scholarly journals Long residence times of rapidly decomposable soil organic matter: application of a multi-phase, multi-component, and vertically-resolved model (TOUGHREACTv1) to soil carbon dynamics

2014 ◽  
Vol 7 (1) ◽  
pp. 815-870 ◽  
Author(s):  
W. J. Riley ◽  
F. M. Maggi ◽  
M. Kleber ◽  
M. S. Torn ◽  
J. Y. Tang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Reactive Transport ◽  
Lignin Content ◽  
Sensitivity Analyses ◽  
Rooting Depth ◽  
Carbon Substrate ◽  
Advective Transport ◽  
Turnover Rates ◽  
Multi Phase

Abstract. Accurate representation of soil organic matter (SOM) dynamics in Earth System Models is critical for future climate prediction, yet large uncertainties exist regarding how, and to what extent, the suite of proposed relevant mechanisms should be included. To investigate how various mechanisms interact to influence SOM storage and dynamics, we developed a SOM reaction network integrated in a one-dimensional, multi-phase, and multi-component reactive transport solver. The model includes representations of bacterial and fungal activity, multiple archetypal polymeric and monomeric carbon substrate groups, aqueous chemistry, aqueous advection and diffusion, gaseous diffusion, and adsorption (and protection) and desorption from the soil mineral phase. The model predictions reasonably matched observed depth-resolved SOM and dissolved organic carbon (DOC) stocks in grassland ecosystems as well as lignin content and fungi to aerobic bacteria ratios. We performed a suite of sensitivity analyses under equilibrium and dynamic conditions to examine the role of dynamic sorption, microbial assimilation rates, and carbon inputs. To our knowledge, observations do not exist to fully test such a complicated model structure or to test the hypotheses used to explain observations of substantial storage of very old SOM below the rooting depth. Nevertheless, we demonstrated that a reasonable combination of sorption parameters, microbial biomass and necromass dynamics, and advective transport can match observations without resorting to an arbitrary depth-dependent decline in SOM turnover rates, as is often done. We conclude that, contrary to assertions derived from existing turnover time based model formulations, observed carbon content and δ14C vertical profiles are consistent with a representation of SOM dynamics consisting of (1) carbon compounds without designated intrinsic turnover times, (2) vertical aqueous transport, and (3) dynamic protection on mineral surfaces.

scholarly journals Long residence times of rapidly decomposable soil organic matter: application of a multi-phase, multi-component, and vertically resolved model (BAMS1) to soil carbon dynamics

2014 ◽  
Vol 7 (4) ◽  
pp. 1335-1355 ◽  
Author(s):  
W. J. Riley ◽  
F. Maggi ◽  
M. Kleber ◽  
M. S. Torn ◽  
J. Y. Tang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Reactive Transport ◽  
Lignin Content ◽  
Reaction Rates ◽  
Sensitivity Analyses ◽  
Rooting Depth ◽  
Carbon Substrate ◽  
Advective Transport ◽  
Multi Phase

Abstract. Accurate representation of soil organic matter (SOM) dynamics in Earth system models is critical for future climate prediction, yet large uncertainties exist regarding how, and to what extent, the suite of proposed relevant mechanisms should be included. To investigate how various mechanisms interact to influence SOM storage and dynamics, we developed an SOM reaction network integrated in a one-dimensional, multi-phase, and multi-component reactive transport solver. The model includes representations of bacterial and fungal activity, multiple archetypal polymeric and monomeric carbon substrate groups, aqueous chemistry, aqueous advection and diffusion, gaseous diffusion, and adsorption (and protection) and desorption from the soil mineral phase. The model predictions reasonably matched observed depth-resolved SOM and dissolved organic matter (DOM) stocks and fluxes, lignin content, and fungi to aerobic bacteria ratios. We performed a suite of sensitivity analyses under equilibrium and dynamic conditions to examine the role of dynamic sorption, microbial assimilation rates, and carbon inputs. To our knowledge, observations do not exist to fully test such a complicated model structure or to test the hypotheses used to explain observations of substantial storage of very old SOM below the rooting depth. Nevertheless, we demonstrated that a reasonable combination of sorption parameters, microbial biomass and necromass dynamics, and advective transport can match observations without resorting to an arbitrary depth-dependent decline in SOM turnover rates, as is often done. We conclude that, contrary to assertions derived from existing turnover time based model formulations, observed carbon content and Δ14C vertical profiles are consistent with a representation of SOM consisting of carbon compounds with relatively fast reaction rates, vertical aqueous transport, and dynamic protection on mineral surfaces.

scholarly journals Soil Organic Matter Decomposition and Turnover in a Tropical Ultisol: Evidence from δ13C, δ15N and Geochemistry

Radiocarbon ◽  
2002 ◽  
Vol 44 (1) ◽  
pp. 93-112 ◽  
Author(s):  
Evelyn S Krull ◽  
Erick A Bestland ◽  
Will P Gates
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Base Cations ◽  
Recent Change ◽  
Soil Profiles ◽  
Turnover Rates ◽  
Kakamega Forest ◽  
Depth Profiles ◽  
Soil Fraction ◽  
Tropical Conditions

Soil organic matter (SOM), leaf litter, and root material of an Ultisol from the tropical rainforest of Kakamega, Kenya, were analyzed for stable carbon (δ13C) and nitrogen (δ15N) isotopic values as well as total organic carbon (TOC) and total nitrogen (TN) contents in order to determine trends in SOM decomposition within a very well-developed soil under tropical conditions. In addition, we quantified mineralogy and chemistry of the inorganic soil fraction. Clay mineralogical variation with depth was small and the abundance of kaolin indicates intense weathering and pedoturbation under humid tropical conditions. The soil chemistry was dominated by silica, aluminium, and iron with calcium, potassium, and magnesium as minor constituents. The relative depletion of base cations compared with silica and aluminium is an indicator for intense weathering and leaching conditions over long periods of time. Depth profiles of δ13C and δ15N showed a distinct enrichment trend down profile with a large (average 13δC = 5.0 and average 15δN= 6.3) and abrupt offset within the uppermost 10–20 cm of the soil. Isotopic enrichment with depth is commonly observed in soil profiles and has been attributed to fractionation during decomposition. However, isotopic offsets within soil profiles that exceed 3 are usually interpreted as a recent change from C4 to C3 dominated vegetation. We argue that the observed isotopic depth profiles along with data from mineralogy and chemistry of the inorganic fraction from the Kakamega Forest soil are a result of intense weathering and high organic matter turnover rates under humid tropical conditions.

scholarly journals Carbon Isotope Measurements to Determine the Turnover of Soil Organic Matter Fractions in a Temperate Forest Soil

Agronomy ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1944
Author(s):  
Dóra Zacháry ◽  
Tibor Filep ◽  
Gergely Jakab ◽  
Mihály Molnár ◽  
Titanilla Kertész ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Depth ◽  
Accurate Determination ◽  
Turnover Rates ◽  
Fractionation Process ◽  
Chemical Structures ◽  
Decomposition Processes ◽  
Ft Ir ◽  
Organic Matter Fractions

Soil organic matter (SOM) is a combination of materials having different origin and with different stabilization and decomposition processes. To determine the different SOM pools and their turnover rates, a silt loam-textured Luvisol from West Hungary was taken from the 0–20 cm soil depth and incubated for 163 days. Maize residues were added to the soil in order to obtain natural 13C enrichment. Four different SOM fractions—particulate organic matter (POM), sand and stable aggregate (S + A), silt- plus clay-sized (s + c) and chemically resistant soil organic carbon (rSOC) fractions—were separated and analyzed using FT-IR, δ13C, and 14C measurements. The mean residence time (MRT) of the new C and the proportion of maize-derived C in the fractions were calculated. The POM fraction was found to be the most labile C pool, as shown by the easily decomposable chemical structures (e.g., aliphatic, O-alkyl, and polysaccharides), the highest proportion (11.7 ± 2.5%) of maize-derived C, and an MRT of 3.6 years. The results revealed that the most stable fraction was the rSOC fraction which had the smallest proportion of maize-derived C (0.18 ± 2.5%) and the highest MRT (250 years), while it was the only fraction with a negative value of Δ14C (−75.0 ± 2.4‰). Overall, the study confirmed the hypothesis that the SOM associated with finer-sized soil particles decomposes the least, highlighting the significance of the fractionation process for more accurate determination of the decomposition processes of SOM pools.

DYNAMICS OF SOIL MICROBIAL BIOMASS AND WATER-SOLUBLE ORGANIC C IN BRETON L AFTER 50 YEARS OF CROPPING TO TWO ROTATIONS

1986 ◽  
Vol 66 (1) ◽  
pp. 1-19 ◽  
Author(s):  
W. B. McGILL ◽  
K. R. CANNON ◽  
J. A. ROBERTSON ◽  
F. D. COOK
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Environmental Conditions ◽  
Management Practices ◽  
Water Soluble ◽  
Turnover Rates ◽  
Organic Matter Quality ◽  
Organic C ◽  
Microbial N

Amounts and turnover rates of biomass and water-soluble organic C (WSOC) were measured at the Breton plots where records of long-term management of a Gray Luvisolic soil are available. Plots (control, manure, and NPKS) which had been cropped to either a wheat-fallow or a wheat-oats-barley-forage-forage rotation for 50 yr were sampled 13 times during 1981 and 1982. Biomass C and flush of microbial N were measured using the chloroform fumigation technique. Long-term crop yields were used to derive C supply to the plots. Regression analyses were used to relate seasonal fluctuations in environmental conditions to biomass and WSOC dynamics. Reinoculation with soil was unnecessary but Lysobacter sp. formed a greater proportion of isolates following incubation of fumigated soil than of unfumigated samples. Reinoculation with Lysobacter sp. is suggested to provide a more standardized biological assay. The 5-yr rotation contained 38% more N but 117% more microbial N than did the 2-yr rotation, and manured treatments contained twice as much microbial N as did NPKS or control plots. A management effect on soil organic matter quality is indicated. Averge turnover rates of biomass were 0.2–3.9 yr−1; being 1.5–2 times faster in the 2-yr rotation than in the 5-yr rotation. Replenishment of the WSOC component would have to occur 26–39 times yr−1 to supply microbial turnover. Most of the biomass must be dormant because annual C inputs are two orders of magnitude less than maintenance energy requirements. Seasonal variations in biomass were most consistently related to losses during desiccation and regrowth upon moistening. Regrowth appears to be at the expense of native soil organic matter. Management practices and environmental conditions therefore affect amount of organic matter by controlling both input of C and biomass turnover. Key words: Crop rotations, Luvisol, organic matter, biomass, soluble C, Breton plots

scholarly journals Measuring and modelling continuous quality distributions of soil organic matter

2009 ◽  
Vol 6 (5) ◽  
pp. 9045-9082 ◽  
Author(s):  
S. Bruun ◽  
G. I. Ågren ◽  
B. T. Christensen ◽  
L. S. Jensen
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Management Practices ◽  
Model Development ◽  
Turnover Rates ◽  
Continuous Distributions ◽  
Continuous Quality ◽  
Direct Interpretation ◽  
Decomposition Models ◽  
Som Decomposition

Abstract. An understanding of the dynamics of soil organic matter (SOM) is important for our ability to develop management practices that preserve soil quality and sequester carbon. Most SOM decomposition models represent the heterogeneity of organic matter by a few discrete compartments with different turnover rates, while other models employ a continuous quality distribution. To make the multi-compartment models more mechanistic in nature, it has been argued that the compartments should be related to soil fractions actually occurring and having a functional role in the soil. In this paper, we make the case that fractionation methods that can measure continuous quality distributions should be developed, and that the temporal development of these distributions should be incorporated into SOM models. The measured continuous SOM quality distributions should hold valuable information not only for model development, but also for direct interpretation. Measuring continuous distributions requires that the measurements along the quality variable are so frequent that the distribution is approaching the underlying continuum. Continuous distributions leads to possible simplifications of the model formulations, which considerably reduce the number of parameters needed to describe SOM turnover. A general framework for SOM models representing SOM across measurable quality distributions is presented and simplifications for specific situations are discussed. Finally, methods that have been used or have the potential to be used to measure continuous quality SOM distributions are reviewed. Generally, existing fractionation methods have to be modified to allow measurement of distributions or new fractionation techniques will have to be developed. Developing the distributional models in concert with the fractionation methods to measure the distributions will be a major task. We hope the current paper will help spawning the interest needed to accommodate this.

scholarly journals THE INFLUENCE OF NITROGEN ON THE DECOMPOSITION OF CROP RESIDUES IN THE SOIL

1962 ◽  
Vol 42 (2) ◽  
pp. 276-288 ◽  
Author(s):  
H. Lueken ◽  
W. L. Hutcheon ◽  
E. A. Paul
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Crop Residues ◽  
Lignin Content ◽  
Organic Matter Content ◽  
Organic Amendments ◽  
Matter Content ◽  
Structural Development ◽  
Residue Decomposition ◽  
Advanced Stages

Additions of mineral nitrogen accelerated the initial decomposition rate of incorporated wheat straw, alfalfa hay and glucose when added to two soils differing widely in organic matter content. However, in the more advanced stages of decomposition the reverse was true, and over the total incubation period larger amounts of carbon were maintained in soils supplemented with nitrogen.In contrast to all other residues used, nitrogen additions to cellulose effected a continuous and substantial increase in residue decomposition. This was the only residue for which the mineralization of soil organic matter did not supply nitrogen adequate for its decomposition within 120 days.The very slow rate of decomposition of sphagnum peat could be attributed to its high lignin content, rather than to the nitrogen levels.Sulphacetolysis analysis, which measures the non-humified carbon, indicated the feasibility of separating non-humified crop residues from the more complex soil organic matter. Addition of organic amendments thus resulted in a drop in the soil humification quotient. Nitrogen resulted in the retention of a significantly higher percentage of the added residue, without a drop in the humification quotient for the high organic matter Melfort soil.Residue applications to soils produced a significant improvement of structural development, especially in the low organic matter soil (Arborfield).

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

2020 ◽  
Vol 17 (6) ◽  
pp. 1393-1413 ◽  
Author(s):  
Moritz Laub ◽  
Michael Scott Demyan ◽  
Yvonne Funkuin Nkwain ◽  
Sergey Blagodatsky ◽  
Thomas Kätterer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Absorption Band ◽  
Parameter Uncertainty ◽  
Turnover Rates ◽  
Bayesian Calibration ◽  
Individual Site ◽  
Bare Fallow

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 Lauchstädt 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 DSI initializations were compared, using two published parameter 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 Lauchstädt. 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' half-life 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.

The use of stable carbon isotopes for estimating soil organic matter turnover rates

Geoderma ◽  
1998 ◽  
Vol 82 (1-3) ◽  
pp. 43-58 ◽  
Author(s):  
Martial Bernoux ◽  
Carlos C Cerri ◽  
Christopher Neill ◽  
Jener F.L de Moraes
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Carbon Isotopes ◽  
Stable Carbon Isotopes ◽  
Stable Carbon ◽  
Turnover Rates ◽  
Organic Matter Turnover ◽  
Soil Organic Matter Turnover

scholarly journals DRIFTS peaks as measured pool size proxy to reduce parameter uncertainty of soil organic matter models

2019 ◽  
Author(s):  
Moritz Laub ◽  
Michael Scott Demyan ◽  
Yvonne Funkuin Nkwain ◽  
Sergey Blagodatsky ◽  
Thomas Kätterer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Parameter Uncertainty ◽  
Stability Index ◽  
Turnover Rates ◽  
Bayesian Calibration ◽  
Agricultural Use ◽  
Bare Fallow

Abstract. The initialization of soil organic matter (SOM) turnover models has been a challenge for decades. Instead of using laborious and error prone size-density fractionation SOM pool partitioning, we propose the inexpensive, rapid, and non destructive Diffuse reflectance mid infrared Fourier transform spectroscopy (DRIFTS) technique on bulk soil samples to gain information on SOM pool partitioning from the spectra. Specifically, the DRIFTS stability index, defined as the ratio of aliphatic C-H (2930 cm−1) to aromatic C=C (1620 cm−1) stretching vibrations, was used to divide SOM into fast and slow cycling pools in the soil organic module of the DAISY model. Long-term bare fallow plots from Bad Lauchstädt (Chernozem, 25 years) and the Ultuna frame trial in Sweden (Cambisol, 50 years) were combined with bare fallow plots of 7 years duration in the Kraichgau and Swabian Jura region in Southwest Germany (Luvisols). All fields had been in agricultural use for centuries before fallow establishment, so classical theory would suggest an initial steady state of SOM, which was hence used to compare the performance of DAISY initializations against the newly established DRIFTS stability index. The test was done using two different published parameter sets (2.7 × 10−6 d−1, 1.4 × 10−4 d−1, 0.1 compared to 4.3 × 10−5 d−1, 1.4 × 10−4 d−1, 0.3 for the turnover rates of slow pool, fast pool and humification efficiency, respectively). The DRIFTS initialization of SOM pools significantly reduced model errors of poor performing model runs assuming steady state, irrespective of the turnover rates used, but the faster turnover parameter set fit better to all sites except Bad Lauchstädt. This suggests that soils under long-term agricultural use were not necessarily at steady state. A Bayesian calibration was applied in a next step to identify the best-fitting turnover rates for the DRIFTS stability index in DAISY, both for each site individually and for a combination of all sites. The two approaches which significantly reduced parameter uncertainty and equifinality were: (1) the addition of the physico-chemically based DRIFTS stability index, and (2) combining several sites into one Bayesian calibration, as derived turnover rates can be strongly site specific. The combination of all four sites showed that SOM is likely lost at relatively fast turnover rates with the 95 % credibility intervals of the slow SOM pools half life ranging from 278 to 1095 years, with 426 years as a value of highest probability density. The credibility intervals of this study were consistent with several recently published Bayesian calibrations of similar SOM models, all turnover rates were considerably faster than earlier models suggested. It is therefore likely that published turnover rates understimate the potential loss of SOM.

scholarly journals Measuring and modeling continuous quality distributions of soil organic matter

2010 ◽  
Vol 7 (1) ◽  
pp. 27-41 ◽  
Author(s):  
S. Bruun ◽  
G. I. Ågren ◽  
B. T. Christensen ◽  
L. S. Jensen
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Management Practices ◽  
Model Development ◽  
Turnover Rates ◽  
Continuous Distributions ◽  
Continuous Quality ◽  
Direct Interpretation ◽  
Decomposition Models ◽  
Som Decomposition

Abstract. An understanding of the dynamics of soil organic matter (SOM) is important for our ability to develop management practices that preserve soil quality and sequester carbon. Most SOM decomposition models represent the heterogeneity of organic matter by a few discrete compartments with different turnover rates, while other models employ a continuous quality distribution. To make the multi-compartment models more mechanistic in nature, it has been argued that the compartments should be related to soil fractions actually occurring and having a functional role in the soil. In this paper, we make the case that fractionation methods that can measure continuous quality distributions should be developed, and that the temporal development of these distributions should be incorporated into SOM models. The measured continuous SOM quality distributions should hold valuable information not only for model development, but also for direct interpretation. Measuring continuous distributions requires that the measurements along the quality variable are so frequent that the distribution approaches the underlying continuum. Continuous distributions lead to possible simplifications of the model formulations, which considerably reduce the number of parameters needed to describe SOM turnover. A general framework for SOM models representing SOM across measurable quality distributions is presented and simplifications for specific situations are discussed. Finally, methods that have been used or have the potential to be used to measure continuous quality SOM distributions are reviewed. Generally, existing fractionation methods will have to be modified to allow measurement of distributions or new fractionation techniques will have to be developed. Developing the distributional models in concert with the fractionation methods to measure the distributions will be a major task. We hope the current paper will help generate the interest needed to accommodate this.

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