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DRIFTS band areas as measured pool size proxy to reduce parameter uncertainty in soil organic matter models

Laub, Moritz and Demyan, Michael Scott and Nkwain, Yvonne Funkuin and Blagodatsky, Sergey and Kätterer, Thomas and Piepho, Hans-Peter and Cadisch, Georg (2020). DRIFTS band areas as measured pool size proxy to reduce parameter uncertainty in soil organic matter models. Biogeosciences. 17 , 1393-1413
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Abstract

Soil organic matter (SOM) turnover models predict changes in SOM due to management and environmental factors. Their initialization remains challenging as partitioning of SOM into different hypothetical pools is intrinsically linked to model assumptions. Diffuse reflectance mid-infrared Fourier transform spectroscopy (DRIFTS) provides information on SOM quality and could yield a measurable pool-partitioning proxy for SOM. This study tested DRIFTS-derived SOM pool partitioning using the Daisy model. The DRIFTS stability index (DSI) of bulk soil samples was defined as the ratio of the area below the aliphatic absorption band (2930 cm(-1)) to the area below the aromatic- carboxylate absorption band (1620 cm(-1)). For pool partitioning, the DSI (2930 cm(-1) / 1620 cm(-1)) was set equal to the ratio of fast-cycling / slow-cycling SOM. Performance was tested by simulating long-term bare fallow plots from the Bad Lauchstadt extreme farmyard manure experiment in Germany (Chernozem, 25 years), the Ultuna continuous soil organic matter field experiment in Sweden (Cambisol, 50 years), and 7 year duration bare fallow plots from the Kraichgau and Swabian Jura regions in southwest Germany (Luvisols). All experiments were at sites that were agricultural fields for centuries before fallow establishment, so classical theory would suggest that a steady state can be assumed for initializing SOM pools. Hence, steady-state and rameter sets that differed in turnover rates and humification efficiency. Initialization using the DSI significantly reduced Daisy model error for total soil organic carbon and microbial carbon in cases where assuming a steady state had poor model performance. This was irrespective of the parameter set, but faster turnover performed better for all sites except for Bad Lauchstadt. These results suggest that soils, although under long-term agricultural use, were not necessarily at a steady state. In a next step, Bayesian-calibration-inferred best-fitting turnover rates for Daisy using the DSI were evaluated for each individual site or for all sites combined. Two approaches significantly reduced parameter uncertainty and equifinality in Bayesian calibrations: (1) adding physicochemical meaning with the DSI (for humification efficiency and slow SOM turnover) and (2) combining all sites (for all parameters). Individual-site-derived turnover rates were strongly site specific. The Bayesian calibration combining all sites suggested a potential for rapid SOM loss with 95 % credibility intervals for the slow SOM pools' halflife being 278 to 1095 years (highest probability density at 426 years). The credibility intervals of this study were consistent with several recently published Bayesian calibrations of similar two-pool SOM models, i.e., with turnover rates being faster than earlier model calibrations suggested; hence they likely underestimated potential SOM losses.

Authors/Creators:Laub, Moritz and Demyan, Michael Scott and Nkwain, Yvonne Funkuin and Blagodatsky, Sergey and Kätterer, Thomas and Piepho, Hans-Peter and Cadisch, Georg
Title:DRIFTS band areas as measured pool size proxy to reduce parameter uncertainty in soil organic matter models
Year of publishing :2020
Volume:17
Page range:1393-1413
Number of Pages:21
Publisher:Copernicus Publications, The European Geosciences Union
ISSN:1726-4170
Language:English
Publication Type:Journal article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 4 Agricultural Sciences > 401 Agricultural, Forestry and Fisheries > Soil Science
Keywords:Soil organic matter (SOM), turnover models, management and environmental factors, Diffuse reflectance mid-infrared Fourier transform spectroscopy (DRIFTS)
URN:NBN:urn:nbn:se:slu:epsilon-p-105151
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-105151
Additional ID:
Type of IDID
DOI10.5194/bg-17-1393-2020
Web of Science (WoS)000521594000001
ID Code:16853
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Dept. of Ecology
(S) > Dept. of Ecology
Deposited By: SLUpub Connector
Deposited On:05 May 2020 08:46
Metadata Last Modified:05 May 2020 08:46

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