The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform

Keith Paustian - One of the best experts on this subject based on the ideXlab platform.

  • aggregate associated soil organic matter as an ecosystem property and a measurement tool
    Soil Biology & Biochemistry, 2014
    Co-Authors: Keith Paustian
    Abstract:

    Abstract Our 2000 paper Soil macroaggregate turnover and microaggregate formation: A mechanism for C sequestration under no-tillage agriculture had its genesis in attempts to identify and isolate soil organic matter (SOM) fractions that reflect the impacts of climate, soil physiochemical properties and physical disturbance on the soil organic carbon balance. A key prerequisite for the investigation was the development of a simple device to isolate the Microaggregates (53–250 μm) contained within stable (i.e., resistant to slaking) macroaggregates (>250 μm) obtained by conventional wet-sieving. By comparing the abundance and C content of micro-within-macroaggregates, the size distribution of intra-aggregate particulate organic matter (iPOM) and isotopically-based estimates of the age of the organic matter in the different fractions, we were able to corroborate our hypothesis that the absence of tillage (i.e., in no-till and native soils) promotes greater longevity of newly-formed macroaggregates, resulting in greater SOM stabilization in Microaggregates formed within stable macroaggregates. Follow-up research has indicated that the microaggregate-within-macroaggregate fraction is 1) potentially a robust indicator for management-induced SOC changes over decadal time scales, 2) of biological origin and therefore useful in interpreting impacts of soil biota on soil C and N dynamics, but not in-situ CO 2 and N 2 O fluxes, 3) useful in complimentary chemical and spectroscopic approaches to relate SOM dynamics to soil structure and attributes of the soil pore space, and 4) a good candidate for being incorporated into models as a measurable fraction.

  • carbon sequestration in Microaggregates of no tillage soils with different clay mineralogy
    Soil Science Society of America Journal, 2004
    Co-Authors: Karolien Denef, Roel Merckx, Keith Paustian
    Abstract:

    Identification of diagnostic soil organic matter (SOM) fractions and the mechanisms controlling their formation and turnover is critical for better understanding of C dynamics in soils. Enhanced microaggregate formation and stabilization of C due to reduced macroaggregate turnover has been proposed as a mechanism promoting C sequestration in no-tillage (NT) compared with conventional tillage (CT) systems in temperate soils dominated by 2:1 clay mineralogy. We evaluated the contribution of macroaggregate-protected Microaggregates to total soil organic carbon (SOC) sequestration in NT relative to CT in three soils differing in clay mineralogy: a 2:1 clay-dominated soil (2:1), a soil with mixed clay mineralogy [2:1 and 1:11 and oxides (mixed), and a soil dominated by (1:1) clay minerals and oxides (1:1). Microaggregates (mM) were isolated from macroaggregates from 0- to 5- and 5- to 20-cm soil layers. Particulate organic matter (POM) located within the Microaggregates (intra-mM-POM) was separated from POM outside of the Microaggregates (inter-mM-POM) and the mineral fraction of the Microaggregates (mineral-mM). In all three soils, total SOC as well as microaggregate-associated C (mM-C) was greater with NT compared with CT. Although less than half of the total SOC under NT was associated with the microaggregate fraction, more than 90% of the total difference in SOC between NT and CT was explained by the difference in mM-C in all three soils. Thus, we identified and isolated a fraction that explains almost the entire difference in total SOC between NT and CT across soils characterized by drastically different clay mineralogy.

  • soil macroaggregate turnover and microaggregate formation a mechanism for c sequestration under no tillage agriculture
    Soil Biology & Biochemistry, 2000
    Co-Authors: E T Elliott, Keith Paustian
    Abstract:

    Soil disturbance from tillage is a major cause of organic matter depletion and reduction in the number and stability of soil aggregates when native ecosystems are converted to agriculture. No-till (NT) cropping systems usually exhibit increased aggregation and soil organic matter relative to conventional tillage (CT). However, the extent of soil organic matter changes in response to NT management varies between soils and the mechanisms of organic matter stabilization in NT systems are unclear. We evaluated a conceptual model which links the turnover of aggregates to soil organic matter dynamics in NT and CT systems; we argue that the rate of macroaggregate formation and degradation (i.e. aggregate turnover) is reduced under NT compared to CT and leads to a formation of stable Microaggregates in which carbon is stabilized and sequestered in the long term. Therefore, the link between macroaggregate turnover, microaggregate formation, and C stabilization within Microaggregates partly determines the observed soil organic matter increases under NT.

  • soil structure and organic matter i distribution of aggregate size classes and aggregate associated carbon
    Soil Science Society of America Journal, 2000
    Co-Authors: Keith Paustian, E T Elliott, C Combrink
    Abstract:

    Cultivation reduces soil C content and changes the distribution and stability of soil aggregates. We investigated the effect of cultivation intensity on aggregate distribution and aggregate C in three soils dominated by 2:1 clay mineralogy and one soil characterized by a mixed (2:1 and 1:1) mineralogy. Each site had native vegetation (NV), no-tillage (NT), and conventional tillage (CT) treatments. Slaked (i.e., air-dried and fast-rewetted) and capillary rewetted soils were separated into four aggregate-size classes ( 2000 μm) by wet sieving. In rewetted soils, the proportion of macroaggregates accounted for 85% of the dry soil weight and was similar across management treatments. In contrast, aggregate distribution from slaked soils increasingly shifted toward more Microaggregates and fewer macroaggregates with increasing cultivation intensity. In soils dominated by 2:1 clay mineralogy, the C content of macroaggregates was 1.65 times greater compared to Microaggregates. These observations support an aggregate hierarchy in which Microaggregates are bound together into macroaggregates by organic binding agents in 2:1 clay-dominated soils. In the soil with mixed mineralogy, aggregate C did not increase with increasing aggregate size. At all sites, rewetted macro- and microaggregate C and slaked microaggregate C differed in the order NV > NT > CT, In contrast, slaked macroaggregate C concentration was similar across management treatments, except in the soil with mixed clay mineralogy. We conclude that increasing cultivation intensity leads to a loss of C-rich macroaggregates and an increase of C-depleted Microaggregates in soils that express aggregate hierarchy.

  • aggregate and soil organic matter dynamics under conventional and no tillage systems
    Soil Science Society of America Journal, 1999
    Co-Authors: E T Elliott, Keith Paustian
    Abstract:

    Tillage generally reduces aggregation and particulate organic matter (POM) content. We hypothesized that reduced C sequestration in conventional tillage (CT) compared with no-tillage (NT) is related to differences in aggregate turnover. Four soils (Haplustoll, Fragiudalf, Hapludalf, and Paleudalf), each with NT, CT, and native vegetation (NV) treatments, were separated into aggregates. Free light fraction (LF) and intraaggregate POM (iPOM) were isolated. At one site we used 13 C natural abundance to differentiate crop- and grassland-derived C. Concentrations of coarse iPOM C (250-2000 μm iPOM in macroaggregates), expressed on a per unit aggregate weight (g iPOM C kg -1 aggregate), did not differ between tillage treatments. In contrast, concentrations of fine iPOM C (53-250 μm iPOM in macroaggregates) were less in CT compared to NT macroaggregates. On a whole soil basis, fine iPOM C was on average 51% less in CT than in NT, and accounted for 21% of the total C difference between NT and CT. The concentration of free LF C was not affected by tillage, but was on average 45% less in the cultivated systems than NV. Proportions of crop-derived C in macroaggregates were similar in NT and CT, but were three times greater in Microaggregates from NT than Microaggregates from CT. We suggest that a faster turnover rate of macroaggregates in CT compared with NT leads to a slower rate of microaggregate formation within macroaggregates and less stabilization of new SOM in free Microaggregates under CT.

Karolien Denef - One of the best experts on this subject based on the ideXlab platform.

  • microaggregate associated carbon as a diagnostic fraction for management induced changes in soil organic carbon in two oxisols
    Soil Biology & Biochemistry, 2007
    Co-Authors: Karolien Denef, Lincoln Zotarelli, Robert M Boddey
    Abstract:

    Abstract Carbon stabilization by macroaggregate-occluded Microaggregates (Mm) has been proposed as a principal mechanism for long-term soil organic carbon (SOC) sequestration in temperate alternative agricultural and (af)forested systems. The aim of this study was to evaluate the importance of the Mm fraction for long-term C stabilization in Oxisols and to validate its diagnostic properties for total SOC changes upon changes in land use. Soil samples were taken from the 0–5 and 5–20 cm soil layers of native forest vegetation (NV), conventional tillage (CT) and no-tillage (NT) systems at an experimental site near Passo Fundo and one near Londrina in Southern Brazil. After aggregate-size separations by wet-sieving, macroaggregate-occluded water-stable Microaggregates (53–250 μm) (Mm) were isolated from large (>2000 μm) and small (>250 μm) macroaggregates. Particulate organic matter located inside the Mm (intra-Mm-POM) and the mineral fraction ( −2 ) among different land use systems were always accompanied by parallel Mm-C stock differences. Though total SOC did not differ among land use systems in the 0–20 cm depth at both sites, Mm-C stocks were greater under NT compared to the CT treatment in the 0–20 cm depth at the Londrina site. We concluded that in these highly weathered tropical soils the Mm-C fraction is a more responsive fraction to management changes than total SOC and represents a diagnostic fraction for present as well as potential total SOC changes upon land-use change.

  • a history of research on the link between micro aggregates soil biota and soil organic matter dynamics
    Soil & Tillage Research, 2004
    Co-Authors: Heleen Bossuyt, Steven Degryze, Karolien Denef
    Abstract:

    Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of Microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) Microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

  • A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics
    Soil and Tillage Research, 2004
    Co-Authors: Johan Six, Steven Degryze, Heleen Bossuyt, Karolien Denef
    Abstract:

    Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of Microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) Microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information. © 2004 Elsevier B.V. All rights reserved.

  • carbon sequestration in Microaggregates of no tillage soils with different clay mineralogy
    Soil Science Society of America Journal, 2004
    Co-Authors: Karolien Denef, Roel Merckx, Keith Paustian
    Abstract:

    Identification of diagnostic soil organic matter (SOM) fractions and the mechanisms controlling their formation and turnover is critical for better understanding of C dynamics in soils. Enhanced microaggregate formation and stabilization of C due to reduced macroaggregate turnover has been proposed as a mechanism promoting C sequestration in no-tillage (NT) compared with conventional tillage (CT) systems in temperate soils dominated by 2:1 clay mineralogy. We evaluated the contribution of macroaggregate-protected Microaggregates to total soil organic carbon (SOC) sequestration in NT relative to CT in three soils differing in clay mineralogy: a 2:1 clay-dominated soil (2:1), a soil with mixed clay mineralogy [2:1 and 1:11 and oxides (mixed), and a soil dominated by (1:1) clay minerals and oxides (1:1). Microaggregates (mM) were isolated from macroaggregates from 0- to 5- and 5- to 20-cm soil layers. Particulate organic matter (POM) located within the Microaggregates (intra-mM-POM) was separated from POM outside of the Microaggregates (inter-mM-POM) and the mineral fraction of the Microaggregates (mineral-mM). In all three soils, total SOC as well as microaggregate-associated C (mM-C) was greater with NT compared with CT. Although less than half of the total SOC under NT was associated with the microaggregate fraction, more than 90% of the total difference in SOC between NT and CT was explained by the difference in mM-C in all three soils. Thus, we identified and isolated a fraction that explains almost the entire difference in total SOC between NT and CT across soils characterized by drastically different clay mineralogy.

Heleen Bossuyt - One of the best experts on this subject based on the ideXlab platform.

  • protection of soil carbon by Microaggregates within earthworm casts
    Soil Biology & Biochemistry, 2005
    Co-Authors: Heleen Bossuyt, Paul F Hendrix
    Abstract:

    Abstract Earthworms are known to play a role in aggregate formation and soil organic matter (SOM) protection. However, it is still unclear at what scale and how quickly earthworms manage to protect SOM. We investigated the effects of Aporrectodea caliginosa on aggregation and aggregate-associated C pools using 13C-labeled sorghum (Sorghum bicolor (L.) Moench) leaf residue. Two incubations were set up. The first incubation consisted of soil samples crushed 2000 μm) and small (250–2000 μm) macroaggregates and Microaggregates (53–250 μm). Eight different pools of aggregate-associated C were quantified: (1) and (2) unprotected C pools in large and small macroaggregates, (3) unprotected C pools in Microaggregates, (4) and (5) protected C pools in large and small macroaggregates, (6) protected C pool in Microaggregates, and (7) and (8) protected C pools in Microaggregates within large and small macroaggregates. In the presence of earthworms, a higher proportion of large macroaggregates was newly formed and these aggregates contained more C and 13C compared to bulk soil. There were no significant differences between the samples with or without earthworms in the C pool-sizes protected by macroaggregates, Microaggregates or Microaggregates within small macroaggregates. However, in the presence of earthworms, the C protected by Microaggregates within large macroaggregates was a significant pool and 22% of this C pool was newly added C. In conclusion, these results clearly indicate the direct involvement of earthworms in providing protection of soil C in Microaggregates within large macroaggregates leading to a possible long-term stabilization of soil C.

  • a history of research on the link between micro aggregates soil biota and soil organic matter dynamics
    Soil & Tillage Research, 2004
    Co-Authors: Heleen Bossuyt, Steven Degryze, Karolien Denef
    Abstract:

    Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of Microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) Microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information.

  • rapid incorporation of carbon from fresh residues into newly formed stable Microaggregates within earthworm casts
    European Journal of Soil Science, 2004
    Co-Authors: Heleen Bossuyt, Paul F Hendrix
    Abstract:

    Summary Earthworms play an important role in protecting carbon in the soil, but the exact influence of their activity on the distribution and protection of C is still poorly understood. We investigated the effect of earthworms on the formation of stable Microaggregates inside newly formed macroaggregates and the distribution of C in them. We crushed (  250 µm) formed. The 13C in fine particulate organic matter between and within the Microaggregates was determined. Earthworms helped to form large macroaggregates (> 2000 µm). These large macroaggregates contained four times more stable Microaggregates than those from samples without earthworms. There was more particulate organic matter within and between Microaggregates in macroaggregates in the presence of earthworms. The larger amounts of organic matter inside stable Microaggregates in casts than in bulk soil after 12 days of incubation (140 mg 13C kg−1 soil compared with 20 mg 13C kg−1 soil) indicates that these Microaggregates are formed rapidly around freshly incorporated residues within casts. In conclusion, earthworms have a direct impact on the formation of stable Microaggregates and the incorporation of organic matter inside these Microaggregates, and it seems likely that their activity is of great significance for the long-term stabilization of organic matter in soils.

  • A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics
    Soil and Tillage Research, 2004
    Co-Authors: Johan Six, Steven Degryze, Heleen Bossuyt, Karolien Denef
    Abstract:

    Since the 1900s, the link between soil biotic activity, soil organic matter (SOM) decomposition and stabilization, and soil aggregate dynamics has been recognized and intensively been studied. By 1950, many studies had, mostly qualitatively, investigated the influence of the five major factors (i.e. soil fauna, microorganisms, roots, inorganics and physical processes) on this link. After 1950, four theoretical mile-stones related to this subject were realized. The first one was when Emerson [Nature 183 (1959) 538] proposed a model of a soil crumb consisting of domains of oriented clay and quartz particles. Next, Edwards and Bremner [J. Soil Sci. 18 (1967) 64] formulated a theory in which the solid-phase reaction between clay minerals, polyvalent cations and SOM is the main process leading to microaggregate formation. Based on this concept, Tisdall and Oades [J. Soil Sci. 62 (1982) 141] coined the aggregate hierarchy concept describing a spatial scale dependence of mechanisms involved in micro- and macroaggregate formation. Oades [Plant Soil 76 (1984) 319] suggested a small, but very important, modification to the aggregate hierarchy concept by theorizing the formation of Microaggregates within macroaggregates. Recent research on aggregate formation and SOM stabilization extensively corroborate this modification and use it as the base for furthering the understanding of SOM dynamics. The major outcomes of adopting this modification are: (1) Microaggregates, rather than macroaggregates protect SOM in the long term; and (2) macroaggregate turnover is a crucial process influencing the stabilization of SOM. Reviewing the progress made over the last 50 years in this area of research reveals that still very few studies are quantitative and/or consider interactive effects between the five factors. The quantification of these relationships is clearly needed to improve our ability to predict changes in soil ecosystems due to management and global change. This quantification can greatly benefit from viewing aggregates as dynamic rather than static entities and relating aggregate measurements with 2D and 3D quantitative spatial information. © 2004 Elsevier B.V. All rights reserved.

  • aggregate protected carbon in no tillage and conventional tillage agroecosystems using carbon 14 labeled plant residue
    Soil Science Society of America Journal, 2002
    Co-Authors: Heleen Bossuyt, Paul F Hendrix
    Abstract:

    No-tillage (NT) management can result in higher soil organic matter (SOM) levels than conventional tillage (CT) practices. The objective was to investigate the underlying mechanisms in which C is protected under NT management, using 14 C-labeled plant residue as a tracer. Samples were collected from the Horseshoe Bend Research area in Athens, GA. Aggregate-size distribution, total C, and 14 C were measured together with different pools of aggregate-associated C and 14 C from 21-d laboratory incubations of intact and crushed macro and Microaggregates. Compared with CT, NT practices resulted in higher total C and 14 C in all aggregate-size classes of the 0- to 2.5- and 2.5- to 5-cm layers, except for 14 C in the 2000-μm aggregate-size class under NT than CT. In contrast, more 14 C was found in the 53- to 250-μm and <53-μm size classes under CT than NT. Unprotected C and 14 C pools, microaggregate-protected and micro within macroaggtegate-protected C and 14 C pools were significantly higher for the 0- to 2.5- and 2.5- to 5-cm layers under NT than CT. Carbon-14 pools were generally higher in CT than in NT at the 5- to 15-cm depth, while total C did not differ between tillage treatments at this depth. The results indicate that (i) more young C ( 14 C) is accumulated in the subsurface soil of CT than NT, but this C is not stabilized in the long term, and (ii) short- and long-term stabilization of C is higher in the soil surface layers under NT compared with CT. This C stabilization occurs mainly at the microaggregate level.

Wulf Amelung - One of the best experts on this subject based on the ideXlab platform.

  • Spatial organization of soil Microaggregates
    2020
    Co-Authors: Eva Lehndorff, Wulf Amelung, Nele Meyer, Andrey Radionov, Lutz Plümmer, Peter Rottmann, Beate Spiering, Stefan Dultz
    Abstract:

    &lt;p&gt;The physical arrangement of soil compounds in Microaggregates is important in many ways, e.g. by controlling soil stability and C sequestration. However, little is known about the spatial arrangement of organic and inorganic compounds in soil Microaggregates, due to the lack of in-situ analyses in undisturbed material. Here we hypothesize that Microaggregates are spatially organized, resulting in deterministic, predictable spatial patterns of different organic matter and mineral phases and that this organization depends on the abundance of specific phases such as on clay mineral content. We separated the water stable, occluded large and small microaggregate fractions from Ap horizons of a sequence of sandy to loamy Luvisols (19 to 35% clay, Scheyern, Germany) and subjected in total 60 individual aggregates to elemental mapping by electron probe micro analysis (EPMA), which recorded C, N, P, Al, Fe, Ca, K, Cl, and Si contents at &amp;#181;m scale resolution. Spatial arrangements of soil organic matter and soil minerals were extracted using cluster analyses. We found a pronounced heterogeneity in aggregate structure and composition, which was not reproducible and largely independent from clay content in soil. However, neighborhood analyses revealed close spatial correlations between organic matter debris (C:N app. 100:10) and microbial organic matter (C:N app. 10:1) indicating a spatial relationship between source and consumer. There was no systematic relationship between soil minerals and organic matter, suggesting that well-established macroscale correlations between contents of pedogenic oxides and clay minerals with soil organic matter storage do not apply to soil Microaggregates.&lt;/p&gt;

  • short term impacts of forest clear cut on p accessibility in soil Microaggregates an oxygen isotope study
    Geoderma, 2018
    Co-Authors: Nina Siebers, Wulf Amelung, Sara L Bauke, Federica Tamburini
    Abstract:

    Abstract Forest clear-cuts may have severe effects on the soil structure and related nutrient cycling, though with yet unknown consequences for nutrient pools such as phosphorus (P) within Microaggregates. We sampled the bulk mineral topsoil prior to clear cut as well as 1 and 2 years thereafter from the experimental forest site Wustebach, Germany, and we assessed the degree of oxygen isotope exchange in HCl-extractable soil phosphate of two microaggregate size fractions ( 18 O-labeled water. We found that after the clear-cut, microaggregate phosphates exchanged significantly more oxygen with the incubation water than before clear cut. One and two years after clear cut, the respective δ 18 O values of soil phosphates (δ 18 O P,HCl ) were elevated by 16 and 38% (

  • Microaggregates in soils
    Journal of Plant Nutrition and Soil Science, 2018
    Co-Authors: Kai Uwe Totsche, Wulf Amelung, Martin H Gerzabek, Georg Guggenberger, Erwin Klumpp, Claudia Knief, Eva Lehndorff, Robert Mikutta, Stephan Peth, Alexander T Prechtel
    Abstract:

    All soils harbor Microaggregates, i.e., compound soil structures smaller than 250 µm. These Microaggregates are composed of diverse mineral, organic and biotic materials that are bound together during pedogenesis by various physical, chemical and biological processes. Consequently, Microaggregates can withstand strong mechanical and physicochemical stresses and survive slaking in water, allowing them to persist in soils for several decades. Together with the physiochemical heterogeneity of their surfaces, the three-dimensional structure of Microaggregates provides a large variety of ecological niches that contribute to the vast biological diversity found in soils. As reported for larger aggregate units, Microaggregates are composed of smaller building units that become more complex with increasing size. In this context, organo-mineral associations can be considered structural units of soil aggregates and as nanoparticulate fractions of the Microaggregates themselves. The mineral phases considered to be the most important as microaggregate forming materials are the clay minerals and Fe- and Al-(hydr)oxides. Within Microaggregates, minerals are bound together primarily by physicochemical and chemical interactions involving cementing and gluing agents. The former comprise, among others, carbonates and the short-range ordered phases of Fe, Mn, and Al. The latter comprise organic materials of diverse origin and probably involve macromolecules and macromolecular mixtures. Work on microaggregate structure and development has largely focused on organic matter stability and turnover. However, little is known concerning the role Microaggregates play in the fate of elements like Si, Fe, Al, P, and S. More recently, the role of Microaggregates in the formation of microhabitats and the biogeography and diversity of microbial communities has been investigated. Little is known regarding how Microaggregates and their properties change in time, which strongly limits our understanding of micro-scale soil structure dynamics. Similarly, only limited information is available on the mechanical stability of Microaggregates, while essentially nothing is known about the flow and transport of fluids and solutes within the micro- and nanoporous microaggregate systems. Any quantitative approaches being developed for the modeling of formation, structure and properties of Microaggregates are, therefore, in their infancy. We respond to the growing awareness of the importance of Microaggregates for the structure, properties and functions of soils by reviewing what is currently known about the formation, composition and turnover of Microaggregates. We aim to provide a better understanding of their role in soil function, and to present the major unknowns in current microaggregate research. We propose a harmonized concept for aggregates in soils that explicitly considers the structure and build-up of Microaggregates and the role of organo-mineral associations. We call for experiments, studies and modeling endeavors that will link information on aggregate forming materials with their functional properties across a range of scales in order to better understand microaggregate formation and turnover. Finally, we hope to inspire a novel cohort of soil scientists that they might focus their research on improving our understanding of the role of Microaggregates within the system of aggregates and so help to develop a unified and quantitative concept of aggregation processes in soils.

  • Soil Carbon Saturation Controls Labile and Stable Carbon Pool Dynamics
    Soil Science Society of America Journal, 2008
    Co-Authors: S. Gulde, Wulf Amelung, H Chung, C. Chang, Johan Six
    Abstract:

    Recently, it has been suggested that soil organic C (SOC) does not always respond linearly to increasing C input, thereby limiting the rate and efficiency of C stabilization in soils. Therefore, we postulated that when a soil is exposed to a broad range of C inputs through a range of manure treatments, it will show C saturation behavior and different SOC pools will saturate at different rates. To test this, different SOC pools were isolated by physical fractionation techniques from a long-term agricultural experiment in Lethbridge, Canada. In this experiment, manure has been applied since 1973 at rates of 0, 60, 120, and 180 Mg ha(-1) yr(-1) (wet weight). In the total mineral soil as well as the small macroaggregates (250-2000 mu m), Microaggregates (53-250 mu m), and the silt plus clay fraction (2000 mu m) were the only water-stable aggregate fraction that increased in C content across all manure input levels. Further physical separation of macroaggregates into subpools by microaggregate isolation showed that coarse (>250 mu m) particulate organic matter (POM) was the fraction that accounted most for the increase in C content of the large macroaggregates. Furthermore, the turnover of large macroaggregates increased with increasing manure applications, as indicated by decreased formation and stabilization of intramicroaggregate POM within the large macroaggregates. We conclude that as C input increases, the mineral fraction of a soil saturates and consequently additional C input will only accumulate in labile soil C pools that have a relatively faster turnover.

  • carbon and nitrogen in the enriched labile fraction along a climosequence of zonal steppe soils in russia
    Soil Science Society of America Journal, 2000
    Co-Authors: Andrej Rodionov, Inga Urusevskaja, Wulf Amelung, Wolfgang Zech
    Abstract:

    Breaking aggregates by plowing resulted in the decomposition of formerly physically protected soil organic matter (SOM), including the enriched labile fraction (ELF), but it was unknown to what extent such effects were controlled by climate. To investigate this question. aggregate-size fractions were obtained from each of five native and adjacent long-term cultivated topsoils across a climosequence in the Russian steppe. After ultrasonic dispersion of small macro(250-2000 μm) and Microaggregates (53-250 μm) at 100 and 500 J mL 1 (only for so-called stable macroaggregates) and a particle-size fractionation, density fractions 2.22 g cm -3 were obtained from the fine silt-sized particles. In all fractions, C and N contents were determined. The stable aggregates were found only at native sites, were almost free of ELF, and showed their C maximum in the two lightest fractions. Cultivation reduced the C and N contents in all aggregates. In small macroaggregates, C losses occurred primarily as ELF, whereas Microaggregates lost C in the fine silt density range of 1.85 to 2.22 g cm 3 . The C partition among the fine silt density fractions was not related to climate. Losses in ELF were also not related to climate, suggesting that ELF represents a C pool that is site-specifically influenced by cultivation. The C losses from fractions <2.07 g cm 3 , however, increased as the climate became dryer and warmer, suggesting that they reveal interactive effects of climate and land use on physically stabilized SOM.

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  • Relationships between soil macroaggregation and humic carbon in a sandy loam soil following conservation tillage
    Journal of Soils and Sediments, 2018
    Co-Authors: Xianfeng Zhang, Anning Zhu, Wenliang Yang, Xiuli Xin, Jiabao Zhang, Shuchun Ge
    Abstract:

    PurposeHumic substances are recalcitrant and might act as persistent binding agents to form macroaggregates. The focus of this study is in investigating the contribution of humic carbon (HC) to soil aggregation in response to various tillage and residue managements.Materials and methodsArable soils following 8-year contrasting managements were collected to determine aggregate size distribution and stability and HC fractions including humic acid (HA) and fulvic acid (FA). The contribution of HC to aggregation was divided into three special effects including positive effect (PE), negative effect (NE), and combined effect (CE), and these effects were measured using aggregate fractionation techniques.Results and discussionAs well as to promote structural stability, HC bounds predominantly with the silt + clay fraction and secondarily with Microaggregates to form larger aggregates. The PE increased with increasing aggregate size, whereas the NE followed the opposite pattern. A positive CE was observed for large and small macroaggregates, whereas the CE for Microaggregates and the silt + clay fraction was negative. Compared to continuous tillage, reduced- and no-tillage decreased the PE for large and small macroaggregates by 1.58–30.98% at the 0–20 cm depth, and straw returning also slightly decreased the corresponding PE relative to straw removing. By contrast, a significantly higher NE for small macroaggregates at the 0–10 cm depth while 6.33–81.11% decreases in CE for large and small macroaggregates at the 0–10 cm depth as well as for large macroaggregates at the 10–20 cm depth, were observed under reduced- and no-tillage. The extraction of HC significantly reduced the aggregate stability and reduced- and no-tillage effectively limited its decrease magnitude. Small macroaggregates and Microaggregates made larger contributions to soil HC accumulation than did other fractions. An averagely increased contribution from large or small macroaggregates was observed under both reduced-/no-tillage and straw returning at the 0–20 cm depth. A significant and positive relationship was found between the mass proportion of macroaggregates and the HC accumulation in 0–20 cm soil. Large macroaggregates had significantly higher HA/FA ratios than small macroaggregates, and reduced- and no-tillage significantly increased these ratios both in large and in small macroaggregates. The CE for large or small macroaggregates was also significantly negatively correlated with their HA/FA ratios.ConclusionsOverall, the HC accumulation in soil is likely to play a key role in macroaggregation, but conservation tillage might decrease the contribution magnitude of HC to large or small macroaggregation through increasing the corresponding HA/FA ratios.

  • effects of tillage and residue managements on organic c accumulation and soil aggregation in a sandy loam soil of the north china plain
    Catena, 2017
    Co-Authors: Xianfeng Zhang, Jiabao Zhang, Wenliang Yang
    Abstract:

    Abstract This paper was primarily devoted to reveal the stock of soil organic carbon (C) as well as its lability and to compare their differences existing among tillage and residue practices, aiming to identify the effects on the accumulation process of organic C and its association with macroaggregation. Arable soils following 8-year contrasting managements were collected to determine aggregate size distribution, organic C content and its lability. A wet-sieving method was used to fractionate aggregate fractions including > 2000 μm large macroaggregates, 2000–250 μm small macroaggregates, 250–53 μm Microaggregates, and