Pore size distribution measurements in swell-shrink soils

A method for the determination of pore size distribution in swell-shrink soils was described. Undisturbed core samples, saturated and drained at 1.5 MPa suction, were filled with a non-polar liquid (xylol), and its retention at suctions lower than 1.5 MPa was measured. Oven dry samples were analyzed in the same way. Derived pore size distributions were compared with those obtained by water desorption. Pore size distributions and their relative changes as a function of water content were related to some soil constituents and properties. Stability factor and sum of montmorillonite and vermiculite significantly influenced the pore size distribution by water release, A higher stability factor resulted in lower relative changes (ratios) in the pore size classes <10 μm and 0.2–10 μm when the samples were drained from saturation to 1.5 MPa suction, however, at extreme dryness, the relative changes were positively correlated to the sum of montmorillonite and vermiculite.     

Use and misuse of PLFA measurements in soils

The determination of the phospholipid fatty acid (PLFA) pattern of soil organisms has become one of the most commonly used methods to study microbial community structure. Here we recapitulate the background of our work applying the PLFA method to soil in the early 1990s. We also stress that although the PLFA method was, and still is, a rapid and sensitive method to detect changes in the microbial community in soil, as with all popular methods it can be misused. We discuss problems in PLFA interpretation, the extent of turn-over of PLFAs in soil, and the flawed use of diversity indices to evaluate PLFA patterns.     

Characterization of subtropical soils by mineral magnetic measurements

Abstract

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 (χ_fd) values. The χ and χ_fd have 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 χ_fd values 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.     

Correction of TDR-based soil water content measurements in conductive soils

Time Domain Reflectometry (TDR) is a widespread technique for measurement of soil water content (SWC). The main assumption behind the use of Time Domain Reflectometry (TDR) is of negligible losses, therefore assuming that only the real part determines the value of the TDR-measured apparent dielectric permittivity. This assumption does not hold for soils where surfaces are conductive (clay soils) or where high concentrations of electrolyte are present in the soil solution (saline soils) because under these conditions the contribution of the imaginary part becomes important. One of the main effects of dielectric losses on the TDR measurement is overestimation of SWC. In this study we present a methodology for separating the real and the imaginary part from the measurement of the apparent dielectric permittivity. This approach allows correction of the SWC overestimation, by using the TDR-measured electrical conductivity as indicator of dielectric losses. Oven-dry gravimetric soil water content was used as an independent method for soil water content assessment. The original SWC overestimation (in respect to the oven-dry gravimetric based measurement) reached values of up to 20% of total soil saturation, after the correction the differences were reduced to a 3–5%. The methodology can be applied based on knowledge of measured permittivity and electrical conductivity only, making it readily applicable to field experiments.     

两种离子液体对Cd2+在四种土壤上吸附的影响

研究了2,3-吡啶二羧酸和咪唑-4,5-二羧酸两种离子液体阳离子部分对Cd2+在四种不同性质土壤上吸附的影响。结果表明,离子液体的存在显著影响了Cd2+在土壤中的吸附,与对照相比,添加1 mmol·L-12,3-吡啶二羧酸使得Cd2+在武进漂洗型水稻土、吴县潴育型水稻土、南京黄褐土和宜兴棕红壤四种土壤上的最大吸附量分别降低209、834、667、509 mg·kg-1,而添加1 mmol·L-1咪唑-4,5-二羧酸使Cd2+最大吸附量分别降低226、54、124、81 mg·kg-1,2,3-吡啶二羧酸对Cd2+在供试土壤上吸附量的影响显著大于咪唑-4,5-二羧酸。基于离子选择电极分析了平衡液中自由态Cd2+含量,发现两种离子液体都能与Cd2+络合,从而降低平衡液中Cd2+含量,其中2,3-吡啶二羧酸与Cd2+的络合能力大于咪唑-4,5-二羧酸。两种离子液体进入环境,会使Cd2+在土壤上的吸附量减少,从而增加Cd2+的移动性和环境风险。     

Stability constant of Fe2+ chelates with soluble ligands from incubated soils

Summary The stability constants (log K) of Fe²⁺ chelates were determined on the basis of the shift in peak potential during the reduction of Fe²⁺ by a consortium of soluble ligands from incubated soils. Log K values ranged from 2.6 to 4.5. On average a change in pH of 1 unit induced a change in log K of 0.92 units. Aeration of the anaerobic decomposition products increased log K. The log K for Fe²⁺ chelates was about 0.8 units larger than that for Mn²⁺ chelates. It is considered that the chelation of ferrous iron plays an important role in the mobility and availability of iron to plants.     

Distribution coefficients of Cd, Co, Ni, and Zn in soils

Batch adsorption experiments were conducted with a mixture of solutes at low equilibrium concentrations of Cd (0.7-12.6 μg1⁻¹), Co (18-118μg1⁻¹, Ni (22-330 μg 1⁻¹), and Zn (40-1480 μg1⁻¹) in 38 different soils. Statistical correlations indicated that metal sorption onto the soils was influenced by the presence of clays and hydrous oxides of Fe and Mn. Based on calculated distribution coefficients for these metals, Co will generally exhibit the highest mobility in soils, but the mobility of Zn will increase faster with decreasing pH. Two types of empirical relationships are developed from these data to estimate values for the distribution coefficients.     

An evaluation of cation exchange capacity measurements for soils in the tropics

Abstract

Comparisons of CEC and exchange acidity neasurements were made on a group of selected West African soils using three commonly used analytical procedures, namely, neutral‐acetate displacement, BaCl₂‐TEA leaching at pH 8, and unbuffered KCl extraction.

The three methods gave large differences in CEC values which followed the order of BaCl₂‐CEC>>NH₄OAc‐CEC> KCl‐CEC. Results of exchange acidity also followed the same order. The high exchange acidity values obtained by the BaCl₂‐TEA (pH 8) method were mainly due to changes in surface charge characteristics of Fe and Al oxides and hydrous oxides. The effective CEC method is recommended for routine soil analysis for highly weathered soils in the tropics.

Regression analysis of the base saturation values obtained from the three methods indicated the data followed a curvilinear relationship. The acetate method was more highly correlated with the effective CEC method than with the BaCl₂ method.     

Waste-Derived Siliceous Materials as a Novel Sorbent for Removal of Ni2+ from Aqueous Solutions

In the present study, the preparation of sorbent from waste-derived siliceous materials has been investigated for the removal of nickel ion (Ni²⁺) from aqueous solutions. Three types of ashes, i.e., rice husk ash (RHA), palm oil fuel ash (PFA), and coal fly ash (CFA), were used in the preparation of sorbent. Batch studies were carried out to examine the effect of various experimental parameters, i.e., RHA/CFA/PFA ratio in the sorbent preparation, contact time, initial concentration of Ni²⁺, agitation rate, and pH. Among all the ratios of the prepared sorbent, it was found that sorbent containing RHA and PFA gave the highest Ni²⁺ removal efficiency. The optimum conditions for Ni²⁺ removal using RHA/PFA sorbent were obtained at contact time of 30?min, Ni²⁺ concentration of 100?mg/L, agitation rate of 130?rpm, and pH?4. During the optimum condition, more than 90% of Ni²⁺ could be removed in all experiment studies. It was also found that the spent RHA/PFA sorbents had a narrow range of particle size distributions as compared to prepared RHA/PFA sorbent. In addition, the surface morphology of the spent RHA/PFA sorbents had more compact structures.     

Soil chemical properties affecting NH4+ sorption in forest soils

Fourteen European forest soils from the boreal to the mediterranean climate on different parent materials were investigated with respect to their ability to store NH₄⁺ in exchangeable form, using sorption isotherms. Distribution coefficients for NH₄⁺ sorption per unit weight of soil were in the range of 0.02 to 0.77. NH₄⁺ sorption coefficients were usually highest in the forest floor of a given soil. NH₄⁺ sorption behaviour of mineral soil horizons was correlated to soil parameters that are determined during routine soil analysis. A combination of CEC and base saturation explained up to 95% of the variability Of NH₄⁺ sorption. In the forest floors, variability in NH₄⁺ sorption could not be explained quantitatively from independent soil parameters. The affinity of the sorption sites for NH₄⁺ was the most important factor for explanation of the variability in NH₄⁺ sorption in the forest floors but was of low importance in mineral soil horizons. As NH₄⁺ exchanges predominantly base cations, susceptibility of NH₄⁺ to transport through the soil profile increases with Iowbase saturation of a soil as well as with low CEC values.     

Activity of protease extracted from rice-rhizosphere soils under double cropping of rice and wheat

Abstract

Protease-active extracts were prepared from 2 rice-rhizosphere and non-rhizosphere soil samples 3 proteolytic isolates from the soil samples which were taken from water logged paddy fields (Gray Lowland Soils) under double cropping of rice and wheat that had been treated with chemical fertilizer (CF) or organic manure (OM). The activities were assayed and characterized using an artificial substrate, benzyloxycarbonyl-L-phenylalanyl-L-tyrosyl-L-leucine (ZFTL). The protease-active extracts from the rhizosphere and non-rhizosphere of the CF and OM soils (abbreviated as CFR, CFN, OMR, and OMN) showed an optimum pH between 7 and 8. The extracts hydrolyzed ZFTL to Tyr-Leu and Leu; generally, Tyr-Leu was the main reaction product. Activities of all the samples were inhibited by EDTA and p-chloromercuribenzoic acid (PCMB) but not by pepstatin and phenylmethanesulfonyl fluoride (PMSF). These results indicate that the main components of the ZFTL-hydrolases in CFR, CFN, 0MR, and OMN were essentially similar.

Optimum pH for the activity of the protease extracted from a Gram negative rod (MNB003)., two actinomycetous isolates (MNA014., MRA017) was about 8, 8, and 8.5, respectively. Extract from the culture of MNB003 hydrolyzed ZFTL to Tyr-Leu., Leu,., the protease activity was inhibited by EDTA., PCMB. Protease activities of the extracts from cultures of the two actinomycetes were inhibited by EDTA but not by PCMB. The extract from culture of MNA014 produced mainly Tyr-Leu from ZFTL while MRA017 produced Leu. Characteristics of the protease activity from cultures of MNB003., MNA014 were similar to those of the enzyme extracted from a paddy field soil under single cropping (Takeuchi., Hayano 1994: Soil Sci. Plant Nutr., 40, 691-695) and from an Andosol under tomato cultivation (Hayano et al. 1987: Biol. Fertil. Soils, 4, 179-183), respectively.     

Growth measurements of saprotrophic fungi and bacteria reveal differences between canopy and forest floor soils

Canopy-held organic matter develops into a distinct soil system separate from the forest floor in wet temperate coniferous forests, creating a natural microcosm. We distinguished between fungal and bacterial components of the decomposer community in one site with Maple (Acer macrophyllum) and one site with Alder (Alnus rubra) by using direct measurements of growth; acetate incorporation into ergosterol, and leucine incorporation for fungi and bacteria, respectively. The higher organic matter content of the canopy soils correlated with higher fungal growth. The relative importance of fungi, indicated by fungal:bacterial growth ratio, was higher in the canopy soil of the Maple site, while there was no difference in the Alder site. The high C:N ratio of the Maple canopy soil likely contributed to this difference. These results demonstrate a divergence between canopy and forest floor that should be explored to gain insights in decomposer ecology using the natural microcosms that the canopy soils provide.     

Enrichment of N2 and Ar in the atmosphere of CO2-consuming soils

The phenomenon of unexplained N₂Ar-enrichment in soil air is quite frequently to be encountered in soil air studies on anthropogenically influenced sites. In the present study two anthropogenic deposits and a calcareous fluvisol were investigated for their soil air composition. While in the alkaline deposits extreme enrichments of N₂ and Ar (N₂ + Ar: up to 99%, v/v) were found as persistent site characteristics, the fluvisol showed only slight (about 1%, v/v) transient N₂/Ar-enrichments in summer. All sites, which did not show substantial vertical seepage percolation, exhibited enhanced CO₂-solubility-either due to strong calcite precipitation or dissolution. So, it was concluded that intensive continuous depletion of CO₂ was responsible for the subsequent convective influx of atmospheric air. From the results obtained it was concluded that an encasement of the concerned soil volume rather impermeable to gas transport as well as intense dissolution of CO₂ in the pore water are prerequisites for substantial N₂/Ar-enrichments in soil air.     

Carbon monoxide as an inhibitor of N2ase activity(C2H2) in control measurements of endogenous formation of ethylene by forest soils

Two problems with the recently suggested method to measure endogenous formation of C₂H₄ in an atmosphere enriched with C₂H₂ and CO in studies of N₂ase activity (C₂H₂) in forest soils were analysed, namely the effect of consumption of CO during incubation and the effect of water-saturated conditions.After an initial addition of 100 ml C₂H₂ and 20 ml CO 1^?1 to soil incubation vessels, CO was gradually consumed and followed by a recovery of N₂ase activity when the concentration of CO was lower than about 10 ml 1^?1. The shortest period within which this concentration was achieved was 1 day when incubating fresh soil cores at 15°C, and it was concluded that longer incubations should be avoided.The inhibition of N₂ase activity by CO was strongly suppressed when all soil pores were filled with water. Dissolved inorganic N (0.1% of dry mass soil) was much more efficient in inhibiting N₂ase activity under such conditions.     

Soil hydrology and CO2 release of peat soils

A simple model to predict soil water components and the CO₂ release for peat soils is presented. It can be used to determine plant water uptake and the CO₂ release as a result of peat mineralization for different types of peat soils, various climate conditions, and groundwater levels. The model considers the thickness of the root zone, its hydraulic characteristics (pF, Ku), the groundwater depth and a soil‐specific function to predict the CO₂ release as a result of peat mineralization. The latter is a mathematical function considering soil temperature and soil matric potential. It is based on measurements from soil cores at varying temperatures and soil water contents using a respiricond equipment. Data was analyzed using nonlinear multiple regression analysis. As a result, CO₂ release equations were gained and incorporated into a soil water simulation model. Groundwater lysimeter measurements were used for model calibration of soil water components, CO₂ release was adapted according long‐term lysimeter data of Mundel (1976). Peat soils have a negative water balance for groundwater depth conditions up to 80—100 cm below surface. Results demonstrate the necessity of a high soil water content i.e. shallow groundwater to avoid peat mineralization and soil degradation. CO₂ losses increase with the thickness of the rooted soil zone and decreases with the degree of soil degradation. Especially the combination of deep groundwater level and high water balance deficits during the vegetation period leads to tremendous CO₂ losses.     

Influence of different temperatures on metal tolerance measurements and growth response in bacterial communities from unpolluted and polluted soils

The effects of temperature on the growth rate and metal toxicity in soil bacterial communities extracted from unpolluted and polluted soils were investigated using the thymidine and leucine incorporation techniques. An agricultural soil, which was contaminated in the laboratory with Cu, Cd, Zn, Ni or Pb, and an uncontaminated forest soil were used. Measurements were made at 0°C and 20°C. Leucine incorporation was found to be as sensitive to heavy metals as thymidine incorporation in the short-term trial used to indicate heavy metal tolerance. Similar IC₅₀ values (the log of the metal concentration that reduced incorporation to 50%) were also obtained at 0 and 20°C, independently of the technique used. Metal tolerance could thus be measured using both techniques at any temperature in the range 0–20°C. In the long-term experiment different temperature-growth relationships were obtained on the basis of the rate of thymidine or leucine incorporation into bacterial assemblages from unpolluted and polluted soils, as judged from the minimum temperature values. This could not be attributed to the metal addition alone since different patterns were observed when different metals were added to the soil. Thus, the minimum temperature for thymidine incorporation was similar in Cu-polluted and unpolluted soil, while in soils polluted with Cd and Zn the minimum temperature increased by 2°C, and Ni and Pb additions increased the minimum temperature by 4°C compared to the unpolluted soil. This suggested that heavy metal pollution led to bacterial communities showing different temperature characteristics to those in the corresponding unpolluted soil. Similar observations were deduced from the minimum temperatures required for leucine incorporation. Three groups of bacterial communities were distinguished according to the growth response to temperature in polluted soils, one group in Cu-polluted soil, a second group in soil polluted with Zn and Cd, and a third group in soils polluted with Ni and Pb.     

Influence of the El Niño and La Niña climate events and litter removal on inorganic nitrogen dynamics in pine forest soils on Central Java,Indonesia

To determine to what extent environmental factors and anthropogenic disturbances dictate N dynamics in tropical forest soils, changes of concentrations of inorganic N in soil were investigated during a period of extreme climatic conditions caused by El Niño and La Niña. This allowed the determination of factors driving the N-dynamics in tropical soils more clearly than during normal seasonal cycles. Three N-limited pine forests in Central Java, Indonesia, were studied monthly for over a year. N-NH₄⁺ and N-NO₃⁻ were abundant in the organic layers, and decreased with increasing depth. Regular litter removal from the forest floor and branch-cutting at two pine forest sites significantly reduced the N-NH₄⁺ concentration in the organic and mineral layers, but had only a minor influence on N-NO₃⁻ concentration. The N-NH₄⁺ and N-NO₃⁻ concentrations and pH showed a distinct seasonal variation with extremely large amplitude in all studied soil layers, this corresponded to variation in soil moisture content. Concentrations were low during the extreme dry period of El Niño of 1997, and significantly increased during the subsequent long wet period of La Niña. The largest changes occurred in the organic top layers and changes were more pronounced than during normal seasonal cycles. It is concluded that N-dynamics in litter and fragmentation layers were most influenced by seasonal precipitation and to a lesser degree by litter removal.     

The precise measurement of concentration gradients of mercury in air over soils: A review of past and recent measurements

Measurements of the atmospheric concentration gradients of mercury (Hg) vapor over soils can be used to determine the direction and magnitude of exchange rates of Hg if certain assumptions are met. However, these gradients are quite small and require highly precise sampling to achieve accurate data. We have developed a sampling and analysis procedure which allows quantification of gradients over background soils. With this procedure we can now measure atmospheric Hg at ambient levels with a precision of ～0.5 to 2% (expressed as relative standard error). This level of precision is well above those published in earlier gradient studies. In our recent studies, gradients measured between 25 and 165 cm above background forest soils at Walker Branch Watershed, Tennessee were quite small, ranging from 0.02 to 0.39 ng/m³ (expressed as concentration differences). These gradients indicated that Hg emission was about 3 times more frequent than dry deposition. Gradients measured over soils at Lake Gårdsjön, Sweden were generally smaller but also indicated bidirectional fluxes. By comparison, gradients above Hg-contaminated soils in Tennessee were far larger as expected, ranging from 0.12 to 5.60 ng/m³. These gradients consistently indicated emission of Hg. A number of tests were performed to validate that these gradients were true indications of Hg exchange rates.