1. Effects of Soil Moisture on Microaggregate Morphology USAXS is the best method because N 2 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 Microaggregate Morphology USAXS is the best method because N 2 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. McCarthy 1, Edmund Perfect 1, Julie D. Jastrow 2, and Jan Ilavsky 3 (1)Department of Geological Sciences, University of Tennessee, Knoxville, TN (jmccart1@utk.edu)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. McCarthy 1, Edmund Perfect 1, Julie D. Jastrow 2, and Jan Ilavsky 3 (1)Department of Geological Sciences, University of Tennessee, Knoxville, TN (jmccart1@utk.edu)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, N 2 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, N 2 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 Discussion (preliminary analysis of data collected in January, 2003) Microaggregate 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 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 RRD 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 CO 2 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 CO 2 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 μ m 10 μ m 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 Sites Contrast 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 Sites Contrast 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