Subsoil Depth Research Articles

Vertical distribution of arsenic and bacterial communities in calcareous farmland amending by organic fertilizer and iron-oxidizing bacteria: Field experiment on concomitant remediation

The migration and transformation mechanisms of arsenic (As) in soil environments necessitate an understanding of its influencing processes. Here, we investigate the subsurface biogeochemical transformation of As and iron (Fe) through amended in the top 20 cm with iron oxidizing bacteria (FeOB) and organic fertilizer (OF). Our comprehensive 400-day field study, conducted in a calcareous soil profile sectioned into 20 cm increments, involved analysis by sequential extraction and assessment of microbial properties. The results reveal that the introduction of additional OF increased the release ratio of As/Fe from the non-specific adsorption fraction (136.47 %) at the subsoil depth (40–60 cm), underscoring the importance of sampling at various depths and time points to accurately elucidate the form, instability, and migration of As within the profile. Examination of bacterial interaction networks indicated a disrupted initial niche in the bottom layer, resulting in a novel cooperative symbiosis. While the addition of FeOB did not lead to the dominance of specific bacterial species, it did enhance the relative abundance of As-tolerant Acidobacteria and Gemmatimonadetes in both surface (39.2 % and 38.76 %) and deeper soils (44.29 % and 23.73 %) compared to the control. Consequently, the amendment of FeOB in conjunction with OF facilitated the formation of poorly amorphous Fe (hydr)oxides in the soil, achieved through abiotic and biotic sequestration processes. Throughout the long-term remediation process, the migration coefficient of bioavailable As within the soil profile decreased, indicating that these practices did not exacerbate As mobilization. This study carries significant implications for enhancing biogeochemical cycling in As-contaminated Sierozem soils and exploring potential bioremediation strategies. Environmental implicationThe long-term exposure of sewage irrigation has potential adverse effects on the local ecosystem, causing serious environmental problems. Microorganisms play a vital role in the migration and transformation of arsenic in calcareous soil in arid areas, which highlights the necessity of understanding its dynamics. The vertical distribution, microbial community and fate of arsenic in calcareous farmland soil profile in northwest China were studied through field experiments. The results of this work have certain significance for the remediation of arsenic-contaminated soil in arid areas, and provide new insights for the migration, transformation and remediation of arsenic in this kind of soil.

Large-scale Field Tests of the Performance of Geogrid-reinforced Piled Embankment over Soft Soil

When constructing superstructures on soft soils, geogrid-reinforced embankments and pile-supported embankments are used widely to improve the soft foundation and prevent issues including excessive settlements and large lateral displacements, so it is crucial to understand and evaluate their performance systematically. This study focuses on a case of piled embankments for a motor-racing circuit under construction in China. Two large-scale field tests of pile-supported embankments with and without reinforcement were carried out to investigate the effect of geosynthetic reinforcement on the improvement of embankments. During long-term monitoring, instruments in the test sites measured earth pressures, settlements, lateral displacements, and pore water pressures, and the performances of the reinforced or unreinforced embankments were examined. Test results from the two test sites under similar loading are compared, and it is concluded that the geosynthetic-reinforcement considerably influences the improvement of load transfer and diminishment of total and differential settlements. The lateral restraint provided by the geogrids also reduced the lateral soil displacement and the influence of subsoil depth. The smaller excessive pore water pressures in the site with reinforcement were associated with the enhanced load transfer due to the geogrids. This study provides an important reference for the design and construction of this circuit and other related projects.

Spatial patterns of vigor by stand density across species groups and its drivers in a pre-harvest ponderosa pine-dominated landscape in northern California

Information on spatial patterns of forest health and stand vigor in historical forests is quite limited, particularly for forests of North America, which have been subsequently harvested. We used forest inventory data from 1934, which pre-dated early 20th century timber harvest, to reconstruct patterns of vigor in overstory trees. Across 4,000 ha of ponderosa pine-dominated forests in the Blacks Mountain Experimental Forest (BMEF), we described the spatial patterns of pre-harvest (1934) forests using a stand density index (SDI) and accounting for different species and vigor classes. We then identified topo-edaphic variables associated with pre-harvest SDI. To do so, we first calculated SDI for two species groups: 1) ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.), and 2) incense-cedar (Calocedrus decurrens (Torr.) Florin) and white fir (Abies concolor (Grod. and Glend.)) as well as for seven vigor classes within these two groups. Second, using Moran’s I, we found four spatially aggregated clusters (Moran’s I = 0.35): 1) ponderosa pine-high vigor, 2) ponderosa pine-low vigor, 3) mixed species-high vigor, and 4) mixed species-low vigor. Most of the pre-harvest landscape consisted of high vigor ponderosa pine clusters with low SDI (relative density (RD) < 0.25). High elevation sections consisted of mixed species clusters of both high and low vigor with high SDI (RD > 0.35). Using classification and regression tree analysis, we identified elevation (m), surface-soil depth (cm), and sub-soil depth (cm) were related to the clusters. A multinominal logistic regression model (kappa = 0.44; classification accuracy = 64.4 %) identified surface stoniness, available water capacity at 150 cm depth and its interaction with sub-soil depth as important variables that were related to clusters. Within ponderosa pine-dominated forests, managers consider dense stands of low vigor trees to be at-risk of insect, disease, and fire. Thus, our results can be used by managers as representative baselines for characterizing (pre-harvest) stand conditions to guide management treatments to support high vigor and low density forest conditions.

Soil depth as a driver of microbial and carbon dynamics in a planted forest (Pinus radiata) pumice soil

Abstract. Forest soils are fundamental in regulating the global carbon (C) cycle; their capacity to accumulate large stores of C means they form a vital role in mitigating the effects of climate change. Understanding the processes that regulate forest soil C dynamics and stabilisation is important to maximise the capacity and longevity of C sequestration. Compared with surface soil layers, little is known about soil C dynamics in subsoil layers, sensu those below 30 cm depth. This knowledge gap creates large uncertainties when estimating the distribution of global soil C stocks and assessing the vulnerability of soil C reserves to climate change. This study aimed to dive deep into the subsoils of Puruki Experimental Forest (New Zealand) and characterise the changes in soil C dynamics and the soil microbiome down to 1 m soil depth. ITS and 16S rRNA sequencing and quantitative real-time PCR were used to measure changes in soil microbial diversity, composition, and abundance. Stable (δ13C) and radioactive (14C) C analyses were performed to assess depth-driven changes in the stability and age of soil C. Our research identified large declines in microbial diversity and abundance with soil depth, alongside significant structural shifts in community membership. Importantly, we conservatively estimate that more than 35 % of soil C stocks are present in subsoil layers below 30 cm. Although the age of soil C steadily increased with depth, reaching a mean radiocarbon age of 1571 yr BP (years before present) in the deepest soil layers, the stability of soil C varied between different subsoil depth increments. These research findings highlight the importance of quantifying subsoil C stocks for accurate C accounting. By performing a broad range of analytical measures, this research has comprehensively characterised the abiotic and biotic properties of a subsoil environment – a frequently understudied but significant component of forest ecosystems.

Vibration characteristics analysis and structure optimization of air-pressure subsoiler

Aiming at the problems of strong vibration, inconsistent subsoiling depth and high failure rate of air-pressure subsoiler, air-pressure subsoiler vibration characteristics was studied. In order to decrease the vibration, For the first time, the vibration characteristics of air-pressure subsoiler were obtained by modal analysis and vibration test. The vibration characteristics of the whole air-blown subsoiler are analyzed Through time domain analysis, it is found that the vibration acceleration of four deep loosening shovel is inconsistent. When the diesel engine is started, it is easy to cause inconsistent subsoiler depth. Then, by analyzing the vibration characteristics of the whole air-pressure subsoiler, it can be known that the external excitation source of the air-blown subsoiler is close to its own natural frequency. In order to avoid resonance caused by the vibration frequency of the external excitation source being close to the natural frequency of the air-pressure subsoiler, and to reduce the inconsistency of the subsoil depth, we optimize the design of air-pressure subsoiler. Instead of diesel engines, the steering gear box is connected with tractor power output shaft to provide power. The modal simulation of the optimized air-pressure subsoiler shows that the first-order natural frequency is obviously improved and the external excitation frequency is successfully avoided. It not only avoids resonance, reduces the damage of resonance components, but improves the service life of the subsoiler, greatly improves the structural reliability of the air-pressure subsoiler, at the same time, removes the main external excitation source, which greatly reduces the vibration in actual production and the inconsistency of subsoiling, which is of great significance in actual production. It provides a reference for the research of vibration characteristics, resonance avoidance and structure optimization of agricultural equipment.

Evaluation of soil arching effect due to partially mobilized shear stress in piled and geosynthetic-reinforced embankment

In piled and geosynthetic-reinforced (PGR) embankment, the arching behavior determines the overburden load on piles and subsoils. Placement of geosynthetic is effective in reducing the relative displacement between pile and subsoil. When the mobilized shear stress is less than the shear strength, partially developed arching will occur. Consequently, existing analytical methods, adopting the ultimate shear strength failure criterion, need to be improved. This study developed a simplified 2D analytical method, which is based on the developing arching effect, to evaluate the load redistribution of the PGR embankment. Then, the influences of embankment height and internal friction angle, subsoil depth, ratio of pile cap width to pile clear spacing (RPC) and geosynthetic tensile stiffness on the critical height ratio, stress concentration ratio, soil arching ratio, geosynthetic tension and axial strain were investigated. This study suggests that a RPC of 1:1.0 and a one-way of single-layer geosynthetic tensile stiffness of 2000 kN/m should be considered as the sensitivity thresholds for the PGR embankment.

Soil erosion affects variations of soil organic carbon and soil respiration along a slope in Northeast China

BackgroundAlthough soil erosion plays a key role in the carbon cycle, a holistic and mechanistic understanding of the soil erosion process within the cycle is still lacking. The aim of this study was therefore to improve our mechanistic understanding of soil organic carbon (SOC) and soil respiration dynamics through an experiment conducted in an eroding black soil farmland landscape in Northeast China.ResultsThe depositional profiles store 5.9 times more SOC than the eroding profiles and 3.3 times more SOC than the non-eroding profiles. A linear correlation between the SOC and 137Cs (Caesium-137) was observed in our study, suggesting that the SOC decreased with increased soil erosion. Furthermore, the fractions of intermediate C and the microaggregate C were lowest at the eroding position and highest at the depositional position. In the depositional topsoil, the input of labile materials plays a promotional role in soil respiration. Conversely, in the subsoil (i.e., below 10 cm), the potential mineralization rates were lowest at the depositional position—due to effective stabilization by physical protection within soil microaggregates. The field results of soil surface respiration also suggest that the depositional topsoil SOC is prone to be mineralized and that SOC at this depositional context is stabilized at subsoil depth. In addition, the high water contents at the depositional position can limit the decomposition rates and stabilize the SOC at the same time.ConclusionsThe findings from this study support that a majority of the SOC at footslope is stored within most of the soil profile (i.e., below 10 cm) and submitted to long-term stabilization, and meanwhile support that the depositional profile emits more CO2 than the summit due to its high amount and quality of SOC.

Soil Quality Analysis for Sustainability of Forest Ecosystem: The Case of Chilimo-Gaji Forest, West Shewa Zone, Ethiopia

The study was conducted to assess the soil quality with respect to the sustainability of Chilimo-Gaji Forest ecosystem using selected soils physicochemical parameters. Soil samples were taken through random sampling from the natural forest land under three different forest user groups (FUGs) in order to determine selected soils physicochemical properties. The result of the present study indicated that total N, available P and K, and % C were higher on the surface soil (0-20cm) than in the subsoil (20-30cm) depth indicating more nutrients are concentrated in the surface soil. The result of the study also revealed that presence of low bulk density ranges from 0.4 to 1.029 and high moisture content of soil ranging 4.89%-7.60%. The result also indicated that there is a higher per cent of carbon and organic matter across the three FUGs with Galessa recording the highest % carbon (7.69) and organic matter (13.25), followed by Gaji and Chilimo FUGs. The study also revealed that forest soil of the study area was very fertile and sustainable as the parameters analyzed indicating the forest ecosystem in the study area is sustainably managed under the new paradigm of participatory forest management. Scaling up participatory forest management to other protected forests in Ethiopia is crucial and plays a key role in the sustainability of healthy forest ecosystem. Keywords : Ethiopia; Forest user groups; physicochemical parameters; Soil organic carbon; Soil quality DOI : 10.7176/JEES/9-3-01 Publication date :March 31 st 2019

A mixed model for landscape soil organic carbon prediction across continuous profile depth in the mountainous subtropics

Due to the spatial variability of soil resources in rapidly changing landscapes, such as rubber expansion areas in mountainous South East Asia, landscape based soil organic carbon (SOC) stock assessments need new approaches to obtain cost effective high-resolution soil maps. 3D modelling presents the opportunity to model changes of soil properties with soil depth and in space in one single model. While most 3D models make use of spatial autocorrelation to create soil maps, it might be feasible for upscaling to neglect the spatial autocorrelation and only model autocorrelation within the soil profiles. We propose a “mixed model over continuous depth” (MMCD), which uses a linear and quadratic term to model changes of soil properties with depth and predicts the spatial distribution of soil properties at the landscape level. As the study area of 43 km2 in South West China was subject to multiple constraints such as sparse road networks, steep terrain, and poor infrastructure, we applied the cost-constrained conditioned Latin hypercube sampling (CCLHS) scheme for soil sampling at 120 locations to a depth of 1 m. The MMCD provides information on the most important drivers of selected soil properties, and their relative importance. In this study, SOC was strongly linked to an interaction of elevation with mean horizon depth (p < 0.001) and to the land use type (p < 0.001). An iterative leave-one-third-out evaluation was performed to compare the MMCD to several established 2D and 3D mapping approaches. The MMCD proofed to be as powerful as these established techniques, with an overall modelling efficiency (EF) of 0.72. All tested models had a strong decrease of accuracy with depth, from an EF of about 0.8 in the topsoil to 0.2 at 0.8 to 1 m subsoil depth. The MMCD was further used to model highly unbalanced SOC density data with 120 independent topsoil observations and only 11 locations with subsoil observations (EF of 0.75), where the computed prediction intervals (95%) accurately covered the range of legacy measurements. Our approach allowed upscaling of SOC density predictions to the surrounding larger nature reserve of 270 km2. The resulting MMCD and 3D maps revealed that on average, 15 and 10% of SOC stocks are expected in the 0.6 to 0.8 m and 0.8 to 1 m soil depth intervals, respectively. The combination of CCLHS and MMCD is particularly suitable for mountainous subtropical areas with poor road networks. However, this approach requires a strong relationship of the soil property of interest with explanatory environmental covariates, as it does not consider spatial autocorrelation for soil mapping. The advantage of this restriction is that it is easy to apply to highly unbalanced datasets and easy to upscale, given that the environmental covariates in the surrounding area are similar to the calibration area.

Modelling Laminated Orthotropic Plate-Foundation Interaction Subjected to Moving Load Using Vlasov Model

In this study, dynamic behavior of laminated orthotropic plates on elastic foundation is investigated adapting the three parameter subsoil model. Analysis of the system is performed by using SAP2000 combining with MATLAB code for calculation of soil parameters of modified Vlasov model. A computing tool is coded in MATLAB for the purpose allowing data exchange simultaneously between SAP2000 and MATLAB via Open Application Programming Interface (OAPI) feature. The consistency of the proposed model is shown comparatively with a numerical example taken from the literature. Later, the effects of lamination scheme, various lamination angles, lamination number, subsoil depth, elasticity modulus of subsoil, plate thickness and velocity of moving load on the behavior of laminated orthotropic plates on elastic foundation are investigated. It can be concluded that it is really convenient to use OAPI feature of SAP2000 to model this complex behavior of laminated orthotropic plates on elastic soil under moving load.

Controlling factors for the stability of subsoil carbon in a Dystric Cambisol

Subsoils store >50 % of the total global soil organic carbon (SOC), and low SOC content and high mean residence times indicate that subsoils have the potential to sequester additional C on the long-term. Nevertheless, the mechanisms controlling the turnover of SOC in subsoils are poorly understood. The aim of this study was to assess the impact of temperature and substrate limitation on subsoil SOC turnover and evaluate the stability of additional C inputs in subsoils.In a 63-day microcosm incubation experiment, CO2 production of undisturbed soil samples from topsoil and two subsoil depth increments was measured at two different temperatures (10°C and 20°C). Additionally, 13C labeled root litter was added to the different samples and measurements of the isotopic signature of the respired CO2 allowed a differentiation between SOC mineralization and root mineralization. The CO2 production per unit soil mass was lower in deep subsoil than in the topsoil, but the CO2 production per unit SOC (specific mineralization) was three times higher in the deepest subsoil than in topsoil. This depth gradient of specific mineralization in undisturbed samples indicates that deep subsoil contained relatively more labile SOC than the topsoil. The temperature sensitivity of SOC mineralization expressed as Q10-q, decreased from around 3 to around 1 with increasing soil depth. In contrast, the mineralization of the added root material was solely determined by the recalcitrance of the added roots as indicated by a similar Q10-q through all three soil depths.Contrary to the SOC mineralization of undisturbed samples, significantly more added root litter was mineralized in the samples from the upper horizons than in the deepest subsoil samples, revealing a non-linear relationship between mineralization of added C and the SOC content. Thus, the distance between substrate units, as indicated by the SOC content, may be key factor for subsoil SOC dynamics. Moreover, root addition caused no positive priming effects in subsoil horizons indicating that enhanced C inputs to the subsoil can increase the SOC content and tap the unused C storage potential of subsoils.

DYNAMIC RESPONSE OF THICK PLATES ON TWO PARAMETER ELASTIC FOUNDATION UNDER TIME VARIABLE LOADING

In this paper, behavior of foundation plates with transverse shear deformation under time variable loading is presented using modified Vlasov foundation model. Finite element formulation of thick plates on elastic foundation is derived by using an 8-noded finite element based on Mindlin plate theory. Selective reduced integration technique is used to avoid shear locking problem which arises when smaller plate thickness is considered for the evaluation of the stiffness matrices. After comparisons are made with the results given in the literature, the effects of the ratio of plate thickness to shorter span of the plate, aspect ratio, subsoil depth, loaded area, time variable loading type and pulse duration of impulsive load on its responses are analyzed. The results demonstrate that these parameters have significant influence on the dynamic behavior of the plate on elastic foundation

Implementation of a Soil Water Extraction Model on a Spatial Domain Using Field Capacity and Apparent Electrical Conductivity Relationships

<abstract><title><italic>Abstract.</italic></title> Relationships were developed between apparent electrical conductivity (EC_a) measured using a Veris 3100 conductivity instrument (Veris Technologies, Inc., Salina, Kans.) and soil hydraulic parameters [field capacity (FC) and permanent wilting point (PWP)] for use in a soil water extraction model to estimate spatial and temporal changes in maize (Zea mays L.) soil water extraction and plant-available water (PAW) at the South Central Agricultural Laboratory near Clay Center, Nebraska, in 2012. Linear relationships were observed between soil hydraulic parameters and EC_a for the top 0.30 m depth, and curvilinear relationships were observed for the sub-layer (0.30-0.90 m). Stronger relationships were observed for the top 0.30 m depth, with R² and RMSD of 0.68 and 0.008 m³ m^-3 for FC and 0.83 and 0.008 m³ m^-3 for PWP, respectively, than for the 0.30 to 0.90 m depth, with R² and RMSD of 0.35 and 0.008 m³ m^-3 for FC and 0.39 and 0.007 m³ m^-3 for PWP, respectively. Spatial and temporal variability in soil water extraction was observed in the 0-0.30 m, 0.30-0.60 m, and 0.60-0.90 m soil depths as well as PAW in the 0.90 m soil profile using the FC vs. EC_a regressions in the soil water extraction model. Irrigation treatment differences were apparent, with less soil water extraction in the 0.30-0.90 m soil layer under rainfed than irrigated conditions. The soil water extraction model using the developed FC vs. Veris EC_a regressions performed satisfactorily compared to soil water balance determined seasonal profile (0-0.90 m) actual crop evapotranspiration (ET_a), with a resulting R² and RMSD of 0.72 and 27 mm, respectively. Further research is needed to investigate different EC_a sensors as well as different methods for developing relationships between soil hydraulic parameters and EC_a, which can include incorporating spatial variability in topsoil and subsoil depth thicknesses prior to regression analysis. The research findings reported here should lead to additional analyses and research for using EC_a as an indirect estimator for soil hydraulic parameters for use in estimating soil water extraction and PAW.

Dynamic Analysis of Thick Plates Including Deep Beams on Elastic Foundations Using Modified Vlasov Model

Dynamic analysis of foundation plate-beam systems with transverse shear deformation is presented using modified Vlasov foundation model. Finite element formulation of the problem is derived by using an 8-node (PBQ8) finite element based on Mindlin plate theory for the plate and a 2-node Hughes element based on Timoshenko beam theory for the beam. Selective reduced integration technique is used to avoid shear locking problem for the evaluation of the stiffness matrices for both the elements. The effect of beam thickness, the aspect ratio of the plate and subsoil depth on the response of plate-beam-soil system is analyzed. Numerical examples show that the displacement, bending moments and shear forces are changed significantly by adding the beams.

Dynamic Analysis of Thick Plates Including Deep Beams on Elastic Foundations Using Modified Vlasov Model

Dynamic analysis of foundation plate-beam systems with transverse shear deformation is presented using modified Vlasov foundation model. Finite element formulation of the problem is derived by using an 8-node (PBQ8) finite element based on Mindlin plate theory for the plate and a 2-node Hughes element based on Timoshenko beam theory for the beam. Selective reduced integration technique is used to avoid shear locking problem for the evaluation of the stiffness matrices for both the elements. The effect of beam thickness, the aspect ratio of the plate and subsoil depth on the response of plate-beam-soil system is analyzed. Numerical examples show that the displacement, bending moments and shear forces are changed significantly by adding the beams.

A parametric study for thick plates resting on elastic foundation with variable soil depth

The soil depth is generally considered to be constant for the analysis of plates resting on elastic foundation in the literature. However, it is most reasonable to have a variable subsoil depth as the plate dimensions get larger. In present study, linearly varying subsoil depth is considered as well as constant, linear and quadratic variation of modulus of elasticity with subsoil depth. Also, a parametric study is performed to demonstrate the behavior of thick plates on elastic foundations with variable soil depth. Modified Vlasov Model is used for the analysis of the plate foundation system, and 8-noded Mindlin plate element incorporating shear strain throughout plate thickness is used for the finite element model. Numerical examples are obtained from the literature to compare results and to show the influence of variable soil stratum depth on the behavior of plates. Displacements, bending moments, and shear forces are presented in tabular and graphical formats. As far as results are compared, it can be concluded that variable soil depth significantly affects the variation of the displacements and therefore the internal forces of the plate while keeping it constant ends up with unrealistic results.

Quantification and Source Identification of Polycyclic Aromatic Hydrocarbons in Core Sediments from Sundarban Mangrove Wetland, India

The distribution and potential sources of 16 polycyclic aromatic hydrocarbons (PAHs) in sediment cores (<63 microm particle size) of the Sundarban mangrove wetland, northeastern coast of Bay of Bengal (India), were investigated by gas chromatography coupled to mass spectrometry. The total concentrations of 16 PAHs ( summation operator(16)PAHs) ranged from 132 to 2938 ng/g, with a mean of 634 ng/g, and the sum of 10 out of 16 priority PAHs ( summation operator(10)PAH) varied from 123 to 2441 ng/g, with a mean of 555 ng/g, and the 5 carcinogenic PAHs (benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, and dibenz[a,h]anthracene) accounted for 68-73% of the priority PAHs. Maximum concentrations of the sediment core were obtained at subsoil depth of 12-16 cm. The prevalence of four to six aromatic ring PAHs and cross-plots of specific isomer ratios such as phenanthrene/anthracene, fluoranthene/pyrene, and methylphenanthrenes/phenanthrene suggested the predominance of wood and coal combustion sources, the atmospheric deposition, and surface runoff to be the major transport pathways. A good correlation existed between the benzo[a]pyrene level and the total PAH concentrations, making this compound a potential molecular marker for PAH pollution. Total TEQ (S) (carc) values calculated for samples varied from 6.95 ng/g TEQ (S) (carc) to 119 ng/g TEQ (S) (carc) , with an average of 59 ng/g dry weight TEQ (S) (carc) . The baseline data can be used for regular monitoring, considering the industrial and agricultural growth around this coastal environment.

Application of the Modified Vlasov Model to the Free Vibration Analysis of Thick Plates Resting on Elastic Foundations

The Modified Vlasov Model is applied to the free vibration analysis of thick plates resting on elastic foundations. The effects of the subsoil depth, plate dimensions and their ratio, the value of the vertical deformation parameter within the subsoil on the frequency parameters of plates on elastic foundations are investigated. A four-noded, twelve degrees of freedom quadrilateral finite element (PBQ4) is used for plate bending analysis based on Mindlin plate theory which is effectively applied to the analysis of thin and thick plates when selective reduced integration technique is used. The first ten natural frequency parameters are presented in tabular and graphical forms to show the effects of the parameters considered in the study. It is concluded that the effect of the subsoil depth on the frequency parameters of the plates on elastic foundation is generally larger than that of the other parameters considered in the study.

Application of the Modified Vlasov Model to the Free Vibration Analysis of Thick Plates Resting on Elastic Foundations

The Modified Vlasov Model is applied to the free vibration analysis of thick plates resting on elastic foundations. The effects of the subsoil depth, plate dimensions and their ratio, the value of the vertical deformation parameter within the subsoil on the frequency parameters of plates on elastic foundations are investigated. A four-noded, twelve degrees of freedom quadrilateral finite element (PBQ4) is used for plate bending analysis based on Mindlin plate theory which is effectively applied to the analysis of thin and thick plates when selective reduced integration technique is used. The first ten natural frequency parameters are presented in tabular and graphical forms to show the effects of the parameters considered in the study. It is concluded that the effect of the subsoil depth on the frequency parameters of the plates on elastic foundation is generally larger than that of the other parameters considered in the study.

English

Alluvial soils in the Upper Coastal Plain soil resource area in the state of Mississippi occur in narrow floodplains. Prime farmland soil was collected in 4 foot increments to a depth of 16 ft. Soil collected from Kirkville and Oaklimiter sites was placed in 5 gallon pots in the greenhouse with five replications. Soil fertility (P, K, Ca, Mg and CEC) increased (P<0.05) as depth increased indicating that deep alluvial subsoils have a greater productive capacity. Soil pH was acidic (4.5 to 5.2) and tended to be similar with depth from the Oaklimiter site, but decreased curvilinearly to a depth of 12 ft from the Kirkville site. Pearl millet was planted in the summers of 2005 and 2006 followed by annual ryegrass in the winters of 2006 and 2007. Soil was remixed and limed with 2 tons dololmite per acre after year one. Pearl millet growth in 2005 increased linearly (P < 0.05) as subsoil depth increased at both sites. Manganese (Mn) levels in pearl millet increased linearly as subsoil depth increased from both soils to greater than 2000 ppm but was apparently not toxic to pearl millet. Ryegrass growth increased curvilinearly to a depth of 12 ft from Oaklimiter subsoils but decreased linearly as depth increased from Kirkville due to elevated Mn levels in ryegrass. Mn levels above 500 ppm were toxic to ryegrass. Liming increased pH to as high as 7.6 in soil from Kirkville and to 7.2 from Oaklimiter and had a neutral impact on pearl millet growth. Ryegrass growth following lime was greater as depth increased from Kirkville subsoils and was similar in Oaklimiter. Mn levels in both pearl millet and ryegrass were reduced to non-toxic levels following lime indicating that lime ameliorated subsoils would be suitable as topsoil.