摘要:

SummaryDetecting small temporal change of spatially varying soil properties demands precise estimation. Design– and model–based methods are compared for estimating temporal change of soil properties over finite areas. Analytical expressions for the estimators and their variances arc derived for the two approaches, and formulae for the expectations of the variances under the random–process model are developed. Among the randomized designs simple, stratified, and systematic random sampling using the arithmetic mean as estimator have been studied. Pairing the sampling positions on the different occasions increases the precision of design–based estimation if the observations are positively cross–correlated. The relative precisions of the means of stratified and systematic samples depends on the spatial correlation. Neither is more precise than the other in all circumstances. The stratified design provides an unbiased estimator for the sampling error, which is not available from systematic samples. Theoretically, the geostatistical global estimator is more precise than the estimates derived from any of the classical designs when many realizations arc repeatedly sampled at random. In practice, with only a single realization of the process, this is no longer relevant. Moreover, errors in estimating the variograms add to the total error of the method. It seems that only by sampling from large auto–correlated random fields can the precisions of the methods be compared

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01808.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryDesign‐based and model‐based methods of estimating temporal change of soil properties over a finite area have been compared. Two large fields of auto‐ and cross‐correlated data were simulated, each representing the spatial distribution of a variable at one time. The fields were then sampled repeatedly. The means of stratified and systematic random samples and geostatistical global estimates were used to infer the mean difference between the fields. All estimators were unbiased, but their variances differed. Pairing the positions on the two occasions increased the precision of the design–based estimates. Systematic sampling was slightly more precise than stratified sampling. Kriging was less precise than both because some of the sample information must be used to estimate the variograms at short lags. Neither balanced differences nor the normal formula for simple random sampling predicted the estimation variances of small (n<50) systematic samples accurately. For larger samples the method of balanced differences performed well. If the spatial variation is unknown in advance and only small samples can be taken then stratified random sampling with two observations per stratum is the preferred design. It resulted in the best combination of precision and accuracy in predicting the sampl

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01809.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA number of image analysis techniques, largely drawn from remote sensing, have been applied to soil thin sections in an attempt (i) to overcome some of the limitations of previous approaches and (ii) to identify some complex soil features.Using different wavelengths and light polarizations, microscopic images of thin sections obtained from different horizons were digitized. It was then possible to carry out a series of experiments including geometric corrections, creation of multilayer images, principal component transformation, classification procedures, morphological analysis and modelling of bi‐dimensional optical anisotropy of the soil matrix.As a special procedure, principal component images were included in the multilayer images, thereby improving the classification on which a morphological analysis was conducted. The reliability of the procedure was tested against point counting and was found to be successful. The overall procedure allowed the combination of brightness and shape classifications. Bi‐dimensional matrix optical anisotropy was detected at 256 levels and plotted as a three‐dimensional perspective view, thus creating a new way of studying this fe

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01810.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryAdsorption of selenite on goethites in NaCl and Na2SO4solutions was performed in a newly designed flow‐through reaction chamber as well as in a traditional batch system. Six goethites with different morphologies were used as adsorbents. For the experiments the goethite was placed in the chamber prior to flushing with the salts. Introduction of the NaCl and Na2SO4solutions only, and in combination with selenite, resulted in different responses with respect to the pH. The pH changes were explained by means of anion‐binding energies, with Cl−

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01811.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe reactions of two organic (citrate and fulvate) and two inorganic (chloride and phosphogypsum) calcium compounds were studied during leaching of columns of unsaturated acidic soil. The potential of these compounds to decrease the aluminium concentration in the soil solution and remove exchangeable aluminium, and their effects on soil acidity are described.The calcium citrate solution increased the soil solution pH from 5 to a maximum value of 7 in the upper portion of the column. In contrast, the fulvate, calcium chloride and phosphogypsum solutions had little effect on soil‐solution pH. Treatment with calcium citrate, or fulvate solution that contained 51 mmNa, removed most of the exchangeable aluminium from the column. The cation exchange sites in the upper portion of the column were saturated with calcium, and the cation exchange capacity of the soil was increased from 35 toc.80 mmolckg−1in the calcium citrate treatment. Leachate from this treatment contained low (<2 mm) calcium concentrations and high aluminium concentrations. In contrast, the above changes were not shown by the calcium chloride and phosphogypsum treatments. In these treatments the calcium concentration in the leachate was equal to that in the inflowing solution, which indicated that calcium was transported through the entire column. These results suggest that calcium alone was ineffective in displacing aluminium from the cation exchange sites and a strong complexing agent such as citrate or fulvate is needed to mobilize the exchangeable alumin

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01812.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryAcidity in the soil surface and subsurface is of major concern in horticulture, cropping and pasture production systems in southern Australia. Broadcast applications of lime to the surface have proved to be ineffective in ameliorating subsurface acidity in the short term. Two calcium‐saturated coal‐derived organic products, an ‘oxi‐product’ (OXPR) and an ‘oxi‐fulvate’ (OXFU), were evaluated for use as liming materials with specific consideration given to amelioration of subsurface acidity. The effects of these two organic products and of lime on the chemical composition of the A1and A2horizons of an acid red podzol were investigated in leaching columns, 20 cm long. OXPR and OXFU supplying 80 or 160 g Ca m−2were compared to 160 g Ca m−2applied as CaCO3and a control receiving no amendments. The effects of CaCO3on exchangeable Al and pH were limited to the surface 2 cm. In contrast, the two organic amendments were effective in decreasing exchangeable Al and increasing pH and exchangeable Ca to depth, the extent being a function of amendment and rate applied. The formation of inorganic and organic complexes were assumed to be responsible for the movement of Al out of the column in the leachate, although significant quantities of Al were precipitated in the column. Significant linear regressions were observed between the ionic strength and Al in the leachate. Significant quantities of Mg and K were displaced by Ca and leached from the column; consequently, this loss must be considered against the benefits of decreased exchangeable Al when assessing fertility f

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01813.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Summarywham, an equilibrium chemical model for soils, waters and sediments, centred on a discrete‐site/ electrostatic model of humic substances (HS), has been used to analysae batch titration data for organic and mineral horizons of acid soils. In most cases, tolerable fits were obtained by optimizing the soil contents of HS and aluminium, while keeping the model parameters (site densities, equilibrium constants, electrostatic terms) fixed. The optimized contents agreed reasonably with those estimated by chemical extraction. For some mineral soil samples, low in HS and high in aluminium, fitting of the titration data was improved by assuming the formation and dissolution of A1(OH)3and adjusting its solubility product. Solid‐solution distributions of base cations (Na+, Mg2+, K+, Ca2+, NH+4) could be explained by non‐specific counterion accumulation, with a small degree of selectivity. The WHAM sub‐model for fulvic acid sorption accounted approximately for observed aqueous‐phase concentrations of organic carbon and organically‐complexe

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01814.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA discrete‐site/electrostatic model of ion binding by humic substances has been applied to proton‐and copper‐binding data for a soil humic acid. The proton data cover thepH range 3–9 and the ionic strength range 0.001m‐0.1m, while those for copper refer to thepH range 4–5, ionic strengths between 0.005mand 0.1m, andp[Cu] values between 3 and 8. The model is able to explain the major observed trends, including the dependence of proton and copper binding on ionic strength and the binding of copper as a function ofpH. However, the calculated ionic strength dependence of copper binding is slightly less than that observed. In addition, the model has been used to predict ratios of protons released to copper bound under different conditions, on the basis of the separately estimated parameters for proton and copper binding. The model correctly predicts the ratios to be between 1 and 2, and to decrease with increasing bound copper

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01815.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe reduction of iron(III) by natural humic acid (NHA) was studied in aqueous solution as a function of pH, time and iron(III) concentration. The information gained from FTIR and ESR spectroscopies as well as potentiometric data suggests that redox reactions occur at a low pH due to the involvement of phenolic groups and radicals. At pH values higher than 3.5 the reaction is strongly inhibited by the formation of iron(III)–humate complexe

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01816.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe organic matter of the soil has a large potential to retain inorganic nitrogen by means of both biotic (microbially mediated) and abiotic (chemical) reactions. We derive one equation with which we analyse the nitrogen retention due to these mechanisms in terms of organic matter properties. We first of all show how to separate gross mineralization from immobilization. We then show that our equation can reproduce studies of microbially–mediated or purely inorganic immobilization. We then apply the theory to soils of different characteristics (typical agricultural and forest soils) and find that the major factor determining the fraction of added inorganic nitrogen that is immobilized is the ratio between soil carbon and inorganic nitrogen concentratio

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1995.tb01817.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY