Soil Formation

Soil Define soil The term soil is derived from the latin word “solum”” which means ground. Therefore can be defined as the uppermost surface layer of loose or unconsolidated material which overlies the crystal cocks and on which plants grow-ORSoil is the natural body of mineral, organic and hutrient constituents wich result from the interaction of the country ack with the environmental

factors of climate, topography. plant and animal life

Factors for Soil Formation

Describe factors for soil formation Soil formation (pedogenesis) is principally initisted by the weathering of the parent rocks. Weathering can be chemical or mechanical. But the type of soil and rate of soil formation depend on a number of interacting factors (interplay of factors) in a particular environment, hence soil is the product ofits own environment Soil continuously changes. ‘The changes are generally slow but in certain circumstances.

especially where human activities are involved, the changes can be rapid, The study of soil involves understanding the factors responsible for its formation, ‘These factors are parent materials, climate, living organisms, topography and time 1 Parent Material (Rock):This is the most important factor in soil formation since it determines the type of soil formed, soil colour, soil depth, the rate of soil formation, soil

structure, soil texture, porosity and mineralogical composition or its fertility. It also influence soil maturity, such that if the rock is hard, It takes a long time for soil to mature while the rate of maturity is fast where the parent rock is soft. The fast maturity of sous, formed from soft rock 1s due to the fast rate of weathering process, Mature soil are deep and productive while immature soils are shallow and less productive,

2 Living Organisms (Biotic):These include the influence of plants, animals as well as human beings, Vegetation influence both chemical and mechanical weathering leading to the development of the soil profile. Also vegetation contribute to soil fertility by adding humus in the soil after dying and decomposing. Some plant roots (legumes) have nodules with bacteria that fix nitrogen into the soil. Plants roots modify the soil by increasing porosity, improving the

soil depth and aeration Micro – organisms are active in decomposition of the organic ratter to form humus Burrowing animals facilitate weathering process by loosening the soil particles.

Lastly man’s activities like cultivation, break up the rocks into smaller fragments. Man also adds humus to the soil which contribute to sol profile development

• Climate: The important variables under climate melude temperature, precipitation and

wind. Temperature affects the rate of decomposition of organic matter, it contribute t0 soil profile development through weathering as well as the rate soil development. Where there is high temperature, soil development tends to be fast due to the fast rate of weathering, and where temperature is low, there is also a low rate of soil development due to the low rate of weathering process. Precipitation also affects soil profile development. In some areas soil is eroded, leading

to soil profile destruction while in areas deposition leads to positive soil development due to accumulation of weathered materials and organic matter: Rainfall adds moisture, which facilitate both chemical and mechanical weathering and hence soil profile development. Wind has both positive and negative impacts on soil profile development. It can erode the soil through deflation leading to soil degradation or it can deposit some materials at the edge of the desert to form the

soil called Hoes,

• Relief (topography):The role of topography in soil formation is mostly indirect. It

influences climate and vegetation. It controls the rate and nature of weathering, removal and deposition (redistribution) of the soil parent materials, The most important aspects of topography 8 a factor of soil formation are slopes; altitudes, aspects and location along the slope. Soil erosion is rapid on steep slopes and less on gentle slopes. Therefore on steep slopes soil profiles are shallow while on gentle slopes they ate expected to be deeper Also leaching are more

pronounced in the upper-slope areas leading among other things to well-drained soil Altitude affects soil mainly through the action of climate and vegetation, Altitude lowers temperature and increases precipitation. Thus leads to zonation of climate, vegetation and soil along hillsides, In terms of aspects, the side that receive more sunshine tends to have well developed soil than the side which receives low amount of sunshine since isolation accelerate plants growth and the

weathering process.

• Time: The time factor may be associated with the age of the country rock especially

those on which soil have been directly formed. tt may also be assoviated with the duration of the ‘operation of soil formation process, that is whether the soil has sufficient time to form mature profiles and associated characteristics or not. When soil formation has taken a long and enough time, soil tends to be more mature, they are usually deep and well developed

The Importance of Soil

Assess the importance of Soil The following is importance of soil formation

• Medium for plant growth.Soil is where most plants grow. Soil provides anchorage for

the plants as well as protection of roots from damage It is where or a medium through which water, air and nutrients are made available to plants. The well-aerated soil facilitates the absorption of water and nutrients from the soil by plants, 2 Soil support animal life.As soil support plant life it also support animal life because plants are the source of foods to animals and this is most for herbivores, Also some animals eat

soil as food in form of salt licks for example pregnant women who lack some minerals in theit bodies,

• Soil provide habitat for living organisms.tn the soil there are some animals living there

‘example burrowing animals like rodents, earthworms and termites 4, Provide sites for agricultural activities. The fertile soil promotes agriculture activities, both animal husbandry and crop cultivation. ‘Ihis is because soil supports the growth of pasture for animals,

• Provide settlement Soil influences distribution of seitiement for example the areas with

good fertile soil are densely populated compared to the areas with poor soil 6 Soil provide building materialsSoil is used in making bricks, tiles and white wash. All these materials are used in building houses, bridges ete. Also soil is used directly in road construction commercial purposes. Also it s used to manufacture fertilizers as it contain minerals for example the fertilizers that contain phosphate eg. [n Minjingu (Manyara) region.

& It provides raw materials for pottery and ceramics.Soil is used in making pots and

Soil Composition and Properties

Soil Composition and Properties

Soil is made up of the following components

• Organic matter (humus)
• Inorganic matters (minerals)

. Soil water and soil air Organic matter (humus) a result of decomposition of animalplans remains

• Itamproves the structure of the soi
• Itregulates the soil temperature.

. It leads to higher agricultural production Inorganic matter (minerals) constitute some nutrients needed by plants for growth Soil water This forms 25% of the toial volume. It is one of the important soil constituents. It is derived essentially from rainfall especially from infiltration; Too much water in the soil leads to leaching and hence loss of nutrients.

Importance of water to soil

• Itregulate the soil temperature
• It control the chemical process like chemical weathering as well as mechanical

weathering

• Ithelps in the solution and transfer of nutrients in the soil

Soil Air

This forms 25% of the total volume and constitutes the soil atmosphere ftom which plants and animals obtain oxygen for theit metabolism. Air accelerates oxidation and biological activities and aerated soil lead to good production while poor aerated soil will lead to poor production

Soil Profile and Characteristics

Soil Profile

Define soil profile Soil profile is the vertical section of the soil from the surface to the parent rock characterized in distinct layers (horizons), usually of different textures and colours. Ideal soil profile has horizons ABC Soil Profile and its Characteristics Mustrate soil profile and its characteristics Physical propertics of the soil include soil profile, soil depth, soil colour, soil texture and soil structure

Chemical properties of the soil includes soil P.H, carbon exchange and leaching ‘tx Soil Layers : ee 3 : eax 0 Horizon (humus) 7 q 4 Horizon (topsoil) q q E Horizon (eluviation layer) + ae : © aces B Horizon (subsoil) .

jae a 4 q oy By © Horizon (regolith) q : R Horizon (bedrock) 4

= BS SON

• A= Horizon = Is the top most layer which include organic matter to foxm Ao. This

horizon varies in colour from place to place example dark to grey. Its also called the zone of ‘cluviation from which the materials are washed down through leaching. +B Horizon — ts also called the zone of accumulation or illviation. In this layer materials washed from the A — horizon are deposited of aeeumulated. Accumulation of washed down materials lead to formation of another layer called Hatd Pan. Horizon A and B are also

referred to as Solum (soil) such that A-—horzon isthe topsoil and B – horizon isthe sub oil

• C~ Horizon is the partially weathered parent rock from which the soil develops. It is

underlain by D — Horizon which is afresh non – weathered parent rock.

Simple Soil Classification

Soil According to Textural Groups

Classify soit according to textural groups

SOIL DEPTH

Soil depth is the variation of soil from place to place due to materials influenced by the nature of the rock as well as duration of the soil forming processes, Soil is shallow especially in steep slopes due to erosion and in areas where the underlying rock is hard. Other places have deep soil due to soft parent rocks.

SOM. COLOUR

Soil colour is determined by the mineralogy composition from which the soil is derived and ‘organic matter content. It varies from one place to another. Soil colour can be used for

classification and description of soil ofa certain place. The colours are grouped int

• Dark (Black, grey, dark grey and dark brown)
• Bright (yellow, orange, red, redish brown)
• Light (whitish — grey, white)

Some soil can have one colour throughout like red earths and yellow brown

SOIL TEXTURE

This refers to the degree of coarseness or fineness of the soil materials especially soil mineral particles. It ean also be referred to as variation inthe particle size. According to soil texture, soil can be classified as 1 Course sand 2 to 0.2: mm diameter 2 Fine sand 02 t0 0.02 mm diameter

• Silt 0.0210 0.00 mum diameter
• Clay less han 0.002 mm
• Loan soil ie. mixture of sand, clay and silt

IMPORTANCE OF SOI TEXTURE

• influences the soil porosity, permeability, compaction, and structure

2 thinftuenees pant growth

• Itin uence cultivation during the agricultural activites
• infuonees sol fertty

SOIL TEMPERATURE

Soil has extain degree of temperature and this tend to vary from place to place due to the to the small amount of insolation recived there. In tropical areas soil are warm due to high

IMPORTANCE OF SOIL TEMPERATURE,

tt controls biochemical and chemical processes especially the decomposition of organic matter and plant growth,

• Itvontros the amount of moisture inthe soil

SOIL POROSITY

This refers to the total volume of pores or spaces between particles of the soil materials in Soil poresity is influenced by

• Soil texture ~ The Finer the particles the greater will be the total surface area. Hence the

soil with fine particles like clay has greater porosity

• Structure of the soil also influences permeability.

SOIL STRUCTURE

This refers to the arrangement of soil particles into aggregate compound particles. Individual undisturbed soil is called ped. The aggrewation of soil particles produce peds of different shapes and sizes when aggregation is absent as in loose sand soil, the soil is described as structure less.

Strongest of the soil is influenced by its organie matter.

IMPORTANCE OF SOIL STRUCTURE,

• Itdetermines water retention capacity and aeration
• isan indicator of soil fertility or sustainability for agricultural activities
• It influences plant growth by influencing the root penetration and water retention

CHEMICAL PROPERTIES

SOIL REACTION (PH)

Soil reaction is the term used to describe the degree of acidity and alkalinity m the soil and it resulis mainly fiom climate. This degree of acidity and alkalinity in the soil is expressed in the Pu, PH jis the value which is measured in terms of the hydrogen ion concentration PH. scale runs from to 14.The PH 7 is neutral. Any condition below 7 is acidic and any condition above 7 is alkaline.

IMPORTANCE OF SOIL PH.

• Ithelps in determining the selection of erops and agricultural distribution
• Itaffects plant growth such that where there is ton much acidity there will be poor plant

growth. This is because the increase of acidity leads to the inerease in leaching which affects soil structure:

LEACHING

This is another chemical property of soil referring to the process in which nutrients are washed down in solution from the top- soil layer. During leaching process the bases are washed down leading to concentration of hydrogen ions which in tum cause the increased acidity in the top soil Leaching is very effective in wet conditions

SIMPLE HYPOTHETICAL PROFILE FOR MATURE SOIL,

The soil profile varies from one place to another depending on the variation in environment conditions For example under deciduous forest, soil with litte organic matter can be produced (brown earth or brown forest soil) while in mid latitude grasslands deep black carth soil (chernozem) is formed,Chemozem has a lot of organic matter. In the desert area the soil profile usually lack the Ao horizon due to scareity or absence of vegetation.

SIMPLE SOIL CLASSIFICATION

Soil classification refers to the grouping of soils according to specific characteristics, such as properties or factors like climate also soil can be classified according to the age, texture and colour. One common classification is that hased on texture According to the soi! texture triangle, there are three main textures namely sand, silt and clay.

This is based on the size of their particles as discussed earlier. The 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%.

• CLAY LOAMESand content between 20% and 45% silt between 15% and 53% clay

between 27% and 40%, This one has sticky distinetion when moist because of clay.

• SILT CLAY LOAMEThe amount of sand is between 27% and 60%, silt between 40%

and 78% and elay between 27% and.40%. The high silt content makes it smooth and has a soapy feeling. Ibis less sticky than clay loam or silt elay

• SLT:This have over 80% silt particles, up to 20% sand and less than 12% clay. It is

predominantly smooth and has a typical Soapy feeling of silt

• SANDY CLAY:Sand between 45% and 65%, silt up to 20% and clay between 39% and

55%. In the presence of sufficient moisture this soil is plastic and sticky clay and sand ate dominant.

• CLAY:The proportion of sand goes up to 45%, while that of silt is up to 40% clay

account for above 40%. The sol i sticky when moist and has a plastie feel. I can be rolled into threads when moist and can be moulded into different shapes. And can retain Fingerprints

• 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 ofthe high proportion of clay

Soil Erosion

Soil Erosion

Define soil erosion In this subtopic there are various concepts to be discussed, these are definition of the term, agents of soil erosion and how they work, types of soil erosion and its effets on social and economic activities, Also, demonstrating ways of controlling soil erasion through the application of various conservation techniques.

Soil erosion is the wearing away, detachment and removal of soil materials from one place to another place through agents like water, wind and ice

How Agents of Soil Erosion Work

Examine how agemis of soll erosion work ‘There are several agents of soil cosion these are water, wind and ice

WATER

Water is the most important agent of soil erosion , the erosion by water involves the following:

• Splash erosioncaused by moving water from rain, this tends to remove some of the

materials from one place to another,

• Sheer erosionwhich involves the removal of the uniform cover of the soil by surface run-

offon gentle slopes.

• Rills erosionthat leads to the formation of small channels called rlls on the surface.
• Gully erosion,that leads to the formation of deep troughs ealled gullies due 1 severe

under cutting

• River erosion.takes place in the specific Chanel ealled river valley

WIND

Wind is another agent of soil erosion. It takes place in arid and semi-arid or where soil is loose The soil in such areas is dry, loose and unprotected because of the scarcity of vegetation. It is turned into dust which is then blown away by wind.

‘Types and Effects of Erosion to Social and Economic Activities Describe types and effects of erosion to social and economic activities ‘There are main two types of soil erosion which are normal geological erosion and accelerated soil erosion

NORMAL GEOLOGICAL EROSION

Is the wide spread type of erosion that occurs wherever there is # natural flow of energy and matier on the earth's surface without man’s influence. Itis fortunately very slow and so not normally injurious to the soil cover ofthe world

ACCELERATED SOIL EROSION

Is the type of erosion associated with man’s activities (man included). It is spectacular (very destructive) therefore it as attracted man’s attention. Its side effeets include physical loss arising From the reduced crop yield and total crop failure and or wasted efforts and money spent on unsuccessful soil conservation projects.

EFFECTS OF SOIL EROSION

Soil erosion leads to the followings effets both socially and economically

• Pollution of water bodies due to the introduction of materials eroded from the

surrounding areas,

• Loss of fertility which in tum causes the reduction in yields or total erop failure
• Migration of people from areas affected to the areas which have not heen affected by
• Over flooding of the rivers as a result of the creation of the small channels leading to the

river system

• Deforestation as a result of the death of plants due to the loss of soil
• Loss of habitat as a result of deforestation caused by the loss of soil
• Soil erosion can lead and accelerate rock weathering by exposing the underlying rock to

the weathering agents like temperature

• It leads to the cost incurred in during the process of conserving the soil, which has been

eroded.

• Soil erosion can destroy transport and communication systems like roads, railway lines

and telephone posts

• Itcan lead to the destruction of houses, rendering people homeless,

Population Growth and Rate of Soil Erosion on the Quality of Life Relate population growth and rate of soil erosion on the quality of life As discussed above we ean see that soil erosion can affect the quality of life of the people positively and negatively.

• When the region is severely affected by the soil ernsion, where crop production is

impeded, when useful soils are carried away, the region experiences shortage of food, This

causes famine and malnutrition. With inadequate nutrition child mortality rate goes up and

population grovth is impeded.

• When the foundation of existing buildings and roads are eroded. Accessibility to areas is

made difficult. Sueh areas are isolated in terms of social services such as hospitals and education Tho general health and welfare of the people become poor leading to increase in mortality and lowering of population.

• When life becomes unbearable in the rural areas because of severe soil erosion, zble-

bodied persons especially mon migrate to urban arcas to other better arcas im search of employment. This reduce population in the affected areas as well as the required man power to develop the areas.

‘The ways of Controlling Soil Erosion through the Application of Various

Conservation Techniques

Demonstrate ways of controlling soil erasion through the application of various conservation techniques The following are the some of the central measures that can be taken to control erosion:

• Afforestation and Reforestation:, fforestation is the planting of trees where no forest

has been known to exist Reforestation is the planting of trees on lan that previously had a forest

• Control of bush fires:When open grassland are burnt the soil is directly exposed to

agents of erosion

• Controlled open grazing:Overgrazing which is another cause of soil erosion should be

avoided by mulching the number of livestock kept on any piece of land.

• Erecting brushwood barriers:On land where gullies have developed, barriers of

brushwood or even stone walls can be constructed across the gullies to help trap the soil.

• Construction of cut-off drains:Cutoff drains are open trenches which are dug aeross the

slope and soil is heaped on their down ~ slope sides to form a kind of ridges. These drains prevent large amount of water that might have resulted in formation of rill, gully and sheet «erosion from down the slope

• Constructing of dams and weirs:These are structure that are built across river’s valley

for the purpose of controlling a river flow or for retaining water in a large reservoir within the valley. They may be made of earth’s (earth dam) and stone (rock fill damn)

• Use of artificial waterways:An artificial waterway is 2 small channel that is constructed

down a slope and into whieh surface run-off collects. Normally water from cut-off drains as well as from terraces should be discharged into rivers or into non-erodible areas such as stony grounds