Soils of the World

International Year of SoilsHealthy Soils for a Healthy Life is the motto of the UN International Year of Soils which aims to “increase awareness and understanding of the importance of soil for food security and essential ecosystem functions.” As explained on the campaign’s website, “soil is the thin layer of material on the Earth’s surface. It is a natural resource consisting of weathered and organic materials, air and water. As it is the medium in which plants establish themselves and grow, the most widely recognized function of soil is its support for food production. Soil provides nutrients and water that are absorbed through plant roots and contribute to the regulation of water and atmospheric gases and therefore play an important role in climate regulation.”
Soil therefore matters most where is is near human population, which at the same time puts soils under extreme pressure in these areas. Soil types not least determine where humans used to settle when they gave up their nomadic lifestyles and started becoming more stationary as farmers. Nowadays, some of the most fertile soils are found in the most densely populated spaces on the planet, which is shown in the following map. The map shows the major soil types classified in the FAO/UNESCO Soil Map of the World reprojected on a gridded population cartogram where a grid is resized to give every person living within a grid cell an equal amount of space (reducing the map in those spaces most where there are fewest people):

Map of major soil groups
(click for larger version)

The colours used in this map differ from the original FAO map and this may not make it the aesthetically most beautiful map. However, this cartogram aims to highlight the most common soil types in those spaces where human settle, while it omits those spaces that are normally given most prominence in a conventional map. The soil types shown in the map “are classified on the basis of a combination of soil properties that are considered indicative of the way they have been formed. The quantity and the depth at which soil characteristics such as organic matter, clay, iron and soluble salt content occur are some of the factors that are used to define the major soil classes” (quoted from the IYS website).
The major soil groups can be described as follows (quoted from the 2008 FAO report: Harmonized world soil database manual):

ACRISOLS (AC): Soils with subsurface accumulation of low activity clays and low base saturation
ALISOLS (AL): Soils with sub-surface accumulation of high activity clays, rich in exchangeable aluminum
ANDOSOLS (AN): Young soils formed from volcanic deposits
ANTHROSOLS (AT): Soils in which human activities have resulted in profound modification of their properties
ARENOSOLS (AR): Sandy soils featuring very weak or no soil development
CALCISOLS (CL): Soils with accumulation of secondary calcium carbonates
CAMBISOLS (CM): Weakly to moderately developed soils
CHERNOZEMS (CH): Soils with a thick, dark topsoil, rich in organic matter with a calcareous subsoil
FERRALSOLS (FR): Deep, strongly weathered soils with a chemically poor, but physically stable subsoil
FLUVISOLS (FL): Young soils in alluvial deposits
GLEYSOLS (GL): Soils with permanent or temporary wetness near the surface
GREYZEMS (GR): Acid soils with a thick, dark topsoil rich in organic matter
GYPSISOLS (GY): Soils with accumulation of secondary gypsum
HISTOSOLS (HS): Soils which are composed of organic materials
KASTANOZEMS (KS): Soils with a thick, dark brown topsoil, rich in organic matter and a calcareous or gypsum-rich subsoil
LEPTOSOLS (LP): Very shallow soils over hard rock or in unconsolidated very gravelly material
LIXISOLS (LX): Soils with subsurface accumulation of low activity clays and high base saturation
LUVISOLS (LV): Soils with subsurface accumulation of high activity clays and high base saturation
NITISOLS (NT): Deep, dark red, brown or yellow clayey soils having a pronounced shiny, nut-shaped structure
PHAEOZEMS (PH): Soils with a thick, dark topsoil rich in organic matter and evidence of removal of carbonates
PLANOSOLS (PL): Soils with a bleached, temporarily water-saturated topsoil on a slowly permeable subsoil
PLINTHOSOLS (PT): Wet soils with an irreversibly hardening mixture of iron, clay and quartz in the subsoil
PODZOLS (PZ): Acid soils with a subsurface accumulation of iron-aluminum-organic compounds
PODZOLUVISOLS (PD): Acid soils with a bleached horizon penetrating into a clay-rich subsurface horizon
REGOSOLS (RG): Soils with very limited soil development
SOLONCHAKS (SC): Strongly saline soils
SOLONETZ (SN): Soils with subsurface clay accumulation, rich in sodium
VERTISOLS (VR): Dark-coloured cracking and swelling clays

Soils in the most densely populated spaces on the planet are perhaps those most under threat – if they are not degraded already. As stated on the campaign’s website, “studies report that approximately 33% of our soils are facing moderate to severe degradation. The current rate of soil degradation threatens the capacity to meet the needs of future generations, unless we reverse this trend through a concerted effort towards the sustainable management of soils.” A lot more awareness will need to be raised amongst all stakeholders to stop this trend.
Global Soil WeekAmongst the efforts to tacke these issues is the Global Soil Week which is just under way this week. The motto Soil: The Substance of Transformation highlights the importance of land and soil to achieve the Sustainable Development Goals as the successors of the Millennium Development Goals. Understanding the importance of soils is a first step in preserving them – and create healthy soils for a healthier and more sustainable life of humanity.

The content on this page has been created by Benjamin Hennig using data published by FAO. Please contact me for further details on the terms of use.

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