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1.
Selenite fixation by soil particle-size separates   总被引:2,自引:0,他引:2  
The fixation of selenite by clay- (< 2 μm), silt- (2–20 μm) and sand-size (20–2000 μm) separates from two arable soils was examined in solutions of 75Se-labelled sodium selenite using a Se/sample ratio of 1/106. Size separates were isolated by ultrasonic dispersion and gravity sedimentation. Selenite fixation was determined after equilibration periods ranging from 5 min to 26 h. Hydrogen peroxide-treated samples were included to examine the effect of organic matter on selenite fixation capacity.
The relative distribution of native Se, C, dithionite/citrate-extractable Fe and Al between size separates was similar. Concentrations in clay were four to nine times higher than in whole soils, silt showing two to five times higher concentrations and sand being very low in Se, C, Fe and Al.
After 1 h, clay, silt and sand fixed 64–65%, 45–61% and <5% of the selenite added, respectively. The fixation on whole soils was 14–18%. After 1 day, fixation on clay, silt, sand and whole soil increased to 78–87%, 67–79%, 3–14% and 31–39%, respectively.
Hydrogen peroxide-treatment reduced the selenite fixation capacity of whole soil, silt and sand to very low levels. Fixation on peroxide-treated clay was in accord with values for pure clay minerals reported in the literature. Generally, the fixation capacity of peroxide-treated natural clay and pure clay minerals was only half that observed for intact clay-size separates, demonstrating the importance of organic matter in soil selenite fixation capacity.  相似文献   

2.
Long-term acidification has been shown to result in a considerable decrease in the amount of organically bound soil Al and in a gradual decrease in the solubility of Al. We examined the solubility of soil organic matter (SOM) and Al in four acid mineral soils (one Arenosol Ah, two Podzol Bh, and one Podzol Bs) as they were leached sequentially using a solution containing 0.001 m HCl and 0.01 m KCl. The acid leaching resulted in relative decreases in Al that were 2–6 times greater than for organic C. The organic C and Al dissolved by the acid leaching originated mainly in the pyrophosphate-extractable fraction of the elements. Protonation seems to be a major mechanism in stabilizing the residual SOM, as indicated by small changes in effective cation exchange capacity with the degree of acid leaching. In the samples of Podzol Bh and Arenosol Ah soils the solubility of Al (defined as log10{Al3+} + 1.5pH) in equilibrium suspensions (0.01 m KCl) was closely related to the ratio of pyrophosphate-extractable Al to pyrophosphate-extractable organic C. The Podzol Bs sample probably contained a small amount of a surface-reactive Al(OH)3 phase, which rapidly became depleted by the acid leaching.  相似文献   

3.
Phosphorus (P) speciation in 21 basaltic and four non-basaltic Irish grassland soils was determined by NaOH–EDTA extraction and 31P NMR spectroscopy. Organic P in basaltic soils ranged between 30 and 697 mg P kg−1 and consisted of phosphate monoesters (84–100%), DNA (0–16%) and phosphonates (0–5%). Inorganic P was mainly phosphate (83–100%) with small concentrations of pyrophosphate (0–17%). Phosphate monoesters were more important as a proportion of extracted P in basaltic soils, probably because of their greater oxalate-extractable Fe and Al contents. Phosphate monoesters appeared to be strongly associated with non-crystalline Al and increased with total soil P concentration, indicating that they do accumulate in grassland soils. In non-basaltic soils myo -inositol hexakisphosphate constituted between 20 and 52% of organic P, while scyllo -inositol hexakisphosphate constituted between 12 and 17%. These compounds were not quantified separately in basaltic soils because of poor NMR resolution in the phosphate monoester region, but appeared to represent a considerable proportion of the organic P in most samples. DNA concentrations were greater in basaltic soils compared with non-basaltic soils and were associated with acidic pH and large total C contents. The inability of the Olsen P test to assess effectively the P status of basaltic soils may result from strong phosphate sorption to Fe and Al oxides, inducing plant utilization of soil organic P. Phosphorus nutrient management should account for this to avoid over-application of P and associated financial and environmental costs.  相似文献   

4.
We have examined the charge characteristics, with special emphasis on the role of free Fe and organic matter, of humid tropical soils from Bambouto Mountains, Western Cameroon. The soils, which are formed from tuff, basalt and trachyte, are dominated by kaolinite and sesquioxides. The amounts of Fe oxides in them increase somewhat with depth. Open 2:1 phyllosilicates are present in trace amounts. The point of zero charge of the variable charge components, pH0, is around 4 in the topsoil (0–20 cm) and around 6 at 100–150 cm depth. In the subsoils, pH0 exceeds soil pH presumably because of large quantities of Fe oxides. Deferration increases both soil pH and pH0, but diminishes the anion exchange capacity. Oxides and oxyhydrates of Fe have positive surface charge, so their removal from the soils would result in overall loss of positive charge. Increases in soil pH would bring about an increase in the cation exchange capacity of the soils. Hence, management practices that reduce soil acidity should reduce loss of essential basic cations via leaching.  相似文献   

5.
To understand the dynamics of soil organic matter in humid regions in Asia, several soil and meteorological properties were tested to estimate the amounts of potentially mineralizable organic carbon (PMC) and nitrogen (PMN) as well as recalcitrant organic carbon (ROC) and nitrogen (RON). Eighty-nine surface soil samples were collected in Thailand, Indonesia and Japan from cropland and forest ecosystems. The fresh soils were incubated for 133 days under constant temperature and moisture conditions, and CO2 emissions and mineral N from the soils were monitored. The PMC and PMN were determined by fitting models to the cumulative curves of the CO2 and mineral N. The ROC and RON were determined by subtracting PMC and PMN from total C and total N, respectively. The soil properties tested included soil pH, sand, silt and clay contents, amounts of the acid oxalate soluble Si, Al and Fe, carbon and nitrogen contents of the light fraction ([LF] < 1.6 g cm−3) and heavy fraction (HF), and the C/N ratio of the LF and HF. The meteorological properties considered were mean annual temperature and precipitation. Using multiple regression analysis and a stepwise method, PMC and PMN was well estimated by the carbon and nitrogen content of LF (LFC and LFN) and the clay content. This suggests the partially labile nature of clay-associating organic matter as well as LFC and LFN. The PMC and PMN were well estimated by LFC and LFN in forest soils and clay contents in cropland soils. Major factors controlling ROC and RON were light fraction-organic matter, amorphous materials and clay content, suggesting the importance of parent materials in estimating the amount of recalcitrant organic matter in humid Asia.  相似文献   

6.
Five soil pedons–two aquic and two udic Haplustalfs and one petrocalcic Natrustalf–from the Indo-Gangetic alluvial plain of Western Uttar Pradesh were investigated to evaluate the pedogenetic processes. Sand/silt ratios indicate that parent material discontinuities are insignificant. Higher K content and lower SiO2/R2O3 ratios of the non-clay fractions in Bt, rather than in the A, horizons suggest maximum weathering at or near the surface.
An almost linear relationship between decrease in molar SiO2/R2O3 and % increase in clay to about 100cm depth in all the pedons, presence of clay argillans in Bt horizons (where % clay, fine/coarse clay ratio and bulk density values are greatest), all indicate that the development of argillic horizons in these soils was due, at least partly, to lessivage of clay. Fe in clay fractions decreases with depth whilst Al increases, but in the fine earth both increase steadily with depth. This, together with crystalline iron concretions in the lower Bt horizons, suggests that in Haplustalfs these horizons are gaining clay by neoformation/ reorganization of illuviated constituents, especially A12O3.  相似文献   

7.
Abstract. The Agricultural Catchments Research Unit model (ACRU) includes a decision support system (DSS) for estimating the water content of soil at field capacity (θ fc ) and wilting point (θ wp ) when these characteristics are not directly measurable. Three methods of estimation are proposed: (a) based on silt and clay content and bulk density, (b) based on clay content only, and (c) based on soil series. These three pedotransfer functions are compared with respect to both the estimation of θ fc and θ wp and the propagation of errors when the actual evapotranspiration of a wheat crop (E) is predicted over the growing season by the ACRU model.
The standard error of estimation was between 0.066 and 0.082 m3/m3 for θ fc , between 0.056 and 0.069 m3/m3 for θ wp and between 29.9 and 34.8 mm of water for E. The method based on silt and clay contents and bulk density predicted θ fc and θ wp for non-swelling soils most precisely. The method based on soil series was better than other methods for swelling soils. It also performed better for estimating available water capacity and consequently for predicting E from a conceptual soil water model. The propagated error of estimating θ fc and θ wp using the DSS reached 15–18% of the simulated E. The error in the prediction of E can reach 26–30% when spatial variation in soil properties is also estimated.  相似文献   

8.
Thirty-one soil solutions were extracted by immiscible displacement with CCl4 under high speed centrifugation from sub-horizons of three podzolic soils from north-eastern Ontario, Canada. The solutions were analysed for major cations and anions and a speciation of dissolved Fe and Al was attempted to distinguish 'free', 'organically bound' and 'inorganically bound' species. Results indicated that the Ae (E) horizon solutions were of low pH and contained mainly organically bound Fe and Al. With depth, pHs increased, ionic strengths decreased and the relative proportion of inorganically bound Fe and Al increased. Although application of phase diagrams permitted only a semi-quantitative interpretation of the data, all horizon solutions, with the exception of some Ae solutions, appeared supersaturated with respect to likely occurring crystalline and amorphous aluminosilicates [kaolinite, halloysite, allophane (Al:Si=l) and imogolite]. Of the phases considered, reactions involving imogolite-allophane, gibbsite-halloysite, gibbsite-allophane and gibbsite-imogolite all appeared reasonable in controlling the content of Al3+ and H4SiO4 in solution, although the presence of gibbsite and imogolite could not be definitely confirmed in these soils.  相似文献   

9.
Natural non-allophanic Andosols often show aluminum (Al) toxicity to Al-sensitive plant roots. The significance of Al–humus complexes to Al toxicity has been emphasized. Allophanic Andosols also possess Al–humus complexes, but they rarely show any toxicity. In the present study, using model substances, we tested the toxicity of Al–humus complexes and its amelioration with allophanic materials. We extracted humic substances from the A horizons of a non-allophanic Andosol and an allophanic Andosol using a NaOH solution, and reacted the humic substances and partially neutralized AlCl3 solution at pH 4. Allophanic material was purified from commercial Kanuma pumice. Plant growth tests were conducted using a medium containing the Al–humus complexes (50 g kg−1), the allophanic material (0, 90, 180 and 360 g kg−1) and perlite. The root growth of barley ( Hordeum vulgare L.) and burdock ( Arctium lappa ) was reduced in the media containing the Al–humus complexes derived from both the non-allophanic and allophanic Andosols when the allophanic material was not added. With the addition of the allophanic materials, particularly in the 360 g kg−1 treatment, the growth of the barley roots was improved markedly. Although the root growth of the burdock tended to improve with allophanic materials, the effect was weaker than that for barley. Monomeric Al in a solution of the medium was not detected (< 0.05 mg L−1) following the addition of 360 g kg−1 of allophanic materials, whereas 0.8–1.7 mg L−1 Al was recorded without the allophanic material.  相似文献   

10.
Abstract. The behaviour of potassium (K) in a range of arable soils was examined by plotting the change in exchangeable K of the topsoil (Δ Kex) at the end of a 3–5 year period against the K balance over the same period (fertilizer K applied minus offtake in crops, estimated from farmers' records of yield and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops MAFF 2000) are valid averages, 10–50% of Δ Kex was explained by the balance, relationships being stronger on shallow/stony soils. Excess fertilizer tended to increase Kex and reduced fertilization decreased it, requiring between 1.2 and 5.4 kg K ha−1 for each mg L−1Δ Kex. However, merely to prevent Kex falling required an extra 20 kg K ha−1 yr−1 fertilizer on Chalk soils and soils formed in the overlying Tertiary and Quaternary deposits, despite clay contents >18%. Whereas, on older geological materials, medium soils needed no extra K and clays gained 17 kg K ha−1 yr−1. It is unlikely that the apparent losses on some soil types are anomalies due to greater crop K contents. Theory and the literature suggest leaching from the topsoil as a major factor; accumulation in the subsoil was not measured. Recommendations for K fertilization of UK soils might be improved by including loss or gain corrections for certain soil types.  相似文献   

11.
Radiocaesium fixation in soils is reported to occur on frayed edge sites of micaceous minerals. The weathering of mica in acid soils may therefore influence the Cs+ fixation process and thereby the mobility of the radiopollutant. We produced a laboratory weathering model biotite → trioctahedral vermiculite → oxidized vermiculite → hydroxy interlayered vermiculite (HIV) and quantified the Cs+ fixation of each mineral both in a fixed K+–Ca2+ background and in acid conditions. The transformation process was achieved through K depletion by Na-tetraphenylboron, oxidation with Br2 and Al-intercalation using NaOH and AlCl3. In a constant K+–Ca2+ background, vermiculite fixed 92–95% of the initial 137Cs+ contamination while biotite and HIV fixed only 18–33%. In acid conditions, the interlayer occupancy by either potassium (biotite) or hydroxy-Al groups (HIV) strongly limited Cs+ fixation to 1–4% of the initial 137Cs+ contamination. Cs+ fixation occurred on vermiculitic sites associated with micaceous wedge zones. Though both oxidized and trioctahedral vermiculites fixed similar Cs+ amounts in a constant K+–Ca2+ background (92–95%), the oxidized vermiculite retained much more radiocaesium in acid conditions (78–84% against 54–59%), because of its dioctahedral character.  相似文献   

12.
Effects of organic matter and calcium on soil structural stability   总被引:2,自引:0,他引:2  
The cationic bridging effect of the calcium ion (Ca2+) and the flocculating ability of clay and organic matter are crucial in the formation and stability of soil aggregates. They are therefore likely to influence the soil's saturated hydraulic conductivity ( K s). We tested the individual effects of these factors on aggregate stability and related hydraulic properties, and studied the influence of clay mineralogy also. Samples from the surface (0–10 cm) of three contrasting soils in Trinidad were used. The soils were treated with three levels of Ca2+ and three levels of organic matter in a 3 × 3 × 3 factorial design and incubated for 14 days. Both aggregate stability and saturated hydraulic conductivity were influenced by all factor combinations. Interactions between soil type and Ca2+ revealed the importance of polyvalent cations in aggregate stability of soils with low activity minerals. The influence of organic matter varied with quantity; the more there was, the more stable the soil became, particularly in the soil containing little clay. Clay dispersion and slaking of expanding minerals occurred even with large additions of Ca2+ and organic matter, emphasizing the overall influence of mineralogy in determining the response of soils to stability treatments.  相似文献   

13.
Aluminium speciation and pH of an acid soil in the presence of fluoride   总被引:2,自引:0,他引:2  
The aim was to determine whether the addition of F to an acid soil reduces the concentration of free Al3+ and other forms that have been shown to be toxic to plants. The ability of two different extracts to reflect Al speciation in the soil solution was also investigated. Addition of F (0-5.2μmolg−1) to an acid soil (pH 4.15, soil solution) increased the pH and total concentrations of Al and F in the soil solution whereas Al3+ remained constant or decreased. Soil solution pH, total soluble Al and Al extracted by 0.01 m CaCl2 are not good predictors of the likelihood of aluminium toxicity in soils containing soluble fluoride.  相似文献   

14.
P-Zn interactions can affect fertilizer use and produce Zn deficiencies with certain crops. Phosphorus-Zn sorption-desorption reactions were studied in topsoil and subsoil samples from three Quebec soils. Soils were equilibrated with P solutions, then with Zn solutions, and finally with solutions containing no P or Zn. The first equilibration evaluated P sorption (Ps), the second evaluated Zn sorption (Zns) after P sorption (Ps), and the third evaluated Zn desorption (ZnD) as related to added P. Subsequently, Zn fractions were extracted sequentially with KNO3 (Zn kno 3), NaOH (ZnNaOH) solutions and concentrated HN03+ H202(ZnHNO,).
One mmole sorbed P resulted in increases of 0.5 to 1.0 meq (mean = 0.72) increases in cation exchange capacity (CEC). Increased Zns with added P was equivalent to 4 to 5% of the increase in CEC induced by Ps in the Uplands (sand) and St. Bernard (loam) soils, and 0.4 to 0.9% in the Dalhousie (clay) soils, while one meq increase in CEC resulted in 1.5-3.5% decrease in ZnD. There existed positive correlations between Ps and extractable soil Fe materials. Phosphate sorption enhanced associations between Zns, ZnD or Zn fractions and soil organic or crystalline Fe contents, confirming that P addition increased specific sorption of Zn on Fe components. Other mechanisms including precipitation, P-induced negative charge and 'bridge' effects are also discussed.  相似文献   

15.
Eleven horizons of acidic soils in mid-Wales developed from Lower Palaeozoic sedimentary rocks were examined. Selective extraction of Al and Si provided evidence against the occurrence of significant quantities of poorly ordered Al-silicates. Fe0 was weakly correlated with Al0, but very closely correlated with Al0 minus Al extracted by cold 5% Na2CO3, implying that poorly ordered Al occurs in part as a substituent in Fe oxide and in part in a form unassociated with Fe oxide. Support for this was obtained by analysis of oxide fractions concentrated from aqueous suspensions by sequential ultracentrifugation and through the examination of synthetic Al-substituted Fe oxides. Fe oxide containing Al substituted at an almost constant level was the dominant constituent of the poorly ordered fraction in four of the five Bs horizons examined. The occurrence of Al in this form is an important mechanism by which Al is retained in aerobic but highly acidic Bs horizons.  相似文献   

16.
When modelling the carbon dynamics of temperate soils, soil organic carbon (SOC) is often represented by three kinetic pools, i.e. fast, slow and passive/inert. Lignin is often considered to be relatively resistant to decomposition, thus possibly contributing to the passive SOC pool. One way to assess SOC turnover under natural conditions is to follow the fate of 13C-labelled biomass in soils. We used compound-specific isotope analysis to analyse CuO oxidation products of lignin from grassland topsoils and from an arable topsoil that had received a natural (by C3-C4 vegetation change) or an artificial (by fumigation with labelled CO2) isotopic label for 9–23 years. Results indicate faster apparent turnover for lignin (5–26 years in grassland, 9–38 years in arable soil) compared with bulk SOC (20–26 years in grassland, 51 years in arable soil). Although these calculated lignin turnover times cannot be extrapolated to the whole soil profiles, this paper provides isotopic evidence that lignin in soils is not preferentially preserved, which is a consistent result from both ways of isotopic labelling. It also demonstrates, however, that a considerable proportion of lignin in temperate soils can be stabilized for at least a few decades.  相似文献   

17.
Peat land has been considered as an alternative type of land for agricultural development especially in the tropics. In the present study, the N-supplying capacity, one of the most important soil properties in terms of crop production, of peat soils was examined. Ten peat soil samples were collected from Indonesia, Malaysia, and Japan. Gross N mineralization in the soil samples was estimated using a zero-order model, and kinetic parameters of mineralization were determined using a simple type model. Soil organic matter composition was investigated using 13C CPMAS NMR. Mineralization potential ( N 0), apparent activation energy ( E a), and mineralization rate constant ( k ) ranged between 571–2,445 mg kg−1, 281–8,181 J mol−1, and 0.009–0.020 d−1, respectively. Although none of the parameters showed a significant correlation with the soil C/N ratio, a negative correlation was observed between the k value and the ratio of the proportion of alkyl C in total C to that of O -alkyl C estimated by 13C CPMAS NMR. The latter suggested that the k values were higher in the peat soils relatively rich in readily decomposable organic matter including carbohydrates.  相似文献   

18.
Application of iron (Fe) -rich amendments to soils has been proposed as a means of decreasing phosphorus (P) losses from soils. However, anoxic conditions following soil saturation are known to increase Fe and P solubility in soils, thus cancelling out the potential benefits. Our aim was to evaluate the effects of continuous oxic, continuous anoxic and alternating anoxic/oxic conditions on P exchangeability and Fe forms in soil amended with Ca(OH)2 and FeSO4. We incubated amended and unamended soils under these conditions for 8 weeks and measured Fe forms and P exchangeability. Under oxic conditions, addition of Ca(OH)2 and FeSO4 resulted in a strong decrease in P exchangeability and an increase in oxalate-extractable Fe. Mössbauer analyses suggested that an unidentified Fe oxide (D1oxide) with a strong sorbing capacity for P was precipitated. Under continuously anoxic conditions, P exchangeability and oxalate-extractable Fe increased with or without the amendments. Mössbauer analyses suggested that there was a partial dissolution of the D1oxide phase, precipitation of another unidentified Fe oxide (S3) and a reduction of structural Fe3+ in phyllosilicate, thereby increasing soil negative charge. These transformations resulted in a strong increase in rapidly exchangeable P. Alternating anoxic and oxic periods induced the dissolution and precipitation of iron oxides and the increase and decrease in P exchangeability. Implications of the results for limiting P losses from grassland soils are discussed.  相似文献   

19.
We examined the aluminium solubility in the upper B horizon of podzols and its relation to the solid phase of the soil in 60 samples covering a pH range from 3.8 to 5.1. Solid phases were characterized by extractions with acid oxalate and pyrophosphate (pH 10). The solubility of Al was studied in a batch experiment in which samples were equilibrated with 1 m m NaCl at 8°C for 5 days. We also monitored the dissolution kinetics of Al and Si, in some samples. The oxalate and pyrophosphate extractions suggested that secondary Al was mainly organically bound in most soils, and imogolite-type materials seemed to constitute much of inorganic secondary Al. No single gibbsite or imogolite equilibrium could explain Al3+ activities. In all samples Al solubility, defined as log{Al3+} + 1.65pH, was closely related to the molar ratio of aluminium to carbon in the pyrophosphate extracts (Alp/Cp). Solubility increased with the Alp/Cp ratio until the latter reached ≈ 0.1. This indicated that solubility was controlled by organic complexation, at least when Alp/Cp was small. Silica dissolved slowly in most soils used in the kinetic experiments. We conclude that imogolite-type materials in the upper B horizon dissolved slowly because of coating with humic substances or ageing or both.  相似文献   

20.
Soil properties may affect the decomposition of added organic materials and inorganic nitrogen (N) production in agricultural soils. Three soils, Potu (Pu), Sankengtzu (Sk) and Erhlin (Eh) soils, mixed with sewage sludge compost (SSC) at application rates of 0 (control), 25, 75 and 150 Mg ha−1 were selected from Taiwan for incubation for 112 days. The aim of the present study was to examine the effects of SSC application rates on the carbon decomposition rate, N transformation and pH changes in three soils with different initial soil pH values (4.8–7.7). The results indicated that the highest peaks of the CO2 evolution rate occurred after 3 days of incubation, for all treatments. The Pu soil (pH 4.8) had a relatively low rate of CO2 evolution, total amounts of CO2 evolution and percentage of added organic C loss, all of which resulted from inhibition of microbial activity under low pH. For the Pu and Sk soils, the concentration of NH4+-N reached its peak after 7–14 days of incubation, which indicated that ammonification might have occurred in the two soils with low initial pH values. NO3-N rapidly accumulated in the first 7 days of incubation in the Eh soil (pH 7.7). The direction and extent of the soil pH changes were influenced by the N in the SSC and the initial soil pH. Ammonification of organic N in the SSC caused the soil pH to increase, whereas nitrification of mineralized N caused the soil pH to decline. Consequently, the initial soil pH greatly affected the rate of carbon decomposition, ammonification and nitrification of SSC.  相似文献   

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