摘要:

SUMMARYA modified differential scanning calorimeter procedure was used to determine the relationship between temperature and unfrozen water content (UWC) in seven clays between 0°C and – 15°C to – 24°C. The procedure, which involved nucleation by a cooling followed by a rapid warming to – 0.l°C, avoided the difficulty of supercooling. Problems caused by temperature lag between the sample and its holder and by slowness of water movement within the sample, important even when cooling clay samples of about 17 mm3at a rate of 0.31 K min−1, were overcome by cooling in a stepwise fashion which allowed time for equilibration between each temperature step. The clays studied included sodium and calcium Wyoming bentonites,<1 μm and 1–2 pm fractions of St Austell kaolinite and three subsoil clays from England. After nucleation and as temperature fell below OT, water froze in two stages in most of the clays. UWCs at the minimum temperatures reached were up to 38% for the bentonites, between 9% and 20% for the subsoil clays and<4% for

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00224.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe relation between temperature, unfrozen water content (UWC) and shrinkage of a number of clays, and the distribution of ice and water within the clays, was studied. The clays included sodium and calcium Wyoming bentonites,<1 μm and 1–2 μm kaolinite and three English subsoil clays. On freezing blocks of these clays (initial size up to approximately 1 cm3) over a period of months, they shrank progressively with reduction in temperature studied except for the<1 μm and 1–2 μm kaolinites, which ceased shrinking at – 0.24°C and – 0.73°C respectively. During shrinkage, the water in the clay blocks migrated to freeze outside the blocks where ice was already nucleated. After equilibration for a month at – 0.19°C and at – 0.73°C, the water contents of the finer clays, excluding ice bands, equalled the UWCs measured previously using a differential scanning calorimeter. Two stages of ice formation were apparent in the curves of UWC vs temperature and were attributed to the different locations of the ice in the clays. Initially, ice formed in bands outside the clay matrix, accompanied by clay shrinkage (Stage 1). After a shrinkage limit had been reached ice began to form within the pores of the clay (Stage 2). Comparisons of the results of these freezing experiments with conventional moisture‐release curves showed that the suction of the unfrozen water in clays was, within experimental error, as predicted by the Schofield equation. Results are also discussed in terms of ice‐water and air‐w

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00225.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe influence of soil amendment with fulvic + humic acid (FH) fractions, obtained from manure or peat, upon the shape, size and numerical density of aggregates in a sandy loam and a clay soil was examined using micromorphological techniques and image analysis. The effect of the FH fraction from manure (FHM) was to produce larger aggregates from the smaller ones, while the FH from peat (FHP) gave rise to a higher numerical density of smaller aggregates. Although the type of structural change was similar in the two soil types, the extent of change per g of FH was greater in the clay soil. Aggregate shape varied with treatment and soil type, but both kinds of organic matter produced vughs and a narrowing of the planes in the two soils which can be considered as signs of structural improvement.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00226.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYBatch titration experiments were carried out with organic soil samples in order to investigate the release to the solution phase of humic substances (HS). Measurements were made of pH, dissolved organic carbon (DOC) concentration, and the concentration of mono‐meric (inorganic + organic) aluminium, as functions of added acid or base. DOC was taken to be entirely due to HS. The results can be interpreted in terms of a model in which the soil is considered to contain two types of HS–mobile or potentially mobile (HSM), and immobile (HSI). The binding of inorganic ions by the HS is calculated using humic ion‐binding model IV, previously developed in this laboratory. Model IV allows the charges on the HS (ZHSM, ZHST) to be calculated; these are determined mainly by the binding of H+ and A13+. Concentrations of HS in solution, [HSaq], are given by the equation:where |ZHSM| is the modulus of ZHSM, nHSMis the carboxyl group content of HSM, cHSMis the soil content of HSM, β is a fitting parameter, and square brackets, [ ], indicate concentrations. For most of the soils a value for β of 3 gives acceptable agreements between measured and calculated values of [HSaq], indicating a major influence of charge on release. The optimized value of cHSMdiffers considerably among soils, whereas cHISvaries by only a factor of about two. Total humic contents (cHSM+ cHSIestimated by model optimization are in approximate agreement with values estimated by extraction of the soils wi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00227.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThree methods of cultivation, conventional tillage (CT), superficial tillage (ST) and no‐tillage (NT), were applied for 17 years to continuous maize. Their effect on soil organic carbon content was investigated through measurements of carbon and13C/12C ratios, using the natural difference in13C content between C3plants and maize, which is a C4plant. Because the soil had carried C3plants before the experiment started, the organic carbon remaining from that time (C3,‐carbon), was distinguished from the carbon derived from maize. Comparison between continuous wheat and maize plots showed that organic matter from both maize and wheat decomposed without significant13C enrichment, whereas older C3‐carbon was enriched by 1.5% compared to that of fresh wheat material. From the initial 3.6 kg C m−2in the topsoil (0–30 cm), 0.95 were mineralized in the CT treatment, but only 0.45 in NT. The mineralization was the same in the tilled layer of ST as in CT. The CT treatment accumulated 1.1 kg C m−2of maize‐derived carbon and the NT treatment 0.8. The mineralization of initial C3‐carbon was the same at all depths between 0 and 30 cm in the NT treatment; 75% of the carbon derived from maize was found in t

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00228.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYA carbonate‐substituted phosphate rock (Gafsa, GPR) was allowed to dissolve in the presence of one or more of the following: an acid pH buffer (a source of protons), hydrous ferric oxide gel (Fe gel, a sink for P), and a cation exchange membrane (CEM, a sink for calcium). This allowed a quantitative evaluation of the individual and combined influences of three of the most important soil‐related factors (pH, P sink, and Ca sink) which control phosphate rock (PR) dissolution in soils.At 44 d, pH alone (pH 6.1 compared to 4.5) had little effect on the extent of dissolution (1.5 and 6.0% dissolution of P, respectively), probably because of the Ca common‐ion effect resulting from the preferential dissolution of the more‐soluble CaCO, accessory phase. The inclusion of a P sink at pH 6.2 resulted in only a 3.2% dissolution of P after 44 d, whereas at pH 4.5 it increased dissolution from 6.0% to 9.8%. This suggests that pH and P sorption have an interactive effect in influencing GPR dissolution.Inclusion of a Ca sink had the largest influence on GPR dissolution. This was due to the ability of the Ca sink to remove accessory CaCO2. At pH 6.2 the dissolution of P was 10 times larger in the presence of a Ca sink than it was in the presence of a P sink. Despite the smaller ratio of Ca sink size to GPR‐Ca content relative to that of the P sink size to GPR‐P content, the Ca sink was more effective in promoting GPR dissolution. The presence of the Ca sink resulted in twice as much dissolution of P at pH 4.5 than at pH 6.5. At pH 4.5, and in the presence of both the Ca sink and the P sink, 95% dissolution of GPR occurred over the 44‐d experi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00229.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYPhosphate (P) sorption and the concomitant release of sulphate (SO,), silicate (Si) and hydroxyl ion (OH) were determined on three allophanic soils from Spain, at different P concentrations. P effectively replaced SO4, Si and OH. However, at every stage of P sorption, the molar ratios of the total amounts of anions released (SO4+ Si + OH) to that of the sorbed P were low.The amount of added P affected the relative proportions of SO4, Si and OH exchanged. At low concentrations of P, phosphate sorption was accompanied mostly by release of the adsorbed SO4with some Si. As more P was sorbed an increasing displacement of OH was also observed.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00230.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYCase studies are presented of the use of soil water measurements to determine the pathways, timing and quantities of natural recharge to groundwater at sites on the Chalk and Triassic Sandstone aquifers in England. Water content and potential have been monitored for several years at seven sites and unsaturated hydraulic conductivity measuredin situat three of the chalk sites. Recharge was estimated using a combination of the zero flux plane (ZFP) method and a simple water balance. Examples of the water balance are presented for three sites.It is shown that a shallow (∼1 m) depth of permeable drift and soil increased the annual drainage from the soil to the underlying formation by about 34% at a pair of sites on the Chalk aquifer. Effects upon drainage timing are equally dramatic. On thin soil directly on chalk, drainage responds quickly to rainfall and, once evaporation starts to exceed rainfall, declines rapidly. On drift‐covered sites, the drainage continues for a much longer period, as it does from the loamy soil overlying the sandstone s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00231.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYKerosene, an industrial petroleum product characterized by the presence of a large number of petroleum hydrocarbons (C9‐C15), was selected as an example of a non‐aqueous pollutant liquid (NAPL) mixture for our studies. Three inert materials (fine, medium and coarse sand) were used in the experiments and the initial amount of kerosene applied ranged from residual to saturated retention capacity.Volatilization in the air phase and saturated mass flow of kerosene in the three sands were studied in the laboratory under controlled conditions. The volatilization was the major physicochemical process affecting the fate of kerosene in the inert porous medium. During volatilization the liquid kerosene changed its composition by gradually losing its light components (C9‐C13), and the viscosity of the remaining liquid kerosene increased. The increase in viscosity led to a decrease in the infiltration rate, for example, by about 20% when the viscosity increased from 1.3 × 10−3to 2.0 × 10−3Pa s. The relationship between the composition of the residual kerosene following volatilization and its mass flow in a sand illustrates the behaviour of non‐aqueous pollutants in inert

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00232.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYSelf‐diffusion coefficients of calcium, sodium, rubidium and caesium on the topsoils and subsoils of contrasting soil series are presented. The distribution ratios of each cation on each soil, at the moisture content of the diffusion experiments, have been calculated by extrapolation from series of suspensions.Diffusion coefficients were found in each case to be greater than expected by considering the liquid phase alone. Surface‐phase impedance factors,fs, were calculated. Although impedance factors are considerably smaller on the surface than in solution, the surface flux may exceed the flux in the liquid phase. Differences of an order of magnitude separated average values offsfor each cation. For a given cation, variations between soils were considerably less. No correlation was found betweenfsand soil mineralogy or composition.Values offswere found to decrease with increasing distribution ratio. Reasons for this observation are discussed, in particular the energy of adsorption of the cations. The possibility of extrapolating these findings to other soils, to potassium and to other cations is discus

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00233.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY