ALBERT

Notes: We have investigated the water retention properties of clayey subsoil horizons according to the variation of clay characteristics. The horizons studied developed on a large range of age and facies of calcareous or calcium-saturated clayey sediments. The water retention properties were studied from −10 hPa to −15 000 hPa water potential using small clods collected in winter when swelling is at a maximum and water content close to field capacity. The specific water content and volume of the clods at field conditions, their specific volume at −15 000 hPa water potential, the clay content, the organic carbon content, the cation exchange capacity, the N2-BET surface area and calcareous content were measured. The clay fabric, which is the spatial distribution of the elementary clay particles, was quantified when the soil was close to field capacity and we could attribute the whole pore volume to the porosity of the clay fabric. Our results show that the water retention properties of the clay vary greatly from one soil to another with respect to the clay fabric. The variation of the latter depends on the cation exchange capacity, the size of elementary particles and hydric stress history of the clay. We show that the water retention properties of the studied clayey soils vary according to the clay content and fabric, the latter being related either to parent material fabric or to both the hydric history of the soil and size of the elementary clay particles.

Notes: Although the swelling of clays has been thoroughly studied, the mechanism by which this occurs in clay soils is not so fully understood. We have developed a technique to study the swelling and three-dimensional deformation of a soil sample during wetting by adapting a triaxial apparatus. This equipment applies a controlled, confined and isotropic pressure to the periphery of the samples. A constant flow of solution is injected into the base of the sample while the lateral and axial deformations are simultaneously controlled. The development of the interstitial pressure, positive or negative, is measured. When the soil is thoroughly wetted, the equipment measures the saturated hydraulic conductivity.The swelling of the soil is not necessarily isotropic, and practically all the possibilities of lateral, isotropic and vertical swelling can be encountered. Furthermore, the swelling can be preceded by significant lateral shrinkage, caused by fissures. The results show the importance of confinement pressure when measuring the swelling of the samples.The adaptation of a triaxial apparatus to the study of the permeability and swelling of soils appears to be promising as it also allows the geometric development of the samples to be traced as well as the changes in the chemical composition of the percolating solutions.

Notes: The dynamics of incorporation of fresh organic residues into the various fractions of soil organic matter have yet to be clarified in terms of chemical structures and mechanisms involved. We studied by 13C-dilution analysis and CPMAS-13C-NMR spectroscopy the distribution of organic carbon from mixed or mulched maize residues into specific defined fractions such as carbohydrates and humic fractions isolated by selective extractants in a year-long incubation of three European soils. The contents of carbohydrates in soil particle size fractions and relative δ13C values showed no retention of carbohydrates from maize but rather decomposition of those from native organic matter in the soil. By contrast, CPMAS-13C-NMR spectra of humic (HA) and fulvic acids (FA) extracted by alkaline solution generally indicated the transfer of maize C (mostly carbohydrates and peptides) into humic materials, whereas spectra of organic matter extracted with an acetone solution (HE) indicated solubilization of an aliphatic-rich, hydrophobic fraction that seemed not to contain any C from maize. The abundance of 13C showed that all humic fractions behaved as a sink for C from maize residues but the FA fraction was related to the turnover of fresh organic matter more than the HA. Removal of hydrophobic components from incubated soils by acetone solution allowed a subsequent extraction of HA and, especially, FA still containing much C from maize. The combination of isotopic measurements and NMR spectra indicated that while hydrophilic compounds from maize were retained in HA and FA, hydrophobic components in the HE fraction had chemical features similar to those of humin. Our results show that the organic compounds released in soils by mineralization of fresh plant residues are stored mainly in the hydrophilic fraction of humic substances which are, in turn, stabilized against microbial degradation by the most hydrophobic humic matter. Our findings suggest that native soil humic substances contribute to the accumulation of new organic matter in soils.

Notes: The 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.

Notes: To investigate the chemical heterogeneity of humic substances in relation to molecular size, fulvic and humic acids were extracted and purified from the surface horizon of a Humic Gleysol in northern Switzerland. A fractionation scheme using hollow-fibre ultrafiltration cartridges was developed and used to obtain four size fractions of the humic acid with nominal molecular weight ranges 〉 300 kDa, 100–300 kDa, 30–100 kDa, and 10–30 kDa. The fulvic acid and all humic acid fractions were characterized by size exclusion chromatography, elemental analysis (C, H, N, S), as well as spectroscopic techniques including UV-VIS, CP-MAS 13C-NMR, FT-IR, and fluorescence spectroscopy.Clear chemical differences between the humic acid size fractions were observed. Smaller size fractions of the soil humic acid contained more chargeable functional groups and a larger percentage of aromatic carbon than the larger size fractions. Conversely, the percentage of aliphatic carbon increased with increasing apparent molecular weight. The chemical composition of the smallest humic acid fraction differed clearly from the fulvic acid fraction, despite similar apparent molecular size and carboxyl carbon content. Small humic acids contained much more aromatic carbon and less aliphatic carbon than the fulvic acid fraction. Apparently, humic size fractions differ in their chemical composition, which can have important implications for their environmental behaviour.

Notes: We investigated the functional role of enchytraeid worms (Oligochaeta) in organic upland soils experimentally, because that role of these animals is little known. We made microcosms of intact soil cores cut from two depths, 0–4 cm and 4–8 cm, of a Cambic Stagnohumic Gley from the Moor House National Nature Reserve (UK). Enchytraeids were added to half of the microcosms, resulting in four treatments: litter (L), litter + enchytraeids (L + E), soil (S) and soil + enchytraeids (S + E). Triplicates of each treatment were established, and all microcosms (60) were then incubated in the dark at 15°C, arranged in a fully randomized design. The experiment ran over 110 days, with five destructive harvests at days 10, 25, 50, 75 and 110, when microbial measurements (soil respiration and biomass C) as well as measures of decomposition (nutrient concentration in leachates) were made. Enchytraeids almost doubled the availability of organic carbon (measured as dissolved organic carbon in soil leachates) in the surface (0–4 cm) microcosms only. There were no effects of enchytraeids on the release of inorganic N or P from either soil horizon, although the release of ammonium and phosphate was correlated with the number of enchytraeids in the microcosms. The depth from which the soil was taken exerted a strong influence on nutrient leaching, with almost six times more ammonium and four times more carbon being leached from the surface (0–4 cm) layer than from the more decomposed (4–8 cm) horizon. There was little nitrate leaching from any of the treatments, with only one-quarter as much nitrate leached from the surface (0–4 cm) as from the subsurface (4–8 cm) horizon. Enchytraeids had no detectable effect on microbial biomass, but they increased microbial respiration by 35% in the surface (0–4 cm) horizon. Because they enhanced microbial activity in this horizon we suggest that enchytraeids indirectly drive the processes of decomposition and nutrient mineralization in organic upland soils.

Notes: This study was carried out to investigate the sorption properties of man-made soil developed from sewage sludge, municipal wastes, brick and mortar debris, harbour sludge, sand fills, fly ash, and wastes from coking plants and coal mines. The composition of organic matter in the samples was analysed, and the sorption isotherms of four reference chemicals (nitrobenzene, atrazine, 2,4-D, pentachlorophenol) were determined. Fly ash, which contains up to 89% of its carbon as Black Carbon, showed a strong affinity to all four chemicals. For the other waste materials, a strong correlation between the logarithm of the Freundlich adsorption constant, Kf, and the logarithm of organic carbon, Co, was established (r = 0.85–0.96). This holds for the non-ionic nitrobenzene and also, within a certain pH range depending on the pKa of the compound, for the three ionizable organic compounds (atrazine: pH 〉 4; 2,4-D: pH 〉 5; PCP: pH 〉 6). At pH near the pKa value the sorption is sensitive to pH. There were no statistically significant differences between the waste materials and the natural soils in the relations between logKf and logCo for either ionic or non-ionic chemicals. This result suggests that the method devised for estimating the sorption of organic chemicals in natural soils based on their content of organic carbon is equally valuable for the waste materials, with the exception of fly ash which contains a large amount of Black Carbon.

Notes: Identifying ‘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.

Notes: 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 β-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 β-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 μm (SF50). These aggregates were associated with strongly humified organic matter. Solutions of diluted pyrophosphate at neutral pH liberated active β-glucosidase from all fractions, although the efficacy of extraction varied according to the type of fraction. The SF50 fraction and aggregates of 2000–100 μm obtained by sieving (SF2000) showed the greatest β-glucosidase activity (34.5 and 36.0%, respectively). Micro- and ultrafiltration of SF50 extracts increased the total β-glucosidase activity, whereas these procedures, applied to the RF2000 fraction, decreased it. Humus–β-glucosidase complexes in the SF50 fraction, between 0.45 μm 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 μm) the optimum was 4.0. The stability of β-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 β-glucosidase complexes extracted and partially purified from the SF50 aggregates.

Notes: Soil acidification and related land degradation are becoming more important worldwide and are challenging the concept of sustainability of current land management systems. We have studied the impact on soil properties of two management systems, one in a tropical savanna, the other in a humid subtropical environment, particularly in relation to their cation chemistry. In Northeast Thailand the properties of an Acrisol cleared of dipterocarp forest some 37 years previously and used for continuous crop production are compared with adjacent undisturbed forest. In southern Queensland, Australia, the properties of a Luvisol used for intensive pasture production for 36 years are compared with those prior to introduction of the management system. Under both regimes, the soil pH fell by about 1 unit, with an increase in aluminium saturation of the cation exchange complex. Organic carbon in the Acrisol greatly decreased, but in the Luvisol it increased significantly. Consequently, the effects on surface charge characteristics were strikingly different, in that the Acrisol had been almost irreversibly degraded, whereas acidification and base diminution in the Luvisol can be easily reversed through conventional management. The amount of degradation caused by each management system has been quantified in terms of a Saturation Index, Su: S u = 100 × (Cu5.5 − Σ)/Cu5.5,where Cu5.5 refers to the cation exchange capacity on the undisturbed (forested) site and Σ is the sum of the base cations at field pH. This index encompasses an assessment of the degree of degradation taking into account the previous land use, in this case forest, and that due to anthropogenic disturbance. For the Queensland Luvisol Su does not change, because the pasture management has not appreciably altered the CEC at pH 5.5. However, for the Thailand site Su increased from 0 to 86%. Consequently in its present state, the surface horizon of this cultivated soil can retain only about 15% of the basic cations it could ideally hold under undisturbed conditions.

Notes: Intense decalcification of fine-grained organic-rich soils subject to periodic oxidation and reduction takes place in the Biesbosch, a freshwater, tidally influenced wetland area in the Rhine–Meuse delta in The Netherlands. Soil chemical (sulphide concentration and pore-water characteristics) and hydrological variables (drainage) were measured in three representative Fluvisols differing in hydrology to identify processes inducing calcium carbonate dissolution. Both oxidation of previously formed iron sulphides during periods of low ground water and infrequent inundation, and increased carbon dioxide pressure in the soil during periods of waterlogging combined with drainage of pore-water solutes, contribute significantly to decalcification of the hydric soils. The effects of these individual processes on decalcification are in the same order of magnitude in the studied soils. Depending on site-specific hydrological conditions, approximately 0.1–0.3% calcium carbonate may be dissolved per year by a combination of these two processes, which is comparable to actual decalcification rates at these sites. Estimates of long-term decalcification rates, based on knowledge of the hydrogeochemistry, may be used to assess the risks accompanying the conversion of agricultural soils into wetlands.

Notes: The inability to predict flow and transport behaviour based on a priori information demonstrates the lack of knowledge we currently have concerning transport-relevant properties or processes, or both. We present an approach in which the behaviour of effective solute transport at the scale of a soil column (100 mm) is predicted by taking into account the spatial structure of the hydraulic properties at the local scale (1 mm). The local absorption coefficients obtained from X-ray tomography, which are linearly related to bulk density, are used as local proxy for hydraulic properties. As a first approximation, two density classes were distinguished, and the three-dimensional structure of the hydraulic properties was implemented in a model of flow and transport. The local hydraulic properties were obtained from a network model, except for the absolute value of the hydraulic conductivity function which was measured. Model simulations were compared with a measured breakthrough curve determined on the same soil sample. The two agreed well, although the local hydraulic properties and parameter structure were determined independently with respect to a breakthrough experiment. Predictions of solute transport at the column scale were sensitive to the difference in saturated hydraulic conductivities of both materials, but not to the local dispersivities. The simulations demonstrate that (i) assuming validity of the Richards equation and the convection–dispersion equation on the local scale leads to a good description of the effective flow and transport behaviour at the column scale without making any assumptions about the governing processes at that scale; (ii) the dispersion parameters, which are notoriously difficult to determine, need not be determined since their effect is included explicitly; and (iii) local absorption coefficients can be used as a local proxy for the parameter field of the hydraulic properties.

Notes: Surface podzolization involves the migration of metal–humus complexes to a depth of a few centimetres. In acid soils derived from loess, this process has been diagnosed mainly by morphological observation. We investigated this process in a toposequence of Luvisols and Cambisols on loess using selective extraction and mineralogical data as well as characteristics of the leaf litter. The humus type (O and OAh horizons) is a moder in the three Luvisols and one of the Cambisols, whereas it is a fibrimor in the two other Cambisols. The contents in total alkaline and alkaline-earth cations range from 35 to 60 cmolc kg−1 in the fibrimor and from 40 to 90 cmolc kg−1 in the moder humus. In the two Cambisols with fibrimor smectite occurs in the clay fraction of the Ah horizon; Fe–humus complexes seem to have moved, but no more than 9 cm, from the Ah to the AB horizon beneath. Relative to the Ah horizon, the upper part of the AB has larger tetraborate-extractable Fe/Al ratio and optical density of the oxalate extract. Such features converge to diagnose surface podzolization in the Cambisols with fibrimor. However, they were not detected in the Cambisol and Luvisols with moder. In the two Cambisols with fibrimor, surface podzolization is consistent with (i) their smaller iron content, (ii) their more advanced weathering stage and (iii) their lower acid neutralizing capacity.

Notes: The conduction of water by soil is fundamental to the way in which soils transport nutrients and pollutants into groundwater. The derivation of relations between water flow and void structure has relied on the implicit assumption that water flows through aligned unconnected cylindrical capillary tubes. We describe a three-dimensionally interconnected model of void structure, called Pore-Cor, which simulates the intrusion of a non-wetting fluid and drainage of a wetting fluid. The model is calibrated by fitting it to the water retention curves of a sandy soil at four depths. The experimental drainage pressures are related to the radii of the entries to the voids by the Laplace equation. The necessities of using this equation, and of employing a simplified void geometry, introduce major approximations into the modelling. Nevertheless, the model is sufficiently precise and versatile to predict trends in other properties usefully. It is illustrated in this work by a close correlation between a predicted and experimental change in saturated hydraulic conductivity with depth, and a realistic unsaturated hydraulic conductivity curve. The saturated and unsaturated hydraulic values are shown to be much more realistic than those predicted by the aligned cylinders model. In addition, the simulations by Pore-Cor indicate that the void network within the sandy soil is acting in a structured rather than a random manner. The Pore-Cor model is currently being used to explain the matrix-flow characteristics of tracers and pollutants.

Notes: In the framework of a structural-and-formational interpretation (SFI) approach to seismic data processing and geological interpretation, specific software/technology tools were created to facilitate sequence stratigraphy analysis and reservoir characterization. The most important tools are two types of time–frequency representation of seismic data: the first is spectrum-time analysis (STAN), which presents a seismic trace as a series of very narrow frequency band traces, while the second tool converts an initial seismic section into a set of sections ranked with preselected frequency bands, narrower than those of the initial section, but wider than those related to STAN traces. Jointly, these two representations reflect both general trends and local temporal and spatial variations of seismic data frequency content. The use of these tools, developed in Russia in the 1980s, facilitates detection of sedimentation cycles and their depositional environments, identification of hierarchies within faulting patterns, and delineation of geological anomalies on seismic sections. This, in turn, provides reliable starting points for palaeotectonic restoration and basin modelling. In many regions, these tools have helped to clarify obscure formation structures under study and to estimate the hydrocarbon potential of these formations.

Notes: Ultrasonic compressional- and shear-wave velocities have been measured on 34 samples of sandstones from hydrocarbon reservoirs. The sandstones are all of low clay content, high porosity, and cover a wide range of permeabilities. They were measured dry and brine-saturated under hydrostatic effective stresses of 10, 20 and 40 MPa. For eight of the sandstones, ultrasonic velocity measurements were made at different partial water saturations in the range from dry to fully saturated. The Gassmann–Biot theory is found to account for most of the changes in velocities at high effective stress levels when the dry sandstones are fully saturated with brine, provided the lower velocities resulting when the dry sandstone initially adsorbs small amounts of moisture are used to determine the elastic properties of the ‘dry’ sandstone. At lower effective stress levels, local flow phenomena due to the presence of open microcracks are assumed to be responsible for measured velocities higher than those predicted by the theory. The partial saturation results are modelled fairly closely by the Gassmann–Biot theory, assuming heterogeneous saturation for P-waves.

Notes: The local cosine/sine basis is a localized version of the cosine/sine basis with a window function which can have arbitrary smoothness. It has orthogonality and good time and frequency localization properties. The adaptive local cosine/sine basis is a best-basis obtained from an overabundant library of cosine/sine packets based on a cost-functional. We propose a 2D semi-adaptive (time-adaptive or space-adaptive) local cosine transform (referred to as a 2D semi-ALCT) and apply it to the SEG–EAEG salt model synthetic data set for compression. From the numerical results, we see that most of the important features of the data set can be well preserved even in the high compression ratio (CR=40:1) case. Using reconstructed data from the highly compressed ALCT coefficients (CR=40:1) for migration, we can still obtain a high-quality image including subsalt structures. Furthermore, we find that the window partition, generated by the 2D semi-ALCT, is well adapted to the characteristics of the seismic data set, and the compression capability of the 2D semi-ALCT is greater than that of the 2D uniform local cosine transform (2D ULCT). We find also that a (32, 32) or (32, 64) minimum (time, space) window size can generate the best compression results for the SEG–EAEG salt data set.

Notes: ‘Coverage’ or ‘fold’ is defined as the multiplicity of common-midpoint (CMP) data. For CMP stacking the coverage is consistent with the number of traces sharing a common reflection point on flat subsurface reflectors. This relationship is not true for dipping reflectors. The deficiencies of CMP stacking with respect to imaging dipping events have long been overcome by the introduction of the dip-moveout (DMO) correction. However, the concept of coverage has not yet satisfactorily been updated to a ‘DMO coverage’ consistent with DMO stacking. A definition of constant-velocity DMO coverage will be proposed here. A subsurface reflector will be illuminated from a given source and receiver location if the time difference between the reflector zero-offset traveltime and the NMO- and DMO-corrected traveltime of the reflection event is less than half a dominant wavelength. Due to the fact that a subsurface reflector location is determined by its zero-offset traveltime, its strike and its dip, the DMO coverage also depends on these three parameters. For every surface location, the proposed DMO coverage consists of a 3D fold distribution over reflector strike, dip and zero-offset traveltime.

Notes: A sensitivity study of elastic parameters in amplitude-variation-with-slowness (AVS) for small- and large-offset seismic data is presented. In order to handle the non-linearity associated with waveform or amplitude beyond the critical slowness, an inversion algorithm based on Bayes' theory is used. A genetic algorithm was used to obtain the a posteriori probability density (PPD) function. The sensitivity analysis is performed on synthetic data containing P-wave as well as converted S-wave reflections. Four different two-layer models, which represent the typical range of AVS responses associated with the gas-sands normally encountered in exploration, were used to examine how well the elastic parameters can be inverted for different parametrizations by comparing the PPD functions. The sensitivity study results suggest that including wide-angle data in the inversion can greatly enhance the quality of inversion. The converted S-wave reflections can provide valuable extra information that can be used to extract elastic parameters. The results with noisy data demonstrate that the contrast of density and three velocity ratios can be estimated robustly with wide-angle reflection data.

Notes: The problem of imaging sedimentary structure obscured by high-velocity layers, such as carbonate, basalt or salt, using conventional seismic techniques is well known. When this problem is encountered in offshore areas, marine electromagnetic data can provide valuable, alternative and complementary constraints on the structure. We concentrate on the use of marine controlled-source electromagnetic (CSEM) sounding in the frequency domain. The feasibility of mapping sub-basalt sedimentary structure using this technique is explored by means of modelling studies which mimic a type of survey which could readily be employed in practice. As a starting point the problem is addressed in terms of 1D resistivity structure. We show that sub-basalt sediments can be detected and their depth of burial quantified to within 200 m in the examples shown. The presence of small-scale inhomogeneities in the basalt (which cause much of the scattering in seismic data) is shown to have no appreciable effect on the ability of the CSEM data to detect the sediments. The modelling is then extended to 2.5 dimensions. Again the presence of sub-basalt sediments can be readily detected and their properties and geometry quantified, especially if the electromagnetic data are combined with constraints from complementary geophysical techniques.

Notes: Transient electromagnetic measurements with short time-delays of transients are used for solving different problems within the upper part of a geoelectric section. However, it is necessary to take into consideration distortions connected with self-transients within the transmitter–receiver system. From the practical point of view, it is important to estimate the minimum time-delay after which these distortions may be neglected. We present such an estimation which uses a simple approximation method for a single-loop (or coincident-loop) configuration. For common values of the loop size (10 m × 10 m to 40 m × 40 m) and of the resistivity of a homogeneous half-space (1–100 Ωm), the minimum time-delay beyond which we can use a standard interpretation is in the range of 2–10 µs. This is equivalent to a minimum depth of investigation in the range of 1–30 m.

Notes: An optimization method is used to select the wavenumbers k for the inverse Fourier transform in 2.5D electrical modelling. The model tests show that with the wavenumbers k selected in this way the inverse Fourier transform performs with satisfactory accuracy.

Notes: Apparent resistivity is a useful concept for initial quickscan interpretation and quality checks in the field, because it represents the resistivity properties of the subsurface better than the raw data. For frequency-domain soundings several apparent-resistivity definitions exist. One definition uses an asymptote for the field of a magnetic dipole in a homogeneous half-space and is useful only for low induction numbers. Another definition uses only the amplitude information of the total magnetic field, although this results in a non-unique apparent resistivity. To overcome this non-uniqueness, a complex derivation using two different source–receiver configurations and several magnetic field values for different frequencies or different offsets is derived in another definition. Using the latter theory, in practice, this means that a wide range of measurements have to be carried out, while commercial systems are not able to measure this wide range. In this paper, an apparent-resistivity concept is applied beyond the low-induction zone, for which the use of different source–receiver configurations is not needed. This apparent-resistivity concept was formerly used to interpret the electromagnetic transients that are associated with the turn-off of the transmitter current. The concept uses both amplitude and phase information and can be applied for a wide range of frequencies and offsets, resulting in a unique apparent resistivity for each individual (offset, frequency) combination. It is based on the projection of the electromagnetic field data on to the curve of the field of a magnetic dipole on a homogeneous half-space and implemented using a non-linear optimization scheme. This results in a fast and efficient estimation of apparent resistivity versus frequency or offset for electromagnetic sounding, and also gives a new perspective on electromagnetic profiling. Numerical results and two case studies are presented. In each case study the results are found to be comparable with those from other existing exploration systems, such as EM31 and EM34. They are obtained with a slight increase of effort in the field but contain more information, especially about the vertical resistivity distribution of the subsurface.

Notes: A new variant of the dry-weight rank method for botanical investigation of grassland is described and its usefulness evaluated. Multipliers proportional to the dominance percentages of the three species with the highest dominance percentages are used instead of fixed multipliers. The method is theoretically more valid and applicable to a broader range of grasslands than the variants with fixed multipliers. It does not involve more costs and gives as good or better predictions of the dry-weight percentages than the variants with fixed multipliers.

Notes: Responses of perennial ryegrass (Lolium perenne L.) to nitrogen (N) fertilizer application rates and timings vary widely, because water is often limiting. Yield response to N fertilizer application during autumn, late-winter and spring, and the associated efficiency of use of these inputs, was assessed under conditions of non-limiting soil moisture during two, one-year lysimeter studies in Canterbury, New Zealand. There were significant (P 〈 0·05) increases in seed and herbage yields with increasing N fertilizer application. Seed yields differed with year; greatest yields were 300 g m−2 in 1996 and 450 g m−2 in 1997. Seed head numbers (r2=0·77), seeds head−1 (r2=0·92) and herbage yield (r2=0·92) were the major determinants of seed yield in both years. Irrigation required to maintain the soil between 70% and 90% of field capacity was directly related (r2=0·94 and 0·99 in 1996 and 1997 respectively) to increases in herbage yield.Seed yield, seed quality (thousand seed weight and percentage of seed 〉 1·85 mg), efficiency of water use, efficiency of N fertilizer use and apparent N fertilizer recovery were greatest when N fertilizer was applied at a rate of 50 kg N ha−1, 50 or 100 kg N ha−1 and 150 kg N ha−1 in autumn, late-winter and spring respectively; further increases in spring N fertilizer stimulated vegetative growth, but not seed yield.As a management strategy, applying N fertilizer to match the N requirements of the crop during the reproductive stage of growth will result in high yields of high quality seed while minimizing environmental impact.

Notes: Current recommendations for the intake of sodium of lactating dairy cows are related to milk yield. A study was conducted to compare the responses of cows of high and low milk production potential to the application of sodium fertilizer to grazed perennial ryegrass pasture. The application of sodium fertilizer increased the intake of herbage dry matter (DM), the time that cows spent grazing and the biting rate. It also increased the concentration of sodium, magnesium and calcium in herbage and decreased the concentration of potassium. Applying sodium fertilizer increased milk yield and milk fat concentration and decreased somatic cell count in the milk of cows of low-production potential only, whereas it increased persistency of milk production in the cows of high-production potential. The concentration of lactose in milk increased in both groups after the application of sodium fertilizer. It is concluded that the optimum dietary sodium concentration for grazing cows does not increase with milk yield, and that most immediate advantage will be gained from increasing the sodium concentration in herbage for low-yielding cows.

Notes: Genetic shifts in plant morphology and reproductive characters under grazing may potentially affect nutritive value and preference. This research was conducted to determine the response of smooth bromegrass (Bromus inermis Leyss.) populations to long-term grazing. Genotypes from five populations of smooth bromegrass that survived 9 years of grazing were compared with genotypes of each population grown from original seed. Plant height was measured and biomass estimated for each genotype, before and after grazing by sheep, in order to assess preference. Genotypes were also tested for nutritive value. The selective effect of competition during establishment and maintenance under grazing was accompanied by genetic shifts in smooth bromegrass plants in these pastures. Survivors had greater plant biomass despite having a decrease in plant height of up to 5%. Preference for survivors, quantified as percentage consumption by sheep, was up to 3% units less than for original populations. The nutritive value of survivors was similar to that of original populations, except for one population, which had a lower neutral-detergent fibre among the survivors after grazing.

Notes: The period of leaf expansion in white clover (Trifolium repens) grown with perennial ryegrass (Lolium perenne) in mixed swards and the relationship between the period of leaf expansion and leaf appearance rate were examined in a field experiment in The Netherlands in which two cutting frequencies (low and high) and three white clover cultivars (Alice, Retor and Gwenda) were used. A significant positive correlation existed between the period of leaf expansion and leaf appearance rate under a low frequency of cutting, indicating that a longer cutting interval might allow the expression of cultivar and environmental differences in both leaf expansion and leaf appearance rate. In most cases, frequent cutting tended to shorten the period of leaf expansion, which may be an important cause of lower dry-matter yield in the high frequency of cutting treatment. The large-leaved cv. Alice had a significantly longer period of leaf expansion than the other cultivars under frequent cutting in autumn. This might partly account for the mixtures with Alice having a greater proportion of white clover than the mixtures with Retor and Gwenda in autumn. Some of the variation between low- and high-frequency cutting treatments in the period of leaf expansion could be explained by mean and minimum temperatures (38% and 15% respectively).

Notes: Understanding the movement of cations in soil, particularly trace metals, is required in many applications such as phytoremediation and pollution control. A dynamic mechanistic model has been developed to describe the long-term root uptake of a surface-applied, strongly adsorbed, pollutant metal cation, such as radiocaesium, from soil. It consists of two submodels. The first calculates uptake per unit root length at a local scale over a root's lifetime, for various initial conditions. The second calculates cumulative uptake at a whole-plant scale for the entire rooting depth as a function of time. The model takes into account the renewal of roots which are considered to have a limited lifetime. Root density may be a function of soil depth and a proportion of roots need not contribute to uptake. Recycling from decaying, or grazed, roots and shoots is considered.Simulations show that removal of cations from soil is exaggerated unless some recycling by roots or shoots is considered or the entire root length does not contribute to uptake. Because of root turnover, uptake is not rapidly limited by diffusive flux of the cation from the bulk soil solution to the solution–root interface. Uptake is very sensitive to root architecture and plant physiology.

Notes: Leaves lying on the forest floor are a major source of dissolved organic substances in soil and surface waters, and these substances have important effects in those environments. We used zero-tension lysimeters to study the chemical characteristics of water percolating through litter from various species of forest trees. The leaching rates were greatest in the autumn and declined rapidly thereafter, especially for deciduous litter. During an annual cycle, 2.5–17% of the initial contents of the carbon in the litter was recovered as dissolved organic carbon in percolates. Humus-like substances, hydrophilic acids and hydrophilic neutral compounds constituted the major fractions of dissolved C. Leachates from deciduous leaf litter were only partly biodegradable, and those from spruce needles were scarcely biodegradable.Low molecular weight organic acids constituted 0–12% of the dissolved organic carbon in the percolates of the first autumn sampling and decreased over time. Acetic and formic acids were present at the largest concentrations, up to 30 μmol l−1 per g litter, and gluconic, pyruvic, fumaric, oxalic and citric acids were also frequent in significant concentrations. Among the aromatic acids, p-hydroxybenzoic acid was identified in four out of five autumn samples. The organic components in litter leachates are important for the microbial activity in soil and surface waters. The organic acids enhance weathering and translocation of metals by their ability to form complexes. Litter is also a source of inorganic ions in soil solutions. The dominant cations in the percolates were K+, Ca2+ and Mg2+, and spruce litter also yielded large quantities of Al and Fe.

Notes: The Kyoto Protocol explicitly allows the storage of carbon (C) in ecosystems resulting from afforestation to be offset against a nation's carbon emissions and paves the way for carbon storage in soils to be eligible as carbon offsets in the future. More information is required about how afforestation affects carbon storage, especially in the soil. We report a study in which soil carbon storage in first-rotation Mediterranean Pinus radiata plantations, established on former cereal fields and vineyards, was measured and modelled. Measurements were made on plantations of several ages, as well as repeat measurements at the same site after 5 years. We tested the ability of two widely used soil organic matter models (RothC and Century) to predict carbon sequestration in Mediterranean forest soils.Increases in the top 5 cm of soil of about 10 g C m−2 year−1 were observed after afforestation of former vineyards, but nitrogen (N) either remained the same or decreased slightly. During afforestation, most organic matter accumulated in the ectorganic layers at a rate of 19 g C m−2 year−1 in former vineyards and 41 g C m−2 year−1 in former cereal fields. The RothC and Century models were sensitive to previous land use and estimated a carbon sequestration potential over 20 years of 950 and 700 g C m−2, respectively. The accurate simulation of the dynamics of soil organic matter by RothC, together with measured above-ground inputs, allowed us to calculate below-ground inputs during afforestation. The Century model simulated total C and N, including the ectorganic horizons, well. Simulations showed a depletion of N in the below-ground fractions during afforestation, with N limitation in the former vineyard but not on former cereal land. The approach demonstrates the potential of models to enhance our understanding of the processes leading to carbon sequestration in soils.

Notes: 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.

Notes: Complexation with organic matter controls the activity of dissolved Al3+ in many soils. The buffering intensity of these soils is largely dependent on the H+/Al3+ exchange ratio, i.e. the number of protons consumed by the solid phase when one Al3+ is released. Here, the H+/Al3+ exchange ratio was determined from batch titrations using solutions of fulvic acid (FA) as a model for soil organic matter. Aluminium was added, from 1.04 to 6.29 mmol Al per g FA, which is within the range of humus-bound Al found in the upper B horizon of podzolized soils. Furthermore, pH was varied with NaOH to give values between 3.5 and 5.0. The H+/Al3+ exchange ratio ranged between 1.49 and 2.23 with a mean of 1.94. It correlated positively with pH and the total concentration of Al present. Theoretically, this can be explained with a partial hydrolysis of bound Al. The slope of logAl (log10 of Al3+ activity) against pH generally underestimated the actual exchange ratio, which can partly be attributed to the systems being diluted (100 mg FA l−1). However, where 4 mmol Al or more had been added per g FA, the logAl slope gradually approached −3 between pH 4.5 and 5.0. This might be the result of a shift from Al3+ activity control by humus complexation to control by Al(OH)3(s).

Notes: Stable macroaggregates (〉 200 μm) of cultivated soils are reported in the literature to be richer in organic carbon, and in young organic carbon in particular, than microaggregates (〈 200 μm). However, the nature of this additional carbon is not yet known. To determine it, we compared the composition of organic matter in stable macroaggregates with that in unstable ones. Macroaggregates 2–3 mm in diameter were separated from two silty cultivated soils from the Paris basin. They were slaked, and the primary particle composition of the resulting fractions was analysed. We used the natural abundance of 13C to quantify the amount of young carbon, derived from a maize crop, in the various size fractions.The stable macroaggregates were richer in total C and in young C (younger than 6 and 23 years respectively in the two soils studied) than the unstable ones. This young C comprised 50% particulate organic matter, 20% associated with silt and 30% with clay particles. We propose a schematic composition of aggregates in these soils in which stable aggregates are formed by the binding of microaggregates by additional young organic matter, predominantly plant debris. Young organic matter is preferentially incorporated and is responsible for aggregation, though it is eventually redistributed among aggregate classes through the destruction and re-formation of the aggregates. We have developed a model to simulate this redistribution. The model shows that stable macroaggregates have a life of a few years, but that microaggregates may exist for decades. We suggest that the stabilization and de-stabilization of macroaggregates in soils is linked to the incorporation and biodegradation of plant debris.

Notes: Both iron oxides and carbonate minerals, such as calcite, can sorb zinc (Zn), and therefore are important in controlling the solution concentration and availability of Zn to plants growing in calcareous soil. When present together, interactions between these components affect their sorption behaviour. We investigated changes in the reactions of Zn with calcite at alkaline pH, as the calcite surface was progressively coated by iron oxide. Coated calcite surfaces were prepared that had from 0.05 to 1.45% iron oxide. The initial concentration of Zn and the amount of iron oxide on the calcite were the most critical factors affecting adsorption, precipitation of solid phases, and the desorbability of sorbed Zn. For pure calcite at small initial Zn concentrations (〈 2.5 × 10−5 m) adsorption was dominant; with increasing concentration, precipitation of hydrozincite (ZHC) became more important. With increasing amounts of iron oxide the amount of Zn adsorbed increased, the desorbability of the Zn decreased, and precipitation became progressively less evident, and at 1.45% iron oxide content there was no evidence of any precipitation of ZHC. The calculated maximum adsorption attributable to the iron oxide coating was inversely proportional to the thickness of the oxides on the calcite, and greatly exceeded that of iron oxide as a separate phase. The common occurrence of iron-coated carbonates in calcareous soils and their capacity to adsorb Zn contributes to the problems of Zn deficiency, for which these soils are noted.

Notes: Ultrasonic 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.

Notes: In semi-arid northern Tanzania, the native woodland is being rapidly cleared and replaced by low input agriculture. This has resulted in pronounced environmental degradation, and in particular loss of phosphorus (P) from the soil. We have used sequential extraction and 31P-NMR to investigate the effects of land use changes, i.e. native woodland, degraded woodland, cultivation for 3 and 15 years and homestead fields where manure was applied, on the amount and structural composition of P in this soil. Clearing and continuous cultivation reduced both organic and inorganic P in the soil. The difference in the amount of organic P from the bulk soil of the fields cultivated for 3 and 15 years was not statistically significant (P 〈 0.05), suggesting that most of the depletion in organic P occurred during the first 3 years of cultivation. By contrast, in the homesteads, there was much organic and inorganic P in the soil. The 31P-NMR revealed that cultivation resulted in a 53% depletion of orthophosphate diester P, whereas only a 30% and 39% reduction of orthophosphate monoester P was found in the bulk soil after 3 and 15 years of cultivation, respectively. These results concur with the suggestion that diester P constitutes more easily mineralizable forms of organic P in soil than does monoester P. Our 31P-NMR also showed that 70% of the inorganic orthophosphate P was depleted from the coarse and fine sand separates as a result of cultivation. The influence of clearing and subsequent cropping on the amount and forms of P was more pronounced in the coarse and fine sand than in the silt and clay, stressing the importance of particle size and chemical properties such as organic matter and oxides in the availability of P in this soil. Our results show that the current low input agricultural practice is not sustainable, and that practices must be developed to combat the ongoing degradation of the soil. A combined use of available organic materials such as animal manure with the judicious use of inorganic fertilizers can replenish the soil's fertility.

Notes: Low-activity clay soils on old planation surfaces of the tropics are generally considered as stable end points of soil formation. It is therefore surprising to find Andisols on them. We characterized the properties of six profiles representative of these soils in the western part of the Nilgiri Hills (2000–2500 m above mean sea level), Southern India, where the present climatic conditions are cool (mean annual temperature 15°C) and humid (mean annual rainfall 2500 mm). Thick (50–80 cm) dark-reddish brown topsoil overlies strongly desilicated yellowish-red materials. This horizon has andic properties to a sufficient depth and the carbon content requirement of the melanic epipedon to place these soils in the Andisol order. Our data as well as the history of the Nilgiri Hills suggest that the formation of these non-allophanic Andisols resulted from the succession of two main steps. First, a ‘lateritic’ weathering cycle led to the relative accumulation of secondary Al and Fe oxides. Later, the accumulation of organic matter favoured by a more recent climatic change induced complexation by organic acids of Al and Fe oxides, and the production of enough metal–humus complexes to give rise to andic properties. Such soils, in which secondary Al and Fe oxides, generally considered as indicators of an advanced weathering stage, are involved in a new cycle of soil formation, are original Andisols.

Notes: Variograms of soil properties are usually obtained by estimating the variogram for distinct lag classes by the method-of-moments and fitting an appropriate model to the estimates. An alternative is to fit a model by maximum likelihood to data on the assumption that they are a realization of a multivariate Gaussian process. This paper compares the two using both simulation and real data.The method-of-moments and maximum likelihood were used to estimate the variograms of data simulated from stationary Gaussian processes. In one example, where the simulated field was sampled at different intensities, maximum likelihood estimation was consistently more efficient than the method-of-moments, but this result was not general and the relative performance of the methods depends on the form of the variogram. Where the nugget variance was relatively small and the correlation range of the data was large the method-of-moments was at an advantage and likewise in the presence of data from a contaminating distribution. When fields were simulated with positive skew this affected the results of both the method-of-moments and maximum likelihood.The two methods were used to estimate variograms from actual metal concentrations in topsoil in the Swiss Jura, and the variograms were used for kriging. Both estimators were susceptible to sampling problems which resulted in over- or underestimation of the variance of three of the metals by kriging. For four other metals the results for kriging using the variogram obtained by maximum likelihood were consistently closer to the theoretical expectation than the results for kriging with the variogram obtained by the method-of-moments, although the differences between the results using the two approaches were not significantly different from each other or from expectation. Soil scientists should use both procedures in their analysis and compare the results.

Notes: Microbial-derived phospholipid fatty acids (PLFAs) can be used to characterize the microbial communities in soil without the need to isolate individual fungi and bacteria. They have been used to assess microbial communities of humus layers under coniferous forest, but nothing is known of their distribution in the deeper soil. To investigate the vertical distribution we sampled nine Podzol profiles on a 100-m-long transect in a coniferous forest and analysed for their microbial biomass and PLFA pattern to a depth of 0.4 m. The transect covered a fertility gradient from Vaccinium vitis-idaea forest site type to Vaccinium myrtillus forest site type. The cores were divided into humus (O) and eluvial (E) layers and below that into 10-cm sections and designated as either illuvial (B) or parent material (C), or as a combination (BC). Two measures of microbial biomass analyses were applied: substrate-induced respiration (SIR) to determine microbial biomass C (Cmic), and the sum of the extracted microbial-derived phospholipid fatty acids (totPLFA). The soil fertility had no effect on the results. The Cmic correlated well with totPLFA (r= 0.86). The microbial biomass decreased with increasing depth. In addition the PLFA pattern changed with increased depth as assessed with principal component analysis, indicating a change in the microbial community structure. The composition of the PLFAs in the O layer differed from that in the E layer and both differed from the upper part of the B layer and from the rest of the BC layers. The deeper parts of the B layer (BC1, BC2 and BC3) were similar to one other. The O layer had more 18:2ω6, a PLFA indicator of fungi, whereas the E layer contained relatively more of the PLFAs 16:1ω9, 18:1ω7 and cy19:0 common in gram-negative bacteria. With increased depth the relative amount of 10Me18:0, the PLFA indicator for actinomycetes, increased. We conclude that the PLFA method is a promising discriminator between the microbial community structures of the horizons in Podzols.

Notes: The rate and extent of soil–solution transfer of orthophosphate ions (Pi) depend both on soil solution Pi concentration and on time. This is so both in experiments on sorption–desorption and in those on isotopic exchange. Because the two methods are based on different principles, it is questionable whether they give a similar quantification of Pi transfer.The amount of isotopically exchangeable Pi, E, was determined over periods of 100 minutes and described as a function of both time and Pi concentration in solution for three soil samples taken from field plots having different P fertilizer histories over 26 years of annual application. In separate experiments, amounts of Pi, Qd, were extracted from soil suspensions using three levels of anion exchange resin strips for periods ranging from 10 minutes to 7 days. Both initial and final solution Pi concentrations were measured. These concentrations and periods of resin-contact were used to predict the difference in E, ΔE, between the initial and final states of the suspension–resin system using extrapolations of the equations fitted to the exchange data. Under conditions in which the solution concentration of Pi decreased during extraction the ΔE values and the resin-extracted Pi values, Qd, were equal. It is thus possible, using the description of E, to predict the amount of Pi released from soil suspension knowing the initial and final solution Pi concentrations and the time it took for the system to pass from the initial to the final state. For the soil studied, identical amounts of mobile Pi, i.e. the Pi which participates in the soil–solution dynamics, may therefore be assessed by either isotopic exchange or desorption.

Notes: Soil invertebrates suffer from contamination of the soil by heavy metals. We have studied the effects of contamination by cadmium, zinc and lead on their communities in soils in northern France by comparing polluted land with non-contaminated sites. We have followed the seasonal variations and effects of soil properties. Saprophagous invertebrates (Diplopoda, Isopoda) and Chilopoda were sampled by pitfall-trapping from February to November in fairly contaminated areas. In addition, a Berlese extraction of the litter in two very highly contaminated sites was conducted during autumn; animals were also trapped during June in the same locations. The most active period for myriapods was spring (April and May), whereas isopods were abundant from April to the end of summer. No clear relation was found relating dominant species or number of myriapods or isopods to concentration of heavy metal in the little-contaminated soils. The dominant species seemed not to be related to pollution but to vegetation or soil characteristics. In the most contaminated sites, with metalliferous grassland and a thick undecomposed litter layer, a threshold in contamination values seemed to be reached: no isopods or millipedes were found, but only Chilopoda and Symphyla.

Notes: Dissolved organic matter is important in translocation and export of nutrients from forest ecosystems. Its mobility in soil is restricted by sorption to mineral surfaces which depends on its chemical properties. Carboxyl and hydroxyl groups form strong bondings to mineral surfaces, whereas the role of N-containing functional groups in the sorption process is less well understood. We examined in laboratory experiments the binding of dissolved organic matter from the forest floor to amorphous Al(OH)3, goethite, kaolinite, and illite and to subsoils in order to compare the sorption and desorption of dissolved organic C with that of dissolved organic N. The mineral samples were equilibrated with acidic solutions of organic matter at pH 4. In the equilibrium solutions organic C and N and their contribution to two operationally defined fractions, namely the so-called hydrophilic and hydrophobic fractions, were determined. We measured neutral and acidic amino sugars to discover the nature of the binding of organic N. Within the hydrophilic and hydrophobic fractions, the sorption and desorption of organic C and N did not differ, indicating that there was no preferential binding of N-containing compounds. The hydrophilic fraction contained more N and sorbed less than the hydrophobic fraction, and so the overall retention of organic N by the mineral phases and subsoils was smaller than that of organic C. Among the amino sugar compounds, muramic acid was preferentially removed from the solution, whereas the neutral amino sugars were sorbed similar to organic C. The results suggest that the sorption of N-containing compounds is favoured by acidic groups and not by amino groups.

Notes: The 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.

Notes: Some acid-based silage additives, which are less corrosive and easier to handle than Formic acid 85% (FA), were evaluated in a laboratory-scale silage experiment. These were Foraform (645 g kg–1 formic acid, 60 g kg–1 NH3), Ensimax [213 g kg–1 formic acid, 200 g kg–1 acetic acid, 190 g kg–1 of dry matter from wood pulp liquor with a high concentration of lignosulphonates (WPL)], and a modified version of Ensimax with a higher proportion of formic acid and a lower proportion of acetic acid. Each single ingredient, and all combinations of ingredients in the original Ensimax, were studied when applied in the quantities they make up in the additive. Untreated silage was used as a negative control and FA as a positive control. The additives were assessed using three different crops and by sealing the silos immediately after filling or after a 24 h delay. Both the full and half of the recommended application rates of the additives and of the single ingredients of Ensimax were studied.No significant differences were found between FA and Foraform when applied at 3 and 4 l t–1, respectively, which provided the crop with the same dose of pure formic acid. Inclusion of WPL in Ensimax did not influence silage fermentation, i.e. the effect of Ensimax could be ascribed to the effect of formic plus acetic acid alone. Compared with Ensimax, the modified version, in which 148 g kg–1 of formic acid was substituted for 150 g kg–1 of acetic acid, clearly improved fermentation in terms of increased concentration of true protein, reduced fermentation of acetic and propionic acid, and reduced ammonia value and pH. When the silos were sealed immediately, sugar concentrations in the silage correlated positively with the application rate of acids, whereas no such relationship was found when the sealing was delayed for 24 h. No consistent relationship was found between the application rate of acids and ethanol concentrations in the silage.Easy-to-handle acidic additives like Foraform and Ensimax may replace FA when applied according to their molar concentration of acids. This means that 4·0 l t–1 of Foraform and 7·3 l t–1 of Ensimax are equivalent to 3 l t–1 of FA.

Notes: Post-flowering tillering responses of ‘Ellett’ and ‘Grasslands Ruanui’ perennial ryegrass (Lolium perenne L.) cultivars after inflorescence production were studied at INRA, Lusignan in France, at near ambient light (absence of light competition, control treatment) and under shading (low-light intensity and low red–far red ratio). A dense sward containing inflorescence bearing plants of both perennial ryegrass cultivars at ambient light was cut to a height of 50 mm above ground level after which the light treatments were imposed. Forty-five days later, data were collected on the number of tillers per plant, the number of new tillers per original tiller and the dry weight of vegetative and reproductive tillers. Regardless of light treatment, cv. ‘Ellett’ had fewer tillers per plant, higher weight per tiller and a higher proportion of reproductive tillers than did cv. ‘Grasslands Ruanui’. Number of tillers per plant and number of new tillers per tiller were consistently reduced under shade compared with the control treatment for both cultivars. When shaded, weight of reproductive tillers of cvs ‘Ellett’ and ‘Grasslands Ruanui’ were 40% and 43%, respectively, less than the control, whereas vegetative tiller weight did not change. In addition, differences between cultivars in the tillering strategy after flowering seem to be unaffected by the light environment. Thus, field observations regarding tillering of cvs ‘Ellett’ and ‘Grasslands Ruanui’ were consistent with current results suggesting different grazing managements are needed after flowering to optimize the replacement of tillers for both cultivars.

Notes: Two experiments were carried out in Guadeloupe to estimate the organic matter intake (OMI) and digestibility (OMD) of a Dichanthium spp. sward, grazed by tethered Creole heifers [mean live weight (LW) 202 ± 2·0 kg], at three daily herbage allowances. Experiment 1 examined herbage allowances of 16, 25 and 31 kg of dry matter (DM) d–1 on a fertilized sward at 21 days of regrowth whereas, in experiment 2, lower allowances of 11, 15 and 19 kg DM d–1 were examined on the same sward, which was unfertilized and grazed at 14 days of regrowth. In each experiment, the herbage was grazed with three groups of two heifers in a 3 × 3 Latin square design. Sward characteristics were described before grazing. OMI was calculated from total faecal output, and OMD was predicted from the crude protein (CP) content of the faeces. The amount of herbage defoliated by the heifers was also estimated on tillers selected at random.Organic matter intakes were on average 26 g and 19 g OM kg–1 LW, and OMD values were 0·740 and 0·665 for Experiments 1 and 2, respectively, and were not affected by allowance. In Experiment 1, the herbage quality was high [0·50 of leaf and 116 g CP kg–1 organic matter (OM)] for a tropical forage, whereas in Experiment 2, the quality of the herbage (0·27 of leaf and 73 g CP kg–1 OM) was lower. These differences were reflected in differences in intake and digestibility in the two experiments.The experimental tropical Dichanthium spp. swards can have intake characteristics similar to those of a temperate sward.

Notes: From 1987 to 1996, the nutritional quality of the main botanical components (grasses, legumes and forbs) in semi-arid grasslands in the dehesa ecosystem in western Spain was analysed. Herbage samples were collected at the end of spring, in 30 locations, at two different topographic positions (upper and lower slope zones). Herbage mass over 2 cm and proportion of botanical components were estimated and samples were analysed for crude protein, neutral-detergent fibre (NDF), hemicellulose, cellulose, lignin and in vitro dry matter digestibility (DMD). Analysis of variance revealed a significant effect of sampling year on the herbage mass, proportion of botanical components and their nutritional quality. The three botanical groups, grasses, legumes and forbs, followed similar year-to-year trends in their crude protein, cellulose and lignin contents and in vitro DMD. Herbage mass was not significantly related to any meteorological variables, suggesting that interannual variation in biomass production of botanically complex pastures cannot be explained by a single factor. However, annual precipitation was significantly related to the proportion of the botanical group that was dominant at each slope zone: grasses in the lower zone and forbs in the upper zone. In the upper zone, spring precipitation explained part of the interannual variation in the NDF, cellulose, lignin contents and in vitro DMD of the botanical components.

Notes: The effect of defoliation on the vegetative, early reproductive and inflorescence stages of tiller development, changes in the dry-matter yield of leaf, stem and inflorescence and the associated changes in forage quality was determined on plants of annual ryegrass (Lolium rigidum Gaud.) and Italian ryegrass (L. multiflorum Lam.). The field study comprised seventy-two plots of 1 m × 2 m, sown with one annual ryegrass and seven Italian ryegrass cultivars with a range of heading dates from early to late; defoliation commenced 6 weeks after germination. During the vegetative stage of growth, plots were defoliated when the tillers had three fully expanded leaves (three-leaf stage). During the early reproductive stage of growth, to simulate a cut for silage, plots were defoliated 6–7 weeks after 0·10 of the tillers displayed nodal development. The subsequent regrowth was defoliated every 3 weeks.Assessments of changes in tiller density, yield and quality were made in the growth cycle that followed three contrasting cutting treatments during the winter–spring period (from 10 July). In treatment 1, this growth cycle (following closing-up before a subsequent conservation cut) commenced on 7 August following two defoliations each taken when the tillers were at the three-leaf stage. In treatment 2, the growth cycle commenced on 16 October following: for early-maturing cultivars, two cuts at the three-leaf stage, a cut for silage and an additional regrowth cut; for medium-maturing cultivars three cuts at the three-leaf stage and a cut for silage; and late-maturing cultivars, five cuts at the three-leaf stage. In treatment 3, defoliation up to 16 October was as for treatment 2, but the growth cycle studied started on 27 November following two additional regrowth cuts for early- and medium-maturing cultivars and cut for silage for the late-maturing cultivars.Tiller development for all cultivars was classified into three stages; vegetative, early reproductive and inflorescence. In treatment 1, in vitro dry-matter digestibility (IVDMD) and crude protein (CP) content were negatively associated with maturation of tillers. IVDMD ranged from 0·85 to 0·60 and CP ranged from 200 to less than 100 g kg–1 dry matter (DM) during the vegetative and inflorescence stages respectively. This large reduction in forage quality was due to an increase in the proportion of stem, inflorescence and dead material, combined with a reduction in the IVDMD and CP content of the stem. A high level of forage quality was retained for longer with later-maturing cultivars, and/or when vegetative tillers were initiated from the defoliation of early reproductive tillers (treatments 2 and 3). However, 15 weeks after the closing-up date in treatment 1, defoliation significantly reduced the density of inflorescences with means (±pooled s.e_m.) of 1560, 1178 and 299 ± 108 tillers m–2, and DM yield of inflorescence with means of 3·0, 0·6 and 0·1 ± 0·15 t ha–1 for treatments 1, 2 and 3 respectively.This study supports the recommendation that annual and Italian ryegrass cultivars should be classified according to maturity date based on the onset of inflorescence emergence, and that the judicious defoliation of early reproductive tillers can be used to promote the initiation of new vegetative tillers which in turn will retain forage quality for longer.

Notes: An experiment was conducted to compare the nutritive value of a range of ensiled forage legumes. Silages were prepared from late second-cut lotus (Lotus corniculatus), first-cut sainfoin (Onobrychis viciifolia) and both early and late second-cut red clover (Trifolium pratense) and lucerne (Medicago sativa). Each experimental silage was offered to six Suffolk-cross wether lambs, aged 10 months, housed in metabolism crates. Voluntary intakes of dry matter ranged from 71 to 81 g kg−1 liveweight0·75 d−1. Voluntary intakes were similar on the lotus, sainfoin and late-cut red clover silages, but the voluntary intake on the lotus silage was significantly higher than that on the lucerne silages and early-cut red clover silage. Digestibility of organic matter in the dry matter was highest for the lotus silage (0·650), and lowest for the sainfoin silage (0·527). Although most of the N in the sainfoin silage appeared to be in an indigestible form, N digestibility was approximately 0·70 for the other legume silages. The highest loss of N in urine, 0·75 of N intake, was recorded for lambs offered the lucerne silage. Differences in N intake, N loss in faeces and N loss in urine led to statistically significant differences in the amount of N retained, with the highest and lowest N balances recorded for the lotus (16 g N d−1) and sainfoin (−2 g N d−1) silages respectively. The results confirm that these high protein forages have high intake potential. While low N digestibility appears to limit the nutritional value of sainfoin, further research could formulate feeding strategies that improve the efficiency with which the protein from red clover, lucerne and lotus is utilized.

Notes: Acoustic analysis of grazing behaviour was found to allow accurate identification of chewing and biting, and estimation of intake by cattle. Four steers grazed six types of turves, three were short (14, 16 and 20 cm tall), leafy turves from mowed Setaria lutescens with high application of N fertilizer, and three were tall (36, 49 and 62 cm tall), mature turves from uncut areas with low application of N fertilizer. Each animal grazed ten bites from each turf type while behaviour was videotaped and grazing sounds were recorded with a wireless microphone taped to the animal’s forehead. The intake was measured by the difference in pre- and post-grazing turf weight, corrected for water loss. Chews and bites differed in acoustic characteristics, with bites producing more output in the 3–8 kHz frequency band. Discriminant analysis of the acoustic characteristics correctly classified chews and bites with 94% accuracy. Intake was predicted with a high degree of accuracy by total energy flux density (fJ m–2) in chewing sounds (EFDC), EFDC per chew and average intensity of chewing sound in the 1–2 and 2–3 kHz bands (R2=0·90, CV=3·6%). Although bite mass ranged from 1·37 to 4·50 g, EFDC per g of intake (CV=0·015) was not affected by treatments or animals. Chewing sounds carried more information about intake than biting sounds and chews per bite. Analysis of grazing sounds has the potential to overcome many of the problems associated with the measurement of grazing intake.

Notes: An experiment was carried out to examine silage fermentation, effluent production and aerobic stability in unwilted grass silage, which was either ensiled without additive or with a commercially available blend of ammonium hexamethanoate, ammonium hexapropionate and octanoic acid (6 l t−1, Maxgrass, BP Chemicals Ltd., Northwich, UK) and to determine alternative approaches to obtaining the same performance in finishing beef cattle.Seventy-two Limousin × Friesian and Charolais × Friesian steers (mean initial live weight 424 kg s.d. 28·3) were blocked into groups of nine according to live weight and previous performance and offered silage, either with or without the additive, and supplemented with 0, 1·5, 3·0 or 4·5 kg d−1 of a concentrate with a crude protein content of 150 g kg−1 DM or allocated to a pre-experimental slaughter group to enable calculation of daily carcass gain. Daily silage intakes were recorded for 112 days. At the end of the experiment, all cattle were slaughtered and daily carcass gain, omental, mesenteric, perinephric and retroperitoneal fat depots [kidney-knob and channel fat (KKCF)], fatness, conformation, subcutaneous fat depth over M. longissimus dorsi muscle and carcass fat, protein and bone contents were assessed.Across all levels of supplementation, cattle offered the silage with the additive showed significantly (P 〈 0·001) higher daily DM intakes than those offered the silage without additive. Cattle offered the silage with the additive but unsupplemented had significantly (P 〈 0·001) higher daily carcass gains than those offered the silage without additive and unsupplemented. The response in carcass gain was 76 and 35 g kg−1 additional concentrate for the silages with and without the additive respectively.

Notes: The ability of grazing sheep to exploit preferred patches of grass species according to their spatial distribution was studied. The choices made by groups of four ewes in three cocksfoot (Dactylis glomerata) plots (80 × 80 m), in which 136 patches (30 × 30 cm) of perennial ryegrass (Lolium perenne) were either randomly distributed (plot Rand) or grouped (plots Ag.1 and Ag.2) to create preferred feeding sites (four rich sites of twenty-five patches and four poorer sites of nine patches) were compared. On measurement days, each group was allocated to one of the three plots, and grazed it in at least four successive 30-min tests. At the end of the experiment the ewes were allowed to graze the plots continuously for 3 months to assess the medium-term effect of grazing sheep on the depletion rate of patches. Behavioural observations showed that, once the ewes had discovered a preferred feeding site in plots Ag.1 or Ag.2, they frequently returned to it within a test and between tests, whereas they failed to learn the precise location of many isolated patches in plot Rand. Thus in 2 h of grazing, the ewes spent 0·40 more time feeding on perennial ryegrass when the patches were grouped than when they were randomly distributed, and perennial ryegrass depletion was greater in plots Ag.1 and Ag.2 than in plot Rand (0·193 vs. 0·105 of initial height). The richer sites were also more depleted than the poorer ones (0·209 vs. 0·152 of initial height). When the plots were continuously grazed, perennial ryegrass depletion remained greater in plots Ag.1 and Ag.2 than in plot Rand for at least 3 weeks. Hence the spatial distribution of patches can affect diet selection by sheep, and so probably their impact on grasslands.

Notes: In a 2 × 2 × 2 factorial experiment, plants of one genotype of tall fescue (Festuca arundinacea) were grown in soil in pots in a glasshouse on two occasions. The treatments were either with (E+) or without (E–) infection by the fungal endophyte Neotyphodium coenophialum; with (N+) or without (N–) inoculation by the root-knot nematode Meloidogyne marylandi; and with or without water deficit stress. In the first experiment, nematode numbers after 5 weeks had increased 10 times in the E–/N– watered pots and 22 times in the E–/N+ stressed plants. Root dry weight was decreased in all E–/N+ pots, compared with E–/N–. In contrast, nematode numbers in all E+/N+ pots decreased to nearly zero and root dry weight was unaffected. Osmotic adjustment in the growing zone of stressed plants was –0·35 MPa in E–/N– pots, but only –0·10 MPa in E–/N+ pots. Osmotic adjustment was greatest (–0·64 MPa) in E+ pots of both nematode treatments and almost no nematodes survived in the N+ pots. In the second experiment, there was complete nematode mortality in the E+ pots. Plant water relations were unaffected by treatments, however. It is concluded that endophyte-enhanced persistence of tall fescue in M. marylandi-infested soils that are prone to drought may be explained at least partly by endophyte protection of roots from nematode damage. Nematode inhibition by the endophyte may operate in addition to direct influences of the endophyte on enhancing drought tolerance of the host.

Notes: Chromolaena odorata (Siam weed) has been classified as a weed plant in West Africa. Data from C. odorata foliage after 4, 6, 8, 10 and 12 weeks of regrowth showed that the leaf fraction had a crude protein content above 194 g kg–1 dry matter (DM) and an average leaf to stem ratio of 2·1:1. Chemical analysis of the leaf fraction of an 8-week-old regrowth indicated a high crude protein content (258 g kg–1 DM) and a high degradable nitrogen content (60·7 g N kg–1 digestible organic matter), but low neutral-detergent fibre (331 g kg–1 DM), acid-detergent lignin (53·1 g kg–1 DM), total extractable phenolic (37·1 g kg–1 DM), extractable tannin (0·72 absorbance at 550 nm) and extractable condensed tannin (1·4 g kg–1 DM) contents. In sacco degradability analysis of the 8-week-old regrowth leaf sample showed a high 48 h organic matter (935 g kg–1 DM) and crude protein (953 g kg–1 DM) degradability. The leaf sample had an organic matter degradability of 670 g kg–1 DM as estimated by cumulative gas production in vitro after 24 h incubation. There was little or no phenolic-related antinutritive factors in C. odorata. Additionally, leaf samples had no effect on rumen protozoa activity estimated as the rate of [14C]leucine Selenomonas ruminantum bacterial protein breakdown. Data from this study suggest that C. odorata leaves are of high nutritive value and might have the potential to be used as a protein supplement to ruminants. There is need for further investigation to test whether C. odorata leaves may have any deleterious effect on the host animal.

Notes: The response of swards which have been previously grazed to N fertilizer applied in early February was studied in two experiments in Northern Ireland. The effect of N fertilizer applied at a range of dates in autumn and spring on swards for out-of-season utilization was studied in a further experiment. Deep soil coring was also undertaken, subsequent to grazing with dairy cows, in grazed and protected areas in November and March to investigate the effect of out-of-season grazing on soil mineral N levels.Dry-matter (DM) yield response to early spring N application in previously grazed swards was low, with no effect on DM yield in February or March. Progressively delaying N application (and commencement of herbage accumulation) in autumn from 8 September until 18 October reduced herbage availability in late autumn and early spring but increased leaf lamina content. The greater the amount of herbage accumulated to 1 December, the lower the tiller density in the following April.N fertilizer had a greater impact on soil mineral N in spring than in late autumn/early winter, suggesting that fertilizer N was more prone to loss in the latter. Soil mineral N was not significantly affected by out-of-season grazing.It is concluded that in well-fertilized, previously grazed swards response to N for out-of-season herbage is low and the probability for N loss is increased. Herbage quality will decline and the sward may be damaged if about 2 t DM ha−1 or more of harvestable herbage accumulates for use in winter or in early spring.

Notes: A linear programming model of a dairy farm, in which grass production and grassland use was originally modelled using one growing period and one area of land, is extended. To include seasonal and spatial elements of variation not allowed for in the original model, the model was modified to reflect three growing periods in the season and then to reflect management of two separate areas of land. The resulting three models were used to assess farm physical planning, economic results and nutrient balances for an average Dutch dairy farm in a situation without and with levies on nutrient surpluses. It is concluded that incorporating seasonal and spatial elements provides greater insight into grassland management. Seasonal model specification does not result in significant changes in farm physical planning, income and nutrient surpluses. Spatial specification has a larger impact if one of the two areas cannot be grazed by dairy cattle.

Notes: Two studies were conducted to examine the effects of incorporating small quantities of straw in the diets of dairy cows. In Experiment 1, forty Holstein Friesian dairy cows were used in a 2 × 4 factorial design experiment, with factors examined consisting of two parities (primiparous and multiparous animals) and four levels of straw inclusion in the diet (0, 0·08, 0·16 and 0·24 of forage dry matter). The basal forage offered in this study was grass silage, and the primiparous and multiparous animals were supplemented with 9·0 and 11·0 kg concentrate d–1 respectively. In Experiment 2, forty-eight Holstein Friesian dairy cows were used in a 2 × 3 factorial design experiment, with factors examined consisting of two basal forage types (grass silage and zero-grazed grass) and three levels of straw inclusion (0, 1·0 and 2·0 kg d–1). All animals were offered 7·0 kg d–1 of a concentrate supplement. Both experiments were partially balanced changeover designs, consisting of two, 4-week periods.In Experiment 1, the total dry-matter intake followed a significant quadratic relationship (P 〈 0·05), increasing with low levels of straw inclusion and decreasing at higher levels of inclusion. With increasing levels of straw inclusion, there was a linear decline in milk yield (P 〈 0·001) and milk protein concentration (P 〈 0·05), but milk fat concentration was unaffected (P 〉 0·05).In Experiment 2, the effect of straw inclusion on total dry-matter intake was quadratic (P 〈 0·001), with intakes being maximum at the 1·0-kg level of straw inclusion. Milk yield exhibited a linear decrease (P 〈 0·001) with increasing level of straw inclusion. Milk fat concentration was lowest at the 1·0 kg rate of straw inclusion (P 〈 0·05), but milk protein concentration was unaffected by straw inclusion. There were no significant interactions between basal forage type and level of straw inclusion for any of the variables examined (P 〉 0·05).Despite small increases in total dry-matter intake at a low level of straw inclusion, there was no evidence that straw inclusion improved either nutrient utilization or animal performance. The reduction in milk yield observed with straw inclusion reflects, to a large extent, a reduction in metabolizable energy intake.

Notes: Two experiments, using intravenous infusion of nutrients, were carried out with the aim of separating milk production responses due to the provision of amino acids as precursors of milk protein synthesis from those due to the provision of amino acids as glucose precursors. Diets were based on grass silage of restricted fermentation and barley-based supplements because it has been suggested that these diets might provide insufficient glucose precursors to meet the needs of lactose synthesis. The silages used in the experiments were of similar lactic acid contents [62 and 63 g kg–1 dry matter (DM)] but of different water-soluble carbohydrate (WSC) contents (206 and 20 g kg–1 DM in Experiments 1 and 2 respectively). In Experiment 1, four dairy cows were given the following treatments in a 4 × 4 Latin square arrangement with periods of 10 d: (1) basal diet (Basal), (2) Basal plus jugular infusion of 182 g d–1 of amino acids simulating casein (TAA), (3) Basal plus 101 g d–1 of essential amino acids (EAA), being the essential amino acid component of the TAA treatment and (4) Basal plus 101 g d–1 of essential amino acids plus 50 g d–1 of glucose (EAA + G), being the glucose equivalent of the non-essential amino acid component of treatment TAA. All infusions increased (P 〈 0·05) the concentration of milk protein compared with Basal but only for TAA was the increase in the yield of milk protein statistically significant (P 〈 0·05), amounting to 68 g d–1. Both TAA and EAA reduced (P 〈 0·05) the concentration of milk fat. There was no difference between EAA and EAA + G treatments.In Experiment 2, five dairy cows were given the following treatments in a 5 × 5 Latin square design with periods of 7 d: (1) basal diet (Basal), (2) Basal plus 182 g d–1 of amino acids simulating casein (TAA), (3) Basal plus 182 g d–1 of non-essential amino acids as in casein (NEAA), (4) Basal plus 100 g d–1 of glucose (G100) and (5) basal plus 230 g d–1 of glucose (G230). G100 supplied the glucose equivalent of NEAA whereas G230 supplied the caloric equivalent of NEAA. Again, only for TAA was the increase in yield of milk protein statistically significant (P 〈 0·05), amounting to 83 g d–1. Neither glucose treatment caused any statistically significant (P 〉 0·05) effect on the yield of milk protein nor the yield of milk lactose.It is concluded that, in both experiments, the primary nutritional limitation on milk protein output was the supply of amino acids as precursors of milk protein, there being no evidence to support a primary limitation due to glucose supply.

Notes: The variation in the dietary cation–anion difference (DCAD) and the urinary pH of dairy cows was examined over the year 1996–97 in Victoria, south-eastern Australia. Mineral concentrations in the pasture and dairy cow milk production were also examined. Three farmlets (A, B and C) under different feeding and management systems were used for the purpose of the study. Feeding management was based on grazed grass with stocking rates of 1·4, 2·5 and 4·7 cows ha–1 for farmlets A, B and C respectively. Cows on farmlets B and C received more supplementary feed than those on the A farmlet.The urine of the cows in each herd was sampled for pH twice monthly, after morning milking. A sample of the feed on offer the previous day was collected and analysed for crude protein, in vitro dry-matter digestibility and macrominerals. Milk yields were recorded on the same day as urine sampling and weather data for the previous day were also collected.Pasture cation–anion difference was not greatly influenced by stocking rate or associated management practices, although mineral concentrations in pasture did vary. Urine pH was unaffected by changes in climate, management strategies (e.g. stocking rate), season and stage of lactation. Moreover, urine pH was also unaffected by changes in DCAD until the DCAD declined below approximately +15 mequiv. 100 g–1 for two consecutive sampling periods.It is concluded that when this threshold for DCAD (+15 mequiv. 100 g–1) is breached, even in late lactation, a decrease in urine pH occurs. In south-eastern Australia, the DCAD offered to non-lactating cows in the last 2 weeks of pregnancy, in spring-calving herds, on a pasture-based diet is nearly always above that regarded as optimum in other feeding systems.

Notes: Surface podzolization has so far been diagnosed from morphological observations, selective extraction and mineralogical investigations. We studied this process in two Cambisol profiles developed in loess, one with a fibrimor humus and the other with a dysmoder humus, by characterizing the chemical composition and the complexing properties of the soil solution. The solutions were sampled bimonthly for 3 years at four depths (4, 8, 13, 25 cm) using both zero-tension and low-tension capillary-wick lysimeters. The leachates from the Ah horizon of the soil with fibrimor contained less nitrate, sulphate and calcium than those from the one with a dysmoder because there was less bioturbation and mineralization in it. Both the complexation capacity and the density of ligand binding sites were larger in the soil solutions of the Ah (4 cm) and AB (8 cm) horizons of the soil with the fibrimor. In this soil, the complexing properties of the liquid phase induced a depletion of inorganic monomeric aluminium. In this environment, the hydroxy interlayered 2:1 clay minerals lose their Al-interlayers and transform into vermiculite and smectite, which in turn weather, producing large amounts of magnesium in the soil solution. This was found to be a major characteristic of weathering by complexation and incipient podzolization in the Cambisol with the fibrimor. In this process, nitric acid probably contributes to mineral dissolution.

Notes: The production of exudates by plant roots and microbes in the rhizosphere, together with intense wetting and drying cycles due to evapotranspiration, stimulate changes in soil structure. We have attempted to separate these two processes using an experimental model with bacterial exopolysaccharides (dextran and xanthan) and root mucilage analogues (polygalacturonic acid, PGA), and up to 10 cycles of wetting and drying. To characterize the soil structure, tensile strength, water sorptivity and ethanol sorptivity of the amended soils were measured, and thin sections were made. Xanthan and PGA induced greater tensile strength of the amended soil, suggesting that they increased the bond energy between particles. Porosity increased with each cycle of wetting and drying, and this increase was less pronounced for the PGA 2 g l−1 than for the xanthan and dextran. This suggests that PGA stabilized the soil against the disruptive effect caused by the wetting and drying. The PGA was the only polysaccharide that influenced water sorptivity and repellency, resulting in slower wetting of the treated soil. Wetting and drying led to an increase of the sorptivity and a decrease of the repellency for all treatments with the exception of the PGA-amended soils. The PGA may therefore stabilize the soil structure in the rhizosphere by increasing the strength of bonds between particles and decreasing the wetting rate.〈section xml:id="abs1-2"〉〈title type="main"〉Influence de mucilages racinaire et microbiens modèles sur la structure du sol et le transport d'eau〈section xml:id="abs1-3"〉〈title type="main"〉RésuméLa production d'exsudats par les plantes et les microbes de la rhizosphère ainsi que les cycles d'humectation–dessiccation très intense due à l'évapotranspiration, entraînent des modifications de la structure du sol. Notre objectif a été de séparer ces deux processus en utilisant un modèle expérimental avec des polysaccharides bactériens (dextran et xanthan) et un analogue d'exsudat racinaire (acide polygalacturonique, APG), et jusqu'à dix cycles d'humectation et dessiccation. Afin de caractériser la structure du sol, la résistance en traction ainsi que l'infiltration de l'eau et de l'éthanol dans le sol amendé par les différents polymères ont été mesurés, et des lames minces ont été réalisées. Le xanthan et l'APG ont provoqué la plus forte augmentation de la résistance en traction, ce qui serait attribuable à une plus grande énergie de liaison entre les particules de sol. La porosité a augmenté avec chaque cycle d'humectation–dessiccation pour tous les traitements et cette augmentation a été moins prononcée pour l'APG 2 g l−1 par rapport au xanthan et au dextran. Cela suggère que l'APG a stabilisé le sol contre la déstructuration provoquée par les cycles d'humectation–dessiccation. L'APG a été le seul polysaccharide qui a influencé– dans le sens d'une diminution – l'infiltration de l'eau dans le sol amendé. Les cycles d'humectation–dessiccation ont entraîné une augmentation de l'infiltration de l'eau dans le sol amendé par les différents polymères à l'exception de l'APG. Ce dernier stabiliserait donc la structure du sol dans la rhizosphère en augmentant la force de liaison entre les particules et en diminuant la vitesse d'humectation du sol.

Notes: Current methods for determining inorganic sulphur (S) in aerated mineral soil horizons often result in underestimates. To overcome this defect we developed a new method combining a batch extraction with 0.5 m NH4F solution at a soil:solution ratio of 1:5 with a subsequent analysis of the mobilized SO42– by ion chromatography. The ammonium fluoride extraction enables us to characterize inorganic sulphate in non-calcareous forest soils. It is more efficient than conventional procedures in which inorganic S is extracted with phosphate or bicarbonate solution. In contrast to the extraction with strongly alkaline reagents (NaOH, KOH, LiOH), the NH4+–NH3 buffer system in NH4F prevents the pH of the suspension from exceeding 9.0 and thus the undesired conversion of organic S into SO42– by auto-oxidation and hydrolysis of ester sulphate. In a comparison we demonstrated that the inorganic S in six German forest soils is underestimated by up to 50% or 200 kg S ha−1 in the uppermost 60 cm, if it is assessed by extraction with 0.016 m KH2PO4 or 0.5 m NaHCO3 instead of 0.5 m NH4F. Conversely, the pool of ester sulphate is overestimated almost threefold.

Notes: Allophanic soils are known to accumulate organic matter, but the underlying mechanism is not well understood. Here we have investigated the sorption of humic acid (HA) by an allophanic clay in the presence of varied concentrations of either CaCl2 or NaCl as background electrolytes. Both the HA and the clay were separated from New Zealand soils. Much more HA was sorbed in CaCl2 than in NaCl of the same ionic strength. Apparently Ca2+ ions were more effective than Na+ ions in screening the negative charge on HA. In CaCl2 the HA molecule might also assume a more compact configuration than in NaCl. In the presence of CaCl2 sorption increased, reached a maximum, and then declined as the concentration of HA in solution was increased. This behaviour was not observed in NaCl where sorption showed a gradual and steady increase with HA concentration. We propose that ligand exchange occurs between the surface hydroxyl groups of allophane and the carboxylate groups of HA. As a result, the allophane–HA complex acquires negative charges, requiring the co-sorption of extraneous cations (Ca2+ or Na+) for charge balance. The Ca2+ co-sorbed can attract more HA to the complex possibly by a cation-bridging mechanism, giving rise to a maximum in sorption. The decline in sorption beyond the maximum may be ascribed to a decrease in the concentration of free Ca2+ ions through binding to HA molecules in solution. The increase in supernatant pH may be attributed to a ligand exchange reaction between the surface hydroxyls of allophane and the carboxylate groups of HA, and proton binding to the allophane–HA complex.

Notes: Most of the nitrous oxide (N2O) in the atmosphere, thought to be involved in global warming, is emitted from soil. Although the main factors controlling the production of N2O in soil are well known, we need more quantitative data on the interactions of soil and the environment in the soil that affect the emission. We therefore studied the effects of irrigation, cropping (fallow, barley with grass undersown) and N fertilization (unfertilized, 103 kg N ha−1) on the composition of soil air and direct N2O emission from soil (using the closed chamber method) in a factorial field experiment on a well-structured loamy clay soil during 1 June−22 October 1993. The measurements were made weekly during the growing season and three times after harvesting. The composition of the soil air did not indicate severe anoxia in any treatment or combination of treatments, but the accumulation of N2O in the soil air indicated that hypoxia was common. At the start of the irrigation the emissions were small, even though there was much ammonium and nitrate in the soil and therefore a potential for emission of N2O produced by both nitrification and denitrification. Larger emissions occurred later. The largest emissions were found when 60–90% of the soil pore space was filled with water. Irrigation and fertilization with N both roughly doubled the cumulative N2O emission. Growing a crop decreased it by a factor of 3–7. Most N2O was lost from the irrigated fertilized soil under fallow (3.5 kg N ha−1), and least from the unirrigated unfertilized soil under barley (0.1 kg N ha−1).

Notes: The difficulties in using complicated models of carbon mineralization and the poor performance of simple ones call for new models that are simple in use and robust in performance. We have developed a model for the mineralization of carbon from experimental data in which the organic matter is treated as a single component. The logarithm of the average relative mineralization rate, K, or rate constant, of a substrate considered as a whole was found to be linearly related to the logarithm of time, t, provided prevailing soil conditions remained unchanged. The equation is: logK = logR–S logt, or K = R t–S, in which R (dimension tS − 1) represents K at t = 1, and S (dimensionless, 1 ≥ S≥ 0) is a measure of the rate at which K decreases over time, also called the speed of ‘ageing’ of the substrate. The quantity of the remaining substrate, Yt, is calculated by Yt = Y0 exp(–Rt1 – S), where Y0 is the initial quantity of the substrate. The actual relative mineralization rate, k, at time t is proportional to K, according to k = (1 − S)K. The model was tested against an assembly of 136 sets of data collected from trials conducted in 14 countries all over the world. They cover materials ranging from glucose, cellulose and plant residues, to farmyard manure, peat and soil organic matter. The results lead to the conclusion that the model describes well the dynamics of organic matter in soil over time varying from months to tens of years, provided major environmental conditions remain unchanged. It can easily be applied in practice and is attractive because of its modest input requirements.

Notes: The aim of the study was to evaluate effects of mobile and immobile water and diffusion-limited transport on the binding and release of ions in soils. The desorption and leaching of calcium in a humic layer of a densely rooted acid forest soil under a beech stand was studied in laboratory experiments by leaching soil columns with a desorption solution and recycling the leachate through the columns. Radioactive tracers were added and monitored in the leachate to evaluate desorption and leaching characteristics of the soil. Parallel experiments were conducted with chloride and calcium to determine transport and desorption parameters independently. The experimental data were then analysed with a transport model, taking into account effects of mobile and immobile soil water fractions, and in the case of calcium assuming an equilibrium Langmuir adsorption isotherm.The transport was highly dependent on the mobility of the soil water, and in particular the fraction of the soil water to which the chemical was confined as a result of ionic properties. For chloride an excluded soil water phase had to be taken into account to explain the experimental findings. Immobile or mobile water and solute transfer and transport properties were not sufficient to explain non-equilibrium effects in the adsorption reactions. Desorption curves agreed with results from batch experiments, provided the leaching experiments were done in such a way that equilibration between the soil solution and the solid matrix adsorption sites was reached, otherwise desorption was delayed and the calculated isotherms do not represent actual equilibrium adsorption–desorption conditions.

Notes: The mineralization of nitrogen from soil organic matter is important when one tries to optimize nitrogen fertilization and assess risks of N losses to the environment, but its measurement is laborious and expensive. We have explored the possibilities for monitoring N mineralization directly using time domain reflectometry (TDR). Net N and S mineralization were monitored over a 101-day period in two layers (0–30 and 30–60 cm) of a loamy sand soil during aerobic incubation in a laboratory experiment. At the same time electrical conductivity of the bulk soil, σa, was measured by TDR. A series of calibration measurements with different amounts of KNO3 at different soil moisture contents was made with the topsoil to calculate the electrical conductivity, σw, of the soil solution from σa and θ. The actual σw was determined from the conductivity of 1:2 soil:water extracts (σ1:2) with a mass balance approach using measured NO3– concentrations, after correction for ions present prior to the addition of KNO3. The average N mineralization rate in the topsoil was small (0.12 mg N kg−1 day−1), and, as expected, very small in the subsoil (0.023 mg N kg−1 day−1). In the top layer NO3– concentrations calculated from σa determined by TDR slightly underestimated measured concentrations in the first 4 weeks, and in the second half of the incubation there was a significant overestimation of measured NO3–. Using the sum of both measured NO3– and SO42– reduced the overestimation. In the subsoil calculated NO3– concentrations strongly and consistently overestimated measured concentrations, although both followed the same trend. As S mineralization in the subsoil was very small, and initial SO42– concentrations were largely taken into account in the calibration relations, SO42– concentrations could not explain the overestimation. The very small NO3– and SO42– concentrations in the B layer, at the lower limit of the concentrations used in the calibrations, are a possible explanation for the discrepancies. A separate calibration for the subsoil could also be required to improve estimates of NO3– concentrations.

Notes: X-ray sedimentation is potentially attractive for estimating the particle-size distribution of soil, but has been thought to overestimate clay fractions because of the iron they contain. We have examined X-ray sedimentation for estimating the particle-size distribution of fully dispersed and of aggregated clay. We obtained good agreement between the pipette and X-ray sedimentation methods using two different kaolinite samples with a small iron concentration. We also studied montmorillonite saturated with Li, Na, K, Mg or Ca to investigate possible effects of hindered settling. For the Ca montmorillonite, we obtained good agreement between X-ray sedimentation and the pipette method at concentrations up to 40 g l−1. We also found that X-ray sedimentation could be used at concentrations less than those recommended by the manufacturer. Hindered settling was observed at concentrations 〉 20 g l−1 for Li- and Na-saturated montmorillonite. Our data suggest that conducting experiments at different mass concentrations is a sensitive test to detect such problems. Finally we used a fractal model to investigate the possible errors that might result from the size dependence of aggregate density and show that the error caused by assuming a single value for particle density of solids is small.

Notes: We have developed a predictive model of denitrification in soils, NEMIS, based on data from a cultivated field composed of denitrification rates measured on undisturbed soil cores and the corresponding soil water-filled pore space, nitrate content and respiration. This model is a multiplicative combination of a potential denitrification rate measured under standard conditions defined in this paper, and dimensionless functions of nitrate content, water-filled pore space and temperature. The model was applied to two further databases obtained independently of its definition. Significant correlation was observed between the simulated and measured denitrification rates. The sensitivity of NEMIS to systematic variations of the input variables and of the coefficients included in the dimensionless functions was tested using these databases. NEMIS seems to be a very useful tool particularly adapted for interpolating a small number of denitrification measurements from a simple database composed of soil potential denitrification rate and the evolution of soil water-filled pore space, nitrate content and temperature. Its main limitation is its high sensitivity to the water-filled pore space from which denitrification starts to occur and which is included in the water function.〈section xml:id="abs1-2"〉〈title type="main"〉NEMIS, un modèle prédictif de la dénitrification à l'échelle de la parcelle cultivée Résumé NEMIS, un modèle prédictif de la dénitrification dans les sols, a été défini à partir d'une base de données obtenue dans un sol cultivé et composée de vitesses de dénitrification mesurées sur des échantillons de sol non remaniés et les valeurs correspondantes de taux de saturation en eau, de teneur en nitrates et de vitesses de respiration. Ce modèle est une combinaison multiplicative entre une vitesse potentielle de dénitrification mesurée dans des conditions standardisées définies dans ce papier et de fonctions sans dimension de la teneur en nitrates, du taux de saturation en eau et de la température du sol. Ce modèle a ensuite été utilisé sur deux jeux de données indépendantes et des corrélations significatives ont été observées entre mesures et simulations. La sensibilité du modèle lors de variations systématiques du niveau des variables d'entrée ainsi que des coefficients inclus dans les fonctions sans dimension a été testée sur ces jeux de données. NEMIS apparaît comme un outil très utile d'interpolation entre quelques points de mesures de dénitrification à partir d'un jeu de données relativement simple comprenant le potentiel de dénitrification du sol et l'évolution du taux de saturation en eau, de la teneur en nitrates et de la température du sol. La principale limite de NEMIS est sa grande sensibilité au taux de saturation en eau du sol à partir duquel le processus de dénitrification commence à fonctionner.

Notes: Network models are idealized geometrical representations of porous media. They allow the simulation of effective hydraulic properties and of solute transport for well-defined porous structures. In this paper, the relation between pore structure and effective properties is studied using a network model which can be adjusted to predefined pore-size distributions and pore topologies. I show that pore topology can be adjusted such that quite different pore-size distributions lead to essentially identical water retention curves. This puts into question the common interpretation of the retention curve as being indicative of the pore-size distribution. However, I also found that both the hydraulic conductivity and the dispersion of a solute depend on the water retention curve and not on the particular combination of pore-size distribution and topology which make it up. This corroborates the widely used approach of inferring relative permeabilities from water retention data.

Notes: The standard estimator of the variogram is sensitive to outlying data, a few of which can cause overestimation of the variogram. This will result in incorrect variances when estimating the value of a soil property by kriging or when designing a sampling grid to map the property to a required precision. Several robust estimators of the variogram, based on location and scale estimation, have been proposed as improvements. They seem to be suitable for analysis of soil data in circumstances where the standard estimator is likely to be affected by outliers. Robust estimators are based on assumptions about the distribution of the data which will not always hold and which need not be made in kriging or in estimating the variogram by the standard estimator.The estimators are reviewed. Simulation studies show that the robust estimators vary in their susceptibility to moderate skew in the underlying distribution, but that the effects of outliers are generally greater. The estimators are applied to some soil data, and the resulting variograms used for ordinary kriging at sites in a separate validation data set. In most cases the variograms derived from the standard estimator gave kriging variances which appeared to overestimate the mean squared error of prediction (MSEP). Kriging with variograms based on robust estimators sometimes gave kriging variances which underestimated the MSEP or did not differ significantly from it. Estimates of kriging variance and the MSEP derived from the validation data were generally close to estimates from cross-validation on the prediction set used to derive the variograms. This indicates that variogram models derived from different estimators could be compared by cross-validation.

Notes: Time-domain reflectometry (TDR) is being used increasingly for measuring the moisture content of porous media. However, successful application for measuring water in soil has been limited to non-deformable soils, and it would be a valuable extension of the technique if it could be used for soils that shrink on drying. We have recently investigated its application to soils rich in clay and organic matter and peats. Here we propose a method for determining moisture content in deformable soils based on the relation between the dielectric constant, K, and the volumetric moisture content, Θ, measured by TDR.Parallel TDR probes with a length of 15 cm and a spacing of 2 cm were placed horizontally in soil cores with a diameter of 20 cm and height of 10 cm taken from a forest. The soil is very porous with large proportions of both silt and clay. The sample weight and travel time of the electromagnetic wave guided by parallel TDR probes were simultaneously measured as a function of time, from saturation to oven-dryness during which the core samples shrank considerably. Vertical and horizontal components of shrinkage were also measured to take the air-exposed region of TDR probe into account in the determination of K. The effect of deformation on volumetric moisture content was formulated for two different expressions, namely actual volumetric moisture content (AVMC) and fictitious (uncorrected) volumetric moisture content (FVMC). The effects of air-exposure and expressions of volumetric moisture content on the relation between K andΘ were examined by fitting the observations with a third-order polynomial. Neglecting the travel time in the air-exposed part or use of the FVMC underestimated the Θ for a given K. The difference was more pronounced between AVMC and FVMC than between two different dielectric constants, i.e. accounting for air-exposure, Kac, and not accounting for air-exposure, Kau. When the existing empirical models were compared with the fitted results, most underestimated the relation based on the AVMC. This indicates that published empirical models do not reflect the effect of deformation on the determination of Θ in our forest soil. Correct use of the Θ expression has more impact on determining moisture content of a deformable soil than the accommodation of travel time through the air-exposed region of TDR probe.

Notes: We define the apparent frequency effect in induced polarization (IP) as the relative difference between apparent resistivities measured using DC excitation on the one hand and high-frequency excitation (when the IP effect vanishes) on the other. Assuming a given threshold for the minimum detectable anomaly in the apparent frequency effect, the depth of detection of a target by IP can be defined as that depth below which the target response is lower than the threshold for a given electrode array. Physical modelling shows that for the various arrays, the depth of detection of a highly conducting and volume polarizable target agrees closely with the depth of detection of an infinitely conducting and non-polarized body of the same shape and size. The greatest depth of detection is obtained with a two-electrode array, followed by a three-electrode array, while the smallest depth of detection is obtained with a Wenner array when the array spread is in-line (i.e. perpendicular to the strike direction). The depth of detection with a Wenner array improves considerably and is almost equal to that of a two-electrode array when the array spread is broadside (i.e. along the strike direction).

Notes: An automatic tomography algorithm, based on differential semblance optimization (DSO), has been used to invert real cross-well seismic data for the background velocity. The method relies on the first-arrival transmitted waves. Given a background velocity model, the traveltimes between the sources and the receivers are computed, then semblance panels are created by back-propagating the data traces. If the velocity model is correct all the first-arrival transmitted waves will be aligned in the semblance panels. The DSO method consists of finding the background velocity by minimizing the L2-norm of the difference between adjacent back-propagated traces. Thanks to the good behaviour of this DSO cost function about the solution, a local (gradient) optimization can be performed. This provides a relatively fast algorithm when ray tracing and analytic computation of the gradient are used.Unfortunately the method fails in the presence of caustics in the data. However, this difficulty can be circumvented by applying suitable masks to the data. This approach is first applied to a synthetic example then to two real data sets: the McElroy data set recorded in West Texas and the NIMR data set recorded in Oman. The results are quite encouraging and similar to those obtained with classical tomography.

Notes: This paper investigates the relative merits and effectiveness of cross-hole resistivity tomography using different electrode configurations for four popular electrode arrays: pole–pole, pole–bipole, bipole–pole and bipole–bipole. By examination of two synthetic models (a dipping conductive strip and a dislocated fault), it is shown that besides the popular pole–pole array, some specified three- and four-electrode configurations, such as pole–bipole AM–N, bipole–pole AM–B and bipole–bipole AM–BN with their multispacing cross-hole profiling and scanning surveys, are useful for cross-hole resistivity tomography. These configurations, compared with the pole–pole array, may reduce or eliminate the effect of remote electrodes (systematic error) and yield satisfactory images with 20% noise-contaminated data. It is also shown that the configurations which have either both current electrodes or both potential electrodes in the same borehole, i.e. pole–bipole A–MN, bipole–pole AB–M and bipole–bipole AB–MN, have a singularity problem in data acquisition, namely low readings of the potential or potential difference in cross-hole surveying, so that the data are easily obscured by background noise and yield images inferior to those from other configurations.

Notes: A simple analytical solution is presented for computing direct current (DC) electric field distortion due to a small cube in a homogeneous half-space, measured with a dipole–dipole array on the surface. Both the transmitter and the receiver may have any orientation; furthermore their position on the horizontal surface and the depth of the cube can be freely selected. It is shown that a simple approximate analytical method may replace more complicated 3D numerical modelling algorithms.The approximation lies in the linearization of the problem: the secondary source (i.e. the cube) is considered as a system of three perpendicular electric dipoles. In spite of this first-order approximation, in the case of realistic depths z (zR≈0.1–0.5, where R is the transmitter–receiver distance), this approximate solution fits very well with true 3D numerical modelling results, and with analogue modelling results if aR≤0.1, where a is the length of the side of the cube. Due to its simplicity, this method could be used for computing DC field distortion effects, estimating parameter-sensitivities, or even determining some initial models for further inversions.

Notes: Conventional approximations of reflection traveltimes assume a small offset-to-depth ratio, and their accuracy decreases with increasing offset-to-depth ratio. Hence, they are not suitable for velocity analysis and stacking of long-offset reflection seismic data. Assuming that the offset is large, rather than small, we present a new traveltime approximation which is exact at infinite offset and has a decreasing accuracy with decreasing offset-to-depth ratio. This approximation has the form of a series containing powers of the offset from 1 to −∞. It is particularly accurate in the presence of a thin high-velocity layer above the reflector, i.e. in a situation where the accuracy of the Taner and Koehler series is poor. This new series can be used to gain insight into the velocity information contained in reflection traveltimes at large offsets, and possibly to improve velocity analysis and stacking of long-offset reflection seismic data.

Notes: The geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore-water salinity. A new field survey technique that can be used for environmental and geotechnical investigations has been developed. This study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt-water intrusion boundary in Yan, State of Kedah, northwest Malaysia. The technique was incorporated into these surveys, and it has proved to be a robust method for accurately mapping the fresh-water/saline-water boundary. The resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the Geological Survey of Malaysia at those sites.

Notes: The solutions of traveltime inversion problems are often not unique because of the poor match between the raypath distribution and the tomographic grid. However, by adapting the local resolution iteratively, by means of a singular value analysis of the tomographic matrix, we can reduce or eliminate the null space influence on our earth image: in this way, we get a much more reliable estimate of the velocity field of seismic waves. We describe an algorithm for an automatic regridding, able to fit the local resolution to the available raypaths, which is based on Delaunay triangulation and Voronoi tessellation. It increases the local pixel density where the null space energy is low or the velocity gradient is large, and reduces it elsewhere. Consequently, the tomographic image can reveal the boundaries of complex objects, but is not affected by the ambiguities that occur when the grid resolution is not adequately supported by the available raypaths.

Notes: Migration is essential to seismic imaging. It is carried out by backward extrapolation of the wavefield registered on the observation surface. The quality of images depends on the accuracy of the wavefield reconstruction at interior subsurface points. From the theory based on the exact solution of the scalar wave equation it is known that, for accurate wave extrapolation, data must be obtained from an infinite observation surface. Limiting of migration apertures, which is inevitable in practice, leads to artefacts in extrapolated fields. The distortion they cause in 2D and 3D imaging is different. In 2D migration, the artefacts known as truncation effects are much weaker than the signals being extrapolated and for this reason attract no special attention. In 3D migration, diffractions caused by an aperture edge are stronger and may create serious problems. For a circular aperture, their amplitudes are comparable to the amplitudes of the signals themselves. The study of aperture diffractions is intended to help in the search for ways of either suppressing them efficiently or deliberately utilizing them in order to improve imaging.In optics, diffractions by an aperture play a constructive role in image making. This research shows that the same may take place in seismic imaging.

Notes: Soundings achieved with the electrostatic method cannot be interpreted correctly with 1D electrical programs if the extension of the array or the conductivity of the ground are too large. A complete calculation taking into account the induction effect due to the frequency must be performed. This paper presents the solutions for overcoming the difficulties encountered in this calculation: the iterative processes which make it possible to determine the kernel functions of the Hankel transforms and the analytic integration of the terms of the electric field. Application to practical cases first illustrates the distortion of the electrostatic curves by reference to DC sounding curves. The limitation in depth of investigation is then emphasized: in practice, the investigation is limited by the skin depth corresponding to the frequency used. The examples of the soundings obtained in the city of Alexandria (Egypt) demonstrate the importance of using the complete calculation for very conductive grounds.

Notes: The use of parallel computers makes simulation of elastic waves feasible throughout large structures by means of recent advances in domain decomposition methods. We introduce a competitive parallel algorithm for the propagation of elastic waves in complex heterogeneous media using finite-element discretization. This parallel method, called the multiblock method, performs more efficiently than classical domain decomposition techniques based on substructuration, such as the Schur complement technique. It reduces considerably the amount of communication amongst processors because the interface problem between subdomains is solved by taking advantage of Huygens' principle for wave propagation. We provide some numerical examples and detailed studies on the efficiency and performance of the algorithm, proving that it is competitive and less costly, from the computational viewpoint, than algorithms based on the Schur technique.

Notes: The ability to analyse shear-wave anisotropy in a mine environment is greatly aided by using multiple source orientations of a reproducible, impulsive shear-wave source. The analysis of what is probably the first controlled source shear-wave experiment in a mine environment demonstrates clearly that shear-wave polarizations and time delays between split shear-wave arrivals are reliably measured because of the use of multiple source orientations rather than a single shear-wave source. Reliability is further aided by modelling the shear-wave source radiation pattern, which allows for the unequivocal discrimination between seismic raypaths where shear-wave splitting did and did not occur. The analysis also demonstrates the great importance of high reproducibility of the seismic source for the use of shear waves in time-lapse surveys to monitor changes in a rockmass.