摘要:

SUMMARYThe transfer function mode) (TFM) and convection‐dispersion equation (CDE) were compared for predicting Cl−transport through a calcareous pelosol during steady, nearsaturated water flow. Large, undisturbed soil cores were used at constant irrigation intensities(q0)between 0.3 and 3 cm h−1, with a step‐change in Cl−concentration. The assumption of a lognormal distribution of travel times–characterized by the mean (μ) and variance (σ2)–permitted the flux‐averaged breakthrough curves (BTCs) to be modelled very accurately by the TFM. The BTCs could be modelled equally well by the CDE when both the mean pore water velocity (v) and dispersion coefficient(D)were optimized simultaneously by the method of least squares, but not when v was put equal toq0/v, whereVwas the mean volumetric water content.The best estimate of v was consistently>q0/v, which suggested that not all the pore water was effective in chloride transport. An operationally defined transport volume (θst) was calculated from the mean () or median (τm) travel times derived from the TFM. Chloride exclusion was not solely responsible for θst() being

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02133.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYRelative gas diffusivity(D/D0)was measured in peat cores equilibrated to set moisture tensions between zero and ‐ l0 kPa, using the radioactive gas85Kr. A relationship between relative diffusivity and the air filled porosity was obtained, which showed lower values ofD/D0at air‐filled porosities above about 0.13m3m−3, and higher values at porosities below about 0.10m3m−3than some of those found in the literature for mineral soils. The likely effects of shrinkage behaviour on drying in the field, on the relationship betweenD/D0and air‐filled porosity, are

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02134.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA mica was inserted into the soil at four sites to try to identify,in situ, the physico‐chemical changes in the soil caused by the introduction of different tree species, and especially conifers. Changes in the chemistry and mineralogy of the mixed‐layered mica, mica‐chlorite, vermiculite, after 11/2and 31/2years in the soil, showed good differentiation between soil horizons and between soil types. Differences due to tree species were present, but small. The mechanisms of mineral evolution can be defined with reference to experimental data obtained in the laboratory. In litter layers, the mica‐chlorite sheet was transformed into a mica‐vermiculite, and exchangeable cations predominated on the exchange sites. In the organo‐mineral horizons, changes varied depending on the soil type: in the podzol, transformation was similar to that in the litter layers, but in thesol brun acide, changes were dominated by the Al fixation on the exchange sites and its rapid hydroxylation which blocks these sites, leading to the formation of Al intergrade minerals.Different tree species produced deviations linked to their ability to cycle cations, and also to the different organic materials produced which can attack the mineral.The method has the potential to define the present soil environment and weathering processes, but it needs a more complete experimental design and the use of statistics to clarify the effects of the parameters and their i

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02135.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYB horizons from a set of 23 Scottish soils were examined by Py/MS multivariate analysis. These soils comprised phaeozems, cambisols, podzols and gleysols.The principal components analysis of 52 mass ion intensities partitioned the set of soils successfully according to morphological classes Bw, Bg and Bs, and established characteristic differences of organic composition between them. Reconstructed factor spectra for the factors effecting this partition showed distinct homologous groups of products to be responsible. These were principally pyrroles, alkenes and aromatic hydrocarbons of low molecular mass. Possible organic origins of these are discussed and related to the organic patterns found in the A horizons.The Bh (humus B) horizons of podzols gave pyrolysates richer in polysaccharide and lignin products than those of other B horizons, suggesting a less decomposed organic matter.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02136.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYIn a field experiment on a dark‐red latosol (haplustox) in the Cerrado of Brazil, green manure, including maize residues, increased yield of maize grain. Samples of soil from the experiment were investigated in the laboratory. Green manure caused no effect on amounts of phosphate extracted by Bray's solutions, nor by anion exchange resin. Adsorption measurements showed that green manure did not affect the total amount of phosphate adsorbed by the soil, in relation to the amount added nor to the concentration of phosphate in solution. However, green manure increased the proportion of added phosphate that became isotopically exchangeable so that after desorbing some phosphate in two stages, 99% of the adsorbed added phosphate was exchangeable in soil with green manure, but 89% was exchangeable in soil without it. Green manure increased the concentration of phosphate in solution that was maintained by a specific amount of exchangeable phosphate held by the soil. Buffer power increased with time, without and with green manure; but it was less in its presence indicating that phosphate was less strongly held, and would be more mobile in soil in the field.The results indicate that easily decomposable organic material, such as green manure and crop residues, makes fertilizer phosphate more effective for crops growing in an oxiso

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02137.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe sorption of inorganic anions by hydrous ferric oxide gel (Fe gel) from 10−1M NaClO4at pH 6.5 decreased in the order: orthophosphate (H2PO4)>arsenate (H2AsO4) = selenite (HseO3)>silicate (H4SiO4)>molybdate (MoO24−)>sulphate (SO24−)>selenate(SeO24−)>chloride (Cl−) = nitrate (NO−3). When each anion was added to Fe gel with an equimolar quantity of H2PO−4, there was no detectable effect of SO24−, SeO24−, Cl−, and NO−3on the amount of H2PO−4sorbed. Other anions depressed H2PO4sorption in the order H2AsO4>HseO3>H4SiO4>MoO24. At the lowest level of anion addition (500 mmol kg−1), H2PO4sorption was depressed by no more than 6% of the sorption level in the absence of a competing anion. In contrast, at the highest level of anion addition (1700 mmol kg‐1of each), H2AsO4decreased H2PO4sorption by 44%. The sorption of SO4−was completely eliminated when this anion was added with equimolar amounts of H2PO4. The ability of anions to compete with H2PO4for sorption sites could not be explained solely by the results obtained for the sorption of each anion alone. Thus, H2AsO4was more competitive than H2PO4when added together, even though more H2PO4than H2AsO4was sorbed when each anion was added alone. Although H2PO4was sorbed in larger amounts, there is no evidence to suggest that H2PO4. H2AsO4, and HseO3w

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02138.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe kinetics of Cu2+desorption from a contaminated Malaysian padi soil, English Supreme kaolinite and Wyoming bentonite are studied using a constant potential titration method. This technique involves maintaining a constant Cu2+‐sensitive electrode potential corresponding to a Cu2+ion activity below that which would naturally be supported by the soil in suspension. This is achieved by the controlled addition of complexing agent. Desorption occurs in response to the artificially reduced solution activity and the rate of the desorption reaction is revealed by the rate of addition of the complexing agent.The desorption results were fitted to three established kinetic equations, all of which showed reasonable agreement with the data. In particular, a two‐constant rate equation demonstrated some consistency between different materials. Both first‐order and ‘diffusion’ kinetic equations appeared to apply within specific titration conditions. Each equation is discussed in terms of its implied desorption mechanism and the inconclusive nature of such mechanisms for short term (<1 hour) desorption reactions is il

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02139.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYEleven soils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA, and dithionite‐EDTA (DE) to fractionate iron (and manganese) oxides. The amounts of cobalt adsorbed and acidity desorbed by the extracted soils as well as by two synthetic iron oxides were determined, using 0.85 mM cobalt in 0.2mNaNO3.No significant correlations were found between cobalt adsorption and the contents of extractable manganese or organic matter, presumably because of their low contents. The major part of the cobalt adsorption (by DE‐extracted samples) was due to the clay fraction and was associated with the release of approximately one proton per adsorbed Co. The remaining cobalt adsorption was attributed to the iron oxides. This portion of adsorbed cobalt was well described by considering soil iron oxides composed of only two fractions, an EDTA‐extractable fraction of high reactivity and a less reactive fraction corresponding to the difference between DE‐extractable iron and EDTA‐extractable iron. Approximately 1.7 protons were released per Co adsorbed by these iron oxide fractions and by the synthetic iron oxides.The amounts of cobalt adsorbed by the soil iron oxides were well predicted from the contents and specific surfaces of the two iron oxide fractions together with the specific cobalt adsorption of synthetic ir

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02140.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYMeasurement of the effect of KC1 addition to a soil suspension in pH‐stat experiments indicates that the pH titration curves of such a multicomponent system are characterized by a Curve of Zero Salt Effect (CZSE) rather than a Point of Zero Salt Effect (PZSE). This curve is most accurately measured as a functional relation between pH and KC1 molarity. The described method is very accurate and, by its rapidity, precludes long‐term changes in the sample which are the bane of classic batch experiments. In analogy, multicomponent soil systems will probably be characterized by a Curve rather than a Point of Zero Net Charge (PZ

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02141.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARY15N‐labelled ammonium nitrate solution was applied in late April to circular, enclosed micro‐plots prepared by pressing open‐ended polypropylene cylinders into an established sward of perennial ryegrass. Cylinders were removed from the ground at intervals between 2 and 370 days after the application and assessments made of the distribution of15N in plant and soil components. Of the added labelled N, 54.7% was recovered in the herbage which was cut four times during the growing season and again at the final sampling date. After two days, 37% of the labelled N was recovered in the soil microbial biomass. Large fluctuations occurred in the amount of15N recovered in the soil microbial biomass over the next 14 days suggesting that rapid cycling of15N occurred between this fraction and the mineral N fraction. After the first cut in late May, translocation of15N occurred more slowly from the roots into the stubble than from stubble into new herbage, so that the amount in the stubble declined more rapidly than did that in the roots. During the winter, there was no net transfer of N from the roots to above‐ground components of the sward. By the end of the growing season, half the15N remaining in the sward was immobilized in the humified fraction of the soil organic matter; some of this was mineralized in the following

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02142.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY