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International Institute for Aerospace Survey, Netherlands (2001)

Soil survey to predict characteristics relevant to land management (Kenya)

Atkilt, Girma

Titre : Soil survey to predict characteristics relevant to land management (Kenya)

Auteur : Atkilt, Girma

Etablissement de soutenance : International Institute for Aerospace Survey, Netherlands

Grade : Master of Science in Geoinformation Science and Earth Observation 2001

It is generally known that management practices such as tillage, fertilisation, insecticides, herbicides applications, etc. may result in changes in the physical and chemical properties of the soil. For example, soil compaction, problems of soil aeration, decline in soil fertility and the effect on soil ecosystem. The results of the different types of management are called “phenoforms” whereas the genetically defined soil types are “genoforms”. The purpose this study was to distinguish and characterise the different phenoforms formed by different types of management in the area of lake Naivasha, Kenya. Genoforms were defined by standard soil survey and classification systems and phenoforms by statistical analysis and classification methods such as the FAO proposed topsoil characterisation (1998) including USDA (1998) and World Reference Base (1998). Twenty-nine observation points with a total of 74 horizons were sampled. Eleven of them were paired (managed vs unmanaged). The observation points that were made in pairs were chosen based on site observation, close to each other, with the same genoform and differing only in management practices. Soil properties including infiltration (I), bulk density (Bd), soil structure, organic mater content, coarse fragments, pH, EC, and penetration resistance (r) were determined. Results and conclusions were made using statistical methods and by inference from principles of soil science. The main soil types of the area are Areni-Vitric Andosols (Eutri) and Sodi-Fluvic Cambisols (Skeletic, Eutric). There is significant difference between managed and unmanaged in two properties : in soil infiltration rate during the first 8 minutes and r of the 2nd horizon. Though not significantly different, suggestive results in soil pH and Bd were found. These both increased with depth. Soils in the volcanic plain have significantly higher Bd and significantly lower pH than those in the lacustrine plain. Organic mater content increases due to management in the volcanic plain soils and decreases in the lacustrine plain. Soil structure can not be a diagnostic criterion in these gravely sandy soils, derived from volcanic ash, due to its weak development. The proposed FAO topsoil classification highlights most of the soil properties useful for management, for example the low nutrient retention, natric, and altaric properties of these soils. On the other hand, production limitations such as excessively drained properties, problems of nematodes, some toxicities, potic nature, and soil capping were not recognised and could be added to improve the usefulness of the classification system.

Sujets : Soils ; Management ; Lake Naivasha, Kenya ; Andosols ; Cambisols ; Classification ; Watershed ;

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Page publiée le 11 janvier 2017, mise à jour le 13 novembre 2019