Soil is a mixture of broken, loose rock fragments and organic matter which can support plant growth. Soil is considered the end product of weathering.

One of the popular classifications of soils divides them into three broad orders, each of which is further divisible into sub-orders. This classification popularly called Marbutt's classification is based on the role of various environmental factors in the development of soils.

According to Marbutt's classification, all soils are grouped into three broad soil orders as zonal order, intrazonal order and azonal order each of which is further divided into sub-orders and soil groups.

The Zonal order includes soils the characteristics of which are dominated by the influence of climate and natural vegetation. Zonal soils are considered fully mature soils and they have a perfectly developed profile. Podzols are an example of such soils.

The Intrazonal order includes the soils the characteristics of which show influence of local features of parent material, terrain or age and the influence of zonal factors like climate and vegetation on the soil characteristics is relatively less significant. Calcimorphic and hydro-morphic soils are examples of this order.

The Azonal order includes the soils that are immature and they generally lack the B horizon in their profile. Alluvial soil is an example of Azonal order.

The fertility of a soil depends upon its mineral and humus content and climate.

Most mature soils have a layered arrangement of strata called horizons. Most mature soils have three horizons, A, B and C. This arrangement of soil layers is called soil profile. Occasionally a thick layer of humus may accumulate over the A horizon of a soil. Such a thick layer of humus is often called the O horizon.

Leaching is the process of removal of minerals in solution from the upper layers to the lower layers of soil.

A set of processes operating under a particular type of environmental conditions leading to evolution of typical characteristics of soils is called a pedogenic regime.

The most important pedogenic regimes are podzolisation, laterisation, calcification, salinisation and gleization.

Podzolisation regime commonly occurs in areas of humid temperate climate and is a typical regime of the coniferous forest regions. Leaching occurs in Podzolisation regime, and is thus low in fertility. These soils generally have accumulation of humus in thick layers. Podzols are typical soils formed through this regime.

Laterisation regime is associated with warm and humid tropical areas where wet and dry season alternate. This is a typical regime of the tropical and equatorial rain forests. Lack of humus is characteristic of soils formed under this regime. These soils are highly porous and display red colour due to the presence of iron oxide and they are low in fertility. Laterites are typical soils formed under this regime.

Calcification is the pedogenic regime associated with areas where evaporation on an average exceeds precipitation (e.g., in regions of mid latitude steppe climate). They usually have high fertility. Calcimorphic soils are typically formed under this regime.

Salinisation regime is associated with poorly drained areas with a desert climate. Lack of drainage channels in the desert and semi desert regions leads to flow and accumulation of surface run-off in local depressions. Due to high concentration of salts in the upper layers, these soils are not suitable for cultivation.

Gleization regime occurs in poorly drained, but not saline, environments in areas of moist and cool or cold climate. These soils are not suitable for cultivation.

The major soil types of the world are podzol soils, laterite soils, prairie soils, chernozem soils, desert soils, calcimorphic soils, tundra soils, hydromorphic soils and alluvial soils.

Podzol soils are zonal soils and they are the most common soils found in areas of cool humid climate in northern Europe, Asia and North America. The soil has an ash gray colour and humus accumulation occurs on the surface. Since they are highly leached, they lack in bases, are acidic in reaction and are not very fertile. They support coniferous forests.

Laterite soils are reddish soils of humid tropical areas. They are typically associated with areas of equatorial and tropical rainy climates. Parts of Kerala and Tamil Nadu in India are of this type and they are sufficiently productive if organic matter is added regularly. The soils of rainy tropical areas have accumulation of iron and aluminium oxides and such types of soils are collectively called as Latosols. Latosols occur in India, Southeast Asia, Zaire Basin and Amazon Basin.

Prairie soils develop in areas of humid continental climate and they are also called as brunizems. Prairies of North America are an important area of these soils. They are light black in colour and also highly fertile and can support large farming populations.

Chernozems are also known as black earths. They are soils of temperate grasslands and they occur extensively in steppe regions in Ukraine, Russia, USA and the Deccan of India (black cotton soils). In India they are also called as regur soils.

Desert soils lack in humus and are brownish in colour. They are usually sandy in texture and contain soluble salts in large amounts. They can be fertile if irrigated. Sahara, Atacama, Arabian Desert and Thar Desert are the major areas of occurrence of these soils.

Calcimorphic soils are intrazonal soils that develop from parent material highly rich in lime. Calcimorphic soils of the sub-humid tropics are fairly fertile. They occur in large areas in South America and also in areas around the Mediterranean Sea.

Tundra soils are soils of cold zones and they are poorly drained. They are stony in texture and have very poor development of soil profile. They are found in tundra regions in Eurasia and North America. Poor grasses are the natural vegetation of these regions.

Hydromorphic soils are associated with marshes, bogs or poorly drained flat uplands. They often contain accumulations of peaty organic matter. Parts of Western Europe and foothills zones of Himalayas have this type of soils. Distribution of these soils is in patches rather than in belts.

Alluvial soils comprise deposits of eroded material transported by rivers from other areas. The Indo-Gangetic plains and Egypt's Nile Valley and Delta are the two of the major areas where soils of this type are found. They are easy to cultivate, are usually fertile and this support large farming population.

Human Geography is one the major divisions of geography. It is concerned with a study of spatial patterns of human activities.

World population crossed the 6 billion mark in 1999 and it crossed the 7 billion mark on October 31, 2011. Currently, the world population is at about 7.8 billion.

Areas that are highly favourable for human occupancy are called the ecumen areas of the world. Areas with a congenial climate and fertile soils are examples of such regions.

The areas where the natural environment is not conducive for human occupancy. They are called the non-ecumen areas. Area of harsh climate – too hot, too cold, too humid or too dry, rugged relief and those having lack of resources are the major non-ecumen areas.

The major regions of population concentration in the world are the East Asian Region, the South Asian Region and the West European Region.

The East Asian Region has the largest concentration and it includes countries like China, Korea, Vietnam, Cambodia, Japan, Indonesia etc. The region accounts for about one-fourth of the total population of the world.

The South Asian Region has the second largest concentration and includes countries like India, Bangladesh, Myanmar, Pakistan and Sri Lanka. The region accounts for more than one-fifth of the total global population.

Western European cluster has the third largest population concentration of the world.

Population structure refers to an analysis of the population on the basis of the characteristics such as age and sex composition etc. Some of the terms used in the population structure are given below:

Birth Rate: Number of live births per 1000 of population per year.

Death Rate: Number of deaths per 1000 of population per year.

Natural Growth Rate: Birth rate minus death rate. The negative growth means a decreasing population and the positive growth means an increasing population.

Infant Mortality Rate: Number of deaths of children below one year of age per 1000 live births.

Life Expectancy: Average age to which a person at the time of birth is expected to live.

Net Reproduction Rate: The rate at which women are replaced by daughters who will have children.

Sex Ratio: Number of females per 1000 males. If the number of females is less than that of the males, the sex ratio is said to be unfavourable to women and vice-versa.

Density of Population: Number of persons living per unit of area (sq.km). It is calculated by dividing the total population by total area.

Agricultural Density of Population: Total Population divided by cultivated area.

Physiological Density of Population: Agricultural population divided by cultivated area.

Economic geography is concerned with the study of spatial patterns of economic activities. All activities relating to production, consumption and exchange of goods are called economic activities.

The economic activities are divided into categories of primary, secondary, tertiary and quaternary activities etc.

Primary activities include activities such as hunting of animals, gathering of plant products such as fruits, and nuts, obtaining minerals from the earth's rocks, fishing and harvesting of crops and trees. These activities are thus concerned with obtaining products from nature directly. Due to the outdoor nature of their work the people engaged in these activities are often called red-collar workers.

Secondary activities are concerned with addition of value to the products of primary activities. These activities include processing and increasing the utility of various products. Ex: production of textiles by processing fibres obtained from animals and plants and production of steel goods by processing iron ore. Workers engaged in the activities of secondary production are often called blue-collar workers.

Tertiary activities are concerned with providing service rather production of tangible goods. These activities include a range of personal and business services. These persons provide the services like those of retail clerks, barbers and secretaries etc. People engaged in these activities are called pink-collar workers.

Quaternary services represent a special type of service work focusing on professional and administrative services. These activities include financial services, health service, information processing, teaching services, government services and entertainment services etc. People engaged in these activities are called white-collar workers.

Quinary activities represent a small number of people. They include chief executives and other top management officers in the government as well as private services. Researchers, legal authorities, financial advisors and professional consultants etc are included in this category. These people are sometimes refereed to as gold-collar workers.

Farming organisation refers to the relationship of the cultivator to the land. This relationship is also called land tenure system. Some of the important systems of farming are Individual Farming, Estate Farming and Co-operative Farming.

Individual Farming is the most common type of farming the world over. The farmer may own (owner occupancy) or lease land from the owner.

Estate Farming has been a typical type of farming in the areas of new lands, where large cultivable areas were available to the settlers from the European continent. It was a traditional type of farming in southern Europe. Such large farms cultivated with the help of a large number of workers are called latifundia in Europe, ranches in North America, haciendas and fazendas in Latin America, stations in Australia and plantations in many other areas.

Co-operative Farming is a typical system of developed countries where the individual farmers pool their land and other resources, cultivate the land and share the return in proportion to their contribution to the farming. Sweden, Netherlands, Belgium and Denmark are well known for this type of farming.

Collective farming is a variant of co-operative farming. Collective farming was adopted in erstwhile Soviet Union, it is based on the principle of social ownership of land and collective labour in which there is no exploitation of a person by another. After the collapse of communism in most of Europe the farmland under this system has gone to the individuals.

A slightly different type of community farming is practiced in Israel on the kibbutizim. Farmers living on the kibbutz work on the land collectively but get no formal payment but they are provided food, housing, clothing, medicate and education etc., and also some spending money. This system is voluntary.

There are various types of cultivation practices, some of the most important are sedentary cultivation, shifting cultivation, terrace cultivation, wet or irrigated cultivation, dry cultivation, crop rotation etc.

Sedentary cultivation is also called as settled cultivation; it is the practice of continued use of land year after year. This is the normal practice in most parts of the world including India.

Shifting cultivation works on the principle just opposite to that of sedentary cultivation. Land under this system is used for a few years until fertility level drops when the farmer moves on to a new plot of land. This type of farming is practiced by less advanced societies in the tropical regions. It is also called as burn and slash cultivation. In India this type of farming is common in areas inhabited by tribal people. It is known as various names such as jhoom in Assam, onam in Kerala, podu in AP and Orissa, and bewar, masha, panda and bera in various parts of Madhya Pradesh. It is called ladang in Malaysia, humah in Indonesia, taungya in Myanmar, tamrai in Thailand and milpa in Africa and Central America.

Terrace cultivation is practiced in mountain areas, where cultivation is done on terraced fields in a manner not very different from settled cultivation in terms of land use. This method is adopted to conserve soil on steep slopes.

Wet or Irrigated cultivation is the practice of farming with the help of irrigation in regions where rainfall is not adequate or where it is highly seasonal. Rice and Sugarcane crops typical of this system of cultivation in India.

Dry cultivation is done in areas where there are no irrigation facilities and the rainfall is also limited in amount. Crops grown in such areas are resistant to dry conditions.

Crop Rotation is the practice of growing different crops in succession so that the soil remains fertile. The crops are so selected that some of them obtain nutrition from the lower layers of the soil while the others have shallow roots. In between are grown leguminous crops which help in enriching the soil with nitrogen.