Geography & History Notes | KCSE, NECTA, ZIMSEC & GCSE

  Soil is a relatively thin layer of unconsolidated mineral and organic material on the immediate surface of the earth. Fertile soil contains approximately 25% of both air and water, about 5% organic matter and about 45% mineral matter. It is important to understand something about how soils are formed to determine the best use of available soils and how to manage their fertility. In general, soil formation starts with rocks that are pushed to the surface of the earth by geological or climactic forces. These rocks then undergo weathering - the chemical alteration and physical breakdown of rock during exposure to the atmosphere, hydrosphere, and biosphere. Through the weathering process, eventually enough essential elements become available to support lichens and other lower forms of plant life. As continuing generations of lichens grow, die, and decay, they leave increasing amounts of organic matter. Naturally-occurring organic acids further hasten decay of the rock. An increasing ...

  Soil is thin upper layer of the earth with unconsolidated materials where plant and animals derive their living. Soil catena refers to the sequence of different soils down a slope. the soil are usually derived from the same or similar parent materials but they vary with relief and drainage. The following are main factors influencing the development of soil catena.   Relief . This is the influence of topography on the surface soil. Slope influence drainage which in turn influence moisture content of the soil. Soil on the upper slopes are likely to be different from those of the valley floor. The upper slopes are generally steeper than the lower ones. They are therefore well drained. On the very steep slopes, the soils are thin because of high rate of erosion. On gentle slopes  the soil is thick because the rates of erosion and weathering are balanced. On the valley floors the soils may be peat or alluvial due to deposition.   Drainage . There is close rel...