Thursday, 13 July 2006 - 8:30 AM

Use of WRB to Classify Soils in the Tropics: Lessons Form East Africa.

Method Kilasara, Sokoine Univ of Agriculture, SUA Main Campus, P.O. Box 3008, Morogoro, Tanzania, Patric Gicheru, Kenya Agricultural Research Institute, Nairobi, Kenya, Edward Ngatunga, Ministry of Adriculture & Food Security, Kilimo 1, Dar es Salaam, Tanzania, C.K.K. Gachene, Univ of Nairobi, Kabete Campus, P.O. Box 30197, Nairobi, 00100, Kenya, and Joel Melio, ARI, Mlingano, Mlingano, P.O. Box 5088 Tanga, Tanga, Tanzania.

Problems of land degradation in arid, semi-arid and dry sub-humid areas had intensified in Sub Sahara Africa over the last decade despite several efforts including the United Nations Rio Conference in 1992, the adoption of Plan of Action to Combat Desertification (PACD) by United Nations Conference on Desertification (UNCOD) in 1994 and the UN Millennium Summit in 2000. Parallel to this, land productivity in the region has remained the least worldwide. This could partly be attributed to the lack of adequate knowledge on soils' behaviour-land productivity relationships. Knowledge on soils' response to catastrophic events such as landslides, accelerated soil erosion, inundation or long-term changes on the land including climate change is patchy and inadequate. Soil characterization is both limited and largely incomplete to meet demands at farm level. Due to lack of national soil classification systems transfer of soil-based information is inadequately coordinated and shared among policy makers and land investors. World Reference Base for Soil Resources (WRB) has an important role to play in terms of land use planning and management in the region. However, WRB was recently introduced in Sub Sahara Africa, hence needs to be adequately evaluated and tested for adoption. A workshop was organized by FAO in East Africa in June 2005 to train professionals dealing with the soil classification, land use planners and land resource managers from the Eastern, Central and Southern countries Africa on the use of WRB. Thirteen soil profiles representative of major soils in East Africa were selected for classification using WRB. The selection included soils formed under a wide range of climatic, topographic and geological conditions as well as land use/cover. The classification was based on both field data acquired by use of the soil profile description manual FAO (1990) and laboratory analytical data. A critical review on the classification of the following soil reference groups was done: Luvisols, Lixisols, Vertisols, Acrisols, Gypsisols, Fluvisols, Nitisols, Regosol, Cambisol, Nitisols, Phaeozems and Planosols. WRB was found to be simple to classify soils. The importance of field data on the classification of the soil reference groups was highly appreciated. However, some limitations were encountered while classifying the following soil reference groups: Vertisols, Gypsisols, Calcisols, Luvisols, Cambisols and Phaeozems. It is proposed to introduce a manganic horizon and the following qualifiers for the soil reference groups in bracket: hypersalic (Vertisols), manganic, ultic (Phaeozems), endostagnic, hyposodic(Cambisols), gypsic (Calcisols) endogleyic and epistagnic (Luvisols). Further studies are proposed with regard to the above observations. It is also proposed to change the order of qualifiers for Vertisols; standardize the laboratory analytical methods for soil classification using WRB and review of the definitions of the cambic horizon in order to avoid inclusion of soils with considerable degree of alteration in the Cambisol reference group Key words: Tropical soil classification, improvements on WRB

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