摘要:

SUMMARYThe rigid‐data model consisting of discrete, sharply bounded internally uniform entities that is used in hierarchical and relational databases of soil profiles, choropleth soil maps and land evaluation classifications ignores important aspects of reality caused by internal inhomogeneity, short‐range spatial variation, measurement error, complexity and imprecision. Considerable loss of information can occur when data that have been classified according to this model are retrieved or combined using the methods of simple Boolean algebra available in most soil and geographical information systems. Fuzzy set theory, which is a generalization of Boolean algebra to situations where data are modelled by entities whose attributes have zones of gradual transition, rather than sharp boundaries, offers a useful alternative to existing methodology. The basic principles of fuzzy sets, operations on fuzzy sets and the derivation of membership functions according to the Semantic Import Model are explained and illustrated with data from case studies in Venezuela and Ke

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01290.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYA problem in the application of geostatistics to soil is to find satisfactory models for variograms of soil properties. It is usually solved by fitting plausible models to the sample variogram by weighted least squares approximation. The residual sum of squares can always be diminished, and the fit improved in that sense, by adding parameters to the model. A satisfactory compromise between goodness of fit and parsimony can be achieved by applying the Akaike Information Criterion (AIC). For a given set of data the variable part of the AIC is estimated bywherenis the number of experimental points on the variogram,Ris the residual sum of squares andpis the number of parameters in the model. The model to choose is the one for whichÂis least.The AIC is closely related to Akaike's earlier final prediction error and the Schwarz criterion. It is also equivalent to anFtest when adding parameters in nested models

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01291.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYDisjunctive kriging is a technique for estimating values of spatially distributed random variables by combining data non‐linearly and with minimum variance. Data are transformed using Hermite polynomials to a normal distribution, and the resultant transformation is assumed to produce a stationary bivariate normal distribution for all pairs of data. Conditional probabilities that the true values exceed or are less than a specified critical threshold can then be calculated. For soil survey both the estimated values of soil properties and their associated probabilities can be mapped isarithmically as aids to decisions on land management.The technique is described and illustrated from two case studies. The pH, exchangeable potassium and available phosphorus are mapped over 77 ha of the Broom's Barn Farm, and in the eastern Border Region of Scotland the available copper and cobalt in the topsoil are mapped. The estimates are similar to those obtained by simple (linear) kriging. The conditional probabilities were estimated for values falling short of the minimum recommended thresholds, and maps of them showed where farmers would be advised to remedy or forestall deficiencies in lime and plant nutrients and to take prophylactic measures for their livestoc

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01292.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYChanges in water storage and gradients of water potential were measured beneath cereal crops grown on Andover soil series for three seasons. The measurements showed that depletion of water from the soil (0‐0.3 m) was 20–29% of the total profile depletion and that from the chalk/soil and chalk layers was 71–80%. Rain showers rewet the soil so that depletion from the non‐soil layers contributed about 35% of the total water use despite containing only 12% of the roots.Water in the chalk/soil and chalk layers was held at matric potentials between – 200 and – 800 kPa and gradients of hydraulic potential indicated upward movement from depths of almost 3 m. Comparisons of measured water depletion beneath the root zone with estimates of upward movement to the rooting zone indicate that substantial upward movement is possible, although the estimates were generally larger than the measured depletion.The estimated contribution of the water moved to the root zone for shoot dry matter production was 8% and 22% for winter and spring cereals r

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01293.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYSolute transport through layered columns (repacked aggregates overlying sand) was studied under steady flow conditions. Predictions of transport were simplified by assuming that the distribution of solute travel times in one layer was not correlated with that in the other. The implications of this assumption were developed for the transfer function model (TFM) and the convection‐dispersion model (CDM) of solute transport. The parameter values in each model were obtained from experiments carried out on columns containing only aggregates or sand.The solutes used were nitrate (surface‐applied) and chloride (previously distributed); predictions of the chloride movement were made using the parameter values for the nitrate. The predictions were tested against experimental values of drainage effluent concentration and solute concentration with depths in the columns (measured at the end of the experiments). The TFM (with an assumed lognormal distribution of travel times) and the CDM did not differ significantly, mainly because the spatial scale of the experiments was small.Because the parameter values for the columns of aggregates or sand were determined from the drainage effluent data, they were average values for whole columns. These parameters were satisfactory for predicting drainage effluent concentration from the two‐layer columns. However, they were not satisfactory for predicting the depth distribution of solute, particularly in the sand, because the water content of the sand increased with depth, unlike that of the aggregates, which was approximately constant with depth. The overall results of this study on materials of differing transport characteristics suggest that the assumption of uncorrelated travel times between layers has a potentially wide application. The approach taken here needs to be tested on undisturbed layered

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01294.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYA mechanistic model to simulate the leaching of nitrate in soil is described. Three flow patterns are accommodated: conventional convective‐dispersion; preferential flow, in which water and solute moving in the larger water‐filled pores fails to equilibrate with that in the smaller pores; and by‐pass flow, in which water (and solute) moves rapidly down cracks and fissures without displacing the soil water. The pattern of flow depends on the rainfall intensity and the hydraulic conductivity of the water‐filled pore space. The performance of the model is examined in terms of its ability to reproduce solute profiles calculated from analytical solutions to transport equations, and in the sensitivity of the output to changes in the main parameters. A second paper (Barraclough, 1989) illustrates the use of the model to reproduce nitrate leaching patterns observed in th

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01295.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYSimulations produced by a mechanistic model are compared with field observations of nitrate leaching from 0.35 ha hydrologically isolated experimental plots. The parameters used in the model are obtained in two ways. First by fitting the model to field observations in one year. These parameters are then used to simulate leaching in other years. Second, model parameters are obtained by fitting eluant profiles from pulse inputs of solute to undisturbed cores in the laboratory. When used with the field‐derived parameters, the model simulates total leaching losses well in other years, although the pattern of loss is only approximately reproduced. The simulation suggests that water and solute flow in drained, structured soils is complex; preferential flow in the upper horizons resulting in 20% of the water‐filled pore space carrying most of the solute flow, and by‐pass flow in the subsoil causing rapid movement of water and solute to the drains. The result is that much of the nitrate in the upper horizons appears to be protected from leaching. When used with laboratory‐derived parameters, the model was a poor predictor of both the pattern and quantity of nitrate

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01296.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYA new field method of obtaining, with minimal disturbance, the unsaturated hydraulic conductivity (K0) and sorptivity (S0) from unconfined disc permeameter measurements is introduced. Conventionally, the sorptivity is obtained from the initial square‐root‐of‐time behaviour of discharge from the disc permeameter. In some cases this can be difficult to measure, in part because multi‐dimensional flows approach quasi‐steady state very rapidly. As an alternative we extend the ponded twin‐ring method to unsaturated discs of several radii. This method has the advantage that only long‐time, quasi‐steady discharges are needed to obtainK0andS0.In the present study, the two methods are tested using data obtained for a fine sandy loam at a supply potential (Ψ0) of – 35 mm and

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01297.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYDifficulty is sometimes experienced in achieving dehydration and acceptable impregnation of undisturbed specimens of clay soil. It is necessary to avoid shrinkage when removing water and disruption of brittle dehydrated specimens when impregnating. Methods for dehydrating clayey soil for structural studies are reviewed. A method using continuous flow and dehydration of acetone or 1,4 dioxane followed by slow impregnation is outlined. Inexpensive techniques for measuring the water content of these two solvents are described.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01298.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYSodium, potassium, magnesium and calcium chloride solutions of four concentrations (0.4, 1.0, 4.0, l0.0meq dm−3) and distilled water were equilibrated with the highly weathered, acidic subsoil of a Plinthic Paleudult from Natal at a soil:solution ratio of 2.2:1, then separated by centrifugation with an immiscible liquid and analysed for inorganic solutes. With each salt, increasing ionic strength resulted in lower solution‐pH (the maximum pH was 4.95 in the distilled water equilibration) and higher aluminium concentration and activity. These effects were much less marked for sodium (maximum ΔpH of 0.47) than for the other cations (maximum ΔpH of 0.83) and both the concentration and activity of aluminium were correspondingly lower (by tenfold at the highest chloride concentration) in the sodium solutions.Irrespective of the nature or concentration of the electrolyte added, pH and the activities of A13+and silica in solution were consistently interrelated in a way which suggests that equilibrium with the gibbsite and poorly crystalline kaolinite in this soil had been closely approached. The results provide a basis for anticipating the effect of infiltrating solutions of fertilizer salts on subsoil acidity and suggest that a beneficial effect may accrue from the presence of sodium in the cation suite of acid

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01299.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY