摘要:

SummaryGas diffusion coefficients for hydrogen through air in packings of 1–2 mm crumbs from a clay loam (both under grass and under arable) and from a sandy loam were measured over a range of water contents as the soils were wetted. Diffusion coefficients decreased with increasing water content (decreasing air content) in three stages: in the first, to specific water contents of 0.08–0.10 gg1, decreases were small indicating the filling of pores less effective for diffusion; in the second, to crumb saturation, decreases were greater, and in the third, to complete saturation, decreases were greatest. Two of these stages are related to swelling: in the first, any slight swelling is contained within the crumb and there is loss to the gas of crumb pores only; in the second, the crumbs swell and there is simultaneous loss of crumb pore space and, more important, inter‐crumb space; in the third, swelling is complete, so, as in nonswelling soil, there is loss of inter‐crumb space only. Pore size and pore shape in the three soils, and pore distribution (intra‐crumb structure) in the grassland clay loam, may also affect diffusion but to a lesser extent: these influences are discussed. On subsequent drying there was little evidence of hysteresis in diffusion with water content, and only a slight indication in the arable clay loam of decreases due to structural degradation during the mea

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01029.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryA manually damaged, smeared layer (pan) was created at plough depth in two clay soils. Soil physical properties, soil water regimes and plant responses were measured in panned and non‐panned soil from 1972 to 1975. Continuity of the pan was readily lost on drying by formation of shrinkage cracks which did not fully close unless the soil had been wet for a long time; thus the occurrence of perched water tables above the pan was rare. The pans had no effect on crop yields. Leaf water potential, effective rooting depth and subsoil water deficits all showed that the pans affected water uptake by roots, but these effects were transient. The results indicate that natural amelioration of pans in these clay soils occurs even after slight drying and that the degree but not duration of drying is importan

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01030.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryChloride transport was investigated in four columns packed with glass spheres, spheres of a cation exchange resin, a loamy sand and a sandy loam, respectively. Using step input, vertical downward flow and relatively high flow‐rates, 0.01mKCl displaced water in the column packed with glass spheres, otherwise 3.33 × 10−4mCaCl2displaced or was displaced by 3.33 × 10−3mCaCl2. The breakthrough curves of chloride were analysed to give dispersion coefficients and mobile volumes. It was found that (i) chloride exchanged between mobile and immobile region in the sandy loam, (ii) the dispersion coefficient (K) was linearly related to pore flow velocity (U) for the individual columns, and that (iii) the ratio of dispersivity (dK/dU) to median grain diameter increased with increasing standard deviation of the logarithmicnormal grain size distr

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01031.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe self diffusion coefficient, in a naturally aggregated soil, of a solute which exists in both liquid and sorbed phases, was measured using a pulse labelling technique. This technique could have given evidence of slow equilibration between the two phases, but none was found. The magnitude of the self diffusion coefficient indicated that the solute is mobile in the sorbed phase. The mobility in the sorbed phase is described by a ‘virtual mobile fraction’. Within the limits set by the heterogeneity of natural aggregates, this was independent of both the volumetric moisture content and the bulk dens

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01032.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe techniques of measuring oxygen concentrations, oxygen flux and redox potential have been adapted for use in lysimeters. The accuracy and precision of the measurements have been improved, as well as their convenience for use in the limited soil volume of lysimeters.Concentrations of dissolved and gaseous oxygen are measured with a membrane covered polarographic electrode. The analysis is made on samples of air or solution carefully extracted from collection vessels permanently in the soil.Oxygen flux is measured with bare platinum electrodes. Careful choice is made of effective voltage for the measurement of equilibrium oxygen related currents.Redox potential is measured by the same platinum electrode and the reproducibility of measurements from permanently installed electrodes was assessed.The effect of soil structure upon the three kinds of measurement was seen and attributed to differences between the volumes of soil sampled by the different instruments.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01033.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe electric charge characteristics of five Ando (B) and two Red‐Yellow B horizon soils and two weathered pumices were studied by measuring the retention of NH4+ and Cl−at different pH values and NH4Cl concentrations. The magnitude of their negative charge (CEC; meq/100g) was dependent on pH and NH4Cl concentration (C;m) as represented by a regression equation: log CEC =apH +blog C +c.The values of the coefficienta(0.017 to 0.342),b(0.031 to 0.274) andc(1.41 to − 1.26) were correlated and depended on the kind of clay minerals present. A similar equation: log AEC =a’ pH +b’ logC+c’ was also found for the positive charge in the Ando soils, but there was little difference in the values ofa’(−0.204 to −0.251),b’(0.181 to 0.253) andc’(2.06 to 2.46) between the soils. It was shown that the equations generally hold for soils with constant and/or variable charges and describe adsorption equilibria in which NH4+ and H+, and Cl−and OH−compete for cation‐ and anionexchange sites, respectively. The significance and utility of th

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01034.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe structure of a humic acid from a New Zealand pasture topsoil has been investigated by1H‐n.m.r. spectroscopy. The work complements a recent13C‐n.m.r. study on the same humic acid. Irradiating the water peak in the spectrum greatly improves spectral quality. The results show that the proton aromaticity of the humic acid (excluding exchangeable protons) is 17%. Considerable amounts of protons in the humic acid are associated with carbohydrates (35%). Useful structural parameters describing the average molecular structure of the humic acid were derived by combining both1H and13C data. Further work is needed to determine both the percentage exchange of protons in alkali and the percentage of inorganic hydrogen in humic acids, before the condensation and the degree of substitution of aromatic rings can be quantitatively estima

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01035.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe structure of the organic matter from the ‘A’ and ‘B’ horizons of Patua loam (New Zealand) which is soluble in sodium deuteroxide has been investigated by conventional13C‐nuclear magnetic resonance spectroscopy. Experiments using inverse gated1H‐decoupling and a variety of pulse delays and weighting functions for Fourier transformation are reported. Sufficient number of transients have been collected for quantitative estimates of the aromaticity of the extract. The results complement an earlier qualitative study on this soil (Wilson&Goh, 1977) and illustrate conditions under which conventional13C‐n.m.r. spectra of humic materials should be obtained.The sodium deuteroxide soluble material from Patua loam ‘A’ and ‘B’ horizons has an estimated aromaticity of 33%. Different carbon types are not well resolved. However, there appear to be seven distinct resonances in the carboxyl region of the A horizon of which at least six are not derived from inorganic sources. Together with results already recorded in the literature, the results illustrate the variability of humic acids isolated from different soils. The nature of this var

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01036.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummarySamples of five soils whose pH in the field had been adjusted to between 5.0 and 7.5 were incubated with water or 0.01mCaCl2at 90% field capacity. Additional samples of the most acid soil were limed to various pH values immediately before incubation.Manganese, zinc and cobalt concentrations in the soil solutions, collected by displacement, decreased as the pH increased; the concentrations in calcium chloride solutions were higher than those in water solutions. The free divalent ions Mn2+, Zn2+ and Co2+ were the major metal species in solution at pH 5 but the proportion of the metals present as the free ion decreased as the pH increased.Differences in the manganese and zinc concentrations in the solutions were due not only to the pH of these solutions but also to the original pH of the soil in the field.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01037.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe ability of copper adsorbed by soil components to desorb back into solution was studied by means of experiments using radioactive64Cu. It was demonstrated that the amounts of copper which can be readily desorbed from soil components are very small.A dialysis equilibration technique was used to examine the distribution of adsorbed copper between individual materials in a multi‐component system. Where only adsorption of copper was involved, the distribution of copper between soil materials was found to agree with predictions based on adsorption studies with individual materials. However, where desorption was involved, as in the experiments on the redistribution of copper between components after an initial adsorption, the results were strongly governed by the poor reversibility of copper adsorption.It is clear that desorption or lack of desorption is very important in affecting plant availability of indigenous or added soil copper and in controlling the distribution of copper added to soil

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb01038.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY