Effects of Soil Moisture on Microaggregate Morphology
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Effects of Soil Moisture on Effects of Soil Moisture on Microaggregate MorphologyMicroaggregate Morphology
• USAXS is the best method because N2 adsorption requires dry samples
• Wet microaggregates (compared to dry microaggregates)
• similar multi-scale structures (Eq. 1)
• Low-Q power law slope is consistently lower for all microaggregate samples
• Higher surface fractal dimension
• Higher degree of scale-invariant roughness
• Caused by swelling of soil organic matter?
• Effects on accessibility of pores and extent of physical protection of organic matter?
Effects of Soil Moisture on Effects of Soil Moisture on Microaggregate MorphologyMicroaggregate Morphology
• USAXS is the best method because N2 adsorption requires dry samples
• Wet microaggregates (compared to dry microaggregates)
• similar multi-scale structures (Eq. 1)
• Low-Q power law slope is consistently lower for all microaggregate samples
• Higher surface fractal dimension
• Higher degree of scale-invariant roughness
• Caused by swelling of soil organic matter?
• Effects on accessibility of pores and extent of physical protection of organic matter?
Determining the Morphology of Soil Microaggregates using USAXS
John F. McCarthy1, Edmund Perfect1, Julie D. Jastrow2, and Jan Ilavsky3
(1)Department of Geological Sciences, University of Tennessee, Knoxville, TN ([email protected])
(2)Environmental Research Division, Argonne National Laboratory; (3) UNICAT, Advanced Photon Source
Determining the Morphology of Soil Microaggregates using USAXS
John F. McCarthy1, Edmund Perfect1, Julie D. Jastrow2, and Jan Ilavsky3
(1)Department of Geological Sciences, University of Tennessee, Knoxville, TN ([email protected])
(2)Environmental Research Division, Argonne National Laboratory; (3) UNICAT, Advanced Photon Source
Goals• Determine the structural and
chemical bases of soil microaggregate formation and stability
Approach• Multiple state-of-science techniques:
• USAXS and SANS, N2 adsorption, SEM, Scanning Transmission X-ray Microscopy
USAXS Objectives• Examine the scale-independent
structure of soil microaggregates
• Effects of soil moisture content on surface morphology and porosity
Goals• Determine the structural and
chemical bases of soil microaggregate formation and stability
Approach• Multiple state-of-science techniques:
• USAXS and SANS, N2 adsorption, SEM, Scanning Transmission X-ray Microscopy
USAXS Objectives• Examine the scale-independent
structure of soil microaggregates
• Effects of soil moisture content on surface morphology and porosity
Results and Results and DiscussionDiscussion
(preliminary analysis of data collected in January, 2003)Microaggregate StructureMicroaggregate Structure
• Complex, multiple size-scale structures
• Unified Guinier/Power-Law Approach • (Eq. 1; Beaucage, G. and D.W. Shaefer .1994. J. Non-
Crystalline Solids 172-174:797-805)
• High-Q Regime
• primary particles are Euclidean solids
• Low-Q Regime
• No evidence of a terminal size
• Power law exponent (P) ~ 3.5• consistent with a scale-invariant
surface fractal structure
Microaggregate StructureMicroaggregate Structure
• Complex, multiple size-scale structures
• Unified Guinier/Power-Law Approach • (Eq. 1; Beaucage, G. and D.W. Shaefer .1994. J. Non-
Crystalline Solids 172-174:797-805)
• High-Q Regime
• primary particles are Euclidean solids
• Low-Q Regime
• No evidence of a terminal size
• Power law exponent (P) ~ 3.5• consistent with a scale-invariant
surface fractal structure
sP
P
q
qRerfB
RqG
q
qRerfRqB
RqGqI
gs
ss
gsubg
3
22
32222
6
3exp
6
3exp
3exp)(
RRDRRD
Preliminary evaluation of microaggregates from the virgin prairie
Background
• Global Climate Change and Carbon Sequestration• Enlarge pools of long-lived organic
matter in soil to reduce atmospheric CO2
• Evaluate agricultural management strategies and land-use options to enhance levels of soil organic matter
• Soil Microaggregates• they protect C against
decomposition, resulting in much longer residence times for C
• why organic matter (OM) in soil microaggregates have such long residence times
Background
• Global Climate Change and Carbon Sequestration• Enlarge pools of long-lived organic
matter in soil to reduce atmospheric CO2
• Evaluate agricultural management strategies and land-use options to enhance levels of soil organic matter
• Soil Microaggregates• they protect C against
decomposition, resulting in much longer residence times for C
• why organic matter (OM) in soil microaggregates have such long residence times
100 μm
10 μm
SOIL MICROAGGREGATES
Scanning Electron
Micrograph of soil
microaggregates
(Defined as soil aggregates in the 53-250 μm size
range)
Higher magnification
view of aggregate structure
Field SitesContrast microaggregate
structure under experimental manipulations that alter accumulation of
soil organic matter
• Chronosequence of tallgrass prairie restoration
• Soil disturbance (till vs no-till)
• Contrasting agronomic management systems (conventional vs organic)
• Contrasting forage management systems
• A range of soil types with contrasting properties that may alter soil microaggregate stability
Field SitesContrast microaggregate
structure under experimental manipulations that alter accumulation of
soil organic matter
• Chronosequence of tallgrass prairie restoration
• Soil disturbance (till vs no-till)
• Contrasting agronomic management systems (conventional vs organic)
• Contrasting forage management systems
• A range of soil types with contrasting properties that may alter soil microaggregate stability
Data from a prairie restoration chronosequence
Contrast virgin prairie with a cultivated agricultural soil