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 (jmccart1@utk.edu)

(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 (jmccart1@utk.edu)

(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