Soils of the - Agriculture and Agri-Food Canada

GIBBON SOILS (GN)
Location and Extent : Gibson soils occupy scattered areas on the Fraser River floodplain as well as smal l
areas in Sumas Valley. The largest areas are in Glen and Matsqui Valleys . Pure map units total about 960 ha whil e
soil complexes dominated by Gibson soils occupy a further 230 ha . The complexes are mainly with Banford an d
Lumbum soils .
Topography and Elevation : Slightly depressional, level, or gently undulating with slopes less than 2
percent is the usual topography of Gibson soils . They lie between 3 and 10 m above sea level .
Parent Material and Texture : Gibson soils have developed from partly decomposed organic deposits ,
between 40 and 120 cm thick, that overlie moderately-fine to medium-textured Fraser River floodplain an d
some lacustrine deposits . The organic material consists mainly of sedge, reed and other deciduous plan t
remains . Surfaces are usually partly (mesic) to well (humic) decomposed while the underlying organic materia l
is mainly partly decomposed, sometimes containing a few, thin undecomposed layers . The subsoil mineral soi l
is silt loam or silty clay loam .
Soil Moisture Characteristics : Gibson soils are very poorly to poorly drained . They are moderatel y
pervious and have very high water holding capacity and slow surface runoff . The watertable is near, an d
sometimes at the surface for most of the winter and early parts of the growing season, then retreats somewha t
during the drier summer months .
General Soil Description : Gibson soils usually have a very dark brown to black, friable, granular, well -
decomposed, organic, cultivated surface layer about 20 cm thick . This is underlain by between 20 and 100 c m
of partly decomposed, dark reddish brown to yellowish-brown, weakly stratified to matted, organic materia l
(individual plant remains are partially recognizable) . The mineral subsoil, occurring at depths between 40 an d
120 cm is massive, gray to olive-gray and silty. Soil reactions vary from strongly to extremely acid in and near th e
surface to strongly acid in the lower subsoil . Soil classification is Terric Mesisol .
Commonly Associated Soils : Banford , Hallert, Lumbum and Glen Valley soils are usually closel y
associated with Gibson soils . Banford soils are similar to Gibson soils except that the organic material is wel l
decomposed rather than only partly decomposed . Lumbum soils are also similar except that the partl y
decomposed organic material is deeper than 120 cm . Glen Valley soils differ by consisting of deep (more tha n
120 cm), raw or only weakly decomposed organic deposits . Hallert soils differ by being composed of
alternating organic and silty strata .
Vegetation : Some areas of Gibson soils are cleared and cultivated for agricultural uses . Uncleared area s
mainly support a variety of water tolerant, deciduous plants including willow, bog birch, blackberry, skun k
cabbage, hardhack, sedges and reeds as well as some western red cedar and western hemlock . Rooting i n
undrained areas is restricted to about 50 cm depth ; it is usually deeper in areas with adequate watertabl e
control .
General Land Use Comments : (1) Poor drainage is the main agricultural limitation of Gibson soils . Wit h
adequate water control and fertilization, hay, pasture, vegetables and other crops can be productively grown .
Overdraining will likely cause accelerated decomposition and subsidence . Watertable control which permit s
progressive lowering of the watertable during the growing season is generally most satisfactory . (2) Very low
bearing strength and high watertables generally preclude most urban-type construction unless the organi c
material is removed or pre-loaded . Excavations will generally contain water and septic tank operation i s
severely impaired by high watertables .
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