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ANDOSOLS. Dr. Selim KAPUR University of Çukurova Departments of Soil Science and Archaeometry Adana, TURKEY kapur@cu.edu.tr. Volcanism is not randomly distributed over the world. It is concentrated near plate boundaries where plate subduction or seafloor spreading takes place. Other

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slide1

ANDOSOLS

Dr. Selim KAPUR

University of Çukurova

Departments of Soil Science and Archaeometry

Adana, TURKEY

kapur@cu.edu.tr

slide2

Volcanism is not randomly distributed over the world. It is

concentrated near plate boundaries where plate

subduction or seafloor spreading takes place. Other

occurrences are linked to deep mantle plumes that

reach the Earth's surface at distinct `hotspots'.

Figure 1 shows the geographic distribution of major

volcanic regions.

Landforms in volcanic regions are strongly influenced by the

chemical and mineralogical composition of the materials that

were deposited during eruptive phases. Volcanic rocks and

magmas are grouped according to their silica contents in

three main categories labeled `Rhyolite' (65-75% SiO2),

`Andesite' (65-55% SiO2) and `Basalt' (55-45% SiO2).

The mineralogical properties and chemical composition

(notably the contents of K2O, Na2O and CaO) distinguish

individual rock types. See Figure 2.This influences profoundly

the character and morphology of volcanic phenomena.

slide3

MAJOR LANDFORMS IN VOLCANIC LANDSCAPES

Figure 1. Volcanic regions of the world

slide5

The Reference Soil Group of the Andosols holds soils developed in volcanic materials.

Common international names are:

Andosols: FAO, Soil Map of the World,

Andisols' :USDA Soil Taxonomy,

Andosols'and `Vitrisols‘: France and `volcanic ash soils'.

ANDOSOL: Black soils of volcanic landscapes

From Japan an (black), and do (soil)

slide6

MAJOR SOIL FORMING LIMITING FACTOR

Steep slopes,

volcanic hazard,

P fixation,

thixotropy

and structural instability

slide7

PARENT MATERIALS

Volcanic ash, tuff, pumice, cinders and other volcanic ejecta

TUFF

PUMICE

http://members.iinet.net.au

http://www.athro.com

slide8

VOLCANIC EJECTA

CINDER

http://volcano.und.nodak.edu

http://helios.bto.ed.ac.uk

slide9

Definition of Andosols

Soils having

a vitric@ or an andic@ horizon starting within 25 cm from the soil surface; and

no diagnostic horizons (unless buried deeper than 50 cm) other than a histic@, fulvic@, melanic@, mollic@, umbric@, ochric@, duric@ or cambic@ horizon.

Common soil units

Vitric*, Silandic*, Aluandic*, Eutrisilic*, Melanic*, Fulvic*, Hydric*, Histic*, Leptic*, Gleyic*, Mollic*, Duric*, Luvic*, Umbric*, Arenic*, Placic*, Pachic*, Calcaric*, Skeletic*, Acroxic*, Vetic* , Sodic*, Dystric*, Eutric*, Haplic*.

slide10

http://www.soils.wisc.edu/

HYDRIC ANDOSOL

VITRIC ANDOSOL

One or more layers within 100cm Water ret 1500kPa of 100% or more

No andic horizon overlying a vittic horizon

slide11

VITRIC ANDOSOL (Central Anatolia)

Dingil, 2003. Ph.D. Thesis

slide12

KEY TO ANDOSOL

SOIL UNITS

GELIC ANDOSOLS

Andosols having permafrost within 200cm of the surface

GLEYIC ANDOSOLS

Andosols with gleyic properties within 100cm of the surface

VITRIC ANDOSOLS

Andosols lacking a smeary consistance or a texture which is silt loam or finer on the weighted average for all horizons within 100cm of the surface or both

MOLLIC ANDOSOLS

Andosols having a mollic A-horizon

UMBRIC ANDOSOLS

Andosols having an umbric A-horizon

HAPLIC ANDOSOLS

Other Andosols

slide13

VITRIC: A vitric horzion must:

1. Have 10% or more volcanic glass and other primary minerals in the fine earth fraction (250-50µm); and

2. Have

ı. a bulk density less than 0.9kg dm3 or

ıı. Alox + ½Feox more than 0.4%, or

ııı. Phospahte retention more than 25%, and

3. Have a thickness of 30cm or more

ANDIC: An andic horizon must have all of the following

1. A bulk density at field capacity (no prior drying) of less than 0.9kg dm3; and

2. 10 percent or more clay and an (Alox + ½Feox) value2 in the fine earth fraction of 2 percent or more; and

3. 70 percent or more phosphate retention; and

4. less than 10 percent volcanic glass in the fine earth fraction; and

5. a thickness of 30 cm or more.

slide14

ENVIRONMENT

Undulating to mountainous, humid, semi-arid?, arctic to tropical regions with a wide range of vegetation types.

PROFILE DEVELOPMENT

A-C or A-B-C profile. Rapid weathering of porous volcanic material resulting in accumulation of stable organo-mineral complexes, and minerals such as allophane, imogolite (Al2 SiO3(OH), and ferrihydrite

slide15

Allophane

Imogolite

http://www.uky.edu

http://www.chem.umass.edu

Allophane commonly occurs as very small hallow rings or spheres having diameters of approximately 35 - 50 Å. This morphology is characteristic of allophane, and can be used in its identification.

Ferrihydrite are hydrous iron oxides. Fe2O3.2FeOOH.2.6H2O. Secondary

mineral in an oxidizing environment, strongly dependant on pH. Functions as allophane. The organically bound Fe is most probably ferrihydrite –Fe.

Imogolite occurs as very small tubes having inside diameters of 10 Å and outside diameters of 20 Å. These tubes may be several µm in length, and often form bundles of two to several hundred tubes. Occasional branching of tubes may occur.

slide17

Topographic sequence of associated soils

ANDOSOLS

CAMBISOLS/LUVISOLS

VERTISOLS

slide18

GENESIS

Presence of andic (rich in allophane) and vitric (rich in volcanic glass)

Allophane

Volcanic glass

http://www.mindat.org

Dingil, M. 2003. Ph.D thesis)

slide19

Development depends on rapid chemical weathering of porous, permeable fine grained volcanic minerals + organic matter eg. Hydrolysis of microcline and augite yieldingsufficient Al and Fe.

KAlSi3O8 + 2 H2O = K+ + Al3+ + 3 SiO2 + 4 OH-

microcline

CaFeSi2O6 + 2 H2O = Ca2+ + Fe2+ + 2 SiO2 + 4 OH-

augite

Fe2andAl3 form stable complexes with humus. However, Fe precipitates eventually to Ferrihydrite

slide20

Aluminum alone protects organic matter against BIODEGRADATION by developing Al-Humus complexes with high metal/organic ratioof limitedmobility

This induces accumulation of organic matter in top soil ie carbon sequestration developing a melanic surface horizon

The liberated silica in the weathering products partly yield allophanes and imogolite.

slide21

Thus Andosols are of binary composition indiacting the competition between Al humus complexes and formation of allophane. Allophane stays stable in weakly acid and neutral conditions whereas the Al-humus complexes are dominant in more acid environments.

The clay contents of Andosols changes over time particularly in the subsoil as allophane and imogolite are transformed to halloysite, kaolinite and at extreme acid conditions to gibsite. Eventually an Andosol may grade into a Luvisol or Podzol depending on precipitation

slide22

Morphology

Typical (?) Andosols have an AC or ABC profile with a dark Ah-horizon (20 - 50 cm thick) on top of a brown B- or C-horizon.

 The average organic matter content of the surface horizon (melanic) is between5-6% but the darkest profiles may contain more.

 The surface horizon is very porous, very friable, and has a crumb or granular structure.

Smeary consistence or a texture which is silt loam or finer and feels greasy within 100cm.It may become almost liquid when rubbed, presumably because of sol-gel transformations under pressure (thixotropy) in Vitric Andosols.

slide23

Hydrology

  • Excellent drainage because of high porosity
  • Gleyic properties at shallow ground water
  • Stagnic in paddy fields

Mineralogy

  • X-ray amorphous materials' of allophane and imogolite, and/or humus complexes of Al and Fe together with opaline silica.
  • Besides primary minerals, ferrihydrite, (disordered) halloysite and kaolinite, gibbsite and various 2:1 and 2:1:1 layer silicates and intergrades can be present.
slide24

Physical Characteristics

  • Good aggregate stability
  • Resistant to water erosion
  • But difficult to disperse for texture analysis
  • Low bulk density, typically (?) less than 0.9g/cm3 at some cases of high hydration is as low as 0.3g/cm3
  • The quantity of available water is generally higher than other mineral soils because of the high water content at the permanent wilting point (1500kPa)
  • Excessive air drying or severe drought conditions develop irreversible deterioration in water holding capacity, ion exchange capacity, soil volume and cohesion of soil particles.Ultimately!,particles fall apart to a fine dust which is susceptible to wind erosion.
slide25

Chemical Characteristics

  • High exchange properties
  • Charge dependent on pH and electrolyte concentration due to high contents of soil organic matter and allophane
  • Figure 2 illustrates the variation of charge by pH. Halloysite and montmorillonite are dominantly permenantly charged
  • Base saturation (BS) values are variable due to the variable charge properties. BS low in strongly leached Andosols of the humid tropics except in young and dry region Andosols
  • These characteristics are attributed to the active Al already present in humus complexes as well as exhangeable, interlayer and as allophane and imogolite
slide26

Figure 2. NH4+ and Cl- retention curves measured in 0.01 M NH4Cl (0.1 M NH4Cl for montmorillonite). (a) montmorillonite; (b) halloysite; (c) allophane 905 (Al:Si=2:1, containing some imogolite); (d) allophane PA (Al:Si=1:1). Wada & Okamura, 1977)

slide27

MANAGEMENT

  • High potential for agricultural production
  • Fertile at unleached conditions at profiles formed on intermediate and basic volcanic ash
  • Active Al is a drawback for phosphate availability –fixation. This may be remediated via liming and addition of silica, organic material and phosphate fertilisers
  • Easy to till with good rootability and water storage except in strongly hydrated cases
  • Sugarcane, tobacco, sweet potatoes (tolerant to low P levels), tea, vegetables, wheat and horticulturalş crops are suitable for the tropic and sub-humid areas.
  • On steep slopes they are best kept under forests or well-managed pastures. In low lands best used for paddy rice cultivation which bears a problem of development of dense hardpans due to the development of Fe and Mn oxides