A first generation digital soil map of a portion of the Uasin Gishu Plateau, Kenya

The western Kenyan highlands are among the most highly populated and productive areas in Kenya\u27s breadbasket regions. It is important, therefore, to make optimal use of available land to enhance food security. The objective of this project was to develop a first generation digital soil map of a portion of the Uasin Gishu Plateau to be used for both teaching and extension. To support digital map production, we sampled five representative pedons and analyzed them for organic matter, pH, extractable K+, Ca 2+, Mg2+, Al+3, and P, effective cation exchange capacity (ECEC), base saturation, soil texture, and clay mineralogy. Pedon KN12 is a poorly drained Vertisol (Typic Endoaquert) in a depression at ~2280 m elevation; pedons KN13 and KN14 are well-drained Oxisols at ~2230 m elevation with a petroferric contact within ~80 cm of the soil surface (Petroferric Eutrudox), and pedons KN15 and KN16 are well-drained Oxisols (Humic Eutrudox) at ~2780 m. All 5 pedons had clay textures throughout. There were no statistically significant differences (p\u3e0.05) in extractable P and K+ levels, but the remaining parameters showed significant differences (p\u3c0.05) among the sites. The Vertisol (KN12) had significantly higher ECEC, Mg2+ , Ca2+, base saturation, and pH, and lower Al +3 saturation than the Oxisols. As expected, base saturation was positively correlated with Ca2+, Mg2+, ECEC, and pH, and negatively correlated with Al+3. X-ray diffraction showed that the clay fraction of the Oxisols was predominately kaolinite with smaller amounts of mica. Goethite and rutile were also identified in KN13, KN15and KN16. The clay fraction of the Vertisol contained interstratified kaolinite-smectite and discrete kaolinite. One Oxisol (KN16) contained hydroxyl-interlayered vermiculite in addition to kaolinite. A Digital Elevation Model (DEM) was used to generate covariates such as topographic wetness index (WTI), percent slope, geomorphons, and altitude above channel network. These covariates were used to create a soil class map of a portion of the Usain Gishu Plateau that is significantly more detailed than the currently available soil maps of the area. A major constraint limiting digital map production in Kenya at this time is the poor spatial resolution (90 m) of the available DEM data