The mechanisms of organic carbon protection and dynamics of <scp>C</scp>‐saturation in <scp>O</scp>xisols vary with particle‐size distribution

Souza, Ivan F.; Almeida, Luís Fernando Januário; Jesus, Guilherme Luiz de; Kleber, Markus; Silva, I. R.

doi:10.1111/ejss.12463

Cited by 23 publications

(14 citation statements)

References 36 publications

(58 reference statements)

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“…Topsoil carbon was highest in the <45 µm fraction (19-43 g kg −1 ) and lowest in the >125 µm fractions (1-8 g kg −1 ), which was also reported by Amelung et al [40], Chivenge et al [41], Dalal and Mayer [42], Desjardins et al [43], and Nelson et al [44]. The silt and clay size fractions are able to store more soil carbon than the sand size fractions [3,42,45] due to the absorption of carbon onto fine sized particles [46,47]. Chivenge et al [41] found that SOC levels were 1 to 3 g kg −1 in the sand size fraction (53-2000 µm), 5 to 12 g kg −1 in the silt size fraction (5-53 µm), and 35 to 48 g kg −1 in the clay size fraction (<5 µm).…”

Section: Total Carbonsupporting

confidence: 65%

Geochemical Fingerprint and Soil Carbon of Sandy Alfisols

2019

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Soil carbon storage is affected by particle-size fractions and Fe oxides. We assessed soil carbon concentrations in different particle-size fractions, determined the soil chemical composition of the soil, and weathering and mineralogy of sandy soils of the Wisconsin Central Sands, USA. Three land uses were studied (agriculture, forest, and prairie). The soils contained a minimum of 830 g sand kg −1 up to 190 cm soil depth. Approximately 46% of the sand was in the 250-500 µm fraction, and 5% was <125 µm. Soil carbon ranged from 5 to 13 g kg −1 in the topsoil, and decreased with depth. The <45 µm fraction tended to have high concentrations of carbon, ranging from 19 to 43 g kg −1 in the topsoil. Silicon content was over 191 g Si kg −1 , and was lowest in the Bt horizons (191-224 g Si kg −1 ). Up to 29 g Fe kg −1 and 39 g Al kg −1 were present in the soil, and were highest in the Bt horizons. These soils were mostly quartz, and diopside was found throughout the soil profiles.Weathering indices, such as the Ruxton Ratio, showed that the C horizons were the least weathered and the Bt horizons were more weathered. We conclude that most of the carbon in these soils is held in the <45 µm fraction, and soil carbon and total Fe were lowest in the coarser size fractions.2 of 22 capacity [16,[18][19][20]. Because of this, sandy soils under agriculture often need irrigation and fertilizer to produce high crop yields [18,21].The Central Sand Plains covers approximately 6% (8900 km 2 ) of Wisconsin, USA. Much of the soils are intensely cultivated and commonly irrigated, limed, and fertilized. The chemical, physical, and biological components of the soil have changed under agriculture [22]. The carbon stocks are on average 41 Mg carbon ha −1 in the top 30 cm, and this is due to decades nitrogen fertilization and irrigation [23]. The soils under agriculture generally have thicker topsoils (28 cm) than soils under grassland (21 cm) and forest (14 cm) [22]. Madison and Lee [24] determined that quartz was the dominant mineral in the sandy soils of Wisconsin (60 to 96%), and feldspars (orthoclase, plagioclase) were the second most dominant mineral (2 to 12%). The percentage of heavy minerals was low (<3%), and they were primarily opaques (magnetite, hematite, ilmenite, leucoxcene), augite, hornblende, garnet, zircon, and tourmaline [24].The main research question that will be addressed in this paper is: how is carbon stored in sandy soils? The overall objective of this research is to gain a better understanding of carbon storage, elemental composition, and mineralogy of sandy soils. The objective of the research was to: (i) assess soil carbon concentrations in different particle-size fractions, (ii) determine the soil elemental composition in the bulk and particle-size fractions, and (iii) assess the mineralogy and degree of weathering of these soils.

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Section: Total Carbonsupporting

confidence: 65%

Geochemical Fingerprint and Soil Carbon of Sandy Alfisols

2019

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“…Whereas sorption interactions with mineral surfaces are probably the dominant mechanisms protecting SOM from decomposition in coarse-textured soils, the additional physical protection afforded by microporous regions of the soil may lead to an enhanced long-term storage of SOM in structured fine-textured soils (e.g. Hassink et al, 1993;Chevallier et al, 2004;Souza et al, 2017;Dignac et al, 2017). Thus, the turnover of both particulate and soluble SOM has been shown to depend on its location in soil pore networks of different diameters and connectivity and with contrasting microbial communities (e.g.…”

Section: Introductionmentioning

confidence: 99%

Modelling dynamic interactions between soil structure and the storage and turnover of soil organic matter

et al. 2020

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Abstract. Models of soil organic carbon (SOC) storage and turnover can be useful tools to analyse the effects of soil and crop management practices and climate change on soil organic carbon stocks. The aggregated structure of soil is known to protect SOC from decomposition and, thus, influence the potential for long-term sequestration. In turn, the turnover and storage of SOC affects soil aggregation, physical and hydraulic properties and the productive capacity of soil. These two-way interactions have not yet been explicitly considered in modelling approaches. In this study, we present and describe a new model of the dynamic feedbacks between soil organic matter (SOM) storage and soil physical properties (porosity, pore size distribution, bulk density and layer thickness). A sensitivity analysis was first performed to understand the behaviour of the model. The identifiability of model parameters was then investigated by calibrating the model against a synthetic data set. This analysis revealed that it would not be possible to unequivocally estimate all of the model parameters from the kind of data usually available in field trials. Based on this information, the model was tested against measurements of bulk density, SOC concentration and limited data on soil water retention and soil surface elevation made during 63 years in a field trial located near Uppsala (Sweden) in three treatments with different organic matter (OM) inputs (bare fallow, animal and green manure). The model was able to accurately reproduce the changes in SOC, soil bulk density and surface elevation observed in the field as well as soil water retention curves measured at the end of the experimental period in 2019 in two of the treatments. Treatment-specific variations in SOC dynamics caused by differences in OM input quality could be simulated very well by modifying the value for the OM retention coefficient ε (0.37 for animal manure and 0.14 for green manure). The model approach presented here may prove useful for management purposes, for example, in an analysis of carbon sequestration or soil degradation under land use and climate change.

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“…Conversely, felsic soils are low in pedogenic oxides and thus have low sorption potential and consequently also the lowest SOC bulk . Clay content, identified as a major factor for stabilizing SOC in temperate soils (Angst et al, 2018) and also in tropical soil systems (Quesada et al, 2020;Souza et al, 2017), was not identified as a major control for our soils. This illustrates the importance of understanding soil geochemical preconditions when identifying controls of C dynamics and that findings are not necessarily transferable, even between comparable soil types and climates.…”

Section: Interpreting Soil Controls For Predicting Soc Dynamicsmentioning

confidence: 79%

The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils

Reichenbach

Fiener

Garland

et al. 2021

SOIL

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Abstract. Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 ± 13.2 % of total SOC stock in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression models, considering depth intervals of 0–10, 30–40 and 60–70 cm, showed that variables affiliated with soil weathering, parent material geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and Δ14C. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils investigated.

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The mechanisms of organic carbon protection and dynamics of C‐saturation in Oxisols vary with particle‐size distribution

Cited by 23 publications

References 36 publications

Geochemical Fingerprint and Soil Carbon of Sandy Alfisols

Geochemical Fingerprint and Soil Carbon of Sandy Alfisols

Modelling dynamic interactions between soil structure and the storage and turnover of soil organic matter

The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils

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