Colony of bacteria
Soils can also be
studied atfeatures
smaller used
The diagnostic
scales soils in
to differentiate
USDA Soil Taxonomy are
~1 micron
primarily macromorphological
Coarse
fragments
Coarse
fragments
Sand
Is the whole
greater than
the sum of
its parts ?
Silt
Clay
Soil micromorphology
- the study of undisturbed soil
samples with the help of microscopic
techniques, in order to identify small
scale features and interpret how they
formed.
http://edafologia.ugr.es/micgraf/media/desinter.gif
Granular
crumb structure
Compacted soil
How are
the primary
particles
The
soil
fabric
arranged in real soils ?
http://www.grdc.com.au/growers/gc/gc48/conference1.htm
Textural porosity
Pores resulting from
random arrangement of
soil particles
Textural porosity
+
Structural
porosity
Total porosity
Vughs
Cracks
Channels and Chambers
Origin of pores in a soil with
annual moldboard plow/disk tillage
Depth (cm)
Lots of tillage pores
Few biopores
Origin of pores in a soil with minimum tillage
Depth (cm)
Fewer tillage pores
Lots of biopores
How were the Dutch soil scientists able to
differentiate between tillage pores and biopores?
Analysis of thin sections !!
Relationships between
coarse and fine materials
in soil fabrics
Distributions of coarse and fine materials
Mostly sand particles
- very few fine materials
Bridging
External coatings
Microaggregates between sand particles
Coatings and microaggregates
Sand embedded in fine matrix
How much
sand
do you
need to add to
Massive
amounts
of sand
a clayey are
soilneeded
to make
it stop
because
sand acting like
needs to
a become
clay? the
dominant component of
the soil structure
Clay dominated
soil matrix with
embedded sand
particles
Sand dominated
soil matrix with clay
coatings
< 20% sand
> 50% clay
>80% sand
<10% clay
Dramatic soil textural modification is a standard part of
golf course construction but is cost prohibitive (and
impractical) in most other situations
Play can resume 10
minutes after rain
stops
Structural development
at the microscale
Angular blocky structure
Platy structure
Granular crumb structure
Clay particles
Tall Grass Prairie
the dominant native
ecosystem in IL
Domains
of clay particles
Multi-valent
High
cations
levels ofsuch
as
Ca+2, Al+3
monovalent
and
Fe+3such
are
cations
important
as Na+ and
binding
K+cause clay
agents
at to
this
domains
scale.
disperse.
Microaggregates
(< 0.25 mm)
35,000 x
Microbial
glues are
important
binding
agents at
this scale
Humic
substances
are also
important
binding
agents at
this scale
Macroaggregates
(>0.25 mm)
Networks of roots and fungal hyphae are
important stabilizers of macroaggregates
http://soils.usda.gov/sqi/concepts/soil_biology/images/M4_Fungi_LR_small.jpg
Soil processes can be studied at the microscale
Dry soil at the end of an extended dry period
http://edafologia.ugr.es/iluv/media/origen1.gif
Eluviation/Illuviation at the microscale
Rain water rapidly infiltrates the surface horizon
http://edafologia.ugr.es/iluv/media/origen2.gif
Eluviation/Illuviation at the microscale
Some clay particles disperse in water filled pores
http://edafologia.ugr.es/iluv/media/origen3.gif
Eluviation/Illuviation at the microscale
Suspended clay moves downward through
macropores to deeper, drier horizons
http://edafologia.ugr.es/iluv/media/origen4.gif
Eluviation/Illuviation at the microscale
Capillary action moves water outward into micropores
http://edafologia.ugr.es/iluv/media/origen5.gif
Eluviation/Illuviation at the microscale
A thin “skin” of oriented clay particles begins
to accumulate on the walls of macropores
http://edafologia.ugr.es/iluv/media/origen6.gif
Eluviation/Illuviation at the microscale
Oriented clay particles coat the walls of dry macropores
http://edafologia.ugr.es/iluv/media/origen7.gif
Many years go by…
The process repeats itself over and over… causing illuvial
clay skins to slowly increase in thickness
http://edafologia.ugr.es/iluv/media/origen8.gif
Oriented clay particles also accumulate
around aggregates
http://edafologia.ugr.es/iluv/media/origen9.gif
Clay particles also orient around
microorganisms.
Coating
http://edafologia.ugr.es/iluv/media/clas14.gif
Infilling
http://edafologia.ugr.es/iluv/media/clas15.gif
Quasi-coating
http://edafologia.ugr.es/iluv/media/clas12.gif
Fragments of illuvial
features
http://edafologia.ugr.es/iluv/media/clas16.gif
Illuvial features at the macro-scale
Clay skins
http://edafologia.ugr.es/iluv/media/rec1.gif
Essential factors for significant
eluviation/illuviation of clay
 Alternating periods of intense rain and drought
 Sufficiently high clay content in surface horizons
 Sufficient macroporosity for downward transport
 Relatively stable land surface
Most of the images in this presentation were
obtained from an invaluable web resource on
soil micromorphology maintained by
Dr. C. Dorronsoro, Department of Pedology,
University of Grenada, Spain
http://edafologia.ugr.es/micgraf/indexw.htm