Key Soil Parameters Research Articles

Large variation in glyphosate mineralization in 21 different agricultural soils explained by soil properties

Glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) have frequently been detected in surface water and groundwaters. Since adequate glyphosate mineralization in soil may reduce its losses to environment, improved understanding of site specific factors underlying pesticide mineralization in soils is needed. The aim of this study was to investigate the relationship between soil properties and glyphosate mineralization. To establish a sound basis for resilient correlations, the study was conducted with a large number of 21 agricultural soils, differing in a variety of soil parameters, such as soil texture, soil organic matter content, pH, exchangeable ions etc. The mineralization experiments were carried out with 14C labelled glyphosate at a soil water tension of −15 kPa and at a soil density of 1.3 g cm−3 at 20 ± 1 °C for an incubation period of 32 days. The results showed that the mineralization of glyphosate in different agricultural soils varied to a great extent, from 7 to 70% of the amount initially applied. Glyphosate mineralization started immediately after application, the highest mineralization rates were observed within the first 4 days in most of the 21 soils. Multiple regression analysis revealed exchangeable acidity (H+ and Al3+), exchangeable Ca2+ ions and ammonium lactate extractable K to be the key soil parameters governing glyphosate mineralization in the examined soils. A highly significant negative correlation between mineralized glyphosate and NaOH-extractable residues (NaOH-ER) in soils strongly suggests that NaOH-ER could be used as a simple and reliable parameter for evaluating the glyphosate mineralization capacity. The NaOH-ER were composed of glyphosate, unknown 14C-residues, and AMPA (12%–65%, 3%–34%, 0%–11% of applied 14C, respectively). Our results highlighted the influential role of soil exchangeable acidity, which should therefore be considered in pesticide risk assessments and management to limit efficiently the environmental transfers of glyphosate.

Microalgae and their effects on metal bioavailability in paddy fields

Heavy metal contamination in paddy soils poses a serious threat to rice quality. However, these risks may be reduced by biological processes that sequester or transform metals into less mobile forms. Microalgae are commonly found in wetland ecosystems, but their effects on soil properties and metal uptake by rice remain unresolved. In this paper, we summarize the available literature to evaluate the role of microalgae in metal bioavailability in paddy fields. Up-to-date information was gathered and analyzed to provide a deeper understanding of metal pollution in paddy soils; factors controlling metal bioavailability; and the types of unicellular algae present, their mechanisms of metal accumulation and detoxification, and their effects on various properties such as pH, redox potential (Eh), and organic matter; as well as the bioavailability of different metal(loid)s in paddy soils. Metal accumulation in rice and its associated risks to human health do not depend on the total amount of metals in soils, but are controlled by metal bioavailability, which in turn is affected by soil chemical properties and biological processes. As an important component of the biota in paddy soils, microalgae not only contribute significantly to carbon and nitrogen fixation through photosynthesis, but also strongly modify key soil parameters including pH, Eh, dissolved oxygen, and organic matter. Such effects undoubtedly have considerable impacts on metal phytoavailability and biogeochemical cycles in paddy fields. Although many studies have been carried out to classify microalgae and describe their ecological functions, the effects of microalgae on metal bioavailability have not been extensively studied and no detailed mechanisms have been elucidated. Therefore, further investigations are warranted in this field. Future research should focus on identifying additional microalgae strains, characterizing their physiological activities, and quantifying their impacts on metal uptake in rice.

Characterizing the influence of stress on foam conditioned sand for EPB tunneling

To guarantee effective EPB TBM face support and performance, it is necessary to understand the mechanical behavior of foam-conditioned soil under realistic pressure conditions. This paper investigates the behavior of foam-conditioned soil under applied total pressures of up to 5bar. The study examines the effect of total stress, effective stress, and key soil parameter void ratio on the behavior of foam-conditioned soil. Shear strength and compression tests were carried out in a field-portable pressurized test chamber on two granular soils with a variety of foam parameters. The results demonstrate that void ratio and effective stress are the main factors that influence the performance of foam-conditioned soil. It was determined that a certain ratio of void ratio to maximum void ratio was required to prevent the development of appreciable effective stress and, thus, high shear strength and low compressibility.

Inhibitory effects of rice residues amendment on Cd phytoavailability: A matter of Cd-organic matter interactions?

Incorporating crop residues into soils, a most common way of organic input into farmland soils, is being encouraged in many parts of the world, while its potential impacts on Cd phytoavailability are not well understood. Here, a Cd-contaminated soil was amended with rice residues (RR, i.e., straw + root mixture) or not (Control) and incubated for 81 days under laboratory-controlled conditions. During the incubation, key soil parameters (e.g., dissolved organic carbon and pH), Cd geochemical fractionation (by BCR sequential extraction), and CaCl2 extracted Cd in soils (by 0.01 M CaCl2 extraction) were quantified to explain the effects of RR amendment on Cd phytoavailability (assessed by 7 day-cultivation of rice seedling in soils). Besides, hydroponic experiments were designed to explore the effects of D-RR-OM (dissolved-RR-organic matter) on the uptake of Cd by rice seedlings (quantified by uptake constant rate, ku, using stable isotope tracing technique). Our results demonstrated that RR amendment reduced Cd phytoavailability by 17–92% compared with Control during incubation, which might be explained by the interactions between Cd and RR-OM (RR-organic matter) in soil or porewater: (1) Cd immobilization due to its association with solid-RR-OM in soils, (2) Cd mobilization by D-RR-OM, and (3) Cd complexation with D-RR-OM in porewater, and thus reduced ku of Cd. Our results suggested that dynamics of RR-OM (e.g., dissolution, decomposition and transformation) in soils, and thus interactions between Cd and solid/dissolved-RR-OM may control Cd phytoavailability under RR amendment. Information gained in this study would further our understanding about Cd phytoavailability in farming soils.

Limited long-term effects of moderate livestock grazing and prescribed early fire on soil and root processes in Sudanian savanna-woodlands, West Africa

Savanna ecosystems are mainly shaped by climate, soil properties and ecological disturbances such as fire and grazing. The biophysical effects of fire and grazing depend both on their intensities and season of occurrence. The long-term effects of fire and grazing on key soil parameters are still largely unknown in West African savanna ecosystems; yet the knowledge of these effects is crucial to our understanding and sustainable management of savanna ecosystems. This study provides scientific evidence of soil responses to both fire and grazing management, and their interactions, based on field-data from two case-studies. The data are drawn from a long-term factorial experiment that has been established since 1992 in two State Forest reserves in Burkina Faso that mainly differ in their soil attributes (i.e. shallow or deep soil). Root biomass, soil CO2 efflux, organic matter content and C/N ratio, and soil water properties were assessed on plots subjected to two different treatments (i.e. moderate grazing and prescribed burning) over a 20year period. The results indicated that at the site with shallow soil, for both root density and organic matter content there was no significant difference between the studied soil depths (i.e. 0–5cm and 5–10cm) nor a significant effect of treatment (both p>0.05). In contrast, at the site with deep soil, root density increases with soil depth (p=0.011); it is 5 times higher at depths of between 5 and 10cm (3.26±1.24g/dm3) compared to the top 5cm (0.67±0.20g/dm3). The organic matter content marginally decreases (p=0.048) with soil depth. The C/N ratio is higher (p<0.05) under an annual early fire treatment compared to the grazing treatments and control, particularly at the deep soil site. In addition, the CO2 efflux varies significantly with the treatment at the two sites (p<0.004); grazed plots have higher respiration rates than control and burnt plots. Finally, water infiltration rates do not vary significantly with fire and grazing after 20-years of treatment. Our results provide an insight into the long-term effects of fire and grazing on soil water infiltration and soil CO2 fluxes in savanna ecosystems. We conclude that effects of fire and grazing on savanna soil processes are limited. We also highlight our contrasting results between the studied soil attributes across the two sites, providing evidence that depending on site differences, the effects of fire and grazing on soil chemical and water properties might change, suggesting caution when making extrapolation in the context of savanna land use planning and management.

Influence of flood-induced scour on dynamic impedances of pile groups considering the stress history of undrained soft clay

Flood-induced scour causes loss of lateral support at bridge foundations and thus modifies their dynamic impedances, which will in turn influence the dynamic behavior and the seismic response of bridges located in seismically active flood-prone regions. When evaluating the seismic performance of scoured bridges, however, few efforts have been made to analyze the dynamic impedances of their foundations, and possible changes in stress history of the remaining soils are also ignored. In reality, the remaining soils around pile foundations undergo an unloading process due to scour and their over-consolidation ratios are increased, which can be expected to change the properties of the remaining soils. Therefore, a three-dimensional numerical model, in which the pile-soil-pile interaction and the radiation problem are accounted for by means of the elastodynamic Green's functions that permit the mutual interactions between all the piles of the group consistently and simultaneously, is employed in this paper to investigate the influence of flood-induced scour on the dynamic impedances of pile groups in soft clay. Accordingly, the key soil parameter of the elastodynamic Green's functions, i.e., Young's modulus of soft clay, is modified in this model to take into account the stress history effect due to scour. A case study to evaluate the dynamic impedances of 3×3 and 4×4 pile groups with various scour depths and pile spacing, considering or ignoring stress history effect, is discussed in this paper. The results show that ignoring the effect of stress history of the remaining soft clay will overestimate the scour affected dynamic impedances of pile groups, which are found to be reduced significantly as the scour depth increases.

Differential effects of plant root systems on nickel, copper and silver bioavailability in contaminated soil

A pot experiment was conducted to investigate the effect of diverse plant species (four herbaceous and four woody species) on the labile pool of six metals (Ag, Cu, Pb, Zn, Ni and Se) present in their rhizosphere. After three months of cultivation, concentrations of trace elements (TE) in above and below-ground biomass of each species were determined. The labile and presumably bioavailable fraction of these TE in the rhizosphere as well as key soil parameters (e.g. pH, electrical conductivity (EC), percent of organic matter and dissolved organic carbon (DOC)) were also measured and compared as a function of plant species. The concentration of TE in plant tissues differed among species. In general and as expected, concentrations were higher in root tissues of tested plants than in above-ground tissues. While the labile pool of several TE in the rhizosphere, notably Ag, Ni, and Cu, was significantly and differently affected by the presence of the plants, pH, EC and percentage of organic matter remained unchanged. In contrast, DOC was higher in the rhizosphere of all tested plants than in soil of the control pots without plants. In addition, there was a positive relationship between Ni and Cu availability concentrations, and DOC levels. This suggests that root systems of different species can have a distinct influence on soil DOC and consequently modify the labile pools of Ni and Cu in the rhizosphere. These findings have important implications for plant selection in phytoremediation projects.

Is anaerobic mineralizable nitrogen suitable as a soil quality/health indicator?

Soil organic matter (SOM) and especially its labile fractions such as particulate organic matter (POM) are very sensitive to soil use and strongly influence soil ecosystem services. Particulate organic matter has been proposed as a soil quality/health indicator but its determination is tedious and time consuming (i.e. manhours). Anaerobic mineralizable nitrogen (AN) is closely related to the soil organic fraction and is very easily determined. Therefore, we proposed to evaluate AN as a soil quality/health indicator through the assessment of its relationship with SOM, POM, soil aggregate stability (AS), and maize (&lt;em&gt;Zea mays&lt;/em&gt; L.) relative yield (RY) under different long term soil uses for cropping at Balcarce, Argentina (37º 45’ 14’’ S, 58º 17’ 52’’ W). Soil samples had been taken at two depths (0-5 and 5-20 cm) in the fall of 1998, 2000, 2003, 2006, 2009, and 2012 from a long term tillage system (TS, conventional (CT) and no-tillage (NT)) and nitrogen fertilization (NF, with and without nitrogen as fertilizer) experiment on a complex of Typic and Petrocalcic Argiudolls. Carbon contents in SOM (SOC), POM (POC) and AN were determined in all soil samples, whereas AS was determined in other soil samples taken in 2006, 2009 and 2012 from the arable layer (0-20 cm). Regardless of TS and NF, SOC, POC and AN decreased with time under cropping at both 5-20 and 0-20 cm. In the uppermost layer (0-5 cm) decreases of all three variables were observed only under CT. Anaerobically mineralized nitrogen variation related to SOC (R&lt;sup&gt;2&lt;/sup&gt; 0.59 - 0.78, &lt;em&gt;P &lt;/em&gt;&amp;lt; 0.05) and especially POC (R&lt;sup&gt;2&lt;/sup&gt; = 0.80-0.85, &lt;em&gt;P &lt;/em&gt;&amp;lt; 0.05) variations. Likewise, changes in maize RY related better (R&lt;sup&gt;2&lt;/sup&gt; 0.92 and 0.95 (&lt;em&gt;P &lt;/em&gt;&amp;lt; 0.05) for CT and NT, respectively) to variation in AN, than to SOC and POC variations. Besides, changes in the aggregate mean weight diameter (DMWD) related acceptably to AN at 0-20 cm (R&lt;sup&gt;2 &lt;/sup&gt;= 0.67, &lt;em&gt;P &lt;/em&gt;&amp;lt; 0.05) and much better at 0-5 cm (R&lt;sup&gt;2 &lt;/sup&gt;= 0.86, &lt;em&gt;P &lt;/em&gt;&amp;lt; 0.05). Both coefficients of determination were higher than those obtained relating DMWD to SOC or POC. Given the easiness of its determination, its sensitivity, and that it relates to the variation of different key soil parameters and crop behavior, AN could be proposed as an effective soil quality/health indicator. However, studies should be carried out taking into account a broader range of soil and management situations in order to validate the trends observed in this work.

Greenhouse gas emission from direct seeded paddy fields under different soil water potentials in Eastern India

In the anticipated water scarcity and global warming scenario; it is imperative to identify suitable irrigation scheduling strategy in paddy fields for increasing water productivity and mitigating greenhouse gas (GHG) emissions. We conducted a two year (dry season of 2014 and 2015) field experiment for irrigation scheduling based on tensiometric measurement of soil water potential (SWP) in order to quantify temporal and seasonal variations in GHGs emissions and their trade off relationship at five levels of SWPs viz. SWP 1 (−20kPa), SWP 2 (−30kPa), SWP 3 (−40kPa), SWP 4 (−50kPa) and SWP 5 (−60kPa), in addition to the traditional practice of growing flooded rice (CF). Fluxes of methane (CH4) and nitrous oxide (N2O) during the growing period were measured using manual closed chamber-gas chromatograph and the carbon dioxide (CO2) flux was measured using an infrared CO2 analyzer. A significant decrease in seasonal cumulative CH4 emission (30–60.2%) was recorded at different SWPs as compared to CF. In contrast, emission of CO2 and N2O increased by 12.9–26.6% and 16.3–22.1% respectively at SWPs 1 and 2; conversely, a significant decrease in emissions of these gases were observed at higher SWPs (SWPs 3–5). Among different SWP treatments, irrigation scheduling at SWP 2 maintained yield at par with CF with water saving of 32.9–41.1% and reduced CH4 emission (43–44.1%). However, due to increase in CO2 and N2O emission at SWP 2, there was no significant reduction in global warming potential (GWP) as compared with CF. Among different rice growth stages GHGs emission were predominant during vegetative growth stage. Regression relationship of GHGs emission with key soil parameters was employed to predict seasonal emissions of GHGs from paddy field. The results of this study suggest that scheduling irrigation at SWP 2 can be an effective strategy in order to save water, maintain rice yield and mitigate CH4 emission from direct seeded paddy fields in eastern India, however further research is needed to identify suitable management strategy for reducing CO2 and N2O emissions at SWP 2 in order to reduce the GWP.

Design of manned lunar rover wheels and improvement in soil mechanics formulas for elastic wheels in consideration of deformation

Most of the current lunar rover vehicle wheels are inconvenient for changing broken wheels and have poor shock absorbing in driving, so they cannot be used to carry people on the moon. To meet the demands for manned lunar transportation, a new wheel possessing a woven metal wire mesh tire and using hub-rim combination slide mechanism is designed in this article. The characteristics of the new wheel is analyzed by comparing with the same-size conventional rover wheels after demonstrating the validity of FEM simulation. The new wheel possesses lighter structure and superior shock absorbing. It also provides stronger traction because the deformation of the designed wheel increases the contact area between the tire and lunar terrain. In order to establish an on-line soil parameter estimation algorithm for low cohesion soil, the stress distribution along a driven deformable wheel on off-road terrain is simplified. The basic mechanics equations of the interaction between the wheel and the lunar soil can be used for analytical analysis. Simulation results show that the soil estimation algorithm can accurately and efficiently identify key soil parameters for loose sand.

Improving fertilizer management in the U.S. and Canada for N2O mitigation: Understanding potential positive and negative side-effects on corn yields

The potential for mitigation of N2O emissions arising from fertilizer management practices in corn systems has been scientifically assessed in recent decades. Given the strong association between fertilizer management and crop productivity, which to a large extent determines farmers’ willingness to adopt such practices, it is essential to incorporate the impacts on yields before any mitigation practice can be recommended. Here, we address this issue by integrating available results via meta-analysis to quantitatively evaluate the effect of fertilizer management practices on N2O emissions and corn yields in the U.S. and Canada. The combined application of nitrification and urease inhibitors represented the best N2O mitigation option of the practices tested, and their use tended to lead to concurrent increases in crop yields. In comparison, polymer-coated urea was less effective at both reducing N2O emissions and increasing corn yields. Substitution of synthetic fertilizers by organic sources served to reduce N2O emissions but at the cost of significant yield penalties. Sidedress fertilizer applications rather than applying all the fertilizer at planting consistently increased crop productivity. No significant effects were found for the use of urea vs. ammonium nitrate or urea ammonium nitrate, nor for fall vs. spring fertilizer application. However, further research is needed to confirm these observations due to the highly variable nature of the data. Two key soil parameters were identified: 1) Soil texture; N2O and crop yield are highly responsive to fertilizer management in fine-texture soils; and 2) C/N ratio; mitigation of N2O emissions without concurrent yield reductions is most frequently achieved in soils with a low C/N ratio (i.e. <12.5). Our study provides a step forward in achieving an integrated understanding of the positive and negative side-effects of fertilizer management practices for N2O mitigation in agriculture.

A novel method for estimating the track-soil parameters based on Kalman and improved strong tracking filters

A tracked vehicle has been widely used in exploring unknown environments and military fields. In current methods for suiting soil conditions, soil parameters need to be given and the traction performance cannot always be satisfied on soft soil. To solve the problem, it is essential to estimate track-soil parameters in real-time. Therefore, a detailed mathematical model is proposed for the first time. Furthermore, a novel algorithm which is composed of Kalman filter (KF) and improved strong tracking filter (STF) is developed for online track-soil estimation and named as KF–ISTF. By this method, the KF is used to estimate slip parameters, and the ISTF is used to estimate motion states. Then the key soil parameters can be estimated by using a suitable soil model. The experimental results show that equipped with the estimation algorithm, the proposed model can be used to estimate the track-soil parameters, and make the traction performance satisfied with soil conditions.

Effects of land cover change on evapotranspiration and streamflow of small catchments in the Upper Xingu River Basin, Central Brazil

Abstract Study region Upper Xingu River Basin, southeastern Amazonia. Study focus This study assessed the influence of land cover changes on evapotranspiration and streamflow in small catchments in the Upper Xingu River Basin (Mato Grosso state, Brazil). Streamflow was measured in catchments with uniform land use for September 1, 2008 to August 31, 2010. We used models to simulate evapotranspiration and streamflow for the four most common land cover types found in the Upper Xingu: tropical forest, cerrado (savanna), pasture, and soybean croplands. We used INLAND to perform single point simulations considering tropical rainforest, cerrado and pasturelands, and AgroIBIS for croplands. New hydrological insights for the region Converting natural vegetation to agriculture substantially modifies evapotranspiration and streamflow in small catchments. Measured mean streamflow in soy catchments was about three times greater than that of forest catchments, while the mean annual amplitude of flow in soy catchments was more than twice that of forest catchments. Simulated mean annual evapotranspiration was 39% lower in agricultural ecosystems (pasture and soybean cropland) than in natural ecosystems (tropical rainforest and cerrado). Observed and simulated mean annual streamflows in agricultural ecosystems were more than 100% higher than in natural ecosystems. The accuracy of the simulations was improved by using field-measured soil hydraulic properties. The inclusion of local measurements of key soil parameters is likely to improve hydrological simulations in other tropical regions.

Cumulative effects of 20 years of fire, grazing and selective tree cutting on soil water infiltration in sudanian savanna-woodland ecosystem of West Africa

Structural and functional dynamics of savanna-woodland ecosystems are mainly shaped by fire, grazing and wood removal which effects depends both on their intensities. The long-term effects of those disturbances on key soil parameters are still largely unknown. We studied the cumulative effect of 20 years of early fire, grazing and selective tree cutting on soil water infiltration at two experimental sites with contrasting soil conditions (deep silty-clay versus shallow silty-sand) in the sudanian savanna-woodland ecosystems of Burkina Faso. Measurements were carried with a single ring infiltrometer at intervals of 5, 10, 20 and 30 minutes. Results showed that Grazing had negative effect at both sites (P&lt;0.0001). Fire has no effect on infiltration rate at deep soil whereas it has a negative effect on shallow one. Selective wood cutting had beneficial effects for infitration rate at the site with shallow soil. Further, all combined effect of the diffreent treatment resulted in decrease infiltration rate as compared with the control (interaction exclosure, no cutting and no fire). The result suggested that projects which aim to manage or improve soil water properties must take in consideration occurrence of disturbances, soils type and avoid disturbance interaction mainly in shallow sandy soils.Keywords: Disturbances, soil water properties, Burkina Faso, soil compaction, early fire, savanna ecosystem.

Cropland age from grassland conversion to cropland affects nitrous oxide emissions

The effects of soil properties and cropland age on atmospheric nitrous oxide (N2O) emissions following the conversion of grassland to cropland in temperate grassland ecosystems are uncertain. In this study, N2O emissions were compared among grassland and cropland soils in the agro-pastoral ecotone of Inner Mongolia over three growing seasons. Four adjacent sites with different land-use histories were selected, including grassland and croplands cultivated for 5, 10, and 50 years after conversion. N2O flux measurements were obtained using a closed-chamber method and were performed continuously during vegetation periods. After the conversion of grassland to cropland, N2O emission initially decreased and thereafter increased in the study sites. The cumulative N2O emissions of the cropland soils 5 and 10 years in age were 10–50% less than those of the grassland, and the N2O emissions from the cropland soil 50 years in age were 10–30% greater than the grassland. When the seasonal emissions were correlated against single soil parameter, the key soil parameter that affected N2O emissions over the entire growing season was the soil moisture content. When the interactions among soil parameters were considered, the amount of N2O emissions could be quantitatively described by a linear combination of two soil variables, the soil ammonium nitrogen (NH4+-N) and moisture concentrations. This study demonstrates how the time of land use conversion from grassland to cropland can positively or negatively affect N2O emission.

Modelling susceptibility of grassland soil to macropore flow

Summary Investigating preferential flow, including macropore flow, is crucial to predicting and preventing point sources of contamination in soil, for example in the vicinity of pumping wells. With a view to advancing groundwater protection, this study aimed (i) to quantify the strength of macropore flow in four representative natural grassland soils on the Swiss plateau, and (ii) to define the parameters that significantly control macropore flow in grassland soil. For each soil type we selected three measurement points on which three successive irrigation experiments were carried out, resulting in a total of 36 irrigations. The strength of macropore flow, parameterized as the cumulated water volume flowing from macropores at a depth of 1 m in response to an irrigation of 60 mm h−1 intensity and 1 h duration, was simulated using the dual-permeability MACRO model. The model calibration was based on the key soil parameters and fine measurements of water content at different depths. Modelling results indicate high performance of macropore flow in all investigated soil types except in gleysols. The volume of water that flowed from macropores and was hence expected to reach groundwater varied between 81% and 94% in brown soils, 59% and 67% in para-brown soils, 43% and 56% in acid brown soils, and 22% and 35% in gleysols. These results show that spreading pesticides and herbicides in pumping well protection zones poses a high risk of contamination and must be strictly prohibited. We also found that organic carbon content was not correlated with the strength of macropore flow, probably due to its very weak variation in our study, while saturated water content showed a negative correlation with macropore flow. The correlation between saturated hydraulic conductivity (Ks) and macropore flow was negative as well, but weak. Macropore flow appears to be controlled by the interaction between the bulk density of the uppermost topsoil layer (0–0.10 m) and the macroporosity of the soil below. This interaction also affects the variations in Ks and saturated water content. Further investigations are needed to better understand the combined effect of all these processes including the exchange between micropore and macropore domains.

Enhanced biological N2 fixation and yield of faba bean (Vicia faba L.) in an acid soil following biochar addition: dissection of causal mechanisms

Acid soils constrain legume growth and biochars have been shown to address these constraints and enhance biological N2 fixation in glasshouse studies. A dissection of causal mechanisms from multiple crop field studies is lacking. In a sub-tropical field study, faba bean (Vicia faba L.) was cultivated in rotation with corn (Zea mays) following amendment of two contrasting biochars, compost and lime in a rhodic ferralsol. Key soil parameters and plant nutrient uptake were investigated alongside stable 15 N isotope methodologies to elucidate the causal mechanisms for enhanced biological N2 fixation and crop productivity. Biological N2 fixation was associated with plant Mo uptake, which was driven by reductions in soil acidity following lime and papermill (PM) biochar amendment. In contrast, crop yield was associated with plant P and B uptake, and amelioration of soil pH constraints. These were most effectively ameliorated by PM biochar as it addressed both pH constraints and low soil nutrient status. While liming resulted in the highest biological N2 fixation, biochars provided greater benefits to faba bean yield by addressing P nutrition and ameliorating Al toxicity.

Simplified procedure for finite element analysis of the longitudinal performance of shield tunnels considering spatial soil variability in longitudinal direction

A simplified procedure based on finite element method (FEM) is developed in this paper for analyzing the longitudinal performance of shield tunnels considering the longitudinal variation of geotechnical parameters. Herein, the spatial variation of soil properties of the ground under the tunnel is explicitly considered. The validity of the FEM solution is verified by analytical solutions and model tests with various assumed scenarios. The random field theory is employed to model the spatial variation (in the longitudinal domain) of the subgrade reaction coefficient, which is a key soil parameter for FEM analysis of the longitudinal performance of shield tunnels. A hypothetical example is presented to demonstrate the capability of the simplified FEM procedure in analyzing the longitudinal performance of a shield tunnel with spatial soil variability. The results show that the overall settlement of the tunnel is mainly affected by the mean of soil properties, while the extent of the tunnel differential settlement is significantly affected by the variation and scale of fluctuation of soil properties.

Long-term changes in soil salinity as influenced by subsoil thickness in a reclaimed coal mine in east-central Alberta

Olatuyi, S. O. and Leskiw, L. A. 2014. Long-term changes in soil salinity as influenced by subsoil thickness in a reclaimed coal mine in east-central Alberta. Can. J. Soil Sci. 94: 605–620. Elevated salinity and sodicity are major challenges to reclamation of surface-mined coal sites in the Alberta Plains region. Research plots were established in 1981 at the Battle River Coal Mine near Forestburg, AB, to determine an optimum depth of subsoil replacement over sodic mine spoil required to sustain agricultural capability. Subsoil thickness was varied at 0, 25, 65, 135, 165 and 335 cm, overlain with 15 cm topsoil. The plots were monitored annually from 1982 to 1986 and were seeded to forage from 1987. Plots were resampled in 2013 to examine long-term changes in soil quality by comparing the results with the historical means for the 1980s. Key soil parameters measured are pH, electrical conductivity (EC), total dissolved salts (TDS), sodium adsorption ratio (SAR) and soluble Na. The soil quality of the root zone (0–40 cm) improved over time in all treatments as EC, TDS, SAR and concentration of Na decreased significantly between the 1980s and 2013. Amounts of EC and soluble Na consistently increased with depth, suggesting salt accumulation was predominantly by downward leaching, but with contribution by upward migration of Na from the underlying spoil. Relative to the native soils in 2013, the root zone quality ratings for EC and SAR in the topsoil/spoil treatment were better than in the shallow-bedrock Solonetzic soil. Ratings for the 25-cm subsoil treatment were also comparable with the local Chernozemic soil, but better than the fine till Solonetzic soil. This study demonstrates that a minimum of 25 cm subsoil and 15 cm topsoil are required for mitigating salinity and sodicity in these reconstructed soils. The resampling in 2013 demonstrates that long-term monitoring is essential to obtain a better understanding of reclamation outcomes.

Digital Soil Mapping: Approaches to Integrate Sensing Techniques to the Prediction of Key Soil Properties

Knowledge about soil properties and their variation in space and time is a key challenge for understanding processes in the vadose zone. As we consider more complex models, applied to larger geographical regions, the demand for information on key soil parameters and thus input variables becomes