the extent of open fen is now much reduced by farming. Woodland is dominated by alder, ash, and willow, whereas fen includes the saw sedge (Cladium mariscus), adder's tongue (Ophioglossum vulgatum), ragged robin (Lychnis flos¬cucuh) and bog pimpernel (Anagallis tenella).

1024c ADVENTURERS' 3

Distribution Map

Note that the yellow shading represents a buffer to highlight the location of very small areas of the association.

Keys to component soil series

South Eastern Region

Typical Landscapes

South Eastern Region

South Eastern Region

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Citation: To use information from this web resource in your work, please cite this as follows:
Cranfield University 2024. The Soils Guide. Available: www.landis.org.uk. Cranfield University, UK. Last accessed 24/04/2024