Rock debris is formed of the layers of the Earth by the process of weathering and erosion. This rock waste is found on the surface of the Earth in a thin or thick layer. In ordinary language, it is called Soil. It is comprised of minerals, organic matter (called humus) derived from decomposed plants, living organisms, air, and water.

Soils differ according to climate, parent material, rainfall, relief of the bedrock, and the proportion of organic material. The study of soils is Pedology.

Types Of Soil

Soil is the layer of broken rock particles and decaying organic matter on the surface of earth, which is essential for the growth of plants. It comprises of all the necessary nutrients that aid the growth and development of plants and trees. There are different types of soils, each one of them varying in its nature and texture. While some soils are deep rooted, the others are present on the margin. They also differentiate in their color, as some may be red while others are black. There are various types of soil and each carries with itself different nutrients, which assists in the growth of various plants and crops.

Sandy Soil: Sandy soil is light and dry in nature. It does not have moisture content and warms up quickly in the spring. Thus, it is good for the production of early crops. Sandy soil is fit for cultivation any time of the year if moisture is available. Since it absorbs water quickly, the plants rooted in it need to be watered frequently.

Type	Constituents
Clay	45% silt, 45% clay and 10% sand.
Clay loam	25% clay. 42% silt and 33% sand
Loam	18% clay, 42% silt and 40% sand.
Silt	13% clay, 82% silt and 5% sand.
Sandy loam	11% clay, 14% silt and 75% sand.

Clay Soil: Clay soil is also called ‘late’ soil, because its wet nature makes it apt for planting seeds in late autumn. The soil serves as an excellent resort for the dry season, as it has a high water retention quality. It is necessary to drain clay soil frequently, for improving its texture. The soil becomes unmanageable during rainy season, as it becomes ‘sticky’. On the other hand, during draught, it becomes ‘rock solid’.

Silt Soil: Slit soil is considered to be the one of the most fertile soils present on earth. It is high in nutrient content and is comparatively heavier than the sandy soil, as it retains moisture easily. However, unlike clay soil, silt soil has a good drainage facility, which makes it very productive.

Loam Soils: Given the tag of being the perfect soil, It is suitable for any and every kind of crops. An amalgamation of three soils, loam soil has best of the characteristic of all.  It has high nutrients content, warms up quickly in summers and rarely dries out in the dry weather. It has become the ideal soil for cultivation.

Peaty Soil: Peaty soils are acidic in content, which makes them sour. This is the most exceptional feature of Peaty soils. Usually found in low-lying areas, these soils require proper drainage, as the place is accustomed to a lot of water clogging. Though peaty soils have less nutrient content, they warm up quickly in the spring, making them excellent if right amount of fertilizers are added.

Chalky Soils: Chalky soil is alkaline in nature and usually poor in nutrients. It requires nourishment, in the form of additional nutrients and soil improvers, for better quality. The soil becomes dry in summers, making it very hard, and would require too much of watering for the plants to grow. The only advantage which such a soil has is its lime content. When deep-rooted, Chalky soil becomes excellent for plant growth and favors good growing conditions as well.

Soil Profile

A soil can be described in terms of its soil profile, that is, a vertical cross-section from ground-level to the bedrock on which the soil sits. The profile is divided into layers called horizons.

O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus.

A Horizon - The layer called topsoil; seeds germinate and plant roots grow in this dark-colored layer. It is made up of humus mixed with mineral particles.

B Horizon - It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.

C Horizon - Also called regolith: the layer beneath the B Horizon and above the R Horizon. It consists of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very little organic material is found in this layer.

R Horizon – It is the un-weathered rock (bedrock) layer that is beneath all the other layers.

Soil Formation

Factors affecting soil formation

Parent material:

This refers to the mineral material or organic material from which the soil is formed. Soils will carry the characteristics of its parent material such as color, texture, structure, mineral composition and so on. For example, if soils are formed from an area with large rocks (parent rocks) of red sandstone, the soils will also be red in color and have the same feel as its parent material.

Time:

Soils can take many years to form. Younger soils have some characteristics from their parent material, but as they age, the addition of organic matter, exposure to moisture and other environmental factors may change its features. With time, they settle and are buried deeper below the surface, taking time to transform. Eventually, they may change from one soil type to another.

Climate:

This is probably the most important factor that can shape the formation of soils. Two important climatic components, temperature and precipitation are key. They determine how quickly weathering will be, and what kind of organic materials may be available on and inside of the soils. Moisture determines the chemical and biological reactions that will occur as the soils are formed. A warmer climate with more rainfall means more vegetative cover and more animal action. It also means more runoff, more percolation and more water erosion. They all help to determine the kind of soils in an area.

Relief:

This refers to the landscape position and the slopes it has. Steep, long slopes mean water will run down faster and potentially erode the surfaces of slopes. The effect will be poor soils on the slopes, and richer deposits at the foot of the slopes. Also, slopes may be exposed to more direct sunlight, which may dry out soil moisture and render it less fertile.

Organisms:

The source and richness of organic matter are down to the living things (plants and animals) that live on and in the soils. Plants, in particular, provide lots of vegetative residues 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 break down organic matter and aid decomposition. Animal droppings, dead insects and animals result in additional decaying organic matter. Microorganisms also help with mineral and nutrient cycling and chemical reactions.

Leaching

It is the process by which water soluble substances are washed through or out of the soil. In tropical areas, leaching of the soil due to heavy rains removes scarce nutrients and can lead to a dramatic loss of soil fertility. Destruction of forests aids the process of leaching. The leaching of soluble minerals in soils can lead to the formation of distinct soil horizons as different minerals are deposited at successively lower levels.

Chemical Fertilizers leached out of the soil drain into rivers, lakes, and ponds and cause water pollution.

Soil Classification

Geographers have classified soil in terms of their areal distribution over the earth's land surfaces which are linked with the climates, parent materials etc. As we know, under similar climatic conditions similar soil types develop.

1. Zonal Soils

2. Intrazonal Soils

3. Azonal soils

Zonal soils are by far the most important and widespread soils. These are exhibiting a mature and well-developed soil profile indicating the fullest play of various soil-forming factors.

They develop on well- drained areas, on parent material which has ramained in the original place for a sufficiently long time to have been affected by various soil- forming processes.

Intrazonal soils are developed under conditions of poor drainage, on regolith where soluble salt contents are high. Soils of bog areas and alkali flats are examples of intrazonal soil. All of them have distinct profile characteristics.

Azonal soil lack well-developed soil profiles which may be due to non-availability of sufficient time for them to develop fully or due to the location on very steep slopes which prohibits profile development. Alluvial soils, dune sands, lithosols (i.e. mountain soils on steep slopes) and organic soils, which develop on peat bogs are examples of azonal soils.

A.	Zonal Soils	B.	Intrazonal Soils
i.	Podzol	i.	Bog soil
ii.	Grey-brown	ii.	Meadow soil
iii.	Red-yellow Podzol	iii.	Saline soil.
iv.	Laterite
v.	Tundra
vi.	Chernozem
vii	Prairie
viii	Chestnut and Brown
ix.	Grey and Red Desert.

These soils from the point of view of area distribution are found in similar latitudes. Soils influence the type of agriculture employed in a particular region - light well-drained soils favour arable farming, whereas heavy clay soils give rise to lush pasture land.

Charactersitics of Major Soils

Chernozem Soils

These are dark coloured soils found in grassland regions, where evaporation exceeds precipitation. The A horizon is rich in humus due to decomposition of a thick litter of dead grass at the surface. The soil is also rich in phosphorous compounds. Minerals and moisture migrate upward due to evaporation, leaving the B and A horizons enriched. The organic content of soil is widely variable, ranging from zero in some arid regions to almost 100% in peats.

Lateritic Soils

These are red residual soils characteristic of tropical rainforests. It is formed by the weathering of basalts, granites, and shales and contains a high percentage of aluminium and iron hydroxides[1]. It may form an impermeable and infertile layer that hinders plant growth.

Podzol Soils

Type of light-coloured soil found predominantly under coniferous forests and on moorlands in cool regions where rainfall exceeds evaporation. The constant downward movement of water leaches nutrients from the upper layers, making podzols poor agricultural soils. The leaching of minerals such as iron, lime, and alumina leads to the formation of a bleached zone, often also depleted of clay. These minerals can accumulate lower down the soil profile to form a hard, impermeable layer which restricts the drainage of water through the soil.

Desert Soils

Desert soils are infertile, lacking in humus and generally grey or red in colour. The few plants capable of surviving such conditions are widely spaced, scrubby and often thorny. Long-rooted plants (phreatophytes) such as the date palm and mesquite commonly grow along dry stream channels. Salt-loving plants (halophytes) such as saltbushes grow in areas of highly saline soils and near the edges of playas (dry saline lakes).

Alluvial Soils

These consist of layer of broken rocky matter, or sediment, formed from material that has been carried in suspension by a river or stream and dropped as the velocity of the current decreases. River plains and deltas are made entirely of alluvial deposits, but smaller pockets can be found in the beds of upland torrents. Alluvial deposits can consist of a whole range of particle sizes, from boulders down through cobbles, pebbles, gravel, sand, silt, and clay. The raw materials are the rocks and soils of upland areas that are loosened by erosion and washed away by mountain streams. Much of the world's richest farmland lies on alluvial deposits. These deposits can also provide an economic source of minerals. River currents produce a sorting action, with particles of heavy material deposited first while lighter materials are washed downstream.

Volcanic soils

Volcanic soils are formed from volcanic ash and cinder deposits. They are rich in metallic minerals and being provided with adequate moisture and humus, are extremely fertile.

Forests

Forests influence the human life directly and indirectly. Forests provide us with various foods and resources. We obtain wood for fuel, buildings, agricultural implements, furniture and paper. Gum, resin, wild rubber are also collected from forests. Indirectly they check the environmental pollution and help in conserving the soil. They are a source of oxygen and sinks for carbon. By supporting variety of flora and fauna, they play a crucial ecological role too.

Forestless Regions

The two main forestless areas are the polar regions, where the growing seasons is short, the ground is ice covered and where rainfall is also very low and the deserts where rainfall is too low (below 225 mm/10 inches) and where the soils are thin, sandy or saline.

Types of Forests

1.         Tropical Hardwood Forests: Found in the regions of high temperature and high rainfall. It includes equatorial and monsoon forests. The equatorial forests extend between 5o north and 5o south of the equator. They are found in the Zaire basin of Africa, the Amazon basin of South America and with some modifications in Malaysia and Indonesia. The equatorial forests in the Amazon basin are also known as Selvas. These are very dense forests marked by tall, green, hard wood trees. Mahogany, Rosewood and Ebony are important trees. Monsoon forests are found in central and northeast India, Myanmar, Vietnam, Thailand, Laos and Cambodia. Sal, Teak and Sisam are important trees of the region.

2.         Temperate Deciduous Hardwood Forests: Central and Western Europe, North-Eastern U.S.A. Central America and eastern Asia have the hard wood deciduous forests. The trees shed their leaves at the onset of winter. Woods are strong, durable, lighter and easier to work on. Important trees are oak, birch, chestnut, maple, Walnut and elm. They are used as building material and for the shipbuilding industry. These forests are densely populated.

3.         Temperate coniferous softwood forests of Taiga- Located between 50o N and 70oN latitudes. They are found in the northern hemisphere running through Canada, Norway, Sweden. Thailand and Central and Eastern Siberia. In Siberia, they are known as taiga forests. They are found on the mountain slopes, between altitudes of 1500 and 2000 meters. These trees are tall, straight with narrow needle like leaves. Most of these trees are evergreen. Pine, cedar, spruce, fir, red wood are some of the important trees.

Biome

It refers to any major ecological community of organism, both plant and animal, usually characterized by the dominant vegetation type, for example Tundra biomes, Tropical Rain Forest biomes, etc. In simpler terms a biome is a large ecosystem where plants, animals, insects, and people live in a certain type of climate.

Biomes are defined in terms of the entire community of living organisms and of their relationships with their immediate environment (and not only with the botanical habitat). Biomes extend over large areas and broadly correspond with climatic regions; characteristic biomes have been identified for all the major climatic regions, emphasizing the ability of living organisms to adapt to a wide variety of environments.

MAJOR BIOMES

Arctic Tundra

The Arctic tundra is a cold, vast, treeless area of low, swampy plains in the far north around the Arctic Ocean. It includes the northern lands of Europe (Lapland and Scandinavia), Asia (Siberia), and North America (Alaska and Canada), as well as most of Greenland. Another type of tundra is the alpine tundra, which is a biome that exists at the tops of high mountains.

Special features:

This is the earth's coldest biome. Since the sun does not rise for nearly six months of the year, it is not unusual for the temperature to be below -30°F in winter. The earth of the Arctic tundra has permanently frozen subsoil, called permafrost, which makes it impossible for trees to grow. Frozen prehistoric animal remains have been found preserved in the permafrost.

In summer, a thin layer of topsoil thaws and creates many pools, lakes, and marshes, a haven for mosquitoes, midges, and blackflies. More than 100 species of migrant birds are attracted by the insect food and the safe feeding ground of the tundra. Other animals that live in this biome include polar bears, Arctic foxes, caribou, and grey wolves. Plants that you might find include small shrubs and cushion plants, and the lichen which cover the many rocks on the tundra's terrain. The Arctic is also famous for the beauty of its flowers during early autumn.

Coniferous Forest

The coniferous forest biome is south of the Arctic tundra. It stretches from Alaska straight across North America to the Atlantic Ocean and across Eurasia. The largest stretch of coniferous forest in the world, circling the earth in the Northern Hemisphere, is called the “taiga.” It supplies the bulk of the world's commercial softwood timber, which is used to make paper.

Special features:

These forests consist mainly of cone-bearing trees such as spruce, hemlock, and fir, which are well suited to the cold climate. The soil is not very fertile however, because there are no leaves to decompose and enrich it. Some animals that thrive in this biome are the ermine, the moose, the red fox, the snowshoe rabbit, and birds such as the crossbill and the great horned owl.

Deciduous Forest

This biome is in the mild temperate zone of the earth. Major regions are found in eastern North America, Europe, and eastern Asia.

Special features:

Deciduous trees lose their leaves in fall. The natural decaying of the fallen leaves enriches the soil and supports all kinds of plant and animal life. The deciduous forest is a lively place, where oak, beech, ash, and maple trees are typical, and wildflowers, berries, and many types of insect and animal life abound. But the fertile soil is also good for people, and in Europe most of the deciduous forest has been destroyed to make room for farms and homes.

Desert

A desert is an area where little or no life exists because of a lack of water. Scientists estimate that about one-fifth of the earth's land surface is desert. Deserts can be found on every continent except Europe. There are two different kinds: hot and dry (such as the Arabian and Sahara deserts) and cold and dry (such as Antarctica and the Gobi desert).

Special features:

The lack of water and intense heat or cold makes this biome inhospitable to most life forms. Most of the plants you'll see in the desert are species of cactus. You might come across yucca, aloe, ocotillo plants, or the tall saguaro cacti. A few animals—mainly reptiles, like snakes and lizards are well adapted to the hot desert. Another famous desert animal is the camel, which can make water from the fat it stores in its hump. The penguins are well-known animals living at the edge of the Antarctic desert.

Grasslands

Grasslands are places with dry climates that are perfect for growing food. They are known throughout the world by different names. In the U.S. they are called prairies and extend from the Midwest to the Rocky Mountains. In South Africa, grasslands are called the veld. Hot, tropical grasslands called savannas are found in South America and Africa. In Eurasia, temperate zone grasslands are called steppes; in South America, pampas.

Special features:

This inland biome is made of vast areas of grassy field. It receives so little rain that very few trees can grow. The U.S. prairies are used to graze cattle and to raise cereal crops. There is little variety of animal life. Some original prairie animals like the wolf and bison have come close to being eliminated from the habitat by hunters. Today, some of the most common grassland animals include the prairie dog and the mule deer in North America, the giraffe and the zebra in Africa, and the lion in Africa and Asia.

Steppes	Temperate grasslands of Eurasia
Prairies	Temperate grasslands of North America
Campos	Sub-tropical grasslands South America
Llanos	Tropical grasslands in North West South America
Pampas	Temperate Grasslands of Argentina.
Savanna	Tropical grasslands of Africa.
Velds	Temperate grasslands of south Africa.

Mountains

Mountains exist on all the continents of the earth. Many of the world's mountains lie in two great belts. The Circum-Pacific chain, often called the Ring of Fire, runs from the west coast of the Americas through New Zealand and Australia and up through the Philippines to Japan. The other major belt, called the Alpine-Himalayan, or Tethyan system, stretches from the Pyrenees in Spain and France through the Alps and on to the Himalayas before ending in Indonesia.

Special features:

Mountains are usually found in groups called chains or ranges, although some stand alone. A mountain biome is very cold and windy. The higher the mountain, the colder and windier the environment. There is also less oxygen at high elevations. The animals of this biome have adapted to the cold, the lack of oxygen, and the rugged landscape. They include the mountain goat, ibex (wild goat), sheep, mountain lion, puma, and yak. All of them are an excellent climber, which means they can move freely in the steep, rocky landscape. Types of plants vary depending on geographic location and altitude. Lower elevations are commonly covered by forests, while very high elevations are usually treeless.

Rainforests

Tropical rainforests are found along the equator in Asia, Africa, South America, Central America, and on many of the Pacific islands. Almost half of the world's tropical rainforests are in the South American country Brazil.

Special features:

Tropical rainforests receive at least 70 inches of rain each year and have more species of plants and animals than any other biome. Many of the plants used in medicine can only be found in tropical rainforests. The combination of heat and moisture makes this biome the perfect environment for more than 15 million plants and animals. The thick vegetation absorbs moisture, which then evaporates and completes the cycle by falling again as rain.

A rainforest grows in three levels. The canopy, or tallest level, has trees between 100 and 200 feet tall. They block most of the sunlight from the levels below. The second level, or understory, contains a mix of small trees, vines, and palms as well as shrubs and ferns. The third and lowest level is the forest floor, where herbs, mosses, and fungi grow.

Some of the animals of the tropical rainforest are the anteater, jaguar, brocket deer, lemur, orangutan, marmoset, macaw, parrot, sloth, and toucan. Among the many plant species are bamboo, banana trees, rubber trees, and cassava.

Biosphere Reserve

Biosphere reserve is any terrestrial or coastal environment that has been internationally recognized as an area for Conservation study and sustained development (as distinct from exploitative development).  Biosphere reserves form an international network of protected areas approved by the International Coordinating Council of UNESCO’S Man and the Biosphere Programme.  In conjunction with the Convention on International Trade in Endangered Species, a total of 194 different bio-geographical provinces have been identified and for each of which at least one biosphere reserve is considered necessary. By December 1985, 243 biosphere reserves had been established in 65 different countries and covering 100 of the bio-geographical provinces.  Marine provinces, however, are poorly represented.

Each reserve must contain an ecosystem that is typical of a bio-geographical realm in terms of its naturalness, diversity and effectiveness as a conservation unit.  Each reserve must exhibit minimal disturbance. Within each reserve at least one core area must exist within which no interference with the natural ecosystems is permitted.  Surrounding the core area there is a transition zone within which experimental research is permitted and beyond this lies a buffer zone, which protects the whole biosphere reserve from agricultural, industrial, and urban land use pressures.

Natural Vegetation of the World

Natural regions	Distribution	Vegetation Characteristics	Vegetation species
Equatorial Rain Forest (10o N & S)	Equatorial region	Evergreen forest with luxuriant growth of variety of vegetation	Hard wood tree like mahogany, ebony, cabinet woods, rosewood.
Tropical Monsoon forest (between 10 to 30o N & S)	Coastal region with a tropical marine climate	Forests are more open and less dense than the equatorial forests, normally deciduous trees with marked dry seasons	Forests have fewer species like teak, sal, sandal wood, bamboo.
Tropical Grassland or Savanna	Sub-tropical interiors of all major continents.	Tall grass and scattered short trees, called Parkland or Bush-veld landscape.	Baobabs and bottle trees acacias etc.
Desert vegetation (Western coasts of continents between latitude 15 to 30o N & S)	The Sahara, Kalahari and Namib desert in Africa, Mohave (California), Atacama (Chile), Australian Desert and others	Very sparse xerophytes or drought resistant scrubs and bushes.	Bulbous cacti, thorny bushes, scattered dwarf acacias and date palms.
Mediterraneas Forest (between 30 to 45o N & S)	Area around the Mediterranean Sea, California (USA), Central Chile, etc.	Transition type of vegetation evergreen forests, evergreen coniferous, Mediterranean bushes, shrubs and wiry and bunchy grasses.	Evergreen trees are cork, oak, gaint sequoia and eucalyptus trees etc.
Temperate Grassland or Steppe	North America (Prairies), Eurasia (Steppes), Hungary (Pustaz), Australia (Downs)	Treeless grassland, vary in appearance and quality of grass also varies with change in season	Rolling plain with tall grasses in Prairies and short grasses in Steppes which are soft and nutritive.
Coniferous forest (from 55o to the Arctic Circle and also the region of mountainous uplands)	Stretches in continuous belt across North America and Eurasia and is also found on the high mountains of other regions	Almost all trees are evergreen and conical in shape with small, thick needle-shaped leaves.	The richest source of softwood occur in pure strands with a few species.
Tundra vegetation	Northern most barren lands of Canada, Coastal region of Greenland and the Arctic Seaboard of Eurasia	Heat deficient region covered with little vegetation of mosses, lichens and stunted trees. Ground is frozen most of the time and also the region has very short summer	Mosses, lichens, sledges and wild flowering shrubs occur in patches.
Temperate Deciduous forest	North-eastern USA, western Europe, north eastern China, southern Chile and New Zealand	Hardwood deciduous trees shed their leaves in winter to protect themselves against the winter snow and frost. They occur in pure strands, which are excellent for lumbering.	Valuable temperate hardwood species are oak, elm, poplar, beech and willow, aspen alder grows in wetter regions.

 

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