bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hypothesis on the pedogenesis of the ‘gley podzols’ of the west coast of South Island, New Zealand
Authors: FARMER V. C. , MEW G. , CLAYDEN B. , LEE R. 
Published: July 2006

SUMMARYThe gley podzols of the west coast of South Island, New Zealand, typically exhibit permanent waterlogging extending from the surface to depths of 1–3 m. Their formation is explained by a continuation of processes which give rise to Peaty Podzols with thin iron pan (Ironpan Stagnopodzols; Placaquods). Iron pans initially formed within the upper B horizon are breached by acidic reducing waters and reform at a succession of lower levels down to 3 m or more below the surface.
Sampling and bulking strategies for estimating soil properties in small regions
Authors: WEBSTER R. , BURGESS T. M. 
Published: July 2006

SUMMARYEstimates of mean values of soil properties within small rectangular blocks of land can be obtained by kriging provided the semi‐variogram is known. This paper describes optimal rectangular grid sampling configurations whereby estimation variances can be minimized. For linear semi‐variograms square blocks are best estimated by sampling at the nodes of a centrally placed grid with its interval equal to the block side divided by the square root of the sample size. For spherical semi‐variograms the same configuration is almost optimal. The estimation variance of a bulked sample can be identical with that of a kriged estimate where the semi‐variogram is linear and equal portions of soil are taken from each node on the optimally configured grid and provided the soil property is additive. For spherical semi‐variograms the above is approximately true. Comparisons with estimates that take no account of known spatial dependence show that the true variances can be much less than those apparent using classical theory, and the necessary sampling effort much less. Within block‐variances are often needed for planning, and an appendix gives two‐dimensional auxiliary functions from which they can be calculated for linear and spherical semi‐variograms.
A lysimeter study of the fate of fertilizer nitrogen in spring barley crops grown on shallow soil overlying Chalk: crop uptake and leaching losses
Authors: DOWDELL R. J. , WEBSTER C. P. , HILL D. , MERCER E. R. 
Published: July 2006

SUMMARYThe objective of this work was to determine the fate of fertilizer nitrogen (labelled with nitrogen‐15) applied to an undisturbed shallow soil overlying Chalk contained in 10 lysimeters (80 cm diameter, 135 cm deep). Measurements are reported of the nitrogen uptake by four spring barley crops and the rate and extent of leaching of nitrate beyond the roots. The crops were fertilized with 0, 80 or 120 kg N ha−1 in each of four years, but only the first application in 1977 was labelled with nitrogen −15. Rainfall and irrigation approximated to the long‐term average, but in two treatments dry or wet spring conditions were imposed for the 10 weeks after sowing the first crop in 1977. The dry matter and grain yields of the spring barley crops varied from year to year in the ranges 8.7–14.0 t ha−1 and 3.5–6.1 t ha−1 respectively. The total nitrogen harvested in the crop approximated to the amount of nitrogen applied in each year with an apparent recovery of fertilizer in the range 38–76%. The recovery of nitrogen derived from fertilizer (labelled with nitrogen‐15) was 46–54% in the first crop and after 2 years rapidly declined to below 1%. The total amount of nitrogen‐15 labelled fertilizer recovered in four barley crops was 49–57% of that applied.Mean annual nitrate concentrations in water draining from the base of the lysimeters were in the range 11.8–26.7 mg N 1−1 and did not differ significantly between nitrogen fertilizer treatments (0, 80 and 120 kg N ha−1 a−1). In all treatments nitrate concentrations varied considerably within each growing season, with a cycle of peaks and troughs. Annual losses of nitrate were in the range 39–128 kg N ha−1, and the mean annual losses over the 4 years varied between lysimeters from 65 to 83 kg N ha−1. Nitrogen‐15 labelled nitrate was detected in the first drainage water collected in autumn following its spring application, 5 months earlier. Recovery of fertilizer‐derived nitrogen in drainage water was greatest during the winter following the second barley crop, and was 3.4–3.7% of the nitrogen‐15 applied. Over the 4 years of the experiment 6.3–6.6% of labelled fertilizer was accounted for in drainage water, representing 2–3% of the total nitrogen lost by leaching.
Decomposition kinetics of straw saccharides and synthesis of microbial saccharides under field conditions
Authors: MURAYAMA S. 
Published: July 2006

SUMMARYThe decomposition of rice and barley straw saccharides under field conditions was well represented by the first‐order kinetics model of Yt=C1e−k1t+C2e−k2t, where Yt is the remaining amount at time t, k1 and k2 are the decomposition rate constants (time−1) for the labile fraction (C1) and the non‐labile fraction (C2), respectively. About 82% of the total saccharide content of the rice straw was in the labile fraction with a rate constant 0.64–0.81, the values for the barley straw being 70–92% and 0.50–0.61, respectively. The non‐labile fraction appeared to persist for a long time, with a half‐value period of 9–59 months. Barley straw and its saccharides decomposed at a slower rate than rice straw. Much more favourable initial decomposition was observed in a paddy field than in an upland field.Mannose, fucose, rhamnose and ribose were synthesized in parallel with the flush of decomposition of straw saccharides.
Modelling the effect of adsorption of phosphate and other anions on the surface charge of variable charge oxides
Authors: BOLAN N. S. , BARROW N. J. 
Published: July 2006

SUMMARYAdsorption of anions by iron and aluminium oxides decreases the charge on the surface. However, the negative charge conveyed to the surface by an adsorbed anion varies with the amount of anion adsorbed. This has been explained qualitatively by postulating a mixture of reactions at different surface coverage (Rajan, 1976) or by postulating different reaction mechanisms at different concentrations of phosphate (Ryden & Syers, 1975). We show that these effects may also be reproduced by the adsorption model of Bowden et al. (1974, 1977, 1980). This model does not require a mixture of equations to describe the variations in charge conveyed to the surface. Instead it describes the electrostatic consequences of adsorption. The charge conveyed to the surface by each increment of phosphate differs from that of the previous increment because each successive increment reacts with a surface with a different net charge.The model also reproduces the observed effects of ionic strength and pH on the charge conveyed to the surface by adsorption. Further, it suggests that differences between anions on the charge conveyed to the surface are explicable in differences in the mean distance of the adsorbed anion from the original surface.
New infrared band assignments for the arsenate ion adsorbed on synthetic goethite (α‐FeOOH)
Authors: LUMSDON D. G. , FRASER A. R. , RUSSELL J. D. , LIVESEY N. T. 
Published: July 2006

SUMMARYInfrared spectroscopy was used to show that arsenate is adsorbed on the surface of synthetic goethite (α‐FeOOH) as the acidic HAsO42‐ ion, replacing singly coordinated surface OH groups. In this respect, arsenate is analogous to phosphate, but its larger size apparently causes it to interact more strongly with some of the OH groups that remain on the surface. This has suggested an alternative assignment for the absorption bands of these OH groups.
The association of cobalt with easily reducible manganese in some acidic permanent grassland soils
Authors: JARVIS S. C. 
Published: July 2006

SUMMARYThe association of cobalt with manganese oxides was examined in some surface and sub‐soils from areas of permanent grassland in England. Hydroquinone (0.2% in ammonium acetate at pH 7.0) was used to extract easily reducible Mn oxides from the soils. Two sequential extractions with this reagent removed significant proportions of the total Co along with the Mn; no significant amounts of iron were extracted. Mn‐rich iron concretions were isolated from two of the soils and these contained from 230 to 880 μg g−1 Co. Approximately 30% of the Co in the concretions was dissolved by two sequential extractions with hydroquinone with concurrent release of considerable amounts of Mn, but, as with the soils, not of Fe. The concretions contained 20–41 mg g−1 Mn and 62–171 mg g−1 Fe that were soluble in acidified H2O2. It was concluded that significant proportions of the Co in soils is associated with Mn oxides, and will show the same sensitivity to changes in acidity and redox potential as Mn.
Distribution of allophane and organic matter in podzol B horizons: reply to Buurman & Van Reeuwijk
Authors: FARMER V.C. 
Published: July 2006

SUMMARYThe macromorphology, micromorphology and chemical nature of illuvial material in podzol B horizons and subsoils can be explained by contributions from two different migrating species: (a) a positively‐charged mixed Al2O3‐Fe2O3‐SiO2‐H2O sol incorporating minor amounts of adsorbed organic matter and silicate clay, and (b) negatively charged organic sols and solutions, carrying minor amounts of Al, Fe and clay. These species can also be generated within B horizons of high root activity. An alternative theory, that requires allophane to be formed in situ in the B horizon by microbial decomposition of precipitated organic complexes, fails to predict the observed distribution of allophane.
Evaluation of the Burns model for nitrate movement in wet sandy soils
Authors: KHANIF Y. M. , VAN CLEEMPUT O. , BAERT L. 
Published: July 2006

SUMMARYA simple model to predict nitrate leaching developed by Burns (1974) was tested. The measured and calculated nitrate concentrations in 100 cm wet sandy soil profiles were compared: the results showed reasonably good agreement between the two values. Adjusting the initial conditions and reducing the segment size from 10 to 5 cm did not improve the accuracy of the prediction. Better agreement was, however, obtained when only the samples above the groundwater table were considered.
Optimal sampling strategies for mapping soil types. I. Distribution of boundary spacings
Authors: BURGESS T. M. , WEBSTER R. 
Published: July 2006

SUMMARYThe pattern of soil types that occur in a region can be described simply in terms of the distributions of spacings between successive soil boundaries and the probabilities of transitions from soil type to soil type. Studies of eight detailed soil maps of England and Wales, representing a very wide range of terrain patterns, showed that in all instances the interboundary spacings measured along sample transects were very satisfactorily described by the gamma distribution. In some instances the shape parameter of the distribution was sensibly 1, so that the simpler negative exponential function fitted the observed distributions well. Transition probability matrices distinguished complex and nondescript soil patterns from the more strongly repetitive ones.
Improved estimation of micro nutrients in hectare plots of the Sonning Series
Authors: WEBSTER R. , NORTCLIFF S. 
Published: July 2006

SUMMARYThe form and degree of spatial dependence in readily extractable iron, manganese, copper and zinc in the topsoil of 1 ha plots on the Sonning Series near Reading have been determined. The results have been used to calculate the sampling effort required to estimate mean values with specified precision. They show that two‐ to three‐fold economies can be achieved for iron and manganese, at least, by taking account of the known spatial dependence and optimally configuring the sampling.
Micromorphology and sub‐microscopy of allophane and imogolite in a podzol Bs horizon: evidence for translocation and origin
Authors: FARMER V. C. , McHARDY W. J. , ROBERTSON L. , WALKER A. , WILSON M. J. 
Published: July 2006

SUMMARYIn thin sections of a cemented Bs horizon, allophane is present as isotropic, or weakly anisotropic, transparent, yellow, commonly fluorescent gel deposits, which line or fill voids, cement sand and silt, and form pseudomorphs of root structures. Atomic ratios of Si: Al range from 1: 2.2 to 1: 3.7 in pale deposits, but drop to 1: 8.8 in regions of organic staining. Fe: Al atomic ratios in transparent deposits range from near zero to 0.4. The local uniformity of the gels indicates that the allophane, with associated iron oxides, is deposited from solution, and is not formed in situ from a precipitated organic complex, or by weathering of minerals in situ. Mineralogical evidence indicates that the origin of the allophane is related to intense acidic weathering of plagioclase and biotites in the Eg and Bhg horizons. A fibrous morphology indicative of imogolite is seen under the scanning electron microscope only in critical point dried specimens.It is proposed that the cracked coatings characteristic of cemented Bs horizons can be interpreted as allophanic deposits, associated with varying amounts of clay and iron oxide, and impregnated with varying amounts of fulvic acids. Such deposits cannot be taken as evidence for the migration of Al and Fe as organic complexes.
Observations of the behaviour of large cores of soil during drainage, and the calculation of hydraulic conductivity
Authors: KNEALE W. R. 
Published: July 2006

SUMMARYThis paper reports observations on the behaviour of large cores of undisturbed clay‐loam soil during the drainage of water under an imposed step in potential. Rates of outflow and the matric potential at various points in the core were recorded during drainage. The volumes of ‘macropore‐channels’(large, continuous voids) were estimated to be 0.005 m3 m−3 in a subsoil sample, and 0.026 m3 m−3 in a topsoil sample from arable land. The calculated values of hydraulic conductivity were found to vary with the size of the step in potential imposed on the sample at the start of each drainage experiment. The available evidence suggested that the apparent K/Ψm relationship was influenced by the rate that air could enter the soil to replace water during drainage. The degree of restriction on air movement was affected by the initial drainage behaviour, and this varied with the imposed step in potential.
The inheritance of soil fabric from joints in the parent rock
Authors: HART D. M. , HESSE P. P. , MITCHELL P. B. 
Published: July 2006

SUMMARYThe origin of ped faces in subsoils has been variously ascribed to the activities of organisms, stress‐strain history and to alternating wetting and drying cycles. At three sites in the Sydney Basin the orientation of ped faces in the in situ B horizons of soils developed in dolerite and shale were measured and found to be similar to the orientation of planar joints in the parent rock. Joints in the rock, when inherited by the soil material, provided flaws which could be exploited by shrink and swell phenomena, gradually becoming permanent features. Horizontal ped faces appeared to be inherited joint or bedding planes, affected by the slope of the site to the extent that their dip increased in a downslope direction. This work confirmed previous soil fabric studies by Lafeber (1965) and demonstrated fabric anisotropy and inheritance from the parent rock.
Concepts of solute leaching in soils: a review of modelling approaches
Authors: ADDISCOTT T. M. , WAGENET R. J. 
Published: July 2006

SUMMARYA number of conceptual models for solute leaching in soil are reviewed, quantitatively compared and classified as far as possible within a framework that makes distinction between deterministic and stochastic, mechanistic and functional and rate and capacity models. They are also discussed with reference to their purpose (viz research or management), complexity, flexibility, transferability and usefulness for field soils. The basic assumptions and structures of the models impose definite limits on the ways in which they can be used. The spatial variability of soil properties caused problems for deterministic models using rate parameters, but stochastic elements can be incorporated in these models. Simpler capacity‐type models and non‐mechanistic stochastic models offer other answers to this problem. Few data sets are available for testing a range of models and few models have been tested on a range of soil types, and very few models have much demonstrable ability to simulate transient field leaching conditions. Examples of a model being tested by someone other than the developer seem very rare.
Adsorption of phosphate by two iron oxides in relation to their porosity
Authors: MADRID L. , DE ARAMBARRI P. 
Published: July 2006

SUMMARYAdsorption and desorption of phosphate by lepidocrocite and hematite, the latter obtained by thermal decomposition of the former, were studied and related to changes in mesoporosity of the solid surface. Differences between the oxides in the accessibility of their surfaces to phosphate seems to control the fractional amounts of ‘rapidly’ and ‘slowly’ adsorbed phosphate. Results of isotopic exchange of the phosphate adsorbed at high surface coverage can also be explained in terms of the mesoporosity of the surfaces.
Fate of fertilizer nitrogen.
Authors: BARRACLOUGH D. , GEENS E. L. , DAVIES G. P. , MAGGS J. M. 
Published: July 2006

SUMMARYResults are presented from a three year lysimeter investigation, employing single (15NH4NO3) and double (15NH415NO3) labelled ammonium nitrate to study the uptake of soil and fertilizer nitrogen by cut ryegrass at 250, 500 and 900 kg N ha−1 a−1. Average annual recoveries of nitrogen were equivalent to 99,76 and 50% of the nitrogen added at 250, 500 and 900 kg N ha−1, respectively.At 250 kg N ha−1 the difference between the overall nitrogen recovery and the fertilizer recovery was almost entirely attributable to pool substitution resulting from mineralization/immobilization turnover (MIT). At 900 kg N ha−1 both the low overall recovery of nitrogen and the low fertilizer recovery reflected the large excess of available nitrogen over crop requirements. No evidence of ‘priming’ was obtained.Analysis of the results from single and double labelled lysimeters using simultaneous equations indicated that at 250 kg N ha−1,∼70% of the nitrogen in the crop was derived from the ammonium pool. At 500 kg N ha−1 this dropped to 64%, while at 900 kg N ha−1 the figure was 59%. There was a suggestion that at the lower application rates, preferential uptake of ammonium was occurring but that as N supply exceeded crop requirements, nitrate was the major N source.Despite the preferential exploitation of the ammonium pool, at 250 and 500 kg N ha−1 pool substitution resulting from MIT resulted in lower recoveries of fertilizer ammonium compared with fertilizer nitrate.
Using soil survey information to characterize the soil‐water state*
Authors: BOUMA J. 
Published: July 2006

SUMMARYUses of soil for a wide variety of purposes are largely governed by interactions between soils and climatic conditions. The soil‐water state at any given moment depends on the hydraulic properties of the soil horizons, the weather and soil drainage. Emphasis in this presentation is on the manner in which the soil‐water state is being characterized in the context of land evaluation. Land evaluation is concerned with the assessment of land performance when used for specified purposes (FAO, 1976). Current and future developments in land evaluation are discussed, emphasizing the particular input of soil survey when using computer simulation models for the soil‐water regime. The soil‐water regime plays a key role in land evaluation, as it governs the soil‐water state at any given time during the year.
A model of ammonia volatilization from applied urea. III. Sensitivity analysis, mechanisms, and applications
Authors: RACHHPAL‐SINGH  , NYE P. H. 
Published: July 2006

SUMMARYA sensitivity analysis of the model described in Part I showed that the proportion of N lost as ammonia from surface applied urea is very sensitive to the initial pH of the soil, its pH buffer capacity, the rate of urea application, and the soil urease activity. Under the conditions tested, the diffusion of bicarbonate ion to the soil surface, to neutralize the acid generated when NH4+ is volatilized as NH3, appeared to be the main process controlling the rate of ammonia volatilization.The amount of ammonia volatilized was not very sensitive to the value of the transfer coefficient between the soil surface and the atmosphere, nor to the soil moisture status if this was around field capacity. Adsorption of ammoniacal‐nitrogen was less important than the soil pH buffer capacity in influencing the ammonia volatilization.Further applications and extensions of the model are discussed.
Microaggregates in red earths and related soils in East and Central Africa, their classification and occurrence
Authors: TRAPNELL C. G. , WEBSTER R. , HESSE P. R. 
Published: July 2006

SUMMARYThis paper describes the microaggregate structure of residual clay soils of the red earth order in East and Central Africa, examined by low‐power microscopy, and the effects of gradual moistening and sudden wetting of the soil. Results showed a markedly angular microstructure termed fragmental, resulting from simple cleavages in the soil mass, a microgranular structure involving minute spherical bodies, either discrete or in small compound aggregates, and two types of intermediate structure. The several types of microaggregate and associated profile characteristics are described in detail, and are compared with those studied more recently in West Africa. The microgranular soils also contain larger pellet bodies originating as residual cores of rotted rock. Present evidence for the distribution of these soils is outlined and possible factors in their occurrence are reviewed, including age of land surface and termite activity.
Variation in amounts of carbon and nitrogen associated with particle size fractions of soils from the Palace Leas meadow hay plots
Authors: SHIEL R. S. 
Published: July 2006

SUMMARYAn increase in carbon (C) content of one of the more acid Palace Leas meadow hay plots (pH 4.0) is shown to occur in the >63 pm size fraction, while there is a reduction in organic matter associated with clay size fraction relative to a less acid plot (pH 5.8). Total nitrogen (N) content also is higher on the more acid plot, but the increase is smaller than for carbon, and leads to a wider overall C:N ratio in the acid plot.The lower N accumulation in the more acid plot is due to the relative increase in coarse (> 2 mm) organic matter, with a high C:N ratio. The technique used for separation of the particle size fractions does not involve removal of coarse organic matter (> 2 mm) or drying of the soil. In the grassland soils studied, coarse organic matter is a significant component (up to 13%) of total C, yet this fraction is frequently removed before analysis. By not drying the soil, separation into particle size fractions is facilitated.