摘要:

SUMMARYGas diffusivity was measured in duplicate soil cores (10 cm long and 6 cm diameter) from depths of 0–10, 10–20 and 20–30 cm, and in beds of 1–2 mm aggregates taken from the same site at the same depths. A steady state method was used, with ethane as the diffusing gas. As the samples dried, the fractional air‐filled pore space increased, from 0. 1 to 0.45 for the cores and from 0.35 to 0.65 for the aggregates. The maximum relative diffusivity of the aggregate samples (0.38) was approximately twice that of the core samples, reflecting the difference in pore space. Equations are presented for calculating the solid, air and water fractions of the samples and for calculating the diffusivity within peds and aggregates. These calculations allowed a comparison of the diffusion/porosity relationship within aggregates

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00320.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThis paper reports observations on the behaviour of large cores of undisturbed clay‐loam soil during the drainage of water under an imposed step in potential. Rates of outflow and the matric potential at various points in the core were recorded during drainage. The volumes of ‘macropore‐channels’(large, continuous voids) were estimated to be 0.005 m3m−3in a subsoil sample, and 0.026 m3m−3in a topsoil sample from arable land. The calculated values of hydraulic conductivity were found to vary with the size of the step in potential imposed on the sample at the start of each drainage experiment. The available evidence suggested that the apparentK/Ψmrelationship was influenced by the rate that air could enter the soil to replace water during drainage. The degree of restriction on air movement was affected by the initial drainage behaviour, and this varied with the imposed step

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00321.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYThe mineralogy and some physical and chemical properties of an Andosol developed in four distinct layers of volcanic ash have been investigated. Analytical methods used include X‐ray diffraction, transmission electron microscopy, particle‐size analyses, infrared spectroscopy, pyrophosphate extracts of C, Al and Fe, and acid‐oxalate extracts of Al, Fe and Si. Three buried A horizons in the ash were also dated by the14C method. The dates obtained indicate burial of A horizonsc. 17700, 14500 and 8600 years B.P., respectively. Halloysite dominates the weathered fraction in the ash older than 17700 B.P., whereas allophane and imogolite with molar A1/Si ratios of 1.7–2.0 are predominant in the younger ash layers. Some kaolinite also occurs in the upper two layers of ash. It is considered possible that the halloysite in the deepest ash layer formed under different climatic conditions from those prevailing at present, rather than due to resilication of allophane under the overburden of ash. The results also demonstrate the mineralogical complexity of soil developed in more than one layer of volca

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00322.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYIron and aluminium hydroxides were precipitated both in the presence and absence of kaolinite. The reaction between phosphate and these hydroxides was measured for periods which ranged from 5 min to 72 h. The effect of time on phosphate sorption was examined by plotting the sorption data according to different, simple, kinetic equations such as the first order, second order, the parabolic diffusion equation, the Elovich equation and the modified Freundlich equation. The effect of time on sorption was also examined by the mechanistic model recently developed by Barrow (1983b) for the sorption and desorption of phosphate by soils.The sorption of phosphate by iron and aluminium hydroxides increased with time and the reaction continued through the period of observation without reaching a true equilibrium. Curvilinear relationships were obtained when the data were plotted according to the simple kinetic equations. These simple kinetic equations fail to describe the effect of time on sorption partly because the mechanism is different from that postulated and partly because they do not consider electrostatic effects when phosphate ions react with a charged surface. The mechanistic model of Barrow (1983b), which takes this effect into account, described effect of both concentration and time on phosphate sorption. According to this model, the increase in phosphate sorption with time was caused by a redistribution of adsorbed phosphate into the interior of the particles of iron and aluminium hydroxides by solid‐state diffusio

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00323.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYSoil samples from long‐term plots annually fertilized with superphosphate since 1952 and also unfertilized (control) plots of an irrigated and intensively grazed pasture in Canterbury, New Zealand, were subjected to a sequential extraction procedure followed by31P nuclear magnetic resonance (NMR) analysis of the soil phosphorus (P) forms present.Overall, 80% of the total organic P (as determined by ignition) was removed from the soil by the sequential extraction procedure. Most of the organic P (90%) detected by NMR was in the monoester fraction. Small quantities of diester and pyrophosphate were also found. Choline phosphate constituted a significant proportion (18–25%) of the monoester P in the acetylacetone and 0.5 M NaOH extracts. Long‐term superphosphate additions resulted in almost all of the P accumulated in the monoester P fraction (up to

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00324.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYFreshly exposed unameliorated spoil and vegetated spoil were analysed for their nitrogen constituents using methods devised for soils. The main components found were non‐exchangeable ammonium (25%), hydrolysable nitrogen (33%) and unidentified non‐hydrolysable nitrogen (62%). Summation of these exceeded 100% because hydrolysis with 6 M HCI extracted much of the non‐exchangeable ammonium. Ammonium in the hydrolysate accounted for over 90% of hydrolysable nitrogen in freshly exposed unameliorated spoil and 70% of hydrolysable nitrogen in vegetated spoil. Correction for this ammonium in the hydrolysate allowed estimates of ‘recent organic’ nitrogen accumulation to be made. These estimates were significantly correlated with spoil mineralizable nitrogen levels. The nature of the nitrogen constituents of colliery spoil and the use of ‘recent organic’ nitrogen estimates in assessing site fertility

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00325.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYFour soils with 6, 12, 23 and 46% clay were fractionated according to particle size after incubation for 5–6 years with14C labelled straw, hemicellulose or glucose: 6–23% of the14C was still present and the amount increased with increasing content of fine particles.clay fractions contained 66–84% of the14C and the silt fractions accounted for 4–19%.<2% was found in the sand fractions and 4–9% was water soluble. The distribution of the native C was: clay, 46–68%; silt, 20–31%; sand, 2–7%.The clay fractions had higher relative proportions of14C than of native C, the reverse being true for the silt fractions. This distribution pattern was not directly related to soil clay content or to kind of organic amendment.The C enrichment factor of clay and silt fractions (per cent C in fraction/per cent C in whole soil) increased with decreasing fraction size for both native and14C. However, clay enrichment factors were higher for14C than for native C, whereas silt enrichment factors were lower.A soil (9% clay) that had been incubated in the field for 18 years with14C labelled straw was also analysed. Labelled C content at sampling was 9% of the initial value. In contrast to the other soils the distribution of labelled and native C was similar in the clay and silt fractions, which contained 55% and 33% of the whole soil C, respectively.The results indicate that clay‐bound organic matter may be important in mediumterm organic matter turnover, whereas silt‐bound organic matter may participate in longer‐term o

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00326.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYWater‐soluble and exchangeable basic cations, and electrical conductivity, were measured in temperate and tropical soils. The ‘availability’ of cations in temperate soils is a function of both the amounts of exchangeable ions and the electrical conductivity of the solution, especially for divalent cations. In tropical soils the solubility of Ca and Mg seems less clear. The implications for some management problems are disc

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00327.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYIn upper mineral horizons, CEC by compulsive and isotopic exchange methods, using Ba2+as the saturating cation, gave higher values than the effective CEC at natural soil pH, and much higher values than CEC determined withmNH4OAc at pH 7. Cumulative Al release during leaching was considerably higher using Mg2+and Ba2+chlorides than K+and NH4+chlorides, and gave a different shape extraction curve. Basal spacing of the dominant dioctahedral vermiculite in the soil clays contracted from 14.5Å to 10.0–10.9 Å when saturated with NH4+and K+, restricting release of interlayer Al. Lower horizons, containing a large proportion of Al‐chlorite in the clay fraction, which did not contract with any of the cations, showed more normal exchange behaviour. On leaching, Al release was slightly greater with K+and NH4+, than with Mg2+and Ba2+, chlorides. The implication of the results for CEC measurements is disc

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00328.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

SUMMARYOrganic matter‐sesquioxide complexes in podzol B horizons are precipitated at specific carbon/sesquioxide ratios. Field data indicate that only part of the potential acidity is neutralized and that the maximum C/R2O2ratio (minimum metal content) at which organic complexes will precipitate depends on pH of the soil and consequently on parent material and profile development. Although C/R2O3ratios may be used regionally to predict the transition from soluble to precipitated complexes, such ratios cannot be used in soil classification or in a general definition of albic and spodic horizon

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1985.tb00329.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY