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Karolien Denef - One of the best experts on this subject based on the ideXlab platform.
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microaggregate associated carbon as a diagnostic fraction for management induced changes in soil organic carbon in two oxisols
Soil Biology & Biochemistry, 2007Co-Authors: Karolien Denef, Lincoln Zotarelli, Robert Michael BoddeyAbstract: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.
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Carbon Sequestration and Soil Aggregation in Center-Pivot Irrigated and Dryland Cultivated Farming Systems
Soil Science Society of America Journal, 2007Co-Authors: Jeroen Gillabel, Karolien Denef, Roel Merckx, John Brenner, Keith PaustianAbstract:Although irrigation is considered a benefi ciary management for increasing soil organic C (SOC) stocks in (semi)arid environments, our understanding of the impact of irrigation on soil organic matter (SOM) dynamics in the fi eld remains limited. We investigated the effect of irrigation on soil C storage in relation to soil aggregation by measuring C stocks of bulk soil and different aggreagate fractions in the top 20-cm layer of center-pivot irrigated vs. dryland farming systems in semiarid southwestern Nebraska. The irrigated fi elds (IRR) showed increased C inputs and larger SOC stocks than the dryland cultivated fi elds (DRY). Fractionation of bulk soil samples into non-microaggregate-associated particulate organic matter (free POM) and microaggregate-associated POM, silt, and clay fractions indicated that the larger bulk SOC stock under IRR was explained solely by an increase in microaggregate-associated C storage Wet sieving of bulk soil showed that microaggregation was remarkably low under DRY and did not increase under IRR, suggesting that the protection of microaggregates inside Macroaggregates was no prerequisite for C sequestration under IRR. The results of this study confi rm the potential of irrigation to increase soil C stocks through preferential sequestration of C inside microaggregates, but question our understanding of the mechanisms underlying this preferential sequestration. Abbreviations: cPOM, coarse particulate organic matter (>250 µm); DRY, dryland cultivated treatment; iPOM, intramicroaggregate particulate organic matter; IRR, center-pivot irrigated treatment; mClay, microaggregate-associated clay fraction; micro-C, microaggregate-associated C; mSilt, microaggregateassociated silt fraction; NV, native vegetation; POM, particulate organic matter; SOC, soil organic carbon; SOM, soil organic matter; TOC, total organic carbon.
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clay mineralogy determines the importance of biological versus abiotic processes for Macroaggregate formation and stabilization
European Journal of Soil Science, 2005Co-Authors: Karolien Denef, Johan SixAbstract:Summary Plant residues, living roots and microbial activity play an important role in aggregate formation and the stabilization of soil organic carbon (SOC), but their impact might differ among soils with different clay mineralogy. We investigated the effect of these organic agents on aggregation and SOC during a 76-day incubation of 2-mm sieved soil from an illitic Kastanozem and a kaolinitic Ferralsol, subjected to the following treatments: (i) control (no residue input or plant growth), (ii) residue input, (iii) living plants, and (iv) residue input and living plants. After 46 and 76 days, aggregate size distribution, aggregate-associated SOC and microbial-C were measured. In both soils, microbial-C was less in the control than in the residue and/or plant treatments. After 46 days, new large Macroaggregates (> 2000 µm) were formed in the control treatment of the kaolinitic soil, but not of the illitic soil. Control Macroaggregates in the kaolinitic soil were formed out of silt and clay particles without accumulating C. Residue input and plant growth had a greater positive effect on Macroaggregate formation in the illitic than in the kaolinitic soil. A stronger relation was found between microbial-C and amount of large Macroaggregates in the illitic than in the kaolinitic soil. We conclude that kaolinitic soils can rapidly form Macroaggregates independent of biological processes due to physical or electrostatic interactions between the 1:1 clay minerals and oxides. However, biological processes led to stronger organic bonds between the illite compared with the kaolinite clay, resulting in more Macroaggregates with long-term stability in the illitic than in the kaolinitic soil.
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a history of research on the link between micro aggregates soil biota and soil organic matter dynamics
Soil & Tillage Research, 2004Co-Authors: Heleen Bossuyt, Steven Degryze, Karolien DenefAbstract: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.
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carbon sequestration in microaggregates of no tillage soils with different clay mineralogy
Soil Science Society of America Journal, 2004Co-Authors: Karolien Denef, Roel Merckx, Keith PaustianAbstract: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.
Keith Paustian - One of the best experts on this subject based on the ideXlab platform.
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aggregate associated soil organic matter as an ecosystem property and a measurement tool
Soil Biology & Biochemistry, 2014Co-Authors: Keith PaustianAbstract: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.
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Carbon Sequestration and Soil Aggregation in Center-Pivot Irrigated and Dryland Cultivated Farming Systems
Soil Science Society of America Journal, 2007Co-Authors: Jeroen Gillabel, Karolien Denef, Roel Merckx, John Brenner, Keith PaustianAbstract:Although irrigation is considered a benefi ciary management for increasing soil organic C (SOC) stocks in (semi)arid environments, our understanding of the impact of irrigation on soil organic matter (SOM) dynamics in the fi eld remains limited. We investigated the effect of irrigation on soil C storage in relation to soil aggregation by measuring C stocks of bulk soil and different aggreagate fractions in the top 20-cm layer of center-pivot irrigated vs. dryland farming systems in semiarid southwestern Nebraska. The irrigated fi elds (IRR) showed increased C inputs and larger SOC stocks than the dryland cultivated fi elds (DRY). Fractionation of bulk soil samples into non-microaggregate-associated particulate organic matter (free POM) and microaggregate-associated POM, silt, and clay fractions indicated that the larger bulk SOC stock under IRR was explained solely by an increase in microaggregate-associated C storage Wet sieving of bulk soil showed that microaggregation was remarkably low under DRY and did not increase under IRR, suggesting that the protection of microaggregates inside Macroaggregates was no prerequisite for C sequestration under IRR. The results of this study confi rm the potential of irrigation to increase soil C stocks through preferential sequestration of C inside microaggregates, but question our understanding of the mechanisms underlying this preferential sequestration. Abbreviations: cPOM, coarse particulate organic matter (>250 µm); DRY, dryland cultivated treatment; iPOM, intramicroaggregate particulate organic matter; IRR, center-pivot irrigated treatment; mClay, microaggregate-associated clay fraction; micro-C, microaggregate-associated C; mSilt, microaggregateassociated silt fraction; NV, native vegetation; POM, particulate organic matter; SOC, soil organic carbon; SOM, soil organic matter; TOC, total organic carbon.
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carbon sequestration in microaggregates of no tillage soils with different clay mineralogy
Soil Science Society of America Journal, 2004Co-Authors: Karolien Denef, Roel Merckx, Keith PaustianAbstract: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.
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measuring and understanding carbon storage in afforested soils by physical fractionation
Soil Science Society of America Journal, 2002Co-Authors: Johan Six, E A Paul, P Callewaert, S Lenders, S De Gryze, Sherri J Morris, E G Gregorich, Keith PaustianAbstract:Forested ecosystems have been identified as potential C sinks. However, the accuracy of measurement and understanding of the underlying mechanisms for soil organic C (SOC) storage in forested ecosystems needs to be improved. The objective of this study was to use aggregate and soil organic matter (SOM) fractionation techniques to identify SOC pools that preferentially stabilize SOC in the long term and elucidate SOC sequestration mechanisms in forested soils. At two sites (Wildlife area, Ohio and Kemptville, Ontario) representing two different soils (Hapludalf and Hapludoll), we sampled soils under agriculture, afforestation, and forest and separated them into aggregates. Different size classes of intra-aggregate particulate organic matter (iPOM) fractions were isolated by dqnsity flotation, dispersion, and sieving. At both sites, aggregation and whole SOC content were greater in the forested than in the agricultural ecosystems. The greater aggregation in forested ecosystems resulted in greater iPOM C concentrations, especially The iPOM C fractions associated with microaggregates (53-250 μm) and microaggregates occluded within Macroaggregates (mM) (250-2000 μm). The sum of C in these fractions (microaggregate protected C) was 468 ± 29, 696 ± 171, 673 ± 70 g C m -2 in the agricultural, afforested, and forested soils at Kemptville, respectively. The difference in the microaggregate protected C between the agricultural and the afforested soils accounted, on average, for 20% of the difference in whole SOC stocks between the soils. We conclude, SOC is stabilized for a relatively longer term within microaggregates formed in afforested and forest systems. Therefore, we suggest a new fractionation scheme to isolate this microaggregate associated SOC for assessing the impact of land use, land management, and climate change on C storage.
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Short-term effects of biological and physical forces on aggregate formation in soils with different clay mineralogy
Plant and Soil, 2002Co-Authors: Karolien Denef, Johan Six, Roel Merckx, Keith PaustianAbstract:The mechanisms resulting in the binding of primary soil particles into stable aggregates vary with soil parent material, climate, vegetation, and management practices. In this study, we investigated short-term effects of: (i) nutrient addition (Hoagland's solution), (ii) organic carbon (OC) input (wheat residue), (iii) drying and wetting action, and (iv) root growth, with or without dry-wet cycles, on aggregate formation and stabilization in three soils differing in weathering status and clay mineralogy. These soils included a young, slightly weathered temperate soil dominated by 2:1 (illite and chlorite) clay minerals; a moderately weathered soil with mixed [2:1 (vermiculite) and 1: 1 (kaolinite)] clay mineralogy and oxides; and a highly weathered tropical soil dominated by 1:1 (kaolinite) clay minerals and oxides. Air-dried soil was dry sieved through a 250 μm sieve to break up all Macroaggregates and 100 g-subsamples were brought to field capacity and incubated for 42 days. After 14 and 42 days, aggregate stability was measured on field moist and air-dried soil, to determine unstable and stable aggregation respectively. In control treatments (i.e., without nutrient or organic matter addition, without roots and at constant moisture), the formation of unstable and stable Macroaggregates (> 250 μm) increased in the order: 2:1 clay soil < mixed clay soil < 1:1 clay soil. After 42 days of incubation, nutrient addition significantly increased both unstable and stable Macroaggregates in the 2:1 and 1:1 clay soils. In all soils, additional OC input increased both unstable and stable Macroaggregate formation. The increase in macroaggregation with OC input was highest for the mixed clay soil and lowest for the 1:1 clay soil. In general, drying and wetting cycles had a positive effect on the formation of Macroaggregates. Root growth caused a decrease in unstable Macroaggregates in all soils. Larger amounts of Macroaggregates were found in the mixed clay and oxides soil when plants were grown under 50% compared to 100% field capacity conditions. We concluded that soils dominated by variable charge clay minerals (1:1 clays and oxides) have higher potential to form stable aggregates when OC concentrations are low. With additional OC inputs, the greatest response in stable Macroaggregate formation occurred in soils with mixed mineralogy, which is probably a result of different binding mechanisms occurring: i.e., electrostatic bindings between 2:1 clays, 1:1 clays and oxides (i.e. mineral-mineral bindings), in addition to OM functioning as a binding agent between 2:1 and 1:1 clays.
Johan Six - One of the best experts on this subject based on the ideXlab platform.
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earthworm lumbricus terrestris mediated redistribution of c and n into large Macroaggregate occluded soil fractions in fine textured no till soils
Applied Soil Ecology, 2019Co-Authors: Jatta Sheehy, Johan Six, Ansa Palojarvi, Visa Nuutinen, Ossi Knuutila, Janne Kaseva, Kristiina ReginaAbstract:Abstract By processing large quantities of crop residues, earthworms enhance the mineralization of organic matter but have also been shown to stabilize soil organic carbon (SOC) into soil fractions like microaggregates (53–250 μm) within Macroaggregates (>250 μm) especially in no-till soils. Our objective was to find direct evidence on the impact of an anecic, soil surface-feeding earthworm, Lumbricus terrestris L., on the redistribution of SOC and soil nitrogen (N) into Macroaggregate-occluded soil fractions of boreal soils. We sampled soil (0–5 cm depth) from the middens of L. terrestris (mounds of collected residue and surface casts at the openings of its permanent burrows) and the adjacent non-midden (bulk) soil at three no-till sites in southern Finland: two clayey sites (sites 1–2) and one coarse textured site (site 3). Compared to bulk soil, the soil in L. terrestris middens featured general increase in aggregate size and content of SOC and N within the large Macroaggregates (>2000 μm) at the clayey sites. The microaggregates within the large Macroaggregates had accumulated more SOC and N in the midden soil especially at site 1 where 99% of the difference in total SOC between midden and bulk soil was associated with this type of SOC stabilization. At site 2, the increase in SOC found in the large Macroaggregates was counteracted by a decrease in SOC in microaggregates within the small Macroaggregates (250–2000 μm). No differences in SOC stored in soil fractions were found between midden and non-midden soil at the coarse soil site 3 with higher top soil decomposition rate compared to sites 1 and 2. Across the study sites, the total amount of SOC was 6% higher in midden soil compared to the bulk soil. These results suggest L. terrestris mediates the storage of SOC and N into better protected soil fractions in clay soils under boreal conditions.
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soil fertility management impacts on soil macrofauna soil aggregation and soil organic matter allocation
Applied Soil Ecology, 2011Co-Authors: Johan Six, Bernard Vanlauwe, F O Ayuke, L Brussaard, D Lelei, C N Kibunja, M M PullemanAbstract:Maintenance of soil organic matter through integrated soil fertility management is important for soil quality and agricultural productivity, and for the persistence of soil faunal diversity and biomass. Little is known about the interactive effects of soil fertility management and soil macrofauna diversity on soil aggregation and SOM dynamics in tropical arable cropping systems. A study was conducted in a long-term trial at Kabete, Central Kenya, to investigate the effects of organic inputs (maize stover or manure) and inorganic fertilizers on soil macrofauna abundance, biomass and taxonomic diversity, water stable aggregation, whole soil and aggregate-associated organic C and N, as well as the relations between these variables. Differently managed arable systems were compared to a long-term green fallow system representing a relatively undisturbed reference. Fallowing, and application of farm yard manure (FYM) in combination with fertilizer, significantly enhanced earthworm diversity and biomass as well as aggregate stability and C and N pools in the top 15 cm of the soil. Earthworm abundance significantly negatively correlated with the percentage of total Macroaggregates and microaggregates within Macroaggregates, but all earthworm parameters positively correlated with whole soil and aggregate associated C and N, unlike termite parameters. Factor analysis showed that 35.3% of the total sample variation in aggregation and C and N in total soil and aggregate fractions was explained by earthworm parameters, and 25.5% by termite parameters. Multiple regression analysis confirmed this outcome. The negative correlation between earthworm abundance and total Macroaggregates and microaggregates within Macroaggregate could be linked to the presence of high numbers of Nematogenia lacuum in the arable treatments without organic amendments, an endogeic species that feeds on excrements of other larger epigeic worms and produces small excrements. Under the conditions studied, differences in earthworm abundance, biomass and diversity were more important drivers of management-induced changes in aggregate stability and soil C and N pools than differences in termite populations. Highlights ? Application of farm yard manure + fertilizer improved aggregate stability and C and N stabilization in soil. ? Application of maize stover did not improve soil aggregation and C and N stabilization. ? Farm yard manure + fertilizer application enhanced earthworm diversity and biomass. ? Higher earthworm diversity and biomass enhanced aggregate and C and N stabilization. ? Earthworms were more important drivers of aggregate and C and N stabilization than termites.
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indications for soil carbon saturation in a temperate agroecosystem
Soil Science Society of America Journal, 2008Co-Authors: Haegeun Chung, John H Grove, Johan SixAbstract:The soil C saturation concept postulates that there is an upper limit to the equilibrium soil C level of mineral soils even when soil C input is increased. To test this concept, we analyzed the relationship between steady-state soil C input and soil organic C (SOC) concentration in a temperate corn (Zea mays L.) agroecosystem experiment located in Lexington, KY. In this experiment, a gradient in plant productivity and consequent C input to the soil was produced with four N application rates (0, 84, 168, and 336 kg N ha −1 yr −1 ) under two disturbance regimes, no-till (NT) and moldboard plowing (MP). We examined whether physical protection of organic matter by soil aggregation and chemical protection by association with silt and clay particles led to SOC saturation. We used wet sieving to physically separate SOC pools that differ in C stabilization potential, and determined the C sequestration in each fraction. Total SOC was positively related to C input, and this was primarily due to C stabilization in small Macroaggregates. In both tillage systems, however, microaggregate C and silt-plus-clay C did not increase with greater C input. Within the small Macroaggregates, coarse particulate organic matter C and microaggregate C increased with C input, but there was no increase in silt-plus-clay C. Our results indicate that soil fractions with low C stabilization potential exhibit C saturation behavior. Apparent C saturation of some of the fractions indicates that SOC pools have a limited capacity to stabilize added C and that such a limit to C stabilization will constrain the ecosystem services provided by these SOC pools. Abbreviations: MP, moldboard plowing; MWD, mean weight diameter; NT, no-till; POM, particulate organic matter; SOC, soil organic carbon; SOM, soil organic matter.
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Soil Carbon Saturation Controls Labile and Stable Carbon Pool Dynamics
Soil Science Society of America Journal, 2008Co-Authors: S Gulde, H. Chung, Wulf Amelung, C. Chang, Johan SixAbstract: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.
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clay mineralogy determines the importance of biological versus abiotic processes for Macroaggregate formation and stabilization
European Journal of Soil Science, 2005Co-Authors: Karolien Denef, Johan SixAbstract:Summary Plant residues, living roots and microbial activity play an important role in aggregate formation and the stabilization of soil organic carbon (SOC), but their impact might differ among soils with different clay mineralogy. We investigated the effect of these organic agents on aggregation and SOC during a 76-day incubation of 2-mm sieved soil from an illitic Kastanozem and a kaolinitic Ferralsol, subjected to the following treatments: (i) control (no residue input or plant growth), (ii) residue input, (iii) living plants, and (iv) residue input and living plants. After 46 and 76 days, aggregate size distribution, aggregate-associated SOC and microbial-C were measured. In both soils, microbial-C was less in the control than in the residue and/or plant treatments. After 46 days, new large Macroaggregates (> 2000 µm) were formed in the control treatment of the kaolinitic soil, but not of the illitic soil. Control Macroaggregates in the kaolinitic soil were formed out of silt and clay particles without accumulating C. Residue input and plant growth had a greater positive effect on Macroaggregate formation in the illitic than in the kaolinitic soil. A stronger relation was found between microbial-C and amount of large Macroaggregates in the illitic than in the kaolinitic soil. We conclude that kaolinitic soils can rapidly form Macroaggregates independent of biological processes due to physical or electrostatic interactions between the 1:1 clay minerals and oxides. However, biological processes led to stronger organic bonds between the illite compared with the kaolinite clay, resulting in more Macroaggregates with long-term stability in the illitic than in the kaolinitic soil.
Roel Merckx - One of the best experts on this subject based on the ideXlab platform.
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Carbon Sequestration and Soil Aggregation in Center-Pivot Irrigated and Dryland Cultivated Farming Systems
Soil Science Society of America Journal, 2007Co-Authors: Jeroen Gillabel, Karolien Denef, Roel Merckx, John Brenner, Keith PaustianAbstract:Although irrigation is considered a benefi ciary management for increasing soil organic C (SOC) stocks in (semi)arid environments, our understanding of the impact of irrigation on soil organic matter (SOM) dynamics in the fi eld remains limited. We investigated the effect of irrigation on soil C storage in relation to soil aggregation by measuring C stocks of bulk soil and different aggreagate fractions in the top 20-cm layer of center-pivot irrigated vs. dryland farming systems in semiarid southwestern Nebraska. The irrigated fi elds (IRR) showed increased C inputs and larger SOC stocks than the dryland cultivated fi elds (DRY). Fractionation of bulk soil samples into non-microaggregate-associated particulate organic matter (free POM) and microaggregate-associated POM, silt, and clay fractions indicated that the larger bulk SOC stock under IRR was explained solely by an increase in microaggregate-associated C storage Wet sieving of bulk soil showed that microaggregation was remarkably low under DRY and did not increase under IRR, suggesting that the protection of microaggregates inside Macroaggregates was no prerequisite for C sequestration under IRR. The results of this study confi rm the potential of irrigation to increase soil C stocks through preferential sequestration of C inside microaggregates, but question our understanding of the mechanisms underlying this preferential sequestration. Abbreviations: cPOM, coarse particulate organic matter (>250 µm); DRY, dryland cultivated treatment; iPOM, intramicroaggregate particulate organic matter; IRR, center-pivot irrigated treatment; mClay, microaggregate-associated clay fraction; micro-C, microaggregate-associated C; mSilt, microaggregateassociated silt fraction; NV, native vegetation; POM, particulate organic matter; SOC, soil organic carbon; SOM, soil organic matter; TOC, total organic carbon.
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a quantification of short term Macroaggregate dynamics influences of wheat residue input and texture
Soil Biology & Biochemistry, 2005Co-Authors: Johan Six, Steven De Gryze, Cynthia Brits, Roel MerckxAbstract:Abstract Soil structure and soil aggregation play an important role in an array of processes such as soil erodibility, organic matter protection and soil fertility. Modeling attempts of these processes would benefit substantially from including soil structural parameters such as soil aggregation. However, quantitative data on soil structural dynamics is lacking. Therefore, we conducted short-term (3 weeks) incubations to acquire necessary soil structural parameters for modeling purposes. Prior to incubation, all structures >53 μm were destroyed from three soils with varying texture but under similar management. Five different amounts of wheat residue, ranging from 0 to 3 wt%, were added to each of these soils. After 3 weeks, samples were analyzed for large water-stable Macroaggregates (>2000 μm) using a wet sieving method and for fungal growth using epifluorescence microscopy. Aggregate formation increased linearly with increasing amounts of residue at a rate of 12.0±1.24 g aggregates g −1 residue added. We found no differences in aggregate formation among the three soils, even though the equilibrium level of Macroaggregates differed in the field. While amounts of water-stable Macroaggregates in the sandy loam and the silt loam soil corresponded well with fungal lengths, this was not the case for the silty clay loam soil. This suggests that fungi are less important in aggregate formation in more clayey soils. Cumulative respiration correlated well ( r =0.89–0.91) with water-stable Macroaggregates for all three soils. A model assuming an aggregate formation rate proportional to the respiration rate was very successful in fitting the measured aggregate amounts. This model predicted about 65% of the changes in aggregation when different amounts were added, and about 85% of the changes in aggregation over time. This model yielded a Macroaggregate turnover time of 40–60 days. The quantitative results presented here can directly be incorporated into models describing and predicting soil aggregate dynamics, as a determining factor for physical protection of organic matter within a soil.
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carbon sequestration in microaggregates of no tillage soils with different clay mineralogy
Soil Science Society of America Journal, 2004Co-Authors: Karolien Denef, Roel Merckx, Keith PaustianAbstract: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.
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Short-term effects of biological and physical forces on aggregate formation in soils with different clay mineralogy
Plant and Soil, 2002Co-Authors: Karolien Denef, Johan Six, Roel Merckx, Keith PaustianAbstract:The mechanisms resulting in the binding of primary soil particles into stable aggregates vary with soil parent material, climate, vegetation, and management practices. In this study, we investigated short-term effects of: (i) nutrient addition (Hoagland's solution), (ii) organic carbon (OC) input (wheat residue), (iii) drying and wetting action, and (iv) root growth, with or without dry-wet cycles, on aggregate formation and stabilization in three soils differing in weathering status and clay mineralogy. These soils included a young, slightly weathered temperate soil dominated by 2:1 (illite and chlorite) clay minerals; a moderately weathered soil with mixed [2:1 (vermiculite) and 1: 1 (kaolinite)] clay mineralogy and oxides; and a highly weathered tropical soil dominated by 1:1 (kaolinite) clay minerals and oxides. Air-dried soil was dry sieved through a 250 μm sieve to break up all Macroaggregates and 100 g-subsamples were brought to field capacity and incubated for 42 days. After 14 and 42 days, aggregate stability was measured on field moist and air-dried soil, to determine unstable and stable aggregation respectively. In control treatments (i.e., without nutrient or organic matter addition, without roots and at constant moisture), the formation of unstable and stable Macroaggregates (> 250 μm) increased in the order: 2:1 clay soil < mixed clay soil < 1:1 clay soil. After 42 days of incubation, nutrient addition significantly increased both unstable and stable Macroaggregates in the 2:1 and 1:1 clay soils. In all soils, additional OC input increased both unstable and stable Macroaggregate formation. The increase in macroaggregation with OC input was highest for the mixed clay soil and lowest for the 1:1 clay soil. In general, drying and wetting cycles had a positive effect on the formation of Macroaggregates. Root growth caused a decrease in unstable Macroaggregates in all soils. Larger amounts of Macroaggregates were found in the mixed clay and oxides soil when plants were grown under 50% compared to 100% field capacity conditions. We concluded that soils dominated by variable charge clay minerals (1:1 clays and oxides) have higher potential to form stable aggregates when OC concentrations are low. With additional OC inputs, the greatest response in stable Macroaggregate formation occurred in soils with mixed mineralogy, which is probably a result of different binding mechanisms occurring: i.e., electrostatic bindings between 2:1 clays, 1:1 clays and oxides (i.e. mineral-mineral bindings), in addition to OM functioning as a binding agent between 2:1 and 1:1 clays.
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influence of dry wet cycles on the interrelationship between aggregate particulate organic matter and microbial community dynamics
Soil Biology & Biochemistry, 2001Co-Authors: Heleen Bossuyt, Johan Six, Karolien Denef, Roel Merckx, Serita D Frey, Edward T Elliott, Keith PaustianAbstract:Abstract Aggregate dynamics and their relationship to the microbial community have been suggested as key factors controlling SOM dynamics. Dry–wet (DW) cycles are thought to enhance aggregate turnover and decomposition of soil organic matter (SOM), particularly in tilled soils. The objective of this study was to evaluate the effects of DW cycles on aggregate stability, SOM dynamics, and fungal and bacterial populations in a Weld silt loam soil (Aridic Paleustoll). Samples, taken from 250 μm sieved air-dried soil (i.e. free of Macroaggregates > 250 μm), were incubated with 13C-labeled wheat residue. In one set of soil samples, fungal growth was suppressed using a fungicide (Captan) in order to discern the effect of dry–wet cycles on fungal and bacterial populations. Aggregate formation was followed during the first 14 d of incubation. After this period, one set of soil samples was subjected to four DW cycles, whereas another set, as a control, was kept at field capacity (FC). Over 74 d, total and wheat-derived respiration, size distribution of water stable aggregates and fungal and bacterial biomass were measured. We determined native and labeled C dynamics of three particulate organic matter (POM) fractions related to soil structure: the free light fraction (LF), and the coarse (250–2000 μm) and fine (53–250 μm) intra-aggregate POM fraction (iPOM). In the fungicide treated soil samples, fungal growth was significantly reduced and no large Macroaggregates (> 2 mm) were formed, whereas without addition of fungicide, fungi represented the largest part of the microbial biomass (66%) and 30% of the soil dry weight was composed of large Macroaggregates. During Macroaggregate formation, labeled free LF-C significantly decreased whereas labeled coarse iPOM-C increased, indicating that macroggregates are formed around fresh wheat residue (free LF), which is consequently incorporated and becomes coarse iPOM. The first drying and wetting event reduced the amount of large Macroaggregates from 30 to 21% of the total soil weight. However, Macroaggregates became slake-resistant after two dry-wet cycles. Fine iPOM-C was significantly lower in soil after two dry–wet cycles compared to soil kept at FC. We conclude that more coarse iPOM is decomposed into fine iPOM in Macroaggregates not exposed to DW cycles due to a slower Macroaggregate turnover. In addition, when Macroaggregates, subjected to dry–wet cycles, became slake-resistant (d 44) and consequently Macroaggregate turnover decreased, fine iPOM accumulated. In conclusion, differences in fine iPOM accumulation in DW vs. control Macroaggregates are attributed to differences in Macroaggregate turnover.
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reciprocal transfer of carbon and nitrogen by decomposer fungi at the soil litter interface
Soil Biology & Biochemistry, 2003Co-Authors: Serita D Frey, E T ElliottAbstract:Abstract We have investigated whether decomposer fungi translocate litter-derived C into the underlying soil while simultaneously translocating soil-derived inorganic N up into the litter layer. We also located and quantified where the translocated C is deposited within the soil aggregate structure. When 13C-labeled wheat straw was decomposed on the surface of soil amended with 15N-labeled inorganic N, we found that C and N were reciprocally transferred by fungi, with a significant quantity (121–151 μg C g−1 whole soil) of litter-derived C being deposited into newly formed Macroaggregates (>250 μm sized aggregates). Fungal inhibition reduced fungal biomass and the bidirectional C and N flux by approximately 50%. The amount of litter-derived C found in Macroaggregates was positively correlated with litter-associated fungal biomass. This fungal-mediated litter-to-soil C transfer, which to our knowledge has not been demonstrated before for saprophytic fungi, may represent an important mechanism by which litter C enters the soil and becomes stabilized as soil organic matter within the Macroaggregate structure.
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soil Macroaggregate turnover and microaggregate formation a mechanism for c sequestration under no tillage agriculture
Soil Biology & Biochemistry, 2000Co-Authors: E T Elliott, Keith PaustianAbstract: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.
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soil structure and organic matter i distribution of aggregate size classes and aggregate associated carbon
Soil Science Society of America Journal, 2000Co-Authors: Keith Paustian, E T Elliott, C CombrinkAbstract: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.
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aggregate and soil organic matter dynamics under conventional and no tillage systems
Soil Science Society of America Journal, 1999Co-Authors: E T Elliott, Keith PaustianAbstract: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.
