摘要:

SummaryThe conventional method used to investigate the pore structure of a core of wet sand is to construct a moisture characteristic curve. The plot summarizes the dimensionless volume obtained from the sample at a given suction pressure. We assume here that pore diameters are selected from an arbitrary normal distribution. The problem of estimating the parameters of this distribution reduces to the solution of a quadratic equation and substitution of the resulting value into a polynomial. There is no necessity to plot the characteristic curve, the only values being needed are the first two moments of the raw distribution.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01061.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryTo interpret experimental results from installations of horizontal piezometers for the purpose of obtaining insituestimates of hydraulic conductivity of saturated soils below the water table, shape factors for a range of cylindrical cavities at the ends of piezometers were obtained using an electric analogue. Those for the particular piezometers used in a field experiment in a clay soil were obtained in the same way and found to be smaller because of the limited number of perforations in the tip forming the cavity. Hydraulic conductivity values obtained with the piezometers were similar to those obtained in laboratory measurements on undisturbed cores of the same soil.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01062.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe effect of applications of distilled water (DW) and saline water (SW) (EC: 5.0 dS m−1) upon the infiltration rates (IR) of crusted soil surfaces was studied using a rain simulator. A sandy loam and silt loam were placed in trays at a slope of 5%. The soils were pre‐wet before each storm and a water table maintained at a depth of 5 cm. IR losses due to crust formation during storms of DW could be reversed by the use of SW in subsequent storms. A minor increase in IR was obtained in the silty loam soil, the crust of which stayed entire during successive rainstorms. Complete reversibility of IR was possible in the sandy loam, the crust of which was destroyed and reformed due to rainfall impact during each successive storm.The cohesion of the particles in the crusted silty loam soil was sufficient to render it resistant to raindrop impact, but cohesion between the particles of the sandy loam was insufficient to prevent reworking by rainfall impact during each storm. Crust formation therefore occurs in each storm in the sandy loam and the IR obtained is a consequence of the EC of the applied water of that storm o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01063.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryEquations are developed to describe the diffusion of two solutes that react with each other in the soil. Examples of such systems are nutrient uptake by a root simultaneously releasing a solubilizing agent, and dissolution of a fertilizer having an acid‐base reaction with the soil. Illustrative analytical solutions of the equations are given for planar, cylindrical and spherical systems. The effect of increasing strength of a solubilizing agent on nutrient uptake by a root is examine

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01064.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe mineralization of native soil organic matter and the simultaneous diffusion of zero NH+4and NO−3to a solution sink of zero N concentration was analysed experimentally and theoretically for a fine sandy loam soil. Experimentally, the NH4and NO3ions produced in an incubated unsaturated soil column were allowed to diffuse through a sintered glass plate into a stirred solution sink. The distribution of NH+4and NO−3in the soil column was measured after various incubation times. The rate of ammonification was measured directly during incubation and the rate of nitrification modelled from nitrifier growth kinetics. A Freundlich equation was used to describe the equilibrium between soluble and exchangeable NH+4in the soil. Terms for the microbial transformation of N and the adsorption‐desorption of NH+4were combined with diffusion equations which were solved numerically using finite difference methods. The model constructed was used to predict the NH+4and NO−3con‐centration distributions in the soil column, and good agreement was obtained between the experimental and predicted concentration profiles. The use of the model for predicting the diffusive flux of mineral N to the outer surfaces of soil peds, where it is vulnerable to leaching, was dem

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01065.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe diffusion of indigenous nitrate from small (0.9) but also decreased with increasing clod size, possibly because of anion exclusion effects.The model simulated bromide diffusion from chalk cubes of mixed sizes better when computations were made for each size than when a single volume‐averaged size wa

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01066.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryDialysis and re‐suspension of red‐brown earths showed dispersion in distilled water independent of the adsorbed cations. Whenever the electrolyte concentration is below the critical coagulation concentration the soil and clay will disperse. Mechanical disturbance greatly enhances the dispersion process. The experiments suggest that the dispersion was influenced by the released salt in the suspensions. The changes with time in the electrolyte composition of dialysed soils and clays showed that the ‘homoionic’ systems are unstable with possible interference with clay dispersion by the generated electrolytes. The importance of free electrolytes, especially calcium, in the management of dispersive red‐brown earths is

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01067.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryA model of phosphate reaction is constructed and its output compared with observations for the sorption and desorption of phosphate by soil. The model has three components: first, the reaction between divalent phosphate ions and a variable‐charge surface; second, the assumption that there is a range of values of surface properties and that these are normally distributed; third, the assumption that the initial adsorption induces a diffusion gradient towards the interior of the particle which begins a solid‐state diffusion process.The model closely describes the effects on sorption of phosphate of: concentration of phosphate, pH, temperature, and time of contact. It also reproduces the effects on desorption of phosphate of: period of prior contact, period and temperature of desorption, and soil: solution ratio. The model is general and should apply to other specifically adsorbed anions and cations. It suggests that phosphate that has reacted with soil for a long period is not ‘fixed’ but has mostly penetrated into the soil particles. The phosphorus can be recovered slowly if a low enough surface activity is

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01068.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummarySorption of phosphate was induced by incubating phosphate with samples of two soils. Both desorption and further sorption of phosphate were then measured on separate subsamples of the incubated soils. The effects of varying the amount of phosphate incubated with the soil and of period of desorption, or of further sorption, were measured on one soil; the effect of period of incubation was measured on the other.Plots of desorbed phosphate versus concentration were continuous with plots of newly sorbed phosphate versus concentration. Neither of these coincided with the plots of the original additions of phosphate. These results were compatible with a model for the reaction between soil and phosphate in which phosphate is initially adsorbed and subsequently diffuses beneath the adsorbing surfaces.Sorption is reversible in the sense that a continuous curve of sorbed and desorbed phosphate is obtained when these are measured in opposite directions by increasing, or decreasing, the solution concentration of phosphate. However, because dynamic processes are involved, an earlier position of a plot of sorbed phosphate against concentration is not retraced when the concentration is changed.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01069.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe specific adsorption of Ca2+and Zn2+by ferrihydrite results in the net release of H+. The rate and H+/M2+exchange stoichiometry of this reaction were monitored with a pH‐stat. A rapid reaction of less than 6 min was followed by a slower reaction which continued at a diminishing rate for at least 2 days. Adsorption of Ca2+at pH 7.8 and Zn2+at pH 5.4 resulted in the net release of 0.92 and 1.70 mol H+/mol M2+adsorbed, respectively. For Zn2+adsorption, this stoichiometry was shown to be independent of pH. These estimates agree well with independent estimates based on the pH dependence of adsorption. The difference between the Ca2+and Zn2+stoichiometries was related to the differing acidity of the –OH2ligands attached to the adsorbed i

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01070.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY