bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factorial kriging analysis: a useful tool for exploring the structure of multivariate spatial soil information
Authors: GOOVAERTS P. 
Published: July 2006

SUMMARYMost studies of relations between soil properties fail to take account of their regionalized nature because of the lack of appropriate methods. This paper describes a geostatistical technique, factorial kriging analysis, that bridges the gap between classical multivariate analysis and a univariate geostatistical approach. The basic feature of the method is the fitting of a linear model of coregionalization, i.e. all experimental simple and cross‐variograms are modelled with a linear combination of basic variogram functions. A particular variance‐covariance matrix, the coregionalization matrix, can then be associated with each spatial scale defined by the range of the basic variogram function. Each coregionalization matrix describes relationships between variables at a given spatial scale. A principal component analysis of these matrices produces a set of components, the regionalized factors, that reflect the main features of the multivariate information for each spatial scale and whose scores are estimated by cokriging.The technique is described and illustrated with three case studies based on a simulated data set and soil survey data. The results are compared with those of the principal component analysis of the variance‐covariance matrix and the variogram matrices.
Measuring phosphorus fluxes through the root zone of a layered sandy soil: comparisons between lysimeter and suction cell solution
Authors: MAGID J. , CHRISTENSEN N. , NIELSEN H. 
Published: July 2006

SUMMARYChemical and physical processes govern the extent to which phosphorus dissolved from the plough layer is retained by or leached from the subsoil. The adsorption capacity of deeper layers, the velocity of solution flux and the amount of soil volume in contact with the leaching soil solution are important determining factors.Soil solution from 90‐cm depth of a layered sandy soil, sampled over a 3‐year period with teflon suction cells, was systematically lower in P content than soil solution sampled with free drainage lysimeters from the same depth. On average 4.6 times as much inorganic P and twice as much organic P was found in lysimeter solutions.Determination of apparent equilibrium solution concentrations of phosphate was performed by means of a series of batch experiments with soil and soil solution of varying initial P content. The results indicated that the suction‐cell solution was close to equilibrium with soil from the 90‐cm layer.Rhodamine dye was applied, and flow paths of soil solution observed. Preferential flow was initiated from layers of finer texture overlying layers of coarser texture.On the basis of these observations it is concluded that suction cells give the best representation of stagnant soil solution, whereas lysimeters give a better representation of mobile soil solution.
The Burns leaching equation
Authors: SCOTTER D. R. , WHITE R. E. , DYSON J. S. 
Published: July 2006

SUMMARYThe simplicity and utility of Burns' leaching equation make it worthy of study. The equation may be written as
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where X is the fraction of initially surface‐resident fertilizer leached below depth z by net rainfall I, in soil with a volumetric water content at ‘field capacity’ of θ. The equation is analysed using transfer functions. The analysis shows that Burns' equation is consistent with an ‘independent flow tube’ soil leaching model, rather than the soil solution being well‐mixed at each soil depth as Burns suggested. The flux and resident soil solution soil concentration profiles are shown to be quite different. An alternative definition of θ is suggested. The behaviour of ‘a Burns soil’ for different initial and boundary conditions is discussed.
Comparisons of methods for measuring the leaching of mineral nitrogen from arable land
Authors: WEBSTER C. P. , SHEPHERD M. A. , GOULDING K. W. T. , LORD E. 
Published: July 2006

SUMMARYComparisons were made between 1988 and 1991 to evaluate three methods of estimating the leaching of mineral nitrogen (N) from unstructured freely draining sandy loam and loamy sand soils. The studies compared the drainage patterns and quantities of N (almost exclusively nitrate) leached from monolith lysimeters with those estimated from ceramic suction cups and soil core extracts. The latter two methods gave direct measurements of the mineral N concentrations in drainage, but required an estimate of the drainage volume calculated from meteorological observations and evapotranspiration equations to give total N leached. A bromide tracer was also used to confirm conclusions from nitrate leaching studies. There was a delay in the onset of drainage from free draining lysimeters because they lack the subsoil matric potential of field soils. However, total annual drainage measured by lysimeters or calculated from meteorological observations was similar, providing that return to field capacity was correctly identified in the field soil. During the first year there were discrepancies between methods which were attributed to soil disturbance during lysimeter and/or ceramic cup installation. In the second and third years of the experiment, estimates of N leaching losses using the lysimeters and ceramic cups were in good agreement. Nitrate concentrations in soil solution at a depth of 130 cm measured from soil core extracts were smaller than found by the other methods during the second year and the peak concentrations were significantly different (P<0.05). However, total overwinter N leached was not significantly different. Thus, while lysimeters and cups can be used to quantify leaching losses on unstructured, free draining soils if used correctly, the use of soil core extracts is questionable.
Cation exchange capacities of organo‐mineral particle‐size fractions in soils from long‐term experiments
Authors: LEINWEBER P. , REUTER G. , BROZIO K. 
Published: July 2006

SUMMARYSoils with and without organic manuring from 10 long‐term manurial experiments in East Germany were fractionated into organo‐mineral particle‐size separates by ultrasonic disaggregation and sedimentation/decantation. The cation exchange capacities (CECs) buffered at pH 8.1 were determined for the size fractions fine+medium clay, coarse clay, fine, medium and coarse silt, sand, and for the total soil samples.In the samples from nine field experiments the CECs decreased with increased equivalent diameters (fine+medium clay: 489–8 13 mmolc kg−1, coarse clay: 367–749 mmolc kg−1, fine silt: 202–587 mmolc kg−1. medium silt: 63–345 mmolc kg−1, coarse silt: 12–128 mmolc kg−1 and sand: 10–156 mmolc kg−1. The CECs varied with genetic soil type, mineralogical composition of the <6.3‐μm particles, and the C and N contents of the size fractions.In a pot experiment examining the role of various organic materials in the early stages of soil formation, the clay‐size fractions had the largest CECs (85–392 mmolc kg−1), followed by the medium‐silt (1 9‐222 mmolc kg−1) and fine‐silt fractions (23–192 mmolc kg−1). The effect of organic amendments on CEC was in general: compost>fresh farmyard manure = straw + mineral fertilizer = mineral fertilizer.
Complexometric gel permeation chromatography of soluble humic substances using Sephadex G‐25
Authors: KUITERS A. T. , MULDER W. 
Published: July 2006

SUMMARYSephadex G‐25 was used with 0.01 m sodium acetate containing a concentration of 3×10−5m Cu(II) as eluent to establish the molecular‐size distribution (MSD) and the Cu complexation of molecular‐weight fractions of organic solutes. The appropriateness of this modified gel permeation method for complexometric measurements on soluble humic Substances was investigated employing various types of soil solutions.The presence of Cu in the eluent had an effect on the MSD obtained by elimination of electrostatic repulsion between gel and solutes. No evidence was found that the presence of Cu in the chromatographic system induced aggregation of the organic substances. The Cu‐binding capacity of the samples as obtained with this gel permeation method was found to increase linearly over a wide sample concentration range varying from 40–2000 mg C dm−3. No interference was observed between the Cu‐complexation by exclusion and inclusion peaks in the chromatograms. The analyses revealed that the fraction apparently low in molecular weight makes a large contribution to the complexation potential of forest soil solutions.
Sulphur cycling in New Zealand hill country pastures. II. The fate of fertilizer sulphur
Authors: SAKADEVAN K. , MACKAY A. D. , HEDLEY M. J. 
Published: July 2006

SUMMARYThe fate of fertilizer sulphur (S) applied as single superphosphate (SSP) to grazed pasture was examined in a field experiment for a period of 18 months using 35S‐labelled SSP. Four sites were selected on the basis of contrasting fertilizer history and land slope. The fertilizer histories since 1981 for the sites were 125 (LF) and 375 (HF) kg ha‐1 a‐1 SSP and the slope gradients were low (LS, 0‐12°) and medium (MS, 13–26°).The amount of fertilizer S taken up by pasture as a fraction of total applied was greater at the LF (12%) than the HF (6%) site, suggesting that pasture at the LF site depended more on fertilizer than pasture at the HF site. At the LF site, fertilizer application did not significantly increase leaching losses of S (13 and 8.6 kg S ha‐1 for fertilized and unfertilized plots, respectively). At the HF site, fertilizer application significantly increased leaching losses of S (38 and 21 kg S ha‐1 for fertilized and unfertilized plots, respectively). The amount of fertilizer S lost by leaching as a fraction of total applied was greater at the HF (20%) than the LF site (7.6%). Most fertilizer S remained as soil organic matter. Plant uptake and leaching losses of fertilizer S were greater in the first year after application. The amount of N lost by leaching was very small in terms of N cycled through soil‐plant system (1 to 6 kg N ha‐1). The majority (> 80%) of the S and N taken up by pasture and lost by leaching was derived from the mineralization of soil organic matter and not from freshly applied fertilizer.
Phosphate sorption by natural hematites
Authors: TORRENT J. , SCHWERTMANN U. , BARRÓN V. 
Published: July 2006

SummaryIron (hydr)oxides are active phosphate sorbents in soils and sediments, but no information exists on phosphate (P) sorption by natural hematites. In this study, we characterized the chemical, mineralogical and P‐sorption properties of 14 hematite‐rich natural materials of different origins. Phosphate sorption was described by a modified Freundlich equation including a time term. Phosphate sorbed at 1d at an equilibrium concentration of 1 mg P dm−3 ranged widely (0.2–1.7 μmol m−2). After 1 d, hematites showed a marked slow sorption. At 75 d, and an equilibrium concentration of 6mg P dm−3, the total amount of P sorbed ranged between 0.8 and 4.1 μmol mp−2. Phosphate‐sorption capacity was influenced by the morphology of the coherently scattering domains: the shorter the domains in the crystallographic c relative to the a direction, the lower the P‐sorption capacity. This has been observed by other authors in synthetic hematites and agrees with the idea that the prismatic faces, which have singly co‐ordinated Fe‐OH groups, are more active in P‐sorption than other faces. The average P sorption capacity of hematites was similar to that of natural goethites (2.6 μmol P m−2) but, in contrast to these, variability among samples was high. In comparison with goethites, hematites show slower sorption and lower affinity for phosphate.
Scale‐dependent correlation between topsoil copper and cobalt concentrations in Scotland
Authors: GOOVAERTS P. , WEBSTER R. 
Published: July 2006

SummaryThe soil of south‐east Scotland is locally deficient in copper and cobalt. Measurements from nearly 3000 fields for which the soil association is known were analysed to study the coregionalization of the two elements and to assess the influence of parent material on the metals' concentrations. The experimental auto‐ and cross‐variograms revealed distinct local (1.5 km) and regional (20 km) scales of spatial variation. A combination of indicator variograms of the soil associations had the same spatial structures, suggesting that parent material influences the concentrations of the metals.The coregionalization between copper and cobalt was modelled as a linear combination of three spatial structures. The resulting structural correlation coefficients showed the two elements to be fairly strongly positively correlated at the regional scale. Kriging allowed determination and mapping of each spatial component; these maps were then compared with the spatial distribution of soil associations in the region. An analysis of variance was performed before and after filtering out the nugget and short‐range spatial components. Classification by soil association (parent material) accounted for a large proportion of the variance at the regional scale, suggesting that the parent material contributes substantially more to the trace element content of the soil than had been thought earlier.
Determination of DTNB‐reactive sulphhydryl groups in soil humic acids: their enrichment in humic acids from volcanic acid soils
Authors: TAKAMATSU T. 
Published: July 2006

SummaryThirteen acid soils were collected from typical volcanic regions in Japan (S content: 0.9–4.1, mean = 2.2g kg−1; pH (H2O): 2.81–3.93, mean = 3.33), as well as nine reference soils (S: 0.6–1.7, mean= 1.1 gkg−1; pH(H2O): 4.10–4.74, mean = 4.47). Humic acids were extracted from the soils separately with 0.1 M NaOH and precipitated by acidification (pH = 2, HCl). After purification, the humic acids were subjected to colorimetric analysis using a DTNB reagent [5,5′‐dithiobis(2–nitrobenzoic acid] for the active ‐SH group. Since humic acids have significant absorption at 4I2 nm, the coloured compound (5–mercapto‐2–nitrobenzoic acid) was separated from the humic acids by ultrafiltration or solvent extraction prior to the colorimetric measurement. Humic acids also caused discoloration of the coloured compound when they coexisted in the reaction solutions. Thus, the reproducible determination of ‐SH was accomplished by employing a standard addition technique (‐SH standard: cysteine). Although ‐SH contents obtained by the ultrafiltration method were considerably higher than those by the solvent‐extraction method, probably due to the denaturation of humic acids by the higher buffer concentration used in the ultrafiltration method, they correlated well with each other. The humic acids from acid soils contained apparently higher concentrations of ‐SH (120–510, mean = 270mg S kg−1 by the ultrafiltration method; 8–110, mean = 38mg S kg−1 by the solvent‐extraction method) compared to those from reference soils [20–260, mean = 90mg S kg−1 by the former; not detectable (<5)‐34, mean = 11 mg S kg−1 by the latter]. This ‐SH enrichment in the humic acids from acid soils may result from the degradation and subsequent humification of S‐rich debris of plants and micro‐organisms and/or direct incorporation of volcanic acid gas (H2S) into the humic acids.
Physical and chemical properties of a sandy loam receiving animal manure, mineral fertilizer or no fertilizer for 90 years
Authors: SCHJØNNING P. , CHRISTENSEN B.T. , CARSTENSEN B. 
Published: July 2006

SummaryNinety years after the start of the Askov long‐term fertilization experiment on sandy loam, bulk soil was taken from the 0–20 cm and 30–35 cm depths of unfertilized (UNF), animal‐manure (FYM) treated and mineral‐fertilized (NPK) plots and analysed for textural composition, carbon content, pH, CEC, particle density and plasticity limits. Undisturbed soil cores (100 cm3) from the 8–12 cm layer were brought to six different matric potentials and subjected to confined uniaxial compression, drop‐cone penetration and annulus shear tests. Water‐retention curves based on seven matric potentials were produced for undisturbed cores from the 8–12 and 30–35 cm layers. In the field, in situ shear strength of plough‐layer soil was determined by a vane shear tester and a torsional shear box.FYM and NPK treatments increased the soil organic carbon content by 23 and 11% of the amount in UNF, respectively. Corresponding increases observed in CEC were 17 and 11%. The water content at the lower and upper plastic limits both decreased from FYM to NPK to UNF. Soil bulk density in the 0‐20 cm layer was reduced in FYM and NPK treatments relative to UNF, whereas the volume of soil pores larger than 30 μm was unaffected by past fertilization.Soil receiving animal manure showed the greatest soil strength when exposed to annulus shear, drop‐cone penetration and confined uniaxial compression tests, Shear strength measurements indicated that the UNF sandy loam soil reacted like a sand, the increase in soil strength upon drying primarily being due to increased internal friction. In contrast, soil from FYM and NPK treatments showed reactions typical of a loamy soil, the increase in soil strength during drying being caused by increased cohesion in the soil matrix. The field tests employed were unable to detect the management‐induced differences in soil physical parameters found in the laboratory tests.This study shows that physical soil properties related to conditions for tillage and traffic, to crop development and erosion are significantly influenced by differences in soil organic matter levels resulting from contrasting methods of fertilizer management. Exhausting a loamy soil by long‐term lack of fertilizer application severely affects the physical properties of the soil.
Slaking characteristics of some Australian and British soils
Authors: CHAN K.Y. , MULLINS C.E. 
Published: July 2006

SummaryAggregates (9.5–12.7 mm) from ten soils were equilibrated at a range of matric suctions (Ψa) between 1 kPa and 100 MPa before immersion in water or wetting on a porous plate at zero suction. The soils were from cultivated and grassland sites and included hardsetting and non‐hardsetting Australian and British soils as well as a Vertisol. The initial rate of wetting of each aggregate, and the composition and size distribution of the slaked fragments were measured. There was a significant inverse linear relation between the amount of slaking produced by plate wetting air‐dry soil (Ψa=100 MPa) and its organic carbon content (r= 0.82***). The three cultivated hardsetting soils shared several common features. Their slaking was the most pronounced after plate wetting and occurred at the smallest Ψa(10 kPa). Their slaking also increased linearly with rate of wetting and the particle‐size distribution of their slaked fragments varied significantly and considerably with Ψa. This last observation demonstrates that it is not always helpful to call the fragments produced by slaking, microaggregates.Possible explanations for our results and their agricultural implications are discussed.
The effects of soil structure on protozoa in a clay‐loam soil
Authors: GRIFFITHS R.S. , YOUNG I.M. 
Published: July 2006

SummaryPhysical disruption of a clay‐loam soil by slaking, grinding and compaction was used to determine the specific effects of soil structure on soil protozoa. Individual air‐dry aggregates (1–2 cm diameter) were wetted slowly, or had their structure disrupted by slaking or grinding. They were then moistened with nutrient solution and incubated, at a matric potential of −10 kPa. The nutrient solution had to supply at least 400 μg C g−1 dry soil before protozoan populations increased measurably. Numbers of ciliate protozoa were enhanced by grinding, regardless of the amount of nutrient added. The moisture content and, therefore, the final nutrient concentration of the disrupted aggregates, changed markedly and could account for the observed increase in protozoan biomass from slowly wet to slaked to ground aggregates. There were no differences in protozoan biomass when the applied nutrient concentration was adjusted so that all treatments contained the same amount of nutrient. Soil cores were prepared from sieved (2–4 mm diameter), ground and ground/compacted soil. Thin sections revealed that the pore space accessible to protozoa decreased in these three treatments from 24% to 13% to 9%, respectively. Protozoan biomass was unaffected by grinding but showed a greater than 30‐fold decrease following compaction that could not be accounted for solely by the reduced pore space. Grinding and compacting could have favoured anaerobic conditions in the core which would have reduced protozoan activity. Soil structure had no measurable direct effect on protozoan populations, but it had a much greater indirect effect through its influence on moisture content and aeration status.
Quantitative determination of plant opal content in soils, using a combined method of heavy liquid separation and alkali dissolution
Authors: HERBAUTS J. , DEHALU F.‐A. , GRUBER W. 
Published: July 2006

SummaryThe aim of this study was to improve the quantitative determination of the plant opal content (i.e. phytoliths) in soils.The proposed method is based on: (i) the separation of plant opal from the silt and sand fractions of the soil, using heavy liquid flotation (aqueous solution of ZnBr2, density = 1.92 g cm−3); (ii) the subsequent determination of alkali‐soluble silicon by atomic absorption spectrometry. Extraction and analytical procedures were tested on a broad sample of temperate and tropical soils with very different phytolith contents.Our investigations lead to the following conclusions: (i) a selective dissolution of opal in alkaline solutions (e.g. hot 0.5 m NaOH as proposed by Jones, 1969) is inaccurate so that a sink‐float method must be used before any dissolution procedure; (ii) to dissolve opal completely, a 0.5 M NaOH dissolution treatment at 150°C can be easily and successfully carried out in steel PTFE‐lined pressure vessels; (iii) the reproducibility of the determination is satisfactory for a step‐by‐step procedure (mean coefficient of variation = 13.4%).The comparison of this new method of quantitative assessment of soil opal with two other methods (gravimetric and phytolith‐counting methods), shows very highly significant correlations (P<0.001). Therefore, this procedure is a useful tool in studies connected with pedological and environmental history.