bluuebunny/crossref_metadata_2025_split huggingface dataset:
The immobilization of nitrogen by straw decomposing in soil
Authors: Cheshire M. V. , Bedrock C. N. , Williams B. L. , Chapman S. J. , Solntseva I. , Thomsen I. 
Published: March 2003

SummaryImmobilization of nitrogen (N) in decomposing straw varies between soils, and the objective of this study was to identify the mechanisms responsible. Internode segments of wheat straw were incubated in Denmark and in Scotland in arable soils fertilized with NH4NO3, labelled with15N, for periods up to 1 year. Straw was recovered from the soils periodically and analysed for microbial biomass and different forms of N using chemical methods and CPMAS15N NMR spectroscopy.The total N content of the straw increased, as long as the soil was not too wet, such that there was overall immobilization. This was accompanied by a rapid increase in the content of amino acid N and to a lesser extent of glucosamine N and a concomitant decrease in the carbohydrate content of the straw. Using direct and plate counts for bacterial and ergosterol content for fungal estimation, we found that fungal biomass was much greater than that of bacteria. This correlated with the forms of N in the straw as determined by CPMAS15N NMR, which showed spectra that were more typical of fungi than of bacteria. It seems that immobilization of N is primarily caused by fungi as they decompose the straw.
Modelling changes in cations in the topsoil of an Amazonian Acrisol in response to additions of wood ash
Authors: Ludwig B. , Khanna P. K. , Hölscher D. , Anurugsa B. 
Published: March 2003

SummaryPredictions of changes in soil solution chemistry and exchangeable cations which occur on ash deposition after slash burning are complex and may be facilitated by the use of chemical models. Multi‐ion sorption in the topsoil of an Amazonian Acrisol was studied by sequentially adding small amounts of electrolytes to soil and mixtures of soil and ash in batch experiments. A chemical equilibrium model that included inorganic complexation, multiple cation exchange and sparingly soluble salts (aluminium hydroxide and magnesian calcites) was used to interpret the results. The model predicted well the pH and sorption values in all experiments in which there was no addition of ash. The model suggested that cation exchange was the main process determining concentrations of soil solutions in all cases where neutral salt solutions were added, and that proton buffering was achieved by the dissolution of Al(OH)3 which was followed by Al3+ adsorption. Calculation of ion activity products in solutions from various batch experiments in soil + ash mixtures suggested that magnesian calcites of differing solubility may be in equilibrium with the activities of Mg2+ and Ca2+ in solution. An incongruent dissolution of Mg resulted in less soluble magnesian calcites in the ash. The model estimated satisfactorily the pH and the sorption of ions for all experiments with differing ash additions to the soil. Most of the Ca and significant amounts of Mg added in the ash are expected to remain for a long time in the soil and may determine the Ca and Mg status of the soil solution, primarily controlled by principles of solubility products.
Closed chamber systems underestimate soil CO2 efflux
Authors: Rayment M. B. 
Published: March 2003

SummaryChamber systems are widely used to measure soil CO2 efflux, using either a closed or an open gas exchange methodology. In comparisons between these two methods fluxes measured with closed systems are often found to be around 10% less than those measured with open systems. One reason why closed chambers might systematically underestimate the true efflux rate is that the effective chamber volume is larger than the volume of the chamber alone, i.e. it includes the volume of air‐filled spaces in the soil. In tests carried out in a northern forest, this error resulted in a closed chamber underestimating the true efflux by up to 30%, with an average underestimation of around 10%.
A re‐evaluation of the enriched labile soil organic matter fraction
Authors: Six J. , Merckx R. , Kimpe K. , Paustian K. , Elliott E. T. 
Published: March 2003

SummaryIdentifying ‘functional' pools of soil organic matter and understanding their response to tillage remains elusive. We have studied the effect of tillage on the enriched labile fraction, thought to derive from microbes and having an intermediate turnover time. Four soils, each under three regimes, long‐term arable use without tillage (NT), long‐term arable under conventional tillage (CT), and native vegetation (NV), were separated into four aggregate size classes. Particle size fractions of macro‐ (250–2000 μm) and microaggregates (53–250 μm) were isolated by sonication and sieving. Subsequently, densiometric and chemical analyses were made on fine‐silt‐sized (2–20 μm) particles to isolate and identify the enriched labile fraction. Across soils, the amounts of C and N in the particle size fractions were highly variable and were strongly influenced by mineralogy, specifically by the contents of Fe and Al oxides. This evidence indicates that the fractionation procedure cannot be standardized across soils. In one soil, C associated with fine‐silt‐sized particles derived from macroaggregates was 567 g C m−2 under NV, 541 g C m−2 under NT, and 135 g C m−2 under CT, whereas C associated with fine‐silt‐sized particles derived from microaggregates was 552, 1018, 1302 g C m−2 in NV, NT and CT, respectively. These and other data indicate that carbon associated with fine‐silt‐sized particles is not significantly affected by tillage. Its location is simply shifted from macroaggregates to microaggregates with increasing tillage intensity. Natural abundance 13C analyses indicated that the enriched labile fraction was the oldest fraction isolated from both macro‐ and microaggregates. We conclude that the enriched labile fraction is a ‘passive' pool of soil organic matter in the soil and is not derived from microbes nor sensitive to cultivation.
Disruption of soil aggregates by varied amounts of ultrasonic energy in fractionation of organic matter of a clay Latosol: carbon, nitrogen and δ13C distribution in particle‐size fractions
Authors: Roscoe R. , Buurman P. , Velthorst E. J. 
Published: March 2003

SummaryUltrasonic energy has been widely used to disrupt soil aggregates before fractionating soil physically when studying soil organic matter (SOM). Nevertheless, there is no consensus about the optimum energy desirable to disrupt the soil. We therefore aimed (i) to quantify the effect of varied ultrasonic energies on the recovery of each particle‐size fraction and their C, N and δ13C distribution, and (ii) to determine an ideal energy to fractionate SOM of a specific soil. Our results show that the 2000–100 μm particle‐size fraction was composed mainly of unstable aggregates and the 100–2 μm fraction of stable aggregates. Energies of 260–275 J ml−1 were sufficient to disrupt most of the unstable aggregates and leave stable aggregates. The use of this threshold energy combined with particle‐size fractionation was not satisfactory for all purposes, since litter‐like material and relatively recalcitrant organic carbon present in stable aggregates > 100 μm were recovered in the same pool. An ultrasonic energy of 825 J ml−1 was not sufficient to stabilize the redistribution of soil mass and organic matter among particle‐size fractions, but at energies exceeding 260–275 J ml−1 relatively stable aggregates would fall apart and cause a mixture of carbon with varied nature in the clay fraction.
Modelling structural changes in tilled topsoil over time as a function of cropping systems
Authors: Roger‐Estrade J. , Richard G. , Boizard H. , Boiffin J. , Caneill J. , Manichon H. 
Published: March 2003

SummaryThe optimization of tillage practices requires the evaluation of the long‐term effects of cropping on changes in soil structure. A model is presented that simulates changes in soil structure in the tilled horizons of cultivated fields. The indicator of soil structure that we have modelled is based on a morphological description of the structure and the assessment of the percentage of severely compacted zones and clods showing no visible porosity in the tilled layer of a soil profile. The model takes into account the spatial variation of the structure induced by traffic and tillage. Severely compacted zones are created under wheel tracks, they are cut and transferred during ploughing, and they are fragmented into fine soil during secondary tillage. The model was evaluated over 7 years in a field trial on loamy soil in three experimental plots, where the crop sequences and field operations induced contrasted changes in the percentage of severely compacted zones and clods. The model satisfactorily reproduced the changes with time of the indicator, and the correspondence between simulated and observed values was fairly good (r= 0.82, model efficiency = 0.61). However, some variations from one year to the next were poorly predicted. The sensitivity analysis did not suggest modification to the parameter values but showed that the performance of the model could be improved if the fragmentation (due to weather and tillage) were more precisely described in the model. Nevertheless the present version of the model and the corresponding simulation program (SISOL) can be used to compare the effects of different technical choices on the evolution of soil structure.
Solid‐state 13C‐NMR dipolar dephasing experiments for quantifying protonated and non‐protonated carbon in soil organic matter and model systems
Authors: Smernik R. J. , Oades J. M. 
Published: March 2003

SummaryDipolar dephasing was investigated as a means for quantitatively differentiating protonated and non‐protonated and molecularly mobile and rigid components in soil organic matter. We experimented on cellulose, hemicelluloses, lignin, a protein, chitin, charcoal, palmitic acid and two waxes which served as model systems for components of soil organic matter. Dipolar dephasing decay curves showed significant deviation from the expected exponential decay (for non‐protonated and methyl carbons) and Gaussian decay (for non‐methyl protonated carbons), partly due to rotational and dipolar modulation. No signal is observed for most protonated carbon (excluding methyl carbon) for a dipolar dephasing delay of 45 μs, and so we generated three subspectra, representing non‐protonated, non‐methyl protonated and methyl carbon classes, requiring the acquisition of just the 0‐ and 45‐μs dipolar dephased spectra. This methodology was applied to eight samples of soil organic matter, allowing the determination of relative contributions of overlapping resonances such as C‐substituted and H‐substituted aromatics (110–145 p.p.m.), carbohydrate anomeric and tannin (90–110 p.p.m.), and amino acid and methoxyl (45–65 p.p.m.). The waxes behaved aberrantly, probably because some of their components are highly mobile. We determined accurately the exponential dipolar dephasing decay rates of non‐protonated carbon resonances, free from the interference of rotational and dipolar modulations.
Interactions of fulvic acid with aluminium and a proto‐imogolite sol: the contribution of E‐horizon eluates to podzolization
Authors: Farmer V. C. , Lumsdon D. G. 
Published: March 2003

SummaryThe podzolization process is examined in the light of measurements of the solubility characteristics of aluminium fulvate, the extent of dissolution of a proto‐imogolite sol by fulvic acid, the adsorption capacity of proto‐imogolite for fulvic acid and aluminium fulvate, and published evidence. Fulvic acid at 500 mg l−1 acting on a proto‐imogolite (PI) preparation containing 0.95 mmol l−1 Al as PI did not bring enough Al into solution at pH 4.5–5.0 over 4–15 months to cause significant precipitation of the fulvic acid. As allophanic Bs horizons of podzols typically have pH ≥ 4.8, fulvic acids entering them in drainage water cannot be quantitatively precipitated by dissolution of Al from the allophane. They are, however, strongly absorbed on the allophane, and this must be the mechanism that removes most of the fulvic acid at the top of the Bs horizon, and which contributes, along with colloidal humus and root decomposition, to the formation of a Bh horizon.We conclude that fulvic acid plays no active role in podzolization, but only recycles Al and Fe, that have been transferred by biological processes to the O horizon, back to the Bh horizon. The podzolization process, which leads to the formation of an allophanic Bs horizon underlying a progressively deepening E horizon, requires the dissolution of Al‐humate and allophanic precipitates at the Bh–Bs interface as well as progressive attack on the more readily weatherable minerals. Inorganic acids, particularly episodic fluxes of nitric acid, could play a major role in this, as well as attack by readily metabolized complexing acids such as oxalic and citric acids released by roots and fungi.In addition to throwing light on the podzolization process, the experimental results provide an explanation of the lower limit to C:Al ratios reported in natural waters, and a check on the applicability of the WHAM chemical equilibrium model to Al–fulvate–proto‐imogolite equilibria. In Ca‐containing fulvate solutions, Al‐fulvate begins to precipitate when C:Al falls below 50, which is also the limiting ratio observed in natural waters. WHAM calculations overestimate by 70–85% the amount of Al‐fulvate formed over 4 months at pH 4.5–5.0 in Ca‐containing fulvate–imogolite systems.
Application of a two‐dimensional model to simulate flow and transport in a macroporous agricultural soil with tile drains
Authors: Abbaspour K. C. , Kohler A. , Simunek J. , Fritsch M. , Schulin R. 
Published: March 2003

SummaryIt is essential that important field processes are taken into account to model water flow and chemical transport accurately in agricultural fields. Recent field studies indicate that transport through macropores can play a major role in the export of solutes and particulates from drained agricultural land into surface water. Non‐ideal drain behaviour may further modify the flow and transport. We extended an existing two‐dimensional flow and transport model for variably saturated soils (SWMS_2D) by adding a macropore domain and an additional Hooghoudt drain boundary condition. The Hooghoudt boundary condition accounts for an entrance head needed to initiate flow into the drains. This paper presents the application of the new model (M‐2D) to an agricultural field in Switzerland. To understand interactions between macropore flow and drains better we simulated water flow and bromide transport for four different field scenarios. We considered both collector drains only with an ideal drain boundary condition (with and without macropores) and collectors and laterals with a Hooghoudt boundary condition (also with and without macropores). For each scenario, inverse modelling was used to identify model parameters using 150 days of data on observed cumulative discharge, water table depth, and tracer concentration. The models were subsequently tested against a 390‐day validation data set. We found that the two additional components (macropore flow, drain entrance head) of the M‐2D model were essential to describe adequately the flow regime and the tracer transport data in the field.
Cation exchange resin and test vermiculite to study soil processes in situ in a toposequence of Luvisol and Cambisol on loess
Authors: Brahy V. , Delvaux B. 
Published: March 2003

SummaryBoth the ion accumulation on cation exchange resin and the transformation of test vermiculite in situ have been used to identify current processes in acid forest soils. We used such test materials to study weathering in a toposequence Dystric Luvisol–Spodo‐Dystric Cambisol on loess under deciduous forest in Belgium. The resin and a trioctahedral vermiculite were inserted for 2 years in the major horizons, down to a depth of 60 cm. The cation accumulation on the resin revealed that four main acid‐consuming systems are currently active in the toposequence. With decreasing acid neutralizing capacity, these systems are in the Luvisols: (i) the pool of exchangeable bases, (ii) the Al‐bearing minerals controlling the Al concentration in the liquid phase; and in the podzolized Cambisols: (iii) the less weatherable K‐bearing minerals, (iv) the Mg‐bearing phyllosilicates made free of Al interlayers in complexing conditions. The loss of cation exchange capacity in the test vermiculite is related to Al interlayering. However, this process masks a significant interlayer accumulation of magnesium, which is generated by the weathering of the test mineral itself. The largest interlayer accumulation of Mg occurs in the podzolized Cambisol, suggesting more intense weathering of the test vermiculite in this soil.
Sorption and transport of metals in preferential flow paths and soil matrix after the addition of wood ash
Authors: Bundt M. , Zimmermann S. , Blaser P. , Hagedorn F. 
Published: March 2003

SummaryAs a consequence of heterogeneous transport in soils, only a small part of the soil might be responsible for sorbing incoming elements. After staining preferential flow paths in forested Dystric Cambisol with a colour dye, we sampled soil material from the flow paths and from the soil matrix. We measured chemical properties and sorption isotherms of these two flow regions and estimated the significance of preferential flow paths for the transport of solutes leached from wood ash applied at the surface. In the A horizon (0–9 cm depth), the cation exchange capacity of the flow paths was 83.8 mmolc kg−1, while that of the soil matrix was only 74.6 mmolc kg−1. The base saturation was 42% and soil organic matter content was 41% larger in flow paths than in the soil matrix. The sorption capacity for Cu was also larger than in the matrix, whereas the sorption capacity for Sr was similar in both flow regions. The impact of the addition of 8 t wood ash ha−1 on soil chemical properties was restricted mainly to the flow paths in the uppermost 20 cm of the soil; it was negligible in the matrix and at greater depths. Concentrations of exchangeable Ca in the flow paths increased nearly 10‐fold during the 6 months following the addition of the wood ash, and those of organically bound Pb by 50%. The opposite effect was found for exchangeable Al. Our results show that only part of the whole soil volume, approximately 50% of 0–20 cm in our study, is involved in transporting and sorbing the elements applied with the wood ash or as tracers. Such differences must be considered when calculating the maximal impact of any addition of fertilizer, wood ash, or liming agent.
Humus composition of soils under forest, coffee and arable cultivation in hilly areas of south Sumatra, Indonesia
Authors: Watanabe A. ,   Sarno, Rumbanraja J. , Tsutsuki K. , Kimura M. 
Published: March 2003

SummaryTo understand the effect of land use changes on the composition of humus in tropical soils, samples from land under primary forest, secondary forest, coffee plantation, and arable crops were investigated at three sites in south Sumatra, Indonesia. Total carbon and total nitrogen contents were 1.7 to 4.3 times and 1.1 to 2.8 times greater in the topsoil under primary forest than under the other types of land use. Following change from primary forest to other uses, the proportion of humic acids in the organic matter of the topsoils decreased while that of the fulvic acid fraction increased. Within the range of land uses, differences in the yields of humic acids and fulvic acid fractions were, respectively, larger and smaller than those in total carbon content. The humic acids were classified into the low and middle classes in the degree of humification. Absorption due to the green fraction of humic acids, Pg, was detected in the UV‐visible spectra of almost all the humic acids. No relation was observed between the degree of humification of humic acids or the strength of Pg absorption in their spectra and land use change. The fulvic acid fractions were fractionated on insoluble polyvinylpyrrolidone (PVP) into the adsorbed fractions consisting of humic substances and the non‐adsorbed fractions consisting of non‐humic substances. A positive correlation between the amount of the fulvic acid fraction and the percentage of the PVP‐adsorbed fraction within it indicated that the variation in the amount of the fulvic acid fraction was attributable to acid‐soluble humic substances. The ionization difference spectra of solutions between pH 12 and pH 7 suggested that the chemical structures of the PVP‐adsorbed fulvic acids have been altered by land use change.
Determination of the free ion concentration of trace metals in soil solution using a soil column Donnan membrane technique
Authors: Weng L. , Temminghoff E. J. M. , Van Riemsdijk W. H. 
Published: March 2003

SummaryAccurate measurement of the free metal ion is difficult, especially for trace metals present in very small concentrations (less than micromolar) in natural systems. The recently developed Donnan membrane technique can measure the concentrations in solution in the presence of inorganic and organic complexing agents. We have developed this method further to make it applicable for analysing soil samples. The major development is the linkage of a soil column with the Donnan cell. The operational aspects of the method, including equilibrium time, buffering capacity and correction for differences in ionic strength, were investigated and optimized. The method was applied to determine concentrations of free Cu2+, Cd2+, Pb2+ and Zn2+ in the soil solution of 15 soil samples (pH 2.9–7.1, organic C < 2.9–137.4 g kg−1, clay 0.2–51.6%). Compared with other speciation methods, the Donnan membrane technique has the advantage of allowing the measurement of several elements simultaneously and it minimizes the disturbance of substrate. The detection limit of the technique is about 10−9 m. This method can be applied to study the biogeochemical behaviour of metals in soils, sediments and other solid materials.
Nutrient storage and turnover in organic layers under tropical montane rain forest in Ecuador
Authors: Wilcke W. , Yasin S. , Abramowski U. , Valarezo C. , Zech W. 
Published: March 2003

SummaryIn tropical montane forests nutrients released from the organic layers of the soil can supply a large part of the vegetation's requirements. We have examined concentrations, storage, and turnover times of nutrients in the organic layer and the fluxes of nutrients by the fall of small litter (leaves, seeds, flowers, small twigs, and plant debris that passed an opening of 0.3 m × 0.3 m) in such a forest in Ecuador. The times taken for litter to turn over were estimated by relating nutrient storage in the organic layer to rate of litterfall and by incubating samples in the laboratory. The organic layer had a thickness of 2–43 cm, a mass of 30–713 t ha−1, and a nutrient storage of 0.87–21 t N, 0.03–0.70 t P, 0.12–2.5 t K, 0.09–3.2 t Ca, and 0.07–1.0 t Mg ha−1. The pH (in H2O) ranged between 3.1 and 7.4 and was correlated with the concentrations of Ca and Mg (r= 0.83 and 0.84, respectively). The quantity of small litter (8.5–9.7 t year−1) and mean concentrations of nutrients in litter (19–22 g N, 0.9–1.6 g P, 6.1–9.1 g K, 12–18 g Ca, and 3.5–5.8 g Mg kg−1) were larger than in many other tropical montane forests. The mean turnover times of elements in the organic layer increased in the order, Mg (7.0 years) < Ca (7.9) < K (8.5) < P (11) < N (14) < S (15) when calculated as the quotient of storage in the organic layer to flux by litterfall; they were < 12 years for N, P, and S in the incubation experiment. Under optimum conditions in the laboratory, the mineralization of S was just as large as the S deposition by litterfall. In weakly acid soils Mn and Zn and in strongly acid soils Ca added in a nutrient solution were immobilized during incubation. Thus, lack of S, Mn, Zn, and Ca might limit plant growth on some soils.