GEOGRAPHY FORM THREE NOTES TOPIC 3: SOIL
GEOGRAPHY FORM THREE NOTES TOPIC 3: SOIL
Soil is the thin upper layer of the earth’s crust which has been weathered from the parents material and decomposed animals and plants. soil support plants growth and animal life.
FACTORS INFLUENCING SOIL FORMATION
Soil formation is sometimes called Pedogenesis The formation of soil is mainly initiated by weathering process. There are several factors which influence soil formation these are as follows
a) PARENT ROCK MATERIAL
This is one of the Achief factors of soil formation. It determines soil type, color, depth, rate of soil formation, structure, texture, porosity and soil fertility. Parent rock influence soil maturity, therefore hard rocks take a long time to mature while soft rocks take a short time to mature. Shallow and poorly productive
The most variable elements under climate are temperature, precipitation (rainfall) and wind Temperature affects decomposition of organic matter hence it influences the development of soil profile Rainfall and wind encourage the formation of soil due to their role in the erosion process On the other hand rainfall adds moisture which encourages chemical and physical weathering
c) LIVING ORGANISM
Some plants have nodules with bacteria which add nitrogen into the soil hence improve aeration of soil. Microorganisms are active in the decomposition of the organic matter to form humus on the other hand barrowing of animals and plant roots facilitate the state of both physical and chemical weathering hence lead to the formation of soil easily.
d) RELIEF [TOPOGRAPHY]
The role of relief in soil formation is mostly in indirect way. Relief influences climate and vegetation. The most important aspect of topography in soil formation, steep slopes areas soils are shallow due to erosion while on a gentle slopes and low land areas soils are deep due to deposition of materials.
This involves the duration that has been taken in the process of soil formation. Time determines the maturity of soil, when soil formation has taken a long time, soil tends to be mature i.e. they are deep and well developed.
IMPORTANCE OF SOIL
Soil is virtual life support to both flora and fauna organism ,because all the organisms depend on the soil as their source of food . soil is therefore important to both plants and animals life in various ways including the following:-
(vi) Habitat for organisms soil functions as a habitat for organisms such as burrowing rodent, earthworms and termite. These organisms perhaps are significant in the process of soil formation
IMPORTANCE OF HUMUS
i) Improving the structure of the soil and its water retaining capacity limits the leaching process and improves the soil acceleration
ii) Storing and supplying nutrients to the plant like nitrogen, phosphorus, potassium, calcium – high production.
iii) Humus regulates the temperature of the soil and soil pH iv) The living micro-organisms help in decomposition.
2. Inorganic matter This forms 45% of the total volume and is made up of minerals from the parent rock. Minerals constitute several nutrients which are needed by plants.
3. Soil water Forms 25% of the total volume and it is one of the most important soil components. It is derived essentially from rainfall especially from infiltration and through flow.
IMPORTANCE OF WATER
a) It regulates temperature in the soil
b) It helps in the solution and transfer of nutrients in the soil
c) Too much water in the soil leads to the leaching of mineral nutrients in the soil
d) It controls chemical processes like weathering as well as mechanical weathering.
4. Soil air It forms 25% of the total volume. It consists of the soil atmosphere from which plants and soil organisms obtain oxygen for their metabolism and dispose of carbon dioxide and other gases.
A: PHYSICAL PROPERTIES
1. SOIL PROFILE
This is the vertical section from the surface to the parent rock characterized by distinct layers usually of different texture and colors.
A- horizon Is the topmost layer and can include organic matter to form humus.
Horizon ‘A’ varies in color from place to place for example dark, grey etc. this zone is also called the zone of Elleviation from which materials are washed down ward. It is in this place where leaching process takes place.
B- horizon This zone is also known as the zone of accumulation. In this layer the materials washed from ‘A’ horizon are deposited or accumulated.
D-horizon (Bedrock) It is the un weathered parent rock. it is the parent in sense that it is the source of the in organic content of the soil
2. SOIL DEPTH
Soil depth varies from place to place depending on maturity. Maturity is influenced by the nature of the rock as well as duration of the soil forming processes which have been operating. Soil depth is important for agricultural activities. Thus deep soil is important for agricultural activities while shallow soil is not good for cultivation.
3. SOIL COLOUR
Soil color is determined by the materials and the mineralogical composition from which the soil is derived and organic matter content. It varies from one place to another. Soil color can be classified and described in terms of; a) Dark [ black, grey, dark brown etc ] and cinnamon b) Bright [ yellow, orange, red, reddish brown and yellow brown ] c) Light [ white, whitish grey]
4. SOIL TEXTURE
This refers to the degree of coarseness of soil (especially soil mineral particles). It can also be referred to as variations in the particle size, caliber or mechanical composition According to the soil texture, soil can be classified as; a) Coarse sand (2 to 0.2mm) b) Fine sand c) Silt (0.02mm) d) Clay (less than 0.002mm) e) Loan soil is a mixture of sand, clay and silt. NB; measuring of soil texture can be done through the use of finger testing
IMPORTANCE OF SOIL TEXTURE
1) It influences soil porosity, permeability, structure and retention capacity
2) It influences plant growth and root penetration
3) It influences the cultivation during agricultural activities
4) It influences soil resistance against erosion
5) It influences soil fertility
5. SOIL POROSITY
These are the total volume of the pores or empty spaces between particles of the soil materials especially in the soil. Soil porosity is mainly influenced by soil texture, organic matter, soil structure, individual undisturbed soil aggregate compounds referred to as peds.
IMPORTANCE OF SOIL STRUCTURE
i) It determines water retention capacity and aeration
ii) It is an indicator of soil fertility or suitability for agricultural activities, settlement locations and construction iii) Good structure facilitates the activities of the micro organism
iv) It influences the cultivation process
v) It influences the plant growth by influencing the root penetration and water retention -Therefore it is quite fundamental to note that the best soil is that which influences the water holding and aeration capacities of the soil.
This is the arrangement of soil particles into aggregate compounds particles. Individual undistributed soil aggregate referred to as peds.
7. SOIL TEMPERATURE
Soil has a certain degree of temperature and this tends to vary from one place to another due to the variation in the climatic condition.
IMPORTANCE OF SOIL TEMPERATURE
1) It controls biochemical and chemical processes especially the decomposition of organic matter and plant growth. Thus plant growth and decomposition tend to be fast in warm areas and slow in cold areas, this is due to the fact that growth cells and micro organisms tend to be very active in the warm areas unlike in the cold areas where they tend to be inactive or less active.
2) It also determines the existence of micro organisms in certain areas. In extremely hot areas and cold areas may not support the survival of animals and other micro organisms
3) It controls the amount of moisture in the soil where there is high evaporation soil moisture is less or the soils are dry
B: CHEMICAL PROPERTIES
These include soil properties like soil reaction (PH), reaction exchange and leaching. Soil reaction ( soil PH) This is the term used to describe the degree of acidity and alkalinity in the soil and it is related mainly to climate. This degree of acidity and alkalinity is expressed in the PH value which is the measure in terms of hydrogen ions concentration held by the soil colloid. Soil PH scale range from 1 to 14 where ph 7 is neutral, the condition below 7 is acidic while the condition above 7 is alkalinity which means it has more alkalis.
IMPORTANCE OF SOIL PH
It helps in determining the selection of crops and agricultural distribution It affects plant growth such that where there is too much acidity there will be poor plant growth. This is because the increase of acidity leads to the increase in leaching with affects soil structure
FACTORS INFLUENCING SOIL FORMATION
Soil formation is sometimes called Pedogenesis. The formation of soil is mainly initiated by weathering process. There are several factors which influence soil formation these are as follows:
e) TIME This involves the duration that has been taken in the process of soil formation. Time determines the maturity of soil, when soil formation has taken a long time, soil tends to be mature i.e. they are deep and well developed.
IMPORTANCE OF SOIL
Soil is virtual life support to both flora and fauna organism , because all the organisms depend on the soil as their source of food . soil is therefore important to both plants and animals life in various ways including the following:-
(vi) Habitat for Organisms soil functions as a habitat for organisms such as burrowing rodent, earthworms and termite. These organisms perhaps are significant in the process of soil formation
SIMPLE SOIL CALSSIFICATION
Soil classification refers to the grouping of soil according to specific characteristics, such as properties or factors like climate also soil can be classified according to the age, texture and color. One common classification is that based on texture. According to the soil texture triangle, there are three main texture namely sand, silt and clay. This is based on the size of their particles as discussed earlier. There percentage content of each one of these determines the type of soil according to texture. Note that sandy soil have sand content of over 45% clay soil have above 27% while silt soil have silt content of above 40%.
SOIL TEXTURE TRIANGLE
SILT CLAY: Sand up to 20% silt between 40% and 60% and clay between 40% and 60%. This soil is composed of almost fine particles throughout. It is smooth and has to some extent the soapy feel of silt but has a degree of stickiness because of the high proportion of clay
Soil erosion is the wearing away, detachment and removal of soil material from one place to another place through the agents like water, wind, ice etc
AGENTS OF SOIL EROSION
1) Water This is the most important agent of soil erosion Erosion by water involves: Splash erosion caused by rain drops Sheet erosion which involves the removal of the maximum cover of soil by surface water Sill erosion which leads to the formation of small channels called sills on the surface Gully erosion that leads to the formation of deep troughs called gullies due to severe under cutting River erosion that takes place in the specific channels called river valleys
2) Wind This is another agent of soil erosion. It takes place in arid and semi-arid areas or where the soil is loose
3) Ice It is also another agent of soil erosion. It takes place in cold areas where there is the formation of ice
4) Gravity This leads to the gradual movement of weathered material down the slope without involving transporting agents.
TYPES OF SOIL EROSION
1) Normal geological erosion It is the wide spread type of erosion that occurs wherever there is a natural flow of energy and matter on the earth’s surface without man’s influence. It is normally very slow and so infectious to the soil cover of the world.
2) Accelerated soil erosion Is the type of erosion associated with man’s activities [man included] it is spectacular in nature therefore it has attracted man’s attention.
FACTORS AFFECTING /ACCELERATING SOIL EROSION
1) Climate Where there is heavy rainfall erosion tends to be severe while where there is low rainfall erosion is low
2) Topography On steep slopes soil erosion can be fast while on gentle slopes the rate of erosion tends to be low
3) Nature of soil This depends on the characteristics or features like texture, structure, permeability e.tc. Unstable soils with coarse textures are prone to severe erosion than fine textured stable soils
4) Vegetation cover Where there is dense vegetation soil erosion is less or low rate unlike where there is scanty or no vegetation cover.
5) Good management of the soil Which involves the way human beings use soil wisely and skillfully and undertaking conservation measures to reduce or mitigate erosion through afforestation.
6) Poor management That involves unwise use of soil through over cultivation, over grazing and deforestation.
7) The increase in pollution This leads to the over exploitation of resources especially minerals, forests and over cultivation.
EFFECTS OF SOIL EROSION
(v) provides sand for building and construction activities. sand which is eroded from steep slope is deposited on river bed from where it is scoped when the water flows in the river has diminished or even stopped. The sand is then used for construction purpose this is common in Mpiji river at Bunju Dar es salaam and most parts of kisarawe II in coastal region.
POPULATION GROWTH AND THE RATE SOIL EROSION ON QUALITY LIFE
• When life becomes unbearable in the rural areas because of severe soil erosion, able-bodied persons especially men migrate to urban areas to other better areas in search of employment.This reduce population in the affected areas as well as the required man power to develop the areas. T
ECHNIQUES FOR SOIL CONSERVATION
There are two types of terraces