bluuebunny/crossref_metadata_2025_split huggingface dataset:
ROCK WEATHERING AND SOIL FORMATION ON HIGH‐ALTITUDE PLATEAUX OF MALAWI
Authors: YOUNG A. , STEPHEN I. 
Published: July 2006

SummaryHumic ferrallitic soils occur at altitudes above 6,000 ft on syenite plateaux. The top‐soil organic‐matter content, 5–10 per cent, exceeds that of all other Malawi latosols. The organic‐matter content of Malawi soils increases rapidly between altitudes of 5,000 and 5,600 ft, corresponding to a fall in mean annual temperature from 65° F to 63° F. The humic top‐soil overlies a yellowish‐red, friable sandy clay or clay with a weak blocky structure. Soils less than 3 ft thick overlie up to 10 ft of weathered rock containing core‐stones. Studies of materials from Zomba Mountain show that, in the formation of weathered rock, the dominant process was bauxitization, with considerable differential removal of silica; gibbsite was derived directly from feldspar. The gravelly bauxitic layer is the parent material for soil formation, in which kaolinization is the dominant weathering process.
THE USE OF MICROPEDOLOGY IN THE STUDY OF SOME ONTARIO PODZOLIC PROFILES
Authors: RENNIE P. J. 
Published: July 2006

SummaryBy adopting a micropedological approach, in which samples were taken at intervals as small as 5 mm, very acute changes in soil pH with depth were revealed. For certain Ontario podzolic profiles under long‐established coniferous forest, pH values changed from around 4 in the topmost humus layer to around 6 at a depth as little as 15 to 20 cm, with little change below this depth. Because much of the magnitude and sharpness of these gradients in properties could be lost by conventional horizon‐sampling, the micropedological approach—used so profitably in some branches of soil science—warrants wider adoption, particularly in shallow profiles.
TOTAL POTASSIUM IN SOILS BY RADIOACTIVITY MEASUREMENTS
Authors: TALIBUDEEN O. , YAMADA Y. 
Published: July 2006

SummaryThe beta‐ and gamma‐analysis methods were fully tested on nineteen British soils; ‘marker’ gamma photo‐peaks of daughter‐elements were used for estimating Th and U, and the 1.46 MeV−40K photo‐peak for K. The photo‐peaks for Th and U that give values for the K contents of the soil closest to the chemically determined values are 208Tl(ThC″)–2.615 MeV and 214Bi(RaC)+–0.609 MeV respecively. Reasonable values for the Th content of these soils are obtained by this method, but U contents seem to be considerably overestimated.
COUNTER DIFFUSION OF Rb86 AND Sr89 IN COMPACTED SOIL
Authors: PHILLIPS R. E. , BROWN D. A. 
Published: July 2006

SummaryCounter‐diffusion coefficients of Rb86 and Sr89 counter diffusing against H+ ions were measured in Dundee silt loam and Sharkey clay soils at differing soil bulk‐densities. The cation exchange complex of each soil was saturated with either Rb+, Sr++, or H+ and washed free of salts before making diffusion measurements. The water content of the soil on an oven‐dry weight basis was maintained at a constant value for all bulk‐densities; 14.2 and 28.0 per cent for the Dundee and Sharkey soils respectively. These moisture contents correspond to a tension of 2/3 bar for sieved soil. The diffusion coefficients were dependent upon concentration. Average counter‐diffusion coefficients were calculated and related to soil bulk‐density.Soil compaction of Dundee silt loam had little or no effect upon the counter diffusion of Rb86. The average counter‐diffusion coefficients of Sr89 in Dundee silt loam and Sharkey clay were significantly and linearly related to bulk‐density; as bulk‐density increased the average counter‐diffusion coefficients increased. The average counter‐diffusion coefficients were approximately 0.5–0.75 of the corresponding self‐diffusion coefficients measured previously in these soils. The applicability of counter‐ and self‐diffusion data to practical field problems are discussed.
SATURATION PERCENTAGE AS A MEASURE OF SOIL TEXTURE IN THE LOWER INDUS BASIN
Authors: STIVEN G. A. , KHAN M. A. 
Published: July 2006

SummaryThe saturation percentage is related to the mechanical constituents of a soil:
image

and is therefore a quantitative expression of soil texture. Profiles may be described in terms of the S.P.; thus

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Maps may be drawn showing quantitative changes in texture, and associated statements of the reliability of an S.P. estimate and the probable error of the position of a textural contour be made.Decomposition of the calcium carbonate component should be avoided in routine soil survey work.
THERMODYNAMICS OF CATION EXCHANGE ON CLAY: Ca‐K‐MONTMORILLONITE
Authors: HUTCHEON A. T. 
Published: July 2006

SummaryRadioactive elution and batch equilibration techniques have been used to obtain isotherms at 30° C, 50°C, and 70° C for the exchange of Ca for K on K‐montmorillonite. From these the changes in enthalpy and entropy were + 3.87 kcal/mole and +6.7 e.u./mole of Ca respectively. The activity coefficient for K decreased from approximately 1.5 to 1 and for Ca from 1 to approximately 0.5 as the fraction of K on the clay increased from 0 to 1. The results are discussed especially in relation to hydration of the ions and adsorption of water on the clay. The entropy of adsorbed water is inferred, from the results, to be less than that for liquid water.
THE HYDROLYTIC EXTRACTION OF CARBOHYDRATES FROM SOIL BY SULPHURIC ACID
Authors: CHESHIRE M. V. , MUNDIE C. M. 
Published: July 2006

SummaryThe parameters of the extraction and hydrolysis of soil carbohydrates by methods involving 24N H2SO4 and N H2SO4 were studied for a sandy granitic loam. Sugars were measured by alkaline ferricyanide, orcinol, anthrone (hexoses), orcinol‐ferric chloride (pentoses), cysteine‐sulphuric acid (methyl pentoses), glucose oxidase (glucose), and also by analysis of the individual sugars by paper chromatography.After shaking the soil with 24N H2SO4 at 20° C a further period of treatment with N H2SO4 at 100° C was required to obtain maximum hydrolysis of the soil carbohydrates. This period decreased from 17 h to 5 h as the time with 24N H2SO4 increased from 2 to 16 h. NH2SO4 at 100° C alone was less efficient. The extraction of pentoses by 24N H2SO4 reached a maximum within 8 h, and methyl pentoses within 4 h, both declining thereafter. The release of hexoses was continuing after 40 h.The best compromise involved extraction with 24N H2SO4 for 16 h followed by hydrolysis with N H2SO4 for 5 h. By this treatment yields of pentoses and methyl pentoses were respectively 99 and 92 per cent of the maximum obtainable.
COPPER DEFICIENCY OF WHEAT IN THE RIFT VALLEY, KENYA
Authors: PINKERTON A. 
Published: July 2006

SummaryThe area in the Rift Valley, Kenya, within which soils are deficient in Cu for wheat crops has been delineated. Deficiency is associated with soils, derived from pumice and ash from the Menengai caldera, which contain less than 3 ppm Cu by analysis with Aspergillus niger (M). In pot tests the yields of tomato as indicator crop for Cu deficiency were found to correlate closely with yields of wheat.Copper sulphate and copper oxychloride when broadcast were both effective in eliminating the deficiency in wheat and resulted in a marked increase in Cu content of the grain. Spraying with either compound, or applying oxychloride as a seed dressing, significantly increased the grain yields but did not result in maximum yield.
SOIL PARTICLE‐SIZE FRACTIONS AND NITROGEN MINERALIZATION
Authors: ROBINSON J. B. D. 
Published: July 2006

SummaryFractionation of East African arable soil samples into size groups < 2 mm has significantly influenced mineralizable N values. There was no evidence to suggest that refined soil fractions of < 2 mm would be an advantage for the determination, by incubation methods, of mineralizable N. Differences were more nearly related to simple physical fractionation of the soil. Organic C, total N, and silt contents of the different particle‐size fractions were positively and significantly correlated with mineralizable N; coarse plus fine sand content of the different soil fractions was negatively and significantly correlated with mineralizable N.
THERMODYNAMICS OF K–Ca ION EXCHANGE IN SOILS1
Authors: DEIST J. , TALIBUDEEN O. 
Published: July 2006

SummaryCation exchange characteristics of the K:Ca saturated forms of five soils were measured at 25°C and 50°C. The rates of isotopic exchange of 42K and 45Ca were too fast to be measured except that of 42K in the K:Ca Harwell soil at 25°C. The slower isotopic exchange of K in this soil was attributed to the presence of a zeolite, clinoptilolite. The intra‐particle diffusion coefficient, Di, of K in this soil increased with K‐saturation to a maximum at about 40 per cent K, probably because of the ‘blocking’ action of the larger hydrated Ca ions at small K‐saturations in clinoptilolite.The CEC, measured by isotopic exchange along the K:Ca adsorption isotherm, decreased with increasing temperature probably because some interlayer spaces collapsed.The standard free energy, enthalpy, and entropy changes were negative for the reaction Ca‐soil+2K+⇌ 2K‐soil+Ca++. These results seem to show that K is more strongly bound than Ca by the soil and that the Ca‐preference shown by the isotherm at small external electrolyte concentration is caused by entropy changes in solution.Calculated activity coefficients of the exchangeable ions changed with K‐saturation similarly at both temperatures but values at 50°C were smaller than at 25°C.
SOIL FACTORS AFFECTING PLANT UPTAKE OF PHOSPHATE
Authors: GUNARY D. , SUTTON C. D. 
Published: July 2006

SummaryShort‐ and long‐term uptake of phosphate by ryegrass grown in pots were both well correlated with combinations of the logarithm of the phosphate concentration in solution (log[P]), with a capacity factor (L‐value). It is suggested that log[P] measures an intensity/kinetic complex that takes account of intensity, rate, and diffusion factors. The best correlation with a single parameter was with phosphate adsorbed by anion‐exchange resin, which gives a good measure of the capacity factor and also some measure of the intensity/kinetic complex. On soils of normal phosphate status, the capacity factor tended to be more important, suggesting local exhaustion of labile phosphate. With enriched soils, the intensity/ kinetic complex measured by log [P] was dominant both for short‐ and long‐term uptake.
WATER RETENTION BY OSMOTIC SWELLING OF CERTAIN COLLOIDAL CLAYS WITH VARYING IONIC COMPOSITION
Authors: EL‐SWAIFY S. A. , HENDERSON D. W. 
Published: July 2006

SummaryExperimental data and theoretical calculations of water retention by osmotic swelling of colloidal homoionic Na‐ and Ca‐montmorillonites, vermiculites, and kaolinites were carried out at several levels of electrolyte concentration, in order to evaluate their respective contributions to the physical response of a soil system to changes in its chemical environment. Similar experiments were conducted for mixed‐ion Na‐Ca‐montmorillonite systems to establish whether a threshold value exists for cation proportions in the exchange positions, at which the physical properties of the system show a sudden change. The results are projected as relationships between the chemical treatment and moisture contents at three equilibrium pressures.Theoretical calculations, based on the diffuse double‐layer model, predict that montmorillonite systems with a certain form of cation saturation and salt content should have greater swelling pressure or higher capability for water retention than vermiculites, which have greater values than kaolinites under similar chemical conditions. This was confirmed by the experimental data, although measured values were consistently higher than those predicted by theory.The studies on mixed‐ion montmorillonites show that mutual existence of the two cation species in the clay‐water system produces a nearlinear relationship between exchangeable Na percentage and the moisture retention at a particular equilibrium pressure.
STUDIES ON THE DECOMPOSITION OF PLANT MATERIAL IN SOIL
Authors: JENKINSON D. S. 
Published: July 2006

SummaryThe organic matter in soils containing decomposing 14C‐labelled ryegrass was fractionated chemically. Earlier work on these soils had shown that they contained a small fraction, heavily labelled relative to the rest of the soil organic matter, that was mineralized when the partially sterilized soils were incubated. Reagents effective in extracting heavily labelled‐C included cold o.in HC1, boiling saturated CaSO4 solution, and o.in Ba(OH)2, but neither these nor any other reagent tested could extract material as heavily labelled as that mineralized when partially sterilized soil was incubated. Reagents that extract heavily labelled‐C are poor extractants for humified material and are not strongly hydrolytic: the more vigorous the hydrolysis the smaller the proportion of labelled‐C in the hydrolysate. The amounts of labelled‐C dissolved by Ba(OH)2 from soils sampled after different periods in the field were directly proportional to the amounts of labelled‐C mineralized by those soils when partially sterilized (by exposure to CHC13 vapour), inoculated and incubated.Balance sheets are presented for the distribution of labelled and unlabelled‐C in fractions separated by hydrolysis with 6N HC1, by NaOH extraction, by neutral pyrophosphate extraction, and by oxidation with H2O2. The fraction remaining after hydrolysis with 6N HC1 was the most lightly labelled and had the widest C/N ratio. The percentage of labelled‐C in the material dissolved by alkali or by pyrophosphate was little more than in the material not dissolved, despite the presence in the soil of fractions differing at least twenty‐fold in intensity of labelling.
THE ASSOCIATION OF MANGANESE AND COBALT IN SOILS—FURTHER OBSERVATIONS
Authors: TAYLOR R. M. 
Published: July 2006

SummarySoil Mn was mineralized either as birnessite or lithiophorite in five out of seven widely distributed soils taken from Bermuda, Europe, and the Middle East countries. The majority of the soil Co was associated with these minerals. This agrees with earlier work on Mn in Australian soils and suggests that these two minerals are the most common soil forms of secondary Mn minerals.
ELECTRON‐MICROSCOPE OBSERVATIONS OF IRON OXIDES IN SOME RED SOILS
Authors: GREENLAND D. J. , OADES J. M. , SHERWIN T. W. 
Published: July 2006

SummaryElectron‐microscope studies of the clay fractions of red soils have shown that free iron oxides are present as small (50–100 A diam) discrete particles frequently clustered to form larger irregular aggregates. Although no evidence of iron‐oxide coatings on clay minerals was found, an association of some of the oxide particles with the edges, but not the faces of kaolinite plates was observed.
A SIMPLE AVAILABLE SOIL NITROGEN INDEX
Authors: ROBINSON J. B. D. 
Published: July 2006

SummaryAvailable soil‐N values in commonly cultivated East African soils were determined in the laboratory by several methods, and correlated with one another.Mineralizable‐N was correlated more with total‐N than with organic‐C. The values of mineralizable‐N (Δ mineral‐N) obtained on aerobic incubation were correlated with crop yield and nitrogen uptake in greenhouse experiments. The yield of dry matter and N uptake by the tomato crop in the absence of applied nitrogen were significantly correlated with Δ mineral‐N in the soils; the degree of correlation decreased with increasing rates of fertilizer‐N applied and Δ mineral‐N and dry‐matter yield were not correlated at the largest rate used. N uptake by the crop was significantly correlated with Δ mineral‐N at all rates of applied nitrogen.The Δ mineral‐N value determined on soil samples conditioned by 6 weeks incubation followed by 3 weeks air drying was considered to provide a good index to available nitrogen.
VARIABILITY OF SOIL CHEMICAL PROPERTIES IN TWO UNCULTIVATED BROWN EARTHS
Authors: BALL D. F. , WILLIAMS W. M. 
Published: July 2006

SummaryThe variability in pH, loss‐on‐ignition, exchangeable cations, extractable phosphate, and soil moisture, has been studied for the 0.15 cm horizon of uncultivated, unfertilized Brown Earths at two upland grassland sites in North Wales. The results show that there is a high degree of variability in samples taken at the same time on circles of 1 m radius at all sampling locations. For example, coefficients of variation for exchangeable cations (except sodium) average 33 per cent for twenty‐two samples taken on the same occasion at three locations. This spatial variability prevented detection of any additional seasonal trends during a 22‐week summer sampling period. It is essential to consider the importance of spatial variability in any pedological or ecological study.
THE EFFECT OF PROLONGED CROPPING ON THE EXCHANGE SURFACES OF THE CLAYS OF BROADBALK FIELD
Authors: BECKETT P. H. T. , NAFADY M. H. M. 
Published: July 2006

SummaryEarlier studies have shown that the K‐(Ca+Mg) exchange isotherms of field soils are not greatly changed by cropping, by additions of K‐fertilizer, nor by moderate release of K from fixed forms. The present work shows that very prolonged K‐enrichment or depletion in the Broadbalk trials has led to substantial differences between the exchange isotherms of soils from adjacent plots in proportion to the severity of their K‐depletion.It is suggested that the changes result from the removal of inter‐lamellar K and the consequent increases in the inter‐lamellar spacings of parts of the clay crystals, which have increased the extent of the surface areas accessible to K‐(Ca+Mg) exchange. It is possible that increases sufficient to cause substantial changes in the exchange isotherms may not be apparent in X‐ray diffraction diagrams. Treatment of the K‐depleted clays with m CaCl2 appears to contract the newly expanded parts of the clay crystals, so that exchange on the occluded surfaces is once again too slow to be observed by the procedures used.
A VISUAL RECORD OF THE DECOMPOSITION OF 14C‐LABELLED FRAGMENTS OF GRASSES AND RYE ADDED TO SOIL
Authors: GROSSBARD ERNA 
Published: July 2006

SummaryThe decomposition of grasses and rye labelled with 14C was studied using ground material and also fragments cut from intact leaves or roots either placed on the soil surface or buried in the soil incubated under various conditions. Autoradiography was used to observe the changes in the decaying plant tissue with a minimum of disturbance. Autoradiograms prepared before incubation and subsequently at intervals reveal an over‐all fall in density of the images, a complete disappearance of 14C in small discrete sites, as well as a dispersion of 14C over distances of several cm from the plant residues.A photoelectric technique was devised by which changes in density could be expressed quantitatively. The log density of autoradiographic images of pellets of ground grasses shows a predominantly, though not completely, linear regression on time of incubation. The method has shown that the process of decomposition is very slow, that in the first stages of decomposition ryegrass decays faster than cocksfoot, and that ground material tends to behave in a different manner to fragments cut from intact tissues. Changes in the area of autoradiographic images with time of incubation could be used as an additional but less sensitive measure of the rate of decomposition.The participation of micro‐organisms (especially fungi) in the breakdown of the plant tissues has been demonstrated by the presence of labelled organisms in the vicinity of plant residues. Labelled fungi are more numerous in the first 3 months of incubation, during which a marked fall in image density of the plant residues occurs. A further decrease in image density is frequently associated with the appearance of fungal resting structures with a greater concentration of 14C than the surrounding plant fragments. Because of their longevity these structures contribute to the fixing of 14C in a different fraction of the biomass. Faecal pellets of soil mesofauna also concentrate 14C and resist decomposition for very long periods of time.
PHOSPHORUS TRANSFORMATIONS IN A CHRONOSEQUENCE OF SOILS DEVELOPED ON WIND‐BLOWN SAND IN NEW ZEALAND
Authors: SYERS J. K. , WALKER T. W. 
Published: July 2006

SummaryThe rate of loss of total P and accumulation of organic P were investigated in a chronosequence of weakly weathered soils developed on wind‐blown sand. The net loss of total P during 10 000 years of soil development was 1910 kg/ha m profile. This calculation assumes a constancy in the total P content of the parent material. An approximately straight‐line plot was obtained for the loss of total P between 500 and 10 000 years. The organic P content of the beach sands was very low but increased rapidly in the early stages of soil development. With increasing time, the rate of accumulation of organic P decreased. The net accumulation of organic P during 10 000 years was 1050 kg/ha m profile. A slow rate of formation of organic P, coupled with a rapid mineralization, has probably limited organic P build‐up. It is suggested that loss of phosphorus by leaching is a consequence of the low phosphate retention capacity of these weakly weathered soils.
THE NATURE AND GENESIS OF CERTAIN ARIDISOLS IN KENYA
Authors: MAKIN J. , SCHILSTRA J. , THEISEN A. A. 
Published: July 2006

SummaryIn the semi‐arid Kenya lowlands, strongly contrasting soil units associated with specific positions in the landscape have developed on various ancient alluvial deposits. The soil pattern may be explained by the differential truncation of a previously solodized plateau. These contrasting soil sequences give rise to associated vegetation catenas.Necessary adaptations are applied to the 7th Approximation soil classification, thereby introducing one new Great Group (Halorthid) and several new subgroups (natric grumustert, natric grumaquert, and typic halorthid).
A VERSATILE METHOD FOR TREATMENT OF CLAY SOILS FOR THIN‐SECTION FABRIC STUDIES
Authors: SINGH R. B. 
Published: July 2006

SummaryIn an earlier investigation three different methods had to be used for the treatment of laboratory‐compacted clay soils prior to the preparation of thin sections for use in fabric studies. The three methods, viz., the Carbowax method, the Araldite‐resin impregnation method, and the Aquax method, had limited application depending on the degree of saturation and the clay‐mineral composition of the soil. A new method has been developed which can be applied to all clay soils irrespective of their mineralogy and degree of saturation. In this method, the pore water of the soil specimen is first replaced with monostyrene using a two‐step diffusion process. Then the specimen is impregnated with an Araldite‐resin mixture which can be cured at a temperature of 55°C. The method has yielded better thin sections than those obtained by any of the three previous methods. Pure montmorillonite soils can be treated with a greater degree of success than hitherto possible.
APPARENT AND PARTIAL MOLAL VOLUMES OF CATION‐SATURATED KAOLINS
Authors: HELMY A. K. , ASSAAD F. F. , HASSAN M. NAGUIB , SADEK H. 
Published: July 2006

SummaryApparent and partial molal volumes of K‐kaolin and K2SO4, Mg‐kaolin and MgSO4, and Ca‐kaolin and CaCl2 as a function of electrolyte and particle concentration were determined from density measurements at 30°C. The apparent (ø) and partial molal volumes (V) of the kaolin or the salts studied increase with concentration and are larger in salt‐clay mixtures. Kaolin saturated with electro‐strictive cations has lower volumes than that saturated with less strictive ones.