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Effects of Soil Moisture on Microaggregate Morphology

RRD. SOIL MICROAGGREGATES. Scanning Electron Micrograph of soil microaggregates (Defined as soil aggregates in the 53-250 μ m size range). 100 μ m. 10 μ m. Higher magnification view of aggregate structure. Determining the Morphology of Soil Microaggregates using USAXS

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Effects of Soil Moisture on Microaggregate Morphology

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  1. RRD SOIL MICROAGGREGATES Scanning Electron Micrograph of soil microaggregates (Defined as soil aggregates in the 53-250 μm size range) 100 μm 10 μm Higher magnification view of aggregate structure • Determining the Morphology of Soil Microaggregates using USAXS • John F. McCarthy1, Edmund Perfect1, Julie D. Jastrow2, and Jan Ilavsky3 • Department of Geological Sciences, University of Tennessee, Knoxville, TN (jmccart1@utk.edu) • Environmental Research Division, Argonne National Laboratory; (3) UNICAT, Advanced Photon Source Results and Discussion (preliminary analysis of data collected in January, 2003) • 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 • 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 • 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 • Effects of Soil Moisture on Microaggregate 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? • 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 Preliminary evaluation of microaggregates from the virgin prairie

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