The Nature and

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The Nature and Properties of Soils
Joel Gruver NCSU Soil Science
http//www.soil.ncsu.edu/lockers/Gruver_J/NPS.ppt
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Leading Soil Science text for 84 years
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The only thing constant about soils is their
variability Nyle Brady
gt 600 soil series in Virginia !!
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What is a soil series ?
Silt loams
20D
15 to 25 percent slopes
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What is a soil series ?
A
and the most descriptive level of USDA Soil
Taxonomy
A soil series is a unique combination of soil
horizons
Frederick soil profile
Bt1
Bt2
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Frederick Fine,
mixed, semiactive, mesic Typic Paleudult
What is USDA Soil Taxonomy ?
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Soil surveys contain practical information about
soil suitability for a variety of uses
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Soil surveys describe inherent soil properties
VA soil surveys describe variation at a scale of
115840
1 inch on the map 15,840 inches in the field
1 inch on the map ¼ mile
1 square inch 40 acres
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Do you have a copy of your county soil survey ?
Contact your local NRCS office
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Geologic variation in the Mid-Atlantic region
Triassic basin
http//www.wm.edu/geology/virginia/
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Typical felsic crystalline system landscape
NCSU Soils technical bulletin 314
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ADDITIONS
LOSSES
Precipitation plus ions, aerosols
and particulates
Sediment
Gas loss N2, N2O, CO2
4 processes of soil formation
Sediment
Dissolved ions
Clay Salts Dissolved OM
Organic residues ? humus Primary ? Secondary
minerals minerals
Dissolved ions
Leaching of solutes
TRANS- LOCATIONS
TRANS- FORMATIONS
Adapted from Stewart (1990)
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Young Soils
Old Soils
Poorly Defined HorizonsLow Degree of
WeatheringSlightly LeachedThin Solum
Well Defined Horizons High Degree of
WeatheringHighly LeachedThick Solum
http//www.mo15.nrcs.usda.gov/features/gallery/
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Biogeochemistry
Water is the main driver of soil change
Chadwick and Chorover ( 2001)
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a grand tour of soil change done with
elegance and scientific rigor. of interest to
ecologists agronomists, foresters, and land
managers. William Reiners and Pedro Sánchez
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Soil body metaphors
A new way to think about soil
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Sand
(0.05 2 mm)
Silt
(0.002 0.05 mm)
Primary mineral particles
Clay
(lt 0.002 mm)
http//ianrpubs.unl.edu/fieldcrops/graphics/soilh2
o2.gif
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The soil skeleton
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Humus
Clay
http//www.ccma.csic.es/dpts/suelos/
Brady and Weil (2002)
The soil skin and connective tissues
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Primary minerals
physical weathering
chemical weathering
K
HCO3-
Cl-
Ca2
Na
SO4-2
sand and silt
dissolved salts
secondary clay minerals
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12 textural classes
USDA Textural triangle
Functional groups
A little clay goes a long way
http//www.oneplan.org/Images/soilMst/SoilTriangle
.gif
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Loamy soils
Favorable physical properties
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Texture strongly influences soil hydraulic
properties
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Easily available water
http//res2.agr.gc.ca/publications/hw/graphics/ep1
6.jpg
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Relationship between soil texture and
probability of leaching
http//res2.agr.ca/stjean/publication/bulletin/nit
rogen-azote_e.pdf
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Is the whole greater than the sum of its parts ?
Silt
Coarse fragments
Coarse fragments
Clay
Sand
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Assembling the particles

Granular peds
Blocky peds
Adapted from Carter (2004)
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Macroaggregates
Microaggregates
Clay-humus complexes
Soil Profile
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Granular crumb structure
Compacted soil
The soil fabric
http//www.grdc.com.au/growers/gc/gc48/conference1
.htm
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Preferential flow of air and water
Pore diameter
Drainage pores
gt 30 µm
Field Capacity
Easily available
Plant available water
Permanent wilting point
0.2 µm
Hygroscopic water
Adapted from Buol (2000)
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Soil Respiratory Circulatory system
http//www.mtm.kuleuven.ac.be/Research/NDT/IDO_SHe
rman_final.ppt
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Soil from a long term experiment in Beltsville, MD
20 yrs sod, 5 yrs CT corn
25 yrs CT corn
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Relatively small differences in SOC
Large differences in soil function
After adding water
1.4 C
140 bu/a
1.0 C
48 bu/a
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Angular blocky structure enhances drainage and
root growth below the plow layer
Ray Weil
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Intensive tillage
Long term no-till
Network of biopores
Plow pan
Ontario Ministry of Ag and Food
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PLOW PAN
Compaction can severely limit root growth
Sub-soil water and nutrients
Brady and Weil (2002)
Brady and Weil (2002)
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Disk pan
Plow pan
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SOM
Mineral particles
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SOM is a complex mixture
Living organisms
Biologically active SOM
Recent residues
Humus
Adapted from Magdoff and Weil (2003)
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Relationship between fine mineral fraction and SOM
Magdoff and Weil (2004)
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OM inputs
Tillage
OM inputs
Tillage
Aggregates form around organic residues
Processes that disrupt aggregates accelerate
decomposition
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• What is humus ????
• Humus is organic matter that has been transformed
  such that its original source is no longer
  apparent The diverse products of humification
  have many common characteristics
• Extreme chemical complexity
• Resistance to further decomposition
• High specific surface and negative charge
• Dark color

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Organic matter functions mainly as it is
decayed and destroyed. Its value lies in its
dynamic nature. W. Albrecht, 1938
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When incorporating organic residues
Remember the fence post principle !!
Schriefer (2000)
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The many benefits of surface residues
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The Soil Stomach
Bacteria Fungi Algae Protozoa Nematodes Microarthr
opods Enchytraeids Earthworms Ants, termites,
spiders Mollusks Others rodents, snakes,
voles, amphibians, etc.
Body size increasing
Microflora
Microfauna
Mesofauna
Macrofauna
Megafauna
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Feed the soil vs. Feed the crop ?
Both strategies are important !
Healthy roots need available nutrients !
Unhealthy roots use nutrients inefficiently
Plants with poorly developed roots tend to have
nutrient deficiency and drought stress symptoms
Acute root disease
Chronic root malfunction
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Holistic approach to healthy roots
Well adapted crop
Healthy soil food web
Adapted from Bailey and Lazarovits (2003)
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How often do you look at crop roots ?
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What are these nobby growths ?
Efficient N fixation Edamame, cowpeas Peanuts Ine
fficient N fixation Snap beans Garden peas Lima
beans
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Mycorrhizal root
Non- mycorrhizal root
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Understanding nutrient uptake
H20
Root exudates activate soil microbes
Transpirational stream
H20
Root growth
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At least 16 elements are essential for the growth
of all plants
Soil
C O H
N K Ca Mg P S
Cl Fe Mn Zn B Cu Mo
air water
macronutrients
micronutrients
V
Ni
Needed by some plants
Si
Co
Na
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Some elements (e.g. Se, I, As, Cr) have been
identified as essential for animals but not for
plants.
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minerals
Where are the nutrients in soil ?
Soil solids contain nutrients
organic matter
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Soil water contains nutrients
H20
H20
K
-
-
Ca2
H20
-
H20
-
Mg2
-
-
Al3
Humus
-
-
H20
H20
H20
exchangeable ions
soil solution
soil soup
H20
H20
H20
H20
Clay
-
H20
Na
-

-
H20

-
K
SO4-2
Ca2
H20
H20
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Whats in the soil soup ??
Ca2
DOM
NO3-
Ca2
Mg2
NO3-
H2PO4-
Ca2
DOM
NH4
NO3-
K
Mg2
Ca2
DOM
NO3-
SO4-2
DOM
Ca2
Adapted from Brady and Weil (2002)
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Re-seasoning the soup
Highly buffered
Poorly buffered
Modified from Havlin et al. (1999)
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The acid infertility complex
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Nutrient availability varies with pH
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Understanding aluminum toxicity
Toxic forms of Al are bioavailable at low pHs
Aluminum toxicity is minimal above pH 5.5
http//www2.ctahr.hawaii.edu/tpss/research_extensi
on/rxsoil/alroot.gif
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Dont over lime !
Liming to a pH value near neutrality in
southeastern soils often produces micronutrient
deficiencies.
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