Earthworms,a means to accelerate removal of hydrocarbons (PAHs) from soil? A mini-review

Contamination of soil with hydrocarbons occurs frequently. Restoring contaminated soils is costly and time consuming. Earthworms accelerate the removal of hydrocarbons as they burrow through soil by rendering contaminants available for microbial degradation, by feeding on the organic matter that harbour contaminants, and by improving soil structure and aeration. Polycyclic aromatic hydrocarbons (PAHs) are recalcitrant hydrocarbons that can contaminate the environment and can thus serve as models to study the factors that control the removal of petroleum from soil. The effect of earthworms on the removal of PAHs was reviewed. It was found that earthworms have the capacity to accelerate the removal of PAHs and their degradation products from soil. However, large numbers of earthworms are required, which might be expensive. Moreover, it may be difficult to provide sufficient organic material as feed while simultaneously maintaining high soil water content to allow burrowing.     

Contribution of Subcommission a (salt affected soils) to the achievements in the investigation and management of saline and Alkali soils 1964–2001

This paper was written by M. Redly soon before her death in September 2010. It summarizes the work of a big team of soil scientists studying the genesis, geography, and method of reclamation of salt-affected soils in the second half of the 20th century. It is also a tribute to I. Szabolcs, the organizer and the first chairman of the Subcommision on Salt-Affected Soils at the ISSS. The work of this subcommision can be considered an inspiring example of international cooperation in solving topical problems of soil science.     

Is ‘grey literature’ a reliable source of data to characterize soils at the scale of a region? A case study in a maritime pine forest in southwestern France

Soil scientists are receiving increasing numbers of requests for expert advice on soil over large areas, but at a high resolution. We tested the use of the soil data contained in sources of information that are not directly accessible (referred to as ‘grey’ data) to accomplish this task. We collected grey data about a pine forest, which is currently the subject of drastic, and questionable, changes in management, including a rapid rate of biomass removal. These grey data (from 266 sites) were compared with soil data obtained directly from our field sampling (83 sites). Our comparisons showed that the two sources of data were consistent when the variables concerned had been sampled and analysed by using methods shared by the soil scientists such as particle‐size distribution. Conversely, significant discrepancies appeared for variables for which different methods existed, such as for CEC. For the latter, using corrective equations gave contrasting results, depending on the soil variable. The final database was used to characterize the soils of the study region. Results showed that soils of the study region (mainly sandy podzols and arenosols) were acidic and particularly oligotrophic. Several important properties (CEC, phosphorus cycling, pH, bulk density) were related to the organic fraction or carbon (C) content of soils. For instance, CEC values were linearly and exclusively dependent on C content. The most oligotrophic sites of the study region were clearly not suitable for the new intensive management of the forest in the long term. For the other sites, the question remains open because some specific data are still needed before drawing conclusions. We conclude that as a complement to conventional soil studies, the grey literature is a useful source of data and information to characterize soils at a regional scale.     

Live and death of streptomyces in soil—what happens to the biomass?

The formation of soil organic matter (SOM) has been proposed to depend on fragmentation of biomass after cell death. However, this is hard to mimic in laboratory experiments showing the process directly. We used heavy metal contamination in order to provide an environment in which one Streptomyces strain, the heavy metal resistant S. mirabilis P16B‐1, could survive while the sensitive strain S. lividans TK24 was expected to die and disintegrate; the necromass fragments would then contribute to SOM formation. Both strains were grown for 30 d in sterile mesocosms containing either highly metal‐contaminated soil from a former uranium‐mining site in Ronneburg, Germany, or control soil from a municipal park, Jena, Germany. The fate and morphology of living and dead bacterial biomass (necromass) was observed using scanning electron microscopy. Attachment of soil particles to the intact mycelium as well as decay of dead biomass was observed. Dead bacterial biomass was identified in form of patchy fragments while the superordinate filamentous structure of the hyphae was still visible and obviously stabilized in soil. The fate of cytosolic compounds was followed using the example of a nickel‐containing superoxide dismutase (NiSOD) which was found to be released after death of cells grown in liquid soil‐extract medium. Activity of the enzyme was proven for concentrated media supernatant by a gel‐based qualitative activity assay. This indicates that NiSOD remains active in soil after cell death. Hence, bacterial cell death results in the release of cytosolic compounds, e.g., intact proteins, as well as the formation of residual cell‐envelope fragments contributing to SOM formation.     

Biodiversity and functioning of ecological communities — why is diversity important in some cases and unimportant in others?

The paper gives an overview of ecological theories and hypotheses that have been raised in order to predict diversity‐function relationships. In particular, those reasons are discussed that may explain the discrepancy between the theoretical expectation for widespread effects of diversity on functioning and the ambiguous empirical evidence for such effects. Structural differences in the ecology of plants, invertebrates, and micro‐organisms are considered which lead to differences in diversity‐function relationships among these groups of organisms. Four criteria are derived that determine diversity‐function relationships: (1) motility of the organisms under consideration, (2) decoupling of population persistence and functional activity in these organisms, (3) species richness of the organisms' community, and (4) equilibrium stability of the considered ecological process. From these criteria the authors predict that measurable effects of diversity on functioning are (a) likely to be found in plants and in micro‐organisms while they are (b) unlikely to be found in the soil fauna. They predict that diversity is (c) likely to affect primary production, soil energy turnover, and nutrient losses from the system, while it is (d) unlikely to durably influence litter decomposition rate. It is shown that these predictions are largely corroborated by empirical evidence compiled from the literature. The issue of spatial and temporal scale is briefly discussed.     

Methane oxidation,nitrification, and counts of methanotrophic bacteria in soils from a long-term fertilization experiment (”︁Ewiger Roggenbau” at Halle)

Aerobic soils are important sinks for atmospheric methane. CH₄ oxidation, mediated mainly by methanotrophic bacteria, is the responsible process, which is strongly inhibited by ammonium accessible for nitrification. An inhibitory effect immediately after fertilization as well as a long-term effect exists, which results from repeated ammonium applications and which is independent from the actual concentration of NH₄⁺-N in soil. This long-term effect could be caused by a shift in the microbial population of the soil. Thus, with soil samples from long-term fertilization treatments of the field experiment ”︁Ewiger Roggenbau” at Halle (Germany) incubation studies were conducted to investigate the interference between CH₄ oxidation and nitrification and to determine the cell numbers of methanotrophic bacteria. Including the treatments PK, NPK, and farmyard manure, which were established in 1878, a close negative correlation between CH₄ oxidation and net nitrification was found (r = —0.92). The CH₄ oxidation rates, determined with an initial concentration of 10 μl CH₄ l^—1, varied between 6.7 and 1.1 μg C kg^—1 d^—1 in the PK and NPK treatment, respectively. After application of NH₄Cl a strong inhibition of CH₄ oxidation occurred, which was 91%, 88%, 81%, and 63% in the treatments PK, NPK, FYM, and U (unfertilized), respectively. After a lag-phase of 2 to 3 weeks an incubation with high CH₄ concentrations (20 Vol.% CH₄) could induce CH₄ oxidizing activity in the NPK treatments under continuous rye or maize cropping. An increase of up to 40 times in comparison to the control under atmospheric CH₄ (2 μl CH₄ l^—1) was observed. A negative correlation (r = —0.74) existed between the CH₄ oxidation rates of the soils without recently applied NH₄⁺ and the numbers of methanotrophic bacteria, determined with the ”︁most probable number” method (MPN). Thus, the MPN technique is not suitable to characterize the physiologically active population of methanotrophic bacteria in soils, which oxidize CH₄ in the atmospheric concentration range. The results of this study suggest that in aerobic arable soils methanotrophic bacteria and not nitrifiers are responsible for CH₄ oxidation.     

Amendment of soils with fresh and post-extraction lavender (Lavandula angustifolia) and lavandin (Lavandula × intermedia) reduce inoculum of Verticillium dahliae and inhibit wilt in strawberry

Soils that were naturally infested with high levels of Verticillium dahliae, the causal agent of wilt disease in strawberry, were amended with fresh and waste lavender, fresh and waste lavandin, hydrosols generated during essential oil production, BioFence™ (a mustard-based defatted seedmeal pellet), or water in microcosms to estimate their efficacy against microslecrotia of the pathogen. Single chemicals and mixtures of the chemicals detected from the substrata were also effective in microcosms. The mixtures were more effective than were the individual chemicals. Microplot evaluation of fresh and waste lavender and lavandin was also made in comparison to BioFence™ and water controls. Lavandin waste was compared to BioFence™ and untreated controls at three sites in field plots that were subsequently planted to strawberry. Disease incidence and severity were measured over time in the field. All of the Lavandula-based materials could be associated with large reductions in the numbers of viable of microsclerotia recovered in all but one experiment with greatest effect in microcosms and smaller effects in microplots and field plots, as could BioFence™ pellets. Due to the high levels of inoculum found at all field sites the reduction in pathogen inoculum density was not necessarily associated with a corresponding reduction in disease incidence, nor with severity as determined by yield. The monoterpenoids associated with the Lavandula spp. are of lower volatility than the isothiocyanates associated with crucifer decomposition and were detected for more than one week after materials were incorporated in soil. This suggests both differences in mode of action and the possibility of combining either the chemicals or the materials that produce them in order to further enhance efficacy. Several non-target effects were considered: numerosity and diversity of bacterial and fungal populations; infection by arbuscular mycorrhizal fungi; and functional diversity of soil microflora. No persistent non-salient effects were detected.     

Should farmers apply fertilizer according to when their daffodils are in flower? Utilizing a “farmer‐science” approach to understanding the impact of soil temperature on spring N fertilizer application in Wales

Perennial ryegrass starts growing when soil temperatures reach 5.5°C for five consecutive days; applying N fertilizer before this risks environmental losses. To test whether daffodil flowering signified when to apply N fertilizer, farmers volunteered to take part in a citizen science study. The PROSOIL project used a “citizen science”, participatory approach to create farmer‐informed science, aiming to increase awareness of the importance of soil health. In 2014, over 300 farmers completed a “How do you manage your soil” survey. The survey included a question on the use of daffodils (Narcissus spp.) to indicate the best time to apply the first nitrogen fertilizer of the season, based on anecdotal feedback from farmers involved in the PROSOIL project. The survey recorded 7% of farmers based their first fertilizer application on when daffodils flowered. To increase farmer awareness of soil temperatures, we provided them with soil thermometers, held workshops and hosted interactive stands at agricultural events in 2014. In autumn 2014, farmers planted daffodil bulbs of the same variety, across Wales, and monitored soil temperatures. Farmers returned postcards once their daffodils were in flower, noting the soil temperature. An assessment of whether daffodil flowering date could indicate when to apply N fertilizer was made. Overall, in spring 2015, daffodils flowered when soil temperature was 6.4(±0.35)°C, suggesting daffodil flowering date is a more reliable indicator for fertilizer application, than first hypothesized. Findings show a scientific validation of local knowledge, regarding the use of daffodils to indicate the “not‐before” date for the first N fertilizer application.     

Optical sensing and chemometric analysis of soil organic carbon – a cost effective alternative to conventional laboratory methods?

Soil organic carbon (SOC) is frequently determined by the Walkley‐Black (WB) method. A limitation of the test is incomplete oxidation of the carbon fraction and underestimation of SOC. Automated dry combustion methods are expensive and slow. Optical sensing and chemometric analysis offer the potential of an economical method capable of quantifying SOC fractions. The aim of this study was to identify the best SOC analysis method to facilitate maximum sampling resolution based on the cost per sample, analytical accuracy and time. A comparative evaluation was made of five techniques; (1) the WB method, (2) total combustion by total organic C analyser, (3) infrared (IR) diffuse reflectance spectroscopy, (4) a portable spectroradiometer and (5) laboratory hyperspectral imaging. This involved assessing equipment costs, consumables and time to derive total analytical cost. The benefits were sample throughput and analytical accuracy. Instrumentation represented the largest input to analytical cost and for optical methods was governed by the spectral range. In contrast to dry combustion, this cost is offset by high sample throughput and minimal consumable requirements for IR spectroscopy and hyperspectral imaging. Hyperspectral imaging is identified as the most rapid technique with potential to scan about 720 samples per day at 90% less cost than the WB method. The opportunity cost of hyperspectral imaging is to forfeit some analytical accuracy associated with the dry combustion method. Dry combustion, despite its high cost per sample, incurs no further costs associated with updating prediction models or developing site or soil specific correction factors.     

Spatial and vertical distribution of <Superscript>137</Superscript>Cs in soils in the erosive area of southeastern Serbia (Pčinja and South Morava River Basins)

Purpose

The area of southeastern Serbia, the P?inja and South Morava River Basins, is under the influence of very strong erosion, and the aim of this study was to investigate the vertical and spatial distribution of the ¹³⁷Cs in the eroded soils of this area.

Materials and methods

Vertical soil profiles were collected with 5-cm increments from the uppermost layer down to 20, 25, 30, 40, and 50 cm of depth, depending on the thickness of the soil layers, i.e., down to the underlying parent rocks. Measurements of ¹³⁷Cs activity concentration were performed by using the HPGe gamma-ray spectrometer ORTEC-AMETEK (34 % relative efficiency and high resolution 1.65 keV at 1.33 MeV for ⁶⁰Co), from its gamma-ray line at 661.2 keV.

Results and discussion

The mean ¹³⁷Cs activity concentration across all 18 soil profiles (for all soil layers) was found to be 20 Bq kg^?1. In the greatest number of soil profiles, the ¹³⁷Cs activity concentration was generally highest in the first soil layer (0–5 cm) and decreased with soil depth, while in a few soil profiles, the peak of either the ¹³⁷Cs activity concentration occurred in the second soil layer (5–10 cm) or the ¹³⁷Cs activity concentration was almost equal throughout the entire soil profile. The mean ¹³⁷Cs activity concentration in the first soil layer (0–5 cm) was found to be 61 Bq kg^?1, and the high coefficient of variation of 92 % pointed out high spatial variability and large range of the ¹³⁷Cs activity concentrations in the study area.

Conclusions

The obtained results indicate that in the greatest number of soil profiles, ¹³⁷Cs is present in the upper layers, with concentration decreasing with depth, as is typical in uncultivated soil. Its spatial distribution was very uneven among the surface soil layers of the investigated sites. One of the main reasons for such pattern of ¹³⁷Cs in the study area may be soil erosion. Additional investigations which would support this hypothesis are required.

     

Potential of AFM–nanothermal analysis to study the microscale thermal characteristics in soils and natural organic matter (NOM)

Purpose  

This exploratory study evaluates the potential of nanothermal analysis (nTA) coupled with atomic force microscopy (AFM) of soil samples for understanding physicochemical processes in soil and for linking the nanospatial and microspatial distribution of thermal characteristics with the macroscopic properties of soil samples.     

Is soil water repellency a function of soil order and proneness to drought? A survey of soils under pasture in the North Island of New Zealand

We conducted a survey of the occurrence of soil water repellency (SWR) in the top 40 mm of soils across 50 sites under pastoral land use in the North Island of New Zealand. The sites represented ten soil orders and covered five classes of proneness to drought. We found at least a moderate persistence of SWR in 35 out of 50 sites (70%) in summer 2009/2010 and a moderate potential persistence of SWR in 49 out of 50 sites (98%) after drying the soils. The soil orders had an influence on the degree and persistence of SWR. Both the degree and persistence of SWR were greatest for the soil orders Podzol, Organic and Recent, and least for the soil order Allophanic. On average, all soil orders had contact angles larger than 94°, with the exception of the soil order Allophanic. We found no relationship between SWR and drought‐proneness. The degree of SWR and its persistence for air‐dried samples were positively correlated with soil carbon and nitrogen contents and negatively with soil bulk density. The persistence of SWR for field‐fresh samples was additionally negatively correlated with the soil water content. We identified a close relationship (R² = 0.84) between the degree and persistence of SWR. The survey results indicate that SWR is at least moderately persistent in a soil with a contact angle larger than 93.8°. Using a water‐drop penetration time of 60 s as the threshold for SWR being moderately persistent, we found that moderately persistent SWR occurred only for volumetric water contents below 45% or a relative saturation of 60%. The latter can be considered to be a generic value of the critical water content for the onset of SWR at the scale of the North Island of New Zealand.     

Isotopic Model (NISOTOP) used to Investigate 15N-Urea Transformations in the Presence of Phenanthrene,Chrysene and Benzo(a)pyrene in a Soil–Plant System

An isotopic model (NISOTOP) has been developed to investigate the effect of the addition to soil of xenobiotics on urea hydrolysis, N mineralization and immobilization, nitrification and plant uptake of nitrogen in a soil-plant system, after addition of ¹⁵N enriched compounds. Therationale of the model follows from the errors in %¹⁵N abundance (^15N _D) and N concentration (C_N) determinations which cause high variability coefficients in the calculation of the amount of nitrogen present in the different compounds derived from the added ¹⁵N enriched urea. The extent of these errors, besides depending on C_N and ^15N _D errors, will also depend on natural ¹⁵N and ¹⁵N of the added compound, and therefore on the experimental conditions. The model is described by 18 first-order differential equations and is numerically solved by Euler's method with a time increment of 0.01 day. As an illustration, the model is applied to the effect of phenanthrene, chrysene and benzo(a)pyrene to a soil-plant system, following the addition of ¹⁵N-urea. These compounds have been chosen as examples of molecules having 3, 4 and 5 fused aromatic rings and are hereafter collectively referred to as PAHs. PAHs at the rate of 2 mg kg^-1 soiland ¹⁵N-urea at the rate of 166.7 mg N kg^-1 soil were added to wheat pots. At harvesting (after 14 days from plantation) the dry matter yield, the total N content and the N concentration of the wheat seedlings were not statistically affected by addition of the PAHs (P = 0.05). The efficiency of N uptake, that is the percentage of fertilizer taken up by the plants at harvesting in the absence of PAHs was 47.3%, while it was 11.7, 15.2 and 14.8% in the presence of phenanthrene, chrysene and benzo(a)pyrene,respectively. The computation of the first-order rate constants of the N transformations showed that N mineralization, nitrification and N-uptake were affected by the addition of phenanthrene, chrysene and benzo(a)pyrene, whilst benzo(a)pyrene inhibited urea hydrolysis more than phenanthrene and chrysene.     

Effect of long‐term cultivation on zinc and copper contents in soils from the bahía blanca horticultural belt (Argentina)

Abstract

The objectives of this work were to quantify the total and available copper (Cu) and zinc (Zn) contents in soils which have been used for intensive agricultural production and to investigate the influence of the soil's properties on the absorption and migration of these metals. Total and available Zn and Cu contents in the topsoil and their variation with depth in Mollisols from the Bahía Blanca (Argentina) horticultural belt have been studied. Total contents of Cu and Zn were extracted by means of acid digestion in Teflon bombs placed in a microwave oven. The available Cu and Zn contents were extracted using the DTPA method and the analysis of Cu and Zn was carried out by atomic absorption spectrophotometry. High contents of Cu and Zn were found in the surface layers of all the plots studied and lower contents were noted in plots recently used for horticulture. The lowest contents were found in control farms. The results showed that 70% of the Zn in the surface layers were found in unavailable form, whereas almost 50% of the Cu was in available form. No relationship was noted between each kind of cultivation and Cu content. Most of the Zn in the different plots was adsorbed or complexed by organic ligands and clay. The variation of Cu and Zn content with the depth indicated a greater mobility of Cu. Most of the Zn was detected in the surface soil, whereas no differences were noted in Cu content between surface and subsoil. The results obtained confirmed the anthropic origin of these metals in the cultivated plots. The correlation found between the different forms of Zn and Cu as well as between their total and available contents suggested that these metals have been applied together via agrochemicals and waste.