Soils of the - Agriculture and Agri-Food Canada

PREST SOILS (PR)
Location and Extent : Prest soils occur in numerous, small, depressional locations on the floodplain of th e
Fraser River. There are about 600 ha of pure map units and 340 ha of soil complexes dominated by Prest soils .
Most complexes are with Page soils and occasionally, with Fairfield, Dewdney and Seabird soils .
Topography and Elevation : Prest soils are nearly level to gently undulating with slopes less than 5 percent .
They are generally depressional in relation to adjacent soils and often occur in meander channels and othe r
similar landscape positions on the floodplain . Elevations are generally less than 10 m above sea level .
Parent Material and Texture : Prest soils have developed from medium and moderately fine textured Frase r
River floodplain deposits that are usually at least 50 cm thick, and overlie medium or fine sand . Surface texture s
range from silt loam to silty clay loam while the subsurface usually is silty clay loam or silty clay . The subsoil i s
mostly silt loam in the upper part, sometimes containing sandy lenses, and changes to sand or loamy sand a t
depth . In uncultivated areas, a shallow organic layer, less than 15 cm thick, is sometimes present on the minera l
soil surface .
Soil Moisture Characteristics : Prest soils are very poorly drained . They are moderately to slowly perviou s
and have high water holding capacity and slow surface runoff . The watertable is either near or above the soi l
surface for most of the winter and during the freshet period of the Fraser River, then recedes slightly during th e
latter part of the summer. Surface ponding is usual during heavy rains .
General Soil Description : Under natural conditions Prest soils have a thin (usually less than 10 cm thick )
layer of organic material derived mainly from reeds, sedge and grass on the soil surface . This is underlain b y
about 20 cm of grayish-brown or brownish-gray, firm, weakly structured silty to clayey material containin g
common to many, dark red to reddish-brown mottles . This grades to about 30 cm of gray, massive, very firm, silt y
or clayey material containing common, yellowish-brown mottles . Under this is gray or olive-gray, massive, silt y
material containing a few, variably coloured mottles and, sometimes, bands of dark gray sand or loamy sand .
Soil reaction varies from very strongly or strongly acid in the upper soil to slightly acid in the subsoil (1 :1 H 2 O) .
Soil classification is mostly Rego Gleysol with occasional variation to Rego Gleysol : peaty phase where th e
organic surface layer is more than 15 cm thick . In a few areas, a shallow variant of Prest soils has been mapped .
The shallow variant is similar to the usual Prest soils except that the underlying sand occurs within 20 to 50 cm o f
the soil surface rather than below at least 50 cm as is usually the case .
Commonly Associated Soils : Page, Hjorth and Fairfield soils are often closely associated with Prest soils ,
either as components of soil complexes or occupying adjacent map polygons . Page soils are similar to Pres t
soils except that they are poorly rather than very poorly drained and occur in slightly higher landscap e
locations . Hjorth soils are similar to Page soils except that they have black surfaces . Fairfield soils differ fro m
Prest soils by being imperfectly drained and lie substantially higher in the landscape .
Vegetation : The natural vegetation of Prest soils is mostly reeds, sedges, grasses and others adapted to ver y
poorly drained conditions, with willow and black cottonwood also sometimes present . Rooting depth is mainl y
restricted to 30 cm by the high watertables .
General Land Use Comments : (1) Poor drainage, high watertables and periodic flooding severely limi t
Prest soils for agriculture . Artificial drainage is required for essentially al j crops (except reed canary grass whic h
is very tolerant of excess moisture) . However, due to the depressional nature of Prest soils, drainage outlets ar e
usually difficult to locate and install . (2) Urban uses are unsuited for Prest soils . High watertables preclud e
basements and other excavations and periodic flooding is usual . Septic tank effluent disposal is severel y
impaired by the very high watertables . In some locations Prest soils can be excavated and used as wate r
storage areas, perhaps for irrigation of adjacent soils .
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