Soil Extraction Methods Research Articles

Can soil phosphorus sorption saturation estimate future potential legacy phosphorus sources?

AbstractVarious soil extraction methods are used to indicate plant available P in soil but do not account for soil specific sorption of subsequent applications of P. Thus, estimates of soil phosphorus sorption saturation (PSS; estimated from Mehlich‐3 extractable P, Al, and Fe) have been used in conjunction with Mehlich‐3 extractable soil phosphorus (M3P) to overcome these limitations. As less is known about the effect of land management on PSS than M3P under field conditions, the effect of field management on PSS was investigated for three pastures over 5 yr (2014–2018). Swine slurry was applied to two fields (Field 1 received 60 kg P and 74 kg N and Field 12 received 60 kg P and 74 kg N ha−1 yr−1), mineral fertilizer to one field (Field 5 received 28 kg P and 64 kg N ha−1 yr−1), and all fields grazed by cattle. Biannual grid‐soil sampling (0.1‐ha grid) showed an increase in PSS in the surface 10 cm of two fields receiving swine slurry (7.8–12.0% and 6.0–11.0% for Fields 1 and 12, respectively; P < .05 level) between 2014 and 2018, while no change in PSS was evident for Field 5 receiving mineral fertilizer (P > .05 level). Compared with published values, measured increases in PSS suggest that soils of Fields 1 and 12 are transitioning from sinks to sources of P in specific areas of the field due to P applications and cattle grazing, and that management should change to minimize the potential for P runoff.

Evaluation of Biochar Nitrate Extraction Methods

Biochar amendment to soil is a method used to mitigate losses of nitrogen leaching through agricultural soils. Multiple methods for extraction of nitrogen have been used, and recent studies have indicated that traditional soil extraction methods underestimate biochar nitrate. This study evaluated the nitrate extraction efficiency of a KCl extraction method under different temperature (20 and 50 °C) and duration (24 and 96 h) conditions. Increasing the duration of extraction from 24 to 96 h did not have a significant impact on extraction efficiency. However, increasing temperature resulted in nitrate extraction efficiencies above 90%. Rinsing the biochar once with deionized (DI) water following filtration after extraction increased the extraction efficiency significantly, but any subsequent rinses were not significant. This study recommends extracting nitrate from biochar using 2 M KCl at 50 °C for a period of 24 h with one additional rinse to increase nitrate recovery above 90%. However, future studies should evaluate this procedure for different types of biochar produced from alternative biomasses and at varying temperatures.

Refining fine fraction soil extraction methods and analysis for mineral exploration

Soils are widely used as geochemical sample media. In transported cover, the soils that host the mobile element signature are the smallest size fractions, so we should consider concentrating the clay size fraction (<2 µm) as an improved sample medium. Twenty-seven bulk reference soils were collected in the vicinity of known mineral deposits (including background areas) that reflect common soil types of Western Australia. A selection of these soils was used in replicate testing to assess differences in particle size, sample weight, dispersants, and how this relates to the Au and Cu geochemistry. Using multiple analysis of variance tests, the submicron fractions showed that, although the <0.2 µm fraction was slightly different to the <2 µm and <0.75 µm fractions, there was no additional value in the extra effort required to extract these submicron fractions, and the <2 µm fraction was favoured. Ultrasonics and rinsing were not required for Au analysis, and during wet separation no Au is lost in solution and only a small fraction of the overall Cu (0.5%) is lost. Using a dispersant was critical for solid recovery and Na-hexametaphosphate (technical or laboratory grade) was found to be the most effective reagent. The <2 µm size fraction showed no significant differences for assays of Au using 0.1, 0.2, 0.5, 1 and 4 g ( P < 0.05) with a microwave-assisted aqua regia digestion being the best analytical method for Au recovery. In addition to the geochemistry, the spectral reflectance variation was investigated with respect to particle size and weight, and showed more variation in the smaller weight fraction of material and a loss of quartz in the fine materials as expected. The integration of results from this study generated a new workflow called UltraFine+™. This workflow provides 40 elements, spectral mineralogy, particle-size distribution, pH, electrical conductivity (EC) and specific surface area, offering more quality data to improve mineral exploration using soil and regolith samples. Supplementary material: Spreadsheets of soils and regolith data from orientation sites and regional map sites analysed with the UltraFine+ method is available at https://doi.org/10.25919/5d1058f8b05fc

Combining microdialysis with metabolomics to characterize the in situ composition of dissolved organic compounds in boreal forest soil

Low-molecular weight organic compounds (LMWOC) play a key role in soil respiration. Thus, a detailed understanding of their dynamics is important for any attempt to describe carbon cycling of ecosystems. Measurements of LMWOC have been compromised by the perturbation associated with traditional soil extraction methods. Due to the fast turnover of LMWOC, there are potential losses of compounds caused by ex situ methods. These losses should be reduced by microdialysis, a novel soil sampling technique that samples the delivery of compounds through induced diffusive flux rates (DFR), representing what an active organism is exposed to in situ, in the undisturbed soil. The present study used microdialysis to measure the DFR of LMWOC in the O-horizon of a boreal forest soil in northern Sweden at four occasions during the middle to end of the growing season. LMWOC was analyzed by untargeted metabolomic profiling, which identified 50 compounds, and targeted mass spectrometry, which quantified seasonal shifts in the abundance of 36 amino acids, organic acids and sugars. The amino acid proportion of the DFR decreased by 85% during the growing season. However, because the decrease in amino acids was compensated for by increases in organic acid and sugar fluxes, the total DFR remained approximately constant during the season. The organic acid pool was dominated by lactate (80%) in the middle of the season and consisted mainly of oxalate (40%) during the later season. A lower amount and more diverse composition of sugars were found compared to previous studies. Six sugars and polyols were detected, with mannitol, arabitol and glucose being the most abundant. Microdialysis has previously been explored to monitor amino acids and inorganic compounds, but the present research demonstrates the potential of the in situ microdialysis sampling when combined with metabolomics. This broadens the application of microdialysis to describing quantitative and qualitative changes in the dynamic composition of the DFRs in undisturbed soil and a similar approach may be used in future studies to study the actual soil processes governing soil LMWOC.

Effective Soil Extraction Method for Cultivating Previously Uncultured Soil Bacteria.

Here, a new medium, named intensive soil extract medium (ISEM), based on new soil extract (NSE) using 80% methanol, was used to efficiently isolate previously uncultured bacteria and new taxonomic candidates, which accounted for 49% and 55% of the total isolates examined (n = 258), respectively. The new isolates were affiliated with seven phyla (Proteobacteria, Acidobacteria, Firmicutes, Actinobacteria, Verrucomicrobia, Planctomycetes, and Bacteroidetes). The result of chemical analysis showed that NSE included more diverse components of low-molecular-weight organic substances than two conventional soil extracts made using distilled water. Cultivation of previously uncultured bacteria is expected to extend knowledge through the discovery of new phenotypic, physiological, and functional properties and even roles of unknown genes.IMPORTANCE Both metagenomics and single-cell sequencing can detect unknown genes from uncultured microbial strains in environments, and either method may find the significant potential metabolites and roles of these strains. However, such gene/genome-based techniques do not allow detailed investigations that are possible with cultures. To solve this problem, various approaches for cultivation of uncultured bacteria have been developed, but there are still difficulties in maintaining pure cultures by subculture.

Assessing phosphorus nutrition of the main European tree species by simple soil extraction methods

In the past few decades, high nitrogen emissions have reversed the nitrogen limitation of trees. Meanwhile, phosphorus (P) appears as a primary limiting nutrient of many forests in Europe. However, a simple and economic standard method for the determination of the plant-available phosphorus in forest soils, which drives the P supply of the trees, is not yet available. Therefore, we tested two soil extraction methods [citric-acid extract (Pcit), according to Hoffmann et al. (1991) and sodium bicarbonate extract (PHCO3), referring to Olsen et al. (1954)] for analyzing all Bavarian soil samples of the second German National Forest Soil Inventory (NFSI), resulting in a big data set with 342 forest sites and 2232 samples. We combined these results with the standardly gathered soil parameters and tested them as predictors for P nutrition indicated by the foliar P concentrations of the four most important tree species: Norway spruce (Picea abies), European beech (Fagus sylvatica), Scots pine (Pinus sylvestris) and pedunculate/sessile oak (Quercus robur/petraea). During the statistical process, we stepwise reduced the complexity of the prediction models. In our analyses, we achieved the best prediction of foliar P using soil information from the organic layer and mineral soil down to depths of 10 cm and 20 cm. Pcit stocks provided by far the best predictions in nearly all cases. Based on this parameter, we derived parametric regression functions to estimate the P nutrition (spruce: R2 = 0.52∗∗∗; beech: R2 = 0.49∗∗∗; pine: R2 = 0.39∗∗∗; oak: R2 = 0.35∗∗∗). Based on logistic regressions, threshold values were deduced for Pcit stocks down to 10 cm soil depth (spruce: 33 kg ha−1; beech: 43 kg ha−1; pine: 32 kg ha−1; oak: 41 kg ha−1), above which P deficiency becomes unlikely. Since these models are based on a large number of sites with diverse geologies and soil conditions, they can be used to estimate the P availability of most forests in Bavaria. Furthermore, the applied methods can be extended to other soil inventories. Estimated P availability based on such functions and thresholds can support sustainable nutrient management of temperate forests.

Evaluating soil extraction methods for chemical characterization of ultramafic soils in Kinabalu Park (Malaysia)

Soils derived from ultramafic bedrock are known for hosting distinct vegetation types as a consequence of atypical soil chemistries consisting of high trace elements concentrations (Ni, Cr, Co) and exchangeable cation imbalances (high Mg:Ca quotients); the high Mg:Ca ratio causes Ca infertility in plant species not adapted to ultramafic soils. Ecological studies use a range of single-stage extraction methods for chemical characterization of such soils in order to be able to interpret plant response, and ultimately to explain plant community composition. Few studies to date have compared different soil extraction methods in relation to tropical ultramafic soils. This study compares eight commonly used extraction methods on a large number of ultramafic soil samples collected from Kinabalu Park (Malaysia). The tested methods were: for trace elements: NH4Ac, DTPA, CaCl2, Sr(NO3)2 and Mehlich-3, for exchangeable cations: NH4Ac and silverthiorea, and for plant-available phosphorus: Mehlich-3 and Olsen-P. These single-stage extraction methods were compared and evaluated for predictive power for chemically characterizing soils, interrelatedness and ecological application. The methods were also contrasted with a sequential extraction scheme. Finally, several operational parameters including molar ratio (0.01 and 0.1 M CaCl2, Sr(NO3)2) and pH buffering (DTPA-TEA) were also evaluated. The majority of single-stage extraction methods are highly inter-correlated and predictive power could be improved by including independent soil parameters (pH, CEC, pseudo-total element concentration) in the multivariate regression equation. Ecological interpretation remains difficult because of lack of experimental studies in relation to plant uptake response and potential phytotoxicity effects on tropical native plants from ultramafic soils.

Extractability of nutrients using Mehlich 3 and ammonium bicarbonate-DTPA methods for selected grassland soils of China

This study aimed to obtain a simple and efficient soil extraction method as an exhaustive and systematic technology guideline for the determination of potentially available phosphorus (P), potassium (K), magnesium (Mg), iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) in various grassland soils covering different regions. In this study, 25 soil samples from 5 different grassland types of China were collected to measure the amounts of potentially available nutrients and to compare the results of Mehlich 3, the ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) and other four methods which are widely used in China (i.e. Olsen, Bray 1, 1 mol/L NH<sub>4</sub>OAc, CaCl<sub>2</sub>-DTPA, called conventional methods). The results showed that the amounts of potentially available nutrients extracted by different methods were significantly different. Moreover, a positively significant correlation was obtained between the amounts of potentially available nutrients extracted by conventional methods and those extracted by Mehlich 3 and AB-DTPA. However, for Mg and Mn, the results from AB-DTPA appeared to have a stronger relationship with the results from the conventional method than with the results from Mehlich 3. These differences might be caused by the effect of soil pH. Our results suggested that both Mehlich 3 and AB-DTPA can be effectively used to measure nutrients availability in grassland soils, while the AB-DTPA will be more recommended to measure the amounts of potentially available nutrients in alkaline soils.

In situ phosphorus dynamics in soil: long-term ion-exchange resin study

Phosphorus (P) availability to soil biota is commonly determined using soil extraction methods, which can mobilise unclearly specified and stable soil P fractions. Alternatively, natural P availability can be estimated using in situ exposition of ferrous-oxide impregnated resin that continually removes P from soil solution. Over 10 consecutive years, we measured phosphate dynamics using such resin in soils of two catchments, differing in their bedrocks (P-poor mica-schist and P-rich granite), P-sorption characteristics (different Al- and Fe-hydroxide pools) and terrestrial P export to receiving waters. The catchment with granitic bedrock loses P in the long-term, while soils on mica-schist permanently accumulate P from atmospheric deposition. We observed substantially higher soil P availability in the organo-mineral horizons along with higher terrestrial P export in the granitic catchment rather than in the mica-schist one. These results indicate that soils developed on the P-rich bedrock, and concurrently with lower P sorption capacity, have high in situ P availability. We further evaluated the main factors affecting soil P availability, using data on long-term environmental and edaphic variables. Soil P availability was partly controlled by abiotic factors such as throughfall chemistry, precipitation amount and the C-to-P ratio of litter. However, we assume that high losses of P in the granitic catchment can also be driven by microbial processes since decomposition activity was the most influential variable of available soil P in this catchment.

Importance of soil extractable phosphorus distribution for mature Norway spruce nutrition and productivity

Phosphorus is an essential nutrient for forest growth. In this study, we assessed the impact of soil extractable phosphorus using two simple extraction methods on nutrition and productivity of Norway spruce in sixteen mature forest stands on different bedrocks and soils in Bavaria, Southern Germany. Representative trees were sampled for needles, twigs, branches, stem bark, and stem wood. Total phosphorus content in the tree parts and soil phosphorus stock extractable with citric acid and sodium bicarbonate up to a soil depth of 80 cm were determined. We found that easily soil extractable phosphorus is a suitable indicator for estimating phosphorus uptake and stand productivity in Norway spruce. In contrast, organic layer phosphorus showed no significant correlation with aboveground biomass phosphorus contents. In the biomass, the highest phosphorus contents were measured in young needles and twigs, but the highest correlation with soil phosphorus was detected for phosphorus contents in needles and bark. The stock of phosphorus extracted by citric acid down to 40 cm soil depth revealed the best correlation with phosphorus in needles and bark. Therefore, as a supplemental or alternative method to needle analysis, our study suggests the use of phosphorus contents in stem bark to evaluate tree phosphorus nutrition. These results highlight the suitability of the citric acid soil extraction method to characterize plant available phosphorus in Norway spruce ecosystems.

Correlating phosphorus extracted by simple soil extraction methods with foliar phosphorus concentrations of Picea abies (L.) H. Karst. and Fagus sylvatica (L.)

AbstractPhosphorus (P) concentrations in needles and leaves of forest trees are declining in the last years in Europe. For a sustainable forest management the knowledge of site specific P nutrition/availability in forest soils is vital, but we are lacking verified simple methods for the estimation of plant available P. Within this study, four soil P extraction methods [water ( ), double‐lactate (Plac), citric acid (Pcit), and sodium bicarbonate ( )], as well as total P content of the soil (Ptot) were tested to investigate which method is best correlated with foliar P concentrations of spruce [Picea abies (L.) H. Karst.] and beech [Fagus sylvatica (L.)]. Mineral soil samples from 5 depth levels of 48 forest sites of the Bavarian sample set of the second National Forest Soil Inventory (BZE II) were stratified according to tree species (spruce and beech) and soil pH (pH < 6.2 and > 6.2), covering the whole range of P nutrition. The extractable amount of P per mass unit of soil increased in the order << Plac < < Pcit, decreased with soil depth, and was higher in soils with pH < 6.2. Citric acid extracted up to 10% of Ptot in acidic soils. Whereas Pcit delivers adequate regression models for P nutrition in the case of spruce (R2 up to 0.53) and beech (R2 up to 0.58) for acidic soils, shows good results for spruce growing on acidic soils (R2 up to 0.66) and for beech on soils with pH > 6.2 (R2 up to 0.57). Plac produces adequate models only for beech on high pH soils (R2 up to 0.64), while did not produce acceptable regression models. Ptot seems suitable to explain the P nutrition status of beech on acidic (R2 up to 0.62) and alkaline soils (R2 up to 0.61). Highest R2s are obtained mostly in soil depths down to 40 cm. As and Pcit showed good results for both investigated tree species, they should be considered preferentially in future studies.

Identification of a Proper Phytoavailable Arsenic Extraction Method Associated with Arsenic Concentration in Edible Part of three Crops in Soils Near Abandoned Mining Areas

This study aimed to investigate correlations between concentrations of extractable Arsenic (As) with varying chemical solutions (0.1 M <TEX>$Ca(NO_3)_2$</TEX>, 0.1 M <TEX>$(NH_4)2HPO_4$</TEX>, 0.5 M EDTA, Mehlich 3, and 0.5 M <TEX>$NaHCO_3$</TEX>) and those of As in crops, and then to seek the most suitable soil extraction method for predicting the potential of As uptake in crops cultivated in soils contaminated with As. For a mesocosm experiment, pepper (Capsicum annuum L.), soybean (Glycine max L.), and rice (Oryza sativa L.) were cultivated for three months in pots containing soils taken from the arable areas near abandoned mines in Korea. Following the cultivation, soil pH and DOC significantly increased by treatments of lime and lime plus compost, respectively, while insignificant influences in changing total and all extractable As concentrations were found in all soils. Arsenic concentration in edible part of all crops considerably depended on the extractable As concentration in the soils, particularly with Mehlich 3. All extractable As concentrations in the soils of C. annuum and G. max were significantly correlated with As concentration in their edible parts. For O. sativa, the extractable concentrations of Mehlich 3 (<TEX>$R^2$</TEX>: 0.18 at p: 0.006) and EDTA (<TEX>$R^2$</TEX>: 0.11 at p: 0.036) showed only marked relationships with As concentration in the edible part. These results may indicate that the Mehlich 3 and EDTA are soil extractants to determine phytoavailable As in soil that provide better prediction for As transfer from soil to crop.

Sorption of Fluorotelomer Sulfonates, Fluorotelomer Sulfonamido Betaines, and a Fluorotelomer Sulfonamido Amine in National Foam Aqueous Film-Forming Foam to Soil.

During fire-fighter training, equipment testing, and emergency responses with aqueous film-forming foams (AFFFs), milligrams per liter concentrations of anionic, zwitterionic, and cationic per- and polyfluoroalkyl substances (PFASs) enter the environment. Because the behavior of zwitterionic and cationic PFASs in the subsurface is unknown, batch sorption experiments were conducted using National Foam AFFF, which contains anionic fluorotelomer sulfonates (FtSs), zwitterionic fluorotelomer sulfonamido betaines (FtSaBs), and cationic 6:2 fluorotelomer sulfonamido amine (FtSaAm). Sorption of the FtSs, FtSaBs, and 6:2 FtSaAm to six soils with varying organic carbon, effective cation-exchange capacity, and anion-exchange capacity was evaluated to determine sorption mechanisms. Due to the poor recovery of the FtSaBs and 6:2 FtSaAm with published PFAS soil extraction methods, a new soil extraction method was developed to achieve good (90-100%) recoveries. The 6:2 FtSaAm was depleted from the aqueous phase in all but one soil, which is attributed to electrostatic and hydrophobic interactions. Sorption of the FtSs was driven by hydrophobic interactions, while the FtSaBs behave more like cations that strongly associate with the solid phase relative to groundwater. Thus, the sorption mechanisms of the FtSs, FtSaBs, and 6:2 FtSaAm are more complex than expected and cannot be predicted by bulk soil properties.

Vegetation affects pool size and composition of amino acids in Tibetan alpine meadow soils

Soil amino acids are of great importance for nitrogen cycling and plant nutrition, especially in the nitrogen-limited ecosystems. However, the factors that influence amino acid pools in alpine meadow soils remain unclear. The aims of this study were to answer the following questions: (1) Do soil amino acid pools under different vegetation cover show appreciable differences in their concentration and composition during the growing season? (2) Is the pool size of soil amino acids in the alpine meadow smaller or larger than those in other ecosystems? Soils were sampled from three sites dominated by three typical types of plants (Kobresia graminifolia, Polygonum viviparum and Elymus nutans) in a Tibetan alpine meadow, respectively, during the growing season. Soils were extracted with water and 2M KCl solution, respectively, and amino acids were quantitatively determined by high performance liquid chromatography. The results show that the pool size of soil exchangeable amino acids extracted by 2M KCl in this alpine meadow is comparable to those in other N-limited ecosystems. The pool size of soil amino acids across the three sites displayed temporal dynamics during the growing season, with the pool size increased from May to July and decreased in August. The P. viviparum soil had the largest amino acid pool among the three sites in May, whereas the largest pool in July and August was found in the K. graminifolia soil. The composition of the soil amino acid pools across the sites changed over the season, with acidic amino acids being abundant (63.6–84.3%) in spring, and neutral amino acids dominating (53.7–66.0%) in summer. The three sites shared five dominant amino acids (lysine, glutamic acid, leucine, alanine, and serine) through June to August; however, the other dominant amino acids (glycine, valine and threonine) varied among the sites and the months. These results suggest that the concentration and composition of amino acid pools in the Tibetan alpine meadow soils could be significantly influenced by the vegetation cover. Additionally, soil sampling time and extraction methods could also exert pronounced effect on the results. The information obtained in this study may help in understanding the influence of plant-soil feedback on soil amino acid pools, and the mechanisms of organic nitrogen uptake by alpine plants.

Predicting phosphorus availability to spring barley (Hordeum vulgare) in agricultural soils of Scandinavia

In order to utilize the limited phosphorus (P) resources most efficiently, it is crucial to limit over- and under-fertilization in plant production. In this study we evaluated the Diffusive Gradients in Thin films (DGT) technique as a method to determine plant P availability in agricultural soils. DGT measurements were compared to a range of well-established and frequently used soil extraction methods. In order to select P responsive soils for field trials in multiple locations, a spring barley (Hordeum vulgare) pot experiment, with 34 soils from different locations in Denmark, Sweden, Norway and Finland was designed and plants were grown with or without P fertilization. The soils were analyzed for P availability with DGT and three soil extraction methods using the following extractants: sodium-bicarbonate (Olsen-P), ammonium lactate (PAL), and ammonium acetate (PAAC). When the plants were harvested after 6 weeks, it was observed that most plants had responded to P fertilization with increased leaf tissue P concentrations and DM, but with poor or no correlations to the P levels measured in soil extracts or with the DGT technique. This observation highlighted the importance of pot size relative to the produced biomass in order to avoid the development of extensive P depletion zones surrounding the roots, as it prevented extrapolation of results to the field scale. Consequently, based on interviews with farmers, nine soils which in previous seasons responded to P fertilization, were selected in Denmark (7) and Norway (2). On each location spring barley was cultivated either with or without P fertilization, and soil analyses were regularly compared with the composition of essential plant nutrients in leaf tissue and with the final grain yields. In the field experiments, 30days after establishment (DAE), all four methods could predict P concentrations in the youngest fully emerged leaf (YFEL) of unfertilized plants. Using a Mitscherlich equation on these data, coefficients of determination (R2) ranged from 0.46 to 0.83. The Olsen-P method performed poorest while the DGT method showed the best correlation. However, three weeks later (56 DAE) the soil tests failed to reflect plant available P, as the correlation with leaf P concentrations had disappeared. At harvest, only plants with a leaf P concentration below 2000μgPg−1DM during early vegetative growth (30 DAE) responded to P fertilization by increasing the grain yield. In summary, these observations suggested that a number of significant external factors, which cannot be reflected by DGT or any soil extraction methodology, inherently limit the validity of soils test in predicting the plant availability of P. This includes the inability of soil test to measure P availability in deeper soil layers and physiochemical parameters limiting P diffusion and uptake such as low soil moisture and temperature.

Short-term soil mineral and organic nitrogen fluxes during moderate and severe drying–rewetting events

Nitrogen (N) availability to plants in dry soil is limited by diffusive flux of N compounds through the soil solution towards the root surface. Conventional soil extraction procedures only provide information about bulk soil N concentrations, which can be distorted during soil sampling, transport, storage and extraction, and hence are of limited use to detect short-term N dynamics. Soil microdialysis is a new tool to monitor diffusive flux of mineral and organic N compounds in situ in high temporal and spatial resolution with minimal disturbance, and is therefore well-suited to determine dynamic fractions of plant-available N in soil microsites.We investigated N availability and mobilization during a drying–rewetting event in a temperate beech forest using soil microdialysis and soil extractions with water. While water extracts mainly revealed mineral N in the form of NH4+ and NO3−, diffusive N fluxes in situ were dominated by amino acids. Microdialysis showed that rewetting of dry soil led to a fast but short-lived mobilization of NO3− and some neutral hydrophilic amino acids (lysine, glutamine, cysteine, glycine), which was not detected in water extracts, and the rewetting N flush was larger with increasing drought duration. Our results suggest that at our temperate forest site plant-available N was dominated by amino acids, a fraction of N that might be missed using conventional soil extraction methods. Considering expected increases in the frequency of extreme climatic events, the observed release of mobile N forms bears the potential of N loss from soil if severe drought is followed by a heavy rain event.

폐금속광산 지역 농작물섭취경로의 인체위해도 산정을 위한 생물농축계수와 토양분석방법에 관한 연구

폐금속광산 지역 농작물섭취경로의 인체위해도 산정을 위한 생물농축계수와 토양분석방법에 관한 연구

EDAPHOLOG monitoring system: automatic, real‐time detection of soil microarthropods

Summary Soil microarthropods as organic matter decomposers play an important role in soil functioning thus providing ecosystem services. However, ecosystem scale investigations on their abundance and dynamics are scarce because their high spatio‐temporal heterogeneity requires huge sample size. Processing and identifying large number of individuals are extremely labour‐intensive. We prototyped a device called EDAPHOLOG monitoring system that consists of (1) a probe that catches and detects microarthropods and estimates their body size; (2) a data logger transmitting data to a central data base; and (3) a Java application for retrieving data. We tested the device in three ways. First, we tested the precision and accuracy of detection and body size estimation of the device in the laboratory using microarthropods of five morphotypes: euedaphic Collembola, haired Collembola, scaled Collembola, Acari and Oribatida. Secondly, we compared the number of individuals collected by EDAPHOLOG traps, pitfall traps and soil extraction method in an alfalfa field. Thirdly, we deployed a total of 100 EDAPHOLOG probes in nine different habitats for over 3 months to demonstrate the applicability of the monitoring system. In the laboratory, EDAPHOLOG detected 95·6% of individuals; even the smallest morphotype (Oribatida, body size (mean ± SE): 0·58 ± 0·04 mm) was detected in 87·5% of cases. For body length estimation, we established a quadratic relationship between the estimated and measured body lengths; however, the R2 of the quadratic model was only 0·32. By comparing the three different sampling methods (EDAPHOLOG, pitfall traps and soil extraction), we concluded that EDAPHOLOG traps better select for soil microarthropods compared to classical pitfall traps, since the latter ones caught also many other arthropod species. Furthermore, the EDAPHOLOG traps caught more epigeic microarthropods and almost the same number of soil‐dwelling euedaphic microarthropods as the numbers collected by soil extraction. During the 3‐month‐long field test, the total numbers of detected and captured individuals agreed very well, although the device tended to overestimate the number probably due to counting also some soil particles falling into the probe. This trend was the same regardless of the total number caught. Surface‐dwelling epigeic and litter‐dwelling hemiedaphic microarthropods dominated the samples although soil‐dwelling euedaphic microarthropods were also caught. EDAPHOLOG is a novel device that consumes little power, rugged enough to operate in the field for extended periods of time, and can be remotely controlled. It detects surface‐ and soil‐dwelling microarthropods real‐time, and with high accuracy; however, it is less accurate to estimate body size. The system is especially suitable in field research focusing on temporal activity of microarthropods. Because it is non‐invasive, studies requiring long‐term monitoring, such as soil remediation or ecosystem restoration projects, will also find EDAPHOLOG useful.

Modified method for theextraction of mRNA from paddy soils.

Paddy soils contain relatively greater organic matter and water contents than other soils thereby limiting effective mRNA extraction. A modification of the conventional mRNA soil extraction method specific to paddy soils is described. Two main modifications for co-extraction of DNA and RNA are: (1) addition of 20% (w/v) sodium dodecyl sulphate to 10% (w/v) hexadecyltrimethylammonium bromide extraction buffer, and (2) fresh soil, initially frozen at -80°C, is immediately immersed in extraction buffer. The high-quality total RNA extracted can be directly used in downstream analyses without an additional step to remove humic acid. RNA purification was conducted to remove 5S rRNA, and the mRNA was enriched by selectively digesting rRNA. cDNA synthesised by reverse transcriptase was not contaminated by the reagents or genomic DNA. The modified method for mRNA extraction from paddy soil is suitable for analysing the expression of microbial genes from fresh paddy soil.

A two-stage extraction procedure for insensitive munition (IM) explosive compounds in soils

The Department of Defense (DoD) is developing a new category of insensitive munitions (IMs) that are more resistant to detonation or promulgation from external stimuli than traditional munition formulations. The new explosive constituent compounds are 2,4-dinitroanisole (DNAN), nitroguanidine (NQ), and nitrotriazolone (NTO). The production and use of IM formulations may result in interaction of IM component compounds with soil. The chemical properties of these IM compounds present unique challenges for extraction from environmental matrices such as soil. A two-stage extraction procedure was developed and tested using several soil types amended with known concentrations of IM compounds. This procedure incorporates both an acidified phase and an organic phase to account for the chemical properties of the IM compounds. The method detection limits (MDLs) for all IM compounds in all soil types were <5 mg/kg and met non-regulatory risk-based Regional Screening Level (RSL) criteria for soil proposed by the U.S. Army Public Health Center. At defined environmentally relevant concentrations, the average recovery of each IM compound in each soil type was consistent and greater than 85%. The two-stage extraction method decreased the influence of soil composition on IM compound recovery. UV analysis of NTO established an isosbestic point based on varied pH at a detection wavelength of 341 nm. The two-stage soil extraction method is equally effective for traditional munition compounds, a potentially important point when examining soils exposed to both traditional and insensitive munitions.