Soils in focus
Soil in focus 6:
Soil cathedrals in the landscape
Termites are small organisms compared to humans, yet they create structures –these large mounds- that are clearly visible in the landscapes of Africa, Asia, Australia and America. There are about 1000 different termite species in Africa and about 360 in Australia. Termites influence the local ecology, especially the soil. Organisms are the engine for soil formation as they process and incorporate large amounts of dead organic material into the soil, thereby changing its properties. This is all the more important in some of the old and weathered soils in Africa, where organic matter is the main source of natural soil fertility. The soil of and around termite mounds have high porosity, affecting water flow and storage in the soil and they have a higher pH and organic carbon content and nitrogen.
Termite hill near Otavi, Namibia
The scientific name of this soil from South Nyanza in Kenya, is a Vermic Phaeozem, where Vermic points to the termite activity in terms of biopores and animal burrows. The reference group Paeozem indicates a soil with a high content of organic matter, in this case created by the termites activity.
Termite mounds often form initially around a tree or a pole. The mounds may form to some meters above the ground and extend to various meters below the surface. The tunnels have a complex internal structure with ventilation shafts for air and temperature regulation, fungus chambers for nourishment and access and transport pathways.
Specific vegetation grows on and around termite mounds that attract herbivores that feed on this apparently more nutritious vegetation. Farmers in Sub Saharan Africa find their yields decreasing because of low and decreasing soil fertility. They are aware of the beneficial properties of termite mound soil. Farmers are integrating termites in their farming system. Crops like banana are planted near them, wood is buried in the soil to attract termites. And sometimes the soil of termite mounds is harvested or ploughed as soil improving amendment. Although there are termites that feed on agricultural crops, they use the leaves for their own farming –fungus gardens-, they do that mainly on exotic crops and not all species are harmful for agricultural crops. These are smart practices using local knowledge of farmers, who depend on agriculture for food.
Soil in focus 5: IYS2015
Soil as an archive: disaster, climate change and revolution
Soil can function as an archive of natural and cultural events in the past. The soil from Iceland shown here bears evidence of natural disaster of a great volcanic eruption with great impact on the climate and society.
The Laki volcano in Iceland is a fissure in earth crust (Photo: Ulrich Latzenhofer)
This soil from Iceland was formed in a valley bottom, were water and dead plants accumulate, forming a peat soil. The soil is formed on a mix of organic material with volcanic ashes and some pure ash layers over peaty material. The lighter coloured ash layers, in between the peat (see lines at 48 – 61 cm depth), are silent witnesses of the humanitarian disaster that followed the dramatic eruption of the Laki volcano in 1783. The dust brought into the atmosphere caused a global lowering of temperatures, negatively affecting crop production, especially in Northern Europe. Deaths were mourned because of starvation and the effects of the fall-out: sulphur and fluoride brought into the atmosphere. In France, famine and poverty were aggravated by the crop failures in 1785 and 1788 caused by climate extremes. The impact of the eruption of the Laki volcano is therefore thought to have been the spark for the French revolution.
The ash layers seen here are pages in the book of the landscape that is soil: an archive for past events, in this case with dramatic consequences for society.
Facts and dates:
2800 BP: ash layer from eruption of Hekla volcano
1783: Icelandic society disrupted (25% of the population died and 50% of the livestock perished from fluorine poisoning.
230.000 victims in the UK (sulphur clouds affecting lungs)
Famines in various countries, including Egypt and India
10 year of climate change globally, but especially in the norther hemisphere
Coldest winter in the US: 1784 Soil classification (WRB, 2006): Mollic Histic Silandic Andosol (Eutric Turbic Drainic)
Soils in focus :4 IYS2015
In the northern hemisphere, the podzol is a common soil in the sandy landscapes of, amongst others, the ice pushed ridges and cover sands. Although typical for zones, the layered and contrasting podzol also occurs in tropical landscapes, where they form in specific environments, especially in quartz rich sediments.
The podzol is recognizable by a top layer of humus-rich soil with a bleached, ash-grey subsurface horizon, the leaching layer (the eluviation or E-horizon), which is referred to in Russian as 'Zola' (= ash). The leached humic acids and iron and aluminium compounds precipitate at some depth, around and between the sand grains, creating a dark accumulation layer; the illuviation (B-) horizon). The illuviation layer may cement at the lower boundary by iron oxidation, thus forming a hard layer (hard pan). The podzolization process can only occur under conditions of precipitation excess and acidic conditions in the soil. That is to say, the release of soluble, organic humic acids, under forest- or heath vegetation, and a soil environment in which the acids are not neutralized because of a lack of easily weatherable minerals or positively charged ions such as, for example, calcium. The organic acids cause the leaching of the iron and aluminium through which a eluviation layer is formed. Below the illuviation horizon, the original sandy parent material, the C-horizon is found. When disturbed through management, in the case of ploughing for example, the bleached eluviation layer is not always recognizable.
|Tropical podzols are prone to severe erosion when left bare. This image shows a degraded podzol in East-Kalimantan.
Photo: S. Mantel.
|Black water stream.
Photo: Tim Ross.
Podzols are limited in extent in tropical regions and are most commonly found in lowlands areas where sandy parent material, in combination with high rainfall and specific vegetation, favours the podzolization process. Hardon used the scientific term "podzol" for tropical soils in 1936 for the first time in his description of quartz-rich sands with poor vegetation on the island Bangka in the South China Sea. Rivers colour ‘coffee-brown’ in these landscapes from the humic acids washed through the soil and drained to the waterways. Podzolization can progress so strongly in these soils that the eluviation layer may eventually disappear altogether and sterile, white sands remain.
Soils in focus :3 IYS2015
With the growth of cities around the globe, soils are more and more influenced by the urban and industrial environment. Technosols are soils that include all kinds of materials made, exposed or transported by human activity that otherwise would not occur under natural conditions at that specific location of the Earth’s surface. The urban soil is exposed to pavement, buildings and pollution. Profile development is often very limited, except for archaeological dumps.
The soil shown here is from under the city of Hilversum. Under 73 cm the original soil, a sandy soil from former heathland, is visible. This soil has been exposed to prolonged waste water infiltration that was channelled to these heathlands in former times (since 1860), when it was still at the edge of the border of the city. This has caused pollution with, amongst other, heavy metals and polyaromatic hydrocarbons. Between about 50 and 73 cm in the profile, artefacts are visible. The layer consists mainly of poorly to non-degradable materials from a former waste dump that was placed on top of the former infiltration fields.
The first half meter of the profile is the result of the expansion of the city of Hilversum in early 20th century, when the soil was covered with construction sand and pavement, streets and houses. Between 2003 and 2006 the soils in this part of the city were remediated. The profile is an archive of past uses and different phases in society. It reflects the development of environmental awareness and perception of community health.
Soils in focus :2 IYS2015:
Plaggen soils are soils with a thick man-made and humus-rich surface layer that is a result of long and continued manuring. These soils typically developed on sandy soils in north-western Europe. The plaggen management system started in medieval times, and in some places even earlier, when farming practices intensified on the sandy soils to meet the needs of a growing population. In the plaggen system, heather sods, with some adhering sand, and other organic materials were commonly spread on the floor of the pot stables where livestock was held during the night. The dung of the cattle mixed with the organic material. Periodically the stable was emptied and the mixed organic material was spread on the farming fields. The whole sand landscape was used in this farming system (an area about 7 to 10 times that of the farming field). The raised agricultural fields, that resulted from the continued additions of organic materials, gave rise to a typical landscape with sharp breaks in elevation and are called Plaggenesch in Germany or Es in Dutch. In situ, the soil quality increased but at the landscape level disaster was created. Wind erosion resulted from removal of vegetative cover of the sandy landscape and antropogene deserts were formed, that would not have developed under natural conditions. This management system stopped abruptly after the introduction of mineral fertilizers.
Soils in focus :1 IYS2015:
Acid sulphate soil (Tidalic Fluvisol, Wang Noi, Ayutthaya, Thailand). These soils change dramatically when drained: sulphuric acid is released in the soil and acidity drops to extreme levels.