Undisturbed Soil Samples Research Articles

Effects of soil physicochemical properties on sweet corn quality in western Thailand

Thailand exports the greatest amount of sweet corn globally; however, its value per unit is low. Soil property knowledge can help to produce sweet corn with the best nutrition and taste qualities that could improve its value. This study investigated the association between soil properties and sweet corn qualitative attributes in western Thailand. Soils and sweet corn samples were taken from 8 soil series at 47 sites in the dry season. Disturbed and undisturbed soil samples were collected and analyzed using physicochemical methods. Five selected sweet corn samples were determined for pod weight without husk, ß carotene concentration, and total soluble solids. Principal component analysis with varimax rotation was used to determine the most important variables and patterns among the physicochemical properties. Three components with eigenvalues greater than 1 explained more than 66% of the total variance. The linear mixed model showed that ß carotene concentration and total soluble solids were linearly correlated with only one principal component factor (R2 = 56.6 and 64.6%, respectively), whereas there were no significant associations for total yield nor pod weight without husk with any of the principal component factors. Cluster analysis indicated that most of the soil sites were Oxyaquic Haplustalfs, Aeric Endoaqualfs, and Typic Haplustalfs with moderately well drained, and producing high-quality sweet corn. These findings should inform land use planning to improve the quality of sweet corn plantations in the dry season in western Thailand.

Agregação do solo e carbono orgânico sob diferentes sistemas de manejos no cerrado mato-grossense

ABSTRACT Soil organic matter is one of the most important indicators of the quality and sustainability of native and cultivated ecosystems, as it influences the chemical and physical properties of the soil, such as cation exchange capacity, aggregation, water retention, and supply of nutrients to plants. This study evaluated the physical properties and distribution of organic carbon in soil aggregates under different management practices. Disturbed and undisturbed soil samples were collected in the 0.0-0.1 m, 0.1-0.2 m, and 0.2-0.3 m layers under conservationist (rainfed and irrigated) and conventional (rainfed) management. The chemical properties and particle size, soil density, and organic carbon content in macro and microaggregates were assessed for the three management types. For conservationist management, in addition to these analyses, the weighted mean diameter, geometric mean diameter, aggregate stability index, and total soil porosity were determined. The data were analyzed using the Kruskal-Wallis test and the t-test, as there was no experimental design, and some of the data did not meet the normality test (Shapiro-Wilk). Soil density and total porosity did not differ for conservationist management (rainfed and irrigated). The irrigated conservationist management exhibited aggregates with larger weighted and geometric mean diameters and a higher aggregate stability index. Conservationist management (rainfed and irrigated) showed higher organic carbon contents in macro and microaggregates.

Effectiveness of liming and subsoiling to ameliorate a compacted arable clay subsoil

ABSTRACT The effectiveness of mechanical subsoiling for alleviating subsoil compaction is controversially discussed, particularly due to the sensitivity of mechanically loosened soils towards re-compaction. In order to improve the alleviation potential by subsoiling it was hypothesized that the loss of soil stability by mechanical subsoiling of compacted soils can be reduced by top and subsoil liming. The primary objective was to evaluate whether (a) mechanical subsoiling (to a depth of 35 cm with a subsoiler or a plough with a pan-breaker) could alleviate compaction in a clayey Stagnosol and (b) whether liming could stabilize soil structure to minimize re-compaction. Undisturbed soil samples were collected to assess physical properties in both "compacted", "subsoiled", and "limed", as well as in untreated plots. The Compaction Verification Tool (CVT) identified potentially harmful soil compaction in the subsoil. The results showed that wheeling increased the extent of harmful subsoil compaction (from 8% to 33%) in the first year, which was accompanied with a reduction in crop yields. Subsoiling with a pan-breaker combined with high liming intensity improved soil physical properties and yields and may have mitigated re-compaction in the loosened subsoil. Nevertheless, it is expected to be not economically viable on the studied clay soil.

Study of the Shear Strength Model of Unsaturated Soil in the Benggang Area of Southern China

Benggangs are a unique type of soil erosion commonly found in southern China, with the gully wall being the most dynamic component of the Benggang system and is crucial for assessing its overall progression. The unsaturated shear strength of soil in Benggang areas is a key factor influencing the stability of the gully wall. However, quantitative analyses of the unsaturated shear strength in the gully walls of Benggangs remain limited. In this study, the soil–water characteristic curves (SWCC) and shear strengths of undisturbed soil samples from four different soil layers in the gully wall of Benggang were measured using a pressure membrane meter and a quadruple direct shear apparatus. The results revealed that the water holding capacity of the soil decreased gradually with increasing matrix suction, and the order of the water holding capacity was the sandy soil layer > transition layer > laterite layer > clastic layer. With an increasing soil water content (SWC), the shear strength, cohesion (c), and internal friction angle (φ) of the four soil layers decreased significantly, and the φ showed a power function decreasing curve (p < 0.05), whereas c in the laterite layer and transition layer exhibited a power function decreasing curve (p < 0.01). The c of the sandy soil layer and clastic layer decreased linearly and logarithmically (p < 0.01) with increasing SWC, respectively. The unsaturated shear strength model for the four soil layers was developed based on the Vanapalli model. The root mean square error (RMSE) of the simulated and measured values was less than 29.349, while the Nash–Sutcliffe efficiency (NSE) and R2 values were greater than 0.638 and 0.788, respectively. The model can be used to analyze and predict the unsaturated shear strength in different layers of Benggang gully walls, providing a theoretical foundation for studying the erosion mechanisms of Benggangs.

Soil Nailing Application for Railways Track Safety on Slope Area

Abstract Railways track at KM 25+100 - KM 25+200 from Jember to Banyuwangi is constructed next to slope area with inclination angle 69°. As railways track mapping report, this area is categorized as a high-potential landslide area that can harm train travel. By using soil nailing method with threaded steel and embedded into the soil for grouting, slope stabilization be improved. Undisturbed soil sampling on 1.5 m depth was carried out and tested to determine soil parameters. Based on the USCS soil classification, the soil at the site is an organic clay with high plasticity. Soil parameters are used to calculate the slope safety factor before and after soil nailing application with the best reinforcement design. By utilizing Plaxis 2D CE V20 Bentley software and manual calculations with the bishop method for comparison, the potential landslide before reinforcement resulted a safety factor value of 1.198 by using Plaxis and 0.97 by calculated manually. Some soil nailing reinforcement planning design is obtained and resulted that soil nailing design with diameter 29 mm, slope angle application on 20° with distance between nail bar at 1m, and nail length 9m have best safety factor value at 1.548. With the best design and >1.5 SF value, the soil nailing design is safe against landslides risk.

Cropping and soil management systems effects on soil organic matter fractions in diversified agricultural fields in the Cerrado

ABSTRACT Soil organic matter (SOM) dynamics can be significantly influenced by various cultivation practices, particularly under environmental and edaphic conditions that enhance and accelerate the transformations of organic materials such as straw, root biomass, and organic fertilizers. This study aimed to evaluate the impact of different cultivation and soil management systems on SOM fractions in agricultural areas of the Cerrado Goiano region. The research was conducted across three areas with diverse production systems: 1) BV area, including soybean monoculture (SM01), integrated crop-livestock-forest (ICLF01), pasture (PA01), and Cerrado vegetation (NV01); 2) ML area, featured soybean-corn monoculture succession (SMS02), agroforestry (AF02), pasture (PA02), and native Cerrado vegetation (NV02); and 3) IF area, comprised soybean-corn succession (SMS03), integrated livestock-forest (ILF03), pasture (PA03), and native Cerrado vegetation (NV03). Disturbed and undisturbed soil samples were collected from two layers: 0.00-0.05 and 0.05-0.10 m. Samples were analyzed for total organic carbon, carbon storage, and SOM physical (granulometric and densimetric) and chemical (fulvic acid, humic acid, and humin) fractionations of soil organic matter (SOM). Additionally, water-floatable light organic matter (LOM), the carbon management index, and its components were determined. Soil organic matter fractions were similarly influenced by the characteristics of cultivation and management systems. However, there were more pronounced differences between systems in the BV area compared to the ML and IF areas. Among the parameters studied, LOM proved to be the most efficient and effective in distinguishing SOM input across different cultivation and soil management systems, particularly in pasture systems.

Nitrogen fertilization allows grazing intensification without degrading soil physical quality

Increasing pasture biomass production through nitrogen fertilization enables greater stocking rate and grazing intensification in pastoral livestock production systems. However, grazing intensification can compromise the soil physical quality if stocking rates exceed the soil bearing capacity to support treading. The objective was to quantify the impact of long-term (12 years) intensified grazing of Panicum maximum Jacq. cv. IPR-86 Milênio on the physical quality of a sandy soil (Luvisol Ferric soil) under subtropical climate. The 12-year field experiment was arranged in a completely randomized split-plot design with four replicates. The approach for moving the animals in and out of the paddocks varied across harvests. In the first five harvests, the period of use and rest was fixed with each paddock being occupied for 5 days followed by 35 days of rest (i.e., 40-day grazing cycle). In the subsequent harvests, the timing for moving animals in and out of each paddock was based on pasture height, with entry set at 0.90 m and exit at 0.40 m. Grazing intensification levels (IL) consisted of different animal stocking rates, grazing cycles, and forage biomass, which varied depending on the nitrogen application doses: 0 (IL-0), 150 (IL-150), 300 (IL-300), and 450 (IL-450) kg of N ha−1 year−1. Undisturbed soil samples were taken at four depths (0–0.10, 0.10–0.20, 0.20–0.30, and 0.30–0.40 m) in two sampling positions (under plants vs. between plants) and used to measure several soil physical properties (e.g., bulk density, macroporosity, mesoporosity, microporosity, water and air storage capacity, available water, pore size distribution, and water retention curve). The impact of grazing intensification on soil physical quality was minor, occurring only between plants and at the 0–0.10 m depth, where an increase in soil bulk density and a decrease in microporosity was observed. Grazing intensification also increased the water retention capacity between plants. Regardless of the sampling position and the grazing IL, water and air storage capacity was not detrimental to plant development. Overall, the increased animal stocking rate resulting from the greater pasture biomass production due to improved nitrogen fertilization does not degrade soil physical quality.

Validation of Double Constant and Falling Head Permeameter for Determination of Hydraulic Conductivity of Soils in the Laboratory

The objective of this research was to validate alternative equipment for determining the hydraulic conductivity of saturated soil (Ksat) in laboratory settings. The aim was to develop a single piece of equipment that could be used to carry out tests using both the constant-head permeameter (CHP) and the falling-head permeameter (FHP) methods with minimal disturbance to the samples. To this end, undisturbed soil samples were collected (in volumetric cylinders with 100 and 250 cm3) from three soil profiles with different textures to evaluate the sensitivity of the double permeameter (DP) in determining Ksat, considering the method, the sample size, and the textural class of the soils. To assess the efficacy of the DP in estimating Ksat, the coefficient of variation (CV) was determined for the two methods (CHP and FHP), the sample size (100 and 250 cm3), and the applied hydraulic head (cwc) (constant: 1.5 and 2.5 cwc; falling: Δhi, upper limit, h1 = 67.6 and h2 = 57.6 cwc; Δhii, medium limit, h1 = 49.3 and h2 = 39.3 cwc; and Δhiii, lower limit, h1 = 31.3 and h2 = 21.3 cwc). The results indicate that the DP may be employed as an alternative permeameter for Ksat tests employing the CHP and FHP methods. The most favorable statistical coefficients were observed in tests conducted with samples of a sandy texture (Profile 3, Ap horizon), particularly those with a larger volume (250 cm3), for both the CHP and FHP methods, irrespective of the applied hydraulic head. The equipment can be utilized within the full range of methodological limits employed in this study, and the appropriate limit must be selected according to the physical properties of the soil to be employed in the tests.

Effects of different land-use types on soil detachment capacity in loess areas

Against the background of similar geomorphological characteristics and environmental temperatures, land-use types alter the soil detachment capacity (Dc) by changing soil properties and root traits. However, there is a lack of in-depth discussion regarding the response of Dc to land-use types in loess areas. The purpose of this study was to quantify the influences of different land-use types in loess areas on Dc, soil erodibility (kr), and critical shear stress (τc) and explore the key factors affecting Dc under runoff erosion based on the links between root traits and soil properties, and combined with PLS-SEM algorithm, a meta-model of Dc influence mechanism was established. Two hundred and seventy undisturbed soil samples were collected from six different land-use types and scoured under nine specific combinations of flow rate and slope (flow rate: 0.167–0.5 L s−1, slope: 10.5–20.8 %). The results showed that with the change in land-use type, Dc changed considerably. The average Dc of the shrubland was only 1/22 of that of the cropland. The change trend of kr was consistent with that of Dc, while the change trend of τc had no obvious regularity. The relationships between the root density parameters and Dc were simulated using the exponential function and Hill curve, respectively, and the predictive effect of the Hill curve was better than that of the exponential function. Compared with the other comprehensive hydraulic parameters, shear stress (τ) was Dc’s most effective predictive factor. Correlation and path analyses revealed that soil organic matter (SOM) and root length density (RLD) were the best indicators of Dc. Furthermore, a dimensionless Dc prediction model suitable for different land-use types was established based on τ, SOM, and RLD, and the model exhibited a high accuracy (R2 = 0.955, NSE = 0.911).

Exploring the Soil Structure Analysis of a Subtropical Watershed by Introducing a Blanket Physico‐Hydraulic Health Index

ABSTRACTMultiple disturbed and undisturbed soil samples were collected to assess the soil structure health in support of water use and management in a subtropical watershed, which is composed of shallow Entisols, near to Canguçu, RS state—Brazil. Various physico‐hydraulic properties related to soil structure, such as bulk density, total, micro and macroporosity, saturated hydraulic conductivity, organic carbon, soil water retention curve (SWRC), and the ranges of plant available water (PAWC) and drainable porosity (DP) were measured to be analyzed. The hydraulic‐energy indices of soil aeration and water retention were determined by integrating the areas under SWRC. Combining these properties with the contents of sand and clay, a unique blanket soil physico‐hydraulic health index (BSPHI) was formulated and applied to investigate the impact of land use and management on the soils of the Ellert Creek Watershed (ECW), thereby supporting soil physical health analysis and, consequently, the analysis of water and human health. The favorable outcomes found in the ECW soils under annual crops indicated good root aeration in the surface layer due to the balance between DP and PAWC. The BSPHI results showed that only about 19% of the areas exhibited unhealthy physical health. The soil structure in pasture areas of ECW was not significantly impacted by the extensive cattle grazing, whereas lands under native forest served as a control for the natural soil quality status. The BSPHI successfully captured small changes in soil structure, regardless of land use and management, highlighting its potential as a promising tool for evaluating soil health by assessing the soil physical quality.

Vegetation degradation reduces aggregate associated carbon by reducing both labile and stable carbon fraction in Northeast China

Vegetation changes can affect soil organic carbon (SOC) content and storage by altering the inputs of plant biomass and the catabolism and anabolism of soil microorganisms. However, influence of vegetation degradation on aggregate associated carbon fractions and the contribution of different aggregates to total SOC in bulk soil remains poorly understood. In this study, undisturbed soil samples were collected from three types of grassland in Songnen grassland: an undegraded grassland (LEY, Leymus chinensis), a moderately degraded grassland (CHL, Chloris virgata), and a severely degraded grassland (SUA, Suaeda heteroptera). Three soil aggregates including macroaggregate (> 0.25 mm), microaggregate (0.053–0.25 mm) and silt and clay fraction (< 0.053 mm) were separated using wet sieving. Contents of total SOC, soil labile and stable carbon in bulk soil and different soil aggregates were measured. Compared with LEY, the mean weight diameter and geometric mean diameter under the degraded vegetation communities reduced by 39.42 % and 28.47 %, respectively. The reduction in SOC contents in bulk soil, macroaggregate, microaggregate and silt and clay fraction resulting from vegetation degradation was 49.81 %, 26.00 %, 76.17 % and 43.65 %, respectively. Under the degraded vegetation communities, contents of soil labile and stable carbon in bulk soil (45.73 % and 52.61 %, respectively), macroaggregate (17.38 % and 31.61 %, respectively), microaggregate (77.83 % and 74.18 %, respectively), and silt and clay fraction (21.20 % and 53.45 %, respectively) were significantly lower than those under LEY. The contribution of macroaggregate, microaggregate and silt and clay fraction to total SOC was 13.27 %, 23.61 % and 63.12 %, respectively. The contribution of soil aggregates to total SOC following vegetation degradation reduced by 53.63 % for microaggregate, but increased by 47.10 % for silt and clay fraction. These findings collectively indicate that vegetation degradation reduces the aggregate associated carbon content by reducing both labile and stable carbon fraction in Songnen grassland, and sustainable vegetation restoration strategies are need to enhance soil carbon storage in Northeast China.

Prediction of resilient modulus with pre-post experimental data of undisturbed subgrade soils using machine learning algorithms

The resilient modulus (MR) of subgrade, which shows relationship between stress and unit deformation of a pavement systems under traffic loads, is a design parameter of the pavement structure. Although a cyclic triaxial test apparatus can be used to directly determine the MR of the subgrade in the laboratory, utilizing prediction models based on easily obtainable soil parameters, is a more efficient method when taking time and cost considerations into account. A comprehensive laboratory testing program is designed to create MR prediction models using machine learning (ML) algorithms. 70 undisturbed soil samples are subjected to MR tests, as well as physical and engineering soil properties tests (water content, field density, specific gravity, gradation, consistency limits, unconfined compressive strength, swell pressure, swell percentage). Soil samples are drilled from a highway that has been in operation for over five years.First, a linear model like MLR is used in the study. Next, nonlinear regression models like RF, GBM, LightGBM, CatBoost, and XGBoost algorithms are used. Research findings showed that nonlinear regression models outperformed linear regression models in predicting the MR (R2 > 0.85), with the XGBoost algorithm yielding the best accuracy (R2 = 0.90). Apart from the primary effects such as confining pressure (σ3) and deviatoric stress (σd), it was found that unconfined compressive strength (qu), natural water content (wn), and swelling percentage (SR) are significant parameters in the prediction of MR among all parameters.

Pore space memory of the Tlalpan pedosedimentary sequence as an indicator of paleopedogenesis

AbstractBackgroundImaging techniques of analysis in undisturbed soil samples are powerful tools for understanding soil properties and functioning. Although micromorphological analysis has always been applied for studying soil genesis, the modern 3D X‐ray Computed Tomography (CT) approach is mostly used in soil physical studies related to soil functioning and ecological services.AimIn this study, we interpret ancient soil formation of the Late Pleistocene pedosedimentary archive of the Tlalpan sequence in the State of Tlaxcala in Central Mexico, based on soil and sediment porosity distribution in 2D and 3D.MethodsIn order to interpret ancient soil formation based on the porosity distribution, we applied both micromorphological (2D) and CT (3D) analyses in undisturbed samples of each horizon of the Tlalpan sequence.ResultsOur micromorphological observations have shown that pore space arrangement is unique for each soil horizon and that it is predetermined by the dominant pedogenetical processes and their succession, such as bioturbation, clay illuviation, and vertic shrinking/swelling. Most of the channels formed by biogenic agents (roots and mesofauna) subsequently underwent shape deformations and/or refilling. The “accommodating planes” type of voids resulted from the development of features of vertic paleosols that, in some cases, erased the past pedogenic pore space organization. Although biogenic turbation, compaction, and clay illuviation mostly affected the macro‐ and mesopores, shrinking/swelling processes affected macro‐ and mesoporosity distribution. The process that was only reflected at the microporosity level is hydroconsolidation.ConclusionsDespite the common idea that textural pores are more resistant to changes compared to meso‐ and macropores, most of soil formation processes registered in the Tlalpan sequence, including anthropogenic impact, were identified in macro‐ and mesopore space. Moreover, the changes that were registered in pore space transformation by 2D and 3D methods of analysis in undisturbed samples are crucial for identifying the sequence of formation processes and, therefore, for paleopedological interpretation. This study shows that the CT is a useful tool to access the soil formation, and pore space memory studied both in 3D and 2D is an important proxy for paleopedological research.

Are bacterial communities and aggregation in fragile soils influenced by the management system?

Light-textured soils are widely distributed globally and, despite their limitations, have been integrated into agricultural production systems. This study aimed to assess how management systems—conventional tillage (CT) and no-till (NT)—affect aggregate formation pathways (physicogenic and biogenic) and bacterial communities. Two management systems (NT and CT) and three cover crops were evaluated: CJ: Crotalária (Crotalaria juncea (40 ​kg ​ha−1); M: Millet (Pennisetum glaucum - 60 ​kg ​ha−1); and C: Cocktail (Crotalária - Crotalaria juncea - 10 ​kg ​ha−1, Jack bean - Canavalia ensiformis - 75 ​kg ​ha−1, and Millet - Pennisetum glaucum - 30 ​kg ​ha−1). Undisturbed soil samples were collected from the crop row at a depth of 0.00–0.10 ​m. Aggregates with diameters between 9.7 and 8.0 ​mm were classified as biogenic or physicogenic. In addition to the chemical attributes of the aggregates, total organic carbon (TOC) and its fractions (mineral-associated organic carbon, MAOC; particulate organic carbon, POC; and free light fraction carbon, FLFC) were quantified. The structure and bacterial composition of the aggregates were also characterized. A higher proportion of biogenic aggregates (53–64%) was observed compared to physicogenic aggregates (36–47%). Cover crops exhibited significant differences in pH, calcium (Ca2+), base saturation, phosphorous (P), and percentage of base saturation. The management systems differed significantly for Ca2+ and P, with CT showing higher values than NT. The management system influenced organic matter accumulation and stabilization in the aggregates, with MAOC content being significantly lower in CT. POC and TOC were also significantly lower in physicogenic aggregates under CT. Bacterial community richness, diversity, and structure were significantly influenced by the management system, with greater richness and diversity in NT compared to CT. Network analysis revealed NT had more nodes and edges (65 and 406, respectively) than CT (52 and 357, respectively. Phyla abundance differed between the systems, with Firmicutes and Entotheonellaeota more abundant in CT, while WPS_2, GAL15, Bdellovibrionota, and Myxococcota were more abundant in NT. Despite the relatively short period of NT implementation (5 years), it had a positive effect on the bacterial community, which may subsequently influence nutrient and carbon content and their fractions in the aggregates.

A Review on Geotechnical Properties of Soil Profile

The geotechnical properties and litho-stratigraphic soil profile of soils in Ikole area of Ekiti State were investigated from the analysis of results of laboratory tests on disturbed and undisturbed soil and water samples obtained from 3 borings. The investigation revealed a subsurface stratification made up of reddish brown granitic clayey sand from existing ground level to a depth of 9m to 12.0m. This is underlain by a layer of mottled, brown, decomposed micaceous sand to a depth of 16.5m - 18m immediately after which are layers of mottled grey, decomposing quartzite sand to about 18.0m to 19.0m depth. This is further underlain by fragments of freshly weathered granitic rock to the termination depth of 19.5m. The consistency limits indicate LL of 44 – 58% and PL of 18 – 26% while the quick undrained triaxial tests indicate undrained cohesion within the range (128.4 - 157) kN/m2 and undrained angle of internal friction (15.0 - 20.0)0. Groundwater was encountered between 6.5m to 7.5m below the existing ground level during the course of soil exploration. The water in the area has pH values of 5.79 to 7.05, the chloride content values range between 12.0mg/l and 16.0mg/l while sulphate content varies from 6.12mg/l to 7.10mg/l.

Bio-fertilizer applications from poultry slaughterhouses in subtropical agriculture – Interactions between soil structure and nitrate dynamics

The No-till system and organic fertilization combined can be a potential strategy to avoid nutrient leaching, as the soil structure plays a crucial role in retaining them. In this study, we evaluated the influence of different rates of a bio-fertilizer made of industrial organic waste (IOW) from a poultry slaughterhouse on the percolation and stocks of nitrate in disturbed and undisturbed soil samples collected from a subtropical no-till field in southern Brazil. In an incubation experiment, we performed a percolation experiment using lysimeters and simulated rainfall for 180 days and evaluated the remaining soil nitrate stock after the incubation period. We set up a completely randomized experiment with three replicates using four IOW rates (equivalent to 0, 2, 4, and 8 Mg ha−1) and two sample types: disturbed and undisturbed soils. Using the bio-fertilizer increased nitrate mineralization from 0.77 to 1.55 kg ha−1 day−1. Overall, the IOW application increased the amount of percolated nitrate, significantly influenced by the simulated rainfall (p < 0.01). The amount of water flushed through the lysimeters was significantly higher for the disturbed soils (p < 0.05, LSD test), suggesting that the loosened structure promoted a higher water flux. No differences were observed between undisturbed and disturbed samples for nitrate percolation, implying that the amount of nitrate in the liquid soil phase may be a more critical factor in determining nitrate leaching than the water flux. The disturbed samples presented significantly higher nitrate percolation with increasing IOW rates, regardless of precipitation. Stocks in the 0–5 cm depth were 6.6 kg ha−1 higher for undisturbed samples (p < 0.05, LSD test). This result suggests preserving the soil structure can significantly increase the nitrate stocks upon IOW application.

Study of soil heterotrophic respiration as a function of soil moisture under different land covers

The relationship between soil heterotrophic respiration (Rh) and soil moisture has been often studied using disturbed soil samples and simple gravimetric and volumetric soil moisture indicators. The objective of this study was to investigate the relationship between Rh and soil moisture in terms of water-filled porosity (WFP), matric potential (Ψm), and relative soil gas diffusivity (Dp/Do) using undisturbed soil cores obtained under different land covers. Soil CO2 efflux, WFP, and Ψm were measured in undisturbed soil samples (250 cm3) collected in the 0–5 cm soil layer (without any vegetation or living roots) under laboratory conditions by combining a CO2 gas analyzer, a scale, and precision mini-tensiometers. For each site and land cover, we also measured soil chemical properties, soil physical properties, and soil microbial composition using phospholipid fatty acid analysis. Grassland soils had the largest total microbial biomass (6275 ng g−1), followed by soils from riparian (5327 ng g−1), and cropland (2745 ng g−1) sites. Bacteria were the dominant group representing 46% (SD = 5%) of the total microbial biomass across all sites and land covers. Maximum Rh was 1.88 (SD = 0.40) μmol CO2 m−2 s−1 in grassland, 1.64 (SD = 0.82) μmol CO2 m−2 s−1 in riparian, and 0.94 (SD = 0.56) μmol CO2 m−2 s−1 in cropland soils. Considering all land cover and soil types, our observations revealed that peak Rh occurred at mean WFP = 0.81 ,Ψm = −6 kPa, and Dp/Do = 0.003. Thus, we recommend avoiding the traditional field capacity definition of −33 kPa for representing peak microbial activity. Water-filled porosity was a more consistent predictor of Rh than Ψm or Dp/Do across soils with contrasting organic matter content, total microbial biomass, soil texture, and soil structure.

Background activity of naturally occurring and reference values of fallout radionuclides in soils of mountainous areas (Armenia)

ABSTRACT Complex mountainous relief and diverse geology that are common for the whole territory of Armenia are strong limiting factors for regional scale geochemical survey, for assessment of the geochemical background of naturally occurring radionuclides (226Ra, 232Th, 40K) and reference values of artificial 137Cs. Sampling transects spanned by altitude in mountain ridges and massifs, representing the main geological formations of the area, are informative enough for a pilot assessment of background and reference activity of radionuclides in soils. A total of 131 undisturbed soil samples were collected from 8 mountain ranges and massifs throughout Armenia. HPGe detector-based gamma spectrometry was used for the quantification of radionuclide activity concentrations. Geology and soil type were the main factors in the formation of radionuclide composition in the soil. The reasonably close estimates of naturally occurring radionuclide background activity were obtained from the application of ‘Median ± 2MAD’ and Tukey’s boxplot methods. The results yielded by both methods could be employed as a background, contingent upon the specific objectives being addressed. The distribution of 137Cs exhibits strong dependence on the altitude and therefore, its reference activity concentrations were estimated at distinct elevation intervals applying the ‘Median ± 2MAD’ method.

Enhancing Deep Excavation Optimization: Selection of an Appropriate Constitutive Model

To minimize the impact on nearby structures during deep excavations, choosing an appropriate soil constitutive model for analysis holds significant importance. This study aims to conduct a comparative analysis of various constitutive soil models—namely, the Mohr–Coulomb (MC) model, the hardening soil (HS) model, the hardening soil small strain (HSS) model, and the soft soil (SS) model—to identify the most suitable model for the lacustrine deposit. To implement these models, the soil’s index properties and mechanical behavior were evaluated from undisturbed soil samples. The numerical simulation and verification of these properties were carried out by comparing the laboratory test results with the outcome of the finite element method; the most suitable constitutive soil model for the soil was identified as the HSS model. Upon analyzing the wall deflection and ground settlement profiles obtained from respective constitutive models, it was observed that the HS and HSS models exhibit similar characteristics and are well-suited for analyzing typical lacustrine soil. In contrast, the MC and SS models yield overly optimistic results with lower wall deflection and ground settlement and fail to predict realistic soil behavior. As a result, this research highlights the significance of selecting the appropriate constitutive soil model and refining the parameters. This optimization process contributes significantly to the design of support systems, enhancing construction efficiency and ensuring overall safety in deep excavation projects.

Effect of Storage Time on the Structural Integrity of Silts and Organic Soils: An Analysis of Moisture Content, Unconfined Compressive Strength, and Elasticity

The impact of storage duration on the geotechnical properties of soils is a recurring issue in the field of geotechnical engineering. Due to the lack of previous research addressing this topic, an experimental study was conducted to evaluate the variation of these properties over time. Undisturbed samples of silty and organic soil from Quito, Ecuador, were obtained. These samples were subjected to unconfined compressive strength (UCS) and moisture content (MC) tests at various intervals (1, 3, 7, 14, 21, 28, and 56 days). Results revealed a significant correlation between MC, UCS, and modulus of elasticity (ME). A progressive increase in UCS and ME was observed as MC decreased, with peak values observed to occur between 20 and 30 days. These findings suggest that matric suction plays a predominant role in increasing cohesion and, consequently, UCS. Therefore, it is concluded that the time elapsed between sample extraction and testing is a critical factor influencing the preservation of MC and, hence, the accurate assessment of the soil’s mechanical properties.