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The formation of soil
Soil is formed from rocks. Different types of rocks are broken down into tiny particles by a process of weathering (mechanical, chemical and biological). These processes which aid soil formation are influenced by several factors. The several factors have interacted to form soil. The main ones include:
Parent rock. The parent rock is the rock material that breaks down to form soil particles. It is therefore one of the factors that determine the nature and quality of the soils. Parent rocks differ in terms of structure. Some rocks are hard while others are soft and therefore respond to weathering processes at different rates. The rate of weathering of a parent rock also differs according to whether there is presence or absence of joints.
Jointed rocks are more susceptible to weathering and readily break down to give rise to soil particles. The colour of the parent rock also determines the rate at which it absorbs heat, expands and contracts and therefore breaks down. Soil formation is likely to be faster on dark coloured rocks compared to shiny ones. The composition of a rock directly determines the nature of the soil nutrients, for example, a quartz rock is likely to lead to the formation of sandy, porous soils while a limestone rock is likely to lead to the formation of soils rich in lime. Weathering of laterite rock, yields thin skeletal and poor laterite soils.
Climate. Climate is another factor that influences soil formation. It influences soil formation mainly through the elements of rainfall and temperature. In humid areas, there is abundant rainfall and therefore adequate water which acts as a medium through which chemical reactions take place to decompose rocks into simpler substances.
Water is a pre-requisite for chemical weathering processes which lead to rock decomposition and hence the formation of soils. Furthermore high temperatures speed up the rate of chemical reactions, It therefore follows that soil formation in hot climates is faster than in cold regions.
Living organisms. Living organisms, namely, plants and animals alter the nature of the parent rock and contribute to the formation of soil particles. Animals for example, contribute to the decomposition of hard and complex minerals into simpler substances. Bacterial organisms secrete solutions which progressively break down rocks even if they are complex. Other organisms such as earth worms help to grind up mineral particles into smaller substances that are necessary for complete soil formation.
Man’s activities. Man also has influence on soil formation through his activities like digging and construction. Apart from animals, the roots of plants usually disintegrate rocks and therefore contribute to the production of particles necessary for soil formation.
Plant leaves are also important in soil formation since they ultimately decay and give rise to humus. Densely vegetated areas are therefore characterised by soils rich in organic content.
Relief. The relief of the land determines the rate of erosion of the surface rocks. Steep slopes are often more susceptible to erosion than gentle ones. This implies that there is a more rapid loss of nutrients on steep slopes compared to gentle ones. This partly explains why only shallow, skeletal soils can form on steep slopes. Although steep slopes are associated with thin soils they are also associated with rapid rates of soil formation because the rate of exposure of the parent rock to agents of weathering is high.
Gentle slopes tend to have deep, mature and well developed soils. This is partly because the rate of removal of soils is low and also because the rate of deposition is high.
Flat landscapes are potential regions where leaching is likely to be promoted and therefore poor soils can form.
Time. The last factor that influences soil formation is time. Time in this context refers to the duration of interaction of soil forming processes and factors. Time is very important because the nature of any soil depends on how long other factors and processes of soil formation have been interacting. If, for example, the parent rock has been exposed to weathering for a long time, soil formation will be more complete compared to another rock that has been exposed to weathering for a comparatively shorter period. This implies that the longer the duration of interaction, the more developed and mature the soils will be.
Parent rock. The parent rock is the rock material that breaks down to form soil particles. It is therefore one of the factors that determine the nature and quality of the soils. Parent rocks differ in terms of structure. Some rocks are hard while others are soft and therefore respond to weathering processes at different rates. The rate of weathering of a parent rock also differs according to whether there is presence or absence of joints.
Jointed rocks are more susceptible to weathering and readily break down to give rise to soil particles. The colour of the parent rock also determines the rate at which it absorbs heat, expands and contracts and therefore breaks down. Soil formation is likely to be faster on dark coloured rocks compared to shiny ones. The composition of a rock directly determines the nature of the soil nutrients, for example, a quartz rock is likely to lead to the formation of sandy, porous soils while a limestone rock is likely to lead to the formation of soils rich in lime. Weathering of laterite rock, yields thin skeletal and poor laterite soils.
Climate. Climate is another factor that influences soil formation. It influences soil formation mainly through the elements of rainfall and temperature. In humid areas, there is abundant rainfall and therefore adequate water which acts as a medium through which chemical reactions take place to decompose rocks into simpler substances.
Water is a pre-requisite for chemical weathering processes which lead to rock decomposition and hence the formation of soils. Furthermore high temperatures speed up the rate of chemical reactions, It therefore follows that soil formation in hot climates is faster than in cold regions.
Living organisms. Living organisms, namely, plants and animals alter the nature of the parent rock and contribute to the formation of soil particles. Animals for example, contribute to the decomposition of hard and complex minerals into simpler substances. Bacterial organisms secrete solutions which progressively break down rocks even if they are complex. Other organisms such as earth worms help to grind up mineral particles into smaller substances that are necessary for complete soil formation.
Man’s activities. Man also has influence on soil formation through his activities like digging and construction. Apart from animals, the roots of plants usually disintegrate rocks and therefore contribute to the production of particles necessary for soil formation.
Plant leaves are also important in soil formation since they ultimately decay and give rise to humus. Densely vegetated areas are therefore characterised by soils rich in organic content.
Relief. The relief of the land determines the rate of erosion of the surface rocks. Steep slopes are often more susceptible to erosion than gentle ones. This implies that there is a more rapid loss of nutrients on steep slopes compared to gentle ones. This partly explains why only shallow, skeletal soils can form on steep slopes. Although steep slopes are associated with thin soils they are also associated with rapid rates of soil formation because the rate of exposure of the parent rock to agents of weathering is high.
Gentle slopes tend to have deep, mature and well developed soils. This is partly because the rate of removal of soils is low and also because the rate of deposition is high.
Flat landscapes are potential regions where leaching is likely to be promoted and therefore poor soils can form.
Time. The last factor that influences soil formation is time. Time in this context refers to the duration of interaction of soil forming processes and factors. Time is very important because the nature of any soil depends on how long other factors and processes of soil formation have been interacting. If, for example, the parent rock has been exposed to weathering for a long time, soil formation will be more complete compared to another rock that has been exposed to weathering for a comparatively shorter period. This implies that the longer the duration of interaction, the more developed and mature the soils will be.