CHAPTER 5 SOIL

Soil, the thin layer of loose particles that covers much of Earth's surface, is derived from weathered rock and decaying organic matter. It is the point at which the earth's atmosphere, geosphere and hydrosphere meet and is the foundation of much of our terrestrial biosphere. It is the basis of primary production, providing the medium for seed germination and root growth, and the nutrients and water required by plants. Almost all our food is derived from soil, one way or another, and we use soil to build houses, roads, dams and other infrastructure. Tiny organisms in the soil transform dead organic materials into nutrients, which plants take up to grow and produce flowers, fruits and seeds. Soil also helps regulate the supply and quality of water through infiltration, percolation, filtering and buffering. Earth's soils contain more carbon than the atmosphere and all its forests combined, and help regulate the climate by absorbing and storing carbon dioxide, nitrous oxide and methane gases. The soil layer provides habitats for countless living organisms, from the smallest bacteria and fungi to the many worms, arthropods and mammals that live there.

As in many parts of Africa, Namibia's soils are generally poor. The country's arid climate with its variable rainfall is often held to be the main factor limiting agriculture, but soils with inherently low fertility and poor physical properties place a major constraint on farming. Crop farmers in more fertile parts of the world would never consider growing crops on soils as marginal as most Namibian soils. Livestock farming would be much more productive in Namibia if its soils were deeper, held more water and supplied more nutrients.

Despite these limitations, the origins, characteristics and types of soils in Namibia are extremely variable and fascinating, as this chapter will show. A number of important references were consulted in the compilation of the information in this chapter,1 and the maps were derived from local and international databases.2

Photo: While broad expanses of soils are widespread on the surface of the earth, their values and properties lie in the detail. The size of particles or grains of soil determine their texture and the volume of air or water that can be held in the pores between them, for example. And it is in their microscopic and chemical detail that the presence or absence of certain minerals, bacteria, fungi and particles of plant and animal material are to be detected.