bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of clayey media parameters on the negative response of a coincident loop1
Authors: El‐Kaliouby Hesham M. , Hussain Safwat A. , Bayoumi Abd El‐Rahim , A.El‐diwany Essam , Hashish Essam A.
Published: April 2006

The aim of this work is to consider the phenomenon of negative response and its detectability in a polarizable half‐space formed of Clay‐water mixture which commonly exists in water aquifers and which can be used as a simple indicator of the presence of Underground water.

We make use of an analytical treatment for the transient voltage induced in a coincident loop lying on a half‐space as a basis for our computations. A Cole‐Cole model is used to represent the Clay with appropriate parameters.

As saturated Clay is characterized by high conductivity and moderate chargeability, it is hardly detectable relative to the practical noise level. However, there are optimum Clay parameters that offer a maximum negative response. It is also observed that for a very short time constant τ in the Cole‐Cole model, the amplitude of the negative response decreases with the decrease of the time constant due to the fast decay of the polarization current.

Finally, it is found that there is an optimum value for the loop radius which gives the largest value of the negative response and this loop radius depends on the model parameters.
P‐ and S‐wave anisotropy of a synthetic sandstone with controlled crack geometryl1
Authors: Rathore J.S. , Fjaer E. , Holt R.M. , Renlie L.
Published: April 2006

A method is reported for the production of synthetic porous sandstones containing cracks of known dimensions and geometry with respect to the matrix. A synthetic sandstone was manufactured from Sand cemented with an epoxy glue. The cracks of known geometry were introduced into the material in the manufacturing stage, by emplacing thin metallic discs in the Sand‐epoxy matrix. These discs were chemically leached out of the consolidated porous sandstone. Acoustic anisotropy. and shear‐wave splitting were observed in the synthetic sandstones. For the dry sample the observed angular dependence of the P‐ and S‐ wave velocities (at 100 kHz) compares well, qualitatively, with the theoretical models of Hudson and of Thomsen. Quantitatively, however, the experimental data fits Hudson's model better. For the case of a saturated sample the experimental results are in excellent agreement with Thomsen's model. Hudson's model, on the other hand, predicts a different angular dependence for P‐waves. This demonstrates that the concept of fluid transfer between cracks and the ambient porosity can be a significant process. The results reported here are from the first successful experiment in which the theoretical models were tested on a porous material containing a known crack geometry.
Use of traveltime skips in refraction analysis to delineate velocity inversion1
Authors: Tewari H.C. , Dixit M.M. , Murty P.R.K.
Published: April 2006

First arrival refraction data does not normally provide any indication of the velocity inversion problem. However, under certain favourable circumstances, when the low‐velocity layer (LVL) is considerably thicker than the overlying higher‐velocity layer (HVL), the velocity inversion can be seen in the form of a traveltime skip. Model Studies show that in such cases the length of the HVL traveltime branch can be used to determine the thickness of the HVL and the magnitude of the traveltime skip in order to determine the thickness of the LVL. This is also applicable in the case of field data.
Frequency‐domain modelling of airborne electromagnetic responses using staggered finite differences1
Authors: Newman Gregory A. , Alumbaugh David L.
Published: April 2006

A 3D frequency‐domain EM modelling code has been implemented for helicopter electromagnetic (HEM) simulations. A vector Helmholtz equation for the electric fields is employed to avoid convergence problems associated with the first‐order Maxwell's equations when air is present. Additional stability is introduced by formulating the problem in terms of the scattered electric fields. With this formulation the impressed dipole source is replaced with an equivalent source, which for the airborne configuration possesses a smoother spatial dependence and is easier to model. In order to compute this equivalent source, a primary field arising from dipole sources of either a whole space or a layered half‐space must be calculated at locations where the conductivity is different from that of the background.

The Helmholtz equation is approximated using finite differences on a staggered grid. After finite‐differencing, a complex‐symmetric matrix system of equations is assembled and preconditioned using Jacobi scaling before it is solved using the quasi‐minimum residual (QMR) method. The modelling code has been compared with other 1D and 3D numerical models and is found to produce results in good agreement.

We have used the solution to simulate novel HEM responses that are computationally intractable using integral equation (IE) solutions. These simulations include a 2D conductor residing at a fault contact with and without topography. Our simulations show that the quadrature response is a very good indicator of the faulted background, while the in‐phase response indicates the presence of the conductor. However when interpreting the in‐phase response, it is possible erroneously to infer a dipping conductor due to the contribution of the faulted background.
Full frequency‐range transient solution for compressional waves in a fluid‐saturated viscoacoustic porous medium1
Authors: Carcione José M. , Ouiroga‐Goode Gerardo
Published: April 2006

An analytical transient solution is obtained for propagation of compressional waves in a homogeneous porous dissipative medium. The solution, based on a generalization of Biot's poroelastic equations, holds for the low‐ and high‐frequency ranges, and includes viscoelastic phenomena of a very general nature, besides the Biot relaxation mechanism. The viscodynamic operator is used to model the dynamic behaviour associated with the relative motion of the fluid in the pores at all frequency ranges. Viscoelasticity is introduced through the standard linear solid which allows the modelling of a general relaxation spectrum. The solution is used to study the influence of the material properties, such as bulk moduli, porosity, viscosity, permeability and intrinsic attenuation, on the kinematic and dynamic characteristics of the two compressional waves supported by the medium. We also obtain snapshots of the static mode arising from the diffusive behaviour of the slow wave at low frequencies.
Near‐surface layer traveltime inversion: a synthetic example1
Authors: Bloor Robert
Published: April 2006

The near‐surface layer is modelled as a constant‐velocity layer with varying thickness. The base of the layer is described by a B‐spline curve. The optimum model is calculated by minimizing, with respect to the model parameters, the difference between traveltimes predicted by the model and those observed in the data. Once a model has been produced, corrections that are dependent on the raypath geometry through the near‐surface layer can be calculated.

The effect of the near‐surface layer is normally considered to be consistent at each shot or geophone station for all traveltimes arriving at that location (the surface‐consistent approximation). This assumption linearizes the problem, allowing timeshifts to be calculated and the traveltimes corrected to a chosen datum, representing static corrections. The single correction at each point is an averaged correction, based on an assumption that is particularly inaccurate in the presence of lateral variations of velocity or thickness of the surface layer, in the presence of large surface layer velocities or in the presence of a thick surface layer. The method presented considers the non‐linear relationship between data and model explicitly, hence the correction that is dependent on the raypath. Linearization removes this dependence and reduces the problem to a surface‐consistent approximation.

The method is applied to synthetic data calculated from a model with surface layer variations. Comparisons are made between the corrected data resulting from the method described here and the conventional surface‐consistent approach. From these results it becomes apparent that the near‐surface layer inversion method presented here can reproduce accurate models and correct for near‐surface layer effects in cases where conventional methods encounter difficulties. Additionally the method can be readily extended to 3D.
Two field applications of the rotating current EM method1
Authors: Hall S.H.
Published: April 2006

The rotating current EM method has been applied to the delineation of two conductive orebodies, Elura near Cobar, NSW, and Thalanga near Charter's Towers, Queensland. The field data were collected in the form of observations of the vertical magnetic field strength ratio and phase difference using a Turam‐style receiver with twin vertical coils. By reconstituting this data back to the ring source field and phase, i.e. the observed Hz, phasor, it is possible to present contoured maps of the EM field. Anomaly phasors are obtained by subtracting theoretical phasors from the observed phasors in the complex plane of the Hz phasor. The theoretical phasors for the finite source are based on horizontally layered, half‐space earth models, computed at each point of the survey grids, then normalized to selected points of the observed fields. Use is made of the intrinsic circular symmetry of the method in X–Y plots of field versus source‐receiver distance to ascertain geoelectric parameters for the earth models. A steel picket fence at Thalanga is modelled by a line source grounded at each end and its Hz, phasor is removed by the same process.

A considerable improvement in anomaly delineation is gained over previous Turam‐style anomalies and the two survey examples illustrate the limitations of the method in the presence of a conductive overburden (Elura) and its abilities in the absence of a conductive overburden (Thalanga).
Seismic inversion through Tabu Search1
Authors: Vinther Rikke , Mosegaard Klaus
Published: April 2006

Highly non‐linear seismic trace inversion problems can be solved efficiently by an implementation of Tabu Search, a meta‐heuristic method related to artificial intelligence. The implementation under consideration is a deterministic, global search that combines the advantages ofa local search, giving a quick descent to local misfit minima, with an ability to cross misfit barriers in the model space. Once Tabu Search has found an area of low misfit, it performs an extensive exploration of its deepest points. This property makes it possible to use Tabu Search for a semiquantitative resolution and uncertainty analysis of the inverse problem.
Event‐oriented velocity estimation based on prestack data in time or depth domain1
Authors: Iversen Einar , Gjøystdal Håvar
Published: April 2006

A 2D reflection tomographic method is described, for the purpose of estimating an improved macrovelocity field for prestack depth migration. An event‐oriented local approach of the ‘layer‐stripping’ type has been developed, where each input event is defined by its traveltime and a traveltime derivative, taken with respect to one of four coordinates in the source/receiver and midpoint half‐offset systems.

Recent work has shown that the results of reflection tomography may be improved by performing event picking in a prestack depth domain. We adopt this approach and allow events to be picked either before or after prestack depth migration. Hence, if events have been picked in a depth domain, such as the common‐shot depth domain or the common‐offset depth domain, then a depth‐time transformation is required before velocity estimation. The event transformation may, for example, be done by conventional kinematic ray tracingr and with respect to the original depth‐migration velocity field. By this means, we expect the input events for velocity updating to become less sensitive to migration velocity errors.

For the purpose of velocity estimation, events are subdivided into two categories; reference horizon events and individual events. The reference horizon events correspond to a fixed offset in order to provide basic information about reflector geometry, whereas individual events, corresponding to any offset, are supposed to provide the additional information needed for velocity estimation. An iterative updating approach is used, based on calculation of derivatives of event reflection points with respect to velocity. The event reflection points are obtained by ray‐theoretical depth conversion, and reflection‐point derivatives are calculated accurately and efficiently from information pertaining to single rays. A number of reference horizon events and a single individual event constitute the minimum information required to update the velocity locally, and the iterations proceed until the individual event reflection point is consistent with those of the reference horizon events. Normally, three to four iterations are sufficient to attain convergence. As a by‐product of the process, we obtain so‐called uncertainty amplification factors, which relate a picking error to the corresponding error in the estimated velocity or depth horizon position.

The vector formulation of the updating relationship makes it applicable to smooth horizons having arbitrary dips and by applying velocity updating in combination with a flexible model‐builder, very general macro‐model structures can be obtained. As a first step in the evaluation of the new method, error‐free traveltime events were generated by applying forward ray tracing within given macrovelocity models. When using such ‘perfect’ observations, the velocity estimation algorithm gave consistent reconstructions of macro‐models containing interfaces with differential dip and curvature, a low‐velocity layer and a layer with a laterally varying velocity function.
Impact of climate change on grassland production and soil carbon worldwide
Authors: PARTON W.J. , SCURLOCK J.M.O. , OJIMA D.S. , SCHIMEL D.S. , HALL D.O. ,   SCOPEGRAM GROUP MEMBERS
Published: April 2006

The impact of climate change and increasing atmospheric CO2 was modelled for 31 temperate and tropical grassland sites, using the CENTURY model. Climate change increased net primary production, except in cold desert steppe regions, and CO2 increased production everywhere. Climate change caused soil carbon to decrease overall, with a loss of 4 Pg from global grasslands after 50 years. Combined climate change and elevated CO2 increased production and reduced global grassland C losses to 2 Pg, with tropical savannas becoming small sinks for soil C. Detection of statistically significant change in plant production would require a 16% change in measured plant production because of high year to year variability in plant production. Most of the predicted changes in plant production are less than 10%.
Historical records of the occurrence of butterflies in Britain: examples showing associations between annual number of records and weather
Authors: POLLARD E. , MOSS D.
Published: April 2006

Historical records (1900–66) from the Lepidoptera Recording Scheme were used to examine associations with weather for three butterfly species Ladoga Camilla, Celastrina argiolus and Nymphalis polychloros. For each species, a series of equations was examined in which the number of records per year was considered to be a function of (1) the number of records in the previous year and (2) temperature or rainfall in the months leading up to the current flight‐period. Significant associations with weather were found for all species. Further multiple regression equations were obtained, using a stepwise procedure to select weather variables contributing separately to annual variation in the number of records. For L. Camilla and C. argiolus, predictions from these equations were significantly correlated with data on changes in abundance for the later period 1976–91. No recent data exist for JV. polychloros, which is now very rare, or possibly extinct, in Britain. Similar historic data are available for other butterfly species and for other taxa. It is suggested that these types of data have potential for the study, and perhaps prediction, of some effects of climate change.
Contrasting effects of tropospheric ozone on five native herbs which coexist in calcareous grassland
Authors: WARWICK KEVIN ROBERT , TAYLOR GAIL
Published: April 2006

The aim of this study was to examine the effects of increased tropospheric ozone concentrations on the growth and morphology of five native herbs commonly found to coexist in calcareous grassland in areas of Britain and continental Europe: Anthyllis vulneraria L., Cirsium acaule (L.) Scop., Festuca ovina L., Pilosella offtcinarum F. Shultz & Shultz‐Bip and Lotus comiculatus L.

In a chronic fumigation (mean O3 concentration of 71 ppb (71 nl 1−1) for 7 h d−1 AOT40 4585 ppb‐h) which lasted for 21 d, the effects of ozone were assessed using classical growth analysis. Large reductions in mean relative growth rates for shoot and root weight and root length were observed for the two legumes (Fabaceae) Lotus corniculatus and Anthyllis vulneraria, although these were only statistically significant for Lotus corniculatus. Significant reductions in specific root length (length per unit dry weight) were found for Cirsium acaule and Pilosella officinarum (Asteraceae), while for Festuca ovina (Poaceae) the allometric coefficient was reduced significantly following exposure to ozone.

An acute fumigation (mean O3 concentration of 196 ppb, 7 h) resulted in a range of visible injury, from no injury (Festuca ovina and Pilosella officinarum) through moderate levels of injury (Cirsium acaule and Lotus corniculatus) to extensive and widespread injury (Anthyllis vulneraria). Scoring of visible damage showed that this was only statistically significant for the two legumes, Lotus corniculatus and Anthyllis vulneraria.

These results suggest that native herbs may differ in their sensitivity to tropospheric ozone. Both chronic and acute exposures revealed that members of the Fabaceae may be most sensitive to ozone pollution, but the study also suggests that subtle changes in root morphology occurred for members of the Asteraceae. These findings are discussed in relation to the critical levels of ozone set recently for plants and the implications of increasing tropospheric ozone for the conservation of native plant communities.
Estimating canopy conductance to ozone uptake from observations of evapotranspiration at the canopy scale and at the leaf scale*
Authors: MASSMAN W.J. , GRANTZ D.A.
Published: April 2006

Stomatal uptake by vegetation is often the major sink for the destruction of tropospheric ozone. Using data obtained during the summer of 1991 at a grape vineyard and a cotton field in the San Joaquin Valley of California, we compare canopy (stomatal) conductances to ozone estimated (1) from eddy covariance ozone flux data (2) from eddy covariance evapotranspiration data and (3) by scaling leaf trans pi rational conductance to the canopy level using a canopy radiative transfer model. These simultaneous data, obtained at two levels of biological organization and for two trace gases, allow us to contrast the pathways for canopy‐atmosphere exchange of water vapour and ozone, to evaluate limitations to scaling from leaf to canopy, and to predict ozone uptake parameters from those governing transpiration. At the vineyard site the eddy covariance ozone results underestimate the ET‐based (eddy covariance and leaf scaling) approaches between 25% and 36%. At the cotton site the ozone‐based results overestimate the ET‐based approaches between 9% and 62%. A number of modelling and measurement uncertainties are of appropriate magnitude to reconcile these estimates. Some of the possible causes for these discrepancies that are discussed include NO effects, mesophyll resistances to ozone uptake and flaws in the K‐theory (first‐order closure) approach on which the canopy‐scale analysis is based. Nevertheless, both canopy and single leaf measurements of conductance for water vapour provide acceptable estimates of conductance for ozone, but further experiments in which all are measured simultaneously are suggested.
Leaf senescence and decline of end‐of‐season gas exchange in five temperate deciduous tree species grown in elevated CO2concentrations
Authors: McCONNAUGHAY K.D.M. , BASSOW S.L. , BERNTSON G.M. , BAZZAZ F.A.
Published: April 2006

We measured rates of leaf senescence and leaf level gas exchange during autumnal senescence for seedlings of five temperate forest tree species under current and elevated atmospheric CO2concentrations and low‐ and high‐nutrient regimes. Relative indices of whole canopy carbon gain, water loss and water use efficiency through the senescent period were calculated based on a simple integrative model combining gas exchange per unit leaf area and standing canopy area per unit time. Seedlings grown under elevated [CO2] generally had smaller canopies than their current [CO2]‐grown counterparts throughout most of the senescent period. This was a result of smaller pre‐senescent canopies or accelerated rates of leaf drop. Leaf‐level photosynthetic rates were higher under elevated [CO2] for grey birch canopies and for low‐nutrient red maple and high‐nutrient ash canopies, but declined rapidly to values below those of their current [CO2] counterparts by midway through the senescent period. CO2enrichment reduced photosynthetic rates for the remaining species throughout some or all of the senescent period. As a result of smaller canopy sizes and reduced photosynthetic rates, elevated [CO2]‐grown seedlings had lower indices of whole canopy end‐of‐season carbon gain with few exceptions. Leaf level transpiration rates were highly variable during autumnal senescence and neither [CO2] nor nutrient regime had consistent effects on water loss per unit leaf area or integrated whole canopy water loss throughout the senescent period. Indices of whole canopy, end‐of‐season estimates of water use efficiency, however, were consistently lower under CO2enrichment, with few exceptions. These results suggest that whole canopy end‐of‐season gas exchange may be altered significantly in an elevated [CO2] world, resulting in reduced carbon gain and water use efficiency for many temperate forest tree seedlings. Seedling growth and survivorship, and ultimately temperate forest regeneration, could be reduced in CO2‐enriched forests of the future.
Responses of a C3 and a C4 perennial grass to elevated CO2 and temperature under different water regimes
Authors: HUNT H. W. , ELLIOTT E. T. , DETLING J. K. , MORGAN J. A. , CHEN D.‐X.
Published: April 2006

An experiment was carried out to determine the effects of elevated CO2, elevated temperatures, and altered water regimes in native shortgrass steppe. Intact soil cores dominated by Bouteloua gracilis, a C4 perennial grass, or Pascopyrum smithii, a C3 perennial grass, were placed in growth chambers with 350 or 700 μL L−1 atmospheric CO2, and under either normal or elevated temperatures. The normal regime mimicked field patterns of diurnal and seasonal temperatures, and the high‐temperature regime was 4 °C warmer. Water was supplied at three different levels in a seasonal pattern similar to that observed in the field.

Total biomass after two growing seasons was 19% greater under elevated CO2, with no significant difference between the C3 and C4 grass. The effect of elevated CO2 on biomass was greatest at the intermediate water level. The positive effect of elevated CO2 on shoot biomass was greater at normal temperatures in B. gracilis, and greater at elevated temperatures in P. smithii. Neither root‐to‐shoot ratio nor production of seed heads was affected by elevated CO2.

Plant tissue N and soil inorganic N concentrations were lower under elevated Co2, but no more so in the C3 than the C4 plant. Elevated CO2 appeared to increase plant N limitation, but there was no strong evidence for an increase in N limitation or a decrease in the size of the CO2 effect from the first to the second growing season. Autumn samples of large roots plus crowns, the perennial organs, had 11% greater total N under elevated CO2, in spite of greater N limitation.
Seasonal response of photosynthesis to elevated CO2in loblolly pine (Pinus taedaL.) over two growing seasons
Authors: LEWIS JAMES D. , TISSUE DAVID T. , STRAIN BOYD R.
Published: April 2006

Trees growing in natural systems undergo seasonal changes in environmental factors that generate seasonal differences in net photosynthetic rates. To examine how seasonal changes in the environment affect the response of net photosynthetic rates to elevated CO2, we grewPinus taedaL. seedlings for three growing seasons in open‐top chambers continuously maintained at either ambient or ambient + 30 Pa CO2. Seedlings were grown in the ground, under natural conditions of light, temperature nd nutrient and water availability. Photosynthetic capacity was measured bimonthly using net photosynthetic rate vs. intercellular CO2partial pressure (A‐Ci) curves. Maximum Rubisco activity (Vcmax) and ribulose 1,5‐bisphosphate regeneration capacity mediated by electron transport (Jmax) and phosphate regeneration (PiRC) were calculated fromA‐Cicurves using a biochemically based model. Rubisco activity, activation state and content, and leaf carbohydrate, chlorophyll and nitrogen concentrations were measured concurrently with photosynthesis measurements. This paper presents results from the second and third years of treatment.

Mean leaf nitrogen concentrations ranged from 13.7 to 23.8 mg g−1, indicating that seedlings were not nitrogen deficient. Relative to ambient CO2seedlings, elevated CO2increased light‐saturated net photosynthetic rates 60–110% during the summer, but < 30% during the winter. A relatively strong correlation between leaf temperature and the relative response of net photosynthetic rates to elevated CO2suggests a strong effect of leaf temperature. During the third growing season, elevated CO2reduced Rubisco activity 30% relative to ambient CO2seedlings, nearly completely balancing Rubisco and RuBP‐regeneration regulation of photosynthesis. However, reductions in Rubisco activity did not eliminate the seasonal pattern in the relative response of net photosynthetic rates to elevated CO2. These results indicate that seasonal differences in the relative response of net photosynthetic rates to elevated CO2are likely to occur in natural systems.
Effects of elevated atmospheric CO2 on fine root length and distribution in an oak‐palmetto scrub ecosystem in central Florida
Authors: DAY FRANK P. , WEBER EVERETT P. , HINKLE C. ROSS , DRAKE BERT G.
Published: April 2006

Atmospheric CO2 concentration is rising and it has been suggested that a portion of the additional carbon is being sequestered in terrestrial vegetation and much of that in below‐ground structures. The objective of the present study was to quantify the effects of elevated atmospheric CO2 on fine root length and distribution with depth with minirhizotrons in an open‐top chamber experiment in an oak‐palmetto scrub ecosystem at Kennedy Space Centre, Florida, USA. Observations were made five times over a period of one and a half years in three ambient chambers (350 p.p.m. CO2), three CO2 enriched chambers (700 p.p.m. CO2), and three unchambered plots. Greater root length densities were produced in the elevated CO2 chambers (14.2 mm cm−2) compared to the ambient chambers (8.7 mm cm−2). More roots may presumably lead to more efficient acquisition of resources. Fine root abundance varied significantly with soil depth, and there appeared to be enhanced proliferation of fine roots near the surface (0–12 cm) and at greater depth (49–61 cm) in the elevated CO2 chambers. The vertical root distribution pattern may be a response to availability of nutrients and water. More studies are needed to determine if increased root length under CO2 enriched conditions actually results in greater sequestering of carbon below ground.
Reefs happen
Authors: KINZIE ROBERT A. , BUDDEMEIER ROBERT W.
Published: April 2006

Corals and coral reefs confront us with a variety of paradoxes in terms of their responses to global change. The species appear evolutionarily long‐lived and stable, and combinations of organisms recur and persist at levels ranging from endosymbiosis to palaeocommunity structure. The fact that these organisms and communities occupy a seemingly precarious environment near the common interface of land, sea, and air suggests that they possess powerful adaptive and acclimative mechanisms, and the special characteristics associated with their range of reproductive options, their modular (colonial) form, and their symbiotic associations provide multiple pathways for adaptation. At the same time, they are widely considered to be vulnerable to anthropogenic stresses, and to show signs of deterioration on a global scale.

Interest in corals is further enhanced by their unique position with regard to the carbon cycle, with inorganic and organic carbon metabolisms that are of comparable magnitudes. The durable limestone structures they create modify the shallow‐water environment, and their mineral skeletons preserve in their isotopic, chemical, and structural characteristics records of past environmental conditions. Whether as survivors, recorders, or victims, their relationship to global change is fascinating and instructive. This paper provides a general background and context for the specific papers that make up this topical issue of Global Change Biology.
Boundary layer budgets for regional estimates of scalar fluxes
Authors: DENMEAD O.T. , RAUPACH M.R. , DUNIN F.X. , CLEUGH H.A. , LEUNING R.
Published: April 2006

The paper considers the theory and application of budget techniques for regional scalar flux estimation using the daytime convective boundary layer (CBL) and the nocturnal boundary layer (NBL). CBL techniques treat the well mixed layer of air between heights of, say, 100 m and 1000 m as an integrator of surface fluxes along the path of a column of air moving over the landscape. They calculate the average surface flux from the scalar concentration in and above the mixed layer, and the CBL height. The flux estimates are averaged over regions of 10–104 km2 extending 10 to 100 km upwind.

An integral form of the CBL budget is used to estimate daily regional rates of CO2 uptake and evaporation from three data sets. There was plausible agreement between the estimates and locally measured fluxes. CBL budgets have great potential for estimating regional scalar fluxes, but there is an urgent need for validation through direct measurements of fluxes and budget parameters.

NBL budgets are useful when low‐level, radiative inversions inhibit vertical mixing. Surface scalar fluxes can then be estimated from the rate of concentration change below the inversion. An example application for estimating the nocturnal CO2 flux is given. While simple in concept, NBL budgets are more difficult to apply in practice because of the unpredictability of the depth of the layer and sometimes, its absence altogether. On the other hand, the depth of the atmospheric mixing chamber is better defined, few assumptions are required and the concentration changes usually will be larger and hence more easily detectable than in CBL budgetting.
Eddy‐correlation system for long‐term monitoring of fluxes of heat, water vapour and CO2
Authors: GRELLE ACHIM , LINDROTH ANDERS
Published: April 2006

An eddy‐correlation system is presented that was designed with special focus on long‐term measurements of turbulent fluxes in the atmospheric boundary layer. It consists of a SOLENT sonic anemometer, a fast temperature sensor, and a LI‐COR LI 6262 closed‐path infrared gas analyser. The use of a fast temperature sensor turned out to be necessary because of errors in the sound virtual temperature measured by the sonic anemometer at high wind speeds. The components are combined with special attention paid to protection against lightning and other environmental stresses. The data acquisition program SOLCOM runs on standalone systems or in a network environment and performs ‘quasi on‐line’ data processing, on‐line graphical display of single data and fluxes, and on‐line correction of the raw data. Raw data can be stored continuously on DAT tapes. All data handling can be done by remote access, thus only a minimum amount of m situ maintenance is required. Power spectra of vertical and longitudinal wind speed, air temperature, air humidity and carbon dioxide concentration showed to follow the ‐2/3 law quite well. There was some noise in the high frequency range of the carbon dioxide spectrum. However, the corresponding cross spectra with the vertical wind component showed less deviation from a straight line in the high frequency range. The sum of convective heat fluxes and soil heat flux showed good agreement with the measured net radiation for several months and it was concluded that the system described here constitute a good platform for long‐term flux measurements over forest.
Early needle senescence and thinning of the crown structure of Picea abies as induced by chronic SO2 pollution. II. Field data basis, model results and tolerance limits
Authors: SLOVIK STEFAN
Published: April 2006

Field data on the sulphur and cation budget of growing Norway spruce canopies (Picea abies [L.] Karst.) are summarized. They are used to test a spruce decline model capable of quantifying effects of chronic SO2 pollution on spruce forests. At ambient SO2 concentrations, acute SO2 damage is rare, but exposure to polluted air produces reversible thinning of the canopy structure with a half‐time of a few years. Canopy thinning in the spruce decline model is highest (i) at elevated SO2 pollution, (ii) in the mountains, (iii) at unfertilized sites with poor K+, Mg2+ or Zn2+ supply, (iv) at low spruce litter decomposition rates, and (v) acidic, shallow soils at high annual precipitation rates in the field and vice versa. Model application using field data from Würzburg (moderate SO2 pollution, alkaline soils, no spruce decline) and from the Erzgebirge (extreme SO2 pollution, acidic soils in the mountains, massive spruce decline) predicts canopy thinning by 2–11% in Würzburg and by 45–70% in the Erzgebirge. The model also predicts different SO2‐tolerance limits for Norway spruce depending on the site elevation and on the nutritional status of the needles. If needle loss of more than 25% (damage class 2) is taken to indicate ‘real damage’ exceeding natural variances, then for optimum soil conditions SO2 tolerance limits range from (27.3 ± 7.4) μg m−3 to (62.6 ± 16.5) μg m−3. For shallow and acidic soils, SO2 tolerance limits range from (22.0 ± 5.5) μg m−3 to (37.4 ± 7.5) μ m−3. These tolerance limits, which are calculated on an ecophysiological data basis for Norway spruce are close to epidemiological SO2‐toIerance limits as recommended by the IUFRO, UN‐ECE and WHO. The observed statistical regression slope of the plot (damaged spruce trees vs. SO2‐pollution) in west Germany is confirmed by modelling (6% error). Model application to other forest trees allows deduction of the observed sequence of SO2‐sensitivity: Abies > Picea > Pinus > Fagus > Quercus. Thus, acute phytotoxicity of SO2 seems not to be involved in ‘forest decline’. Chronic SO2‐pollution induces massive canopy thinning of Abies alba and Picea abies only at unfavourable sites, where natural stress factors and secondary effects of SO2pollution act together to produce tree decline.
THE USE OF SODIUM METABISULPHITE IN SILAGE MAKING
Authors: Murdoch J. C. , Holdsworth Muriel C.
Published: April 2006

Three trials in which metabisulphite was used as a silage additive are described and the results discussed.

The data from two small‐scale trials suggests that metabisulphite and molasses each have a similar effect on the quality of the silage produced, and that wilting appeared to be more effective than either of these two additives.

A comparison of silages in two large‐scale trials indicates the necessity for uniform distribution of the metabisulphite.
FURTHER OBSERVATIONS ON GRASSLAND MANAGEMENT FOR MEAT PRODUCTION
Authors: Alder F. E. , Redford R. A.
Published: April 2006

This paper deals with the second three years (April 1954 to March 1957) of a grazing‐management trial in the form of a pilot farm. The whole area of 35.5 acres was run as a self‐contained unit with the object of providing grazing for as long a period of the year as possible. A system of rotational grazing was used throughout with strip‐ and fold‐grazing at certain seasons. Excess herbage was conserved as silage and hay and fed back to stock during the winter. Beef‐type steers and ewes and lambs grazed the pastures, the saleable products being fat cattle, lambs and wool. Results are presented and discussed in relation to stock numbers, animal health, herbage production and botanical composition, fertilizer application and the levels of production achieved. Over‐all average fertilizer dressings per acre for the three years were equivalent to 5 cwt. per acre nitro‐chalk, 2 cwt. per acre superphosphate and 1 cwt. per acre muriate of potash. The outputs of utilised starch equivalent in 1954–5, 1955–6 and 1956–7 were 2970, 2850 and 2280 1b. per acre, respectively. On the basis of the six years' results it is concluded that high production can be achieved from a system where the object is an extended grazing season; that broadcast leys can be used for winter grazing and the botanical composition of the sward maintained; that self‐fed silage can be a satisfactory feed for fattening cattle; that a grazing plan is a valuable guide to management; and that the pilot‐farm method is of value for certain agronomic experiments.
THE USE OF EPIDERMAL CHARACTERISTICS FOR THE IDENTIFICATION OF GRASSES IN THE LEAFY STAGE
Authors: Davies Ieuan
Published: April 2006

The possibility of using microscopic characteristics of the leaf epidermis as aids to the identification of some British agricultural grasses in the vegetative condition has been investigated.

The occurrence of the following types of differentiated cells on the leaf‐sheath was markedly affected by the stage of growth of the tiller: silica cells, silico‐suberose couples, cork cells, asperities and incipient asperities. These cells were frequently absent or confined to the base of the sheath in vegetative tillers, but they occurred over most of the sheath in culm leaves. Silica cells tended to preponderate in young tillers and silico‐suberose couples and cork cells in the reproductive stage. The inter‐nerve epidermis of the leaf‐blade was generally the least affected by growth stage; although less differentiated than the sheath, it was found to be the most useful location for identification purposes. Species separable on the basis of the above‐mentioned characters of the leaf‐blade were:—

Tall fescue (Festuca arundinacea) from meadow fescue (F. pratensis)

Heath‐grass (Sieglingia decumbens) from smooth‐stalked meadow grass (Poa pratensis)

Sheep's fescue (F. ovina), from mat‐grass (Nardus stricta) wavy hair‐grass (Deschampsia flexuosa) and bristle‐leaved bent (Agrostis setacea).

Timothy (Phleum pratense), meadow foxtail (Ahpecurus pratensis) and bent (Agrostis spp.) were separable on the following characteristics, which were not affected by growth stage: the occurrence of crystal clusters precipitated by hot water in timothy and occasionally in meadow foxtail, but not in Agrostis species, the peculiar shape of undifferentiated cells of the nerve epidermis in Agrostis species, and the dense cover of asperities on the ligules of Agrostis spp. and Ahpecurus pratensis.
PARTIAL WILTING OF GRASS CROPS FOR SILAGE
Authors: Nash M. J.
Published: April 2006

The possibilities of the wilting process have been investigated, with the ultimate object of determining its effect on the quality of farm silage. Attention has been confined mainly to mild or partial wilting, rather than severe wilting, since the danger of ensiling excessively dry material, especially when it is not chopped, is well recognised.

Preliminary field tests were conducted to determine the rate and extent of the fall in moisture content in long and in bruised herbage, wilted for periods not exceeding 24 hours. Subsequently the wilted silages were made in experimental silos and, finally, in trench silos on a farm scale. This first paper deals with the field trials. Results show that important reductions in moisture content can be obtained in all but very poor weather. In good weather, moisture content may easily fall from the 80% to the 70% level; in poor weather (cool, overcast, with occasional showers) moisture loss still occurs.
CHANGES IN CHEMICAL COMPOSITION AND THE LOSS OF NUTRIENTS IN TRIPODED AND SWATH‐CURED HAY
Authors: Murdoch J. C. , Foot A. S. , Head M. J. , Holdsworth Muriel C. , Hosking Zena D. , Line C.
Published: April 2006

The changes in chemical composition during haymaking, the loss of nutrients in the field and during storage, and the nutritive value of swath‐cured and tripoded hay were compared. In good weather no advantage was gained by tripoding the hay. The nutritive value of the hays made by the two methods was similar and the loss of dry matter in the field slightly lower in the swath‐cured hay. In a bad season, however, the nutrient loss in the swath‐cured hay greatly exceeded that occurring in the tripoded hay and the starch equivalent, as shown by the results of digestibility trials, was markedly lower for the swath‐cured.
THE EFFECT OF PRE‐WILTING HERBAGE ON THE COMPOSITION OF SILAGE AND ITS INTAKE BY COWS
Authors: Murdoch J. C.
Published: April 2006

Lucerne was ensiled at various dry matter contents, within the range of 19·8% to 39·6%. An increase was found in lactic acid production, with a consequent decrease in volatile acid and volatile base content, up to the level of 33·9% dry matter.

The dry matter intake of cows was increased by feeding silage with a high dry matter content.
LEY DETERIORATION AND SOIL INSECTS
Authors: Heath G. W.
Published: April 2006

Two insecticides were applied to a 5‐year‐old ley and their effects on yield and soil fauna were studied a year later. Aldrin (2 lb. actual toxicant per acre) or dieldrin (1 lb. actual toxicant per acre) was incorporated in a standard dressing of compound fertilizer.

One year after treatment the yield of dry matter was significantly higher on dieldrin plots than on plots receiving fertilizer alone. The soil fauna was examined in dieldrin and control plots. The wireworm (Agriotes spp.) populations were 80,000 and 400,000 per acre respectively. The increase in herbage yield was ascribed to the reduction in the number of wireworms. Mite and Collembola populations were very significantly reduced by dieldrin: the effect of this reduction on the breakdown of soil organic matter is discussed. A reduction in numbers of predaceous insects also followed insecticidal treatment, but it is thought that the resurgence rate of these insects would keep pace with that of wireworms.
A REVIEW OF NUTRIENT LOSSES AND EFFICIENCY OF CONSERVING HERBAGE AS SILAGE, BARN‐DRIED HAY AND FIELD‐CURED HAY
Authors: Carter W. R. B.
Published: April 2006

A review of American literature indicates that barn drying of hay and silage making are both greatly superior to the field curing of hay in preserving nutrients. This is true of total dry matter, crude protein, ether extract and ash; crude‐fibre losses are greater in silage making. Energy losses run parallel with dry matter. Bam drying of hay with heat preserves a rather greater proportion of nutrients than does silage making.

Chemical composition and digestibility are mostly a function of stage of maturity of the crop at the time of cutting. Actual carbohydrate (energy) losses are greater than protein losses in all methods. The influence of method of conservation is unimportant if conservation is properly carried out, but considerable deterioration can result from bad application. Field‐cured hay usually suffers most in this respect, due to weather damage.

The conservation processes reviewed have no influence per se on feeding value where each is applied under ideal conditions. Differences found in practice are usually linked to the stage of maturity or to weather damage, which explains the usually superior feeding value of silage and barn‐dried hay over field‐cured hay.

When the efficiency of each method is compared by determining the quantity of milk produced from equal areas of forage, conserved in the three different ways, barn‐dried hay is somewhat superior to silage, but both are greatly superior to field‐cured hay.
THE DELAYED APPLICATION OF NITROGEN FOR THE ESTABLISHMENT OF SURFACE‐SEEDED SWARDS
Authors: Roberts H. W.
Published: April 2006

It has been observed that, where surface seeding has been attempted, disappointing results occur on some sites due to delays in sowing the seeds mixture after lime and fertilizer applications have been made.

An experiment is described in which the time of application of nitrogen, in relation to the establishment and development of S24 and S23 perennial ryegrass seedlings in pots, was varied. The results of trials on this aspect of surface seeding, under conditions experienced in the north of Scotland, are also given.

More efficient utilization of nitrogen was obtained when applications were delayed until the seedlings had developed sufficiently to utilize the applied nitrogen. This delay enhanced the establishment of sown grasses under conditions where natural species, capable of responding to applied nitrogen, were present.

Where surface seeding is undertaken, consideration should be given to delaying the application of nitrogen until the sown seeds have brairded.
SOME PHYSIOLOGICAL CHARACTERISTICS AND THE AGRONOMIC IMPORTANCE OF DIPTERA DAMAGE TO GRASSES
Authors: Emecz Tibor I.
Published: April 2006

Shoot‐fly larvae cause considerable damage to cultivated grasses; it is greatest when overwintering tillers are lost, resulting in delayed emergence, decreased number of flowering heads and reduced yield of dry matter.

An increase in the number of tillers, which often follows the damage, cannot counter‐balance the losses because the new tillers are smaller.

Different varieties within species, and different genotypes within varieties, show varying degrees of susceptibility to damage, and of capacity to recover from it. Favourable growing conditions promote recovery and reduce losses.

Non‐cultivated grasses and unploughed leys are sources of infection, not only to cereals but also to cultivated grasses, and it is advisable not to put single plants or seed areas adjacent to old swards. The glasshouse is a special source of infection as it provides conditions favourable for the flies to produce extra generations at unusual times.

The importance of further investigations and the development of more economical protective techniques is stressed.
INTER‐VARIETY VARIATION IN RHODES GRASS (CHLORIS GA YANA KUNTH)
Authors: Hutton E. M.
Published: April 2006

The characters in 25 varieties of Rhodes grass introduced from Africa have been studied with a view to improving on Australian Commercial. Only the diploid Katambora and a tetraploid variety from Kenya appeared to possess a higher yield potential than Commercial. Sixty per cent of the varieties are tetraploid, the rest diploid. A degree of association occurred between the level of ploidy and some Rhodes grass characters.

Although Rhodes grass appears to be xenogamous, all the critical evidence points to an apodictic form of reproduction. Viable caryopses were extracted from harvested “seed” and the percentage of florets setting caryopses was low. Rhodes grass caryopses germinate fairly well and have a higher resistance than usual to irradiation by gamma rays.