Soil: Compilation of Essays on Soil | Geography

Here is a compilation of essays on ‘Soil’ for class 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Soil’ especially written for school and college students.

Essay on Soil

Essay Contents:

1. Essay on the Introduction to Soil
2. Essay on the Soil-A Living and Dynamic System
3. Essay on the Biotic Components of Soil-Number and Activities
4. Essay on the Interaction between Climate, Soil and Soil Biota
5. Essay on the Formation of Soil
6. Essay on the Soil Types
7. Essay on the Soil Profile
8. Essay on the Types of Soil Particles
9. Essay on the Soil Nature and Distribution of Vegetation

Essay # 1. Introduction to Soil:

In the last two or three decade’s environmentalists throughout the globe are really worried about the trend of climatic change experienced by mother earth. The history of earth reveals that the climate on earth was not always uniform rather it exhibited some great changes in different geologic era. The climatic changes in pre historic earth were probably due to astronomical or geologic reasons.

But with the advent of human civilization and advancement of technological knowhow the climatic scenario has shown a rapid change, even at a faster rate than the earlier ones. All the ecosystems with their biotic and abiotic components have either been affected by this climatic change or going to be affected very soon. Soil, as a part of terrestrial ecosystem, is not an exception to this.

---

Essay # 2. Soil-A Living and Dynamic System:

Soil as a habitat, as a part of terrestrial ecosystem and as an abode of innumerable number of organisms is tremendously complex and has often been considered to be a living and dynamic system. It is the shallow upper layer of earth’s crust and is derived from the massive rocks through a process of weathering. Both climate and biosphere are believed to play a significant role in the formation of soil and in the development of soil profile.

The colour, texture, physicochemical nature and biotic components of soils exhibit wide range of variation in different climatic regions on earth surface. Besides being considered as a living and dynamic system, soil has also been regarded as a three phase system, the solid, liquid and gaseous phases. The solid phase is being represented by soil particles (of varying sizes) and organic matter.

The particles, sand, silt and clay are derived from weathered rocks and are present in varying proportions in different types of soils. The soil organic matter, an important source of nutrients is a heterogeneous mixture of comminuted and partly decomposed fragments of litter, animal carcasses and dead microbial cell. The water present in small or large amount in any soil represents the liquid phase. Soil air found in soil pores represents the gaseous phase of soil.

The oxygen and nitrogen ratio in soil air is more or less identical to atmospheric air. But the content of carbon dioxide is comparatively higher in soil air, it is about 0.03 per cent by volume in atmospheric air while it is more than 0.2 per cent in soil air. But water vapour content in both atmospheric air and soil air exhibits variation and depends on climatic factors like temperature, humidity, rainfall, etc.

The formation of soil depends on five factors viz., parent material, topography, time, climate and biosphere. The first three are called passive factors since they represent soil forming mass and conditions affecting it.

The last two viz. climate and biosphere are termed active factors since they supply energy to act upon the soil forming mass for the process of soil formation. Temperature and moisture are two important climatic agents that take active part in soil formation. The biosphere which includes both plant and animal world exerts significant influence on soil genesis.

The weathered materials or parent materials (developed through rock weathering) combine with organic matter and lead to formation of soil for which soil has often been referred to as “organo-mineral complex”. But the soil formation is not complete or it is not considered to be mature until the materials of soil are arranged in distinct layers or horizons forming the soil profile.

It has now been established that exact nature of mature soil profile depends upon the interactions between climatic factors, the biological agents, the topography of the land and nature of the parent rock.

---

ADVERTISEMENTS:

Essay # 3. Biotic Components of Soil-Number and Activities:

i. Microflora:

Among the microbial organisms present in soil, bacteria outnumber all other groups in numerical abundance and are the most important participant of varied biological activities going on in soil. The bacteria in soil have numerous morphological and physiological adaptations that enable them to utilize their habitat effectively and successfully. The most important physiological adaptation is their capability to slow down the metabolic rate in order to obtain relatively high growth rate from meager resources available in soil.

The decomposition of animal and plant residues in soil are effectively carried out by heterotrophic bacteria which are numerous in number and their substrate selectivity varies from species to species. In addition to their participation in decomposition process some heterotrophic bacteria are known to take part in non-symbiotic nitrogen fixation.

The actinomycetes (intermediate forms between bacteria and fungi) are mostly free living saprophytic soil-form that are capable of decomposing various carbonaceous substances. In addition, they are known to degrade many polymers such as chitin, cellulose and hemicelluloses at a relatively higher soil pH. Many of the soil actinomycetes are known to exude antibiotics like streptomycin which is effective in controlling many human diseases.

The fungal flora in soil are major contributors of soil microbial biomass. They are obligate aerobes and heterotrophs and their main role in soil is the decomposition of organic matter from the simplest sugars and amino acids to the most resistant polymers such as lignin and complex soil humic acids.

Since fungi exhibit greater tolerance to acidity than bacterial heterotrophs, the decomposition of organic matter in more acid soil is predominantly a fungal process. For which in acid forest soils, fungal population is more favoured than bacterial flora. The symbiotic as well as mycorrhizal association of fungi with plant root is of considerable importance in regulating nutrient uptake, disease resistance, water relations and ultimately growth of associated plant partner.

The algal population in soil is photoautotrophic in metabolism and are largely restricted to surface soils or large cracks where sunlight can reach. The algae are known to produce large amount of polysaccharides that act as aggregating agents and help in developing and maintaining stable soil structures.

The microbial community in soil is considered to be the main driving force in soil ecosystem because it is this biomass that controls the rate of decomposition, mineralization, humification, nitrification and other biogeochemical processes in soil. But they are not evenly distributed and prefer certain niches or rhizospheric regions which may contain organic and inorganic substances as well as some amount of moisture. But the activity and performance of these microbial components in soil depend to a considerable extent on the presence of faunal community that are closely associated with the microbes.

ii. Soil Fauna:

The faunal component in soil is represented by animals of different phyla which according to body size are divided into three – microfauna, mesofauna and macrofauna. The protozoans belong to microfauna category and include flagellates, ciliates and amoebae. These forms secrete mucin or mucilaginous substances which help to bind the particles together leading to the formation of soil aggregates.

Soil nematodes have received much attention of the researchers for their damaging role as plant parasites in agricultural fields. But many of them are known to be free-living. They are abundant in soil and take active part in destruction of dead plant materials and also in the decomposition of animal matter. Earthworms and enchytracids (potworms), two important component of annelidan fauna, contribute a lot in decomposition of litter.

They are known to possess enzymes in their gut that accelerates the degradation of organic matter and thus help in releasing nutrients. In addition, the burrows and channels created by them allow easy penetration of air and water and make soil relatively porous. The casts released by earthworms are rich in mineral contents and they are in a more easily available form. Earthworms help considerably in aggregate formation in soil which is evident from large number of aggregates in earthworm rich soil.

The arthropod fauna in soil is fairly rich and include varieties of forms such as acarines, collembolans, centipedes, millipedes, isopods, pseudoscorpions and different insects notable among them are ants, termites, beetles, gryllotalpids, earwigs etc. In addition, different types of insect larvae are also well represented. Some component of arthropod fauna by accelerating the fragmentation of litter (comminution) leads to the completion of decomposition of litter layer that has already been initiated by micro-organisms.

The burrowing forms like ants and termites not only help in aeration and movement of water but also help in mixing and translocation of materials in soil profile. Non-borrowers like mites and collembolans help in aeration and drainage by eating decayed plant roots and thus leaving channels containing organically rich faecal matter. The microphytic feeders and carnivorous forms of arthropods may help in keeping down the population of harmful fungi and nematodes.

The land snails and slugs constitute important component of molluscan fauna in tropics and subtropics. They are found either on soil surface or in crevices or may be encountered below the soil surface. Land snails are known to prefer decomposed plant material probably because of the growth of fungal hyphae.

Thus feeding on surface vegetation and subsequent movement downwards indicate the probable role of molluscans in incorporating organic matter into the mineral structure of soil. But their role in decomposition of litter has not been established. They probably take part in breaking and altering the physicochemical nature of the Utter which subsequently promotes fungal and microbial growth.

Vertebrates like snakes, lizards, toads, frogs and burrowing mammals take shelter in soil temporarily or make this habitat as their permanent abode. But their role in modification or change of the physicochemical or biological properties of soil rather appear to be insignificant and has not attracted the attention of soil biologists for extensive study.

---

Essay # 4. Interaction between Climate, Soil and Soil Biota:

It is well known that air currents, water currents, snow cover and land mass influence the global climate while the climate of a region is influenced by latitude, altitude and availability of large bodies of water. The regional climate is a dominant factor that controls the formation of all soil, since it circumscribes the forms and rates of local weathering, the translocation of weathered products and other pedogenetic processes.

In case of global weathering climate is the major determinant of weathering process through its control of temperature and moisture, water flux and decomposition rates of organic material. In extremely cold climate weathering is practically a physical process while in cool and temperate climate a limited biochemical weathering may occur. But in hot and humid tropical climate geochemical weathering dominates that extend over very long period.

Climate is known to have a significant bearing on the decomposition process participated by soil biota. Decomposition of organic residues and the maintenance of soil structure are largely complimentary process in most soils. Because organic matter exerts significant effect on soil structure by acting as important cementing agent which binds soil particles together to form larger aggregates.

Decomposition, a very important biological process in soil may be defined as the sequence of organic matter transformation occurring after death of organism. These transformations involve two simultaneous but complimentary processes: mineralization and humification.

The first one is a catabolic process through which the elements contained in organic form within the biological tissues are converted to inorganic forms such as nitrate, phosphate and sulphate ions while the second one is an anabolic process where organic molecules are condensed into degradation resistant polymers called ‘Humus’ which may persist little altered for decades and centuries.

In order to assess the degree of importance in the involvement of decomposition process, Di Castri (1988) made a hierarchical analysis of the factors and placed climatic factors (moisture and temperature) in the first position being followed by edaphic factors, physical and chemical properties of decomposition resources and biological interaction between macro and microorganisms respectively.

We know that under normal situation of the environment the biotic components of the soil through their activities release different types of nutrients in the soil that are being taken up by the plants for their growth and development. This transfer process becomes more effective if there is a synchronization between the release of nutrients and their uptake by plants.

Thus the biotic components with the release of nutrients make the soil more fertile since the soil is able to satisfy plant demands for nutrients, water and an adequate aerated physical matrix for the growth of the plant roots. The activities of the biota become more significant when the two most important climatic agents like temperature and moisture are at the optimum level.

With the seasonal variation of these two factors the activity also undergoes changes. But when the climate experiences irregular and completely different changes all the activities are jeopardized and the fertile soil either becomes infertile or less productive or may even be converted into a barren land.

---

Essay # 5. Formation of Soil:

The soil formation occurs in two stages:

(i) Weathering of Rocks:

It may involve chemical weathering due to hydration, hydrolysis, carbonation, oxidation-reduction or chelation of rock material; physical weathering due to heating and cooling, wetting, and drying, freezing, glaciation and action of wind (sand blasts); or biological weathering by bacteria, fungi and lichens due to their acids.

(ii) Pedogenesis:

In this, the weathered mineral matter and the decomposed organic matter undergo biochemical, biophysical and geochemical changes to form the fully developed true soil. So the process of soil development is called pedogenesis. Pedogenesis is more active in superficial layer of earth. Study of formation of soil is called pedology.

---

Essay # 6. Soil Types:

On the basis of its formation, the soils are classified into two major categories:

(i) Residual Soils:

These are formed by weathering and pedogenesis of the rock.

(ii) Transported Soils:

Transported soils transported by various agencies and are of four types:

a. Alluvial soils, transported by water.

b. Colluvial soils, transported by gravity.

c. Eolian soils, transported by air.

d. Glacial soils, transported by slipping of glaciers.

---

Essay # 7. Soil Profile:

On the basis of colour, hardness and other properties, the soil shows a sequence of more or less distinct layers, called horizons, superimposed one upon the other. This succession is due to differential activity of climatic and biotic factors upon the original parent rock so these layers differ in their physical, chemical and biological properties. This succession of superimposed horizons is called soil profile.

As many as four horizons are differentiated:

(i) A-Horizon:

It occupies the topmost horizon of true soil. It is rich in mineral and decomposed organic matter (humus).

It is further sub-divided into five regions:

i. A00^– or O₁. It forms the uppermost layer and has fleshly fallen organic matter like leaves, twigs, flowers, etc. and is well-developed in forests.

ii. A00^– or O₂. In this layer, decomposition of organic matter starts. So the upper part has the organic matter, in initial stages of decomposition called detritus, while lower layer has fairly decomposed matter called duff.

iii. A₂-region. It is dark-coloured and has abundant minerals mixed with humus.

iv. A₁-region. It is light-coloured part and has low humus and minerals (mainly sand). It is also called zone of eluviations (or leaching) e.g. leaching of Fe, Al etc.

v. A₃-region. A transitional area between A and B horizons.

(ii) B-Horizon:

It is coarse textured dark coloured horizon containing large amounts of aluminium and iron compounds. It is also called zone of illuviation (redeposition of minerals). It is subdivided into three zones namely B₁, B₂ and B₃.

Two horizons A and B together constitute the solum. The solums along with the horizon O collectively form the top soil.

(iii) C-Horizon or Subsoil:

It is made up of incompletely weathered rocks. If weathering is fast then this horizon is poorly developed.

(iv) D-or R-Horizon:

It represents the unweathered parent rock, also called bed rock. It forms the base of soil profile.

---

Essay # 8. Types of Soil Particles:

These particles vary in size and on this basis, soil particles are divided into following categories:

i. Gravel = more than 2 mm

ii. Coarse sand = 2 to 0.2 mm

iii. Fine sand = 0.2 to 0.02 mm

iv. Silt = 0.02 to 0.002 mm

v. Clay = less than 0.002 mm

On the basis of relative proportion of these particles, soils are of following types:

i. Sandy Soil:

It is formed of 85% sand and 15% clay and silt. It is also called light soil. It has high porosity (percentage of pore-spaces in a given volume of soil) so has loose soil with low water holding capacity. It also has large temperature fluctuations. It is characterized by the xerophytic plantations. This soil is not rich in nutrients and is less fertile.

ii. Clayey Soil:

It is formed of 50% clay and 50% silt or sand or both. It is also called cold or heavy soil. It has fine pore spaces so very high water holding capacity. The temperature does not fluctuate much. It does not allow easy penetration of roots and has less waterlogging capacity and presence of CO₂.

iii. Silt Soil:

It has 90% silt and 10% sand. It has good soil porosity and water holding capacity but is poor in nutrient supply.

iv. Loamy Soil:

It consists of 70% sand and 30% clay or silt or both. It is best soil for the plant growth because of its good water holding capacity, water infiltration and adequate aeration. Root penetration is also good in loamy soils.

Minerals, also called biogenic nutrients, are essential for the proper growth of organisms so the type and distribution of plants and animals are determined by specific distribution of minerals. Deficiency or absence or excess of minerals results in abnormal growth or even death of organisms.

v. Plants found in nitrogen-deficient soil have either nitrogen-fixing symbiotic bacteria e.g. leguminous plants, or become insectivorous (e.g. Nepenthes—pitcher plant, Utricularia—bladder-wort etc.). Similarly, crustaceans also flourish only in that water which contains calcium.

vi. Snails occur in soils rich in calcium content.

vii. Halophytes and some sea animals have salt secreting glands.

viii. Soil, deficient in copper and cobalt, is unfit for raising cattle.

High concentration of minerals greatly limits the distribution of animals e.g. Dead Sea and Great Salt Lake (areas with high salt contents) are devoid of much vegetation.

---

Essay # 9. Soil Nature and Distribution of Vegetation:

The type of soil (sandy, loamy or clayey) and its water retention, aeration and mineral contents determine the nature of plants and animals.

On the basis of these characters of soil, the plants are divided into following ecological categories:

i. Halophyets:

The plants found on saline soils e.g. Rhizophora, Heritiera, etc.

ii. Psammophytes:

The plants found on sandy soils.

iii. Lithophytes:

The plants found on rocky surface.

iv. Chasmophytes:

The plants found in rock- crevices.

v. Oxylophytes (Calcifuges):

The plants found on acidic soils e.g. maize, barley, potato, Rumex and Rhododendron.

vi. Calciphytes:

The plants growing on calcium-rich soils.

Various minerals of soil are dissolved in soil water to form soil solution.

On the basis of mineral matter present in the soil solution, the soils are divided into two categories:

i. Oligotrophic Soils:

Have sub-optimum concentration of minerals in the soil solution.

ii. Eutrophic Soils:

Have almost optimum concentration of minerals in the soil solution.

(ii) Organic Matter:

The organic matter is added by the decomposition of plant and animal remains and the excreta of animals. Organic matter is found upto 20-30 cm below from the surface of the soil.

It is present in following forms:

a. Litter:

Undecomposed organic matter. It is formed of dead plant material fallen on the floor.

b. Duff:

Partially decomposed organic matter by the saprophytic action of actinomycetes, fungi and bacteria.

c. Humus:

It is fully decomposed and finally divided dark and amorphous organic matter. Chemically, it contains carbohydrates, sugar alcohols, lipids (fats, oils and waxes), tannins, resins, lignin, amino acids, purines, pyrimidines, alkaloids, carotenoids, etc. It contains 55-60’X, carbon, 35-40% oxygen, about 5% hydrogen and roughly 5% nitrogen. The formation of humus is called humification whereas the breaking of humus into minerals, CO₂ and water is called mineralizations.

Organic matter is a good source of minerals to plants. It increases water holding capacity, porosity and aeration of the soil.

(iii) Soil Water:

Soil water is more important than any other ecological factor in distribution of plants because it is required for meeting the metabolic and transportational needs of soil flora, soil fauna and the process of humification.

Soil water is derived from rain. Rain water occurs in following forms:

a. Run-Away Water:

It is drained away from the soil surface along the slope and is also called runoff. Its amount depends upon soil permeability, soil moisture, degree of slope and number of ditches.

b. Gravitational Water:

It is that amount of water which percolates downward under the force of gravity and finally reaches the water table.

c. Capillary Water:

The water held up by capillary forces between the soil particles in the micropores is called -Capillary water. This is the best form of water available to the plants.

d. Hygroscopic Water:

The water held by soil colloids tightly adsorbed on their surface is called hygroscopic water. It is non-available to plants.

e. Combined or Chemical Water:

A small quantity of water remains chemically bound to soil substances e.g. CuSO₄, 5H₂O, MgSO₂, 7H₂O. It is known as combined or chemical water and is not available to plants.

The total amount of water which a soil can retain per unit of its dry weight after the gravitational percolation has stopped, is called its water holding or field capacity. The capillary, hygroscopic and combined forms of water constitute the field capacity. It is represented as the ratio of maximum amount of water retained per l00g weight of soil. It differs with different types of soils. It is only 5% of the dry weight in sandy soils, 15-25% in sandy loam, 25-35% in typical loams and upto 45% in clay soils.

Soil water affects the plant life to a large extent because water acts as a medium for nutrient absorption and also influences the microbial population of soil.

(iv) Soil Air:

Soil air is present in the pores of the soil and is necessary for respiration of roots and soil flora and fauna. If the soil is not water-logged, its pores partly contain water and partly air. The soil air is slightly rich in CO₂ and poorer in O₂ due to respiratory activities of underground parts of plants and micro-organisms.

The oxygen of soil air is an important factor controlling soil fertility because it is required by humus forming micro­organisms, nitrogen-fixing bacteria and other soil organisms like earthworms which increase the soil fertility. It is also required for seed germination, development and growth of roots, absorption of water and minerals by roots, respiration of underground parts like rhizomes, tubers, bulbs, corms etc.

Some amounts of other gases like ammonia, methane, hydrogen sulfide and hydrogen may be present in the soil due to bacterial activity of decomposition.

(v) Soil Organisms:

The organisms found in the soil are divided into three categories, on the basis of their size:

a. Macrofauna.

It mainly includes animals like rabbits, rats and moles. These live partly or wholly inside the soil.

b. Mesofauna.

It mainly includes arthropods (beetles, insect larvae, termites, centipedes, and millipedes), annelids (earthworms), nematodes and mollusks (snails and slugs).

c. Microfauna.

It represents the soil microflora and microfauna and includes algae, fungi, bacteria, actinomycetes, protozoans, etc. The algal components mainly include blue-green algae e.g. Nostoc.

These perform following functions:

(a) N₂ fixation in the soil by free-living Azotobactor, Closteridium, etc. Decomposition of organic matter leading to form humus e.g. earthworms, millipedes, slugs, snails, insect larvae, etc.

(b) Nutrient cycling.

(c) Pedogenesis.

(d) Bring sub-soil to the surface so improve soil aeration.

(e) Produce antibiotics (antagonistic to toxins produced in some soils.)