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1.
A quantitative assessment was made of the effect of the proportion of sand, silt, clay, and organic matter in twenty-six soils on the available-water capacities (AWC) of the soils. The AWC of a soil was negatively correlated with percentage coarse sand and positively correlated with the percentages of International fine sand (or American silt) and organic C. Using a regression equation, the AWC's of the soils were estimated from mechanical analysis data with a mean accuracy of ± 16 per cent of the mean AWC.  相似文献   

2.
The nature of the inositol pentaphosphate and hexaphosphate isomers in a number of contrasting Canadian and Scottish soils has been examined. The mixed esters were extracted from the soil with alkali and separated from other soil phosphates by anion-exchange chromatography using HCOONH4 as eluent. The composition of the mixture was established by anion-exchange chromatography using a gradient of HC1 as eluent, followed by paper chromatography of the esters thus separated, and by paper chromatography of the hydrolysis products. Esters of myo- and scylloinositol together constituted more than 90 per cent of the mixture in most cases. Relatively small amounts of dl-inositol and neoinositol were detected in hydrolysates and it was estimated that esters of these cyclitols did not exceed 10 per cent and 1 per cent, respectively, of the total. The ratio of myo-+dl-inositol hexaphosphates to scylloinositol hexaphosphate ranged from 1.1 to 2.7 in the Canadian soils and 1.8 to 4.6 in the Scottish soils. The ratio of hexaphosphates to pentaphosphates ranged from 0.9 to 2.4 in the Canadian soils and 3.0 to 4.3 in the Scottish soils. The three soils with the highest pH values contained relatively large amounts of scyllo- relative to myoinositol hexaphosphate, but one very acid soil also contained a high proportion of this isomer and no consistent relationship was noted between the constitution of the inositol polyphosphate fraction and any other soil property.  相似文献   

3.
THE INFLUENCE OF TEXTURE ON THE MOISTURE CHARACTERISTICS OF SOIL   总被引：1，自引：0，他引：1  
A quantitative assessment was made of the effect of the proportion of sand, silt, clay, and organic matter in twenty-six soils on the moisture contents at the upper and lower limits of available-water of the soils. Regression equations were obtained which enabled the moisture contents to be estimated on a weight or volume basis from mechanical analysis data using either International or American size grades. The accuracy of estimating the upper limit of available-water from the various equations ranged from ±9 to 22 per cent: for the lower limit from ±8 to 16 per cent of the measured values. Mean values of the moisture contents at the upper and lower limits of available-water for each textural class were calculated from the average particle-size composition for each class and from the regressions obtained.  相似文献   

4.
The mineralogical composition of clays (< 2μm) in representative profiles of all soil types of Israel was investigated. The soils were classified according to their clay mineral assemblages into three groups. I. Montmorillonitic soils. Montmorillonite is the dominant mineral and exceeds 65 per cent of the total minerals found; each of the other minerals comprises less than 15 per cent. 2. Montmorillonitic-kaolinitic soils. The soil clay fractions contain 50-60 per cent montmorillonite and 15-25 per cent kaolinite, generally adding up to more than 75 per cent of the clay fraction. 3. Montmorillonitic-calcitic soils. The clays contain more than 10 per cent calcite. Montmorillonite is the dominant clay mineral (except for one soil type, mountain rendzina, where calcite is dominant). The first and second assemblages are typical of the soils of the Mediterranean zone, whereas the soils of the desert zone are characterized by the third assemblage. The origin of montmorillonite, kaolinite, and illite, the three main clay minerals, was found to be detritic, as was the origin of palygorskite which was mainly found in the calcite rich soils of the desert zone. The cation exchange capacity of montmorillonite seems to be higher under higher precipitation. Montmorillonite content and cation exchange capacity of the clays were found to be highly correlated. The carbonate content of the clay fraction and the amount of carbonate in the soil were also highly correlated.  相似文献   

5.
A study was made of the qualitative and quantitative distribution of aerobic heterotrophic bacteria in the two mineral horizons of a developing podsol soil under Pinus. There was no significant difference in the total numbers or in the kinds of bacteria between the two horizons. In the acidic A1 horizon (pH, 3.6) Bacillus spp. comprised 58 per cent of the population, the remainder being composed of Gram-negative rods (15 per cent), pleomorphic rods (14 per cent), Gram-positive cocci (10 per cent) and streptomycetes (3 per cent). The corresponding figures for the C horizon (pH, 8.6) were Bacillus (23 per cent), Gram-negative rods (37 per cent), pleomorphic rods (10 per cent), Gram-positive cocci (17 per cent) and streptomycetes (13 per cent). These differences in distribution could not be related to any one environmental factor. The data from this investigation lend support to the view that different soil types can be distinguished by their bacterial floras. Bacillus subtilis, B. cereus and the Gram-positive cocci were biochemically and fermentatively active and many of the streptomycetes were able to degrade complex organic molecules. The Gram-negative and pleomorphic forms were apparently metabolically inactive.  相似文献   

6.
Removal of topsoil, mainly for making bricks, is one of the main causes of soil loss around large urban centres of the Humid Pampa, Argentina. In about 7 per cent of La Plata County, the 20–40 cm thick A‐horizon has been removed for that purpose. Most of the affected areas were originally prime farmland; however, with removal of the A‐horizon they became unsuitable for agriculture, including grazing, since the exposed Bt‐horizon is unsuited for plant growth due to its high clay content (45–65 per cent) and the low nutrient levels. Since trees survive better on poor soils than do agricultural crops, the possibility of afforestating desurfaced soils has been studied. Eucalyptus are one of the major species used in tree planting programmes aimed at reclaiming degraded soils since they are fast growing and can grow to commercial size in a wide range of soils and climatic conditions. The work reported here was done in a desurfaced Vertic Argiudoll and a similar non‐desurfaced soil (control). Three Eucalyptus species were tested, i.e. E. camaldulensis, E. viminalis and E. dunnii. Their height and diameter (dbh) growth were 47.9 to 75.8 per cent less and timber volume 86.5 to 98.5 per cent less on the desurfaced soil. E. camaldulensis grew best in all the parameters in the desurfaced soil. Although tree growth was poor, afforestation may be an alternative use for desurfaced soils where agriculture and livestock breeding are not possible. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

7.
The chemical nature and distribution patterns of the forms of N in a podzolic soil profile from central Sweden, developed under a stand of Norway spruce, were studied. Total N, native fixed NH4, acid hydrolysable-N, and the amounts of ammonia, hexosamine, and amino-acid N in the hydrolysate were determined. From 17 to 27 per cent of the N was insoluble in 6N HC1, the highest percentage being in the A2 horizon. Amino-acids in the acid hydrolysates decreased from 50 per cent of the total N content of the soil in the humus layer (A0) to 24 per cent in the B horizon. Amino-acid composition varied little in samples from different horizons. Hexosamine-N was 11–14 per cent of the total soil N, tending to increase with depth. Approximately 15 per cent of the total soil N was found in the soil hydrolysate as NH4. Values for native fixed NH4 extracted by N HF: N HCl were 34–80 ppm but were reduced to 10–17 ppm when corrected for the NH4 released by N HCl only. The figures thus obtained are considerably lower than those reported by other workers.  相似文献   

8.
The change in soil carbon (C) stock over a 19–31‐year period (mean 25 years) has been measured at 179 sites on a 20‐km grid across Scotland. Sampling was by horizon from a profile pit. Although soil bulk density determinations were absent at the first sampling time, we used bulk density values from the second sampling time calibrated against NIR spectra to predict the missing values. There was no detectable change in overall total soil C stock (mean ± standard error, to a depth of 100 cm), which was 266 ± 15 and 270 ± 15 t C ha?1 for the first and second sampling times, respectively, or generally in C stock within specific vegetation or soil types. The exception was for soils under woodland, excluding those on deep peat, which exhibited a significant (P = 0.05) gain of 1.0 t C ha?1 year?1. Soils under woodland (mainly coniferous plantation) also showed a significant (P = 0.04) increase in C content (g kg?1), a significant decrease in bulk density (P = 0.006) and an increase in the thickness of the Litter‐Fermentation‐Humus (LFH) layer (P = 0.06). Recalculating the C stock to a depth of 15 cm showed a significant increase in overall C stock (when deep peat sites were excluded) as well as specifically in moorland and woodland soils, suggesting that had we sampled only to 15 cm, we would have reached a different conclusion. Both improved grassland soils and those initially under arable cultivation showed a significant decrease in C content. However, the mean thickness of Ap horizons increased from 29 to 32 cm, with a concomitant decrease in C content and a slight increase in bulk density; this we ascribe to deeper ploughing between the sample periods. In the context of possible soil C losses, we can be 95% confident that the mean loss does not exceed 0.2% year?1 and 99% confident that it does not exceed 0.4% year?1.  相似文献   

9.
THE HIGH- AND LOW-ENERGY PHOSPHATE ADSORBING SURFACES IN CALCAREOUS SOILS   总被引：2，自引：0，他引：2  
The two-surface Langmuir equation was used to study P adsorption by 24 calcareous soils (pH 7.2-7.6; 0.8-24.2 per cent CaCO3) from the Sherborne soil series, which are derived from Jurassic limestone. High-energy P adsorption capacities (x″m) ranged from 140–345 μg P/g and were most closely correlated with dithionite-soluble Fe. Hydrous oxides therefore appear to provide the principal sites, even in calcareous soils, on which P is strongly adsorbed (x″m 6–51 ml/μg P). The low-energy adsorption capacities (x″m) ranged from 400–663 μg P/g and were correlated with organic matter contents and the total surface areas of CaCO3 but not with per cent CaCO3, pH, or dithionite-soluble Fe. Total surface areas of CaCO3 in the soils ranged from 4.0 to 8.5 m2/g soil. Low-energy P adsorption capacities agree reasonably with values (100 pg P/m2) for the sorption of phosphate on Jurassic limestones but phosphate was bonded much less strongly by soil carbonates (k″= 0.08–0.45 ml/μg P) than by limestones (k～10.0 ml/μg P). Low-energy P adsorption in these soils is tentatively ascribed to adsorption on sites already occupied by organic anions (and probably also by bicarbonate and silicate ions) which lessen the bonding energy of co-adsorbed P.  相似文献   

10.
Soils of the Countesswells and Insch series incubated with 14C labelled glucose or plant materials have been separated into clay (< 2 μm), silt, (2–20 μm), fine sand (20–250 μm) and coarse sand (>250μm) fractions and the distribution of individual labelled and unlabelled sugars was determined in each fraction. Both soils contained about 10–15 per cent clay, 18–23 per cent silt and about 60 per cent fine and coarse sand. For all soil samples the concentrations of sugars were usually greatest in the clay, slightly less in the silt, with values in the sand fractions being five or ten times lower, except when fresh plant material was present. In 14C glucose amended Insch soil, 55 per cent of the radioactivity in sugars (predominantly hexoses) occurred in the clay, 36 per cent in the silt, 3 per cent in the fine sand and 6 per cent in the coarse sand after 28 days incubation. For the Countesswells soil the values were 55, 42, 2 and 1 per cent respectively. In 14C ryegrass amended soil before incubation. 77 per cent of the radioactivity in sugars (predominantly glucose, arabinose and xylose) was in the coarse sand. After one year's incubation this had fallen to 59 per cent. In soil amended with 14C cereal rye straw the distribution of radioactivity in sugars after four years incubation was: clay, 21 per cent; silt, 43 per cent; fine sand, 21 per cent; coarse sand, 4 per cent. These distributions were compared with that of the naturally occurring sugars: clay, 31–42 per cent; silt, 40–43 per cent; fine sand, 3–11 per cent; coarse sand, 12–20 per cent.  相似文献   

11.
Data for mechanical and chemical analyses are presented with tabulated mean and median values based on fifty-five freely drained and ten poorly drained soils. The soils are relatively coarsed textured. The sand content of the mineral fraction is about 70 per cent (mean value) for freely drained and about 45 per cent (mean value) for poorly drained soils. Organic C is generally high in freely drained soils but relatively low in poorly drained soils, because of accumulating aeolian matter in the latter group, mean values are 8.2 in freely drained and 16.5 per cent in poorly drained soils. The C/N ratio is about 15 for each soil group. The cation exchange properties including pH seem to be dominated by organic matter, which may contribute to the total CEC of the soils about 165–300 me/100 g C. CEC of soils is usually 40–50 me/100 g. For some selected soils CEC of the separated mineral fractions was confirmed experimentally through ammonia retention. The pH level, especially of the freely drained soils, is relatively high (mostly 5.4–6.3) in spite of low degree of base saturation (mostly 10–30 per cent), a characteristic probably derived from the parent material. A highly significant correlation exists between pH and organic C. Proportionally exchangeable Ca seems low, while Mg and Na may be abundant. In some soils exchangeable Mg may exceed Ca.  相似文献   

12.
CHANGES IN THE CHEMICAL NATURE OF SOIL ORGANIC PHOSPHATE DURING PEDOGENESIS   总被引：1，自引：0，他引：1  
In two chronosequences of soils, total organic phosphate (P0) accumulated rapidly during the first 50 years of soil development, when organic matter increased and pH decreased. The rate of P0 accumulation then declined with age of soil until a ‘steady state’ was reached. The amounts of phospholipid, inositol phosphates and humic acid—P0 followed the same trends as the total P0. Parent materials and very young soils contained largely citric acid-soluble P0, but after less than 50 years, surface horizons accumulated sufficient organic matter to complex a considerable proportion of the P0. An upper limit of 20–5 per cent citric acid-soluble P0 and 70–80 per cent NaOH-soluble P0 was attained within 50 years of soil formation in the surface layers, and this slowly extended down the profile so that, after 10000 years, the soil had 20 per cent citric acid soluble-P0 and 70 per cent NaOH-soluble P0 to a depth of 1 m.  相似文献   

13.
MICROMORPHOLOGICAL QUANTIFICATION OF CLAY ILLUVIATION   总被引：2，自引：0，他引：2  
Three concepts are introduced to describe the extent of clay illuviation phenomena quantitatively for pedogenic interpretations: (1) the degree of clay illuviation per thin section or (sub)horizon, subdivided into 5 classes, ranging from negligible (< 0.3 per cent by vol.) to very strong (> 7 per cent by vol.) clay illuviation; (2) the degree of reworking of the illuviated clay, subdivided into 3 classes, ranging from weak (< 30 per cent reworking) to strong (> 70 per cent); (3) the profile clay illuviation index: the sum of products of clay illuviation percentage per (sub)horizon and horizon thickness (in cm). The index ranges from very low (< 50 per cent cm) to very high (> 700 per cent cm). A distinction was made between the profile index based on the in situ illuviation features only and that based on all the illuviation features.  相似文献   

14.
Relationships between the adsorption of p-chloroaniline and the original adsorbate concentration were investigated for five soils ranging in organic matter content from 1.7 to 8.1 per cent and in clay content from 0.5 to 21 per cent. Adsorption data were analyzed applying the linear form of the Freundlich equation. To evaluate the general relationship between adsorption of p-chloroaniline by soils and the solution concentration (C0), values of partition coefficient (Kp), reflecting the magnitude of distribution of chemical at equilibrium between soil colloids and solution were calculated. The experiments showed that the regression parameters were significantly correlated with the soil organic matter content. A comparison of the experimental results obtained with other soils and the calculated values gave satisfactory agreement.  相似文献   

15.
We studied the acid‐base properties of 16 fulvic acids and 16 humic acids isolated from the surface (3–15 cm) and subsurface (> 45 cm) horizons of two types of acid forest soils, derived respectively from amphibolite and granite rocks, under five different types of vegetation. The observed differences between the contents of humic substances in the two types of soils were related to the degree of Al‐saturation of the soil organic matter, as indicated by the molar ratio between pyrophosphate extractable Al and C. Humic fractions were characterized in terms of elemental composition, and CPMAS 13C NMR spectrometry. The contents of carboxylic and phenolic groups were estimated by potentiometric titrations conducted in 0.1 m KNO3 in a nitrogen atmosphere. The fulvic acids contained more carboxylic groups but less phenolic groups than the humic acids: the ratio of phenolic to carboxylic groups in the humic acids was 0.48 ± 0.10 and in the fulvic acids 0.23 ± 0.05. The mean values of the protonation constants of each of the humic substance fractions can be used as generic parameters for describing the proton binding properties. The fulvic acids isolated from the subsurface horizon of the soil contained between 2.6 and 23% more carboxylic groups, and the humic acids between 8 and 43% more carboxylic groups than those isolated from the surface horizon of the same soil.  相似文献   

16.
CONTENT OF INOSITOL PHOSPHATES IN SOME ENGLISH AND NIGERIAN SOILS   总被引：1，自引：0，他引：1  
The mono-, di-, tri-, tetra-, penta-, and hexaphosphates of inositpl accounted for between 11·2 and 30·4 per cent of the organic P in three English and four Nigerian soils. M yoinositol hexaphosphate was the component present in greatest amount in all soils. The lower esters (mono-, di-, and triphosphates) accounted for less than 3 per cent of the organic P in all soils, with the lowest amounts in the soils from Nigeria. For the penta- and hexaphosphates the ratio of myo- plus dl- isomers to scyll oinositol varied from 2·9 to over 10, the highest ratio occurring in the soils from Nigeria. Examination of the techniques showed that they gave approximately correct estimates of the inositol phosphates. The organic P in soil which was not estimated as inositol phosphate occurred in other forms.  相似文献   

17.
DISTRIBUTION OF CARBON DIOXIDE IN THE AQUEOUS PHASE OF AEROBIC SOILS   总被引：1，自引：0，他引：1  
Theory predicts that in the aqueous phase of aerobic soils carbon dioxide concentration/distance gradients are 1·35 times as large as those for oxygen. Because of differences in solubility, the partial pressure/distance gradients of carbon dioxide should be less than one-twentieth of the gradients of oxygen partial pressure. Experiments were carried out to test this prediction. In some experiments oxygen partial pressures were measured directly by means of a micro-electrode and carbon dioxide indirectly by methods involving microelectrode determinations of specific conductance in agar-CaCO3 gel. Measurements were made in models of water-saturated soil consisting of yeast cells embedded in agar-CaCO3 gel, around plant roots in agar-CaCO3 gel and within water-saturated soil. Oxygen partial pressures fell by 5–15 per cent of an atmosphere over distances of 0·2–0·4 cm whereas carbon dioxide partial pressures increased by less than 0·3 per cent of an atmosphere over the same distance. In other experiments different thicknesses of water-saturated soil were incubated with their upper surfaces exposed to air. The mean oxygen partial pressure fell by 7–13 per cent of an atmosphere with increasing the thickness from 0·2 to 0·4 cm whereas the carbon dioxide partial pressure never increased by more than 0·2 per cent of an atmosphere. Both sets of evidence confirm the theoretical prediction. It is concluded that the partial pressure of carbon dioxide in the aqueous phase of soils containing no oxygen-free zones, would never, even at the surfaces of roots, be more than 1 per cent of atmosphere greater than in the gas phase.  相似文献   

18.
The mineralogical composition and retention properties for radioisotopes (20Sr and 137Cs) of soils developed in five basalt flows of age varying from 6000 years to about four million years occurring in western Victoria were investigated. The trend of mineral weathering has been almost exclusively to amorphous material, kaolinite-plus-halloysite, and chlorite, the more soluble products of weathering having been removed. The most significant changes in clay mineralogical composition with time are the progressive decrease in the Si02/Al2O3 molar ratio of the amorphous material in the clay fraction of the surface horizons, from an initial value of approximately 4 to values of approximately 2, and the progressive increase in the amount of kaolinite-plus-halloysite, both in the topsoil and at depth, with age of the basalt flow. The amount of kaolinite plus halloysite increases from approximately 20 per cent of the clay of soil developed in the basalt flow 6000 years old to approximately 50 per cent of that of soil in basalt about four million years old. Evidence for the presence of halloysite was obtained by electron microscopy studies. The amorphous material and chlorite contents, each of which constitutes between 20 and 50 per cent of the clay fractions, decrease concurrently with the increase in kaolinite-plushalloysite content. Fixation of Sr by whole soil samples was controlled by the organic matter and free iron oxide contents rather than by the mineralogy of the samples. A high proportion of the added Cs was sorbed by whole soil samples. Much of the sorbed Cs was not readily replaced by CaCl, washings but was replaced in part by subsequent washing with NaCl of pH 5.3 and almost entirely by subsequent NH4Cl washings. Much of the Sr and Cs deposited on these soils by rainfall and dry fall-out would be sorbed; the ease of replacement suggests that these elements would be available for further movement through the food chain.  相似文献   

19.
邹德生 《土壤学报》1993,30(3):324-332
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20.
STUDIES ON THE DECOMPOSITION OF PLANT MATERIAL IN SOIL   总被引：6，自引：0，他引：6  
Soil samples taken during an experiment on the decomposition of 14C-labelled ryegrass in soil under field conditions (see Part I) were air-dried, irradiated, exposed to CHCl3 or CH3Br vapours, oven-dried or autoclaved. After these treatments the soils were inoculated, incubated, and the output of CO2 measured. All these methods of partially (or, in some cases, completely) sterilizing soil rendered a small heavily labelled fraction of the soil organic matter decomposable. This fraction is postulated to be the soil biomass. Treatments involving heat or irradiation rendered small additional amounts of the soil organic matter decomposable (by processes other than the killing of organisms). Incubating unsterilized soil with partially sterilized soil did not decrease evolution of CO2. This suggests that partial sterilization does not increase mineralization by destroying toxic substances that inhibit microbial growth, or by disturbing a host: predator balance in the unsterilized soil. The longer the labelled ryegrass was allowed to decompose in the field, the less labelled-CO2 was evolved after partial sterilization. In contrast, the same amount of unlabelled-CO2 was evolved from a soil that had been incubated 1 or 4 years with ryegrass. The labelled part of the biomass is considered to be largely zymogenic (with a half life of approximately 1.5 years), the unlabelled part largely autochthonous, remaining almost constant over the 3-year period. It is suggested that the size of the soil biomass can be roughly estimated from the size of the flush of CO2 after CHCl3 vapour treatment. Calculated on this basis, 2.3–3.5 Per cent the unlabelled-C in these soils (i.e. the C present in the soil before the labelled ryegrass was added) was in the biomass. Of the original ryegrass C added, 10–12 per cent was in the biomass after 1 year, decreasing to 4 per cent after 4 years.  相似文献   

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