摘要:

SummaryA review of water retention functions based upon fractal soil structures is presented. We consider the modelling approach for a fractal fabric, a fractal pore boundary and a fractal pore space, identifying the latter case as one of particular complexity. In each case, the water retention function is derived from the pore volume distribution arising from the structural model in question. We examine published models and highlight problems, namely lack of generality and inconsistency with the assumed fractal structure. The models considered in this paper do not account for the effects of pore connectivity, and as such their validity as a necessary condition for the existence of fractal structure is questionable.

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01365.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryA semi‐quantitative method is developed to assess the relative weathering of tropical sandy soils. Individual quartz sand grains are classified on the frequency and the size of dissolution etch pits in their surfaces, using scanning electron microscopy (SEM). A scale with five grain‐type classes reflecting increasing intensity of etching is defined, and the relative frequency of each of these classes in horizons of selected soil profiles is determined. To summarize the information contained in the frequency distribution a weighted score, the weathering score, is calculated. This score assesses the relative weathering of individual horizons, and it makes it easy to compare them with other horizons within the same or from other profiles. It is useful in detecting weathering trends and differences between horizons of tropical sandy so

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01366.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummarySecond derivative diffuse reflectance spectroscopy (DRS) in the visible range has been used to characterize changes in colour and identify the nature of Fe oxides which withstand reduction during experimental yellowing of reddish materials. It is accepted that haematite dissolves preferentially and faster than goethite, and Al‐substitution controls the dissolution kinetics of Fe oxides. However, DRS has shown that haematite is more resistant than predicted and that some Fe‐oxides, probably trapped within kaolinite particles, are inaccessible to solvents. DRS allows the nature of dissolved phases at each deferration step to be determined and changes in Al‐content of residual phases throughout deferration to be followed. It also demonstrated that Helmholtz coordinates correlate very well with changes in Fe‐oxide mineralogy and are preferable to redness ratings when monitoring differential dissolution of Fe oxides through colour measurements. DRS is a powerful and sensitive technique for monitoring the dissolution of Fe oxides i

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01367.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummarySingle rainfall events play an important agricultural and ecological role, especially in dry regions where precipitation is erratic. Infiltration, redistribution and evaporation of single quantities of water are important in this context and have been investigated in the laboratory.Three soils of differing texture were packed at two uniform initial water potentials (– 100 MPa and –1.5 MPa) into columns, after which 12.7, 25.4 and 50.8 mm of water were applied as a single irrigation. The columns were maintained in a controlled hot and dry atmosphere (evaporativity = 16.7 mm d‐1) for up to 30 days, during which water‐content profiles were measured at intervals.Infiltration was rapid to depths ranging between 35 and 250 mm. Thereafter redistribution was small. Evaporation caused the water profile to develop three zones: dry between the soil surface and the drying front, dry below the wetting front, and an intermediate wetter zone between the drying and wetting fronts. As evaporation continued, the drying front moved deeper into the soil and the water content in the intermediate zone decreased.During the first few hours evaporation was rapid and constant, at the evaporativity of the atmosphere. Subsequently, evaporation was slower. Total evaporation(E)increased with time(t)asEα tnfort>1 d, where n = 0.24 for a loamy sand, 0.33 for a clay loam and 0.31 for a silty clay loam.Weighted‐mean soil‐water diffusivities, averaged over the profile above the wetting front, ranged between 1000–2000 mm2d−1at the start of the falling‐rate stage and 200–400 mm2d−1near air‐dryness, in reasonable agreement with the few r

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01368.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryResults from a previous study, in which two different forms of sulphur fertilizer were applied to a grazed pasture, were re‐examined to show that the movement of sulphate to subsurface drains over three consecutive drainage seasons could be satisfactorily predicted using a simplified analytical form of the transfer function model (TFM). Two simple parametric forms: the exponential Burns and lognormal functions, were used for the probability density function for solute travel, and more realistic assumptions about the biologically mediated source‐sink terms were incorporated. Sensitivity analysis showed that the model's prediction was very sensitive to the retardation coefficient for sulphate relative to the non‐adsorbed solute chloride and the volume of soil water that is effective in solute transport. The procedures can be easily adapted for management pur

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01369.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe effect of two hydroxides (NaOH and KOH) and two chlorides (NaCl and KCl) on aggregate stability and saturated hydraulic conductivity (Ks) was studied in three New Zealand soils using concentrations (0.003, 0.03, and 0.3m) typical of the range ofpH found in strongly alkaline industrial liquid wastes. The different solutions were used as pretreatments prior to aggregate stability measurements and as influent solutions forKsmeasurements.The concentration of hydroxide appeared to be the most important factor affecting aggregate stability andKSin all soils. Aggregate stability andKsdecreased with increasing hydroxide concentration, but were generally unaffected by chloride solutions. RelativeKsdecreased to100% with chloride solutions, but decreased substantially when distilled water replaced the chloride solutions. Differences in aggregate stability andKsdue to the cation present (either Na+or K+) appeared to be very small. A surface crust formed in the upper 1 cm of the soils leached with hydroxide solutions. This surface crust had substantially less organic carbon than the upper 1 cm of soil from the cores leached with chloride.A two‐stage process explains the decrease inkswhen strongly alkaline solutions are applied to soil. First, organic matter dissolution decreases aggregate stability, with the rate of organic matter dissolution depending on hydroxide concentration; and second, increased repulsion of soil particles (due to increasedpH) causes movement of dislodged particles into pore spaces, resulting in decreasedK

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01370.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryIn the Congo, near Pointe‐Noire,PinusandEucalyptuswere planted on the savanna for 30 years. We have characterized the effects of this change on land‐use on the composition of carbohydrates in whole soil and particle‐size fractions of the soil. Carbohydrates represent variable proportions of the total soil organic carbon (TOC) of various particle size fractions. The largest proportions of sugar‐C were found in the savanna soil with as much as 250 mg g−1TOC in the coarsest plant remains and approximately 190 mg g−1TOC in the finest organo‐mineral fractions, whereas there was always less sugar in plantation soils. The monosaccharide xylose and mannose have different distributions: xylose appears to be the marker of the vegetal inheritance, whereas the dominance of mannose in the clay fraction bears the signature of current microbial sugar synthesis.The quantitative and qualitative evolution of the whole soil carbohydrates was studied as a function of plantation age. Carbohydrate‐C represents 131 mg g−1of the soil organic carbon in the savanna soil, but decreases to an average value of 75 mg g−1in plantations more than 6 years old. This appears to be due mainly to the stimulation of the mineralization of the glucose, which represented 60% of the total sugars in savanna soil and only 45–48% in tree plantations. The ratio [arabinose + galactose + fucose]/[rhamnose + xylose], which is the largest in the oldest plantations, is significant for evaluating the replacement of carbohydrates of the original grass savanna

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01371.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummarySoil samples from the A horizon of an Eutrochrept under spruce forest and permanent grass were fractionated into clay‐, silt‐ and sand‐size separates. Humic acids extracted from each fraction were analysed by pyrolysis‐gas chromatography‐mass spectrometry. Protection of functional groups by simultaneous pyrolysis and methylation yielded pyrolysates in which methyl esters of fatty acids, aliphatic dicarboxylic acids, abietic acids, phenolic acids and benzenecarboxylic acids were represented. However, methylation was not complete, and unmethylated compounds were also present. Spectra showed differences in humic acid composition between size separates as well as across land use regimes. The abundance of lignin‐derived pyrolysis products increased with decreasing particle size, and was greater in soil under spruce than in soil under grass. Also, the lipid components differed, with hexadecanoic and docosanoic acid methyl esters being the dominant compounds in humic acids from soil under spruce and hexadecanoic and octadecanoic acid methyl esters in the humic acids from grassland. A good correlation was found between previous13CNMR and wet chemical data and pyrolysis data, indicating that pyrolysis‐methylation can be used for fast detailed chemical characterization of humic acids extracted from s

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01372.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe composition of soil organic matter (SOM) on sewage farms south of Berlin was investigated by solid‐state CP/MAS13C‐NMR and pyrolysis‐field ionization mass spectrometry (Py‐FIMS) of freeze‐dried sewage solids and soil samples of differing contamination. These were an untreated soil (USOIL), a former sewage farm used as arable land since 1990 (SF90A), and a recent sewage farm (SF1994). The CP/MAS13C‐NMR spectra showed enrichments of the sewage‐treated soils with aliphatic C and C in OCH3‐groups and amino acids. In the Py‐FI mass spectra the major markers of sewage and SOM in sewage farm soils were (i) N‐containing compounds, in particular peptides, (ii) dimethylphthalate (m/z 194), (iii) sterols, and (iv) signals in the mass range m/z 502 to 554 of mono‐ and diaryl esters which were substituted by long aliphatic chains. The latter signals were intense in the sewage solids, increased in intensity from sample SF90A to SF1994; but they were not present in the USOIL, thus clearly indicating anthropogenic origin. Temperature‐resolved Py‐FIMS showed that the SOM compounds in the sewage farm soils were generally incorporated into bonds with widely different stabilities which could be relevant for SOM turnover and environmental effects. This is demonstrated for the trapping of dimethylphthalate in a

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01373.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryOrganically‐bound Al in acidic, base‐poor sandy soils seems to be a major contributor to dissolved Al. This hypothesis has been tested under field conditions at two intensely acidified sites. The research was conducted at the agricultural trial fields at Lyczyn, Poland, which have been fertilized continuously for 30 yr with 130 kg ha−1a−1N (as NH4NO3or urea). The effect of depletion of Al on its solubility was also studied.Field data confirmed that mobilized Al originates largely in the organically bound fraction of soil Al. Depletion of this fraction resulted in a considerable decrease in the mobility of Al such that, at pH = 3.0 and reaction times of a few weeks, small amounts of Al were mobilized. Apparently, the rate at which Al is dissolved from structural silicates, which are abundant in the soil investigated, is small. This suggests that at sites in Poland most exposed to acid deposition, where the rates of soil acidification and depletion of organically‐bound Al are greatest, both the concentration of Al and the soil solution pH are expected to decline

ISSN:1351-0754    

DOI:10.1111/j.1365-2389.1996.tb01374.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY