摘要:

SUMMARYComputer simulation of the soil water regime was used to calculate moisture deficits for Pleistocene and fluvial Holocene clay soils for a 30‐year period. Hydraulic conductivity(K‐h)and moisture retention(h‐θ)data were derived for major horizons in both soils as well as functions to characterize bypass flow and effects of horizontal planar voids on upward unsaturated flow of water from the water‐table to the root zone. Calculated moisture deficits in Holocene soils occurred earlier during the year and were more pronounced during the summer period. Differences between the two soils could be attributed to more pronounced formation of horizontal planar voids in the Holocene soil, which was associated with more pronounced swelling and shrinkage of the undisturbed soil material. The relatively low swelling and shrinkage of the undisturbed Pleistocene soil material was attributed to very dense packing of the elementary soil p

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02154.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYFour basaltic profiles located in northern Cross River State of Nigeria are described and characterized. The soils are classified as Typic Tropohumult and show strong acidity, low effective CEC, low N and available P. Organic matter levels of the surface soils are high. All the soils are well drained in spite of high YO clay, which is apparently kaolinitic, with moderate to high A1 saturation. Higher agricultural productivity of these soils is restricted by low effective CEC and strong acidity. Measures to combat these problems are suggested.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02155.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA set of well‐drained soils in Galicia, formed from gabbros, amphibolites and schists, with udic moisture and mesic temperature regimes, are studied. All but one of the surface horizons show an‘exchange complex dominated by amorphous material’(ECDAM); consequently, most soils are classified as Andosols (FAO) or as different subgroups of Dystrandepts (Soil Taxonomy). The soils on gabbros and amphibolites frequently have‘andic properties’so, following the ICOMAND proposals, five of the 12 soils studied may be characterized as Andisols. Many of the five soils have properties comparable to those of soils from volcanic areas, especially to those called‘non‐allophanic Andosols’, which have an abundance of active‐Al, mainly in the form of A

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02156.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYDetailed micromorphological observations and associated electron probe microanalyses are used to examine the proposition that kaolinite and gibbsite in the B horizon of a humus iron podzol could arise by transformation of allophanic deposits. The B horizon of this podzol is highly complex. In the upper B horizon, this complexity is due to alternating episodes of the influx of organic matter and the deposition of allophanic material; evidence for the separate deposition of allophane and organic matter is presented. Material within the B horizon that has gibbsiporphyric fabric appears to have arisen by crystallization of gibbsite from aluminium‐rich gels deposited before the main influx of allophanic material; there is no convincing evidence that allophanic material has transformed to kaolinite or gibbsit

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02157.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYLateritic soils developed from dolerite contained larger amounts of goethite and haematite than those developed from granite. The goethite/(goethite + haematite) ratio in granitic soils ranged from 0.55 to 1 and from 0.29 to 0.83 in doleritic soils. Maghemite ranged in abundance from 0 to 10% and it only occurred in duricrust. Mole % Al substitution ranged from 16 to 33% in goethite and from 2.5 to 10% in haematite and was similar for both granitic and doleritic soils. Al substitution in maghemite was<5%. A significant, positive correlation (P<0.01) occurred between Al substitution in goethite and the amount of gibbsite in the soil. The dehydroxylation temperature of goethite ranged from 292 to 334°C and was positively correlated with the mole % Al substitution. Goethite crystals varied in size from 16 to 26 nm and haematite crystals from 18 to 59 nm. Goethite and haematite crystals occurred as aggregates of subrounded platy crystals.Iron oxides obtained by NaOH treatment contained much of the minor element contents of the soils; mean concentrations (μg g−1) were: Zn 19.9, Cu 31, Mn 68, Ni 140, Co 32, Cr 394 and V 696. These minor elements were most abundant in iron oxides derived from dolerite, but were not preferentially associated with goethite or haemat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02158.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYInfiltration from ring infiltrometers of different radii was measured into four soil materials contained in laboratory tanks. The infiltration per unit area was larger the smaller the ring size, coming to a steady state at an earlier time. Scaling based on similar media theory was applied to the results using a microscopic characteristic length defined in terms of the hydraulic conductivity of the saturated soil and a macroscopic characteristic length taken as the radius of the ring. The relationships between scaled cumulative infiltration and scaled time merged into a single relationship at small scaled times for all soil materials and for all sizes of ring, but were different for the different soils and for the various ring radii at large scaled times. The relationship at small times was used as a type curve to interpretin situmeasurements with ring infiltrometers on three field soils in terms of the hydraulic conductivity of the saturated soil. These estimates of hydraulic conductivity pertained to the small volume of soil near the surface which was wetted during the measurement. Large variations in hydraulic conductivity values were found from experiments with small sized rings, but little variation was found for large sized rings. The technique provides a simple method of investigating soil structural changes near the surface.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02159.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThis paper describes the design and operation of a simple tension infiltrometer which imposes pressure potentials at the soil surface(hb)of –0.5, – 2 and –9 cm water, corresponding to equivalent diameters (ed) of the largest conducting pore of 6, 1.5 and 0.3 mm respectively. Infiltration measurements obtained in Evesham series clay soil were fitted to Philip's (1957) two‐term infiltration equation. Results were interpreted using information on the number, type and size of conducting macropores obtained in a dye tracing experiment. Significantly larger values of effective hydraulic conductivity athb=–0.5 cm were attributed to the flow of water in large shrinkage cracks which constituted nearly 90% of the total conducting macroporosity. Measured fluxes athb=–9 cm were related to sorption and swelling in the clay matrix, since within the range of infiltration times considered (t<0.5 h), the gravity or steady state component of infiltration was negligible. Rainfall intensity/duration data for a large number of storms at Silsoe were used to demonstrate that in dry soil nearly 70% of rainfall infiltrates in the clay matrix, and that the infiltration capacity of macropores ofed≤1.5 mm is only ra

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02160.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA disc of CaCO3was brought into contact with a column of moist acid soil, incubated for 6 days, the soil cut into thin sections, and the pH measured. The pH profile suggested that the rate of dissolution was controlled by the rate of acid‐base diffusion in the soil near the interface of the soil and the CaCO3disc.A mechanistic model was developed, containing no arbitrary assumptions or fitting parameters, to predict the rate of neutralization of acid soil by CaCO3particles of different size grades and at different application rates. The course of neutralization of soil at pH 3.0 and 4.9 with fine, medium and coarse grades of CaCO3was measured and compared with the model predictions. The agreement was satisfactory within the limits imposed by experimental difficultie

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02161.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYSelf‐diffusion coefficients of sodium and calcium were measured on a range of moist subsoils. The ratio of concentrations of each isotope in the liquid phase and on the surface at the water content of the diffusion run was obtained from both the extrapolation of ratios measured at a range of soil:solution ratios, and, where possible, by measurement on expressed soil solution.The diffusion coefficients were considerably greater than would be predicted if only the liquid phase contributed to diffusion. Surface phase impedance factors,fs, were calculated for each soil.fsfor sodium was between 1/5 and 1/2 of the liquid phase impedance factor,fL;fsfor calcium was between 1/9 and 1/20 offL. Values offswere not obviously related to the clay mineralogy, the proportion of internal to external cation adsorption, the volumetric water content, or the p

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02162.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYSamples of freshSphagnumpeat from a raised bog were amended with14C‐labelled glycine. The distribution of14C between particle size fractions obtained by wet sieving (sieve sizes 1, 0.5, 0.25, 0.15 and 0.05mm) was determined immediately on control (unincubated) samples and after 1, 6 and 12 months incubation at 10°C. The recovery of glycine in solution was almost 100%. During the incubation with14C‐glycine,14CO2was released within the first 20 weeks, equivalent to 51.5% of the added14C, but thereafter very little14CO2was evolved. After 26 weeks a substantial amount of14C was distributed amongst all the fractions, but the greatest incorporation (4.47%) occurred in the finest fraction (0.005–0.05 mm). Labelling of the other particle size fractions was<2.3% of added14C. Carbohydrate accounted for 23% of14C in the finest fraction and the sugars, rhamnose, arabinose, xylose, mannose, galactose and glucose all became labelled. Rhamnose showed the greatest, and arabinose, galactose and xylose the least, increase in specific activity; glucose and mannose had intermediate values. It was concluded that the finest fraction in peat contains a significant proportion of the microbially‐synthesized

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02163.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY