Soil geochemistry as a driver of soil organic matter composition: insights from a soil chronosequence

Abstract. A central question in carbon research is how stabilization mechanisms in soil change over time with soil development and how this is reflected in qualitative changes of soil organic matter (SOM). To address this matter, we assessed the influence of soil geochemistry on bulk SOM composition along a soil chronosequence in California, USA spanning 3 million years. This was done by combining data on soil mineralogy and texture from previous studies with additional measurements on total carbon (C), stable isotope values (δ13C and δ15N), and spectral information derived from Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). To assess qualitative shifts in bulk SOM, we analysed the peak areas of simple plant-derived (S-POM), complex plant-derived (C-POM), and predominantly microbially derived OM (MOM) and their changes in abundance across soils varying several millennia to millions of years in weathering and soil development. We observed that SOM became increasingly stabilized and microbially-derived (lower C : N ratio, increasing δ13C and δ15N) as soil weathering progresses. Peak areas of S-POM (i.e. aliphatic root exudates) did not change over time, while peak areas of C-POM (lignin) and MOM (components of microbial cell walls (amides, quinones, and ketones)) increased over time and depth and were closely related to clay content and pedogenic iron oxides. Hence, our study suggests that with progressing soil development, SOM composition co-varies with changes in the mineral matrix. Our study indicates that a discrimination in favour of structurally more complex OM compounds (C-POM, MOM) gains importance as the mineral soil matrix becomes increasingly weathered.

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Effect of systematic application of mineral fertilizers and long-term aftereffect of liming on the organic matter of light-grey forest soil

Agricultural science Euro-North-East ◽

10.30766/2072-9081.2020.21.2.160-168 ◽

2020 ◽

Vol 21 (2) ◽

pp. 160-168

Author(s):

N. A. Kodochilova ◽

T. S. Buzynina ◽

L. D. Varlamova ◽

E. A. Katerova

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Forest Soil ◽

Humus Content ◽

Total Carbon ◽

Mineral Fertilizers ◽

Fertilized Soil ◽

Grey Forest Soil ◽

Nizhny Novgorod Region

The studies on assessment of changes in the content and composition of soil organic matter under the influence of the systematic use of mineral fertilizers (NPK)1, (NPK)2, (NPK)3 against the background of the aftereffect of single liming in doses of 1.0 and 2.0 h. a. (control – variants without fertilizers and lime) were conducted in the conditions of the Nizhny Novgorod region in a long – term stationary experiment on light-grey forest soil. The research was carried out upon comple-tion of the fifth rotation of the eight-field crop rotation. The results of the study showed that for 40 years (from 1978 to 2018) the humus content in the soil (0-20 cm) decreased by 0.19-0.52 abs. % in variants as compared to the original (1.60 %); though, humus mineralization was less evident against the background of long-term use of mineral fertilizers compared to non-fertilized control. The higher humus content in the topsoil was noted in the variants with minimal (NPK)1 and increased (NPK)2 doses of fertilizer – 1.41 and 1.25 %, respectively. The humus content in non-fertilized soil and when applying high (NPK)3 doses of mineral fertilizers was almost identical – 1.08-1.09 %. The predominant group in the composition of humus were humic acids, the content of which in the experiment on average was 37.8 % of the total carbon with an evident decrease from 42.6 % in the control to 31.8% when applying increased doses of mineral fertilizers. The aftereffect of liming, carried out in 1978, was unstable and did not significantly affect the content and composition of soil organic matter.

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The Use of Radiocarbon to Measure the Effects of Earthworms On Soil Development

Radiocarbon ◽

10.1017/s0033822200010298 ◽

1980 ◽

Vol 22 (3) ◽

pp. 892-896 ◽

Cited By ~ 13

Author(s):

J D Stout ◽

K M Goh

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Soil Profile ◽

Mineral Soil ◽

Soil Development ◽

Plant Debris ◽

Grassland Soils ◽

Fresh Plant

Δ14C and δ13C values for organic matter in forest and grassland soils, in the presence or absence of earthworms, indicate that it should be possible to quantify the effects of earthworms on soil organic matter by this means. Without earthworms, both in forest and grassland soils, plant debris tends to accumulate on the surface of the mineral soil and little organic matter is incorporated into or is translocated down the soil profile. Where earthworms are present, there is much more marked incorporation of fresh plant debris in the mineral soil. This is shown especially by the pulse of ‘bomb’ carbon and also by the δ13C values.

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Twenty-Five Years of Radiocarbon Dating Soils: Paradigm of Erring and Learning

Radiocarbon ◽

10.1017/s0033822200063803 ◽

1992 ◽

Vol 34 (3) ◽

pp. 541-549 ◽

Cited By ~ 77

Author(s):

H. W. Scharpenseel ◽

Peter Becker-Heidmann

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Soil Formation ◽

Clay Content ◽

Solvent System ◽

Total Carbon ◽

Earthworm Casts ◽

Initiation Point ◽

Organic Matter Fractions ◽

Soil Dating

Soil organic matter sequesters close to three times the carbon existing totally in the living biomass and nearly the same for the total carbon in the atmosphere. Models, such as Jenkinson's or Parton's Century model, help to define soil organic matter fractions of different functions, based on residence time/14C age. Rejuvenation of soil carbon was felt to be the principal impediment to absolute soil dating, in addition to the ambiguity of the initiation point of soil formation and soil age. Recent studies, for example, of Becker-Heidmann (1989), indicate that a soil 14C age of >1000 yr cannot have >0.1% rejuvenation in the total soil organic matter compartments/fractions to be possible and sustainable. Always problematic in earlier observations were age vs. depth increases, in 14C profile curves showing an inflection of reduced age in the deepest samples, i.e., from the rim of the organic matter containing epipedon. We attribute this phenomenon, in mollic horizons, to earthworm casts in the terminal part of the escape tube. Becker-Heidmann (1989) has shown, in thin layer soil profile dating, a highly significant correlation between the highest 14C ages and the highest clay content. Thus, optimization of soil dating is, to a lesser degree, related to the applied extracting solvent system than to soil texture fractions. Such observations allow us to mitigate error ranges inherent in dating dynamic soil systems.

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Using active fractions of soil organic matter as indicators of the sustainability of Ferrosol farming systems

Soil Research ◽

10.1071/s98064 ◽

1999 ◽

Vol 37 (2) ◽

pp. 279 ◽

Cited By ~ 16

Author(s):

M. J. Bell ◽

P. W. Moody ◽

S. A. Yo ◽

R. D. Connolly

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Management Practices ◽

Cropping Systems ◽

Cropping System ◽

Farming Systems ◽

Total Carbon ◽

Critical Concentrations ◽

Aggregate Breakdown ◽

Eastern Australia

Chemical and physical degradation of Red Ferrosols in eastern Australia is a major issue necessitating the development of more sustainable cropping systems. This paper derives critical concentrations of the active (permanganate-oxidisable) fraction of soil organic matter (C1) which maximise soil water recharge and minimise the likelihood of surface runoff in these soils. Ferrosol soils were collected from commercial properties in both north and south Queensland, while additional data were made available from a similar collection of Tasmanian Ferrosols. Sites represented a range of management histories, from grazed and ungrazed grass pastures to continuously cropped soil under various tillage systems. The concentration of both total carbon (C) and C1 varied among regions and farming systems. C1 was the primary factor controlling aggregate breakdown, measured by the percentage of aggregates <0·125 mm (P125) in the surface crust after simulated rainfall. The rates of change in P125 per unit change in C1 were not significantly different (P < 0·05) for soils from the different localities. However, soils from the coastal Burnett (south-east Queensland) always produced lower P125 (i.e. less aggregate breakdown) than did soils from the inland Burnett and north Queensland locations given the same concentration of C1. This difference was not associated with a particular land use. The ‘critical’ concentrations of C1 for each region were taken as the C1 concentrations that would allow an infiltration rate greater than or equal to the intensity of a 1 in 1 or 1 in 10 year frequency rainfall event of 30 min duration. This analysis also provided an indication of the risk associated with the concentrations of C1 currently characterising each farming system in each rainfall environment. None of the conventionally tilled Queensland Ferrosols contained sufficient C1 to cope with rainfall events expected to occur with a 1 in 10 frequency, while in many situations the C1 concentration was sufficiently low that runoff events would be expected on an annual basis. Our data suggest that management practices designed both to maximise C inputs and to maintain a high proportion of active C should be seen as essential steps towards developing a more sustainable cropping system.

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Soil organic carbon fractions in a Vertisol under irrigated cotton production as affected by burning and incorporating cotton stubble

Soil Research ◽

10.1071/s97117 ◽

1998 ◽

Vol 36 (4) ◽

pp. 655 ◽

Cited By ~ 31

Author(s):

A. Conteh ◽

G. J. Blair ◽

I. J. Rochester

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Organic Matter Content ◽

Matter Content ◽

Total Carbon ◽

Cotton Production ◽

Labile Carbon ◽

Total N ◽

The Difference ◽

Organic Matter Fractions

The contribution of cotton stubble to the soil organic matter content of Vertisols under cotton production is not well understood. A 3-year experiment was conducted at the Australian Cotton Research Institute to study the effects of burning and incorporating cotton stubble on the recovery of fertiliser nitrogen (N), lint yield, and organic matter levels. This study reports on the changes in soil organic matter fractions as affected by burning and incorporating cotton stubble into the soil. Soil samples collected at the start and end of the 3-year experiment were analysed for total carbon (CT), total N (NT), and δ13C (a measure of 13C/12C isotopic ratios). Labile carbon (CL) was determined by ease of oxidation and non-labile carbon (CNL) was calculated as the difference between CT and CL. Based on the changes in CT, CL, and CNL, a carbon management index (CMI) was calculated. Further analyses were made for total polysaccharides (PT), labile polysaccharides (PL), and light fraction C (LF-C). Stubble management did not significantly affect the NT content of the soil. After 3 years, the stubble-incorporated plots had a significantly higher content of CT, CL, and polysaccharides. Incorporation of stubble into the soil increased the CMI by 41%, whereas burning decreased the CMI by 6%. The amount of LF-C obtained after 3 years in the stubble-incorporated soil was almost double that obtained in the stubble-burnt soil. It was concluded that for sustainable management of soil organic matter in the Vertisols used for cotton production, stubble produced in the system should be incorporated instead of burnt.

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Free light fraction carbon and nitrogen, a physically uncomplexed soil organic matter distribution within subtropical grass and leucaena–grass pastures

Soil Research ◽

10.1071/sr18162 ◽

2018 ◽

Vol 56 (8) ◽

pp. 820 ◽

Cited By ~ 2

Author(s):

K. A. Conrad ◽

R. C. Dalal ◽

D. E. Allen ◽

R. Fujinuma ◽

Neal W. Menzies

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Soil Depth ◽

Light Fraction ◽

Grass Species ◽

Pasture Grass ◽

Total N ◽

Δ13c And Δ15n ◽

Organic C ◽

C And N

Quantifying the size and turnover of physically uncomplexed soil organic matter (SOM) is crucial for the understanding of nutrient cycling and storage of soil organic carbon (SOC). However, the C and nitrogen (N) dynamics of SOM fractions in leucaena (Leucaena leucocephala)–grass pastures remains unclear. We assessed the potential of leucaena to sequester labile, free light fraction (fLF) C and N in soil by estimating the origin, quantity and vertical distribution of physically unprotected SOM. The soil from a chronosequence of seasonally grazed leucaena stands (0–40 years) was sampled to a depth of 0.2m and soil and fLF were analysed for organic C, N and δ13C and δ15N. On average, the fLF formed 20% of SOC and 14% of total N stocks in the upper 0.1m of soil from leucaena rows and showed a peak of fLF-C and fLF-N stocks in the 22-year-stand. The fLF δ13C and fLF δ15N values indicated that leucaena produced 37% of fLF-C and 28% of fLF-N in the upper 0.1m of soil from leucaena rows. Irrespective of pasture type or soil depth, the majority of fLF-C originated from the accompanying C4 pasture-grass species. This study suggests that fLF-C and fLF-N, the labile SOM, can form a significant portion of total SOM, especially in leucaena–grass pastures.

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Maximum soil organic matter decomposition along temperature gradient in Colombian topsoils: Dry Forests

10.5194/egusphere-egu21-5938 ◽

2021 ◽

Author(s):

Gerardo Ojeda ◽

Hernando García ◽

Susanne Woche ◽

Jorg Bachmann ◽

Georg Guggenberger ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Organic Carbon ◽

Temperature Gradient ◽

Soil Organic Carbon ◽

Soil Respiration ◽

Maximum Rate ◽

Field Capacity ◽

Total Carbon ◽

Som Decomposition

Contextualization: In 2011, it was published a curious conundrum, which forms the basis of the present study: why, when organic matter is thermodynamically unstable, does it persist in soils, sometimes for thousands of years? The question challenges the idea that the recalcitrant or labile character of soil organic matter (SOM) is a sufficient argument to ensure SOM persistence. Temperature could play an important role in SOM decomposition, especially in tropics. Particularly, tropical dry forest (TDF) represents an important ecosystem with unique biodiversity and fertile soils in Colombia. At present, the increase in population density and consequently, in the demands of energy and arable land, have led to its degradation.&#160;Knowledge gap: Although the mentioned question was formulated several years ago, it has still to be answered, hence limiting the development of new soil organic carbon (SOC) models or the quantification of its ecosystem services. A key point, in terms of soil carbon storage, is to determine the maximum rate of CO2 emissions from soils (Rmax). Traditionally, it is considered that Rmax occurs at the 50% of field capacity. Unfortunately, information about the environmental conditions under which this maximum occurs is scarce.&#160;Purpose: The main objectives of this study were: (a) determine the maximum rate of soil respiration or CO2 emissions from soil in TDF soils and (b) to estimate the main environmental drivers of maximum SOM decomposition along a temperature gradient (20&#176;, 30&#176;, 40&#176;C) in incubated soils.&#160;Methodology: Soils pertained to permanent plots were sampled in six different TDF of Colombia. The evolution of CO2 emissions (monitored by an infrared gas analyser), relative humidity and soil temperature were recorded in time on incubated soils samples. Temperature was maintained constant at 20&#176;C, 30&#176;C and 40&#176;C during soil incubations under soil drying conditions. Additionally, elemental composition (Fe, Ca, O, Al, Si, K, Mg, Na) of SOM and chemical composition of soil organic carbon (SOC: aromatic-C, O-alkyl-C, Aliphatic-C, Phenolic and Ketonic-C) were determined by X-ray photoelectron spectroscopy (XPS).&#160;Results and conclusions: The majority of TDF soil samples (90.7%) presented that its peak of CO2 emissions occurs at soil-water contents higher than saturation (0 MPa), at 20&#176;, 30&#176; and 40&#176;C. Clearly, to consider that the maximum soil respiration rate could be observed at the 50% of field capacity, underestimated the real maximum value of carbon mineralization (48-68%.) Globally, increases in the Rmax values corresponded to increases in electrical conductivity, soil desorption rates, total carbon and nitrogen contents, and decreases in bulk density (BD) and aggregate stability. Taking into account the temperature gradient, increments in calcium and aromatic carbon contents corresponded to decrements in Rmax values but only at 30&#176;C and 40&#176;C, respectively. Some authors indicated that at high soil moisture contents, iron reduction could be release protected carbon. However, no significant relation between Fe and Rmax was observed. Consequently, physical and chemical properties related to SOM accessibility and decomposability by microbial activity, were the main drivers and controls of maximum SOM decomposition rates.

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Changes in soil organic carbon and nitrogen after 47 years with different tillage, stubble and fertiliser management in a Vertisol of north-eastern Australia

Soil Research ◽

10.1071/sr19314 ◽

2020 ◽

Vol 58 (4) ◽

pp. 346

Author(s):

K. L. Page ◽

R. C. Dalal ◽

S. H. Reeves ◽

W. J. Wang ◽

Somasundaram Jayaraman ◽

...

Keyword(s):

Organic Matter ◽

Soil Organic Matter ◽

Organic Carbon ◽

Soil Organic Carbon ◽

Management Practices ◽

Crop Residues ◽

Residue Management ◽

Eastern Australia ◽

North Eastern ◽

Over Time

No-till (NT) farming has been widely adopted to assist in reducing erosion, lowering fuel costs, conserving soil moisture and improving soil physical, chemical and biological characteristics. Improvements in soil characteristics are often driven by the greater soil organic matter accumulation (as measured by soil organic carbon (SOC)) in NT compared to conventional tillage (CT) farming systems. However, to fully understand the effect of NT it is important to understand temporal changes in SOC by monitoring over an extended period. We investigated the long-term effect of NT and stubble retention (SR) on changes in SOC and total soil nitrogen (STN) using results from an experiment that has been running for 50 years in a semi-arid subtropical region of north-eastern Australia. In this experiment, the effects of tillage (CT vs NT), residue management (stubble burning (SB) vs SR), and nitrogen (N) fertiliser (0 and 90 kg-N ha–1) were measured in a balanced factorial experiment on a Vertisol (Ustic Pellusert). The use of NT, SR and N fertiliser generally improved SOC (by up to 12.8%) and STN stocks (by up to 31.7%) in the 0–0.1 m layer relative to CT, SB and no N fertiliser, with the greatest stocks observed where all three treatments were used in combination. However, declines in SOC (up to 20%) and STN (up to 25%) occurred in all treatments over the course of the experiment, indicating that changes in management practices were unable to prevent a loss of soil organic matter over time in this farming system. However, the NT and SR treatments did lose less SOC than CT and SB treatments, and SR also reduced STN loss. The δ13C analysis of samples collected in 2008 and 2015 highlighted that crop residues have significantly contributed to SOC stocks at the site and that their contribution is increasing over time.

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Soil organic matter dynamics in a North America tallgrass prairie after 9 yr of experimental warming

Biogeosciences ◽

10.5194/bg-8-1487-2011 ◽

2011 ◽

Vol 8 (6) ◽

pp. 1487-1498 ◽

Cited By ~ 46

Author(s):

X. Cheng ◽

Y. Luo ◽

X. Xu ◽

R. Sherry ◽

Q. Zhang

Keyword(s):

Organic Matter ◽

Global Warming ◽

Soil Organic Matter ◽

North America ◽

Tallgrass Prairie ◽

Decay Rates ◽

Experimental Warming ◽

Δ13c And Δ15n ◽

Soil C ◽

C Input

Abstract. The influence of global warming on soil organic matter (SOM) dynamics in terrestrial ecosystems remains unclear. In this study, we combined soil fractionation with isotope analyses to examine SOM dynamics after nine years of experimental warming in a North America tallgrass prairie. Soil samples from the control plots and the warmed plots were separated into four aggregate sizes (>2000 μm, 250–2000 μm, 53–250 μm, and <53 μm), and three density fractions (free light fraction – LF, intra-aggregate particulate organic matter – iPOM, and mineral-associated organic matter – mSOM). All fractions were analyzed for their carbon (C) and nitrogen (N) content, and δ13C and δ15N values. Warming did not significantly effect soil aggregate distribution and stability but increased C4-derived C input into all fractions with the greatest in LF. Warming also stimulated decay rates of C in whole soil and all aggregate sizes. C in LF turned over faster than that in iPOM in the warmed soils. The δ15N values of soil fractions were more enriched in the warmed soils than those in the control, indicating that warming accelerated loss of soil N. The δ15N values changed from low to high, while C:N ratios changed from high to low in the order LF, iPOM, and mSOM due to increased degree of decomposition and mineral association. Overall, warming increased the input of C4-derived C by 11.6 %, which was offset by the accelerated loss of soil C. Our results suggest that global warming simultaneously stimulates C input via shift in species composition and decomposition of SOM, resulting in negligible net change in soil C.

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Modelling the genesis of equatorial podzols: age and implications for carbon fluxes

Biogeosciences ◽

10.5194/bg-14-2429-2017 ◽

2017 ◽

Vol 14 (9) ◽

pp. 2429-2440 ◽

Cited By ~ 4

Author(s):

Cédric Doupoux ◽

Patricia Merdy ◽

Célia Régina Montes ◽

Naoise Nunan ◽

Adolpho José Melfi ◽

...

Keyword(s):

Organic Matter ◽

Carbon Fluxes ◽

Total Carbon ◽

Organic C ◽

Perched Water Table ◽

C Dynamics ◽

14C Age ◽

Order Of Magnitude ◽

Over Time ◽

Main Carbon

Abstract. Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon River. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and 14C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carbon-containing horizons, i.e. the topsoil and deep Bh. We performed retrocalculations to take into account the bomb carbon in the young topsoil horizons (calculated apparent 14C age from 62 to 109 years). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (calculated apparent 14C age 6.8  ×  103 and 8.4  ×  103 years) and two profiles with a very old Bh (calculated apparent 14C age 23.2  ×  103 and 25.1  ×  103 years). The calculated fluxes from the topsoil to the perched water table indicate that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15  ×  103 and 130  ×  103 years for the two younger and two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15  ×  103–25  ×  103 and 150  ×  103–250  ×  103 years, respectively.

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