486
MAPSYMBOL
DESCRIPTION OF PHYSIOGRAPHY
SOIL CLASSIFICATION
A
Deep poorly drained heavy soils on level
plain with recent alluvial deposits.
flat flood
1.
2.
3.
Utric Fluvisols
Utric Gley sols
Pellic vertisols
C
Deep excessively drained sands, sands to sandy lo
ams over sandy clayson level to gently undulating
coastal plain.
1.
2.
3.
4.
Albic Arenosols
Cambie 'Arenosols
Othic Luvisols
Eutrigle sols
soil properties considered in describing
the profiles. In this survey the level of
mapping the area was limited only to main
land type.
2.5 Map compillation and Field work
During field work, location of pits and
observation on mapping Unit, boundaries
were marked on 1:100,000 topographical map.
Field surveying traverses were made along
the farm boundary and across the farm area.
Nearly, all profile pits were dug to depths
of 150cm in order to check the ground water
table and the soil parent material. Each
horizon in a profile was examined for the
study of soil development. The major pa
rameters commonly looked for in the profile
are depth of individual horizon, colour
(dry and moist), texture, structure, consi
stency porosity, parent material, presence/
absence of roots and fauna, presence of
carbonates, concretions and cracks. pH,
Conductivity, texture were measured separa
tely in the laboratory together with other
chemical analyses. Colour notations were
referred to the Munsel Coloiir Chart (Soil
Test inc. USA, 1971 Edition). Profile
pits were described using (Guidelines for Soil
Profile Pescription - FA0) and soil samples
were sent to the Laboratory for some physi
cal and chemical analyses. The final soil
map was produced at a scale of 1:10,000
as proposed by the client to facilitate
farm planning and land use purposes.
Due to field obstacles earlier observed
during the reconnaisance field trip, soil
observations at the far southern parts of
the project area on the alluvial plain,
were not made. Soils in these parts were
extrapolated from aerial photo-interpre
tation and the physiographical map. Nor
mally the alluvial plain area, consists
of poorly drained heavy clay soils subje
cted to frequent flooding by river over
flow’s of the Ruvu River, whereas the Coa
stal Plain soils range from deep excessi
vely drained sands to sandy clay loams.
3. SOIL CLASSIFICATION AND MAPPING
3.1 Soil Laboratory data and results
1. pH and Ec were determined by using
the 1:5 soil to water ratio method.
2. Particle size analysis was carried
out using the hydrometer.
3» Available phosphorus was determined
by using the Dickman and Bray 1 method.
4. Exchangeable cations Na, K, Ca, Mg,
were determined by leaching the soils in
Ammonium Acetate extracting solution IN.
5. Organic carbon % was determined by
using the Walkley and Black method.
6. Available Nitrogen % was determined
using the Alkaline permanganate method.
7. C.E.C. was not determined but was
approvimated by adding the total of bases.
3.2. Results
1. From soil analytical data the soils
in the area are non-saline. However the
subsoils have an increased amount of solu
ble salts. In general the pH of the soils
indicate that the soils are acidic. It
will be necessary to raise the pH to about
7.0 as the pH common to most plants is 6-8.
SCALE 1:500,000.
MI
QUATERNARY.
Coastal plain deposits reworked clays
silts, sands and rare grovels
QUANTERNARY
Alluvial deposits (clays, silts, sands and
rare gravels.)
NEOGENS (MIOCENE PLIOCENE)
Undifterentated sedimentary deposits interbecfded .sandy
c * :y , and clayey sands ¿ravel scattered thoughoul in a
clay matrix
Cretaceous
thin
san d stones
sandy limestones and shales
Figure 3 Geology* of the farm area