Soil Survey, Genesis and Classification Along a Transect Underlain by Quaternary Sediments in Kilifi County, Kenya

Abstract

Soil resource data is at an increasing demand to provide efficient information on soil properties that we rely on for crop production, grassland and forest sustenance. A pedogenesis study was conducted in Kilifi County, Kenya, for the purpose of generating soil information and map of the area. Five representative pedons were identified on various sedimentary parent materials and landscape positions. These included Mavueni pedon located on the coastal lowland underlain by Magarini sand, Ngombeni pedon on a valley bottom underlain by Upper Jurassic shales, Vyambani and Ngamani pedons located on the coastal uplands also underlain by Upper Jurassic shales and Kitsoeni pedon located on the coastal uplands underlain by Kambe Limestone. These representative pedons were opened and described following the FAO guidelines for soil description. Soil samples were collected horizon wise for laboratory analysis for the purpose of soil classification. Representative rock samples were also collected from each pedon for petrography and geochemical analysis to determine the influence of parent material on soils. Variations in soil properties were observed across the pedons and within some pedons. The soil depth ranged from shallow in Vyambani, moderately deep in Ngamani and very deep in Ngombeni, Mavueni and Kitsoeni. Drainage ranged from poorly drained in Ngombeni to well drained in Kitsoeni. Variation in soil colour was also observed. Soils in Kitsoeni were observed to have dark reddish brown colour throughout the profile, brown to dark reddish brown colour in Mavueni, dark reddish brown to reddish brown in Vyambani, very dark grayish to olive brown in Ngamani and brown, gray and black in Ngombeni. The soil texture was clay in Ngombeni, Vyambani and Ngamani, sandy clay to sandy clay loam in Mavueni and sand clay loam in Kitsoeni. Sand content ranged between 31- 73%, clay 21- 47%, and silt 2- 28%. Bulk density ranged between 1.3 to 1.7g/cm3 and porosity was slightly low (39- 41%) in Mavueni and Kitsoeni and slightly high Ngombeni, Vyambani and Ngamani (39- 47%). Saturated hydraulic conductivity was moderately rapid to rapid (5- 7-5cm/h) in Kitsoeni, slow to moderate (1- 2cm/h) in Mavueni and very slow (<1g/cm) in Ngombeni, Vyambani and Ngamani. pHwater was observed to be moderately acidic to moderately alkaline (5.3- 8.6). The CEC was low to medium (2- 10cmolkg-1) in Mavueni and Kitsoeni and relatively high (19- 24cmolkg-1) in Ngombeni, Vyambani and Ngamani. The soils were non-sodic (ESP <15%) except for Ap and Bt1 in Mavueni and B and BC in..................................................................................................