bluuebunny/crossref_metadata_2025_split huggingface dataset:
Root impact on the stability and types of micro‐ aggregates in silty soil under maize
Authors: Watteau F. , Villemin G. , Burtin G. , Jocteur‐Monrozier L. 
Published: September 2005

SummaryWe wished to assess the impact of maize roots on the stability, nature and formation of soil organomineral aggregates under field conditions. We sampled coarse‐textured soil, cropped with maize for 3 years, and combined in situ study of the root system with evaluation of soil structural stability. We examined root morphology (i) on thin sections of still recognizable root tissues, and (ii) at the interfaces between roots and soil, using transmission electron microscopy (TEM) to differentiate between fine and coarse roots. Soil structural stability was evaluated in relation to a spatial gradient of increasing distance from the roots. For that we distinguished between soil adhering to roots and that not adhering in the rhizosphere, and soil between the rows of this crop, and used two methods of granulodensimetric soil fractionation involving different disaggregation strengths. We isolated and identified the organomineral associations in the soil fractions determining soil stability. We found that the roots at the soil–root interface generated stable aggregates of 2–20 µm size, which were much involved in the structural stability of the soil adhering to roots. We identified by TEM several types of organomineral associations that depended on the nature of the plant or microbial organic matter. The distribution of the different types of aggregates varied according to their positions in relation to the roots. We showed that humification of roots contributes significantly to the development of stable organomineral associations in the soil.
Humus components and biogenic structures under tropical slash‐and‐burn agriculture
Authors: Topoliantz S. , Ponge J.‐F. , Lavelle P. 
Published: September 2005

SummarySlash‐and‐burn cultivation in the humid tropics can cause changes in the composition of topsoil, depending on the duration of the fallow. We studied differences between practices, using the small‐volume micromorphological method, to quantify the distribution of solid components in the topsoil, concentrating on plant organs and biogenic structures created by soil animals. We compared samples of topsoil from five plots, two at Maripasoula, an Aluku village along the Maroni river (French Guiana), with short fallow (= 8 years), and the other three at Elahe, a Wayana village along the same river, with long fallow (= 25 years). At both sites structures created by arthropods other than ants gave way to ones formed by ants and annelids under the influence of fire and cultivation. This change was more abrupt under long fallow, because of the time needed to restore the arthropod community. Charcoal and charred plant material were incorporated by earthworms into the mineral soil, forming dark grey to black aggregates. Charcoal became mixed with the mineral soil faster at Elahe than at Maripasoula, where it accumulated in the topsoil. The reason seems to be an imbalance between charcoal inputs (from repeated fires) and the capacity of burrowing animals (earthworms, ants) to mix it with the mineral soil.
Effect of earthworm activity (Aporrectodea giardi) on atrazine adsorption and biodegradation
Authors: Alekseeva T. , Besse P. , Binet F. , Delort A. M. , Forano C. , Josselin N. , Sancelme M. , Tixier C. 
Published: September 2005

SummaryWe investigated the influence of earthworm (Aporrectodea giardi) activity on soil properties and on atrazine (AT) adsorption and biodegradation by comparing a coarse‐textured smectite‐free wetland soil (Brittany, France) with the earthworm casts derived from the top horizon of this soil. Casts are characterized by lower pH, are enriched in organic carbon (OC) and clay content, have a larger cation exchange capacity, and a greater exchangeable Ca content. The clay mineralogy of the soil studied and casts is characterized by a muscovite–kaolinite–chlorite association. In addition, the clay fraction of the soil contains lepidocrocite (γ‐FeOOH), which was not found in the casts. Atrazine adsorption isotherms were reasonably well described by the Freundlich equation and were all non‐linear. The mean amounts of adsorbed AT for starting concentrations of 3–30 mg litre−1 ranged from 8 to 34%, being largest in earthworm casts. Soil AT adsorption capacity was well correlated with OC content. Non‐decomposed organic matter present in the coarse size fractions and specific compounds present in earthworm casts (proteins, mono‐ and polysaccharides, polyphenols, sugars, lignin) and microbial and fungal biomass contribute to AT adsorption. Weak electrostatic (physical) sorption of AT on organic compounds and on mineral surfaces prevails. For casts, the formation of additional hydrophobic interactions between AT and SOM is proposed. We also studied AT biodegradation by the model bacterium Pseudomonas sp. strain ADP in the presence of soils or earthworm casts. An enhancement of the AT disappearance rate was observed in the presence of all the solid matrices tested compared with that obtained in an aqueous medium. The biodegradation rate was shown to be dependent not only on the OC content of the solid matrix, but mainly on its composition and structure.
The cation exchange capacity of a sandy soil in southern Brazil: an estimation of permanent and pH‐dependent charges
Authors: Bortoluzzi E. C. , Tessier D. , Rheinheimer D. S. , Julien J. L. 
Published: September 2005

SummaryIn soils in general, the cation exchange capacity is an important factor in soil fertility because it determines both cation retention and selectivity, and in turn controls most of the other soil properties. The main goal of this paper was to estimate the cation exchange capacity (CEC) and the contribution of permanent charges and pH‐dependent charges and their respective importance in soil CEC as a function of pH, clay and organic matter content in soils. A multiple regression method was developed from 75 samples under different soil management practices. The permanent charge (∼ 140 mmolc kg−1 of clay) estimated by this approach was independent of the analytical method used, i.e. a French method (MF) and a Brazilian method (MB), and is consistent with the presence of 2:1 clay minerals. However, the pH‐dependent charges were closely related to the buffering capacity inherent in each protocol (MF protocol using NH4+, and MB using a SMP solution proposed earlier by other workers, both at pH 7). For the MF protocol, the proposed method appeared to be well adapted for reproducing soil component properties under different management conditions. In the soil samples studied, the contribution of organic carbon to negative charges ranged from 12.3 to 55.8% of effective CEC and from 14.1 to 59.2% of CEC at pH 7. However, the clay contribution, notably its permanent charges, can contribute to 31% and more of the CEC in the lower horizons of soil profiles. The proposed approach can accurately evaluate the effective and pH 7 CECs when the MF protocol is used but evaluation is less accurate with the MB protocol.
Distribution of soil organic carbon and phosphorus on an eroded hillslope of the rangeland in the northern Tibet Plateau, China
Authors: Zhang J. H. , Liu S. Z. , Zhong X. H. 
Published: September 2005

SummarySome studies on the relationship between soil erosion and subsequent redeposition of eroded soils in the same field and soil quality have been conducted in croplands, yet few studies have revealed this relationship in rangelands. We selected a toposequence with a slope of 30% and a horizontal length of 342 m from the rangeland in the northern Tibet Autonomous Region, China (31°16′N, 92°09′E) to determine the relationship between soil erosion, soil organic carbon (SOC) content and available P patterns within a hillslope landscape. Soil samples for the determination of 137Cs as well as SOC, available P and particle‐size fractions were collected at 20 m intervals along a transect of this hillslope. Soil redistribution was caused primarily by wind erosion at toe‐slope positions, but primarily by water erosion at the hillslope positions above the toe‐slope. In upper‐ and mid‐slope portions (0 m to 244 m horizontal length), SOC content is closely correlated to 137Cs concentration (r = 0.74, P < 0.01, n= 15), suggesting that SOC distribution along the slope was similar to 137Cs distribution, which itself was dependent on topographic changes. However, SOC contents in toe‐slope portions are less than those above the toe‐slope (i.e. upper‐ and mid‐slope portions), and the correlation between 137Cs and SOC in the toe‐slope portion is weaker than that above the toe‐slope. A highly significant correlation (r = 0.72, P < 0.001, n= 20) between 137Cs concentration and available P was found within the whole hillslope landscape, implying the distribution pattern of available P was somewhat different from that of SOC. We suggest that the distribution of SOC within the hillslope landscape is also affected by factors such as assimilation rates due to difference in grassland productivity at different points and different biological oxidation rates of carbon related to patterns of moisture distribution.
Effects of cereal roots on detachment rates of single‐ and double‐drilled topsoils during concentrated flow
Authors: Gyssels G. , Poesen J. , Liu G. , Van Dessel W. , Knapen A. , De Baets S. 
Published: September 2005

SummaryFarmers in Europe want to control soil erosion in ways that are easily incorporated in their normal practices. We have investigated the possibility of reducing soil erosion by concentrated flow (i.e. rill and gully erosion) through increasing the root density of cereal crops.In situroot density measurements on cereal fields were combined with laboratory flume experiments on samples, taken in single‐ and double‐drilled fields, of which the above‐ground biomass was clipped. During the laboratory experiments no significant effect of root densities on critical shear stress or channel erodibility was observed because of interactions with other changing parameters (e.g. ageing effects). Therefore, the expected relative detachment rates as a function of plant root density were calculated using an empirical equation. During the first 75 days of the crop growth season relative soil detachment rates for single‐drilled field parcels can be reduced up to 50% compared with a rootless field, whereas relative soil detachment rates in double‐drilled field parcels can be reduced up to 60% in this period. Thereafter, plant roots in double‐drilled field parcels reduce relative soil detachment rates on average by 9% compared with single‐drilled field parcels (up to an absolute maximum of 90% compared with rootless soils). During the growing season, not only root density increases but also the vegetation cover changes, which enhances soil protection from erosion. Therefore, cereal roots will help to conserve the soil when seed is drilled at double rates, especially during the early growth stages and in fields with medium risk of concentrated flow.
Trace element distributions in soils developed in loess deposits from northern France
Authors: Sterckeman T. , Douay F. , Baize D. , Fourrier H. , Proix N. , Schvartz C. , Carignan J. 
Published: September 2005

SummaryA pedo‐geochemical survey was carried out in the Nord‐Pas de Calais region (France) on soils developed in loess deposits. Total concentrations of Al, Fe and 18 trace elements, as well as common soil characteristics, were determined in samples from 52 surface and 97 deep horizons developed in these loess deposits. The Pb isotopic composition was determined in two sola. The composition of deep horizons, compared with that of the upper continental crust, with that of horizons developed from 21 other sedimentary rocks from the region and with that of loess from various parts of the world, confirms that loess from the Nord‐Pas de Calais region derives from multi‐recycled and well‐mixed ancient sedimentary rocks. Correlation analysis shows that least mobile (i.e. ionic potential (Z/r) is between 3 and 7) geogenic elements (Bi, Co, Cr, Cu, In, Ni, Pb, Sn, Tl, V, Zn) are associated with the fraction <2 µm (which we define as ‘lutum’). More mobile elements (As, Cd, Hg, Mn, Mo, Sb, Se) are less associated with this fraction. Cadmium is particularly linked to Mn. The distribution of [trace element]/([Al] or [Fe]) in the French loess gives the background content for soils developed from most sedimentary materials in northwestern Europe. Topsoils are enriched with all the trace elements examined, except Co, Cr and Ni. Enrichments with Cd, Cu, Mn and Zn are greater in cultivated soils than in forest soils. Enrichments with Pb and with Cu, Hg, Mo, Sb, Se and Sn are mainly due to human contamination through atmospheric fallout. Organic matter seems to act as a sink for all the exogenous trace elements.
Effect of ionic strength and clay mineralogy on Na–Ca exchange and the SAR–ESP relationship
Authors: Kopittke P. M. , So H. B. , Menzies N. W. 
Published: September 2005

SummaryThe relationship between sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) for all soils has traditionally been assumed to be similar to that developed by the United States Salinity Laboratory (USSL) in 1954. However, under certain conditions, this relationship has been shown not to be constant, but to vary with both ionic strength and clay mineralogy. We conducted a detailed experiment to determine the effect of ionic strength on the Na+–Ca2+ exchange of four clay minerals (kaolinite, illite, pyrophyllite, and montmorillonite), with results related to the diffuse double‐layer (DDL) model. Clays in which external exchange sites dominated (kaolinite and pyrophyllite) tended to show an overall preference for Na+, with the magnitude of this preference increasing with decreasing ESP. For these external surfaces, increases in ionic strength were found to increase preference for Na+. Although illite (2:1 non‐expanding mineral) was expected to be dominated by external surfaces, this clay displayed an overall preference for Ca2+, possibly indicating the opening of quasicrystals and the formation of internal exchange surfaces. For the expanding 2:1 clay, montmorillonite, Na+–Ca2+ exchange varied due to the formation of quasicrystals (and internal exchange surfaces) from individual clay platelets. At small ionic strength and large ESP, the clay platelets dispersed and were dominated by external exchange surfaces (displaying preference for Na+). However, as ionic strength increased and ESP decreased, quasicrystals (and internal exchange surfaces) formed, and preference for Ca2+ increased. Therefore, the relationship between SAR and ESP is not constant and should be determined directly for the soil of interest.
Root dynamics and demography in shortgrass steppe under elevated CO2, and comments on minirhizotron methodology
Authors: Milchunas D. G. , Morgan J. A. , Mosier A. R. , LeCain D. R. 
Published: September 2005

AbstractThe dynamics and demography of roots were followed for 5 years that spanned wet and drought periods in native, semiarid shortgrass steppe grassland exposed to ambient and elevated atmospheric CO2 treatments. Elevated compared with ambient CO2 concentrations resulted in greater root‐length growth (+52%), root‐length losses (+37%), and total pool sizes (+41%). The greater standing pool of roots under elevated compared with ambient CO2 was because of the greater number of roots (+35%), not because individuals were longer. Loss rates increased relatively less than growth rates because life spans were longer (+41%). The diameter of roots was larger under elevated compared with ambient CO2 only in the upper soil profile. Elevated CO2 affected root architecture through increased branching.Growth‐to‐loss ratio regressions to time of equilibrium indicate very long turnover times of 5.8, 7.0, and 5.3 years for control, ambient, and elevated CO2, respectively. Production was greater under elevated compared with ambient CO2 both below‐ and aboveground, and the above‐ to belowground ratios did not differ between treatments. However, estimates of belowground production differed among methods of calculation using minirhizotron data, as well as between minirhizotron and root‐ingrowth methods. Users of minirhizotrons may need to consider equilibration in terms of both new growth and disappearance, rather than just growth.Large temporal pulses of root initiation and termination rates of entire individuals were observed (analogous to birth–death rates), and precipitation explained more of the variance in root initiation than termination. There was a dampening of the pulsing in root initiation and termination under elevated CO2 during both wet and dry periods, which may be because of conservation of soil water reducing the suddenness of wet pulses and duration and severity of dry pulses. However, a very low degree of synchrony was observed between growth and disappearance (production and decomposition).
The fate of 15N added to high Arctic tundra to mimic increased inputs of atmospheric nitrogen released from a melting snowpack
Authors: Tye A. M. , Young S. D. , Crout N. M. J. , West H. M. , Stapleton L. M. , Poulton P. R. , Laybourn‐Parry J. 
Published: September 2005

AbstractIncreases in the long‐range aerial transport of reactive N species from low to high latitudes will lead to increased accumulation in the Arctic snowpack, followed by release during the early summer thaw. We followed the release of simulated snowpack N, and its subsequent fate over three growing seasons, on two contrasting high Arctic tundra types on Spitsbergen (79°N). Applications of 15N (99 atom%) at 0.1 and 0.5 g N m−2 were made immediately after snowmelt in 2001 as either Na15NO3 or 15NH4Cl. These applications are approximately 1 × and 5 × the yearly atmospheric deposition rates. The vegetation at the principal experimental site was dominated by bryophytes and Salix polaris while at the second site, vegetation included bryophytes, graminoids and lichens. Audits of the applied 15N were undertaken, over two or three growing seasons, by determining the amounts of labeled N in the soil (0–3 and 3–10 cm), soil microbial biomass and different vegetation fractions.Initial partitioning of the 15N at the first sampling time showed that ∼60% of the applied 15N was recovered in soil, litter and plants, regardless of N form or application rate, indicating that rapid immobilization into organic forms had occurred at both sites. Substantial incorporation of the 15N was found in the microbial biomass in the humus layer and in the bryophyte and lichen fractions. After initial partitioning there appeared to be little change in the total 15N recovered over the following two or three seasons in each of the sampled fractions, indicating highly conservative N retention. The most obvious transfer of 15N, following assimilation, was from the microbial biomass into stable forms of humus, with an apparent half‐life of just over 1 year. At the principal site the microbial biomass and vascular plants were found to immobilize the greatest proportion of 15N compared with their total N concentration. In the more diverse tundra of the second site, lichen species and graminoids competed effectively for 15NH4‐N and 15NO3‐N, respectively. Results suggest that Arctic tundra habitats have a considerable capacity to immobilize additional inorganic N released from the snow pack. However, with 40% of the applied 15N apparently lost there is potential for N enrichment in the surrounding fjordal systems during the spring thaw.
Recovery of Enterococcus faecalis after single‐ or multiple‐visit root canal treatments carried out in infected teeth ex vivo
Authors: Vivacqua‐Gomes N. , Gurgel‐Filho E. D. , Gomes B. P. F. A. , Ferraz C. C. R. , Zaia A. A. , Souza‐Filho F. J. 
Published: September 2005

AbstractAim  To assess the presence of Enterococcus faecalis after root canal treatment in single or multiple visits in an ex vivo model.Methodology  Forty‐five premolar teeth were infected ex vivo with E. faecalis for 60 days. The canals were then prepared using a crowndown technique with System GT and Gates–Glidden burs and irrigated with 2% chlorhexidine gel. The specimens were divided into five groups (G1, G2, G3, G4 and G5) according to the time elapsed between chemical–mechanical preparation and root canal filling, the irrigant solution used and the use or nonuse of a calcium hydroxide intra‐canal medicament. The teeth were then root‐filled and incubated for 60 days at 37 °C. Dentine chips were removed from the canal walls with sequential sterile round burs at low speed. The samples obtained with each bur were immediately collected in separate test tubes containing Brain–Heart Infusion broth. These samples were placed onto agar plates and colony forming units were counted after 24 h at 37 °C. Data were ranked and analysed using the Kruskal–Wallis statistical test.Results  Enterococcus faecalis was recovered from 20% (three of 15 specimens) of G1 (chlorhexidine irrigation and immediate root filling in a single visit), 25% (four of 15 specimens) of G2 (chlorhexidine irrigation and filling after 14 days use of a calcium hydroxide dressing in multiple visits), 40% (two of five specimens) of G3 (chlorhexidine irrigation and filling after 7 days), 60% (three of five specimens) of G4 (saline irrigation and filling after 7 days) and from 100% (five of five specimens) of G5 (saline irrigation and immediate filling without sealer).Conclusions  Neither single‐ nor multiple‐visit root canal treatment ex vivo, eliminated E. faecalis completely from dentinal tubules. Up to 60 days after root filling, E. faecalis remained viable inside dentinal tubules. When no sealer was used, E. faecalis presented a higher growth rate.
Ex vivo evaluation of the capacity of the Tri Auto ZX to locate the apical foramen during root canal retreatment
Authors: Alves A. M. H. , Felippe M. C. S. , Felippe W. T. , Rocha M. J. C. 
Published: September 2005

AbstractAim  To evaluate ex vivo the capacity of the Tri Auto ZX to locate the apical foramen during root canal retreatment.Methodology  The root canals of 62 maxillary and mandibular canines were prepared to a length 1 mm short of the apical foramen, to an apical size 35 using 1% sodium hypochlorite as an irrigant. Once prepared, the length of each tooth was measured directly using a size 15 K‐Flexofile introduced in the canal until the tip was visible at the apical foramen. After the file was removed, its length was recorded to a precision of 0.01 mm using a calliper. These direct lengths (DL) became the ‘gold standard’ for comparison with the electronic lengths (EL) derived from the Tri Auto ZX. After direct measurement, the tooth was measured electronically (EL1) and the canals were filled using lateral condensation of gutta‐percha cones and sealer. Seven days later the root filling was removed using solvent, Gates‐Glidden burs, and K‐files, and new electronic lengths determined (EL2). The electronic lengths (EL1 and EL2) were compared with the DL, and the differences were analysed statistically using the proportions test and Student's t‐test.Results  At a tolerance limit of ±0.5 mm, EL1 coincided with the DL in 76% of cases. Lengths obtained in the presence of remnant of filling material (EL2) coincided in 81% of cases. The proportions test used to compare these percentages showed no statistically significant difference between EL1 and EL2 (P > 0.05). The Student's t‐test revealed a statistically significant difference (P < 0.05) between the means of the differences between DL/EL1 (−0.36 mm) and DL/EL2 (−0.04 mm).Conclusion  The Tri Auto ZX was accurate to ±0.5 mm in more than 80% of teeth following removal of root fillings.