Home About us Contact
|
Home About us Contact | ||
|
|
||
Soil Aggregates (soil + aggregate)
Selected AbstractsElevated carbon dioxide and irrigation effects on water stable aggregates in a Sorghum field: a possible role for arbuscular mycorrhizal fungiGLOBAL CHANGE BIOLOGY, Issue 3 2001Matthias C. Rillig Summary While soil biota and processes are becoming increasingly appreciated as important parameters for consideration in global change studies, the fundamental characteristic of soil structure is a neglected area of research. In a sorghum [Sorghum bicolor (L.) Moench] field experiment in which CO2[supplied using free-air CO2 enrichment (FACE) technology] was crossed factorially with an irrigation treatment, soil aggregate (1,2 mm) water stability increased in response to elevated CO2. Aggregate water stability was increased by 40% and 20% in response to CO2, at ample and limited water supply treatments, respectively. Soil hyphal lengths of arbuscular mycorrhizal fungi (AMF) increased strongly (with a threefold increase in the dry treatment) in response to CO2, and the concentrations of one fraction (easily extractable glomalin, EEG) of the AMF-produced protein glomalin were also increased. Two fractions of glomalin, and AMF hyphal lengths were all positively correlated with soil aggregate water stability. The present results further support the hypothesis that AMF can become important in global change scenarios. Although in this field study a causal relationship between hyphal length, glomalin and aggregate stability cannot be demonstrated, the present data do suggest that AMF could mediate changes in soil structure under elevated CO2. This could be of great importance in agricultural systems threatened by erosional soil loss. [source] Effect of mass-transfer limitations on bioavailability of sorbed naphthalene in synthetic model soil matricesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2000Hendricus Mulder Abstract External and internal mass-transfer resistances influencing the bioavailability of sorbed naphthalene in a synthetic model matrix for soil aggregates were investigated in batch experiments in mixed reactors. Amberlite® adsorption resins (XAD4 and XAD7) were used as the synthetic model for soil aggregates. The effect of hydrodynamic conditions in the slurry phase on the diffusive transport across a stagnant film surrounding the model particles was studied. In addition, a mechanistic model was developed based on mass balances, diffusion equations, a nonlinear sorption isotherm, and microbial degradation kinetics. Experimental results could be explained well with this model. In the absence of external transfer limitations, intraparticle effective diffusion coefficients of (3.55 ± 0.10) × 10,9 m2/s and (5.29 ± 0.86) × 10,10 m2/s were determined for naphthalene in Amberlite XAD4 and XAD7, respectively. [source] Factors controlling aggregation in a minimum and a conventionally tilled undulating fieldEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2007S. De Gryze Summary Wind and water erosion induce breakdown of soil aggregates and loss of soil organic matter. Whereas most of the relations between aggregation and its driving factors have been established on a plot scale, these relations might be very different within an undulating landscape where both erosion (by wind or water) and deposition occur. The aim of this study was to investigate to what degree spatial patterns in soil variables influence spatial patterns in aggregation under different tillage intensities. We studied an agricultural field of about 3 ha in the silty region of Belgium. The site was split into a conventional tillage (CT) and a minimum tillage (MT) system. Within the field, 396 geo-referenced surface soil samples (0,5 cm) were taken and analyzed for organic matter content, quantity of aggregates and a number of other soil properties. Under CT, 28.5% of the total sample variation was explained by the occurrence of depositional areas, 20.8% by the amount of soil organic matter, and 13.8% by the presence of a clay-rich B horizon which surfaced due to progressive water and tillage erosion. Regression analysis revealed that 27% of the variation in the quantity of macroaggregates (>0.25 mm) was accounted for by these three factors. Under MT, 27.1% of the total sample variation was related to the surface cover of Tertiary sand, 22.6% to the amount of soil organic matter, and 13% to erodibility. These three factors explained 53% of the variation in the quantity of macroaggregates. In the CT system, the correlation between grass- or maize- carbon and the quantity of macroaggregates was strongly linked to erodibility, while this was not the case in the MT system. We concluded that at this site, macroaggregation is dominated by landscape-scale processes (such as water or tillage erosion) rather than determined by the commonly considered local variables (such as small variations in texture or organic matter content). [source] Modelling of colloid leaching from unsaturated, aggregated soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007M. Laegdsmand Summary The migration of colloids in soils can enhance the leaching of strongly sorbing contaminants. We present a model for the simulation of colloid leaching from unsaturated, aggregated soil media under stationary flow. Transport in the intra-aggregate pores is simulated by convection,dispersion, and transport in the interaggregate pores, and a stagnant layer of water surrounding the aggregates, is simulated by diffusion. The model describes the release of colloids from soil aggregates, sorption and desorption processes at the air,water interfaces, and flocculation and subsequent straining from the flowing water. All three processes were simulated as functions of ionic strength. Transport of ions in intra-aggregate pores was simulated by Fickian diffusion. The model was calibrated against experimental results of colloid leaching from columns packed with natural soil aggregates. The aggregates were of two soils differing in organic matter content. On each soil a single calibrated parameter set could describe the experiments with the three ionic strengths. The parameters for release of colloids from the aggregate surface and the sorption properties of the air,water interface were different for the two soils. The key parameters for leaching were the thickness of the stagnant layer of water surrounding the aggregates, the mechanical dispersion, the maximum concentration of colloids at the surface of the aggregates, the sorption capacity and rate coefficient of the colloids at the air,water interface, and the colloid diffusion coefficient. Simulations were also done with two additional irrigation intensities at one ionic strength. Simulated leaching was greater than measured leaching at both irrigation intensities, but the diffusion-controlled release of colloids from the aggregates was simulated correctly. [source] Aggregate-occluded black carbon in soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2006S. Brodowski Summary The great stability of black carbon (BC) in soils may not be solely attributable to its refractory structure but also to poor accessibility when physically enveloped by soil particles. Our aim was to elucidate the intensity of physical entrapment of BC within soil aggregates. For this purpose, the A horizon of a forest, and of a grassland soil, and of three soils under tillage, were sampled at the experimental station Rotthalmünster, Germany. Black carbon was assessed in water-stable aggregates and aggregate-density fractions using benzene polycarboxylic acids as specific markers. The greatest BC concentrations made up 7.2% of organic carbon and were found in the < 53 ,m fraction. The smallest BC concentrations occurred in the large macroaggregate fractions (> 2 mm). This pattern has been sustained even after tillage. The C-normalized BC concentrations were significantly greater (P < 0.05) in the occluded particulate organic matter (OPOM) fractions than in the free particulate organic matter (FPOM) and the mineral fractions. This enrichment of BC compared with organic carbon in the OPOM fractions amounted to factors of 1.5,2.7. Hence, BC was embedded within microaggregates in preference to other organic carbon compounds. Only 2.5,3.5% of BC was located in the OPOM fraction < 1.6 g cm,3, but 22,24% in the OPOM fraction with a density of 1.6,2.0 g cm,3. This suggests that BC possibly acted as a binding agent or was selectively enriched during decomposition of protected SOM, or both. Physical inclusion, particularly within microaggregates, could therefore contribute to the long mean-residence times of soil-inherent BC. [source] Effect of root mucilage and modelled root exudates on soil structureEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2000O. Traoré Summary Plant roots release in the rhizosphere diverse organic materials which may have different effects on soil structure. We have evaluated the effect of natural and modelled root-released materials on soil aggregates and the biodegradation of carbon from roots in the soil. The effects of root mucilage from maize and of a modelled soluble exudate were compared with those of simple compounds (glucose, polygalacturonic acid). For all treatments, soil was amended with 2 g C kg,1 soil and incubated for 30 days at 25°C. The biodegradation of mucilage was similar to that of polygalacturonic acid, and slower than the decomposition of modelled exudates and glucose. Addition of all substrates increased the stability of aggregates, but the duration of this effect depended on the chemical nature of the material. Compared with the control, the proportion of stable aggregates after 30 days of incubation was multiplied by 3.8 for root mucilage, by 4.2 for modelled soluble exudates, by 2.5 for polygalacturonic acid and by 2.0 for glucose. The different fractions of root exudates in the rhizosphere evidently affected the aggregate stability. [source] Characterization of ,- d -glucosidase extracted from soil fractionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2000M. D. Busto Summary One way to study the state in which stabilized extracellular enzymes persist and are active in the soil is by extraction from the soil, with subsequent fractionation of enzyme,organomineral complexes and characterization of such complexes. In order to investigate the location and characteristics of soil ,-glucosidase, three soil fractions were obtained both from real (undisturbed) soil aggregates and from structural (dispersed in water and physically disrupted) aggregates using two different granulometric procedures. The ,-glucosidase activity of the fraction was then assayed. When the aggregates were dispersed, more than 73% of activity was in the soil microaggregates with diameters of less than 50 ,m (SF50). These aggregates were associated with strongly humified organic matter. Solutions of diluted pyrophosphate at neutral pH liberated active ,-glucosidase from all fractions, although the efficacy of extraction varied according to the type of fraction. The SF50 fraction and aggregates of 2000,100 ,m obtained by sieving (SF2000) showed the greatest ,-glucosidase activity (34.5 and 36.0%, respectively). Micro- and ultrafiltration of SF50 extracts increased the total ,-glucosidase activity, whereas these procedures, applied to the RF2000 fraction, decreased it. Humus,,-glucosidase complexes in the SF50 fraction, between 0.45 ,m and 105 nominal molecular weight limit ( nmwl) (SF50II) and < 105nmwl (SF50III) showed an optimum pH at 5.4, and in the SF50I fraction (> 0.45 ,m) the optimum was 4.0. The stability of ,-glucosidase in the aggregates of the smallest size SF50II and SF50III decreased at acid pHs. The presence of two enzymes (or two forms of the same enzyme) catalysing the same reaction with different values of Michaelis constant and maximum velocity was observed in all but one of the ,-glucosidase complexes extracted and partially purified from the SF50 aggregates. [source] Carbon sequestration under Miscanthus: a study of 13C distribution in soil aggregatesGCB BIOENERGY, Issue 5 2009MARTA DONDINI Abstract The growing of bioenergy crops has been widely suggested as a key strategy in mitigating anthropogenic CO2 emissions. However, the full mitigation potential of these crops cannot be assessed without taking into account their effect on soil carbon (C) dynamics. Therefore, we analyzed the C dynamics through four soil depths under a 14-year-old Miscanthus plantation, established on former arable land. An adjacent arable field was used as a reference site. Combining soil organic matter (SOM) fractionation with 13C natural abundance analyses, we were able to trace the fate of Miscanthus -derived C in various physically protected soil fractions. Integrated through the whole soil profile, the total amount of soil organic carbon (SOC) was higher under Miscanthus than under arable crop, this difference was largely due to the input of new C. The C stock of the macroaggregates (M) under Miscanthus was significantly higher than those in the arable land. Additionally, the C content of the micro-within macroaggregates (mM) were higher in the Miscanthus soil as compared with the arable soil. Analysis of the intramicroaggregates particulate organic matter (POM) suggested that the increase C storage in mM under Miscanthus was caused by a decrease in disturbance of M. Thus, the difference in C content between the two land use systems is largely caused by soil C storage in physically protected SOM fractions. We conclude that when Miscanthus is planted on former arable land, the resulting increase in soil C storage contributes considerably to its CO2 mitigation potential. [source] Interactive effects of elevated CO2, N deposition and climate change on extracellular enzyme activity and soil density fractionation in a California annual grasslandGLOBAL CHANGE BIOLOGY, Issue 10 2005Hugh A. L. Henry Abstract Elevated CO2, N deposition and climate change can alter ecosystem-level nutrient cycling both directly and indirectly. We explored the interactive effects of these environmental changes on extracellular enzyme activity and organic matter fractionation in soils of a California annual grassland. The activities of hydrolases (polysaccharide-degrading enzymes and phosphatase) increased significantly in response to nitrate addition, which coincided with an increase in soluble C concentrations under ambient CO2. Water addition and elevated CO2 had negative but nonadditive effects on the activities of these enzymes. In contrast, water addition resulted in an increase in the activities of lignin-degrading enzymes (phenol oxidase and peroxidase), and a decrease in the free light fraction (FLF) of soil organic matter. Independent of treatment effects, lignin content in the FLF was negatively correlated with the quantity of FLF across all samples. Lignin concentrations were lower in the aggregate-occluded light fraction (OLF) than the FLF, and there was no correlation between percent lignin and OLF quantity, which was consistent with the protection of soil organic matter in aggregates. Elevated CO2 decreased the quantity of OLF and increased the OLF lignin concentration, however, which is consistent with increased degradation resulting from increased turnover of soil aggregates. Overall, these results suggest that the effects of N addition on hydrolase activity are offset by the interactive effects of water addition and elevated CO2, whereas water and elevated CO2 may cause an increase in the breakdown of soil organic matter as a result of their effects on lignin-degrading enzymes and soil aggregation, respectively. [source] Potential of low cost close-range photogrammetry system in soil microtopography quantificationHYDROLOGICAL PROCESSES, Issue 10 2009Mohamed A. M. Abd Elbasit Abstract Soil microtopography is a dynamic soil property which affects most soil-surface and water interaction processes. The importance of soil microtopography has been recognized for a long time, but only limited reports are available in the literature. In this study, the potential of using consumer-grade cameras and close-range photogrammetry procedures to quantify soil microtopography at plot-scale level (,1 m2) were assessed. Five fabricated gypsum surfaces with different degrees of roughness were used to simulate the soil surface conditions with different soil aggregates. The surfaces' digital elevation model (DEM) was generated using the photogrammetry system (PHM) involving a consumer-grade camera, and pin-microrelief meter (PM). The DEM generated using the PHM was assessed for accuracy, roughness indices (RI), depression area percentage (DA%), depression storage capacity (DSC), and micro-rills delineation in comparison with the PM. The accuracy was evaluated using the root mean square error (RMSE) in the x-, y-, and z-directions. Visual comparison between the 3D-visions of the DEM showed strong agreement between the DEM generated by the PHM and the PM, and between the PHM and the 2D images for the different gypsum surfaces. The average RMSE in the x-. y-, and z-direction were 2·08, 1·52, and 0·82 mm for the rough surface, and 4·42, 1·65, and 3·22 mm for the smooth surface. The RIs calculated from the two methods were highly correlated. The small discrepancy between the two methods was discussed. The micro-rills delineation was also similar for the two methods regarding the network density. The grid size did not effect the RI calculation, and has a strong influence on the DA%, DSC, and the delineated micro-rills orders. Results suggest that a consumer-grade camera and close-range photogrammetry have the potential to quantify the soil microtopography. Copyright © 2009 John Wiley & Sons, Ltd. [source] Fluid biomulching based on poly(vinyl alcohol) and fillers from renewable resourcesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008E. Chiellini Abstract This article reports on the results obtained in an investigation on the application of biodegradable polymeric materials in the agricultural practice of mulching. Particular attention has been devoted to the effect of biobased mulching films generated in situ by low-pressure spraying of polymeric water dispersions on the various cultivars. In a field trial, the effectiveness of the hydromulching (liquid-mulching) technique was assessed by the monitoring of the growth and yield of lettuce and corn, which were used as reference plants. Conventional plastic films and straw mulching (SM) were compared with liquid-mulching treatments based on poly(vinyl alcohol) and natural fillers derived from agroindustrial wastes (sugar cane bagasse, wheat flour, saw dust, and wheat straw). An improvement of the biomass yield of the two selected plants with respect to conventional polyethylene mulching was attained in various liquid-mulching formulations with positive effects on the maintenance of soil structure. Alternative fluid-mulching treatments based on biodegradable components were effective in preserving soil aggregates and improving some crop growth parameters. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] A comparison of two methods for the isolation of free and occluded particulate organic matterJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2005Angelika Kölbl Abstract Various methods exist for the isolation of particulate organic matter (POM), one of the soil-organic-matter (SOM) fractions reacting most sensitive on land-use or soil-management changes. A combination of density separation and ultrasonic treatment allows to isolate two types of POM: (1) free POM and (2) POM occluded in soil aggregates. POM fractions are closely linked to their biochemical function for the formation and stabilization of aggregates, therefore methods using different aggregate sizes may result in different POM fractions isolated. We evaluated two physical fractionation procedures to reveal whether they yield different POM fractions with respect to amount and composition, using grassland and arable soils with sandy-loam to sandy,clay-loam texture and thus low macroaggregate stability. Method I used air-dried aggregates of <2.0 mm size and a low-energy sonication for aggregate disruption, method II used field-moist aggregates <6.3 mm and a high-energy,sonication procedure for aggregate disruption. POM fractions were analyzed by elemental analysis (C, N) and CPMAS 13C-NMR spectroscopy. With both methods, about similar proportions of the SOM are isolated as free or occluded POM, respectively. The free- and occluded-POM fractions obtained with method I are also rather similar in C and N concentration and composition as shown by 13C-NMR spectroscopy. Method II isolates a free- and occluded-POM fraction with significantly different C and N concentrations. NMR spectra revealed significant differences in the chemical composition of both fractions from method II, with the occluded POM having lower amounts of O-alkyl C and higher amounts of aryl C and alkyl C than the free POM. Due to the use of larger, field-moist aggregates with minimized sample pretreatment, two distinctly different POM fractions are isolated with method II, likely to be more closely linked to their biochemical function for the formation and stabilization of aggregates. High-energy sonication as in method II also disrupts small microaggregates <63 µm and releases fine intraaggregate POM. This fraction seems to be a significant component of occluded POM, that allows a differentiation between free and occluded POM in sandy soils with significant microaggregation. It can be concluded, that microaggregation in arable soils with sandy texture is responsible for the storage of a more degraded occluded POM, that conversely supports the stabilization of fine microaggregates. Ein Vergleich zweier Methoden zur Isolierung von freier und okkludierter partikulärer organischer Substanz Partikuläres organisches Material (POM) wird im Hinblick auf die Landnutzung als sensitive Fraktion der organischen Bodensubstanz (SOM) angesehen, aber die unterschiedlichen Methoden seiner Isolierung erschweren den Vergleich zwischen verschiedenen Studien. Wir haben zwei physikalische Fraktionierungsmethoden ausgewertet, um zu zeigen, ob sie im Hinblick auf Menge und Zusammensetzung zu unterschiedlichen POM-Fraktionen führen. Hierfür wurden Proben von Grünland- und Ackerböden verwendet. Für Methode I wurden luftgetrocknete Aggregate der Größe <2 mm verwendet, zu deren Zerstörung eine Ultraschallbehandlung mit geringem Energieeintrag eingesetzt wurde. Für Methode II wurden feldfeuchte Aggregate der Größe <6.3 mm und eine Ultraschallbehandlung mit vergleichsweise hoher Energie zur Aggregatzerstörung herangezogen. Mit beiden Methoden konnten zwei POM-Gruppen gewonnen werden: (1) freies POM und (2) in Bodenaggregaten eingeschlossenes POM. Die POM-Fraktionen wurden mittels Elementanalyse (C, N) und CPMAS- 13C-NMR,Spektroskopie untersucht. Methode I zeigte im Hinblick auf Menge und Zusammensetzung nur sehr geringe Unterschiede zwischen freien und okkludierten POM-Fraktionen. Methode II isolierte freie und okkludierte POM-Fraktionen mit signifikant unterschiedlichen C- und N-Konzentrationen. Auch die NMR-Spektren zeigten Unterschiede in der chemischen Zusammensetzung der mit Methode II gewonnenen Fraktionen, die sich in signifikant geringeren O-Alkyl-C-Gehalten bei höheren Aryl-C- und Alkyl-C-Gehalten des okkludierten POM nachweisen ließen. Die Verwendung von größeren, feldfeuchten Aggregaten und die Minimierung der Probenvorbehandlung führt zu einer besseren Differenzierung beider POM-Fraktionen, die wahrscheinlich ihre biologische Funktion besser widerspiegelt. Zusätzlich führt eine Ultraschall-Behandlung mit hohem Energieeintrag zur Zerstörung von kleinen Mikroaggregaten <63 µm und damit zur Freisetzung von feinem Intraaggregat-POM. Diese Fraktion scheint in sandigen Böden mit niedriger Makroaggregat-Stabilität aussagekräftiger zwischen freier und okkludierter POM unterscheiden zu können. Folglich ist eine an das Bodenmaterial angepasste Probenvorbehandlung und Fraktionierungsmethode entscheidend, um eine präzise Charakterisierung der POM-Fraktionen zu gewährleisten. [source] A 15N-aided artificial atmosphere gas flow technique for online determination of soil N2 release using the zeolite Köstrolith SX6®RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2006Oliver Spott N2 is one of the major gaseous nitrogen compounds released by soils due to N-transformation processes. Since it is also the major constituent of the earth's atmosphere (78.08% vol.), the determination of soil N2 release is still one of the main methodological challenges with respect to a complete evaluation of the gaseous N-loss of soils. Commonly used approaches are based either on a C2H2 inhibition technique, an artificial atmosphere or a 15N-tracer technique, and are designed either as closed systems (non-steady state) or gas flow systems (steady state). The intention of this work has been to upgrade the current gas flow technique using an artificial atmosphere for a 15N-aided determination of the soil N2 release simultaneously with N2O. A 15N-aided artificial atmosphere gas flow approach has been developed, which allows a simultaneous online determination of N2 as well as N2O fluxes from an open soil system (steady state). Fluxes of both gases can be determined continuously over long incubation periods and with high sampling frequency. The N2 selective molecular sieve Köstrolith SX6® was tested successfully for the first time for dinitrogen collection. The presented paper mainly focuses on N2 flux determination. For validation purposes soil aggregates of a Haplic Phaeozem were incubated under aerobic (21 and 6 vol.% O2) and anaerobic conditions. Significant amounts of N2 were released only during anaerobic incubation (0.4 and 640.2,pmol N2 h,1,g,1 dry soil). However, some N2 formation also occurred during aerobic incubation. It was also found that, during ongoing denitrification, introduced [NO3], will be more strongly delivered to microorganisms than the original soil [NO3],. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||