Soil Characteristics

Aridisoils

The zonal so or most common soil type in the HDB is arid soils. This aspect links heavily with climate and vegetation. This is usually infertile and is particularly influenced by the hot daytime temperatures and lack of rainfall.

Parent rock and Mechanical weathering

The parent material is usually formed from mechanical weathering like exfoliation. The high diurnal temperature range allows mechanical weathering to take place. The texture of the soil tends to be coarse and gravely because exfoliation leaves behind angular pieces of scree

Deflation

In addition fine particles are blown away by winds and leave just coarser grained particles behind. This process is known as deflation.

washed material from rainfall and floods create deeper aridisoils

Material can be washed from mountainous areas into desert areas by torrential convectional rain and flash flooding. Some low lying areas have developed deeper Aridisols as a result. Heavy rainfall can result in flash flooding and gully erosion, when heavy rainfall erodes small channels in the soil surface.

Oases and Iriigation as fertilization

Aridisols can become fertile and produce plant life. They require water to do this. In the Sahara deserts this can happen in oases. Irrigation has been successful in some parts of California and Arizona.

Lack of humus

Humus comes from the process of humification. This process involves the decay of plant litter into a jelly like substance that is rich in nutrients. The coarse texture and sparse or non-existent vegetation prevents the development of humus.

lack of microorgansims and plant litter for humus

In the desert there is a lack of both microorganism and plant litter to create humus. Some humus can be found around the roots of plants in Aridisols but it is not widely distributed throughout the soil. This gives the soil a pale grey colour.

Chemical weathering is prevented, lack of layers and structure to soil.

The low level of precipitation and high temperatures in hot deserts prevents chemical weathering. This means the soil can be deep but does not have clear layers of top soil, sub soil, and bedrock. The lack of organic matter also contributes to this.

Capillary action and salinisation

This means that groundwater is drawn up through the soil in a process known as capillary action. When the groundwater evaporates it leaves behind minerals like salt. Salt pans can begin to develop on the surface. This process is known as salinisation.

Hard pans prevent plant growth. Calcium deposited as hard pan

Nutrients that have been leached through the soil are drawn back up through capillary action. Similarly to salinisation it causes calcium to be deposited as a hard pan on the surface of the soil. A hard pan is impermeable and it can prevent the growth of plants.

Calcification reduces productivity. Calcium hard pan = caliche

The PH of the soil becomes alkaline if calcification takes place. This further reduces the productivity of the soil. The cement like layer of calcium is also known as a caliche.

Shallow lakes formed on hard pans

In the Kalahari desert, limited rainfall from January to March creates shallow lakes where the water cannot pass through the salt pans.