Subsoil Samples Research Articles

English

The spatial variability structure of soil attributes in a certain area might influence the semivariogram fitting model and, consequently, the attribute behavior mapping in this area leading to different decisions regarding crop management. This study aimed to identify, characterize and quantify the spatial variability of chemical attributes and the clay content in the superficial layer of a Gleysoils mapping unit (MU) at reconnaissance scale in the coastal plain of Rio Grande do Sul, through descriptive statistics and geostatistics and compare the results taking into consideration the existence of three Gleysoils mapping units at semi-detailed scale through the scaled semivariogram technique. A 403 ha area located in the Rio Grande do Sul Coastal Plain, in the city of Jaguarao was sub-divided into three mapping units (GL-mo, GL-mo.lv and GL-lv), a sampling grid with 403 points, 100 m far one from another was established. In a 5 m radius around each sampling point, 10 sub-samples of disturbed soil were collected from the 0-0.20 m layer, making up a soil compound sample, and the following attributes were determined for each sample: pH in water, organic carbon, phosphorus, potassium, sodium, calcium, magnesium, aluminum, potential acidity and clay content. The cation Exchange capacity (pH=7.0) and base saturation were also calculated. The identification, characterization and quantification of the spatial variability of attributes from the soil Ap horizons were carried out through descriptive statistics and geostatistics, considering the mapping unit at the reconnaissance scale and the three units at the semi-detailed scale. In the geostatistics analysis, the scaled semivariogram technique was employed aiming to compare the spatial variability structure for each soil attribute in the total area and in the three MUs at the semi-detailed scale. Regarding the descriptive statistics, the Ap horizon attributes behavior in GL-lv was similar to that in the total area of the soil layer under analysis; however, when considering the spatial coordinates, the spatial variability structure of the GL-mo.lv attributes was the one that best described the attributes variability in the total area. The scaled semivariogram technique revealed that the spatial behavior of the attributes pH and exchangeable sodium was similar, regardless of the evaluation scale adopted or the factor used for the scaled semivariogram.

Uso de percepción remota y SIG en la selección de sitios de muestreo de suelos para la Región de Magallanes

The agricultural farms in Magallanes Region comprise vast areas, which makes complex the quantification of vegetal communities in all paddocks, and the planning of soil sampling based on these communities, due to the time and cost involved. This study proposes a method to determine homogenous zones for soil sampling, according to Geographic Information Systems and remote sensing techniques, based on open source data and software. The specific aim is determining the number of sub-samples to generate a soil composite sample. The results obtained showed a classification of vegetation with an 85.6% of global reliability from Landsat 8 data and identified the plane lands (50.3% of farm total area) using Models of Digital Elevation of ASTER GDEM. The overall information allowed to generate 237.9 hectares defined like homogenous areas for different vegetal communities. Once the homogenous areas are determined, the sampling should be selected according to the community that will be assessed, and to the site that is intended to be studied or intervened. Subsequently, the estimation of the number of soil sub-samples is determined according to the area to sample and its homogeneity features. This procedure would help reduce mistakes in soil sampling.

Soils Characteristics of Forest Phytocoenoses Occupied by Self-Regenerating Populations of Quercus Rubra in Silesian Upland / Właściwości Fizykochemiczne Gleb Na Stanowiskach Z Odnowieniem Dębu Czerwonego Na Wyżynie Śląskiej

Abstract Northern Red Oak is a tree species native to North America. In Polish flora it has status of invasive plants. In the years 2008-2011 autoecological studies were conducted aiming at examination on what type of soils the species tends to regenerate ie appearance of seedlings in the vicinity of maternal trees. In total 250 phytosociological relevés and 100 soil samples (400 soil subsamples) were collected. It was observed that majority stands (almost 80%) of Northern Red Oak occupy sites very strongly acid and strongly acid. In reference to pH in KCl results are a little different, however, sites with soil very strongly acid (pH = 4.1-5.0) and stronly acid (pH < 4.1) also predominate. The investigated soils were typified by very low values of magnesium (< 10 mg/1000 g), phosphorus (< 3 mg/100 g) and potassium (< 7 mg/100 g). Total nitrogen in studied sites dominated in two the lowest classes (> 0.25%). The sites of Q. rubra are rich in organic carbon. Almost 50% of all sites covers two highest classes of concentration of this element ie 4.0-8.0% and > 8.0%. Soils where seedlings of Northern Red Oak were encountered, were characterized by humus medium for mezotrophic and eutrophic broad-leaved forests and mixed coniferous forests - more than 60% had ratio of carbon and nitrogen CN > 25. In several sites this ratio reached 50. The lower values in case of content of calcium and loss on ignition dominate. The studies showed that soils on which species grows and also spontaneously regenerates are typical for coniferous and mixed coniferous forests, however, in natural range Q. rubra is component of deciduous forests. It could be associated with the fact of more frequent introduction of Northern Red Oak into poorer sites than the consequence of its habitat requirements.

Study of subsoil in former petrol stations in SE of Spain: Physicochemical characterization and hydrocarbon contamination assessment

Former petrol stations are potential zones with hydrocarbon contaminated soil due to either underground storage tanks leakage or spills from fuel dispensing activities. Volatile Organic Compounds (VOCs) in gasoline, like benzene and semi-volatile organics in diesel, are carcinogenic and very toxic substances which can involve a serious risk for ecosystem and human health. For that reason, three former petrol stations (SE Spain) were selected to be studied by electrical resistivity (ERT). Then, electrical anomalies potentially originated by diesel/gasoline pollution assisted in collecting subsurface samples which were analyzed in order to establish the contamination degree of those areas. To properly undertake that task a special sampling was designed. This special sampling relied on subsurface samples carefully preserved at field through using a KCl solution to minimize any volatilization loss. Headspace and gas chromatography–mass spectrometry (GC–MS) was the most suitable and reliable technique to quantify the VOCs content in subsurface. Since the amount of VOCs into subsoil samples are near the detection limits, it was compulsory to measure the content of VOCs in situ by using a portable photoionization detector (PID). A gas chromatography with flame ionization detector (GC–FID) was used to provide the Total Petroleum Hydrocarbon (TPH) value after a solid/fluid pressurized extraction was accomplished. Through establishing subsoil moisture, clay content or/and pH value relationships to hydrocarbon content in subsurface samples a more suitably physicochemical characterization of subsoil was obtained.Results show that VOCs concentrations in subsoil samples from the studied petrol stations are around μg/kg levels. Total Petroleum Hydrocarbon values range between 17mg/kg soil and 5000mg/kg wet soil (mg/kg levels) suggests that diesel and gasoline leaks from Underground Storage Tanks (UST) have been released. In fact, the TPH maximum value was found at a depth of 6m, a zone located between two close USTs, which were found at 4m deep. On the basis of our results we can confirm that organic compounds transference took place in the studied areas and where this transference had a vertical movement component. Minimum subsoil moisture content values were related to maximum TPH values since the vapor phase and the subsurface hydrocarbon retention process increase when subsurface moisture levels decrease. Adsorption of hydrocarbons on the subsoil tended to be pH and clay content dependent. Thus, the adsorption process took place at a maximum rate when pH values reached the minimum value. It is important to highlight that at maximum adsorption rate protonation phenomena are promoted. Also, minimum subsurface clay content speeds up infiltration processes of organic compound to deeper layers. As a consequence, to avoid subsurface and groundwater being polluted from petrol station activities is needed a suitable and appropriate subsoil physicochemical characterization. Thus, a subsurface physicochemical characterization will support in properly designing and planning appropriate remediation works accounting for that subsurface hydrocarbon concentration.

Effect of hydrothermally carbonized char application on trace gas emissions from two sandy soil horizons.

The application of biochar to soil is a potential tool for the long-term sequestration of C and a possible mitigation of greenhouse gas (GHG) emissions. Among the various processes available to produce biochar, hydrothermal carbonization is one technique that is suitable for moist feedstock like digestates from biogas production. The aim of this study was to investigate the stability of C and emissions of NO after the addition of (i) digested wheat ( L.) straw (digestate) and (ii) hydrothermally carbonized (HTC) char of wheat straw as well as (iii) HTC char of digested wheat straw to two soil horizons that differed in C content. The HTC chars were obtained from wheat straw and digested wheat straw that were hydrothermally carbonized at 230°C for 6 h. The digestate and HTC chars were mixed with soil and incubated in 125-mL vessels. The GHG emissions of CO and NO were measured at regular intervals. Additionally, after 108 d, N was applied in the form of NHNO equivalent to 100 kg N ha. After 500 d of incubation, the digestate had lost 34% of C, while the soil mixture with the corresponding HTC char lost 12% of C in the form of CO from the topsoil. The estimated bi-exponential half-life of the recalcitrant C was more than 50% longer for the carbonized material than for the untreated digestate. The NO emissions from both HTC chars were significantly reduced compared with untreated digestate. The reductions were up to 64% for the topsoil and 60% for the subsoil samples. These laboratory results show that HTC holds the potential to increase the C stability of fermented and carbonized biomasses and to reduce NO emissions.

Soil P fractions in a volcanic soil chronosequence of Central Mexico and their relationship to foliar P in pine trees

AbstractPhosphorus (P) is a major plant nutrient, however, its availability in volcanic ash soils is presumed to be small, due to its specific sorption on short‐range order minerals. We analyzed distinct P fractions in volcanic ash soils of different age (60 to > 100,000 y BP) under pine forests in Central Mexico to investigate their changes along a chronosequence of Regosols, Andosols, and Lixisols, and to evaluate if P availability limits tree growth at any particular stage. Top soil and subsoil samples were first analyzed by the Tiessen and Moir method, which failed to extract exhaustively “organic” and “occluded P”, and “P associated with apatite”. Therefore, we modified the fractionation scheme by including a “recalcitrant organic P” fraction obtained from the difference between P determined in air‐dried subsamples and subsamples burned at 300°C; P adsorbed to short‐range order minerals was assessed in an extraction with NH4‐oxalate, and P in primary minerals by subtracting the sum of all other fractions from total P contents determined by XRF. This we did after discovering that primary P occurred in the form of fluorapatite included in plagioclase, volcanic glass or olivine. We also measured P contents in pine needles and related these with the “mobile soil P” fractions. The results show that “organic P” reaches maximum contents in 10,000‐y old soil, as does P associated with short‐range order minerals, while P occluded into crystalline oxides increases constantly over time. After 100,000 y, 31% of total P still remains in the form of primary P in A horizons. “Mobile P” was constant > 40 mg kg−1 in Regosols and Andosols and related positively with foliar P contents, which were within adequate nutritional ranges. Only in Lixisols small “mobile P” concentrations in soil correspond with inadequate P contents in pine needles.

Influence of Soil Properties on Amounts of Bicarbonate-Extractable P in Soils Incubated With Three Thai Phosphate Rocks of Contrasting Mineralogies

Top- and sub-soil (0–15; 15–100 cm) samples were collected from nine acid soil series of Ultisols and Oxisols from high rainfall areas, Southeast Coastal region of Thailand. Most of them had low soil pH in water (pH Rat-PR > Kan-PR > Roi-PR. Increases in bicarbonate-extractable P (ΔPBC) in soil incubated with PR and MCP were highest at 14 days. Stepwise regression indicated that there was no single soil property that adequately predicted the increases in extractable P (ΔPBC) because of addition of PR and MCP. Soil properties that were most closely and positively related to ΔPBC were the ability of soils to provide hydrogen ions for PR dissolution and the initial amount of available P in the soils.

Paddy soil heavy metal contamination and uptake in rice plants from the adjacent area of Barapukuria coal mine, northwest Bangladesh

This study was carried out to estimate the heavy metal contamination in paddy soil and subsoil and uptake by rice plants collected from Barapukuria coal mine area of Bangladesh. The mean contents of As, Cr, Cu, Mn, Ni, Pb, and Zn in paddy soil and subsoil exceed the world averages, and the observed soils are moderately to extremely polluted with inputs from mining activities. Correlation and regression model analyses suggest that pH and TOC have distinct effect on the availability of observed metals in soils. Sequential extraction of paddy soil and subsoil samples demonstrate that the mobility of heavy metals increases in the order of Cu > Zn > Pb > Fe > Cr > Ni > Mn > As. The uptake of metals in rice root is much higher than those in straw and rice grains. Arsenic, Cr, and Pb uptake in rice grains are 6.87-, 1.58-, and 5.26-fold higher than the maximum permissible concentration which shows a tendency of transformation of these elements from contaminated soil to rice plants.

The effect of temperature‐induced soil water repellency on transient capillary pressure–water content relations during capillary rise

SummaryLong‐term capillary rise experiments (0 to about 89 000 hour) were performed at 19°C on homogenized and heat‐treated podsolic forest top‐ and subsoil samples. These were packed into columns, the bases of which were then partially immersed, at constant depth, in water reservoirs to simulate a constant water table. Selected columns were equipped with tensiometer and TDR probes. Other columns were removed at prescribed times and divided into 2‐cm horizontal segments whose volumetric water contents were determined. The degree of saturation was then estimated by comparison with the capillary rise in duplicate arrangements of samples immersed in ethanol. It was found that the heat treatments conferred increased water repellency (WR) on the soil, which increased with temperature (significantly so at greater than 60°C). This had a profound effect on the capillary rise characteristics and development of water content in the soil behind the wetting front, indicating an effective, albeit slow, reduction in effective WR. This has implications for hydraulic modelling of soils with significant WR and demonstrates that sub‐surface WR exerts a significant influence on capillary rise from a water table and suggests that commonly used indicators of surface WR using droplet tests may not be useful for such modelling purposes.

Using OSL to assess hypotheses related to the impacts of land use change with the early nineteenth century arrival of Europeans in south‐eastern Australia: an exploratory case study from Grabben Gullen Creek, New South Wales

ABSTRACTA common explanation for intense soil erosion and gullying in SE Australia is the introduction by Europeans of new land use practices following their arrival in Australia in the late 18th century. Eucalyptus woodlands were cleared to introduce farming, and valley bottoms, characterized by chains of ponds with organic‐rich swampy meadow (SM) soils, were subsequently buried by thick deposits of ‘post‐settlement alluvium’ (PSA) generated by erosion in the catchment. In this study, optically stimulated luminescence (OSL) is used to evaluate the source(s) of the PSA in Grabben Gullen Creek (GGC), Australia. We use a portable OSL reader to measure total photon counts on bulk polymineral and polygrain‐size samples from nine profiles along the Creek. We use these luminescence signals as geotracers of sediment source(s) and transport pathways. We obtained higher luminescence signals in the PSA than in the SM sediments, suggesting different sources and fluvial transport conditions for these two widespread sedimentary units. Portable OSL reader data from soils in the GGC catchment that are potential sources for the SM sediments and PSA show that the high luminescence signals recorded in the PSA are similar to those from subsoil samples in granite soils, suggesting that the PSA was derived by gullying of granite subsoils. In the SM sediments, luminescence signals decrease upwards from the base of the profile, as expected in well‐reset fluvial deposits, but with one or more changes in gradient in the profile of photon counts with depth, most likely indicating changes in sediment deposition rates. To calculate deposition rates in the SM sediments, several samples were dated using OSL. The OSL ages produced low scatter in the equivalent doses, confirming the well‐reset nature of the grains composing the SM and indicating a process of sediment transport in dilute flows, as is interpreted from the portable OSL signals. Copyright © 2014 John Wiley & Sons, Ltd.

Traffic-induced soil compaction during manure spreading in spring in South-East Norway

The objective of this study was to evaluate long-term effects of two tillage regimes (ploughing and minimum tillage) on the bearing capacity of a clay rich soil, by using two different slurry tankers (4.1 and 6.6 Mg wheel load) and contrasting wheeling frequencies (1 and 10 passes). The soil strength was assessed by laboratory measurements of the precompression stress (Pc) at −6 kPa in topsoil (20 cm) and subsoil (40 and 60 cm) samples. Stress propagation, elastic and plastic deformation during wheeling were measured in the field with combined stress-state-transducer and displacement transducer system. Results presented in this study show that minimum tilled soil had 74% higher Pc than ploughed soil in the upper soil layer, whilst differences were less distinct in subsoil. Wheeling increased Pc at all soil depths. Compared to ploughing, higher strength in the upper layer of minimum tilled soil led on average to 60% and 48% reductions in the major principal stress with the use of the light and heavy slurry tanker, respectively. The extent of the major principal stress was dependent on the ground pressure in the topsoil. The first pass of a wheel caused the greatest damage in some cases, but all wheelings led to accumulative plastic deformation in both vertical and horizontal directions. Wheeling with high intensity would have exceeded Pc in all cases when soil was at a matric potential of −6 kPa. The results show that soil water content is an important factor influencing bearing capacity. Drier soil (−100 kPa), in combination with minimum tillage, limited the occurrence of stresses exceeding Pc in the upper soil layer.

Rapid estimation of soil engineering properties using diffuse reflectance near infrared spectroscopy

Materials testing involve complex reference methods and several soil tests have been used for indexing material functional attributes for civil engineering applications. However, conventional laboratory methods are expensive, slow and often imprecise. The potential of soil diffuse reflectance near infrared (NIR) spectroscopy for the rapid estimation of selected key engineering soil properties was investigated. Two samples sets representing different soils from across the Lake Victoria basin of Kenya were used for the study: A model calibration set (n = 136) was obtained using a conditioned Latin hypercube sampling, and a validation set (n = 120) using a spatially stratified random sampling strategy. Spectral measurements were obtained for air-dried (<2 mm) soil sub-samples using a Fourier-transform diffuse reflectance near infrared (NIR) spectrometer. Soil laboratory reference data were also obtained for liquid limit (LL), plastic limit (PL), plasticity index (PI), linear shrinkage (LS), coefficient of linear extensibility (COLE), volumetric shrinkage (VS), clay activity number (Ac), total clay content, air-dried moisture content, and cation exchange capacity (CEC). Soil reference data were calibrated to smoothed first derivative NIR spectra using partial least squares (PLS) regression. At the calibration stage, coefficient of determination for full cross-validation (R2) of ≥0.70 was obtained for CEC, mc, LL, PI, LS, COLE and VS. Further independent validation gave R2 ≥ 0.70 and RPD (ratio of reference data SD and root mean square error of prediction) 1.7–2.2 for LL, PI, mc and CEC. The results suggested that NIR–PLS has potential for the rapid estimation of several key soil engineering properties. Further work should focus on extending calibration libraries using more diverse soil types and testing alternative infrared diffuse reflectance based methods.

Effect of application rate of a nitrification inhibitor, dicyandiamide (DCD), on nitrification rate, and ammonia-oxidizing bacteria and archaea growth in a grazed pasture soil: An incubation study

Dicyandiamide (DCD) has been used commercially in New Zealand to reduce nitrate leaching and N2O emissions in grazed pastures. However, there is a lack of information in the literature on the optimum rate of DCD to achieve the environmental benefits while at the same time reducing the cost of the technology. The objective of this study was to determine the effect of DCD application rate on its effectiveness to inhibit ammonia oxidizer growth and nitrification rate in a grazed pasture soil. The soil was a Templeton silt loam (Immature Pallic Soil; Udic Haplustepts) collected from Lincoln University Research Dairy Farm with a mixed pasture consisting of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) and was incubated alone (control) or with cow urine at 700 kg N/ha with 6 rates of DCD [0, 2.5, 5, 7.5, 10 (applied twice), 15 and 20 kg/ha] in incubation vessels. The incubation vessels were placed randomly in an incubator with a constant temperature of 12 °C. During 112 days of incubation, soil subsamples were taken at different time intervals to measure the concentrations of NO3 −-N and NH4 +-N and the amoA gene copy numbers of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). DCD applied at all the different rates inhibited nitrification in urine-treated soils, but the effectiveness increased with DCD application rate. In addition, AOB growth and the amounts of nitrate-N in the soil were significantly related to the application rate of DCD. However, AOA population abundance showed no relationship to the application rate of DCD. The DCD rate at which the AOB growth rate and nitrate-N concentration were halved (effective dosage that causes 50 % reduction in nitrification rate, or ED50) was about 10 kg DCD/ha. These results suggest that DCD applied at relatively low rates still slowed down the nitrification rate, and the current recommended rate of 10 kg DCD/ha for DCD use in New Zealand grazed pastures would result in a 50 % reduction in nitrification rate in this soil. The actual rate of DCD application used would depend on the cost of the product and the environmental and agronomic benefits that would result from its use.

Investigating landfill contamination by visualizing geophysical data.

Geophysical experts aimed to establish a method to identify contamination by landfill leakage without chemically analyzing subsoil samples, which is time-consuming and expensive. To that end, researchers developed a software package that let the experts create 3D visualizations of geophysical data acquired around the landfill and apply statistical analysis to detect anomalous values. The data used, electrical resistivity, are typically sparse. So, the application employs kriging to interpolate the data and provide a volumetric representation of the subsoil resistivity. To avoid invalid conclusions, the visualization also represents uncertainty. The application enabled the experts to better understand the phenomenon and to develop and validate their method. Their evaluation of the application indicated that it helped them throughout the method's development and significantly eased their workload.

Metals and metalloids in primary gold mining districts of Western Bolivia: anthropogenic and natural sources

Topsoil and subsoil samples located adjacent and distant from the mining operations sites were collected. Most total metals showed no significant differences between topsoil and subsoil or proximity, suggesting that they derive from endogenous parent material. There was an increment in Hg in topsoils adjacent to the mining operation sites, indicating a deposition of Hg from the amalgamation areas. Higher values of total, extractable and soluble As were observed adjacent to the mining operation sites, probably related to the presence of residues, rich in arsenopyrite. Organic matter and clay contents control the concentrations of EDTA-extractable Cd and Zn, while soil acidity was associated with the behaviour of As, Hg and Cu. In contrast the concentration of EDTA-extractable Pb was directly affected by its total concentration. In general, soluble metals were highly independent, without significant correlations with any soil physical and chemical properties.

First Report of the Root-Knot Nematode Meloidogyne arenaria Infecting Noni in China.

Noni (Morinda citrifolia) is an important medicinal plant and its fruit and root are of high value. In recent years, noni has been cultivated widely on Hainan Island, China. A survey of eight commercial noni fields in four counties found that most fields had plants with symptoms consistent with damage caused by root-knot nematodes. Above-ground symptoms included reduced vigor, plant stunting, and chlorosis. Affected roots were galled, swollen, cracked, and rotten. Fruit loss associated with diseased plants was quantified as 85%. In each field, three samples were taken consisting of 15 cm wide × 20 cm deep soil (containing roots). The nematode population was extracted and quantified according to Barker (1). Nematodes were found in all soil and root samples with population densities ranging from 450 to 835 eggs and second-stage juveniles (J2s) per 200 g subsample of soil, and 685 to 985 eggs and J2s per 10 g sub-sample of fresh roots. Three single egg masses were respectively hand-picked from one sample of diseased noni roots and inoculated onto tomato plants grown with sterilized soil at 20 to 28°C in the greenhouse. After 8 weeks, nematodes were extracted from the roots of tomato plants and identified by morphology, enzyme analysis, and molecular characterization. Morphology of the female perineal patterns showed a low dorsal arch with large lateral lines separating the striae of the dorsal and ventral sectors, leading to the tail terminus; and wavy, coarse striae with forking at lateral lines and short irregular striae near the lateral lines. Enzyme analysis of the esterase phenotype was also typical of the A1 phenotype in M. arenaria. Based on the perineal pattern and esterase phenotype, the Meloidogyne species was identified as M. arenaria (Est A1) (3). Total genomic DNA was extracted from ca. 10 μl of packed second-stage juveniles (J2s) using the method of Cenis (2). The primers C2F3 (5'-GGTCAATGTTCAGAAATTTGTGG-3') and 1108 (5'-TACCTTTGACCAATCACGCT-3') (4) was used to amplify the intergenic region between COII and LrRNA genes of the mtDNA and an amplification product (1,700 bp) was obtained, similar to M. hispanica, M. incognita, and M. javanica. Root-knot nematodes (Meloidogyne spp.) have been reported to be cause disease on noni in Hawaii. However, to our knowledge, this is the first report of M. arenaria (Est A1) infecting noni in China.

Seasonal Characteristics of Subsoil Salinity of Coastal Parks in Shanghai

Vegetation in coastal parks is more sensitive and fragile to subsoil salinity. 600 subsoil samples in a newly-developed coastal park and 1800 subsoil samples in three old non-coastal parks in Shanghai, China were collected. The subsoil salinity of coastal park is 4.83 times higher than that of non-coastal parks. The average subsoil salinities in Spring and Winter are higher than that in Summer and Autumn. Collaborative vertical trend of subsoil salinity for four seasons is significant (p&lt;0.05). Therefore, the ditches should be adjusted for salt elimination according to location of highly saline plaques, and seepage interception projects should be set up between green-space and unimproved land and the vegetation should be watered more frequently in Spring than that in other seasons.

Fractionation of U, Th, Ra and Pb from boreal forest soils by sequential extractions

To determine the mobility of natural radionuclides in boreal forest soil, a five-step sequential extraction procedure was carried out on soil samples taken from various depths down to 3m on Olkiluoto Island, Finland, where there are plans to construct a spent nuclear fuel disposal repository in the bedrock. The extracted fractions studied were exchangeable, acid-soluble, reducible, oxidizable and tightly bound. It was found that the extractability of most of the radionuclides studied was dependent on the sample grain size and depth. All the elements were concentrated in the smallest grain size samples (<0.063mm). The extraction behaviour of Th, however, did not vary with sample depth, and only about 10% of the Th was extracted by the time of the final extraction step. Stable Pb and 210Pb, as well as Ba and Ra concentrations were strongly correlated in the extractions. Radium and Ba were leached more readily than the other elements; approximately 17% of the total Ra was found in the first fraction extracted, representing exchangeable ions. Uranium was more mobile in the topsoil horizons than in the lower horizons. In the topsoil samples, an average of 51% of the extractable U was leached in the second extraction step, representing the elements soluble in weak acids, whereas only 13% of the U in the subsoil samples was extracted in this step. This is probably due to changes in soil redox conditions lower down the soil profile. The extraction behaviour of Pb and Fe also suggests the presence of more reducing conditions in the deeper soil horizons, because the percentage of extractable Pb and Fe in the oxidizable fraction increased with sample depth.

Using Vis-NIR Spectroscopy for Monitoring Temporal Changes in Soil Organic Carbon

Monitoring the spatial and temporal changes in soil organic carbon (SOC) brought about by climate change and agricultural practices is challenging because existing SOC monitoring methods are very time and resource consuming. This study examined the use of visible near-infrared spectroscopy (Vis-NIR) as a speedy method to predict SOC and to monitor spatial and temporal changes in SOC compared with labor-intensive traditional laboratory (TL) measurements. For SOC prediction, topsoil (0–25 cm) and subsoil (25–50 cm) samples in the Danish soil spectral library for the years 1986 and 2009 were used. Empirical Bayesian Kriging was used to map SOC. The Vis-NIR predictions indicated that average topsoil and subsoil SOC had decreased slightly in Denmark from 1986 to 2009, and this was confirmed by TL measurements of SOC. In East Denmark, Vis-NIR predictions differed significantly from the measured SOC values. For subsoil samples, the ability of Vis-NIR to predict SOC levels varied. In West Jutland, Central Jutland, North Jutland, and Thy, Vis-NIR–predicted SOC levels did not differ from TL-measured levels, showing good predictive ability. For topsoil samples, the spatial pattern of change in TL-measured and predicted SOC was consistent during the 23-year study period, but there were significant discrepancies in the corresponding SOC change patterns for subsoil samples. To conclude, Vis-NIR is a promising method for monitoring spatial and temporal changes in SOC at the national scale, especially in the topsoil. Some difficulties can arise in low SOC subsoils, so more systematic work is needed to improve the method for practical applications.

Geochemical assessment of agricultural soil: A case study in Songnen-Plain (Northeastern China)

Agricultural soil pollution is a serious problem that can endanger ecology, food safety, and human health. The study evaluated the accumulation and distribution of major and trace elements in the agricultural soil of the Gannan area in the northwest Songnen-Plain, a very important base of grain production in northeastern China. To identify the concentrations and sources of pollutants and also to assess the soil environmental quality, a total of 2400 topsoil (0–20 cm) samples and 10 subsoil (180–200 cm) samples were collected. Then 6 major elements (CaO, Fe2O3, K2O, MgO, Na2O, SiO2), 18 trace elements (As, B, Cd, Co, Cr, Cu, F, Hg, I, Mo, Mn, N, Ni, P, Pb, Se, S, and Zn), pH, and Corg (organic carbon) were analyzed. The accumulation of Cd, Cu, Pb, Zn, Hg, and F was apparent in the agricultural soils. Correlation coefficient analysis showed that most major and trace elements, as well as pH and Corg, were significantly positive correlated in agricultural soil. Principal component analysis (PCA) indicated two main anthropogenic sources for trace elements in agricultural topsoil. The first component including B, Cr, Cu, Mg, Ni, and Zn, represented a mixture of atmospheric deposition and livestock manures; whereas the second component, relating to Ca, F, Cd, Hg, Se, and P, suggested the inorganic fertilizers and lime, as well as agrochemicals. Spatial distribution patterns using GIS contour maps and an integrated soil pollution index were established for the selected metal concentrations. In general, the range of RI (the potential ecological risk index) was from 43.6 to 556, with a mean value of 106, indicating low ecological risk in this study area. This study indicated that more attention should be paid to metal pollution of agricultural soil in the rural area to safeguard both soil and food safety.