Land resources inventory and suitability assessment for the major land use types in Morogoro urban district, Tanzania

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 55S and longitudes 37 o 33 and 37 o 51E. 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.