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European soil : a global perspective

Soil of the Mediterranean Region

The presence of a Salic horizon is essential to differentiateSolonchaks from other soil types such as Gleysols. Mollic,Calcic and Gypsic Solonchaks may be associated withKastanozems, Phaeozems, Calcisols and Gypsisols. SalineVertisols occur very occasionally in the semi arid parts ofsouthern Europe.

On the other hand, Solonetz (see figure below), rich inexchangeable sodium and magnesium ions, are confined toflat lands and are found with Gleysols and Solonchaks. Incoastal areas, they can be associated with Fluvisols. Thetransition of Solonetz to Gypsisols and Calcisols occurs dueto the accumulation of gypsum and calcite below thediagnostic Natric horizon, as found in semi arid conditionsof Spain and Turkey. Extensive areas of saline soil occur inMorocco, Tunisia, Algeria, Egypt and throughout the MiddleEast. One dominant factor for the expansion of saline soilin the Mediterranean is the introduction of irrigation andthe intensification of crop production.

The polygonal development on the surface a of Solonetz insouthern Turkey (HO).

Solonchaks and Solonetz are very difficult soil types tomanage and require extensive effort to be productive.However, they are widely used for arable farming andextensive grazing. The production of salt tolerant crops(Atriplex) on unused grasslands seems to be a highlyprofitable and environmentally friendly practise used inseveral countries of the Mediterranean region.

Andosols

Andosols occur in the volcanic regions of southern Europe,primarily in Italy, France and with minor distributions in theundulating mountainous of Turkey. They are associatedwith Cambisols, Podzols and Luvisols in France, Cambisols inItaly whereas in Turkey with Calcisols, Leptosols andadjacent Fluvisols. Determination of Andosols has beenhighly controversial within the Mediterranean context dueto the lack of the bulk density requirement (0.9 g/cm3),organic matter content as well as morphological-fieldcharacteristics such as thixotropy (the smeary feeling thatdevelops due to the sol-gel transformations under pressure).

Andosols of the western slope of Mount Etna in Sicily, Italyformed by lava flows with tephra – fragmented rocks deposited bypyroclastic flows from an erupting volcano (CD).

Andosols are cultivated for a variety of crops. Theyrepresent soil ecosystems that are vulnerable todisturbances, especially to soil sealing, which may lead tothe development of landslides (southern Italy and easternTurkey) and erosion. The unavailability of phosphorous istheir main chemical constraint of soil fertility.

Kastanozems and Phaeozems

The distribution of Kastanozems in southern Europe is verylimited and mainly associated with Leptosols, Cambisol,Calcisols and Fluvisols. They occasionally associate withGypsisols, Solonchaks and Solonetz in depressions ofwarmer and drier areas. Some Kastanozems are covered byforests or are used for grazing. Other areas are cultivatedfor cereals and occasionally for irrigated crops. The build upof salts may be a problem for these fertile and productivesoil types if water is not well managed during irrigation.

Phaeozem is a soil with a distinct dark surface colour andhigh organic matter content. In the Mediterranean regionLeptic, Vertic, Gleyic, Luvic, Pachic, Calcaric, Skeletic, Siltic,Dystric, Chromic, and Haplic represent the most commonsoil units. They are found in Spain, France, Italy, the WesternBalkans, Albania, Greece, Turkey, Israel, Lebanon, Syria, andMorocco. Phaeozems in rain fed, flat or gently undulatingenvironments, become very productive especially forcereals. Under irrigation, a great variety of crops, includingsugar beet, vegetables or fodder, may be cultivated. Insloping mountain areas, they are suitable for forestry ormanaged grazing. If mismanaged, Phaeozems inmountainous regions could be seriously threatened byerosion. The lack of the Mollic horizon in many parts of theMediterranean mountains is the best evidence of historicsoil erosion.

Umbrisols

Umbrisols occur mainly in the northwest of Portugal andSpain with smaller patches in the Balkans. Umbrisols areassociated moist but free-draining conditions, namelyPhaeozems, which ultimately integrate by cultivation toAnthrosols. Cambisols and Leptosols may also be associatedto Umbrisols as well as being adjacent in the landscape.

Regions of cleared forests, converted to short grasses,widely used as grazing lands, dominate Umbrisols in thenorthwestern part of the Mediterranean. Thus, themanagement in this context has aimed the introduction ofimproved pasture and correction of soil acidity by liming.Cambisols, Luvisols and Leptosols at higher elevations facesimilar problems as Umbrisols.

Gypsisols, Durisols and Calcisols

These are the typical soil types that form under arid or semi-arid conditions. With the exception of Calcisols, theirextension is limited in the northern Mediterranean areas buthighly visible in the southern countries. In the arid regionsof North Africa and the Middle East, mud and debris floodsformed the so-called “wadis” located in areas of low relief.Many wadis were formed during the Late Pleistocene toEarly Holocene period between between 13,000 and 8,000years ago. Consecutive mudflow occurrences have beenresponsible for the development of Calcisols with variablecontents of secondary carbonate (lime) accumulation,leading to the development of Calcic and Petrocalcichorizons within a depth of 100 cm or deeper and oftengrading to ‘calcrete’.

Gypsisols are characterised by the substantial accumulationof secondary gypsum (CaSO4). The natural vegetation ismade of xerophytic plants (cacti are xerophytic shrubs) andephemeral grasses. The largest concentration of Gypsisols inthe Mediterranean occurs in the Libyan Desert, Jordan,Syria, parts of Central Anatolia and Cyprus. The agriculturaluse of Gypsisols depends on the gypsum content in theupper topsoil layer. If the gypsum content is low they canbe used for production of small grains, cotton, and foragecrops. In the Gypsisols of alluvial plains, irrigation anddrainage are necessary for the cultivation of crops, fruittrees, and grapes. However large areas are used only forextensive grazing.

Durisols contain cemented secondary silica (SiO2) in theupper one meter of the soil. Their typical feature is thepresence of a hard-cemented layer identified as the“duripan phase”. In the Mediterranean, they occur on leveland slightly sloping alluvial plains, terraces and gentlysloping piedmont plains mainly in Jordan, Syria, Morocco,Tunisia, and Algeria. They are often found in associationwith Gypsisols, Calcisols, Solonchaks, Solonetz, Vertisols,Arenosols, and Cambisols.

Tabular gypsum (calcium sulphate) crystals in Gypsisols viewed ina polarizing microscope at x100 magnification (EA & SK).

A Gypsisol profile from Spain (JB).

Pedogenetically, Gypsisols are characterised by the presenceof Duric and Petroduric horizons that practically limit theeffective soil depth available to plant roots. In fact, thePetroduric horizon can vary between 10 cm to 4 m in depth.In addition, Durisols could have an Argic, Cambic or Calcichorizon above the Petroduric horizon. The agricultural useof Durisols is limited to extensive grazing.

Calcisols occupy large areas in Spain while in Turkey andCyprus where they are ranked the second most dominantsoil after Leptosols. Minor distributions are also found inItaly, France, Greece and Albania. The major soil unitsinclude the Vertic, Luvic, Petric, and Haplic categories.Petric and Luvic Calcisols represent the dominant calcretesof Turkey, Cyprus, Spain as well as North Africa and theMiddle East. Calcisols are associated with Leptosols athigher elevation and with Gleysols, Vertisols, andSolonchaks in lower depressions.

A striking example of a calcrete. The picture shows a massivesecondary accumulation of soft lime forming thisCcalcic horizon(the white zone) in the hilly areas of Central Albania (PZ).

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