Land resources of central Nigeria Agricultural development ...

physical weathering with the production of laterite in many areas. Alkaline
or saline soils were not recorded in the Kaduna Plains. The topography,
being essentially gently sloping, generates rates of surface-water run-off
which concentrate sand and coarse material near the surface, while the
significance of the biotic factor centres around the role of man, vegetation
and soil fauna: all have modified the fertility and possibly texture of
the surface soil.
Interaction between these factors in the Kaduna Plains have resulted in
soils that are, in general, yellowish to reddish, deep, well drained and fine
or medium textured. They tend to have coarse textured surface horizons and
iron concretions, mottles and quartz fragments in the subsoil and to have
poorly to moderately developed structure. They are predominantly strongly
weathered, mainly poor in nutrients and have a thin organic surface horizon
that is easily eroded. Surface capping or crusting in silty or fine sandy
topsoils is widespread. With the exception of this phenomenon and from
the point of view of cropping, therefore, they are physically adequate but
chemically or nutritionally only poor to moderate.
Soil patterns
The land systems shown on Separate Map 1 are soil associations in the sense
that they are patterns of geographically associated soils. Several soil
series are widespread in the Kaduna Plains. However, it is rare for any
single series to be restricted to one land system and the usual case is
for seven or eight common series to recur together, but in differing
proportions, over several land systems.
Toposequences, in which the same arrangement of soils occur from crest
through valley sides to lower slopes, can be found but neither consistently
within one land system nor between land systems. This is believed to
result partly from the intricate pattern of parent rocks within Basement
Complex areas and partly from the geomorphological history which has resulted
in such areas having a relatively level surface relief. Surface reworking
has tended to infill valleys and further emphasises the uniformity of
landforms.
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