摘要:

SUMMARYThe thermocouple psychrometer method and the pressure plate apparatus method werecompared for determining the energy status of soil water, and it has been shown that the resulting soil water characteristic curves might differ significantly. Ψtdetermined by the psychrometer method was always higher than Ψm, determined with the pressure plate method. Thus, the soil water characteristic curve determined with the pressure plate method may not represent the true condition of soil water, and the actual matric potential may be considerably higher than that assumed from the applied chamber pressure. This suggests the need for careful examination of the pressure plate method for determining the soil water characteristic curv

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00368.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYAn anisotropic state was induced in saturated clay cores by unidirectional compression. The cores were allowed to dry slowly in the laboratory and the resulting linear shrinkage was measured in all three dimensions. The rate of shrinkage was less in the precom‐pressed direction than in the other directions. An analysis is given for characterizing the anisotropic shrinkage.An analysis is made of the vertical soil movement occurring in response to wetting or drying within the profile in which volume changes are anisotropic. It is shown that for saturated clays the ratio of added water (expressed as a depth) to the vertical soil displacement is greater than or equal to unity, though it is unlikely to exceed 5. When the soil volume properties are isotropic, the ratio has one of two integer values: 1 when the soil is constrained to move only vertically, and 3 when it is free to change volume in three dimensions. The measured value should be used for modelling changes in crack geometr

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00369.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYA study is presented of the self‐diffusion of sodium in a sub‐soil. Impedance factors (fs)associated with the surface phase have been derived, representing the mobility of sorbed sodium ions relative to mobility in an ideal solution. Effects of drying, of cationic com‐position and of enrichment with either native clay fraction or ‘pure’ clay minerals were investigated. The liquid phase impedance factor (fL) without added clay was 0.29: clay enrichment affected soil structure and hencefL. Values offswere in the range 0.19–0.05, and were about one‐third offL. The value off, decreased as clay content increased, being halved when 50% native clay or 10% clay mineral was added. In a sodium saturated soilfswas 0.06, less than half that in a calcium s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00370.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYTwo surface soils (Patua and Tokomaru) of contrasting mineralogy were incubated with several levels of either CaCO3or HC1. The effects of ionic strength on pH, on surface charge, and on the adsorption of phosphate and sulphate were measured in three concentrations of NaCl.The pH at which the net surface charge was zero (point of net zero charge—PZC) was 1.8 for the Tokomaru soil and 4.6 for the Patua soil: differences that can be related to mineralogical composition. There was an analogous point of zero salt effect (PZSE) that occurred at pH 2.8 for the Tokomaru soil and at 4.6 for the Patua soil. The presence of permanent negative charge in the Tokomaru soil resulted in an increase in PZSE over PZC.The effect of ionic strength on adsorption varied greatly between phosphate and sulphate. For phosphate, there was a characteristic pH above which increasing ionic strength increased adsorption and below which the reverse occurred. This pH (PZSE for adsorption) was higher than the PZC of the soil and was 4.1 for the Tokomaru soil and 5.3 for the Patua soil. In contrast, increasing ionic strength always decreased sulphate adsorption and the adsorption curves obtained in solutions of different ionic strengths converged above pH 7.0. If increasing ionic strength decreases adsorption, the potential in the plane of adsorption must be positive. Also, if increasing ionic strength increases adsorption, the potential must be negative. This suggests that, depending upon pH, phosphate is adsorbed when the potential in the plane of adsorption is either positive or negative, whereas sulphate is absorbed only when the potential is positiv

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00371.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe uptake of labelled and unlabelled N by wheat was measured in pot and field experiments with15N‐labelled fertilizer. Soils from two sites on the same series were used in the pot experiment; one had been bare‐fallowed for 22 years and contained 1.6% organic C, the other had been under grass for many years and contained 3.8% organic C. Fertilizer N increased the uptake of unlabelled soil N in both soils, i.e. there was a positive ‘added nitrogen interaction’ (ANI). There was no ANI in the field experiment. A simulation model is used to show how positive ANIs can arise as a result of ‘pool substitution’—labelled inorganic fertilizer N standing proxy for unlabelled inorganic soil N that would otherwise have been immobilized. In the low‐organic fallow soil, pool substitution accounted for the whole of the observed ANI and fertilizer N did not enhance either gross or net mineralization of soil N. Pool substitution also operated in the high organic grassland soil, but here net mineralization of soil N increased with increasing additions of fertilizer, giving rise to a ‘real’ ANI in addition to the larger ‘apparent’ ANI caused by pool substitution. This increase in net mineralization is probably caused by adecreasein immobilization of N as fertilizer N additions increase, not by an increase in gross mineralization of soil N. For pool substitution to operate, fertilizer N and soil inorganic N must occupy the same pool. This occurred in the pot experiment but not in the field experiment, where fertilizer and soil inorganic N remained separate and there was no ANI. When pool substitution occurs, fertilizer use efficiency is predictably lower as measured by the isotopic method than as measured by the conventional

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00372.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYSamples were collected from five soil series, developed on different parent materials and occurring widely in intensively cultivated areas of Northern India. Potassium in these soils was desorbed by electro‐ultrafiltration, and collected in different fractions by applying successively higher voltages and temperature. K was also determined by extraction with M neutral ammonium acetate and M boiling nitric acid. Potassium desorption using EUF differentiated between soil series and between low K and high K soils. The K‐buffering capacity of the soil was associated with soil text

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00373.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe sorption of Co by individual soil components was studied at solution Co concentrations that were within the range found in natural soil solutions. Soil‐derived oxide materials sorbed by far the greatest amounts of Co although substantial amounts were also sorbed by organic materials (humic and fulvic acids). Clay minerals and non‐pedogenic iron and manganese oxides sorbed relatively little Co. It is considered that clay minerals are unlikely to have a significant influence on the sorption of Co by whole soils.Cobalt sorbed by soil oxide material was not readily desorbed back into solution and, in addition, rapidly became non‐isotopically exchangeable with solution Co. In contrast, Co was relatively easily desorbed from humic acid and a large proportion of the Co sorbed by humic acid remained isotopically exchangeable. Cobalt sorbed by montmorillonite was more easily desorbed than that sorbed by soil oxide but less easily than that sorbed by humic acid.Cobalt sorption isotherms for whole soils at low site coverage were essentially linear and the gradients of isotherms increased with pH. A comparison of isotherm gradients for whole soils and individual soil components supported the suggestion that Co sorption in whole soils is largely controlled by soil oxide mate

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00374.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYThe removal of zinc from solution has been studied for seven soils of varying properties. The presence of a background electrolyte as an ionic strength buffer and the nature of the anions and cations in solution have also been examined. This process has been considered as both a surface adsorption and a precipitation mechanism. Evidence presented suggests a role for a precipitation mechanism involving zinc and iron, which is independent of pH. Iron concentration in solution decreased with increasing zinc concentration; the ion product pZn+2pFe was constant (15.00, SD 1.00) over all seven soils. A further indicator of a precipitation mechanism was the shape of the Langmuir plot at low equilibrium concentrations of zinc in solution.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00375.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYIn this paper podzols of free‐draining sands in south‐eastern Queensland are examined. The 14 profiles represent a chronosequence from young incipient podzols, to ancient ‘giant podzols’ of Pleistocene age, with a spodic horizon at a depth of 8–10 m.Carbon, Fe and Al were determined in pyrophosphate, and Fe, Al and Si in oxalate extracts. The resulting profile distributions were modelled by three expressions, fitted for each attribute, which accounted for surface accumulation, B horizon development and a phase (B/C horizon) of constant composition with depth.The parameters may be used to characterize soil profiles. They show that there is a tendency for the accumulation of carbon in the B horizon to be reflected by Fe and particularly A1 accumulation, which supports the proposition that carbon is directly associated with the transport of A1 and Fe.A feature of many of these soils is a deeply weathered surface with little tendency for commensurate development of an illuvial horizon. Rates of removal of Fe and Al from the A horizon were obtained by comparison of the depths of leaching with age estimates based on geomorphology, and they indicate a non‐linear rate of increase in the thickness of th

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00376.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

SUMMARYMost soil properties vary down a soil profile. In nearly every case a graph of the value of the property against depth (the ‘true’ curve) is smooth. However, a soil sample is usually taken from the whole of a horizon so that its analysis is the mean value for the horizon, and a graph of analyses against horizon depth is a ‘stepped’ profile. It is possible to produce a smooth profile by attributing each analysis to the mid‐depth of its horizon and fitting a polynomial or spline curve through these values, but the former may produce erratic results, and both of them produce curves in which the true maxima and minima may be considerably damped.This paper explores the possibility of deriving a better reconstruction of the true profile from the same number of analyses by:(a)taking the samples for analysis from narrow layers at depths that appear to correspond to maxima, minima, or points of inflexion on the true curve, and fitting spline curves through their values;(b)fitting a modified ‘equal‐area’ spline curve to conventional whole‐horizon samples.The latter is considerably superior and, in most cases, achieves a surprisingly close reconstruction of the true profile from which the s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1986.tb00377.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY