摘要:

This paper reports the use of mineral magnetic measurement techniques to characterize the iron oxide assemblage within soils of varying parent material type and water regime from subtropical region in Zhejiang Province, China. Results show that dryland soils formed on Quaternary red clay, limestone, arenaceous shale, and diluvium, exhibit a distinct ferrimagnetic profile with a magnetic susceptibility (χ) enhancement in surface horizon. This enhancement is interpreted as being due to pedogenic superparamagnetic (SP) ferrimagnetic grains, which is supported by a higher frequency dependent susceptibility (χfd) values. The χ and χfdhave highly significant positive linear relationship with dithionite‐citrate‐bicarbonate (DCB) extractable iron (Fed) content. The upper horizon of paddy soil has extremely lower χ and χfdvalues than dryland soils formed on the same parent material. Soil with poorly‐drained condition has distinctly lower absolute χ and saturation isothermal remanent magnetization (SIRM) value than associated well‐drained soil. It indicates that reduction state is an important factor responsible for loss of SP ferrimagnetic minerals in soils.

ISSN:0010-3624    

DOI:10.1080/00103620009370416

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Metal availability in soils is often assessed by means of extraction with chemical solutions, among others the chelating agent DTPA (diethylenetriaminepentaacetic acid) and the non‐buffered salt calcium chloride (CaCl2). The same procedures are used for polluted soils that were originally created to assess the nutrient status of arable soils. We studied the influence of various parameters (type of shaker, shaking time, soil to solution ratio, and concentration of chemical extractant) and modify the DTPA and CaCl2extraction procedures to make them suitable for the study of polluted soils. The chosen extraction ratio and extractant concentration were the followings: 8 g/20 mL of 0.1MCaCl2and 2 g/20 mL of 0.005MDTPA. The optimized procedures were applied to nine soil samples affected by different sources of pollution (mine works, vehicle emissions, and various industries). Cadmium (Cd) showed the highest extractability with both extractants. Depending on the soil, copper (Cu) and zinc (Zn) (using DPTA) and Cu and manganese (Mn) (using CaCl2) were the followings in the extractable amounts. Cadmium, Cu, and Zn were highly correlated in both extractions and with total contents.

ISSN:0010-3624    

DOI:10.1080/00103620009370417

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Laboratory experiments were carried out to evaluate lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) sorption‐desorption by three soils of contrasting characteristics. Talamanca (silt loam, montmorillonite, Calcic Haploxeralfs), Mazowe (clay, kaolinite, Rhodic Kandiustalf), and Realejos (sandy silt loam, allophane, Typic Hapludands). A second objective was to study the effect of nitriloacetic acid (NTA) on the sorption process. The Talamanca soil, which had a native pH of 6.4 and presented the highest effective cation exchange capacity (ECEC), sorbed more of each of the metal tested than did the other two soils. When the other two soils were compared metal sorption was also related to pH and ECEC. The very low sorption capacity showed by Realejos may be attributed to the low net surface negative charge density of this soil, arising from its allophanic nature. A common feature of the three soils was the relative strong sorption of both Pb and Cu relative to Cd and Zn with Pb showing the highest sorption levels. The selectivity sequences of metals retention were Pb>Cu>Zn>Cd for Talamanca soil, Pb>Cu>Zn≈Cd for Mazowe, and Pb>Cu>Cd>Zn for Realejos. Metal desorption values were low. The order of metal desorption (Cd≈Zn>Cu>Pb) was the same for the three soils studied. Quantitative differences observed in the extractability of the sorbed metals between the soils (Realejos>Mazowe>Talamanca) indicated that soil properties which enhanced metal sorption contributed at the same time to slow down the backward reaction. The addition of NTA to the soil suspension significantly depressed metal sorption by the three soils investigated. Compared with the free ligand system Pb, Cu, Zn, and Cd sorption in the presence of NTA decreased roughly 50%.

ISSN:0010-3624    

DOI:10.1080/00103620009370418

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Mustard (Brassica campestrisL.) cv. T9 was grown in refined sand at three levels of boron (B), deficient (0.0033 ppm), normal (0.33 ppm), and excess (3.3 ppm), each at three levels of zinc (Zn), low (0.00065 ppm) adequate (0.065 ppm), and high (6.5 ppm). The B deficiency effects were accentuated by low zinc viz., the decreased biomass, B and Zn concentrations in leaves and seeds and the activity of carbonic anhydrase and accumulation of reducing sugars and stimulated activities of peroxidase, ribonuclease, and acid phosphatase in B deficient leaves were aggravated further. Synergism was also observed between the two nutrients when both B and Zn were in excess together as excess B accelerated the effects of high Zn by lowering further the reduced biomass, economic yield, and carbonic anhydrase activity and raised further the increased concentration of B and Zn in leaves and seeds, reducing sugars and activity of peroxidase obtained in excess Zn. In mustard, additive effects of high Zn and low B was reflected when high Zn increased the reduced biomass, seed yield, leaf B, and decreased the stimulated activities of peroxidase, ribonuclease, acid phosphatase, and high concentration of non‐reducing sugars to some extent in low B.

ISSN:0010-3624    

DOI:10.1080/00103620009370419

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Although there is generally no physical problem with salt‐affected soils when irrigated with saline and sodic waters, physical deterioration of the soils often results when leached with good quality (low salt and low sodium) irrigation water or by rain. Two major mechanisms of swelling and dispersion of clay particles have been proposed to be responsible for reduction in hydraulic conductivity (HC). The type and amount of clay minerals are major factors influencing the swelling and dispersion properties of soil in the presence of saline‐sodic solutions. The study was initiated to improve the understanding of swelling and dispersion processes in response to saline‐sodic conditions, particularly the role of the type and amount of clay minerals of the tested soils and the concentration of the leaching solutions. The study was conducted in a series of two leaching experiments. In the first experimental soil samples were leached with solutions of different combinations of 100 meq (NaCl+CaCl2)L‐1and sodium adsorption ratio (SARs) 5, 10, 15, and 20. In the second, 8 samples of them selected to be leached with solutions of the same SARs of 5, 10, 15, and 20, but the higher concentration of 1000 meq (NaCl+CaCl2)L‐1. The changes in the HCs were determined through the concept of “the Sensitivity Index‐SI values”;. In general, solutions with lower concentrations and higher SAR resulted in greater reductions in the soil HC (i.e, SI value), and the SI values and SAR level showed a negative linear relationship. With respect to the regression equations between the SI values and the swelling/dispersion processes, and the relatively coarse texture as well as the mineralogical composition of the tested soils which shows the dominant clay minerals in almost all tested soils is non‐expanding dispersive quartz, illite and chlorite, it may be concluded that the slaking of the soil structure is responsible for blockage of the conducting pores and reduction in the HCs of the tested soils.

ISSN:0010-3624    

DOI:10.1080/00103620009370420

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Saline‐sodic irrigation water, coupled with low annual rainfall and high evapotranspiration in the arid and semi‐arid regions have resulted in accumulation of soluble salts in the soil solution and of cations (especially sodium ions) on exchange sites, which can alter the structure and, consequently, affect the soil hydraulic conductivity (HC). Among the different factors, the amount of gypsum applied and the flow rate of leaching solution are major factors influencing the HC of the soil in the presence of saline sodic solutions. The study was initiated to improve the understanding of swelling and dispersion processes (as two major mechanisms responsible for reduction in HC) in response to saline‐sodic conditions, in particular, the role of gypsum application and the flow rate of leaching solutions. The study was conducted in a series of two leaching experiments. In the first set, different rates of gypsum (i.e., 0, 10, 20, and 30 tons ha‐1) were mixed with 4 soil samples and leached with a saline‐sodic solution of concentration of 100 meq (NaCl+CaCl2)L‐1with sodium adsorption ratio (SAR) 20 and the base flow rate (BFR) of 15 mL min‐1. In the second set of experiments, the same soils treated with the same gypsum level and the same leaching solutions as in the first set, but leached with the BFR of 5 mL min‐1instead of the BFR of 15 mL min‐1. In general, the gypsum application modified the suppressing effect of salinity and sodicity on the HC values of the tested soils, and the effects were more pronounced for higher rates of gypsum applied. However, increase in the BFR from 5 to 15 mL min‐1, significantly masked this recovering effect of gypsum application, and the effect was reflected in both swelling and dispersion processes.

ISSN:0010-3624    

DOI:10.1080/00103620009370421

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Differential thermogravimetry (DTG), differential scanning calorimetry (DSC), and stepwise thermogravimetry (STG), together with two acid hydrolysis methods (hydrolysis with hydrochloric acid in a single step, and hydrolysis with sulfuric acid in two steps), were evaluated to determine the quality of four plant materials (Medicago sativa, Eucalyptus globulus, Quercus ilex,andPinus halepensis) before and after mixing with a red earth. These quality indices were then compared with the same materials in the field, whether their decomposition could be predicted. All the thermal methods gave poor results. In both DTG and DSC, the presence of the mineral matrix gave rise to strong distortions in the spectra. Since the spectrum of any mixture is not simply the sum of the spectra of the two components (organic matter + mineral matter), these distortions could not be corrected by simply subtracting the spectrum of the red earth alone. STG trials also gave poor results, because the presence of the mineral matrix greatly increased the quality indices, and reduced the ability of the method to distinguish between organic matter qualities. In view of our results, the usefulness of thermal methods in the characterization of soil organic matter would seem to be restricted to certain organic horizons (L, F, and perhaps H). In contrast, methods based on acid hydrolysis were comparatively more satisfactory. Their resolution (ability to distinguish organic matter qualities) was much higher than that of thermal methods. However, they were able to distinguish carbon more accurately than nitrogen. The sulfuric acid method, unlike the hydrochloric acid method, was affected by the presence of a mineral matrix. While both methods could be improved, in their present form they seem to operate as good predictors of carbon and nitrogen mineralization.

ISSN:0010-3624    

DOI:10.1080/00103620009370422

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The object of this work was to study the influence of humic extracts prepared from peat, sheep manure, and compost from municipal solid waste on germination and growth of ryegrass. Germination tests, using different concentrations of humic extracts, showed that doses higher than 20% (v/v) inhibited seed germination. Therefore, doses of 20 and 10% were used in a first growth experiment, using a control consisting of a complete nutrient solution. A 20% dose caused adverse effects on plant growth. Hence, doses of 10 and 5% were used in the next growth experiments. Also, plants were watered with the extracts or with the nutrient solution (control) and with distilled water alternately in the next experiments. After the first cut of the ryegrass, sixteen days after the sowing, the watering was implemented only with distilled water in order to assess the residual effects of the different fertilizers. A second cut was performed thirty six days after the sowing. The harvested ryegrass was analyzed for: a) fresh weight; b) dry matter; c) nitrogen, phosphorus, and potassium contents; d) chlorophylls; and e) carotenoids. The data show that the best effects were achieved with sheep manure extracts, followed by compost and peat. Differences among the three kinds of fertilizers were more remarkable than those between the two doses of the same fertilizer.

ISSN:0010-3624    

DOI:10.1080/00103620009370423

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In order to better understand some of the factors likely to affect measurements of KC1 extractable acidity, experiments were conducted using synthetic solutions and extracts from a wide range of contrasting soils. The reagents used for measuring exchangeable acidity (i.e., KC1 and KF) were also examined to evaluate the effects of chemical impurities on acidity measurements. Two commonly used titrimetric methods were adapted and tested to determine the accuracy and precision of acidity measurements. The exchangeable acidity of soil extracts was investigated by extraction methods, extractant concentration, and extractant volume. Results from the soil extract experiments indicated that continuous shaking has no significant effect on acidity measurements. Filtration, however, is critical, especially for acidic organic‐rich soils, since aluminum (Al) ions can be lost during centrifugation. Extractant concentration and volume had variable effects on the acidity measurements for individual soils. In general, the modified Yuan's method is preferable to the modified Thomas’ method for estimating exchangeable Al. To ensure successful determination of exchangeable acidity, we recommend using a wider KCl:soil ratio (>15:1, v/w) for organic soils with low base saturation and allophanic Andisols. In sum, potassium chloride and potassium fluoride extraction for estimating exchangeable acidity is applicable for most soils.

ISSN:0010-3624    

DOI:10.1080/00103620009370424

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Researchers frequently must store water samples >24 h after collection until chemical analyses can be accomplished. Samples are commonly stored in darkness at near‐freezing temperatures until analysis, but effects of this storage method on soil water chemistry are not well‐documented. Soil water samples were collected from eastern hemlock [Tsuga canadensis(L.) Carriere] stands and analyzed initially and over time to determine if nitrate (NC3‐), chloride (Cl‐), sulfate (SO42‐), ammonium (NH4+), and/or total nitrogen (TN) concentrations changed when samples were stored in darkness at 2–4°C. Subsamples were analyzed <24 h after collection and reanalyzed five times in a 12 to 24 wk period following sample collection. Nitrate concentrations remained stable for at least one wk and were only slightly lower than initial concentrations after 3–16 wk of storage. Chloride and SO42‐remained stable for 16 wk, while TN remained stable for 8 wk and decreased slightly after 24 wk. Most NH4+concentrations were below the limit of quantification, but concentrations of samples with quantifiable NH4+decreased in the first week of storage. Overall, cold storage in darkness was effective for preserving NO3‐, Cl‐, SO42‐, and TN concentrations in soil water, but NH4+analyses should probably be performed as soon as possible after sample collection.

ISSN:0010-3624    

DOI:10.1080/00103620009370425

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor