Aridity

• • Of the total land area of the world, the hyper-arid zone covers 4.2 percent, the arid zone 14.6 percent, and the semiarid zone 12.2 percent. Therefore, almost one-third of the total area of the world is arid land.

  • The hyper-arid zone comprises dryland areas without vegetation, with the exception of a few scattered shrubs. True nomadic pastoralism is frequently practiced. Annual rainfall is low, rarely exceeding 100 millimetres. The rains are infrequent and irregular, sometimes with no rain during long periods of several years.

  • The arid zone is characterized by pastoralism and no farming except with irrigation. For the most part, the native vegetation is sparse, being comprised of annual and perennial grasses and other herbaceous vegetation, and shrubs and small trees. There is high rainfall variability, with annual amounts ranging between 100 and 300 millimetres.

  • The semi-arid zone can support rain-fed agriculture with more or less sustained levels of production. Sedentary livestock production also occurs. Native vegetation is represented by a variety of species, such as grasses and grass-like plants, fortes and half-shrubs, and shrubs and trees. Annual precipitation varies from 300-600 to 700-800 millimetres, with summer rains, and from 200-250 to 450-500 millimetres with winter rains.

  • Soil fertility is the ability of a soil to provide nutrients for plant growth. Not all soils in arid environments lack the necessary nutrients to be productive but the lack of available water limits plant growth and agricultural potential.

Irrigation

• • Flood irrigation

    • Results in a large surface area of water since furrows between crops will be filled with water. It is simple, relatively cheap, requires little energy and can use lower quality water than other systems. Conventional furrow systems are only 60% efficient in water absorption by the plants.

  • Sprinkler irrigation

    • Sprinkler systems use spray nozzles and pressurized water and can either be movable (such as center-pivot) or fixed. The most efficient systems are Low Energy Precision Application (95%) and Low Elevation Spray Application (88%) sprinklers. They are an adaptation of center-pivot irrigation in which the nozzles extend right down to the ground so the water is supplied only and exactly where it is needed and can be applied at low pressure. This saves water as less is lost to wind or evaporation from the foliage and energy as well as preventing soil erosion caused by runoff of excess water. On the down side sprinkler systems are expensive to install and may become less efficient when it is dry or windy, and they may damage crops by frequently wetting non-root areas.

  • Drip irrigation

    • This is where water is supplied at very low pressure, very slowly, directly to a plant's roots from plastic tubing. It is the most efficient form of irrigation at 97%, results in very little erosion. However it is also the most expensive form of irrigation

Adapted from - Mission 2012