摘要:

SUMMARYThe paper is addressed to soil scientists who use Time‐Domain Reflectometry (TDR) technology to measure soil moisture. The practical aspects of the measurement calibration are discussed, and an empirical approach to establishing the existence of a universal calibration function is presented.Samples of 11 mineral soil horizons and seven organic soil horizons with different chemical and physical properties (including magnetic properties) were selected with the aim of determining their dielectric constant‐volumetric water content relationship as calibration functions for TDR soil moisture measurements. These samples were supplemented by other, soil‐like, capillary‐porous reference materials (montmorillonite, glass beads, washed sand and a sand from a C horizon).The study showed that a unique calibration function for mineral soils and another distinct calibration function for organic soils can be esta

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00115.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYIn the fifth year of a traffic management experiment on grassland comparing conventional (C), reduced ground pressure (R) and zero (Z) systems, differences in soil structure were characterized in the upper 100 mm. Soil bulk density and vane shear strength increased between systems in the order Z, R, C. A more detailed description of the soil structural differences between traffic systems, and between depths within systems, was obtained by an image‐interpretation technique. Rapid‐hardening epoxy resin, containing fluorescent dye, was added to the soil in the field condition, and the macroporosity was quantified by image analysis. All measured attributes (bulk density, vane shear strength and those from image analysis) showed that soil structure was superior in the zero (Z) and reduced ground pressure (R) traffic systems compared to that of the conventional (C) system. Porosity and pore or solid surface area of the Z system were greater, and aggregate size was smaller, than in the C system. In general, R was intermediate between Z and C. At about 10–30 mm in the reduced ground pressure system, there was a zone of low porosity that resembled much of the soil in the conventional system. Macroporosity and roots were concentrated close to the soil surface under the C and R systems. In the absence of traffic, or under the R system, the surface of the ground was rougher than that under the C s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00116.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYMeasurements were made of the contact angle for glycerol, di‐iodomethane and cis‐decalin drops settled on the surface of pellets prepared from sodium forms of clay fractions of soils before and after successive removal of organic matter, iron and aluminium. On the basis of contact angles thus measured and a modified Young equation, the dispersive and non‐dispersive components of the surface free energy of the clay fractions were calculated. It was found that the non‐dispersive component decreased linearly with an increase in organic matter content, and with Fe and Al in the clay fractions of the soils studied. However, the dispersive component was not dependent on organic matter content, but decreased with increasing content of Fe and Al in the clay fractions

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00117.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYPublished reports on the effect of temperature on the sorption of ions by soil, or soil constituents, are in conflict with regard to the direction of the effect and its interpretation. It is argued that, in many cases, increased sorption with increased temperature is due to an increased rate of the reaction that follows adsorption. The effects of temperature on the adsorption reaction itself are complex because of separate effects on the ions in solution, on the charge on the surface, and on the affinity of the ions for the surface. On balance, adsorption of anions should decrease with increasing temperature, and adsorption of cations should increase. However, decreased adsorption of cations is possible, particularly at high pH. With one exception, these conclusions are consistent for all published reports seen.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYModel humic macromolecules, obtained by auto‐oxidation of the catechol‐glycine system, were adsorbed on poorly ordered hydrous iron oxides, Fe(OH)2.8. The pH was nearly constant atc.6 in order to simulate natural soil and river environments. When the amount of organic carbon adsorbed on 1 g of poorly ordered ferrihydrite increased from 0 to 70 mg, the ligand OH exchange was very small, but the zero point of charge of suspensions progressively shifted from 7.3 to 5.6, and net surface charge, which was initially positive, progressively became negative, suggesting an adsorption mechanism with positive charge neutralization. Consequently, colloidal stability changed from rapid to slow flocculation. The ferrihydrite‐haematite exothermic reaction partially shifted from 400°C to higher temperatures as a function of adsorbed organic matter, and ferrihydrite solubility progressively increased by formation of soluble iron‐organic complexes.These results were explained more satisfactorily by the concept of colloidal organ‐ mineral association than by organic coatings o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYPoorly ordered ferrihydrites, more or less associated with synthetic humic macro‐molecules, were added to a poorly structured temperate silty soil. Manipulation of the net soil charge through these additions was measured by potentiometric titration and cation exchange capacity. The consequences of anchoring positively charged Fe hydrous oxides on negative permanent clay surface charges were studied. Both cementation and aggregate water‐stability increased with increase in adsorbed iron. The aggregation process was studied by using micromorphology and ultramicromorphology, water retention curves, mercury porosimetry and a fractal approach. Aggregate water‐stability was studied when the soils were air‐dried, with some irreversible aggregation, and oven‐dried or wetted from – 1.5 MPa to – 1 kPa thereafter. Soils with added Fe(III) polycation–humic macro‐molecule associations were less positively charged, less cemented and less stable than soils amended with Fe(III) polycations alone. The effect of these treatments on sla

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00120.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYIron oxides from 39 soils derived from various parent materials in south‐western Australia have been studied using a variety of techniques. Goethite and hematite were the only two Fe oxides present. The goethite/(goethite+hematite) ratio ranged from 0.18 to 1.0, and was highest in soils on acidic igneous rocks, decreasing for soils on alluvial and mafic parent materials. In a few soils derived from acid rocks only goethite was present. The redness rating of soils increased linearly with increasing amount of hematite. Al substitution in goethite ranged from 13 to 35 mol%, with higher values for soils on acid igneous rocks (median value = 26 mol%) than for soils on mafic (19 mol%) and alluvial (17 mol%) parent materials. Substitution of A1 in hematite ranged from 4 to 23 mol%, and was greatest in soils on mafic parent materials (median value = 12 mol% A1). A1 substitution in hematite was about half of that in associated goethite. The dehydroxylation temperature for goethite increased linearly with increasing A1 substitution. Goethite and hematite had similar crystal sizes (c. 20 nm), and both were in the form of irregular plates.Dissolution with 1 M HCl of iron oxides concentrated from the soils by 5 M NaOH digestion could be described both by the Cube Root Law and by Kabai's equation. Only one straight line was obtained for the dissolution data using Kabai's equation for samples containing both goethite and hematite, in contrast to the results of other workers. Major proportions of the Co, Cr, Cu, Mn, Ni and Zn in the soils were concentrated with the iron oxides, and the dissolution kinetics of these elements indicate that some may be present in the structure of the iron oxide

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYThe adsorption of carbendazim by peat and montmorillonite was studied as a function of the exchangeable cations and temperature. The adsorption on soils was also studied.The kinetics of carbendazim adsorption on peat showed that adsorption equilibrium was reached within 1 h. The order of adsorption of carbendazim on peat was as follows: H+‐peat>Cu2+‐peat>Co2+‐peat>Mg2+‐peat>K+‐peat, and the thermodynamic parameters appeared to suggest an adsorption mechanism involving hydrogen bonds, although in the H+, Cu2+and Co2+samples a protonation process and adsorption of the protonated species were also likely.The kinetics of carbendazim adsorption on montmorillonite (mont.) showed that equilibrium was reached within 1 h. The order of adsorption was: H+‐mont.>Cu2+‐mont.>Co2+‐mont.>Ca2+‐mont., the adsorption on the H+and Cu2+samples being much greater than that on the other samples. For the H+and Cu2+samples, the thermodynamic parameters appeared to suggest a double mechanism: physical adsorption, and protonation and adsorption by ion exchange. The most probable mechanism for the adsorption of carbendazim on the Co2+and Ca2+samples was physical bonding.The capacity for adsorption of this fungicide on soil was dependent on the organic matter, nitrogen and clay content, as well as on the cation exchange capacity. No significant correlation was found with pH, C/N ratio or

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYTransformations of sodium acetate, ammonium sulphate, urea and wheat straw in peat have been studied by determining the distribution of15N‐labelled material, and by13C and15N nuclear magnetic resonance spectroscopy (NMR) using cross polarization (CP) and magic‐angle spinning (MAS). Samples of an oligotrophic blanket peat were incubated for 6 months at 15°C with15N ammonium sulphate,15N urea,13C15N urea,15N‐labelled wheat straw or13C sodium acetate. The incubated samples were separated into fractions of>1 mm, 1–0.5 mm, 0.5–0.25 mm, 0.25–0.15 mm, 0.15–0.05 mm, 0.05–0.005 mm and a water‐soluble fraction by wet sieving, and were then freeze‐dried. The distribution of15N between the fractions was obtained after isotope‐ratio analysis by mass spectrometry, and the 0.5–0.25 mm, 0.05–0.005 mm and water‐soluble fractions from the incubations were examined by13C and15N NMR.13C‐labelled acetate increased carbohydrate resonances in the 0.05–0.005 mm and soluble material, but an organic acid derived from the substrate was still present 6 months later. Incorporation of15N from ammonium sulphate into the peat was low, and more than 50% of the added N was detected in the soluble fraction still present as15NH+4. As carbohydrate and soluble organic matter were detected in the peat, it was concluded that microbial activity and N immobilization were restricted by poor aeration and low pH. Urea, in contrast, interacted with all the fractions examined, with some15N being incorporated into a range of compounds that included protein, peptides, amides, amino acids and carbamates or lactam derivatives. A small proportion of labelled15N from wheat straw, orginally present in the>1 mm and 14.5 mm fractions, had moved into the 0.05–0.005 fraction during incubation and sieving. The13C spectra suggested that the presence of the straw may have stimulated de

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SUMMARYTitration curves of humic acids extracted from different sources were fitted using a continuous distribution model. The meanpKvalues and distribution variances were calculated in the fitting procedure and they proved to be useful in differentiation of the humic acids under examination.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1992.tb00124.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY