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Cranfield University 2017. The Soils Guide. Available: www.landis.org.uk. Cranfield University, UK. Last accessed 21/10/2017

0711w CROFT PASCOE

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Soil and site characteristics

Slowly permeable seasonally waterlogged silty and fine loamy soils and some similar soils with only slight seasonal waterlogging. Shallow well drained loamy soils on rocky cliffs and valley sides. Some fine silty soils affected by groundwater.

Geology

Aeolian silty drift over ultrabasic and basic igneous rocks

Cropping and Land Use

Permanent and short term grassland with dairying and stock rearing; cliff and wet lowland heath habitats; recreation.

Component soil series

Subgroup Series name Percentage WRB 2006 link
7.11 CROFT PASCOE 20% Eutric Albic Luvic Stagnosols
7.11 TENERIFFE 20% Siltic Dystric Luvic Stagnosols
5.72 ARROWAN 20% Ruptic Stagnic Luvisols
8.31 TRABOE 20% Siltic Dystric Gleysols
7.13 ZOAR 10% Dystric Stagnosols
3.13 KYNANCE 10% Brunic Dystric Leptosols

Covers 56 km2 in England and Wales

Soilscapes Classification

17
Slowly permeable seasonally wet acid loamy and clayey soils

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Detailed Description

This association comprises soils on serpentine and gabbro rocks and in silty drift on the Lizard Peninsula of Cornwall. The main soils are Croft Pascoe series, typical stagnogley soils, Zoar series, cambic stagnogley soils, Arrowan series, stagnogleyic argillic brown earths, Kynance series, brown rankers, Traboe series, typical cambic gley soils, and Teneriffe series, typical stagnogley soils. Brief descriptions of these are given below. All, except Zoar series, are associated with the serpentine outcrops. There are also several minor component soils over serpentine, others on the gabbro outcrop and two in Pliocene gravels.

Soil distribution is closely linked to the thickness of silty drift. Where the drift is thin (40 to 80 cm) there are coarse silty over fine silty Croft Pascoe soils with slowly permeable serpentinitic subsoils. These soils are waterlogged for lengthy periods, but associated Arrowan soils have a drier regime. On level ground, where the silty drift is very thin or mixed with the underlying serpentinitic material, fine silty Teneriffe soils are found. More rarely, deep, clayey Predannack soils occupy similar sites. In depressions and by streams silty drift is absent or thoroughly mixed with underlying soil materials. Traboe series and Chiverton soils are affected by groundwater, the perenially-waterlogged Chiverton soils having humose or peaty topsoils.

Steep, rocky cliff and valley slopes carry well drained shallow fine loamy soils of the Kynance and Black Head series together with less permeable, slightly mottled Coverack soils. Shallow impermeable loamy Holestraw and clayey Predannack soils which are waterlogged during the winter are found close to the cliff edge on the gently sloping rocky serpentine platform. Limited areas of thick silty drift on flat land carry well drained, permeable, stoneless, coarse silty Gwavas soils. The flatter parts of the gabbro outcrop with its cover of Pliocene drift are included within this association, but the more dissected gabbro, schist and gneiss country of the Lizard Peninsula is not. Fine loamy soils of the Zoar series are common on gentle slopes, whilst similar Trevenwith soils and better drained Trelan soils are developed where gabbro is interlayered with serpentine. Fine loamy soils of the Polcoverack series and wetter Chywoone soils occupy depressions and stream-line sites affected by groundwater. The Crousa gravels, marine clays and gravels overlying the gabbro in places give Berkhamsted and Oak soils, with slowly permeable, red mottled, clayey subsoils below fine loamy and pebbly upper horizons.


Soil Water Regime

Croft Pascoe and Teneriffe soils have slowly permeable subsoils and are seasonally waterlogged (Wetness Class IV). Arrowan soils are less wet (Wetness Class II or III) and permeable Kynance and Black Head soils are well drained (Wetness Class I) but Zoar and Traboe soils are seasonally waterlogged by groundwater (Wetness Class IV). The responsiveness of these soils to artificial drainage is varied. Surplus winter rain generally drains laterally at shallow depth on level ground, and saturated Croft Pascoe, Teneriffe and Zoar soils will only slowly accept more water. An algal mat covering the surface of these soils under heathland is evidence of extensive surface wetness in winter. The main soils have ample reserves of moisture and are non-droughty for most crops in most years.

Cropping and Land Use

Much of the land is under heath or permanent grassland and only the soils on gabbro are cultivated. Most of the soils have moderate or large retained water capacities, which combined with a relatively high rainfall, give only a short time for risk-free cultivation. Boulders and rock outcrops on slopes discourage agricultural improvement and soil acidity, wetness and poor nutrient availability have limited the use of many of the soils. Potential yields of grass are large because of the long growing season and moist climate but Croft Pascoe, Teneriffe and Zoar soils poach readily and are wet for long periods in spring and autumn. Although grass is the main crop some Gwavas soils are used for horticulture. Cereals are rarely grown and mainly supply farm needs. Severe exposure to strong, salt laden winds limits potential productivity over much of the plateau.

Although the serpentine rock and its derived soils contain large amounts of nickel, chromium and vanadium there is little evidence of trace element toxicity in crops or livestock, probably because most topsoils are formed in overlying silty drift. Such topsoils are naturally acid, but those of soils derived directly from serpentine have a high pH. Serpentine soils are base-rich and their exchange complex is dominated by magnesium with little or no calcium, except where the soils have been limed. Gabbro-derived soils are also normally base rich but calcium dominates the exchange complex. Unimproved silty drift soils have little available phosphorus, but on long-farmed land phosphorus and potassium reserves are usually adequate.

The semi-natural vegetation of the peninsula is nationally important and there are twelve sites of Special Scientific Interest and four National Nature reserves covering large portions of the heathland and cliffland. Several rare plant species are confined to the Lizard Peninsula, particularly clover species on cliffland, whilst the Cornish Heath (Erica vagans) is abundant on the base rich soils of the serpentine and gabbro heaths. The rich flora of the Lizard springs from its variety of habitats, varied soils and geology, and warm oceanic climate. The comparatively large areas of natural and semi-natural vegetation are in themselves an important factor in the survival of species now rare or absent elsewhere in Britain following widespread destruction of their habitats.

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