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We have already known the first factor that influences the formation of soil.
Now, we will learn another factor that influences soil formation.
Vegetation has a large effect on soil formation. Soils formed under forests tend to be more weathered because forests grow in higher rainfall areas. Soils formed in prairie, tend to be located in areas of less precipitation, grasses tend to use the moisture provided reducing the water movement through the soil profile and form organic matter in large quantities and to a deeper depth in the soil surface than forest soils.
Slope and aspect are two features of topography that affect soil formation. Slope refers to steepness from horizontal and aspect is the direction the slope faces relative to the sun. The steepness of the slope affects the amount of deposition or erosion of soil material.
A soil that is level is the most developed as there is no loss or gain of material to slow the soil forming process. The aspect of the slope affects the amount of water that moves through the soil.
The north side tends to have more water because of less evaporation and therefore may have more vegetation. The soil chemical processes are slowed on the north aspect because of the colder soil temperatures. A soil with a southern aspect tends to have grass vegetation, warmer soil temperatures, and more evaporation.
In a landscape, a sequence of soils with different horizons caused by differences in their depth to the water table is called a catena. A catena normally consists of four soil series. The soils are located on the summit, shoulder, backslope, and footslope.
The drainage or depth to water table is well drained for the summit, moderately well drained on the shoulder, somewhat poorly drained on the backslope, and poorly drained on the footslope. The summit and backslope are the most developed soils in this group of soils.
And now, the last factor Time.
Soil forming processes take time to show their effects. The clock of soil formation starts ticking when a landslide express new rock to the weathering environment, when a flooding river deposits a new layer of sediment, when a glacier melts and dumps its load of mineral debris.
When we speak of a young or mature soil, we are not so much referring to the age of the soil in years.Time interacts with the other factors of soil formation.
During first 100 years, lichens and mosses establish themselves on the bare exposed rock and begin to accelerate its breakdown and the accumulation of dust and organic matter, Within a few hundred years, grasses, shrubs and stunted trees have taken root in a deepening layer of disintegrated rock and soil, adding greatly to the accumulation of organic materials and to the formation of A and C horizons. Thus, Soil organisms slowly transform the surface plant litter into a distinct O horizon. As the entire profile continues to deepen over time, the zone of weathered, unconsolidated rock may become many meters thick.
Now, we will learn another factor that influences soil formation.
Climate
It is the most important among the four factors that act on parent material. The principal climatic variables influencing soil formation are precipitation and temperature. Both of it accelerates the weathering process.
Precipitation:
We know that water is essential for all the major chemical weathering reactions. For the formation of soil, water must penetrate into the soil. The greater the depth of water penetration, the greater the depth of weathering soil and development. Water percolating through the soil profile transports soluble and suspended materials from the upper to the lower layers. Thus, percolating water stimulates weathering reactions and helps differentiate soil horizons.
Precipitation:
We know that water is essential for all the major chemical weathering reactions. For the formation of soil, water must penetrate into the soil. The greater the depth of water penetration, the greater the depth of weathering soil and development. Water percolating through the soil profile transports soluble and suspended materials from the upper to the lower layers. Thus, percolating water stimulates weathering reactions and helps differentiate soil horizons.
The deficiency of water is a major factor in determining the characteristics of soils of dry regions. Soluble salts are not leached from these soils. In some cases they build up to levels that curtail plant growth.
Temperature:
Temperature and moisture both influence the organic matter content of soil through their effects on the balance between plant growth and microbial decomposition. If warm temperature and abundant water are present in the profile at the same time, the processes of weathering, leaching and plant growth will be maximized. Climate also influences the natural vegetation. Humid climates favor the growth of trees.
Thus, climate exerts its influence partly through a second soil forming factors.
The next factor is Biota. It means the living organisms.
The source and richness of organic matter is down to the living things that live on and in the soils. Plants provide lots of vegetative residue that are added to soils. Their roots also hold the soils and protect them from wind and water erosion. They shelter the soils from the sun and other environmental conditions, helping the soils to retain the needed moisture for chemical and biological reactions. Fungi, bacteria, insects, earthworms, and burrowing animals help with soil aeration. Worms help breakdown organic matter and aid decomposition. Animal droppings, dead insects and animals result in more decaying organic matter. Microorganisms also help with mineral and nutrient cycling and chemical reactions.
Temperature:
Temperature and moisture both influence the organic matter content of soil through their effects on the balance between plant growth and microbial decomposition. If warm temperature and abundant water are present in the profile at the same time, the processes of weathering, leaching and plant growth will be maximized. Climate also influences the natural vegetation. Humid climates favor the growth of trees.
Thus, climate exerts its influence partly through a second soil forming factors.
The next factor is Biota. It means the living organisms.
Biota
The source and richness of organic matter is down to the living things that live on and in the soils. Plants provide lots of vegetative residue that are added to soils. Their roots also hold the soils and protect them from wind and water erosion. They shelter the soils from the sun and other environmental conditions, helping the soils to retain the needed moisture for chemical and biological reactions. Fungi, bacteria, insects, earthworms, and burrowing animals help with soil aeration. Worms help breakdown organic matter and aid decomposition. Animal droppings, dead insects and animals result in more decaying organic matter. Microorganisms also help with mineral and nutrient cycling and chemical reactions.
Besides earthworms, termites and other small animals bring about considerable soil mixing as they burrow through the soil. Earthworms ingest soil particles and organic residues, enhancing the availability of plant nutrients in the material that passes through their bodies.
Now, it is time to know about another soil forming factor Topography.
Topography
A soil that is level is the most developed as there is no loss or gain of material to slow the soil forming process. The aspect of the slope affects the amount of water that moves through the soil.
The north side tends to have more water because of less evaporation and therefore may have more vegetation. The soil chemical processes are slowed on the north aspect because of the colder soil temperatures. A soil with a southern aspect tends to have grass vegetation, warmer soil temperatures, and more evaporation.
In a landscape, a sequence of soils with different horizons caused by differences in their depth to the water table is called a catena. A catena normally consists of four soil series. The soils are located on the summit, shoulder, backslope, and footslope.
Time
Soil forming processes take time to show their effects. The clock of soil formation starts ticking when a landslide express new rock to the weathering environment, when a flooding river deposits a new layer of sediment, when a glacier melts and dumps its load of mineral debris.
When we speak of a young or mature soil, we are not so much referring to the age of the soil in years.Time interacts with the other factors of soil formation.
During first 100 years, lichens and mosses establish themselves on the bare exposed rock and begin to accelerate its breakdown and the accumulation of dust and organic matter, Within a few hundred years, grasses, shrubs and stunted trees have taken root in a deepening layer of disintegrated rock and soil, adding greatly to the accumulation of organic materials and to the formation of A and C horizons. Thus, Soil organisms slowly transform the surface plant litter into a distinct O horizon. As the entire profile continues to deepen over time, the zone of weathered, unconsolidated rock may become many meters thick.
Reference:
Brady, N.C. and Weil, R.R., The nature and properties of soil. 13th Edition.
Boul, S.W., F.D. Hole, R.J. McCraken, and R.J. Southard. Soil Genesis and classification. 4th Edition.
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