bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some effects of mound‐building termites on the soils of a semi‐arid area of Kenya
Authors: POMEROY D. E. 
Published: July 2006

SummaryThe nutrient status of soils from Macrotermes termite mounds, in and around Kajiado District, reflects that of the subsoils more closely than in some other studies, notably Watson (1977). Consequently the growth of vegetation on and around mounds was not noticeably enhanced, except in grasslands and in higher rainfall areas. There was no evidence that mounds acted as wicks.Mound soils contained greater concentrations of calcium, magnesium and potassium than subsoils in almost all cases where subsoil values were low, suggesting that the termites’ activities enhanced the nutrient status of mound soils. The nutrients were probably derived from their food, and the effects increased in some cases by their selection of clay on clay‐poor soils. Nevertheless, the overall effects of Macrotermes on rangeland soils are probably small.The distribution of Macrotermes is remarkably unaffected by soil types; they construct mounds on almost all soils except those consisting largely of montmorillonite.
Extraction of inorganic forms of translocated Al, Fe and Si from a podzol Bs horizon
Authors: FARMER V. C. , RUSSELL J. D. , SMITH B. F. L. 
Published: July 2006

SummaryA range of extractants commonly used in soil studies, both to clean up the crystalline clay minerals by dissolving poorly ordered phases, and to assist in the classification of soils, has been used to assess their efficiency in extracting inorganic forms of translocated Al, Fe and Si from a podzol Bs horizon. A 4 h extraction with ammonium oxalate pH 3 is the most efficient single procedure for these phases. It is concluded that satisfactory characterization of a podzol B horizon requires the use of two extractants: acid oxalate to assess the total amounts of Al, Fe and Si in non‐crystalline weathering products, and pyrophosphate to assess the amounts in organic forms. Dithionite‐citrate‐bicarbonate gives a measure of total free iron oxides, but extracts only an ill‐defined fraction of the allophane‐imogolite complex.
Nitrogen uptake by wheat in relation to water regime and depth of N placement in a loamy sand soil: measurement and model simulation*
Authors: SHARMA B. R. , CHAUDHARY T. N. 
Published: July 2006

SUMMARYNitrate‐N distribution in soil, root‐length, rate of water uptake and flux of nitrate‐N to wheat roots as influenced by moisture regime and depth of nitrogen placement were studied in 60 cm diameter by 180 cm deep metal columns filled with loamy sand soil. The contribution of the different soil depths in the root zone towards total N uptake was calculated employing a convective‐diffusion model and compared with the experimentally measured N uptake by wheat plants. Under non‐irrigated conditions with surface‐mixing of N(Ns) concentrations of nitrate, root‐lengths and water uptake rates were high only in the upper soil layers. With deep placement of N(Nd), the lower layers also contributed significantly towards total N uptake and total N uptake was greater with Nd than with Ns. In spite of many simplifying assumptions and certain estimates the predicted values of N uptake were quite close to those measured experimentally.
The strength of unsaturated mixtures of sand and kaolin and the concept of effective stress
Authors: MULLINS C. E. , PANAYIOTOPOULOS K. P. 
Published: July 2006

SUMMARYPastes containing sand and 0, 5, 20 and 80 g kaolin kg−1 mixture were equilibrated at matric potentials of – 2, – 10, – 100 and – 1000 kN m−2 or allowed to air‐dry. The strength of cylindrical samples was determined in unconfined compression and by the indirect tensile strength test. Measured strengths are explained using the Coulomb‐Mohr theory and the concept of effective stress. At pore water tensions greater than 10 kN m−2 effective stress was the dominant factor in determining compressive and tensile strength. The contrast between this behaviour and that of friable topsoils is discussed.
A combined penetrometer and surface relief meter for studying drill coulter performance
Authors: GOODMAN D. , ROWSE H. R. 
Published: July 2006

SUMMARYA miniature penetrometer which measures soil strength in a vertical section across a drill line is described. It has a cone diameter of 3.6 mm and a range and resolution of 0–5000 and 5.4 kPa respectively. Data are recorded directly on to a portable digital tape logger which interfaces directly with a microcomputer for data analysis. The use of a horizontal reference height, rather than the soil, enables measurement of the soil surface relief. Results are presented showing the mean soil strength in a vertical section (200 mm wide by 130 mm deep) in drill lines in autumn and spring cultivated soil, with a horizontal and vertical resolution of 10 and 3 mm respectively.
Definition and use of the term ‘pedoderm’
Authors: WALKER P. H. , BECKMANN G. G. , BREWER R. 
Published: July 2006

SUMMARYA new system for soil studies has been proposed by Butler based on his earlier Kcycle concept. In doing so, he has re‐defined ‘pedoderm’, the soil stratigraphic term originally defined in the Australian Soil‐Stratigraphic Proposal (ASSP). Some aspects of soil stratigraphy are discussed and the ASSP outlined. From these considerations we conclude that the re‐definition of pedoderm is inappropriate.We strongly recommend the original definition and usage of the term pedoderm. It was widely discussed among earth scientists and was developed by the careful testing of a number of alternative proposals. The term with its original definition has recently been adopted by the INQUA/Paleopedology Working Group on Soil Stratigraphy.
The effect of soil pH and high urea concentrations on urease activity in soil
Authors: SINGH RACHHPAL , NYE P. H. 
Published: July 2006

SUMMARYThe rate of hydrolysis of urea in soil over the wide range of concentrations, up to 10 moles N per dm3 soil solution, found in fertilizer practice, was examined in Begbroke sandy loam adjusted to different pH values.On rewetting air‐dry soil, urease activity increased rapidly, reached a maximum within the first 24 h and then decreased slowly to level off after about 4 days. Pretreatment of the soil with urea or ammonium had no effect on the urease activity.Urease activity increased with substrate concentration, reached an optimum value and then decreased with rising urea concentration. The results could be explained by substrate inhibition at higher urea concentrations, and the data are well described by a modified Michaelis‐Menten equation involving three parameters, Vmax, Km and Ki where Ki is an inhibition constant. Km decreased linearily with rise in pH whereas Ki increased slightly between pH 4.9 and 7.0 and steeply between 7.0 and 8.4. Vmax increased with rise in pH, reached a maximum value at pH 6.0 and then declined at higher pHs.There was a further reaction, reaching a maximum rate at a urea concentration of about 0.2 molar N in the soil solution, that followed Michaelis‐Menten kinetics. Km for this high affinity reaction increased up to pH 7.2 and then decreased at higher pH values; Vmax increased up to pH 6.8 and then decreased. The contribution of the high affinity reaction was small except at low concentrations of urea.
Soil properties relating to the sediment volume of Ando soils
Authors: EGASHIRA K. , WATANUKI T. 
Published: July 2006

SUMMARYSoil properties relating to the sediment volume of Ando soils varied depending on their physical state. The water content is a useful index property for the sediment volume of field‐moist soils. The sediment volume of air‐dried soils increased with decreasing clay content and with increasing organic carbon content. The water retention at 52% relative humidity was related to the sediment volume of soils subjected to a sonic wave treatment. An explanation of this behaviour is given in terms of the tendency of Ando soils to form water‐stable aggregates.
The automatic recognition and measurement of soil pore types by image analysis and computer programs
Authors: RINGROSE‐VOASE A. J. , BULLOCK P. 
Published: July 2006

SUMMARYA system, ANOPOR, has been developed which uses the Quantimet 720 image analyser to recognize and measure the different types of pores in impregnated soil blocks. The system is concerned with three types of pores: channels, planar voids (cracks and fissures) and vughs but is not suitable for highly interconnected pore patterns. Each of the three types has a different origin and function and presents a different two‐dimensional (2‐D) shape when sectioned.A learning set consisting of these three pore classes was used to teach the system how to recognize statistically soil pores in images using measurements made by Quantimet. To describe the pore outlines in 2‐D, shape factors giving the best class separation of the learning set in the pattern space were derived. Bayes equation was used to give the probability of a pore belonging to a particular class by comparing its position in the pattern space with the learning set. Class boundaries were determined which ANOPOR uses to allocate each pore in any image to the most likely class. The system measures the proportion of the pore space attributable to each class and the perimeter and intercept density for each. The system is used to measure the pore patterns in three soil horizons.
Traces of 2:1 layer‐silicate clays in Oxisols from Brazil, and their significance for potassium nutrition
Authors: ARKCOLL D. B. , GOULDING K. W. T. , HUGHES J. C. 
Published: July 2006

SUMMARYThe recuperation of the soil during bush fallows after a period of cultivation is an important part of the success of shifting cultivation in the lowland humid tropics. However, the sources of the nutrients which enable the observed rapid growth on apparently exhausted soils has never been satisfactorily explained. Some soils from the Manaus region of Brazil have been examined in an attempt to identify reserves of potassium. X‐ray diffraction, physical and chemical analyses, and microcalorimetric measurements of K‐Ca exchange show that small reserves of K occur in 2:1 clay minerals which exist in trace amounts in the soils. The results suggest that the clay fraction of the soil may play a more important role in nutrient supply than previously realized. The reserves are considered in terms of the land use of the area.
Mineralogical changes with depth in a layered Andosol near Bandung, Java (Indonesia)
Authors: CHARTRES C. J. , VAN REULER H. 
Published: July 2006

SUMMARYThe mineralogy and some physical and chemical properties of an Andosol developed in four distinct layers of volcanic ash have been investigated. Analytical methods used include X‐ray diffraction, transmission electron microscopy, particle‐size analyses, infrared spectroscopy, pyrophosphate extracts of C, Al and Fe, and acid‐oxalate extracts of Al, Fe and Si. Three buried A horizons in the ash were also dated by the 14C method. The dates obtained indicate burial of A horizons c. 17700, 14500 and 8600 years B.P., respectively. Halloysite dominates the weathered fraction in the ash older than 17700 B.P., whereas allophane and imogolite with molar A1/Si ratios of 1.7–2.0 are predominant in the younger ash layers. Some kaolinite also occurs in the upper two layers of ash. It is considered possible that the halloysite in the deepest ash layer formed under different climatic conditions from those prevailing at present, rather than due to resilication of allophane under the overburden of ash. The results also demonstrate the mineralogical complexity of soil developed in more than one layer of volcanic ash.
Nature and distribution of soil phosphorus as revealed by a sequential extraction method followed by 31P nuclear magnetic resonance analysis
Authors: CONDRON L. M. , GOH K. M. , NEWMAN R. H. 
Published: July 2006

SUMMARYSoil samples from long‐term plots annually fertilized with superphosphate since 1952 and also unfertilized (control) plots of an irrigated and intensively grazed pasture in Canterbury, New Zealand, were subjected to a sequential extraction procedure followed by 31P nuclear magnetic resonance (NMR) analysis of the soil phosphorus (P) forms present.Overall, 80% of the total organic P (as determined by ignition) was removed from the soil by the sequential extraction procedure. Most of the organic P (90%) detected by NMR was in the monoester fraction. Small quantities of diester and pyrophosphate were also found. Choline phosphate constituted a significant proportion (18–25%) of the monoester P in the acetylacetone and 0.5 M NaOH extracts. Long‐term superphosphate additions resulted in almost all of the P accumulated in the monoester P fraction (up to 99%).
The effect of mole drainage on soil temperatures under pasture
Authors: SCOTTER D. R. , HORNE D. J. 
Published: July 2006

SUMMARYDrainage is often claimed to increase soil temperatures in early spring by decreasing the soil's heat capacity. Measurements of water table depth, soil water content and soil temperature were made during winter and spring on mole‐pipe drained and undrained plots of a silt loam soil under pasture. Despite differences in water table depth and soil water content, drainage had no observable effect on soil temperature.Laboratory measurements of the thermal properties of soil cores at a matric potential of −4kPa and then at saturation showed the volumetric heat capacity increased from 3.1 to 3.3 MJ m−3 K−1, with a proportional increase in the thermal conductivity from 1.1 to 1.2 W m−1 K−1. The thermal diffusivity remained unchanged. These values were used in a numerical simulation of the effects of drainage on the seasonal and diurnal oscillations in soil temperature. It is argued that the soil heat flux under pasture in spring is unaffected by drainage. The predicted temperature differences due to drainage are of the order of 0.2°C. As differences of this magnitude were observed between replicate thermometers in the field, it follows from the calculations above that any differences in soil temperature due to drainage would be too small to detect.
The cause of redness in some buried and non‐buried soils in eastern England
Authors: KEMP R. A. 
Published: July 2006

SUMMARYRelationships were examined between colours and the amounts of extractable‐iron or of individual iron oxides present in <2μm fractions of samples from buried and non‐buried soils in eastern England. Colour was expressed in terms of a redness rating (RR). Oxalate‐extractable iron (Feo), dithionite‐extractable iron (Fed) and goethite contents were not significantly correlated with RR. There was, however, a strong correlation between RR and hematite content.These preliminary results provide some justification for the assumptions concerning relationships between reddish colours and hematite content, which are implicit in the paleo‐argillic concept of the Soil Survey of England and Wales. However, reddish colours (particularly within the 7.5 YR and possibly the 5 YR hue range) should not be used in isolation as an indiscriminate indicator of pre‐Devensian pedogenesis in Britain.
Crystallochemistry and surface properties of biogenic opal
Authors: BARTOLI F. 
Published: July 2006

SUMMARYThe very low solubility of phytoliths or biogenic silicas (which are minor constituents of most soils) and their ability to stabilize nitrogenous fulvic acids in podzols are attributed to chemisorbed AlVI on the surface making the silica less soluble and the surface OH groups very reactive towards organic anions in an acid medium. The surface Si/Al ratio of phytoliths is very low (1.5–8) in comparison with the Si/Al ratio (8–20) for the whole sample. The pK values of the reactions in which surface groups are involved are pK1= 1.8 for deciduous phytoliths to 3.8 for more aluminous coniferous phytoliths; the pK2 range is 8.2–9.0. The zero point of charge which is correlated with pK values varies from 5 to 6.
Interactions between fertilizer nitrogen and soil nitrogen—the so‐called ‘priming’ effect
Authors: JENKINSON D. S. , FOX R. H. , RAYNER J. H. 
Published: July 2006

SUMMARYExperiments with 15N labelled fertilizers often show that plants given fertilizer N take up more N from the soil than plants not given N—the priming effect or ‘added nitrogen interaction’(ANI). This paper is a theoretical study of ANIs and how they can affect the interpretation of experiments with 15N labelled fertilizers. ANIs can be ‘Real’, if for example, fertilizer N increases the volume of soil explored by roots, or ‘apparent’, caused by pool substitution or by isotope displacement reactions. Pool substitution is the process by which added labelled N stands proxy for native unlabelled N that would otherwise have been removed from that pool. Microbial immobilization of N, whether driven by the decomposition of soil organic matter or by the decomposition of plant roots, can lead to pool substitution and is the dominant cause of apparent ANIs. Denitrification and plant uptake of N can also, under special circumstances, lead to pool substitution and thus give rise to apparent ANIs. Isotope displacement reactions, in which the added labelled N displaces native unlabelled N from a ‘bound’ pool, can lead to apparent ANIs but are only likely to be of significance in exceptional circumstances.The relationship between ANIs, ‘A’ values and N fertilizer uptake efficiencies are examined by means of a simple model for uptake of 15N‐labelled fertilizer by a crop. A positive ‘apparent’ ANI is accompanied by an ‘A’ value that changes as fertilizer applications increase. Likewise, a positive ‘apparent’ ANI also causes fertilizer uptake efficiency to appear lower when measured by the uptake of 15N than when measured by the non‐isotopic ‘difference’ method.
Compaction by wheels: a numerical model for agricultural soils
Authors: SMITH D. L. O. 
Published: July 2006

SUMMARYA simple, numerical model was developed to predict changes in soil dry bulk density resulting from the passage of wheels. The model uses Söhne's solutions to estimate stress increases, and empirical isotropic stress‐strain data to predict soil volume changes. Predicted and measured increases in bulk density, resulting from the passage of various agricultural vehicles, compared favourably at most depths but the model underestimated the compaction of loose soil in close proximity to underlying dense layers. The model may also be used to compare the compaction caused by various types and arrangements of wheels and to assess the contribution made by a particular input variable. Examples of such uses are given.
Simultaneous nitrification and diffusion in soil. II. The effects at levels of ammonium chloride which inhibit nitrification
Authors: DARRAH P. R. , WHITE R. E. , NYE P. H. 
Published: July 2006

SUMMARYThe physicochemical and microbiological changes occurring in a fine sandy loam soil following the application of ammonium chloride were followed experimentally and with a simulation model. Two levels of ammonium addition were used corresponding to application rates of 37 and 143 kg ha−1. The measured concentration profiles of ammonium nitrate and pH, which developed in soil columns as a result of the diffusion and simultaneous nitrification of the added NH4+, were measured at different incubation times. The measured profiles suggested that nitrification was inhibited at the site of application of the ammonium salt. This inhibition was attributed to an effect of increased osmotic pressure or chloride ion in the soil. A simulation model was developed to account for the inhibition by examining and testing two hypotheses about the response of nitrifiers to a fluctuating osmotic pressure. These were the irreversible inhibition model, which assumed that exposure to high osmotic pressures irreversibly inactivated a portion of the nitrifier population, and the reversible inhibition model, which assumed that the nitrifiers would recover after exposure to high osmotic pressures. The model included terms for the adsorption equilibria of NH4+ and soil acidity with the soil solid phase, and the influence of other ions on the rate of diffusion of each diffusing ion. The inputs to the model were based on parameters obtained independently of the diffusion experiments. Good agreement was found between experimental and predicted concentration profiles for both models although the reversible inhibition model gave the better simulation of the data.
Nitrous oxide emission from a grassland soil fertilized with slurry and calcium nitrate
Authors: EGGINTON GWEN M. , SMITH K. A. 
Published: July 2006

SUMMARYConcentrations of nitrous oxide (N2O) and oxygen were monitored over a 2‐yr period in an imperfectly drained grassland soil receiving applications of N as cattle slurry or Ca(NO3)2. In both years N2O concentrations in the different treatments were in the order nitrate > slurry > control. Gaseous diffusion coefficients were determined in soil cores by a krypton‐85 tracer method and used to calculate approximate N2O fluxes from the soil. Only 1–5 kg N ha−1 was lost as N2O after a single application of > 1200 kg N ha −1 as slurry compared with 3–11 kg N ha −1 lost after 100 kg was added as NO3−. Total gaseous losses (N2O+N2) could be expected to be higher in both cases.
Straw incorporation and soil organic matter in macro‐aggregates and particle size separates
Authors: CHRISTENSEN BENT T. 
Published: July 2006

SUMMARYTwo field experiments in which straw has been removed or incorporated for 17 yr (loamy sand) and 10 yr (sandy clay loam) were sampled to examine the effect of straw on the C and N contents in whole soil samples, macro‐aggregate fractions and primary particle‐size separates. The particle size composition of the aggregate fractions was determined. Aggregates were isolated by dry sieving.Straw incorporation increased the number of 1–20 mm aggregates in the loamy sand but no effect was noted in the sandy clay loam. Straw had no effect on the particle size composition of the various aggregate fractions. After correction for loose sand that accumulated in the aggregate fractions during dry sieving, macro‐aggregates appeared to be enriched in clay and silt compared with whole soil samples. Because of the possible detachment of sand particles from the exterior surface of aggregates during sieving operations, it was inferred that the particle size composition of macro‐aggregates is similar to that of the bulk soil.The organic matter contents of the aggregate fractions were closely correlated with their clay + silt contents. Differences in the organic matter content of clay isolated from whole soil samples and aggregate fractions were generally small. This was also true for the silt‐size separates. In both soils, straw incorporation increased the organic matter content of nearly all clay and silt separates; for silt this was generally twice that observed for clay.The amounts of soil C, derived from straw, left in the loamy sand and sandy clay loam at the time of sampling were 4.4 and 4.5 t ha−1, corresponding to 12 and 21% of the straw C added. The C/N ratios of the straw‐derived soil organic matter were 11 and 12 for the loamy sand and sandy clay loam, respectively.
A recording penetrometer to measure the strength of soil in relation to the stresses exerted by a walking cow
Authors: SCHOLEFIELD D. , HALL D. M. 
Published: July 2006

SUMMARYA penetrometer has been designed for field use to simulate the stresses exerted on the ground by the hoof of a walking cow, and to measure the resulting deformation of the soil. The extent of deformation produced by the penetrometer in two intact topsoils under pasture was found to be small and independent of water content, whilst significant correlations between soil strength and water content were obtained using a cone penetrometer and a hand‐held shear vane. The results imply that the deep hoofprints associated with poached pasture are not produced immediately upon treading wet soil, but only after a progressive loss of soil strength due to repeated treading. Thus the rate of loss, which is deduced to be a measure of the susceptibility of pasture to poaching, cannot be estimated directly from a single measure of soil strength.