bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phosphate sorption by calcareous Vertisols and Inceptisols as evaluated from extended P‐sorption curves
Authors: CASTRO B. , TORRENT J. 
Published: March 2003

SummaryThe plant availability of phosphate applied to calcareous soils is affected by precipitation and adsorption reactions, the relative significance of which is not well known. We used extended P‐sorption curves obtained at phosphate addition rates up to 340 mmol P kg−1 soil to examine the relative contribution of precipitation and adsorption by 24 calcareous Spanish Vertisols and Inceptisols. Adsorption was dominant at 1 day and at small rates of addition (10–35 mmol P kg−1). With increasing clay and Fe and Al oxides contents of the soil, more phosphate was sorbed before the sorption curve bent upwards, as a result of Ca phosphate precipitation. Sorption curves showed a nearly vertical intermediate region, the length of which increased with time, suggesting that a Ca phosphate buffered the concentration of P in solution. The buffering concentration decreased with time, suggesting a progressive transformation of more to less soluble forms of Ca phosphate. A phase less soluble than octacalcium phosphate seemed to control the concentration of P in solution at 180 days in most soils. The apparent solubility of this phase decreased with increasing carbonate content in the soil. Precipitation of poorly soluble Ca phosphates apparently predominated up to a P addition dose ranging from about 30 mmol P kg−1 in some soils to more than 340 mmol P kg−1 in others. At larger doses, the way additional P was bound to the solid phase was different; phosphate was probably adsorbed, at least in part, to low‐affinity sites on silicate clays and oxides.The proportion of sorbed phosphate that was isotopically exchangeable decreased with time, soil carbonate content and P addition dose for doses <100 mmol P kg−1. This is consistent with the idea that P in Ca phosphates is less isotopically exchangeable than P adsorbed on mineral surfaces. At larger additions of P, isotopic exchangeability was unrelated to the soil properties measured, probably because there was a variety of sorbed P forms influenced in turn by different soil components.
Neural network models to predict soil water retention
Authors: Koekkoek E. J. W. , Booltink H. 
Published: March 2003

SummarySoil water retention curves are needed to describe the availability of soil water to plants and to model movement of water through unsaturated soils. Measuring these characteristics is time‐consuming, labour‐intensive and therefore expensive. This study was conducted to develop and evaluate functions based on neural networks to predict soil water retention characteristics. Dutch and Scottish data sets were available; they contained data on 178 and 165 soil horizons, respectively. A series of three neural networks (A, B and C) was developed. Neural network A had the following input variables: topsoil, bulk density, organic matter, clay, silt and sand content. In addition neural network B had matric potential as input, and network C included soil structural data expressed as the upper and lower boundary of the ped‐size class. Neural network A had three output variables: the volumetric water content at matric potentials of 0, –100 and –15 000 hPa. Both models B and C had volumetric water content, at the matric potential given as input, as output variable. The networks were tested against independent data that were extracted from the original sets of soil profiles. Accuracy of the predictions was quantified by the root of the mean squared difference (RMSE) between the measured and the predicted water contents, and the coefficient of determination (R2). For network A the RMSE varied for the three estimated water contents from 0.0264 to 0.0476 cm3 cm–3, and R2 varied from 0.80 to 0.93 for the individual model outputs. Networks B and C had an RMSE of 0.0435 and 0.0426 cm3 cm–3, respectively. For both networks, R2 was 0.89. The neural networks performed somewhat better than previous regression functions, but the improvements were not significant.
Dynamics of dissolved organic nitrogen and carbon in a Central European Norway spruce ecosystem
Authors: Michalzik B. , Matzner E. 
Published: March 2003

SummaryDissolved organic nitrogen and carbon (DOC) are significant in the C and N cycle in terrestrial ecosystems. Little is known about their dynamics in the field and the factors regulating their concentrations and fluxes. We followed the fluxes and concentrations of the two in a Norway spruce (Picea abies (L.) Karst.) forest ecosystem in Germany from 1995 to 1997 by sampling at fortnightly intervals. Bulk precipitation, throughfall, forest floor percolates from different horizons and soil solutions from different depths were analysed for major ions, dissolved organic N and DOC. The largest fluxes and concentrations were observed in percolates of the Oi layer, which contain amino N and amino sugar N as the major components. The average ratio of dissolved organic C to N in forest floor percolates corresponded to the C/N ratio of the solid phase. Concentrations and fluxes were highly dynamic with time and decreased with depth. The largest fluxes in forest floor percolates occurred when the snow melted. The concentrations and fluxes of dissolved organic N were significantly correlated with DOC, but the correlation was weak, indicating different mechanisms of release and consumption. The dynamics of dissolved organic N and DOC in forest floor percolates were not explained by pH and ionic strength of the soil solution nor by the water flux, despite large variations in these. Furthermore, the release of these fractions from the forest floor was not related to the quality and amount of throughfall. Concentrations of dissolved organic N in forest floor percolates increased with soil temperature, while temperature effects on DOC were less pronounced, but their fluxes from the forest floor were not correlated with temperature. In the growing season concentrations of both dissolved organic N and C in forest floor percolates decreased with increasing intensity of throughfall. Thus, the average throughfall intensity was more important than the amount of percolate in regulating their concentrations in forest floor percolates. Our data emphasize the role of dissolved organic N and DOC in the N and C cycle of forest ecosystems.
Short‐range spatial variation of nitrous oxide fluxes in relation to compaction and straw residues
Authors: Ball B. C. , Horgan G. W. , Parker J. P. 
Published: March 2003

SummaryThe spatial heterogeneity of N2O flux at short distances (0.1–2 m) was characterized in relation to various soil physical and chemical properties and the location of incorporated crop residues in arable soils. Plots were prepared with uniform compaction (either zero or compacted by a laden two‐wheel‐drive tractor) in two field experiments, one under winter barley (Hordeum vulgare), the other under oil‐seed rape (Brassica napus). Flux measurements were made of N2O using small chambers (7.3 cm diameter) placed at intervals of approximately 10 cm along a transect (c. 2 m long) across the direction of application of the treatments of compaction and residue incorporation. The flux of N2O and many other measurements showed large variation over short distances, particularly when fluxes were small. The spatial variation of the flux was not closely related to the soil properties. Correlations showed that cone resistance, air permeability and closeness to incorporated residues were as important as soil NO3, NH4 and soluble C in determining flux of N2O from non‐compacted soils. Most properties of compacted soils did not correlate with N2O flux. Correlation and multiple regression analysis failed to establish consistent relations between soil environmental variables and N2O flux, but principal component regression indicated that, overall, N2O flux increased with decreasing distance from straw residues and air permeability, and with increasing cone resistance and wet bulk density.
Modelling pH buffering and aluminium solubility in European forest soils
Authors: Lofts S. , Woof C. , Tipping E. , Clarke N. , Mulder J. 
Published: March 2003

SummaryThe pH buffering and aluminium solubility characteristics of acid soil are important in determining the soil's response to changes in precipitation acidity. The chemistry of soil organic matter (humic substances) plays a key role in both processes, yet is complex and still poorly understood. Nevertheless, models of humic substance chemistry have been developed, one of which is WHAM–S, which contains a model (Model V) of proton and metal binding at discrete sites on humic substances and considers electrostatic effects on the binding strength. Here we have tested the ability of WHAM–S to model solution pH and Al using batch titration studies on organic and mineral soil horizons from forested sites in Norway, Germany and Spain, with ambient pH values from 3.73 to 5.73. We optimized the model predictions by adjusting the amounts of soil aluminium and humic substances within defined limits, taking the contents of copper chloride‐extractable Al and the base‐extractable organic matter as starting values. The model simulated both pH and dissolved Al well with optimized amounts of aluminium and humic substances within the defined limits (root mean squared error for pH from 0.01 to 0.22, for p[Al]aq (total dissolved Al) from 0.03 to 0.49, five data points). Control of dissolved Al by dissolved organic matter was important particularly at above‐ambient pH. In two mineral horizons we improved the fits by assuming that Al could precipitate as Al(OH)3. The optimized model also gave reasonable predictions of pH and dissolved Al in supernatants obtained by repeated leaching of the soil horizons. The results show that humic substances dominate the control of pH and dissolved Al in most of the horizons studied. Control by Al(OH)3 occurs but is the exception.
Estimation of the phosphorus sorption capacity of acidic soils in Ireland
Authors: Maguire R. O. , Foy R. H. , Bailey J. S. , Sims J. T. 
Published: March 2003

SummaryThe test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Alox + Feox), where Alox and Feox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil−1, and a value of 0.5 is commonly used for the scaling factor α in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (Pox) so that DPS = Pox/PSC.The relation between PSC and Alox, Feox and Pox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Alox and Feox extracted, but there was also a negative correlation with Pox. When PSC was calculated as the sum of the measured sorption after 252 days and Pox, the multiple regression of PSC on Alox and Feox gave the equation PSC = 36.6 + 0.61 Alox+ 0.31 Feox with a coefficient of determination (R2) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Alox and Feox did not overlap, indicating a significantly larger regression coefficient of P sorption on Alox than on Feox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Alox and Feox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P < 0.001), the impact of this variable was small as its inclusion in the multiple regression increased R2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0–3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water‐soluble P than either the Olsen or Morgan tests for P in soil.
A study of the factors controlling the adsorption of Cr(III) on modified montmorillonites
Authors: Bakhti A. , Derriche Z. , Iddou A. , Larid M. 
Published: March 2003

SummaryWe have examined the way that the metallic ion Cr(III) is held by Na‐montmorillonite and alumina pillared clay. We used several physico‐chemical methods of analysis (X‐ray powder diffraction, infrared absorption spectrometry, thermal analysis and chemical composition) to determine the structural formula of the Na‐montmorillonite, and to clarify the effect of the introduction of the Al13 polycations between the clay layers on its physico‐chemical and structural properties. Our results show that the strength of chromium retention increases with pH. This effect is more marked in pillared than in unpillared clays. It seems that the mechanism of fixing of the metallic cations on pillared clays is more complex than a simple cationic exchange and involves the surface groups of the pillars. In other words, chromium adsorption on pillared montmorillonite is more like adsorption on an amphoteric oxide surface (such as Al2O3) than on a non‐pillared clay.Etude des facteurs contrôlant l'adsorption de Cr(III) sur des montmorillonites modifiéesRésuméNous avons examiné les possibilités de fixation de l'ion métallique Cr(III) sur une montmorillonite sodique et pontée. Les différentes analyses physico‐chimiques (Rayons‐X, Spectroscopie Infrarouge, Analyse Thermique Différentielle et composition chimique) ont permis d'une part, d'établir la formule structurale de l'argile sodique et d'autre part de mettre en évidence l'effet du pontage de l'argile par des polycations hydroxyaluminiques sur ses propriétés physico‐chimiques et structurales. Nos résultats montrent que le pouvoir de rétention du chrome augmente avec le pH. Ce paramètre affecte davantage son comportement dans les argiles pontées. Il apparaît que le mécanisme de fixation du Cr(III) sur les argiles à piliers est différent d'un simple échange cationique. L'adsorption dans ce cas met en jeu les groupements de la surface des piliers. En d'autres termes, le mécanisme d'adsorption des cations du chrome sur une montmorillonite pontée se rapproche de l'adsorption sur une surface d'oxyde amphotère (tel que Al2O3) plutôt que l'adsorption sur une argile non pontée.
Modelling cracking stages of saturated soils as they dry and shrink
Authors: Chertkov V. Y. 
Published: March 2003

SummaryCracks that form when clay soils shrink on drying eventually form a network that determines transport properties. I propose and validate a model for (i) analysing the initial cracking stages of shrinking saturated soils, (ii) estimating the minimum dimension of quasi‐brittle cracks capable of developing in such conditions, and (iii) determining relations between the minimum crack dimension and other characteristic dimensions of the soil structure. Shrinkage cracks in soils can be classified on the concept of the minimum quasi‐brittle crack capable of developing at shrinkage. I use the model of developing a shrinkage crack in a semi‐infinite brittle medium with constant relevant properties, desiccating in conditions of shock drying. The model is generalized to the cracking of a saturated clay soil with a limited maximum crack depth. The available data justify the use of constant elastic, strength, diffusivity, and shrinkage properties of clay soil. The critical point of crack development is the existence of the minimum crack capable of developing in the particular conditions. The dimension of the crack is related to the soil properties. The crack goes through stages of delay, jump, stable growth with approximately constant velocity, and then quick decline until it stops. I show that the minimum crack dimension is related to the mean dimension of soil particles, the thickness of an upper intensive‐cracking layer, and the mean spacing of primary cracks at the soil surface.
When is a measured soil organic matter fraction equivalent to a model pool?
Authors: Smith J. U. , Smith P. , Monaghan R. , MacDonald A. J. 
Published: March 2003

SummaryDynamic simulation models are important tools for rationalizing complex changes in soil organic matter. Most such models for organic matter can be described as having either a pool structure or a continuous one. A pool structure can offer advantages in ease of use and transferability. Some pools are easily measured, whereas others cannot be measured directly. New methods of fractionation are being developed in an attempt to base models on measurable fractions. A requirement for such models is a demonstration that the measured fraction and model pool are equivalent. A measured fraction is equivalent to a model pool only if, within acceptable limits, it is unique as well as non‐composite. If the measured fraction is not unique, describing it as a separate pool adds no extra information, while the added complexity can increase propagation of errors. If it is composite then the characteristics of the fraction will change with changing environment as a result of changing proportions of subpools. This will produce a model that cannot be applied without deriving parameters afresh: such a model is of greatly reduced value. Here we develop methods to examine if a fraction is both unique and non‐composite. The tests for unique and composite pools were applied to the SUNDIAL (simulation of nitrogen dynamics in arable land) model of organic matter and nitrogen turnover in soil. Results suggest that the debris, biomass and humus pools are unique, but biomass and humus are composed of two or more subpools. This worked example illustrates how, given suitable data, any pool‐based model can be tested by these methods.
Influence of former agricultural land use on net nitrate production in forest soils
Authors: Jussy J. H. , Koerner W. , Dambrine É. , Dupouey J. L. , Benoit M. 
Published: March 2003

SummaryExcept where nitrate is added to the soil artificially, nitrate is leached from forest soils only if it is produced. Although the factors influencing nitrification have been widely studied, nitrification activity still cannot be simply predicted from ecosystem characteristics. In France, about half of the present forest area was agricultural in 1850. Previous work suggested that former cultivation could be a major factor influencing nitrogen availability in forest soils.Using laboratory incubations, we compared the net production of ammonium and nitrate in soils from formerly manured lands planted with conifers 70–100 years ago with that in soils of surrounding ancient coniferous forests. Net nitrate production, available P content, and natural abundance of nitrogen 15, δ15N, were greater in soils from formerly manured plots than other land, whereas the C:N ratio of the soil was less. The difference in net nitrate production between previously manured sites and adjacent ancient forests was related to differences in δ15N values in the soil but not evidently to other soil properties. Because soil δ15N increases with the intensity of organic manuring, these results suggest that nitrification in forest soils depends on previous manurial practices under agriculture. In this context, the soil δ15N might be used as an indicator of both previous agricultural land use and potential nitrification. Because a significant proportion of West European forests grow on previously cultivated soils, past land use should be taken into account when evaluating the risks of nitrate leaching from forests.
Larval transport and retention of the spiny lobster, Panulirus argus, in the coastal zone of the Florida Keys, USA
Authors: Yeung Cynthia , Lee Thomas N. 
Published: March 2003

AbstractThe spiny lobster Panulirus argus is of ecological and commercial importance in the South Florida coast of the continental USA and throughout the Intra‐Americas Sea. Essential spiny lobster habitat in South Florida is primarily located in the Florida Keys coastal zone (including the Dry Tortugas), where the dynamic regional circulation coupled with the long planktonic larval duration (6–12 months) of P. argus raises questions of larval retention and recruitment. Locally spawned phyllosomata entrained in the Florida Current are likely to be expatriated out of the Straits of Florida, which implies that the local spiny lobster population is sustained by the transport of larval recruits from upstream locations. We examined the physical processes that may influence recruitment. Transport processes in the Keys coastal zone are spatially variable. Observed and modelled data suggest that the upper Keys is a point of onshore larval transport via the inshore meandering of the Florida Current, and the lower Keys to Dry Tortugas region apoint of retention through wind‐driven onshore/countercurrents and eddy recirculation. Eddies that propagate between the Dry Tortugas and the lower Keys facilitate the exchange of larvae between the Florida Current and the coastal zone. Northerly wind events associated with cold fronts can enhance recirculation of larvae in the upper Keys. The association of older larvae with the Florida Current front supports the hypothesis that spiny lobster larval recruits come from upstream sources in the Caribbean.
Seasonal dynamics of free and attached heterotrophic nanoflagellates in an oligomesotrophic lake
Authors: Carrias Jean‐François , Amblard Christian , Quiblier‐Lloberas Catherine , Bourdier Gilles 
Published: March 2003

1. The seasonal development of heterotrophic nanoflagellates (HNF), bacteria, rotiferans and crustacean zooplankton was studied in the epilimnion of Lake Pavin, an oligomesotrophic lake in the Massif Central of France.2. HNF abundance varied from 0.1 to 2.5 × 103 mL–1. Free‐living HNF reached their highest density in spring when the copepod Acanthodiaptomus denticornis dominated the metazooplankton. They were present in low numbers when rotifers and cladocerans were numerous.3. Attached HNF, consisting of bicoecids and choanoflagellates, were fixed to large diatoms and to the colonial cyanobacterium Anabaena flos‐aquae. The abundance of attached HNF was significantly correlated to bacterial abundance, which fluctuated between 1.1 and 2.7 × 106 mL–1. Highest abundance of these epiphytic protists was recorded when free‐living heterotrophic nanoflagellates declined.4. The comparison of the dynamics of heterotrophic nanoflagellates, bacteria, and the impact of zooplankton grazing suggested that prey abundance, the presence of suitable attachment sites and limited competition from the free‐living forms were the main factors controlling the development of the epiphytic flagellate protists. In contrast, the low abundance of free‐living forms during the period of rotiferan and cladoceran development suggests the prevalence of a top‐down control by predation of the metazoopankton.