Below the shoulder of -the hill the slope "becomes straight. The soil profile
has a thin cover of sandy material which is "being transported downwards. This
texture of the topsoil is locally Sandy Loam when deep, otherwise Loam to Clay
loam,under the influence of the mixing with underlying material "by ploughing.
The ploughfurrows have "been eroded less deeply than on the shoulder, small
obstructions cause some deposition in the furrows. They start to have a narrow
flat "bottom of some cm width.
The straight slope can "be considered a transport slope ( Carson et al.1972)
A brownish cover of Sandy Loam moves relatively fast over the subsoil of red
Clay loam.
In the lower slope the inclination decreases again. Deposition in the
ploughfurrows is dominant in a zonecf 5-15 meter, depending on the concavity
of the short footslope. Coarse material of sand and gravel has accumulated
here. The texture is Loamy sand or Sandy loam, locally slightly gravelly. Finer
material is carried by the runoff into the drainageway, and is deposited down
streams in the valleybottoms.
On the steeper parts of the slope there are a few gullies which
occur only along the field boundaries which follow the slope. As it is the
custom of the farmers to plough the field up to six times a year, to keep the
soil open and destroy the weeds, small incisions which develop in the plough
rills are obliterated regularly, before they can develop into a real gully.
Ploughing does not take place however in the narrow zone between two
fields. Here gullies may develop. When the tillage is done obliquely to the slope,
the field boundary collects the water from the ploughfurrows. Often
shallow to deep gullies are found at the field boundaries. Sometimes these
gullies at the field boundaries develop branches along parcel boundaries.
In the drainageway the runoff along the fo'ot of the slope is locally
undercutting the slope colluvium. Tillage is done across the drainageway up
the other slope. In this way some of the gravel and coarse sand from the
footslope colluvium is distributed over the landsurface.
The field description largely explains the greytones which are observed
on the AP. The coarser colluvium has a light greytone. The exposed red clay
subsoil has a very dark greytone. The pattern of the dark greytone on the
slope does not exactly follow the contour but is slightly inclined.
Types of rainwater erosion features(Fairbridge 1968 ,Richter 1 965 ,Comm.1 966 )
The rainwater erosion features of the soil erosion toposequence on the
Coto Alto are presented in figure 3.There is some more detail than the usual
distinction between sheet-,rill- and gully erosion.Rills which develop into
linear erosion and rills which develop laterally but do not incise very much
(braids) are distinguished (Young 1972, Carson § Kirkby 1972). In the first
case soil conservation usually has to pay special attention to the preven
tion of the concentration of the runoff.
Brief general description of the rainwater erosion features
Rainsplash .lt is dominant in case of low runoff and nearly level land.Soil