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International Institute for Aerospace Survey and Earth Sciences ITC, Netherlands (1988)

Characterisation of soils sequence derived from volcanic tuff in the Loita Plains southwest of Kenya with a view to their genesis, classification and management

Okoth, P F

Titre : Characterisation of soils sequence derived from volcanic tuff in the Loita Plains southwest of Kenya with a view to their genesis, classification and management

Auteur : Okoth, P F

Etablissement de soutenance : International Institute for Aerospace Survey and Earth Sciences ITC, Netherlands

Grade : Master of Science MSc 1988

Résumé
This study has characterized six soil sequences derived from volcanic tuff in the Loita Plains, Southwest Kenya and explored their genesis, classification and management problems. The Loita Plains falls in a semi-arid to subhumid climate with an average annual precipitation of 664-737mm. The mean minimum temperatures range between 7.2 and 11.3 C with an absolute minimum night temperature of 0.3 C. The mean maximum temperatures range between 21.4 and 26.9 C. The mean annual temperature is 16.5 C. The mean annual evaporation and evapotranspiration are 129 and 102 mm respectively. The area is on Quarternary volcanic ash and tuffs except on hills where quarzitic rocks of the Pre-cambrian age stick out. Most of the area is under grassland or bushed grassland except the northern part wi th extensive wheat cultivations. From the characterization of the soils, most andic properties are lacking in the soils. The bulk density ranges between 1.1 and 1.7 and moisture retention capacity has a mean value of 56.8 wt%. The carbon contents range between 0.01 to 2.63%. The pH for the topsoils is an average of 6.6 and 8.2 for the subsoils due to their high sodium contents. Though X-ray analysis find the soils amorphous, Very little active Al and Fe oxides is obtained by dissolution analysis. Kaolinite, halloysite, mica and or illite are the dominant crystalline clay minerals wi th traces of quartz and feldspars identified by X-ray analysis. Out of the six toposequences described, three soil association groups are identified according to soil distribution wi thin the landscape. They include, Bar Kitabu Lomanera group, the Maji Moto group and the Angata Loita group. Mostly they are comprised of Alfisols in the midslope and footslope positions and Mollisols on the summit position. Management problems connected wi th erosion, structural instability, compacted subsoils and fertili y have been identified and possible management practises suggested

Mots Clés : Loita plains, Kenya / Soils / Tuff / Ash / Alfisols / Mollisols

Présentation (KIPS) )

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