Cm Of Soil Surface Research Articles

Role of coffee plantation in reducing erosion under coarse textured soil in wet tropical region

Water erosion is one phenomenon causing land degradation in a wet area. The research was aimed to evaluate the total of soil erosion under coffee plantations having coarse textured soil in wet tropical regions. This research was taken out on a coffee plantation in Sibarasok, Maninjau having rather to very steep slope and high annual rainfall, with Inceptisol soil order. Soil samples were taken from 6 land units (Coffee-86 y having 0-8%, 25-45%, and >45%, Coffee 5 y-15-25%, Coffee 8 y-25-45%, and forest >45% as control). The samples of soil were prepared and analyzed in the Laboratory of Soil, Department of Soil Science and Land Resource, Andalas University. The actual amount of soil eroded was predicted using the USLE formula. Then, it was compared to the tolerated (Etol) soil erosion. The result showed that the predicted amount of soil eroded was quite low (<10 T/Ha/y), except under coffee having >45% slope. The highest soil eroded in the very steep slope was due to its low SOM content and permeability, with an erosion hazard level of 1.2. Compared to tolerated erosion (Etol), the actual soil erosion predicted was lower than the Etol. The fiber roots of the coffee dominating the top 5 cm of soil surface as well as high SOM content and hydraulic conductivity rate caused the soil on the top to become tightly held avoiding erosion.

Soil adsorption and transport of lead in the presence of perovskite solar cell-derived organic cations

Perovskite photovoltaics offer a highly efficient and low-cost solar energy harvesting technology. However, the presence of lead (Pb) cations in photovoltaic halide perovskite (HaPs) materials is concerning, and quantifying the environmental hazard of accidental Pb2+ leaching into the soil is crucial for assessing the sustainability of this technology. Pb2+ from inorganic salts was previously found to remain in the upper soil layers due to adsorption. However, Pb-HaPs contain additional organic and inorganic cations, and competitive cation adsorption may affect Pb2+ retention in soils. Therefore, we measured, analyzed by simulations and report the depths to which Pb2+ from HaPs penetrates into 3 types of agricultural soil. Most of the HaP-leached Pb2+ is found to be retained already in the first cm of the soil columns, and subsequent rain events do not induce Pb2+ penetration below the first few cm of soil surface. Surprisingly, organic co-cations from the dissolved HaP are found to enhance the Pb2+ adsorption capacity in clay-rich soil, compared to non-HaP-based Pb2+ sources. Our results imply that installation over soil types with improved Pb2+ adsorption, and removal of only the contaminated topsoil, are sufficient means to prevent ground water contamination by HaP-leached Pb2+.

Prediction of soil textural constituents using reflected spectra in eastern Mazandaran Province

Textural components of soil play an essential role in erodibility and should be considered in many projects of conservation and environmental modeling processes. Traditional methods of determining soil texture are usually laborious, expensive and time consuming along with destructive effects on the environment. Meanwhile, spectroscopic technology using the spectral features and signatures from the whole reflected spectra of soil surface promises a competent method to study soil constituents. To investigate this issue, 113 points were selected and sampled randomly from 0-15 cm of soil surface in eastern parts of Mazandaran Province, Iran. Samples were haphazardly divided into 91 for model building and 22 for final verification and accuracy assessment processes. Applying the enhanced PLS-algorithm plus the FLOOCV approach along with spectral transformations and pre-processing, the modeling of each textural components were accomplished. Spectrally, sand and clay fractions were modeled with high accuracy as: R2c= 0.89, RMSEc= 7.42, SEc= 7.46 for sand and R2c= 0.82, RMSEc= 6.88, SEc= 6.92 for the clay content. Whereas, the silt predictive model was slightly weaker than the other constituents. The most effective spectral ranges involved in the modeling process, were also detected and recognized based on beta & spectral weight analyses and Marten’s uncertainty test. Additionally, the most influential spectroscopic ranges included were the visible, NIR and SWIR regions with the specified wavelengths. In general, the efficacy of spectroscopic technology in soil texture studies has been proven by this research. Using the computed spectral models, we are able to study the soil textural components at large scales faster, safer, timelier and also cheaper. That is absolutely true and applicable using the regionalized remotely sensed data but requires further investigation in different geographical regions.

Soil Water Behavior of Sandy Soils under Semiarid Conditions in the Shendong Mining Area (China)

The soil water behavior of sandy soils was studied under semiarid conditions in the Shendong mining area (China). The soil water content (θ) was measured under different depths and topographies using an HH2 moisture meter. The infiltration process was studied using a Guelph soil permeameter. A set of hydrodynamic variables was calculated in the laboratory. The θ of the first 20 cm was the lowest and increased with depth. The content of soil water increased from the top slope to the bottom slope. The infiltration experiments showed that the steady state infiltration rate was &gt;40 mm h−1 in most cases. Owing to the higher contents of sand and soil macropores at the top of the slope and the top 0–20 cm of surface soil, the initial infiltration rate and steady infiltration rate were higher. The average available water capacity was 18.28%, which was consistent with the predominance of a sandy textural fraction. The results of a soil water retention curve and a rainfall simulation experiment showed that there was a low soil water retention capacity throughout the whole profile. This study contributes to the understanding of several aspects of the soil water behavior of sandy soils and provides key information for environmental management and land reclamation under semiarid conditions in the Shendong mining area.

Modeling of Soil Sand Particles Using Spectroscopy Technology

ABSTRACT The advent of lab diffuse reflectance spectroscopy (LDRS) that exploits the fundamental vibration, overtones and combination of functional groups of soil components makes the soil study easier. The present research intends to predict sand content utilizing the proximal soil sensing (PSS) tech. Thus, in accord with the supplementary data layers and stratified randomized sampling (SRS) method, eventually, 128 samples were gathered from 20 cm of soil surface of Mazandaran Province, Iran. First of all, the sample set was subdivided into two subsets: calibration (96) and validation (32). Using the multivariate regression analysis-partial least squares regression (PLSR) algorithm with leave-one-out cross-validation (LOOCV) technique and some pre-processing algorithms, such as spectral averaging, smoothing and 1st derivative (1st-D), the definitive calibration model with two & four latent vectors (LVs/LFs) and correlation coefficient (RP), determination coefficient (R2 P), root mean square error (RMSEP), ratio of performance to deviation (RPDP) and ratio of performance to interquartile distance (RPIQP) respectively: 0.83&0.82, 0.68&0.67,8.68&8.83%,1.78&1.75,2.45&2.41, were validated and spotted as the most appropriate predictive model for the sand content prediction in the study region. Last, the potentiality of the visible-near infrared diffuse reflectance spectroscopy (VNIR-DRS) for sand content estimation in Mazandaran soils was proved. Also, it is feasible to upscale the sand prediction process utilizing the principal resulted model and the key spectral domains via airborne/satellite hyperspectral data, which emphatically shows the LDRS importance as a commencement point for characterizing the informative optical wavelengths. Likewise, that will be the infrastructure for spaceborne data modeling and upscaling process.

Reflectance study of soil silt using proximal sensing in Northern Iran

The study of silt fractions using the traditional methods, especially on large scales, is time-consuming, laborious, and costly. The present work intends to investigate the spectral behaviors of the soil silt fraction using reflectance spectroscopy technology. Accordingly, 128 soil samples were collected from 20cm of soil surface of Mazandaran province, northern Iran. First, the sample set was subdivided into calibration and validation subsets. Spectral signatures of silt components were detected utilizing the PLSR algorithm and Cross-Validation technique. The final model with 4 LFs was calibrated with these specs: Rc: 0.55, RMSEc: 8.31%, RPDc: 1.20, and RPIQc:1.71 and was eventually selected as the best model for studying the soil silt of Mazandaran province. The obtained spectral wavebands with the highest correlation coefficients (R(CCmax)) indicate the high impact as the independent predictors in the processes of modeling. Finally, the capability of the proximal sensing technology (VNIR-PS) was proved in examining the silt content of Mazandaran province. Also, the most influential spectral domains and ranges were detected and recognized. Our findings can be used as a basis for studying silt content on a large scale by applying the upscaling process via airborne/satellite hyperspectral data. Subject classification codes: Soil Conservation, Proximal Soil Sensing, Soil Spectral Modeling

EFFECT OF SOME SOIL CONDITIONERS ON PHYSICAL AND CHEMICAL PROPERTIES OF NORTH SINAI SANDY SOILS

A pot experiment was carried out during the early winter of 2016-2017 at the Experimental Farm of Faculty of Environmental Agricultural Sciences, Arish University, to evaluate the use of some soil conditioners on physical and chemical properties of Arish sandy soil, Wheat (Triticum aestivum L.,CV Sakha 94) plants were grown in pots, A surface sandy soil sample (0-15cm) from the Experimental Farm of the Faculty was used in the study. Each conditioner was homogenously distributed on the soil surface and then were mixed with the upper 15 cm of soil surface. Grains of wheat were sown in each pot containing 20 Kg soil. NPK fertilizers were added as recommended. Vinasse, humic acid and polyacrylamide were added at three rates (0.5,1.0 and1.5(W/W)). The experimental design was complete randomized with four replicates for each treatment. Results of pH showed that the effect of applied both vinasse and humic acid to the soil in different rates led to slightly decrease on pH values gradually by increasing the rate of application. The result of acrylamide polymer show that the effect of the application to the soil led to increase pH values gradually by increasing the rate of application. Results of EC in soil show that the effect of applied vinasse, humic acid and acrylamide polymer to the soil in different rates led to increase on EC values gradually by increasing the rate of application. Also, data showed an increase in available N, P and K at all application, the higher value of N observed on application of vinasse on rates of V2 at the initial soil sampling periods, V3 at the mid-season and harvesting soil sampling periods. The higher value of P observed on application of vinasse on rates V3 at the initial soil sampling periods and HA3 at the mid-season and harvesting soil sampling periods and the higher value of K observed with application of V3 at all experiment periods. Except vinasse treatments, the mean values of organic matter, significantly increased with increasing the rates of the application the higher value HA3. Also, data indicate that for all studied levels of vinasse significantly increase soil organic matter values comparing to control treatments, HA3 achieve the highest increasing values of OM while application of PAM3 treatment was the superior for increasing soil OM. All studied levels of vinasse significantly increased soil bulk density. Apparently, HA2 and HA3 achieved the highest reducing values of BD. Such decreases represent about 8.05% and 7.89% lower than control treatment for the previously mentioned two HA rates and PAM3 treatment was the superior to other PAM3 for reducing soil BD, such decrease was 0.13 Mg m-3at the development stage of soil sampling and represent about 8.87% lower than control treatment. Results also revealed that there was a pronounced decreasing in soil Ks at the Initial period of soil sampling. Soil moisture content in both field capacity and witting point were increase along most of the studied soil sampling stages. The highest N, P and K content in grains was found for addition V3. Also, the highest grains yield was found for addition (vinasse)V3 while the control treatment had the lowest values.

Soil salinity analysis of Urmia Lake Basin using Landsat-8 OLI and Sentinel-2A based spectral indices and electrical conductivity measurements

Abstract Soil salinization is one of the significant soil degradation problems especially faced in arid and semi-arid regions of the world. It poses a high threat to soil productivity in agricultural lands. The demand for economic and rapid detection and temporal monitoring of soil salinity has been rising recently. Satellite imagery and remote sensing approaches are the significant tools for accurate prediction and mapping of soil salinity in various regions of the world. This study aims to compare Landsat- 8 OLI and Sentinel-2A derived soil salinity maps of the western part of Urmia Lake in Iran by applying three different salinity indices in conjunction with field measurements. Totally 70 soil samples were collected from top 20 cm of surface soil in October 2016 from an area of 18 km2. Landsat-8 OLI and Sentinel-2A images were acquired in the same month; both images were atmospherically and radiometrically corrected prior to applying soil salinity indices. After comparing Normalized Difference Vegetation Index (NDVI) value of corresponding pixel for each sample with its electrical conductivity (EC) value, 54 soil samples with various EC ranges were selected for mapping. Among them, 42 samples were used for establishing the regression model and remaining 12 samples were utilized to validate the model. Multiple and linear regression analyses were conducted to correlate the EC data with their corresponding soil salinity spectral index values derived from visible bands of satellite images. The results revealed that soil salinity indices extracted from both Landsat-8 OLI and Sentinel-2A visible bands estimated soil salinity with acceptable accuracy of R2 0.73 and 0.74, respectively. Multiple linear regression analysis using both Landsat- 8 OLI and Sentinel-2A data demonstrated higher accuracy with R2 value of 0.77 and 0.75, respectively, compared to linear regression. This study proves that various soil salinity classes with different EC ranges can be estimated by correlating ground measurement data with satellite data.

Strategic tillage may sustain the benefits of long-term no-till in a Vertisol under Mediterranean climate

Long-term no-till or reduced tillage may decline functioning ability of soils due to surface/subsurface compaction and/or stratification of plant nutrients. A long-term (ten years) field experiment was established in 2006 in the Çukurova region of Turkey to evaluate the impact of tillage on the physical properties of a soil under a Mediterranean climate. The tillage systems investigated included two conventional (CT-1 and CT-2), three reduced (RT-1, RT-2 and RT-3) and two no-till (NT and ST), including strategic/occasional tillage. Nine-year old undisturbed no-till plots were divided into two categories and half of these plots were plowed by a moldboard plow in November 2015, and this practice was defined as strategic tillage (ST), while remaining half of the plots left undisturbed. Soil samples were collected from disturbed and undisturbed plots of NT as well as plots under other tillage systems from three soil depths (i.e., 0–10, 10–20 and 20–30 cm) in November 2016. The crop rotation at the experimental areas was winter wheat (Triticum aestivum L.), soybean (Glycine max. L.) – grain maize (Zea mays L.) – winter wheat. Soil samples were analyzed for aggregate stability (AS), mean weight diameter (MWD), bulk density (BD), water filled pore space (WFPS), water content at field capacity (FC), permanent wilting point (PWP), available water content (PAW), micropores (MiP), macropores (MaP), total porosity (TP), and penetration resistance (PR). The ST decreased MWD of surface soil compared to NT by 7.2%, while MWD under ST was higher than NT by 78.0% and 103.6% for 10–20 and 20–30 cm depths, respectively. The NT and RT resulted higher BD and PR, and lower MaP and TP than CT and ST in all three depths, though the values were generally not limiting for crop growth. The ST significantly (P < 0.01) decreased BD and PR within 30 cm of soil surface. However, water content at FC, PWP and also PAW in 0–10 and 10–20 cm depths were significantly reduced with ST compared to NT. The ST significantly (P < 0.01) increased the MaP and TP compared to NT which favors better aeration and water movement. The mean WFPS under NT, RT-2 and RT-3 systems in 0–10 cm and with all tillage systems (except ST in 10–20 cm) in subsurface layers were higher than 60%, which is considered a threshold for nitrogen losses as N2O fluxes. Implementation of ST into conservational practices under Mediterranean climate could be a viable management option to overcome some of the disadvantages of long-term conservation tillage and thereby to improve physical soil conditions for crop growth, air and water movement.

Effect of biochar application method on nitrogen leaching and hydraulic conductivity in a silty clay soil

Biochar is anticipated to be an effective option for mitigating nitrogen (N) leaching and improving the hydraulic characteristics of soil, particularly sandy soil. However, little attention has been paid to understanding the effect of biochar on N leaching and hydraulic conductivity (K) in fine-textured soil. Additionally, whether different biochar application methods have different effects on N leaching and K remains unclear. Therefore, our objective in this study is to determine the effects of biochar with different application methods on nitrate/ammonium leaching and K in silty clay soil. The three biochar application patterns were as follows: A, biochar was mixed into 0–10 cm of surface soil; B, biochar was mixed into 10–20 cm of subsurface soil; and C, biochar was mixed evenly into 0–20 cm of plow layer soil. In addition, biochar was added at three rates, namely, 1%, 2% and 4% (mass ratios), and a soil column without biochar addition served as the control (CK). Our results demonstrated that the choice of biochar application method significantly influenced N leaching and soil K and balance between the soil K and N leaching, particularly for nitrate. Additionally, the leaching of N in silty clay soil occurred mainly in nitrate form. Compared with the CK, all 1% biochar treatments increased nitrate leaching (except C1%, which showed no differences from the CK) and tended to decrease K. However, all 4% biochar treatments increased nitrate leaching due to a high K. All 2% biochar treatments significantly reduced nitrate leaching by 8.3–17.0%, and B2% significantly increased the saturated hydraulic conductivity (Ksat) of soil by 20.9%. Hence, the mixing of biochar at a rate of 2% into the subsurface soil effectively mitigated N leaching and increased K in silty clay soil. These findings could have some implications for the field application of biochar. For instance, the combination of subsurface biochar application with that of fertilizer to roots in orchards or with deep tillage in fields, which would mimic the B2% model, would yield multiple benefits, including lower costs.

Germination Biology of Two Invasive Physalis Species and Implications for Their Management in Arid and Semi-arid Regions

Two Solanaceae invasive plant species (Physalis angulata L. and P. philadelphica Lam. var. immaculata Waterfall) infest several arable crops and natural habitats in Southeastern Anatolia region, Turkey. However, almost no information is available regarding germination biology of both species. We performed several experiments to infer the effects of environmental factors on seed germination and seedling emergence of different populations of both species collected from various locations with different elevations and habitat characteristics. Seed dormancy level of all populations was decreased with increasing age of the seeds. Seed dormancy of freshly harvested and aged seeds of all populations was effectively released by running tap water. Germination was slightly affected by photoperiods, which suggests that seeds are slightly photoblastic. All seeds germinated under wide range of temperature (15–40 °C), pH (4–10), osmotic potential (0 to −1.2 MPa) and salinity (0–400 mM sodium chloride) levels. The germination ability of both plant species under wide range of environmental conditions suggests further invasion potential towards non-infested areas in the country. Increasing seed burial depth significantly reduced the seedling emergence, and seeds buried below 4 cm of soil surface were unable to emerge. In arable lands, soil inversion to maximum depth of emergence (i.e., 6 cm) followed by conservational tillage could be utilized as a viable management option.

Genesis and Classification of Oil Polluted Technosols in Southern Tehran

Technosols are modified soils affected by human activities. This study investigated genesis, classification and physicochemical properties of four pedons of Technosols developed on refused oil refinery materials and compared them with two unpolluted pedons. Mineralogical studies showed smectite as a dominant clay mineral with other clay minerals. These clay minerals adsorb oil compounds in their interlayer spaces and reduce their mobility and decomposition. Different micromorphological features resulting from oil compounds in soils, including depletion zones, types of coatings (quasi and hypocoating) and features due to horizontal and vertical movement of oil compound in soil showed dynamics of oil compounds and their effects on soil forming process. The refused petroleum compounds decrease pH and increase organic carbon, amorphous form of Iron in soils. Taking into account the presence of high amounts of gypsum and carbonate in polluted soil, the studied soils were classified as Typic Calcigypsids in Soil Taxonomy but in WRB system, due to the presence of impermeable geomembrane within 100 cm of soil surface, they were classified as Linic Technosols, showing the more precision of WRB system in their classification.

Establishing geochemical baselines in forest soils for environmental risk assessment in the Montague and Goldenville gold districts, Nova Scotia, Canada

Mine tailings at historical gold districts in Nova Scotia, Canada, contain high concentrations of arsenic (As) and mercury (Hg), which may represent a risk to ecosystems and human health. Two sites, Montague and Goldenville, are of particular concern as tailings are located close to residences and are occasionally used for racing off-road vehicles. Risk-assessment calculations require knowledge of the naturally occurring concentrations of As and Hg in soils overlying mineralized bedrock within these gold districts. In this study, we collected samples of the top 0–5 cm of surface soil (the Public Health layer) from 46 sites near Montague, and 39 sites near Goldenville. Samples of individual soil horizons (H, Ae, B, and C) were also taken from selected sites to evaluate the vertical distribution of elements in the soil profile. Results show that the concentrations of As and Hg in all soil horizons are generally higher down-ice, southeasterly, of the ore zones in both districts, reflecting glacial erosion and transport of mineralized bedrock. Analysis of the top 0–5 cm of soils shows the following ranges in As and Hg concentrations (&lt;2 mm size fraction): Montague: As, 4–273 mg/kg (median 42 mg/kg); Hg, 72–490 µg/kg (median 164 µg/kg); Goldenville: As, 2–140 mg/kg (median 13 mg/kg); Hg, 39–312 µg/kg (median 114 µg/kg). In general, the concentrations of As are highest in the B and C horizons, whereas Hg concentrations are highest in humus (H). Results from this study have been used to assess the distribution of tailings at these sites, and to help guide risk-management decisions.

Rice–wheat cropping system: tillage, mulch, and nitrogen effects on soil carbon sequestration and crop productivity

Maintenance of organic carbon in soil (SOC) is critically important for sustained agricultural productivity and environmental quality. This paper presents SOC resulting from differences in tillage types and demonstrates how mulch and nitrogen (N) application can mediate the tillage functions on SOC and crop productivities. The results are derived from a 4-year field-scale study carried out in a low-land under sub-tropical hot and humid environment of Nepal. It compared eight treatment combinations, viz., tillage (no-tillage and conventional tillage), mulch (no-mulch and 12 Mg ha−1 year−1 of mulch), and N application (recommended versus leaf color chart method) under rice–wheat cropping system. Seasonal grain and biomass yields of these crops were recorded and at the end of the 4-year study, quantified the organic carbon stock of soil; Within 15 cm of surface soil, SOC stock (Mg C ha−1) was statistically (p < 0.05) higher on no-tillage plots (11.2–11.8) than on conventional tillage plots (9.2–10.5). The treatment effect was more pronounced on winter wheat productivity where conventional tillage combined with straw-mulch exceled the performance of no-tillage. Clearly, no-tillage had the environmental benefit, and conventional tillage had the crop productivity benefit.

Spatial variability of topsoil chemical properties

Soil properties vary spatially and temporally because of soil formation processes, land use pattern, fertilizations etc. Geo-statistics, remote sensing and GIS offer some of the best tools and techniques to capture the spatial variability of soil properties. Study area chosen for the investigation is situated in the coastal zone, covering a part of Dakshina Kannada and Udupi Districts, Karnataka. Study area predominantly consists of sandy, loamy sand and gravelly elay soils. Harvested agricultural paddy fields were identified as soil sampling locations. A total of 260 soil samples were collected from top 0-20 cm of soil surface and were air dried. Measurement of topsoil chemical properties such as Organic Matter (OM), pH, Electrical Conductivity (EC), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca) and Iron Oxide (Fe2O3) were carried out as per Indian Standard Codes. Descriptive statistics were computed, correlation between the soil properties was explored and also soil properties were interpolated and mapped using IDW interpolation method. Soil properties have very large variability. In this region topography and vegetation is homogeneous, and no erosion activity is observed. So the only reason for the high variability of soil properties is agricultural practices. Correlation among soil properties is not consistent. There is no significant influence of soil type on soil properties range. Restoration of small scale farmers is important in food security point of view.

Can livestock and fires convert the sub-tropical mountain rangelands of central Argentina into a rocky desert?

Soil erosion, as a result of livestock grazing, has been widely reported for arid and semiarid ecosystems, but information is lacking in more mesic ecosystems where erosion is generally studied in relation to agriculture. To test the hypothesis that, in the high-mountain rangelands of Córdoba (Argentina), grazing by livestock can drive the system into a rocky desert, 200 4 × 4 m plots under different livestock stocking rates and timings of grazing were monitored for 5 years. Four indicators of soil erosion: change rate of rock surface and of total bare surface, advance rate of erosion edges, and their activity persistence were estimated for each plot. Erosion edges are steps with a vertical bare soil surface, whose advance usually leaves behind an exposed rock area. For each plot, the average annual stocking rate for the 5-year period, and an index of seasonality, were calculated. Multiple regressions were used to analyse the data. Under high stocking rates, rock and bare surface increased, edges advanced faster and persisted more actively, while under low or nil stocking rates, rock and bare surface decreased and edges tended to stabilise. From these results, it was estimated that under high stocking rates, 18% of the whole area could be transformed into rocky surface in 400 years. As fire is a usual tool for this rangeland management, surface soil loss during 1 year in 77 burned and unburned plots, with and without post-fire livestock grazing, were compared. Burned plots lost 0.6 cm of surface soil when grazed, and 0.4 cm when ungrazed, while unburned plots lost less than 0.05 cm when grazed, and gained 0.07 cm when ungrazed. It was concluded that the present-day combination of livestock and fire management has the potential to convert this rangeland into a rocky desert. It is suggested that commercial livestock production, as it is carried on at present, is not sustainable, and some suggestions on changes necessary for a future sustainable grazing industry are made.

Using fallout plutonium as a probe for erosion assessment

A study has been carried out to assess the potential of using fallout plutonium (Pu), which originated from atmospheric nuclear-weapons tests, as a tool to investigate recent erosional processes within the lower Cotter water-supply catchment in the Australian Capital Territory. This catchment, which was predominantly pine plantation, was severely affected by a major bush fire in 2003. Accelerator mass spectrometry has been used to measure Pu in soil samples collected from a number of sites across the catchment. The results indicate that less than 1 cm of surface soil had been lost since the early 1960s over much of the catchment. Areas of more erodible soil have, however, lost 2–4 cm of topsoil, and a loss of ∼6 cm of soil was identified at one particular site.

Carbon sequestration in secondary pasture soils: a chronosequence study in the South African Highveld

Soil restoration is a means of combating desertification in semi‐arid and arid parts of the world. There, vast areas of the cropped soil degrade, particularly because of the loss of organic matter. One approach to reverse this loss is the conversion of cropland into permanent grassland for use as pasture. This study was designed to evaluate how fast and to what degree degraded cropland may re‐sequester soil organic carbon (SOC) when converted into permanent secondary pasture. Topsoil samples (0–5, 5–10 and 10–20 cm) were taken from chronosequences of secondary pastures (1 to 31 years old) at three agro‐ecosystems in the semi‐arid Highveld of South Africa. Long‐term croplands and primary grassland used as pastures served as the controls. In bulk soil samples (&lt;2 mm) and their clay (&lt;2 µm), silt (2–20 µm), fine sand (20–250 µm) and coarse sand (250–2000 µm) fractions, the contents of carbon (C) and nitrogen were determined. In all three agro‐ecosystems, using a mono‐exponential model, the SOC stocks increased exponentially until a maximum was reached 10–95 years after land conversion. This gain in SOC was clearly pronounced for the top 0–5 cm of soil, but hardly detectable at 10–20‐cm depth. The sand fractions recovered organic C more rapidly but less completely than did the finer size separates. Overall, between 9.0 and 15.3 t of SOC were sequestered in the 0–20 cm of surface soil by this land conversion. Thus, the SOC recovery in the secondary pastures resulted in SOC stocks that were 29.6–93.9% greater than those in the arable land. Yet, in no agro‐ecosystem, at any soil depth, nor in any soil fraction, did the measured SOC content reach that of the primary grassland. In part this can be attributed to a slightly finer texture of the primary grassland that had not lost silt through wind erosion or had never been used as arable land because of slightly elevated clay contents. Overall it appears, however, that previous losses of SOM cannot easily be rectified, suggesting that the native primary grassland soils are only partially resilient to land‐use change.

Direct estimation of nitrate, total and fractionated water extractable organic carbon (WEOC) in an agricultural soil using direct UV absorbance deconvolution

In this study, a multiwavelength UV spectral deconvolution (UVSD) procedure is proposed as a robust and simple procedure for direct estimation of carbon and nitrate contents in soil water extracts. Soil samples were collected from an open-air field cultivated with maize at 3 different depths, 30 cm each, between 0 and 90 cm of soil surface during a period of 7 months. Fractionation of water extractable organic carbon (WEOC) into hydrophobic (Hpo-WEOC), transphilic (Tpi-WEOC), and hydrophilic (Hpi-WEOC) fractions is performed using XAD-8 and XAD-4 resins connected in series. In order to perform UVSD, 3 representative reference spectra of WEOC fractions were selected automatically, in addition to a 4th spectrum representative of NO 3 − selected manually in order to compose the deconvolution basis. The restitution of UV spectra was made in the range 235–350 nm. Through exploitation of soil water extract UV spectra, it was possible in a single-step deconvolution procedure to determine the organic carbon (mg C l −1) and NO 3 − (mg l −1) concentrations and to differentiate and to quantitatively estimate carbon content of WEOC fractions. Statistical tests indicated satisfactory correlations between values estimated using UVSD and those determined by conventional reference methods for each parameter determined. The ranges of concentrations of carbon and NO 3 − in the soil water extracts studied are between 3.00 and 15.00 mg C l −1 and 60–300 mg l −1, respectively. The limits of quantification (LQ) and of detection (LD) of WEOC and NO 3 − were found to be 0.10 and 0.05 mg C l −1, and 0.10 and 0.03 mg l −1, respectively.

Elevation, substrate, and the potential for climate-induced tree migration in the White Mountains, New Hampshire, USA

We assessed the potential for climate-induced migration of tree species along elevation gradients in the White Mountains of New Hampshire. To do so, we determined the extent to which tree species abundances were associated with elevation, site, and substrate-related variables over a range of elevations (530–880 m) that included the transition from northern hardwoods to spruce-fir forest in the White Mountain National Forest (USA). One-hundred and ten, 400 m 2 plots were established along three elevational transects; transects were separated from each other by at least 9 km. In each plot, site and substrate characteristics were measured and all stems ≥2.5 cm dbh were tallied. Species importance values were calculated and those of the five most abundant tree species – balsam fir, red spruce, sugar maple, American beech, and yellow birch – were regressed on elevation and site–substrate characteristics. Plots were ordinated using detrended correspondence analysis and their first and second axis scores were regressed on elevation and site–substrate characteristics. Both elevation and site–substrate characteristics – parent material type in particular – were important predictors of importance value. Balsam fir and red spruce abundance increased with elevation and, at all elevations, reached greatest abundance on shallow-to-rock parent materials. Fir showed greater abundance on north-facing than on south-facing slopes. Sugar maple and American beech declined with elevation and both, but especially sugar maple, were associated with fine and compact tills. Yellow birch, which did not show any association with substrate characteristics, increased to about 770 m, then declined. The frequency of different parent material types changed with elevation, with deep, fine and compact tills becoming less frequent – and shallow soils (rock within 50 cm of soil surface) becoming more frequent – with elevation. If the tree species–substrate associations described here are causal, then the elevational patterns of species abundance observed today are a consequence of both edaphic and climatic factors. As a consequence, vegetation response to climatic warming may be complex. While warming may result in upward migration of yellow birch and American beech, sugar maple, confronted with reduced availability of suitable substrate at high elevations, will likely show little upward response. Red spruce and balsam fir may persist on thin soils at lower elevations unless displaced by eastern hemlock. Thus, climatic warming will likely alter traditionally recognized tree assemblages in this region.