Table 2. Characteristics of the Agro-Ecological zones
Zone 16
Zone 8
Zone 14
Zone 4
Zone 3
climate (KC3PPEN classi
fication)
BSwh
(dry hot steppe climate)
Cwa (some Cwb)
(warm temperate with hot
(warm) summers)
Cwa and Cwb
(warm temperate with
hot / warm summers)
Cwb
(warm temperate with
warm summers)
Cwb
(warm temperate with
warm summers)
Dominant altitude (m.a.s.l.)
Less than 1000
1100 - 1700
1600 - 2000
800 - 1600
1600 - 2800
Mean annual rainfall (mm)
550 - 600
600 - 900
900 - 950
1100 - 1300
1200 - 1600
physiographic charac
teristics
Flat to slightly undu
lating pediplains with
some alluvium and sub
parallel drainage pat
tern; rocky hills
Highland pediplains
with inselbergs and
some periodically swampy
depressions; rocky
mountains and hills
Undulating highland pla
teaus with numerous pe
rennially swampy drain
age lines (bottomlands)
and depressions
Rolling to hilly with
deep valleys in the
south; undulating to
rolling upland plateau
in the north
Hills, mountains and
undulating highland
plateaus
Dominant vegetation /
land use
Open Acacia-thornbush /
grazing; annual crops
on alluvium
Miombo, Commiphora,
Combretum / annual crops
(maize, tobacco),
grazing
Wooded grassland with
miombo, Parinari and
Uapaka species / graz
ing, some cultivation
(maize), pine affores
tation
Miombo woodland, grass
land / grazing, culti
vation (tea, maize),
wattle plantations
Grassland, forest rem
nants / grazing, culti
vation (maize, wheat,
potatoes, tea, pyre-
thrum), wattle planta-
tations
Dominant soils
Well-drained dark to
yellow-brown loams,
dark cracking clays,
red loams; mos soils
saline
Well-drained moderately
leached red clays and
loams, yellow sands and
loams, some dark crack
ing clay
Well-drained, highly
leached yellow clay
(partly with dark top
soil), poorly drained
clays in bottomlands
and depressions
Well-drained moderately
and highly leached red
clay (often with humic
topsoil)
Well-drained highly
leached red clay
(often with humic top
soil), locally soils
derived from volcanic
ash
hills: rock and very
shallow soils
hills: rock and very
shallow soils
Hills: rock and very
shallow soils
Hills and ridges:
rock and very shallow
soils
Hills and ridges:
rock and very shallow
soils (partly with co
vering of volcanic ash)
many inselbergs and some scattered periodically
flooded depressions. Another great part of the zone
consists of rocky hills and mountains. A large por
tion of the pediplains is cultivated, mainly with
maize. The hills are covered by miombo woodland.
The main soils are moderately leached red clay
and loam, yellow to yellow brown sand and loam and
some scattered patches of dark cracking clay. The
footslopes around the inselbergs are often strongly
affected by gully erosion. Some other areas are se
verely degraded by sheet erosion.
In this zone the information obtained from the
satellite imagery and those from the aerial photo
graphs completed each other ideally. The spectral
reflectance characteristics of the soil surface
were again the dominant mapping support. Therefore
most boundaries were mapped from the satellite ima
gery. As in Zone 16, the IHS image allowed a much
better colour differentiation than the FCC (compare
Figure 2).
The synoptic view of large areas with the help of
the satellite imagery was especially useful to de
lineate extensive complex mapping units with asso
ciations of several soils. These units have very
gradual boundaries which could only be delineated
on the basis of a change in the general colour pat
tern.
The aerial photographs were mainly utilized to
map erosion gullies which are not visible on any of
the two types of satellite imagery. Some relief-de
pendent soil boundaries (e.g. river terraces) were
also delineated on the aerial photographs as were
small depressions and narrow floodplains. Due to
the smaller scale these little features could hard
ly or not at all be identified on the satellite
imagery. Some of the soil boundaries which could be
identified on the photos were too detailed for the
scale of the survey.
General mapping problems were caused by some
burnt areas which appear on the satellite imagery
very similar to areas of dark cracking clay. Dif
ferentiation within the red soils posed another
difficulty. Despite very important differences
(e.g. soil depth, texture, degree of leaching, sto
niness etc.) all red soils have the same or very
similar reflectance characteristics. Thus they all
give the same colour on the satellite images res
pectively the same graytone on the aerial photo
graphs .
6.3 Zone 14
With an annual rainfall of about 950 mm, Zone 14
has an intermediate position between the low rain
fall zones 16 and 8 and the high rainfall zones 4
and 3. The greatest port of Zone 14 consists of an
undulating highland plateau with straight, narrow,
perennially swampy drainage lines ("bottomlands").
Typical features of this zone are several larger
and smaller swamps and periodically swampy depres
sions ("mbugas") often fringed by numerous alluvial
fans.
Most of the area is covered by grassland and
wooded grassland. Some extensive areas are affor
ested with pine species.
The dominant soil of the zone is a deep highly
leached yellow clay, in some higher areas with a
humic topisoil. The depressions and alluvial fans
are characterized by a variety of imperfectly and
poorly drained soils. In the southwest of the zone
some extensive areas with red and yellow sands oc
cur.
In Zone 14 the aerial photographs were the main
mapping support. Most soil boundaries are relief-
dependent and could excellently be mapped from the
photos and even directly from the contour lines of
the toposheets.
The satellite imagery was useful to delineate the
agro-ecological land units, but within these units
neither of the two types of imagery showed much
soil-related differentiation. In contrast to Zones
16 and 8 not the soil colour but the vegetation /
land use determines the reflectance characteristics
of the area. Therefore most boundaries visible on
the satellite imagery are related to land-use chan
ges which showed very limited correlation with soil
differences. Merely major bottomlands could easily
be identified from the satellite imagery.
6.4 Zone 4 and Zone 3
With annual rainfalls of about 1200 mm (Zone 4)
and about 1400 mm (Zone 3) both zones belong to the
high rainfall area of the Iringa Region. Dense,
fairly uniform vegetation covers of miombo wood
land, grassland and forest remnants are typical for
these two zones. The area shows considerable relief
differences with elevations up to about 1800 metres
in Zone 4 and 2900 metres in Zone 3.
