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Title: Using fourier-transform mid-infrared spectroscopy to distinguish soil organic matter composition dynamics in aggregate fractions of two agroecosystems

Author
item FULTZ, LISA - Louisiana State University
item MOORE-KUCERA, JENNIFER - Texas State University
item Calderon, Francisco
item Acosta-Martinez, Veronica

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2014
Publication Date: 11/11/2014
Publication URL: http://handle.nal.usda.gov/10113/61924
Citation: Fultz, L., Moore-Kucera, J., Calderon, F.J., Acosta Martinez, V. 2014. Using fourier-transform mid-infrared spectroscopy to distinguish soil organic matter composition dynamics in aggregate fractions of two agroecosystems. Soil Science Society of America Journal. 78:1940-1948.

Interpretive Summary: In this work, we investigated the chemistry of different size soil aggregates using mid-infrared spectroscopy (MidIR). Soils from different agronomic managements were sieved to separate large aggregates from smaller aggregate size classes, as well as obtaining organic matter that was occluded within the aggregates. MidIR is a quick and non destructive way of gathering chemical information from soils and plant tissues. Our data showed that different aggregate size classes vary in their mineral as well as organic composition. Particular organic matter, which can exist inside soil aggregates, had spectral properties that suggest it is prone to decomposition. Dissecting the soil this way takes us a step closer to understanding how soil carbon accumulates in soils and the possible mechanisms that are at play in soil quality improvements.

Technical Abstract: The relationship between soil organic carbon (SOC) content and quality of SOC as impacted by land management is not well understood and may influence long-term storage of SOC. To better understand the potential for SOC storage in specific aggregate pools (i.e. physically protected intra-aggregate C) a wet-sieving aggregate fractionation method was coupled with Fourier-transform mid-infrared (MidIR) spectroscopy analysis to determine the chemical composition of water-stable (macroaggregates, microaggregates, and silt+clay) and intra-aggregate (particulate organic matter (POM), microaggregates, and silt+clay) fractions in an integrated crop-livestock (ICL) system and continuous cotton (CTN) production. The ICLsystem included a paddock of grazed WW B. Dahl - Old World Bluestem (Bothriochloa bladhii (Retz) S.T. Blake; bluestem) and a no-till crop rotation of wheat-fallow-rye-cotton (Triticum aestivum L., NA, Secale cereale L, and Gosspium hirsutum L.; respectively) for livestock grazing and cotton production. Distance-based redundancy analysis of the MidIR spectra distinguished the intra-aggregate POM from the other fractions. The intra-aggregate POMfraction was correlated with relatively high absorbance of spectra characteristic of esters, phenolic C-O and/ or carboxylates, while macro- and microaggregates where correlated with spectra characteristic of a mixture of carbonyl C=O, aromatic CH, and carboxylic functional groups. Differences attributed to management were identifiable in intra-aggregate POM and both silt+clay fractions. Within the intra-aggregate POM fraction, bluestem was characterized by possibly labile functional groups with absorbance at 2800-3000 cm-1 and 3300-3450 cm-1 . Both rotations appeared to be driving the differences in the silt+clay fractions with more labile functional groups found in the following rye and cotton planting.