Land resources inventory and suitability assessment for the major land use types in Morogoro urban district, Tanzania
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Date
2001
Journal Title
Journal ISSN
Volume Title
Publisher
Sokoine University of Agriculture
Abstract
Land resources inventory and suitability assessment of Morogoro Urban District was
carried out to asses the potentials and constraints of the various land units for the
production of smallholder low input rainfed maize, rice, sorghum, beans, banana and
vegetables. The study covered a total area of approximately 52,125 ha. Morogoro Urban
District is situated almost at the heart of Morogoro District, between latitudes 6 o 37 and
6 o 55S and longitudes 37 o 33 and 37 o 51E. The district is bordered by Uluguru
Mountains on the south eastern side and Mindu and Nguru ya Ndege hills on the western
side. A bigger part of the district comprises plains of various forms and areal extent.
Relief and slope aspect have a great influence on the climate of the district. Areas higher
in the landscape such as the Morningside are cooler than those lower in the landscape
such as Tungi. The trend of rainfall reveals a similar influence of altitude on rainfall.
Rainfall is higher at high altitudes and tends to be lower at low altitudes. Areas on the
leeward side of the Uluguru Mountains receive relatively lower rainfall than those on the
windward side. The onset dates for rainfall are unreliable, although the rainy season
continues for 4 to 5 months. During the growing period, rainfall is lowest in the month
of May whereas peak rainfall is normally received in April. Climatic data of the district
reveal a gradual decrease in rainfall from the east towards the west and northwest. In the
Tungi-Mkonowamara areas a rather dry condition prevails. The SUA-Kingolwira areas
receive relatively more rainfall than Tungi-Mkonowamara area. This trend can be
attributed to the rainshadow effect of the Uluguru Mountains.
The geology of Morogoro Urban District comprises four major rock/lithology types.
These include hornblende-pyroxene granulites, muscovite-biotite gneiss and migmatites,
colluvium and alluvium. The hornblende-pyroxene granulites are the dominant rock
types and occupy the major part of the Uluguru Mountains and foothills. The dominant
minerals in these rocks are calcium-rich plagioclase, hypersthene ((Mg,Fe)SiO 3 ) and
diopside (Ca,MgSi 2 O 6 ). The muscovite-biotite gneisses and migmatites are dominant in
the Mindu-Lugala hills and a bigger part of the Tungi-Mkonowamara peneplains. They
are of a high metamorphic grade containing equal amounts of potassium-feldspars
(microcline) and sodium-rich plagioclase (oligoclase). Quartz is present in fairly high
amounts. Colluvial materials of diverse mineralogical composition dominate most of the
piedmont slopes and peneplains. Alluvial materials are dominant in the river terraces and
flood plains.
Climate and its effects on geological processes influence evolution of landforms in the
study area. Marked influence on landforms by water erosion as well as colluvio-alluvial
processes were observed in the field and through soil profile development. In the current
study, six major landform types were identified in the district. The landforms of the
Uluguru Mountains display a marked variation in altitude, relief and intensity of
dissection. The strongly dissected ridges (1500-2000 m asl) are a manifestation ofMsanya et al.
v
intense erosion in form of mass movements. The Uluguru mountain foothills (600-900 m
asl) are predominantly steep convex slopes. The Mindu-Lugala hills situated at an
altitude range of 700-1100 m asl are strongly dissected with hilly topography. The
Mzinga-Bigwa piedmonts consist of glacis and alluvial fans. They are gently sloping and
are characterised by moderate to severe erosion. Extensive areas of alluvial fans and hill
wash sands are found around the strongly dissected Mindu-Lugala hills. Whereas the
piedmont slopes associated with the Uluguru Mountains are gently undulating, those of
the Mindu-Lugala hills have an undulating topography. Other major important landforms
in the district are the peneplains which are situated at an altitude of 300-600 m asl. The
peneplains consist of ridge summits and slopes alternating with narrow valley bottoms.
The valleys, being flat to almost flat with river terraces and flood plains occurring at an
altitudes lower than 400 m asl.
Climate, landform patterns and parent materials have had profound influence on types
and distribution of soils in the district. Soil profile development reveals marked
influence of mass removal of soils by water erosion particularly mass movements in the
mountains and colluvio-alluvial processes in the piedmont slopes and peneplains. There
is a considerable variation in soil depth, texture, drainage condition and soil chemical
properties among the landform units. The mountain ridge slopes have relatively shallow
soils and gravely soil textures. This can be attributed to severe erosion caused by mass
removal of soil materials mainly by high rainfall. The piedmont slopes and peneplains
with colluvial material derived from granulites and mixed gneisses have very deep soils
with high amounts of clay content. This is due to constant addition of new soil materials
and in situ weathering coupled with low rate of erosion. Landforms associated with
migmatites like Mindu-Lugala piedmont slopes and Tungi Mkonowamara peneplains
have the highest amount of sand content. This can be explained by the nature of the
parent materials which are richer in felsic minerals. Valley soils have medium textures
and are stratified as a result of cyclic deposition of materials of diverse origin.
The mineralogy of the soils of the Uluguru Mountains, the piedmont slopes and the
peneplains are mainly kaolinitic. The soils of the mountain ridges have high content of
gibbsite in the clay fraction, which can be attributed to rapid weathering and strong
leaching caused by high rainfall and excessive drainage. Soils of the river terraces and
flood plains have relatively high contents of smectite and illite in the clay fraction,
revealing the relative young age of the soils.
Soils of the mountains are slightly acidic to acidic (pH<5.5). Piedmonts have nearly
neutral reaction (pH 6.0-7.5) except for the glacis which are strongly acidic (pH<5.5).
Most soils of the peneplains are moderately acid except for those associated with
migmatites, which are strongly acid (pH<5.5). Valleys have nearly neutral to alkaline
soils with ESP ranging between 5 and 37%. Organic carbon and nitrogen levels for all
soils are very low with values less than 1.0% and 0.1% respectively. Available P is alsoMsanya et al.
vi
low (<5 mg/kg). Nutrient retention capacity of soils is low (CEC <12 cmol(+)/kg) except
in the valleys where nutrient retention is high (CEC 20-30 cmol(+)/kg ).
According to FAO-World Reference Base nine major soil types were identified and
classified. The soils of the strongly dissected mountain ridge slopes are Leptosols,
Lixisols, Luvisols and Cambisols. Dominant soils on the piedmonts and peneplains are
Lixisols and Acrisols while the ridge side slopes on the peneplains have soils classified
as Cambisols. The soils of the river terraces and flood plains are Fluvisols, Vertisols and
Gleysols while those of the Mindu hills and surrounding areas are classified as
Leptosols, Cambisols and Arenosols.
Six major land utilisation types namely; smallholder low input rainfed maize, rice,
sorghum, beans, bananas and vegetables were identified and evaluated in Morogoro
Urban District. Land suitability classification indicates that, none of the land mapping
units is highly suitable for all the studied land utilisation types. This is because its
natural fertility has been depleted over time through leaching, erosion and nutrient
mining through continuous cropping. Among the six LUTs, vegetable production was
more suited to the area for it could be grown in about 80% of the area. Beans rank the
second followed by maize. Sorghum was found to be the fourth LUT in the area while
rice was the least. Moisture supply soil fertility and erosion hazards are among the most
limiting factors for production of most crops in the area.
Deliberate efforts should be taken to establish critical zones for afforestation, reduce
burning through introduction of by laws and appropriate training programmes, use of
grass barriers and cultivation of perennial crops. Further research on soil erosion
particularly mass movements, gullying and sheet wash is prerequisite in order to come
up with acceptable soil conservation packages for the district.
It is strongly suggested that emphasis should be put on the use of organic and non
acidifying fertilisers and afforestation of hilltops. Use of indigenous fertilisers such as
rock phosphate and manures could immensely contribute to the improvement of soil
fertility in Morogoro Urban District.
Water harvesting techniques, growing of drought tolerant crops and use of organic
fertilisers will improve the sustainability of agricultural production in the area. The focus
should be on the use of integrated nutrient management techniques.
Provision of drainage systems in the poorly drained areas will control and keep the
ground water levels low. This will also enhance regular flushing of the soils thus
avoiding the building up of harmful levels of salts. Saline soils could also be managed
through proper crop selection and planting of saline tolerant crops. Sorghum withstands
poor drainage condition and can cope very well with drought and saline conditions.Msanya et al.
vii
Frequent floods especially by the Ngerengere river could be reduced by flood protection
works like construction of ditches and dikes with outlets to the present natural drainage
system. Agricultural mechanisation and use of organic fertilisers will in the long run
improve soil structure of the lands in the district and ultimately enhance soil workability.
Description
Keywords
land resources, Morogoro, Land resources inventory, Land use types, Land evaluation