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SOIL FORMATION AND TOPOGRAPHY

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Presentation ByMr. Allah Dad Khan

Agriculture Adviser Sohni Dharti TV KPK Bureau

TOPOGRAPHY IS A FIELD

of geoscience and planetary science comprising the study of surface shape and features of the Earth and other observable astronomical objects including planets, moons, and asteroids. It is also the description of such surface shapes and features (especially their depiction in maps). The topography of an area could also mean the surface shape and features themselves

FACTORS OF SOIL FORMATION

1.Climate and soil formation 2.Biota and soil formation 3.Parent Material and soil formation 4.Time and soil formation 5.Organisms and soil formation 6.Topography and soil formation

1.CLIMATE AND SOIL FORMATION

1. Arid : Minimal leaching, slow dissolu2. Humid: Extensive leaching, rapid

Extensive leaching, rapid dissolution dissolution

3. Cool : Active physical weathering, slow Active physical weathering, slow chemical weathering. Buildup of OM.

4. Warm: Strong chemical weathering, rapid Strong chemical weathering, rapid OM decay (nutrient cycling) OM decay (nutrient cycling)

CLIMATE AND SOIL FORMATION CONTD Climate is dominant factor in soil

formation, climate influence soil formation largely through precipitation and temp and air.

CLIMATE AND SOIL FORMATION CONTD Precipitation:I. i. It primarily regulates the moisture air regime of

the soil and determines the leading trends in soil profile depending upon available percolating water.

II. ii. Rainfall also affects profile development through erosion producing thin soils on steep slopes and deposition of soil material down hill.

III. iii. The intensity, frequency and distribution of precipitation influence the course of soil formation.

IV. iv. With increasing moisture, nitrogen and carbon content, clay content, aggregation, saturation capacity and exchangeable hydrogen tend to increase.

V. v. Exchangeable base and pH value tends to decrease with increasing moisture.

CLIMATE AND SOIL FORMATION CONTD Temperature:

Temperature affects the velocity of chemical reactions, which approximately doubles for every 100C increase in temperature. It influences the organic matter decomposition and microbial activities in soil though the evapotranspiration phenomenon. Temperature also determines the efficiency of rainfall. In general, with increase in temperature the depth of weathering and clay content show increase on the contrary nitrogen, organic matter, silica, alumina and base alumina

ratio tends to decrease with rising temperature.

2.BIOTA AND SOIL FORMATION 1. Diversity and activity Diversity and activity 2. Plant canopy Plant canopy

a. Root exudates promote weathering� b. Root exudates promote weathering � c. Grasslands: Base Grasslands: Base

ations cations, humus , humus -mineral mineral interaction (strong A horizon). interaction (strong A horizon). �

d.Forest: Lower base saturation, less humus a. Confers: low B.S., less incorporated OM b. Deciduous: Higher B.S., more OM

3.PARENT MATERIAL AND SOIL FORMATION

A. Solid Rock 1.Basalat ( Mafic) ; High Base Saturaion

2. Granite(Felsic) : Lower Base Saturation

B. Transporated Material 1. Alluvium

2.Colluvium c. Eolian

PARENT MATERIAL TRANSPORTED Agent Deposit

Graviy Colluvial

Water Alluvial

Marine

Lacustrine

Ice Glacial

Wind Eolian

ALLUVIAL DEPOSITSEnergy of water determines size of

particles transported -Flood plains, terraces (old flood plains), deltas are rich, fertile soils (typically) -Alluvial fans are coarser in texture but remain productive

WEATHERING OF PARENT MATERIAL

1. Mechanical/Physical a) Thermal expansion/contractionb) Freeze/thaw /Frost Widging �c) –Erosion (water, ice, wind)d) –Biological (plant roots…)e) Grinding of rocks/Abrasion

WEATHERING OF PARENT MATERIAL

2. Chemical a) – Hydration b) – Hydrolysis c) – Acidic Decomposition d) Water, inorganic and organic acids �e) – Complexation Decomposition f) Organic acids�g) – Reductive/oxidative dissolution

FACTORS THAT INFLUENCE CHEMICAL WEATHERING Climate 

Living Organisms      bioturbation      acid production and mineral decomposition Time Mineral composition     Goldich Dissolution Series      (Bowen's Reaction Series)

Chemical Weathering Products     Clays     Metals ores     Rounding of boulders (chemical exfoliation)

WEATHERING STAGES IB=N SOIL FORMATION

1. Initial – Unweathered parent material.2. Juvenile – Weathering started but much

of the original material still Unweathered.3. Virile – Easily weatherable mineral fairly

decomposes, clay content has increased.4. Sensile – Decomposition reaches at final

decomposition stage only most resistance minerals survive.

5. Final – Soil development completed under prevailing conditions.

4. TIME AND SOIL FORMATION A. Recent : Little profile development

( Weakly Weathered , Little Clay movement)

Primary Minerals Present B. Old : Well Developed Horizon Secondary Minerals

5. ORGANISMS AND SOIL FORMATION The organisms living in and on the soil form distinct soil

types. Coniferous forests have acidic leaf litter that form soils classed asinceptisols. Mixed or deciduous forests leave a larger layer of humus, changing the elements that are either leeched or accumulated in the soil, and thereby forming soils classed as alfisols. Prairies have very high humus accumulation, creating a dark, thick A horizon characteristic ofmollisols

Plant and animal activity produces humic acids that are powerful erosion agents.  Plants can physically erode as well as chemically erode.  Plants stabilize soil profiles, Animals (including man) tend to destabilize the soil profile, increasing erosion.

TOPOGRAPHY AND SOIL FORMATION

Topography and soil formation: The prominent types of topography designations as given in FAO guidelines are:

1. Flat or almost flat: Land surface with slope less than 2%

2. Undulating: Land surface with slope between 2-8%

3. Rolling: Land surface with slope between 8-16%

4. Hilly: Land surface with slope between 16-30%

5. Steepy dissected: Land surface with slope greater than 30%

6. TOPOGRAPHY AND SOIL FORMATION : SLOPE AND ASPECT

1. Warmer Drier : Less develpoped2. Cold Wet : More Developed ,more clay3. Shallow Soils4. Deep Soils : Fine textured

TOPOGRAPHY AND SOIL FORMATION  

Topography has a significant impact on soil formation as it determines runoff of water, and its orientation affects microclimate which in turn affects vegetation. For soil to form, the parent material needs to lie relatively undisturbed so soil horizon processes can proceed. Water moving across the surface strips parent material away impeding soil development. Water erosion is more effective on steeper, un vegetated 

Blue iceberg

PROCESS OF SOIL FORMATION

1.Transformations:Mineral weathering, OM Mineral weathering, OM decomp

2.Translocations : Transport of inorganic and organic material

3.Additions : OM, particles ( OM, particles (eolian, aluvial aluvial, colluvial colluvial )

4.Losses : a. Erosión b.Leaching

SOIL DEVELOPMENT PROCESS SPECIFIC A.PEDOGENIC PROCESSES

Pedogenesis is   (from the Greek pedo-, or pedon, meaning 'soil, earth,' and genesis, meaning 'origin, birth')

be defined as the process of soil development. Late in the 19th century, scientists Hilgard in the United States and the Russian Dukuchaev both suggested independently that pedogenesis was principally controlled by climate and vegetation.

This idea was based on the observation that comparable soils developed in spatially separate areas when their climate and vegetation were

similar.

SOIL DEVELOPMENT PROCESS PEDOGENESIS CONTD

 In the 1940s, Hans Jenny extended these ideas based on the observations of many subsequent studies examining the processes involved in the formation of soils. Jenny believed that the kinds of soils that develop in a particular area are largely determined by five interrelated factors: climate; living organisms;parent material; topography; and time

PRINCIPAL PEDOGENIC SOIL DEVT PROCESSES

A large number of processes are responsible for the formation of soils. This fact is evident by the large number of different types of soils that have been classified by soil scientists . However, at the macro-scale we can suggest that there are five main principal pedogenic processes acting on soils. These processes are laterization, podzolization, calcification, salinization, and gleization.

1. LATERIZATION 

In this process, silica is removed while iron and alumina remain behind in the upper surface / layers and usually there are no well-defined horizon. Laterization is favoured by rapid decomposition of parent rocks under climates with high temperature and sufficient moisture for intense leaching. Podsolization and latrization produce soils that belong to the pedalfer (iron accumulating) group.

2. PODZOLIZATION

Podzolization is negative of calcification where as calcification tends to concentrate calcium in the lower part ‘B’ horizon podsolization reaches the entire solum. Apart from the calcium the other bases are also removed and the whole soil becomes distinctly acidic. Process is mainly acid leaching.

3. CALCIFICATION

It is the process of precipitation and accumulation of calcium carbonate (CaCO3) in some part of the profile. The accumulation of CaCO3may result in the development of acidic soil. Such soil belonging to group called pedacal.

4. SALINIZATION Salinization is a process that functions in the

similar way to calcification. It differs from calcification in that the salt deposits occur at or very near the soil surface. Salinization also takes place in much drier climates. Accumulation of soluble salts under dry climate or no rainfall. Salts accumulate on soil surface. Na+, K++, Ca++, Mg++. Soil becomes saline due to high rate of evaporation, reclaimed by leaching, flooding. (pH8.5) Grow salt tolerant crops, shevri, Dhaincha.

5. GLEIZATION  It is a process of soil formation resulting in the

development of glei (or gley horizon) in the lower part of soil profile above the parent material due to poor drainage condition and where water logged conditions prevail such soils are called hydromorphic soils. Gleying may be observed at any depth depending on the depth of ground water.

6. PEDOTURBATIONInversion of soil takes place in deep black cotton soils

which contain montmorillonite clay colloid (vertisol) has max swelling shrinkage capacity. As alternate weting and drying, expansion and contraction takes place due to which cracks is formed. Due to crack formation A horizon goes down and soil B horizon comes up. These are also known as self ploughed soils. Therefore in dry farming technique ploughing once in three years is recommended to conserve the soil moisture and since the inversion of soil takes place naturally there is no need of ploughing every year.

7. DECALCIFICATION

It is the reverse of classification i.e. the process of removal of CaCO3 or Ca ions from soil by leaching.

8. ALKALINIZATION

Accumulation of sodium salts only like Na2Co3 and Na2(CO3)2.

B. FUNDAMENTAL PROCESSES OF SOIL FORMATION

1. Humification: Helps in formation of surface layer, called Ao horizon. Its characteristics depends upon the nature of vegetational residue and the way it becomes decomposes and synthesized into new organic compounds. The percolating water passes through this humus layer dissolves certain organic acids affect the development of lower A and B.

B. FUNDAMENTAL PROCESSES OF SOIL FORMATION CONTD2. Eluviation: Elevation means washing

out. It is a process of removal of constituents in suspension or solution by the percolating water from the upper to the lower layer. Mechanical eluviation removes finer suspended fraction of soils, producing textural profiles by a coarse texture.

B. FUNDAMENTAL PROCESSES OF SOIL FORMATION 3. Illuviation: The process of deposition of

soil material (Removed from the eluvial horizon) in the lower layer is known as illuviation. The horizons formed by this process are termed illuvial horizons.

TOPOGRAPHY MODIFIES Topography generally modifies the development

of soil on a local or regional scale. Pedogenesis is primarily influenced by topography's effect on microclimate and drainage. Soils developing on moderate to gentle slopes are often better drained than soils found at the bottom of valleys. Good drainage enhances an number of pedogenic processes of illuviation and eluviation that are responsible for the development of soil horizons. Under conditions of poor drainage, soils tend to be immature.

TOPOGRAPHY MODFIES CONTD

Steep topographic gradients inhibit the development of soils because of erosion. Erosion can retard the development through the continued removal of surface sediments. Soil microclimate is also influenced by topography. In the Northern Hemisphere, south facing slopes tend to be warmer and drier than north facing slopes. This difference results in the soils of the two areas being different in terms of depth, texture, biological activity, and soil profile development.

TOPOGRAPHY COORELATION WITH CLIMATE

Soils tend to show a strong geographical correlation with climate, especially at the global scale. Energy and precipitation strongly influence physical and chemical reactions on parent material. Climate also determines vegetation cover which in turn influences soil development. Precipitation also affects horizon development factors like the translocation of dissolved ions through the soil. As time passes, climate tends to be a prime influence on soil properties while the influence of parent material is less.

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