Tanzania Agricultural Research Institute

Author(s) : TARI Mlingano

A SOTER database of Tanzania, scale 1:2,000,000 have been available since 1998 (Eschweiler, 1998). The main source of information for this SOTER database has been the earlier work of De Pauw (1984). His map “Soils and Physiography” (1983) at scale 1:2 million and report on “Soils, Physiography and Agro-Ecological Zones of Tanzania” (1984) served as basis for the delineation of the SOTER units. The map displays the land units within their broader physiographic zones and describes for each unit the dominant parent material, slope and hypsometry. The report also gives the relation between the landform unit and the generalized soil pattern (position of the soils in the landscape) and the distribution of dominant and subdominant soils. This information formed the basis of the SOTER database (SDB) for Tanzania (Eschweiler, 1998). Representative profile information has been taken from the SDB of Tanzania (Eschweiler, 1998). The procedures followed for the Tanzanian SOTER database have been somewhat different from the other SOTERSAF databases. It has followed the guidelines developed for the SOTER database at scale 1:2,5 million (Batjes and Van Engelen, 1997). Although derived from the Global and National Soil and Terrain Digital Database, scale 1:1 million (Van Engelen and Wen, 1995), this database has a restricted number of attributes. As a consequence of smaller scale, the number of attributes has been reduced from 124 in the original database to 74. This was justified because of most discarded attributes no data are available. The GIS database included about 100 polygons, which on the De Pauw’s map had been classified as miscellaneous landforms, such as undifferentiated rocky terrain, rocky hills, escarpments, slopes, canyons, etc. These had not been further specified in the original SOTER database for Tanzania. However for the SOTERSAF, these have been redefined and regrouped in a number of SOTER units. Depending on the physiographic zone in which the polygons occur, and with the additional information of a Digital Elevation Model (DEM) with 1km grid (Gtopo30), they have been classified in 14 new SOTER units, ranging between medium-gradient hills, escarpments and high-gradient 4 mountains. Some (small) polygons, often inselberg areas, have been erased from the map and in the database added as terrain components to the SOTER unit in which they occurred.