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PubMed1997

Modelling Rooting Depth and Soil Strength in a Drying Soil Profile

A combined root growth and water extraction model is described that simulates the affects of mechanical impedance on root elongation in soil. The model simulates the vertical redistribution of water in the soil profile, water uptake by plant roots, and the effects of decreasing water content on increasing soil strength and decreasing the root elongation rate. The modelling approach is quite general and can be applied to any soil for which a relation can be defined between root elongation and penetrometer resistance. By definition this excludes soils that contain a large proportion of continuous channels through which roots can grow unimpeded. Root elongation rate is calculated as a function of the penetrometer resistance which is determined by the soil water content. Use of the model is illustrated using input data for a sandy loam soil. The results confirm reports in the literature that the depth of water extraction can exceed the rooting depth. The increase in mechanical impedance to root growth due to this water extraction restricted the maximum rooting depth attained, and this limited the depth of soil from which a crop could extract water and nutrients. This study highlighted the lack of published data sets for single crop/soil combinations containing both the strength/root growth information and the hydraulic conductivity characteristics necessary for this type of model. Copyright 1997 Academic Press Limited

Journal Article↗
PubMed2005

Unsmooth cuticles of soil animals and theoretical analysis of their hydrophobicity and anti-soil-adhesion mechanism.

Soil adhesion is a natural phenomenon, and it is harmful to terrain machines and tillage equipment that have soil as their work medium, such as automobiles, tractors, earth-moving machines, spades, hoes, and plows. Soil adhesion increases motion resistance and energy consumption, quickens damage to the soil-engaging components, and lowers work quality. The biomimetic research has provided a promising method to solve the soil adhesion problem. In this work, the cuticles of typical soil animals were observed by scanning electron microscopy (SEM) and their wettability and mechanism of antiadhesion were analyzed in theory. The results of experimental observation have shown that the cuticles of soil animals have different unsmooth appearances, such as pimple-shaped, pit-like, and undee structures. But for the cross sections of the unsmooth cuticles, their common character is undee. Theoretical analysis has indicated that the larger the ratio of the amplitude of the wave to the period of the wave, the stronger the hydrophobicity, the more easily the composite interface between the liquid and the unsmooth cuticles forms, and the function of reducing soil adhesion of the unsmooth cuticles will be better.

Journal Article↗
PubMed2000

Effects of long-term contamination of DDT on soil microflora with special reference to soil algae and algal transformation of DDT.

DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) and its principle metabolites, DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) are widespread environmental contaminants but little information is available concerning their effects on non-target microflora (especially microalgae and cyanobacteria) and their activities in long-term contaminated soils. For this reason a long-term DDT-contaminated soil was screened for DDT residues and toxicity to microorganisms (bacteria, fungi, algae), microbial biomass and dehydrogenase activity. Also, five pure cultures isolated from various sites (two unicellular green algae and three dinitrogen-fixing cyanobacteria) were tested for their ability to metabolise DDT. Viable counts of bacteria and algae declined with increasing DDT contamination while fungal counts, microbial biomass and dehydrogenase activity increased in medium-level contaminated soil (27 mg DDT residues kg(-1) soil). All the tested parameters were greatly inhibited in high-level contaminated soil (34 mg DDT residues kg(-1) soil). Species composition of algae and cyanobacteria was altered in contaminated soils and sensitive species were eliminated in the medium and high contaminated soils suggesting that these organisms could be useful as bioindicators of pollution. Microbial biomass and dehydrogenase activity may not serve as good bioindicators of pollution since these parameters were potentially influenced by the increase in fungal (probably DDT resistant) counts. All the tested algal species metabolised DDT to DDE and DDD; however, transformation to DDD was more significant in the case of dinitrogen-fixing cyanobacteria.

Journal Article↗
PubMed1995

Forms of cadmium in sandy soils after amendment with soils of higher fixing capacity.

Most of the Cd applied through phosphatic fertilizers in sandy soils tends to stay in mobile forms (soluble or exchangeable) and hence the risk of it leaching to underground water or its uptake by plants is higher. A sequential extraction procedure was used to assess the efficacy of amending materials (soils containing inorganic or organic adsorption components) on the re-distribution of forms of Cd in a sandy soil. Amendment of the sandy soil with each of the three soils (yellow earth, lateritic podzolic and peaty sand) was generally effective in altering the more mobile or available forms of Cd to immobile or unavailable forms. The extent of alteration varied with the type of component present in the amendment soil, pH and the rate of Cd addition. The yellow earth was more effective at pH 7, whereas the peaty sand was equally effective at both pH 4 and 7 in altering the mobile to immobile forms. The lateritic podzolic soil was the least effective of the soils used at any of the pH values.

Journal Article↗
PubMed2000

Direct determination of soil surface-bound polycyclic aromatic hydrocarbons in petroleum-contaminated soils by real-time aerosol mass spectrometry

Soil surface-bound polycyclic aromatic hydrocarbons (PAHs) were identified by use of Real-Time Aerosol Mass Spectrometry (RTAMS) in two NIST standard research material (SRM) soils (Montana SRM 2710 and Peruvian SRM 4355) each contaminated separately with three common petroleum hydrocarbons (diesel fuel, gasoline, and kerosene). The described contaminated soil analysis required no sample preparation. Direct laser desorption/ionization mass spectrometric analysis of individual soil particles contaminated with each of the petroleum hydrocarbons at three different contamination levels (0.8, 8, and 80 ppth (wt/wt)) yielded detectable PAH cation distributions that ranged from m/z 128 to 234, depending on the fuel contaminant. The same analysis performed on uncontaminated SRM soils revealed very little (Peruvian) to no (Montana) detectable PAH species. Size analysis showed that most of the individual soil particles analyzed were between 1 and 5 microm in diameter. Tandem mass spectrometry (MS/MS) experiments identified alkyl-substituted two- and three-ringed PAHs in all three petroleum hydrocarbon contaminated soils. However, due to similarities in fragmentation patterns, MS/MS analysis of higher MW species (m/z > 200) was unable to distinguish between the possibility of highly alkyl-substituted three-ringed PAHs and hydrogenated four-ringed PAHs. The described technique offers the direct, rapid determination and characterization of surface-bound PAHs in petroleum-contaminated soils at part-per-million levels without prior extraction, separation, or other sample preparation methods.

Journal Article↗
PubMed1992

Development and application of a new method to extract bacterial DNA from soil based on separation of bacteria from soil with cation-exchange resin.

A new method for the extraction of bacterial DNA from soil has been developed. Soil samples of 50 g were dispersed, and bacteria were released by use of a cation-exchange resin; subsequently, bacteria were separated from soil particles by low-speed centrifugation and lysed with lysozyme and ionic detergent, and the DNA was then purified by CsCl-ethidium bromide equilibrium density centrifugation. The extracted DNA was of high molecular weight and sufficiently pure for restriction enzyme digestion, DNA-DNA hybridization, and amplification by the polymerase chain reaction. The advantages of the new method are that the separation of bacteria from soil is considerably faster than by repeated blending, more samples can be handled, and furthermore no aerosols are formed during separation. Also, we investigated whether the CsCl-ethidium bromide equilibrium density centrifugation could be replaced by purification using Gene-Clean. However, this method produced DNAs which were insufficiently pure for several types of analysis. The new method was used to study survival of a 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading Pseudomonas cepacia DBO1 (pRO101) in unamended soil and in soil amended with 2,4-D. We found that the degrading strain, irrespective of inoculation level, was able to grow to the same high numbers in soil amended with 2,4-D, while the strain in nonamended soil were maintained at the inoculation level. Detection based on DNA extraction and subsequent dot blot DNA-DNA hybridization was in accordance with detection by plating on selective medium.

Journal Article↗
PubMed1996

Toxicity of dimethoate to some soil animal species in different soil types.

Toxicity of dimethoate (insecticide) to an earthworm (Aporrectodea caliginosa tuberculata), a collembola (Folsomia candida), and an enchytraeid worm (Enchytraeus crypticus/variatus) was studied in three different soil types (artificial soil, clayey soil, and humus sandy soil). Parameters measured were survival and biomass change of the earthworms and survival and reproduction of the collembolas and enchytraeids. The degradation of dimethoate was analyzed too. Toxic effects were observed at the concentrations of some mg/kg dry soil. The biomass reduction of the earthworms occurred at lower concentrations than reduction in survival. The collembolas were more susceptible to dimethoate than the enchytraeids. High organic matter content of the soil reduced the toxic effects. The degradation of dimethoate was rather slow in the soils and under conditions tested. Half-life varied between 41 and 84 days.

Analysis of Variance↗
PubMed2006

Assessment of spatial variability in some soil properties as related to soil salinity and alkalinity in Bafra plain in northern Turkey.

The objectives of this study were to assess the variability in soil properties affecting salinity and alkalinity, and to analyze spatial distribution patterns of salinity (EC) and alkalinity (ESP) in the plain, which was used irrigation agriculture with low quality waters. Soil samples were collected from 0-30 cm, 30-60 cm, 60-90 cm and 90-120 cm soil depths at 60 sampling sites. Soil pH had the minimum variability, and hydraulic conductivity (Ks) had the maximum variability at all depths. The mean values of pH, EC, ESP and Ks increased while the mean values of CEC decreased with soil depth. Values pH, EC and ESP were generally high in the east and northeastern sides. Soil properties indicated moderate to strong spatial dependence. ESP and pH were moderately spatially dependent for three of the four depths, EC exhibited moderate spatial dependence for one of the four depths, CEC had a moderate spatial dependence at all depths, and Ks exhibited a strong spatial dependence. EC, CEC, and ESP were considerably variable in small distances. The spatial variability in small distances of EC, CEC, pH and ESP generally increased with depth. All geostatistical range values were greater than 1230 m. It was inferred that the strong spatial dependency of soil properties would be resulted in extrinsic factors such as ground water level, drainage, irrigation systems and microtopography.

Agriculture↗
PubMed2004

Anaerobic biodegradation of no. 2 diesel fuel in soil: a soil column study.

Soil and sediments are contaminated with petroleum hydrocarbons in many parts of the world. Anaerobic degradation of petroleum hydrocarbon is very relevant in removing oil spills in the anaerobic zones of soil and sediments. This research investigates the possibility of degrading no. diesel fuel under anaerobic conditions. Anaerobic packed soil columns were used to simulate and study in situ bioremediation of soil contaminated with diesel fuel. Several anaerobic conditions were evaluated in soil columns, including sulfate reducing, nitrate reducing, methanogenic, and mixed electron acceptor conditions. The objectives were to determine the extent of diesel fuel degradation in soil columns under various anaerobic conditions and identify the best conditions for efficient removal of diesel fuel. Diesel fuels were degraded significantly under all conditions compared to no electron supplemented soil column (natural attenuation). However, the rate of diesel degradation was the highest under mixed electron acceptor conditions followed in order by sulfate reducing, nitrate reducing, and methanogenic conditions. Under mixed electron acceptor condition 81% of diesel fuel was degraded within 310 days. While under sulfate reducing condition 54.5% degradation of diesel fuel was observed for the same period. This study showed evidence for diesel fuel metabolism in a mixed microbial population system similar to any contaminated field sites, where heterogeneous microbial population exists.

Anaerobiosis↗
PubMed2005

Evaluation of soil flushing potential for clean-up of desert soil contaminated by industrial wastewater.

The flushing potential of a desert loess soil contaminated by the flame retardant Tetrabromobisphenol A (TBBPA), chloride (Cl(-)) and bromide (Br(-)) was studied in undisturbed laboratory column experiments (20 cm diameter, 45 cm long) and a small field plot (2 x 2 m). While the soluble inorganic ions (Cl(-) and Br(-)) were efficiently flushed from the soil profile after less than three pore volumes (PV) of water, about 50% of the initial amount of TBBPA in the soil was also flushed, despite its hydrophobic nature. TBBPA leaching was made possible due to a significant increase in the pH of the soil solution from 7.5 to 9, which increased TBBPA aqueous solubility. The remaining TBBPA mass in the soil was not mobilized from its initial location in the topsoil due to the decrease in pH at this horizon. In situ soil flushing demonstrated that this method is a feasible treatment for reducing soil contamination at this site.

Desert Climate↗
PubMed2006

Sorption kinetics and leachability of heavy metal from the contaminated soil amended with immobilizing agent (humus soil and hydroxyapatite).

Release of heavy metals onto the soil as a result of agricultural and industrial activities may pose a serious threat to the environment. This study investigated the kinetics of sorption of heavy metals on the non-humus soil amended with (1:3) humus soil and 1% hydroxyapatite used for in situ immobilization and leachability of heavy metals from these soils. For this, a batch equilibrium experiment was performed to evaluate metal sorption in the presence of 0.05 M KNO(3) background electrolyte solutions. The Langmuir isotherms applied for sorption studies showed that the amount of metal sorbed on the amended soil decreased in the order of Pb(2+)>Zn(2+)>Cd(2+). The data suggested the possibility of immobilization of Pb due to sorption process and immobilization of Zn and Cd by other processes like co-precipitation and ion exchange. The sorption kinetics data showed the pseudo-second-order reaction kinetics rather than pseudo-first-order kinetics. Leachability study was performed at various pHs (ranging from 3 to 10). Leachability rate was slowest for the Pb(2+) followed by Zn(2+) and Cd(2+). Out of the metal adsorbed on the soil only 6.1-21.6% of Pb, 7.3-39% of Zn and 9.3-44.3% of Cd leached out from the amended soil.

Acetic Acid↗
PubMed2006

Impact of river overflowing on trace element contamination of volcanic soils in south Italy: part I. Trace element speciation in relation to soil properties.

Volcanic soils affected by different numbers of polluted river flooding events were investigated. Chromium and Cu were the major soil contaminants. Nickel, Fe, Zn and Mn total content never exceeded the Italian mandatory limits. The distribution of Cr and Cu total contents among studied soils indicated that only Cr contamination was related to overflowing events. In polluted soils, sequential chemical extractions revealed a preferential association of Cr and Cu with organic forms. A progressive Cr insolubilization with ageing was observed. Significant amounts of Cr and Cu were extracted by NH(4)-oxalate, suggesting metals association with short-range-order aluminosilicates and organo-mineral complexes. Possible methodological drawbacks in the use of the EU-BCR chemical speciation protocol on volcanic soils are discussed. Micromorphology and SEM/WDS analyses revealed Cr and Cu enriched silt and clay coatings in surface and subsurface soil horizons, suggesting a transfer of metal-rich sediments along the soil pore network with water movement.

Chromium↗
PubMed2006

Contrasting pattern of methanotrophs in dry tropical forest soils: effect of soil nitrogen, carbon and moisture.

Population dynamics of methane-oxidizing bacteria (MOB) was measured for 2 consecutive years for four forest and one savanna sites in seasonally dry tropical regions of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of soils. There were significant differences in MOB population size during the 2 years (mean 0.40 and 0.48 x 10(5) cells g(-1) dry soil), and at different sites (mean 0.38-0.59 x 10(5) cells g(-1) dry soil). The mean population size of MOB was higher (P<0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and MOB population size during summer (the driest period) and a negative relation during the rest of the year. The number of MOB was consistently higher for the Kotwa hill base site than rest of the sites having higher soil organic C and total N. The results suggested that in seasonally dry tropical forests the moisture, C and N status of the soil regulates the population size of MOB (methanotrophs) in the long term.

Carbon↗
PubMed2003

Effects of EDTA and low molecular weight organic acids on soil solution properties of a heavy metal polluted soil.

A pot experiment was conducted to study the effects of EDTA and low molecular weight organic acids (LMWOA) on the pH, total organic carbon (TOC) and heavy metals in the soil solution in the rhizosphere of Brassica juncea grown in a paddy soil contaminated with Cu, Zn, Pb and Cd. The results show that EDTA and LMWOA have no effect on the soil solution pH. EDTA addition significantly increased the TOC concentrations in the soil solution. The TOC concentrations in treatments with EDTA were significantly higher than those in treatments with LMWOA. Adding 3 mmol kg(-1) EDTA to the soil markedly increased the total concentrations of Cu, Zn, Pb and Cd in the soil solution. Compared to EDTA, LMWOA had a very small effect on the metal concentrations. Total concentrations in the soil solution followed the sequence: EDTA >> citric acid (CA) approximately oxalic acid (OA) approximately malic acid (MA) for Cu and Pb; EDTA >> MA >> CA approximately OA for Zn; and EDTA >> MA >> CA > OA for Cd. The labile concentrations of Cu, Zn, Pb and Cd showed similar trends to the total concentrations.

Cadmium↗
PubMed2003

Changes in soil microbial biomass and Zn extractability over time following zn addition to a paddy soil.

A laboratory incubation study was conducted using a paddy soil spiked with two quantities of Zn as soluble Zn(NO3)2 and unamended controls. Three single extractants (1 M ammonium acetate (pH 7.0), 0.43 M acetic acid and 0.05 M EDTA) were used to assess the bioavailability of Zn. Biological community assessments were made microbial biomass (chloroform fumigation), soil basal respiration and dehydrogenase activity. During the 84-day period of the experiment, addition of Zn at both 500 and 1,000 mg kg(-1) had little detectable effect on soil pH. The concentration of NH4OAc-extractable Zn decreased rapidly within the initial six weeks. The concentration of HOAc-extractable Zn showed no decrease during 84 days incubation. EDTA-extractable Zn was greater than NH4OAc- and HOAc-extractable fractions, and showed a similar trend to NH4OAc-extractable after incubation. Microbial biomass, soil basal respiration and dehydrogenase activity all decreased over time during 84 days incubation. Addition of Zn resulted in a significant increase in specific respiration (qCO2). Microbial biomass and dehydrogenase activity did not appear to be influenced by added Zn, probably due to the strong buffering capacity of the soil. The Zn extracted by EDTA, HOAc and NH4OAc showed close relationships with each other (p < 0.001). Zinc extracted by 0.05 M EDTA and NH4OAc were highly correlated with soil basal respiration and specific respiration rate (p < 0.01). The results suggest that NH4OAc-extractable Zn combined with soil specific respiration could be used as parameters for risk assessment.

Acetates↗
PubMed2003

Soil microbial parameters and luminescent bacteria assays as indicators for in situ bioremediation of TNT-contaminated soils.

In situ bioremediation is increasingly being discussed as a useful strategy for cleaning up contaminated soils. Compared to established ex situ procedures, meaningful and reliable approaches for monitoring the remediation processes and their efficiency are of special importance. The subject of this study was the significance of two bioassays for monitoring purposes. The work was performed within the scope of a research project on the in situ bioremediation of topsoil contaminated with 2,4,6-trinitrotoluene (TNT). To evaluate changes within different experimental fields during a 17-month remediation period, the results of soil microbial assays and luminescent bacteria assays were compared with chemical monitoring data. The luminescent bacteria assays showed a significant reduction of the water-soluble soil toxicants in the treated fields. This bioassay proved to be a sensitive screening indicator of toxicity and may effectively aid the ecotoxicological interpretation of chemical monitoring data. Microbial biomass (C(mic)), the metabolic quotient (qCO2), and the ratio of microbial to organic carbon (C(mic)/C(org)) showed a highly significant correlation with total concentrations of TNT in the soil. But, in contrast to luminescent bacteria assays, this approach did not reveal any recovery of the soil at the end of the remediation period. There is clear evidence for persistent adverse effects of chronic TNT contamination on the site-specific microbial community and the local carbon cycle in the soil. The study clearly exhibits the differences between, as well as the complementary value of both bioassay approaches for monitoring short-term and long-term effects of soil contamination and the efficiency of remediation.

Bacteria↗
PubMed1999

Anaerobic incorporation of the radiolabeled explosive TNT and metabolites into the organic soil matrix of contaminated soil after different treatment procedures.

Four bioreactor designs were performed to evaluate the level of incorporation of 14C-labeled 2,4,6-trinitrotoluene (TNT) and metabolites into the organic soil matrix of different anaerobically treated contaminated soils. The contaminated soils were amended with molasses slivers (80:20% per weight) as auxiliary substrate to enhance microbial activity. After 5 weeks (bioreactors 1 and 2), 8 weeks (bioreactor 3) and 12 weeks (bioreactor 4) of anaerobic incubation, we determined 41%, 58%, 72%, and 54%, respectively, of the initially applied radioactivity immobilized in various soil fractions. After alkaline hydrolyses of the solvent-extracted soils, low quantities of radiolabel were found in the humic and fulvic acid fractions, whereas the bulk of 14C activity was found to be strongly bound to the humin fraction (solid soil residues). The amounts of solvent extractable radioactivity were 53%, 40%, 16%, and 29% for bioreactors 1, 2, 3, and 4, respectively. The level of TNT transformation at the end of the experiments was within 90-94%. Regarding the results presented in this study, we can assume that there is the possibility of high incorporation levels of TNT metabolites into the soil organic matrix mediated by microbial cometabolism under strictly anoxic conditions.

Bacteria, Anaerobic↗
PubMed2000

Sorption of non-ionic surfactants to soil: the role of soil mineral composition.

In this study, the importance of individual soil mineral constituents on non-ionic surfactant sorption is evaluated by employing scanning electron microscopy (SEM) equipped with energy-dispersive X-ray analysis (EDAX) to observe microchemical surface composition of model soil colloids and relate surface microchemical composition to the sorption behavior of a non-ionic surfactant, Polyethylene Glyco Mono-p-nonylphenyl Ether (A9PE10), on selected model soil colloids. This information is critical to understanding the fate and transport of this class of contaminants in subsurface. Results obtained from this study indicate that a correlation between the atomic ratio of Si:(Al + Fe) on soil mineral surface and A9PE10 sorption capacity exist, where those soil with larger value of Si:(Al + Fe) ratio exhibit higher sorption capacity. This allows us to predict that the non-ionic surfactant sorption capacity for soil decrease with progressively increasing states of soil maturity.

Absorption↗