What is SOIL?

Soils form the outermost layer of the earth's surface, consisting of weathered/ micro rock particles, minerals, weathered bedrock (regolith), organic matter (both dead and alive), air and water. Soil is considered as the skin of the earth (W.B. Logan) with interfaces between lithosphere, hydrosphere, atmosphere and biosphere. The formation of a layer of 30cm soil may take between 1000 to 10000 years (minimum soil depth for agricultural production is 150 mm). Because of its very slow formation process, soil can be considered as non-renewable resource.

How it develops?
From the weathering of bedrock by the agents of erosion
Climate, topography, vegetation cover, land use influence the nature and properties of soil
Biological processes result in further development
Soil can therefore vary even over a very small area (with a single field)

Glossary of the terms you need to know to understand Soil Geography
  • Field capacity denotes the maximum amount of water that a mass of soil can hold. Excess rainfall, above the soil field capacity may cause waterlogging, overland flow (rills) or mud flow and consequent loss of soil.
  • Soil texture is determined by relative proportion of sand, silt and clay compounds in soil, control porosity and permeability.
  • Permeable: A surface that will allow water to pass through it.
  • Non-permeable: A surface that will not allow water to pass through it. This means that water can not infiltrate.
  • Porous: An object (or ground) that can hold water i.e. it has pores where water can be stored.
  • Non-porous: An object (or ground) that can not hold water i.e. it does not have any pores
  • Leaching involves removal of soluble material in lower horizon.
  • Soil salinization- is the upward movement of soluble salts by capillary action and their deposition in the surface horizons, forming a toxic crust. Excessive evaporation also leads to soil salinization. Salt affected soils are common in arid areas, coastal zones where capillary action brings soils to the upper part of the soil.
  • Humus is a dark soil material and colloidal substance, refers to any organic matter after being decomposed, has reached a point of stability (remains unchanged for centuries if conditions do not change). Humus has very high water holding capacity. Humus is thus contributes to moisture and nutrient retention and increase soil's cation exchange capacity (chelation)...encourage plant growth...fertility and buffer excessive acidic or alkaline condition, increase soil's capacity to withstand drought condition, prevent leaching of nutrients. Humus controls soil buffering capacity (capacity of soil to absorb contaminants)
  • Colloid is a very stable substance microscopically dispersed throughout another substance. Soil colloids are the smallest stable parts of the soil, include clay +humus...carry base exchange (Bases are the positive ions like Ca+, Na+) ...retain soil fertility and helps in plants growth....in return plant release hydrogen ions that tend to make the soil more acidic with time. Thus prolonged agricultural activity without proper land management tends to make the soil acidic.
  • Chelation is a process of binding of metallic ions.
  • Ions are charged particles (created as a result of soil reaction with water or with any solution presence in the soil). Positively charged ions are cations while negatively charged ions are anions. e.g. in Nacl- Na+ and Cl- ions are present.
  • Latosolisation: is the process of tropical red soil creation. Under sustained warm wet condition bacterial activity decomposes vegetation quickly...... prolong leaching create absence of humic acids...chelation is rare....iron, aluminium remain insoluble and accumulates as red clay.
  • pH scale: The acidity or alkalinity of a soil is measured in pH scale (0 to 14). Pure water has pH 7 (neutral to slightly alkaline). 0 to 4 is highly acidic. pH is a measure of hydrogen ions, controls soil reaction.
  • Saturated soil: Soil that can hold no more water.
  • Unsaturated soil: Soil that still has space between its pores and can hold more water.
  • Water table: The line between saturated and unsaturated soil. The water table can go up and down depending on the amount of rainfall and the amount of water being used.

Soil/land Degradation

Involves both the physical loss (erosion) and reduction in quality of topsoil associated with nutrient decline and contamination. It has significant impact in agriculture, pollution, flooding and environment. Globally, 15% of the earth's land area has already been degraded. During the last 40 years nearly one-third of the world's cropland has been abandoned because of soil degradation.
Types of soil degradation
  • Quantitative loss or erosion by climatic components- water (surface runoff, overland flow, gully and rill erosion) and wind (wide fetch, bare top soil due to deforestation)
  • Biological degradation (loss of humus and biota)
  • Physical degradation (change in structure-permeability, porosity, change in texture- sand, silt and clay content)
  • Chemical degradation (change in soil pH, acidification, salinization, toxicity and declining overall fertility)

Food supply will be affected by soil erosion
Deforestation-soil erosion and its impact
Desertification threatens Niger's Nomads

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Alternative farming techniques

Vertical organic urban farming
Hydroponic Farming
Agroforestry Explained
Agroforestry changing
farmers lives in Vietnam


Water is one of the most unique molecules known to man
We are comprised of mostly water

Unique properties of water molecules
A water molecule consists of two hydrogen atoms and one oxygen atom. The three atoms make an angle; the H-O-H angle is approximately 104.5 degrees. The center of each hydrogen atom is approximately 0.0957 nm from the center of the oxygen atom
In the solid state, the particles of matter are usually much closer together than they are in the liquid state. So if you put a solid into its corresponding liquid, it sinks. But this is not true of water. Its solid state is less dense than its liquid state, so it floats. Water behaves differently from most other chemical compounds. In almost all substances the atoms and molecules move closer together as they get colder. They then solidify. Water, however, attains its greatest density at four degrees Celsius because the water molecules are packed closest together at this temperature. Many freshwater lakes have a temperature of four degrees at their deepest point because the heavy water sinks to the bottom. But surprisingly, to reach the solid ice phase, the water molecules again move farther apart. This phenomenon is referred to as the water anomaly. Ice is lighter and floats at the surface. This is seen in the large ocean regions at polar latitudes, which are partly covered by ice. The reason for this anomaly lies in the unusual properties of the water molecule (H2O). Its oxygen atom (O) and the two hydrogen atoms (H) are asymmetrically arranged. This produces a dipole, a molecule with one negatively and one positively charged end.
Another unique property of water is its ability to dissolve a large variety of chemical substances. Water is sometimes called the universal solvent because it can dissolve so many things. water has the highest surface tension of any common liquid except mercury. It is the tendency of water molecules to attract to each other or cohere to each other at the surface of water. Because of this adhesion and cohesion properties water plays an important role in the internal transport system of plants and animals.
The other widely-cited anomalous property of water is its high boiling point. a molecule as light as H2O "should" boil at around –90°C; that is, it would ideally exist in the world as a gas rather than a liquid if H-bonding were not present.
Water influences climate not only in its liquid and solid states. H2O in the form of water vapour in the atmosphere has a decisive impact on the heat budget of the Earth; water vapour alone is responsible for about two thirds of the natural greenhouse effect. In addition, it amplifies the impact of other substances on ­climate. For example, if the temperature rises as a result of higher carbon dioxide levels, then the water vapour content also ­increases because the warmer atmosphere can sustainably hold more water vapour. Because of its dipole molecule, water absorbs infrared radiation very efficiently. As a result, it approximately doubles the warming originally caused by carbon dioxide.

Water Crisis: The water Usage and Supply situation

  • Water is the most essential and pivotal resource. It is the largest single component of the human body, and is essential for life. The longest a person can survive with out water and food is about 8-10 days.
  • The Stockholm International water Institute has estimated that each person on earth needs a minimum of 1000 m3 of water per year for drinking, hygiene and growing food for sustenance. Whether this water is available depends on where people live on the planet as water supply is extremely inequitable.
  • Water scarcity affects every continent. For about 40% of the world population lack of water is a constant threat. By 2025, almost half of the would population (around 4 billion people) will live under condition of severe water threat specially in Africa, Middle East and south Asia. UN estimates states that by 2025 around 1800 million people will be living in the countries or regions with absolute water scarcity and around two-thirds of the world population would be around stress condition.
  • The situation is getting worse as the demand for water is doubling in every 20 years. In 20th century, global water consumption grew 6 fold.
  • Colorado river is running dry and no more reaches the sea. Most of its water has been diverted to irrigated agriculture, so that in a normal year, no water at all reaches the river’s mouth.
  • Yemen and Jordon are withdrawing 30% more from ground water resources than is being annually replenished
  • In Africa around 200 million people at present live in severe water stressed situation
  • Half of the world's wetlands have disappeared in the last 30 years. 20% of the fresh water species are engendered or extinct
  • Many important aquifers are seriously depleted. water table in many parts of the world are dropping at an alarming rate. Ground water recharge is a slow process, drained faster can not be replenished.
  • The quantity of water used today for all purpose exceeds 4700 cubic kilometers per year. Agriculture is the largest user, consuming two-thirds of all water drawn from rivers, lakes and groundwater. Since 1960, water use for crop irrigation has risen by 60-70%. Industry uses about 20% available water and municipal sector (domestic use) uses about 10% ( refer page 63 of text book)

Water : A precious resource
Why to care about water?
Water changes the quality of life
Water Walk

What is sanitation?

-safe collection, storage, treatment and disposal/reuse/recycling of human excreta
-management/reuse/recycling of solid wastes (trash or rubbish)
-drainage and disposal/reuse/recycling of household waste water (often referred to as grey water)
-collection and management of industrial waste products; and management of hazardous wastes (including hospital wastes, and chemical/ radioactive and other dangerous substances)

Importance of sanitation
The discharge of untreated waste water and excreta into the environment can affect human health in several ways
  • By polluting drinking water;
  • Entry into the food chain, for example via fruits, vegetables or fish and shellfish;
  • Bathing, recreational and other contact with contaminated waters;
  • By providing breeding sites for flies and insects that spread diseases

WHO and UNICEF recommended improved sanitation system:
  • Flush Toilet - disposes of human liquid and solid waste, by using water to flush it through a drainpipe to another location for disposal.
  • Connection to a piped sewer system- Off-site disposal
  • Connection to a septic system. A septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations. This is an on -site disposal
  • Ventilated improved pit (VIP) latrine. A pit toilet is a dry toilet system which collects human excrement in a large container and ranges from a simple slit trench to more elaborate systems with ventilation.
  • Waste water treatment

Sanitation crisis: Infographics from Water Aid
Water crisis and poor sanitation in Kibera,
UNDP report
Worst Pollutants


Importance of and challenges to Forest Conservation
Source: Taken from FAO Infographics : http://www.fao.org/resources/infographics/infographics-details/en/c/325836/
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Class Work : Article Review Review Article from National Geographic on deforestationReview NASAs Article on Tropical DeforestationReview WWF article on the threats and causes of deforestation

FUN LEARNINGMillionaire game on soil-water and resource consumption


Click here to see TED video from a lover of marine biodiversity
Introduction to Biodiversity
Philippines as a biodiversity hotspot
Climate change and biodiversity

Article ReviewArticle from NAT GEO on the types and importance of biodiversityA glossary of definitions and terms relating to biodiversityGuardian article on Mass ExtinctionCountries with the largest rainforest coverage

Population Resource Relationship

Overpopulation vs over consumption
Origin of limit to growth
Limit to growth
Overpopulation myth?