bluuebunny/crossref_metadata_2025_split huggingface dataset:
High energy ultraviolet photo‐oxidation: a novel technique for studying physically protected organic matter in clay‐ and silt‐sized aggregates
Authors: SKJEMSTAD J. O. , JANIK L. J. , HEAD M. J. , McCLURE S. G. 
Published: July 2006

SUMMARYA novel approach to the study of organic‐matter distribution in soil microaggregates (<20 μm) using high‐energy ultraviolet (UV) radiation in the presence of oxygen (photo‐oxidation) is reported. The method quantitatively destroyed complex organic materials through oxidation, even in the presence of clay, provided the organic materials were directly exposed to the UV radiation.Photo‐oxidation of clay and silt fractions for periods up to 8 h demonstrated that a considerable proportion of the organic matter was physically protected within clay‐ and silt‐sized aggregates. In some clay fractions, up to 23% of the organic carbon could be considered as physically protected whereas in silt fractions this was as high as 36%.Infrared spectroscopy demonstrated that the materials external to both clay‐ and silt‐sized aggregates were largely proteinaecous in nature, while the materials in the interior of the aggregates resembled humic acids. These humic materials appeared to be physically shielded against photo‐oxidation, rather than being chemically recalcitrant. Using the clay‐ and silt‐sized fractions from one soil, 14C accelerator mass spectrometry demonstrated that, although both clay and silt fractions contained essentially modern carbon, after 4 h of photo‐oxidation much older organic carbon with a mean resonance time (MRT) of between 200±80 and 320±80 years before the present (BP) remained. This protection from photo‐oxidation, therefore, appears to mirror the process which physically protects organic substances in soils against microbial degradation. Photo‐oxidation of the clay‐plus‐silt fractions also resulted in a considerable reduction in particle size as the organic‐cementing agents, consisting of proteinaecous and humic materials, were oxidized.Using data from the photo‐oxidation method along with infrared spectroscopy, radiocarbon dating and scanning electron microscopy, a simple model is proposed that spatially relates the various organic structures present to their positions in the mineral aggregates.
Fluorescence spectroscopy of aqueous pine litter extracts: effects of humification and aluminium complexation
Authors: TAM S.‐C. , SPOSITO G. 
Published: July 2006

SUMMARYFluorescence excitation, emission, and synchronous‐scan spectra were obtained for aqueous extracts of needle and litter layer (O‐horizon) samples from ponderosa pine collected at a plantation site. The spectral lineshapes differed markedly between the needle and litter samples, and showed an increasing overall intensity with increasing extent of humification (increasing depth in the litter layer). At a dissolved organic C (DOC) concentration of 100 g m−3, these effects were accompanied by a general shift in spectral density from lower to higher wavelength such that, in the excitation spectra, there was increasing prominence of a peak at 390 nm. When the DOC concentration was decreased from 100 to 25 g m−3, the overall spectral intensity decreased and the peak at 390 nm in the excitation spectra of the litter samples gave way to a rising peak at 340 nm. Changes in pH from 4 to 5, characteristic of the undiluted litter extracts, produced little effect on the spectra. The addition of A1 at 40 mmol m−3 generally produced enhancement of the fluorescence intensity in all three kinds of spectra for the needle and upper litter‐layer extracts at 100 g C m−3 and pH 4. Spectral density below 320 nm in the excitation and synchronous‐scan spectra of the needle solution (possibly attributable to gentisic acid on the basis of model experiments) was, however, diminished by Al addition. For the lower litter‐layer extracts, A1 addition decreased the fluorescence intensity in excitation and emission spectra, whereas it increased the intensity in synchronous‐scan spectra. These trends indicated that the water‐soluble fluorophores in the litter layer differed significantly from those in the fresh needles, and changed with the extent of humification. The 390‐nm peak in the excitation spectrum, particularly its behaviour in the presence of added Al, may be useful as a spectral signature of products formed by litter humification processes.
Nitrate leaching from grazed grassland lysimeters: effects of fertilizer input, field drainage, age of sward and patterns of weather
Authors: SCHOLEFIELD D. , TYSON K. C. , GARWOOD E. A. , ARMSTRONG A. C. , HAWKINS J. , STONE A. C. 
Published: July 2006

SUMMARYDrained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long‐term experimental site in south‐west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha‐1 per annum to the existing permanent sward, or at 400 kg N ha‐1 to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V‐notch weirs and sampled daily for the analysis of nitrate‐N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5, 133.8 and 55.7 kg ha‐1 from the old sward that received 200 and 400 kg N ha‐1, and from the reseed that received 400 kg N ha‐1 fertilizer, respectively. Ploughing and reseeding resulted in a two‐fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm‐3 for the drained old sward that received 400 kg N ha‐1 fertilizer, to 12 mg dm‐3 for the undrained sward at 200 kg N ha‐1 fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm‐3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate concentration for a given load.
Changes in microbial biomass C, soil carbohydrate composition and aggregate stability induced by growth of selected crop and forage species under field conditions
Authors: HAYNES R. J. , FRANCIS G. S. 
Published: July 2006

SUMMARYThe effects of growth of various crop and forage species on microbial biomass C, soil carbohydrate content and monosaccharide composition, and mean weight diameter (MWD) were investigated in two field experiments. One experiment was conducted over one growing season (4 months) whereas the other had been conducted for three consecutive growing seasons (32 months). In the four‐month experiment, aggregate stability (estimated as MWD) of soil from experimental plots followed the order Italian ryegrass > prairie grass > phacelia = pea = maize. At the 32‐month site the order was perennial ryegrass > annual ryegrass > perennial white clover = barley. At both sites crops with the greatest root mass and root length density had the greatest effect on increasing MWD. In all cases, rhizosphere soil had a significantly higher microbial biomass and MWD than non‐rhizosphere soil. However, organic C, total content of acid‐hydrolysable carbohydrate and content of individual monosaccharides in acid hydrolysates were similar in rhizosphere and non‐rhizosphere soil.The fraction of soil carbohydrate extractable with hot water (representing about 6‐8% of the total carbohydrate content) was significantly higher in the rhizosphere soil. This fraction has a galactose plus mannose over arabinose plus xylose ratio of 2.1–2.3 indicating that it was predominantly of microbial origin. It is suggested that the carbohydrate fraction extractable with hot water is made up of exocellular microbial polysaccharides that are involved in stabilizing soil aggregates in the rhizosphere. By comparison with arable crop species, grass species have a larger root mass and root length density, and therefore a higher microbial biomass and larger production of carbohydrate extractable with hot water. As a result they have a more marked effect on improving soil aggregate stability.
Water uptake by aggregates
Authors: YOUNGS E. C. , LEEDS‐HARRISON P. B. , GARNETT R. S. 
Published: July 2006

SummaryThe Green & Ampt infiltration analysis is applied to the problem of the water uptake by aggregates when they are surrounded by water. Two situations are analysed, namely, when there is free escape of the displaced air and when there is no escape of the air. These extreme situations provide bounds for estimating the water uptake for the practical case when some air escapes through the aggregate's surface in the form of bubbles as the aggregate wets up. It is shown that the rate of water uptake is directly proportional to the square of the sorptivity of the aggregate material and inversely proportional to the square of the final water uptake. Experiments on spherical stabilized clay aggregates of different radii were in agreement with the theoretical analysis that predicted the observed very rapid wetting up. The analysis also showed that when there was free escape of air, the rate of advance of the wetting front into cylindrical and spherical aggregates decreased from an initially infinite value to a minimum value and then increased to an infinitely large value when the front reached the centre of the aggregate, in contrast to the continually decreasing rate into plate‐like aggregates. This was demonstrated in experiments on the radial water movement into a fine sand contained in a cone.The analysis and experimental results indicate that preferential macropore flow in aggregated soils can be initiated very rapidly when air entrapment occurs within the aggregates.
The self‐diffusion of strongly adsorbed anions in soil: a two‐path model to simulate restricted access to exchange sites
Authors: NYE P. H. , STAUNTON S. 
Published: July 2006

SummaryThe consequences of slow diffusion of strongly adsorbed solutes into soil aggregates are not fully understood. The distribution of 32P after diffusing down a soil column cannot be explained from a consideration of liquid‐phase impedance factor and isotopic exchange alone, as can that of 36CI.A model was developed that considers the soil to provide linked parallel intra‐aggregate and inter‐aggregate pathways. With this geometry, simulations agreed fairly well with experimental data when the intra‐aggregate impedance factor was 0.001, using other model parameters that had been determined in independent equilibration studies. With this intra‐aggregate impedance factor, the model yielded straight‐line plots for chloride and the overall impedance factor derived agreed closely with the experimental one. The intra‐aggregate impedance factor for 32P also agreed with the rate of reaction of the rapidly‐exchanging P fraction previously determined. The slowly‐exchanging P fraction has little influence on the P concentration profiles up to 10 d, but the small exchanged amount does have an effect at run times of 57 d.The slow intra‐aggregate diffusion of strongly adsorbed solutes decreases the amount adsorbed from a surface source of supply, and it also decreases the amount that is taken up by a surface sink. However, the interaggregate solution concentration remote from a source of supply is considerably increased, which may be important if the solute is a pollutant or a nutrient.
Critical state parameters derived from constant cell volume triaxial tests
Authors: O'SULLIVAN M.F. , CAMPBELL D.J. , HETTIARATCHI D.R.P. 
Published: July 2006

SummaryCritical state parameters were determined in constant cell volume triaxial tests on three remoulded agricultural topsoils, a sandy loam, a clay loam and a clay. Tests were made at a range of water contents. The normal consolidation lines tended to be linear on a semi‐logarithmic plot up to a degree of saturation of c. 0.85, above which the soil was incompressible but highly deformable. The slopes of the projected critical state lines were slightly greater than the slopes of the normal consolidation lines for all three soils. For each soil, both lines pivoted about a point as water content increased and, for the two lighter‐textured soils, the increases in compactibility tended to be greatest near the plastic limit. For all three soils, strength remained fairly constant with increasing water content until the soil was at around 70‐85% of the cone penetrometer plastic limit. Strength then decreased with increasing water content, with the smallest decrease in the sandy loam.
Evaluating soil maps for prediction of soil water properties
Authors: LEENHARDT D. , VOLTZ M. , BORNAND M. , WEBSTER R. 
Published: July 2006

SummaryConventional soil survey stratifies a region into mapping classes and characterizes each by a representative soil profile within it. The efficacy of the procedure for predicting particle‐size fractions, bulk density, water retention, and available water capacity (AWC) of the soil at previously unvisited sites on the Plain of Languedoc in southern France is evaluated for three scales of survey (1/10 000, 1/25 000 and 1/100 000) and is compared to that of prediction from stratified random and simple random samples. Data from 85 soil profiles on a random transect were used for evaluation.Classification partitioned the variation of the measured properties, except for AWC, well at the 1/10 000 and 1/25 000 scales, whereas classification at the 1/100 000 scale was less effective. At the 1/10 000 and 1/25 000 scales both classification and stratified random sampling were better for prediction than simple random sampling for the same total sample. On average the representative profiles proved substantially better predictors than the stratified random samples, but in most situations where soil stratification performed well efficiencies of the two predictors were similar. In essence, the more successful the classification was the more difficult it was to improve prediction by selecting representatives instead of sampling randomly within classes. These results confirmed statistically that the soil surveyor can exercise intuition and judgement to classify and select representatives.
Conservation of mineral nitrogen in restored soils at opencast coal mine sites: II. The effects of inhibition of nitrification and organic amendments on nitrogen losses and soil microbial biomass
Authors: WILLIAMSON J.C. , JOHNSON D.B. 
Published: July 2006

SummarySoils stored in stockpiles during opencast mining operations accumulate significant quantities of ammonium (of the order of 200 μg NH4+‐N g−1 soil) within the predominantly anaerobic cores of mounds. Upon stockpile dismantling and land restoration, this NH+4‐N is rapidly oxidized to NO−3‐N, which is readily lost from newly restored soil ecosystems by leaching and denitrification. Experiments were set up to examine how these significant reserves of mineral N might be conserved in such situations. Application of the nitrification inhibitor dicyandiamide was successful in minimizing NO3−‐N lost by leaching, though large concentrations of NH4+‐N were detected in drainage waters. Straw incorporation decreased nitrate leaching by up to 40%; biomass C was some 40% greater in straw‐amended than in unamended soils after 14 weeks, though biomass N was similar in both. Addition of nitrogen‐free organic materials (glucose, starch and cellulose) produced different results, with glucose amendment showing the greatest reduction in nitrate leaching in the short term (due to an apparent stimulation of denitrification) whereas addition of cellulose resulted in the most effective conservation of nitrogen over 14 weeks; this was due, at least in part, to uptake of mineral N by the soil microbial biomass.
Influence of soil properties on the response to phosphorus in some tropical soils: I. Initial response to fertilizer
Authors: WARREN G.P. 
Published: July 2006

SummaryThe availability of fertilizer P in six P‐deficient tropical soils from Brazil, Kenya, Malaysia and Indonesia was assessed by grass in a pot experiment. Grass dry matter yield (D) and fertilizer P(F) were fitted to a Mitscherlich equation: D= a−b exp(−cF), and P uptake (U) and F to the linear equation: U=α+βF. Fitted parameter β equals the proportion of P recovered in one crop and it varied widely between soils, ranging from 12 to 51%. Quantitative assessments of fertilizer‐P availability could also be made using dry‐matter data alone if the rates of fertilizer used were well distributed along the response curve, when Mitscherlich parameter c was correlated well with β.Chemical measurements were made on uncropped soil. Phosphate sorption isotherms were measured, using 32P to assess exchangeable and non‐exchangeable phosphate. The availability parameters c and β were correlated best with parameter be, the phosphate buffer capacity derived from the fitted Freundlich isotherm for exchangeable phosphate, suggesting that the mobility of exchangeable phosphate is a major influence on P availability. Al and Fe were extracted with acid oxalate, citrate‐dithionite and pyrophosphate reagents, and parameters c and β correlated best with Al extracted by acid oxalate. These relationships were inverse, showing that Al in disordered mineral forms lowers the availability of fertilizer P.
Adsorption of radiocaesium on various soils: consequences of the effects of soil: solution composition on the distribution coefficient
Authors: STAUNTON S. 
Published: July 2006

SummaryThe adsorption of a radioisotope of caesium, 137Cs, has been interpretation and ratio and solution measured on four soils with differing clay mineralogies. All measurements have been made using unwashed soils in suspensions shaken for 2 h at 20°C. The effects of concentration in potassium and caesium, the nature of the background electrolyte and the soil:solution ratio have been investigated. The results are expressed either as the distribution coefficient, KD or as Freundlich isotherms.The distribution coefficient of each of the soils decreases markedly as the concentration of caesium increases. The adsorption properties of the soils are not determined by the dominant clay mineralogy alone. Adsorption is always lower in 0.01 m CaCl2 solution than in water. The addition of potassium has relatively little effect on adsorption of trace amounts of caesium; however, KD decreases with increasing concentrations of stable caesium. The major reason for the dependence of KD on the soil: solution ratio is found to be the non‐linear adsorption isotherm; the influence of the varying compositions of the solution and exchange complex is minor.The validity of the use of a single KD value as an indicator of adsorption capacity and the meaning of the relative values of the Freundlich parameters are considered. The implications of these findings for the use of radiotracers and the usefulness of KD as an indicator of bioavailability are discussed.
Ionic‐strength and pH effects on the sorption of cadmium and the surface charge of soils
Authors: NAIDU R. , BOLAN N.S. , KOOKANA R. S. , TILLER K.G. 
Published: July 2006

SummaryTwo Oxisols (Mena and Malanda), a Xeralf and a Xerert from Australia and an Andept (Patua) and a Fragiaqualf (Tokomaru) from New Zealand were used to examine the effect of pH and ionic strength on the surface charge of soil and sorption of cadmium. Adsorption of Cd was measured using water, 0.01 mol dmp−3 Ca(NO3)2, and various concentrations of NaNO3 (0.01–1.5 mol dm−3) as background solutions at a range of pH values (3–8).In all soils, the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (point of net zero charge, PZC) differed between the soils. The PZC was higher for soils dominated by variable‐charge components (Oxisols and Andept) than soils dominated by permanent charge (Xeralf, Xerert and Fragiaqualf). For all soils, the adsorption of Cd increased with an increase in pH and most of the variation in adsorption with pH was explained by the variation in negative surface charge. The effect of ionic strength on Cd adsorption varied between the soils and with the pH. In Oxisols, which are dominated by variable‐charge components, there was a characteristic pH below which increasing ionic strength of NaNO3 increased Cd adsorption and above which the reverse occurred. In all the soils in the normal pH range (i.e. pH>PZC), the adsorption of Cd always decreased with an increase in ionic strength irrespective of pH. If increasing ionic strength decreases cation adsorption, then the potential in the plane of adsorption is negative. Also, if increasing ionic strength increases adsorption below the PZC, then the potential in the plane of adsorption must be positive. These observations suggest that, depending upon the pH and PZC, Cd is adsorbed when potential in the plane of adsorption is either positive or negative providing evidence for both specific and non‐specific adsorption of Cd. Adsorption of Cd was approximately doubled when Na rather than Ca was used as the index cation.
Simulating diffusion in a Boolean model of soil pores
Authors: HORGAN G.W. , BALL B.C. 
Published: July 2006

SummaryThe diffusion of gas through a model of the structure of soil pores was simulated on a computer. This was done to test the model's usefulness for studying diffusion in real soil and to obtain insights into how soil pore geometry affects diffusion. A model of randomly‐placed overlapping spheres was used to represent the soil solids, the pores being what remains. Various simulated porosities and average sphere radii produced pore networks which resembled those in real soil aggregates. Our diffusion simulations gave three results: steady‐state flux, time delay and rate of increase of flux. The porosity and sphere size were varied to investigate their effects on these diffusion properties. Results were comparable with those from experimental work. Further analysis allowed us to express the geometry of pore simulations in terms of average pore path length and connectivity. Evidence of non‐Fickian behaviour was obtained, particularly in the early stages of the simulated diffusion.
AN INTERNATIONAL EXPERIMENT ON THE EFFECT OF AGE AND STORAGE CONDITIONS ON VIABILITY AND DORMANCY OF AVENA FATUA SEEDS
Authors: THURSTON J. M. 
Published: July 2006

Summary. Freshly collected ripe seeds of Avena fatua were first kept out of doors on the surface of the soil for 0 to 3 monehs, and then stored dry in the laboratory for 0 to 6 months before testing for dormancy and viability. Results from six European countries agreed well. Only 10% of ripe seeds germinated immediately alter collection and germination rose to 50% by December or January in all countries except Denmark. Viability was scarcely affected by age or storage conditions, except that many seeds died out of doors during winter in Denmark and Germany. The percentage of dormant seeds in December was greater in Denmark than elsewhere, possibly because the seeds were of a different type. Seeds may not behave the same in normal agricultural conditions as they did in this experiment. Une expérience internationale sur l'influence de l'âge et des conditions de conservation sur la viabilité et la dormance de semences d'Avena fatua