# Coupling Pyrolysis with Mid-infrared Spectroscopy (Py-MIRS) to Fingerprint Biochemical Quality of Soil Organic Matter

Yvonne Funkuin Nkwain, Scott Demyan, Frank Rasche, Marie-France Dignac, Elke Schulz, Thomas Kätterer, Torsten Müller, Georg Cadisch

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Yvonne Funkuin Nkwain, Scott Demyan, Frank Rasche, Marie-France Dignac, Elke Schulz, et al. Coupling Pyrolysis with Mid-infrared Spectroscopy (Py-MIRS) to Fingerprint Biochemical Quality of Soil Organic Matter. Tropentag, Sep 2017, Bonn, Germany. hal-01608846

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Coupling Pyrolysis with Mid-infrared Spectroscopy (Py-MIRS) to
Fingerprint Biochemical Quality of Soil Organic Matter

YVONNE FUNKUIN NKWAIN<fnref n="1" />, SCOTT DEMYAN<fnref n="2" />, FRANK RASCHE<fnref n="3" />, MARIE-FRANCE DIGNAC<fnref n="4" />,
ELKE SCHULZ<fnref n="5" />, THOMAS KÄTTERER<fnref n="6" />, TORSTEN MÜLLER<fnref n="7" />, GEORG CADISCH<fnref n="8" />

Abstract

A novel method coupling pyrolysis with mid-infrared spectroscopy (Py-MIRS) was deve-
loped to characterise soil organic matter (SOM) quality in soils with different management
and land use types while overcoming acknowledged constraints of analytical techniques such
as mineral interferences and associated secondary reactions. The set-up generates pyrolysis
fingerprint spectra from which individual pyrolysis products can be related to biochemical
SOM quality. For method development, pyrolysis temperature, heating rate and pyrolysis
time were optimised using pure organic substances (e.g., glucose, xylan, quebracho). The
preferred experimental conditions were 700 °C, 20 °C ms⁻<fnref n="1" /> and 30 s, respectively, ensuring
maximum pyrolysis yield efficiency, while reducing the formation of secondary compounds.
Soil test samples were taken from (i) the Static Fertilisation Experiment, Bad Lauchstädt,
Germany (Chernozem), (ii) the Frame Experiment Ultuna, Sweden (Cambisol) and (iii)
the Observatory for Environmental Research (ORE-ACBB) Experiment, Lusignan, France
(Cambisol). The results were used to evaluate the changes in SOM biochemical characte-
ristics due to management practices and land use type. The pyrolysis products consisted
mainly of organic compounds with aliphatic and aromatic structures, polysaccharides and
carboxyl groups, alkenes as well as methane, carbon dioxide, carbon monoxide. Differences
in peak areas of the different SOM compounds were observed providing insights into ma-
nagement and land use type related biochemical SOM quality. Py-MIRS results indicated
that the SOM quality in soils receiving organic and mineral fertiliser inputs differed from
that in samples of bare fallow and control soils. However, there were no distinct effects of

<footnote n="1">¹University of Hohenheim, Inst. of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), Germany</footnote>

<footnote n="2">²University of Hohenheim, Inst. of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), Germany</footnote>

<footnote n="3">³University of Hohenheim, Inst. of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), Germany</footnote>

<footnote n="4">⁴French National Institute for Agricultural Research, Functional ecology and ecotoxicology of agroecosystems, France</footnote>

<footnote n="5">⁵Helmholtz Centre for Environmental Research, Dept. of Soil Ecology,</footnote>

<footnote n="6">⁶Swedish University of Agricultural Sciences, Department of Soil Ecology, Sweden</footnote>

<footnote n="7">⁷University of Hohenheim, Inst. of Crop Science, Germany</footnote>

<footnote n="8">⁸University of Hohenheim, Inst. of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute), Germany</footnote>
fertilisation and land use on aromatic compounds evolved in the soils. Notwithstanding,
the coupling of pyrolysis with mid-infrared spectroscopy allowed via semi-quantification of
pyrolysis products a rapid monitoring of SOM biochemical quality changes due to mana-
gement and land use type with high degree of reproducibility. The proposed technique has
considerable potential for the initialisation of SOM pools in dynamic SOM models.It was
concluded that Py-MIRS represents an effective and reproducible technique to characterise
SOM biochemical quality changes as a result of differing management practices and land
use change.

**Keywords:** Fertilisation, land use, mid-infrared spectroscopy, pyrolysis, soil organic matter