Intact Soil Samples Research Articles

WGAN-Based Realization Process of Gravel Soil for Hydraulic Property Simulation

Gravel soil faces significant engineering challenges such as leakage erosion and soil flow due to its complex composition and susceptibility to groundwater effects. This study integrates the entire machine learning process, including pre- and post-processing of images, WGAN implementation, and validation of hydraulic and morphological properties. Obtaining intact gravel soil samples is difficult and costly due to their erodible nature in the Li River, China. A μ-CT scanning series is employed to capture detailed images with three microstructural characteristics of gravel soil, forming the basis for training datasets using WGANs. This approach allows the generation of similar 3D realizations that replicate the microstructural characteristics and hydraulic behaviors of a prototype of gravel soils. Through computational fluid dynamics (CFD) simulations, the effectiveness of the realizations in hydraulic behavior within reconstructed porous structures is verified. This process indirectly validates the consistency between the realization′s microstructure and the prototype. This integrated methodology not only enhances understanding but also aids in the optimization of engineering designs and applications in geotechnical and materials science disciplines.

Shear strength parameters identification of loess interface based on borehole micro static cone penetration system

BackgroundLoess is prone to large deformation and flow slide due to natural and artificial interfaces inside. The strength of these interfaces controls the mechanical properties of loess. Obtaining their mechanical parameters through in-situ testing is essential for evaluating the mechanical stability in loess engineering with interfaces.MethodsBy developing a borehole micro static cone penetration system and creating various types of loess with interfaces, extensive borehole penetration model tests were conducted to observe changes in cone tip resistance during penetration. The response surface method was used to analyze the impact of various test conditions on the calculated resistance. A three-dimensional surface fitting method was employed to establish the relationship between penetration parameters and shear strength parameters, which was validated through in-situ testing.ResultsThe developed borehole micro static cone penetration system achieves overall miniaturization while providing significant penetration power and ensuring an effective penetration distance. Cone tip resistance development during penetration can be divided into three stages: initial, rapid increase, and slow increase. The transition times between these stages vary for different soils. Calculated resistance is positively correlated with dry density and normal stress and negatively correlated with water content. A quadratic positive correlation was established between calculated resistance and shear strength parameters during penetration. In composite soils, the interaction between water content and normal stress is strong. Compared to intact soil samples, the shear strength parameters of composite soils are more prominently influenced by water content.ConclusionA system for testing interface mechanical parameters was innovatively developed, fulfilling the need to obtain interface shear strength parameters for deep soil. This study can provide support for ensuring the long-term stability of the loess slope or subgrade with interfaces.

The distribution of particulate organic matter in the heterogeneous soil matrix - Balancing between aerobic respiration and denitrification

Denitrification, a key process in soil nitrogen cycling, occurs predominantly within microbial hotspots, such as those around particulate organic matter (POM), where denitrifiers use nitrate as an alternative electron acceptor. For accurate prediction of dinitrogen (N2) and nitrous oxide (N2O) emissions from denitrification, a precise quantification of these microscale hotspots is required. The distribution of POM is of crucial importance in this context, as the local oxygen (O2) balance is governed not only by its high O2 demand but also by the local O2 availability.Employing a unique combination of X-ray CT imaging, microscale O2 measurements, and 15N labeling, we were able to quantify hotspots of aerobic respiration and denitrification. We analyzed greenhouse gas (GHG) fluxes, soil oxygen supply, and the distribution of POM in intact soil samples from grassland and cropland under different moisture conditions. Our findings reveal that both proximal and distal POM, identified through X-ray CT imaging, contribute to GHG emissions. The distal POM, i.e. POM at distant locations to air-filled pores, emerged as a primary driver of denitrification within structured soils of both land uses. Thus, the higher denitrification rates in the grassland could be attributed to the higher content of distal POM. Conversely, despite possessing compacted areas that could favor denitrification, the cropland had only small amounts of distal POM to stimulate denitrification in it. This underlines the complex interaction between soil structural heterogeneity, organic carbon supply, and microbial hotspot formation and thus contributes to a better understanding of soil-related GHG emissions.In summary, our study provides a holistic understanding of soil-borne greenhouse gas emissions and emphasizes the need to refine predictive models for soil denitrification and N2O emissions by incorporating the microscale distribution of POM.

Centrifuge modeling of loess slope failure induced by rising water level utilizing intact sample

Understanding the failure process of bottom-saturated loess slopes is of great significance in loess areas where flood irrigation is commonly utilized to alleviate the scarcity of precipitation. In this study, the failure process of a loess slope with an increased groundwater level was recreated and the multiple failure modes of loess landslides were revealed. A centrifugal model test was conducted using a groundwater-recharge device. An intact loess sample retrieved from the Heifangtai Loess Terrace was employed in the test. The model test was monitored using a video recorder, high-speed camera, and soil/pore water pressure sensors, and the results were validated by utilizing an intermittently investigated field landslide. Based on the monitored data and acceleration, the test was divided into three periods: the initial acceleration period with no water inlet (0–40 g), bottom saturation period (40–60 g), and failure occurrence period (60–80 g). The soil/pore water pressure and degree of deformation were relatively low, with a steadily increasing trend during the first two periods. With the enrichment of the soil water content, retrogressive sliding, deep subsidence, and surface sinkhole failures occurred successively up to areas with relatively high pore water pressure during the last period. The results of the field landslide investigation showed multiple failure modes, as observed in the model test. The results suggest that the coexistence of multiple failure modes could gradually evolve into croplands and promote water infiltration into the deep loess, increasing the groundwater level and accelerating the failure process of the slope. Despite the overall effects of multiple failure patterns on the evolution of the slope, each failure pattern had a relatively independent evolutionary process within a certain area, which could be further analyzed for the early recognition of loess landslides. This study also indicates that the challenges of centrifuge modeling for water-related materials with intact soil samples are the boundary conditions and data monitoring within the model.

Predicting saturated and near-saturated hydraulic conductivity using artificial neural networks and multiple linear regression in calcareous soils.

Hydraulic conductivity (Kψ) is one of the most important soil properties that influences water and chemical movement within the soil and is a vital factor in various management practices, like drainage, irrigation, erosion control, and flood protection. Therefore, it is an essential component in soil monitoring and managerial practices. The importance of Kψ in soil-water relationship, difficulties for its measurement in the field, and its high variability led us to evaluate the potential of stepwise multiple linear regression (SMLR), and multilayer perceptron (MLPNNs) and radial-basis function (RBFNNs) neural networks approaches to predict Kψ at tensions of 15, 10, 5, and 0 cm (K15, K10, K5, and K0, respectively) using easily measurable attributes in calcareous soils. A total of 102 intact (by stainless steel rings) and composite (using spade from 0-20 cm depth) soil samples were collected from different land uses of Fars Province, Iran. The common physico-chemical attributes were determined by the common standard laboratory approaches. Additionally, the mentioned hydraulic attributes were measured using a tension-disc infiltrometer (with a 10 cm radius) in situ. Results revealed that the most of studied soil structure-related parameters (soil organic matter, soluble sodium, sodium adsorption ratio, mean weight diameter of aggregates, pH, and bulk density) are more correlated with K5 and K0 than particle-size distribution-related parameters (sand, silt, and standard deviation and geometric mean diameter of particles size). For K15 and K10, the opposite results were obtained. The applied approaches predicted K15, K10, K5, and K0 with determination coefficient of validation data (R2val) of 0.52 to 0.63 for SMLR; 0.71 to 0.82 for MLPNNs; and 0.58 to 0.78 for RBFNNs. In general, the capability of the applied methods for predicting Kψ at all the applied tensions was ranked as MLPNNs > RBFNNs > SMLR. Although the SMLR method provided easy to use pedotransfer functions for predicting Kψ in calcareous soils, the present study suggests using the MLPNNs approach due to its high capability for generating accurate predictions.

Topographic correction of visible near‐infrared reflectance spectra for horizon‐scale soil organic carbon mapping

AbstractUnderstanding soil organic carbon (SOC) response to global change has been hindered by an inability to map SOC at horizon scales relevant to coupled hydrologic and biogeochemical processes. Standard SOC measurements rely on homogenized samples taken from distinct depth intervals. Such sampling prevents an examination of fine‐scale SOC distribution within a soil horizon. Visible near‐infrared hyperspectral imaging (HSI) has been applied to intact monoliths and split cores surfaces to overcome this limitation. However, the roughness of these surfaces can influence HSI spectra by scattering reflected light in different directions posing challenges to fine‐scale SOC mapping. Here, we examine the influence of prescribed surface orientation on reflected spectra, develop a method for correcting topographic effects, and calibrate a partial least squares regression (PLSR) model for SOC prediction. Two empirical models that account for surface slope, aspect, and wavelength and two theoretical models that account for the geometry of the spectrometer were compared using 681 homogenized soil samples from across the United States that were packed into sample wells and presented to the spectrometer at 91 orientations. The empirical approach outperformed the more complex geometric models in correcting spectra taken at non‐flat configurations. Topographically corrected spectra reduced bias and error in SOC predicted by PLSR, particularly at slope angles greater than 30°. Our approach clears the way for investigating the spatial distributions of multiple soil properties on rough intact soil samples.

Land Management and Soil Quality in Sago-Based Agroforestry System: A Study on Mooi Tribe’s Ecological Knowledge (Sorong, Southwest Papua) and Modern Ecological Knowledge (MEK)

Sago farmers from the Mooi tribe in Sorong Regency - Southwest Papua have consumed and cultivated sago for generations. This research aims to understand the local ecological knowledge (LEK) of sago farmers in managing their land to maintain soil quality in sago agroforestry, compared with modern/scientific environmental understanding. The survey was conducted from February to October 2021 in three sub-districts, Sorong Regency, using an exploratory descriptive method among Mooi sago farmers. Intact soil samples were taken to measure soil physical properties and disturbed soil samples to analyze soil chemical properties (pH, C-Organic, Total N, P, K, CEC, base saturation). The results of this research show that what sago farmers have in common with the unique habits of the Mooi tribe's harvest system is that they harvest enough sago starch to consume or sell if there is too much of it. According to sago farmers, the best land for growing sago is close to a water source and is not affected by soil biota and fertilization. and sago farmers will leave ella sago dregs on the land. Meanwhile, according to MEK, starch formation decreases in flooded land and the remaining sago dregs are very good for making compost and animal feed. In sago forests where sago grows naturally, the soil texture is dominated by silt, having a pH of 5.8-7.2; High total organic C 2.8-5.2%, P 14.08-66.44 mg/kg, K 755.3 – 1626.8 mg/kg, CEC 18-40 cmol(+)/kg, and base saturation 30 – 134%. These values are relatively higher than on land with a sago-based agroforestry system.

Sugarcane growth variation based on rainfall and soil permeability in Takalar, Indonesia

The germination and sprouting phases of sugar cane are critical periods that determine productivity. This phase occurs when the sugar cane is 1-3 months old and requires an adequate supply of water to support the formation of shoots. Poor soil conditions and high rainfall can cause the failure of bud formation. This study aims to determine the relationship between rainfall and soil permeability in successfully constructing sugarcane shoots. We divided the 1 ha research area into nine points (A, B, C, D, E, F, G, H, I) to observe plant growth and soil permeability. The growth factors measured included the number of stems, diameter, and plant height, measured by zigzag. Intact soil samples at a 0-15 cm depth were then analyzed in the laboratory using Darcy’s law to determine the value of soil permeability. The results showed variations in sugarcane growth in the nine study plots. The average number of sugarcane stalks is eight stalks/meter with a height of 159 cm and a diameter of 3 cm. The low soil permeability value of 0.13-0.5 cm/hour cannot compensate for the average rainfall during the budding phase, thereby suppressing plant growth by up to 50% of the average productivity that should be.

One-Dimensional Consolidation Test with Pore Pressure Measurements — An Accelerated Procedure

Abstract Consolidation properties of cohesive soils are often determined using the controlled-strain loading (CSL) consolidation test. It was well recognized in the literature that the consolidation properties, such as compression index (Cc), coefficient of consolidation (cv), and preconsolidation pressure (σc′), depend on the axial strain rate adopted for conducting the CSL test. Fixing the appropriate axial strain rate is often a challenge in CSL tests. The conventional incremental load (IL) consolidation test suffers from the limitation that it takes long time to complete the test. In the present study, an accelerated IL consolidation testing procedure with pore water pressure measurements is developed in an attempt to overcome the limitations of the CSL and conventional IL consolidation tests. The duration of the IL is controlled such that the subsequent IL is applied once the excess pore pressure dissipates to 15 % of the total applied stress (pore pressure ratio, Ru, is 0.15). The testing procedure is validated by performing a series of experiments on six reconstituted and four intact soil samples. The consolidation parameters obtained from the proposed method compares very well with conventional IL test as well as with the CSL consolidation test, suggesting its validity. The proposed method is about 3 times faster when compared with the standard CSL test. Therefore, the proposed method is a viable alternative to the CSL consolidation test.

The profile of soil fertility and yield of coffee in the land with a different slope (Case study in Way Tenong District, West Lampung Regency)

This study aims to analyze the level of soil fertility, the condition of the physical properties of the soil, and the level of soil erodibility on coffee plantations with various slope levels. Observations were made on coffee plantations in two villages in Way Tenong District, West Lampung Regency, namely Fajar Bulan Village and Puralaksana Village, in April 2022. The number of sampling points in each village is 6 points. Composite soil samples were taken to analyze the chemical properties of the soil, including pH, C-Organic, N-Total, P content, and soil cation exchange capacity. Meanwhile, intact soil samples were used to determine the values of bulk density, soil porosity, soil texture, and soil moisture content. The analysis was carried out at the Laboratory of Institute for Agricultural Technology Assessment (BPTP) Lampung. Based on the soil pH levels at the sampling location, the soil reactions were acid with pH < 5, with only one location with a pH above 5 (FB 1). Soil organic matter content in most locations was still low, except for FB 1 location. The slope of the slopes at the soil sampling location varied from flat (0 - 10%) to mountainous (>60%). Based on physical properties, soil density is generally high (the highest BD is 1.59) and low porosity value. The coffee yields tend to decline from 2019-2021.

The importance of marshes providing soil stabilization to resist fast-flow erosion in case of a dike breach.

Salt marshes provide valuable ecosystem services including coastal protection by reducing wave loading on dikes and seawalls. If the topsoil is erosion resistant to fast‐flowing water, it may also reduce breach depth if a dike fails. In this experiment, we quantified the topsoil erosion resistance from marshes and bare tidal flats with different soil types to understand the extent to which they can help reduce breach depth. Intact soil samples were collected from 11 locations in the Netherlands at different tidal elevations and then exposed for 3 h to 2.3 m/s currents. To the samples that remained stable after flow exposure, an artificial crack was made to test their stability following soil disturbance. All samples from the tidal flats were completely eroded, regardless of sediment type. In contrast, all samples from well‐established marsh plateaus were stable as long as no disturbances were made, including those with sandy subsoils. After creating artificial cracks, samples with a thin cohesive top layer on top of sandy subsoil collapsed, while marshes with silty subsoils remained stable. Pioneer marshes on sandy substrate without a cohesive top layer were the only vegetated soils that completely eroded. The lower erosion of marshes with either sandy or silty soils compared to bare tidal flats was best explained by the presence of a top layer with belowground biomass, high organic content, high water content, and low bulk density. When analyzing the erodibility of marshes only, fine root density was the best predictor of erosion resistance. This study demonstrates the importance of preserving, restoring, or creating salt marshes, to obtain a topsoil that is erosion resistant under fast‐flowing water, which helps reduce breach dimensions if a dike fails. The probability of topsoil erosion in established marshes with sandy subsoil is higher than in silty marshes. A silty layer of cohesive sediment on top of the sand provides extra erosion resistance as long as it does not break. Pioneer marshes that have not developed a cohesive top layer are erosion sensitive, especially in sandy soils. For future marsh creations, using fine‐grained sediments or a mixture of sand with silt or clay is recommended.

Soil–air phase characteristics: Response to texture, density, and land use in Greenland and Denmark

AbstractSoil aeration is a key parameter for sustainable and productive agriculture. The intensification of agricultural activity in Greenland involves land use (LU) and LU change, affecting the soil–air phase. The combined effects of natural compaction (bulk density, ρb), texture (texture uniformity index; TUI), and LU on the soil–air phase of subarctic soils are not well known. This study aims to identify and compare the main drivers for air‐filled porosity (ε) and soil‐structure changes within and across sites in Greenland and Denmark. We analyzed comprehensive data sets of ε, relative gas diffusivity Dp/Do), and air‐permeability (ka) measured on intact soil samples from South Greenland (pasture) and Denmark (cultivated, urban, and forest). The mechanical robustness of the air phase was evaluated by linear models of ε as a function of ρb (H‐model). The ratio of ka to Dp/Do served as a soil‐structure index (Ω); the latter significantly correlated to TUI. The Greenlandic pasture soils did not show signs of well‐developed soil structure (low Ω‐values), whereas low H‐values suggested the soils were mechanically robust compared to similar‐textured cultivated soils. The soil–air characteristic curve (ε vs. pF) was parameterized, and the moisture control parameter was accurately predicted by TUI and LU (R2 = .95). Overall, the ρb was found to control the air‐phase functions within a field. However, considering changes in ε‐levels across different fields, texture, LU, and other environmental factors became statistically more relevant than ρb. A modeled response surface for changes in ε with soil conditions may, in perspective, be useful for better‐predicting gas transport in soil, both within and across fields.

Erosion hazard index analysis of several land uses in Watatu Village, Donggala Regency

Watatu Village is one of the villages located in Donggala Regency and as the capital city of South Banawa Sub-District which has significant potential in the agricultural sector, including cocoa plantations, oil palm trees, and paddy fields. This research aims as a source of information correlated to land-use policies and the erosion hazard index in Watatu Village, South Banawa Sub-District, Donggala Regency. The research was carried out by using the descriptive explorative method, and the observed variables were carried out through a survey. Soil sampling was determined purposively (purposive sampling) based on the category of land use and slope at the research location. Intact and incomplete soil samples were taken as many as 21 samples at seven land-use units. Sample analysis was performed at the Soil Science Laboratory on the Erosion Hazard Index, namely (1) soil texture, (2) soil structure, (3) organic matter content, and (4) permeability, and (5) bulk density. The results of the Erosion Hazard Index analysis showed that the high erosion hazard index was found in Land use unit 2 (mixed gardens), Land use unit 4 (cocoa gardens), Land use unit 5 (mixed gardens), and Land use unit 7 (Shrub). Thereby, conservation actions needed to preserve the environment to prevent or inhibit the rate of erosion and maintain the stability of land use.

Evaluation of soil organic matter from integrated production systems using laser-induced fluorescence spectroscopy

Agricultural areas under integrated production systems, such as Integrated Crop-Livestock-Forest System (CLFS), have the potential to sequestrate carbon (C) since both Soil Organic Matter (SOM) content and trees biomass increase thus mitigating the emission of greenhouse gases (GHGs) from agriculture. Regarding soil aspects, the C content stands out as the main indicator, but the structural aspect of SOM is also relevant since it plays a key role in the chemical stability of C compounds and the soil lifetime of C compounds. Laser-Induced Fluorescence Spectroscopy (LIFS) is an effective technique to evaluate the SOM humification index (HLIFS) from practically intact whole soil samples under different agricultural systems. Thus, the objective of this study was to analyze the SOM humification index in different integrated systems, such as Integrated Crop-Livestock-Forest System (CLFS), Integrated Livestock-Forest System (LFS), Integrated Crop-Livestock System (CLS), and in references areas, such as Intensive Pasture (INT), Extensive Pasture (EXT) and Native Forest (NF). For this purpose, samples of Red-yellow Latosol (Haplorthox by Soil taxonomy) from the experimental site located at Embrapa Pecuária Sudeste (Southeast of Brazil) were collected five years after the establishment of the integrated systems. Samples were collected at soil depths of 0–5, 5–10, 10–20, 20–30, 30–40, 40–60, 60–80, and 80–100 cm. Pellets of the whole soil samples were prepared for LIFS analysis. In these areas, SOM humification indices (HLIFS) presented the following descending order: CLS > EXT > INT > LFS > CLFS > NF. Previous results have shown a greater soil organic carbon stock in these integrated production systems than in the NF area, suggesting C sequestration in agricultural soil. In the present study, SOM was classified by LIFS as more chemically stable in integrated production systems than in native vegetation. Higher amounts of fluorescent compounds were identified from LIFS data, probably resulting from condensed aromatic groups. SOM with more recalcitrant groups normally has a longer lifetime in the soil, indicating a long-term contribution to mitigating climate change by avoiding fast SOM decomposition and CO2 return to the atmosphere. Also, for the first time, this study was able to identify a positive correlation (R = 0.79) between the SOM humification index (HLIFS) and the Cation Exchange Capacity (CEC)/C content ratio of whole soil samples, another innovative contribution from soil LIFS analyses.

Time-lapse approach to correct deficiencies of 2D soil zymography

Membrane zymography is commonly used in rhizosphere ecology to map enzyme activities in intact soil samples and plant roots. The method consists of incubating a membrane saturated with an enzyme-specific fluorogenic substrate on the soil/root surface followed by measurements of fluorescence intensity of the product in the membrane. The traditional zymography is based on assumptions that fluorescence on membrane images is linearly increasing with time during zymography and an increase in product content is numerically equal to enzyme activity in soil below the membrane. These assumptions are unlikely to hold in experimental settings. Here we introduce a new zymography technique, time-lapse zymography (TLZ); the approach that eliminates the need for assumptions of the traditional zymography and provides more realistic estimates of enzymatic activities. We assessed the new technique in a series of laboratory and modeling experiments, including quantification of the fluorescent product diffusion (e.g. MUF: 4-methylumbelliferone) from plant roots, enzyme activity measurements on the roots, and HYDRUS-2D & HP2 software calibration with obtained data. The calibrated model was used to analyze the processes governing spatial and temporal dynamics of MUF contents in the membrane. The results indicated that the enzyme diffusion within the membrane-soil system was negligible, and measured zymograms were adequately reproduced solely by accounting for substrate and product diffusions and for catalytic enzyme reaction described by the Michaelis-Menten equation. TLZ enabled identifying and using linear parts on MUF time series and accounting for MUF losses in each zymogram pixel, considerably improving the accuracy as compared to the traditional method. Results demonstrated that enzymatic activity from only a thin soil layer (~0.2 mm) is adequately represented in zymograms.

Nitrogen and phosphorus co‐limit mineralization of labile carbon in deep subsoil

AbstractThe growth of deep‐rooted crops has the potential to increase carbon deposition within deep subsoil layers, thereby contributing to climate change mitigation. Yet, the mechanisms of labile carbon stabilization in deep subsoils remain uncertain. Here we studied the effect of nitrogen, phosphorus and sulphur limitations on the microbial mineralization of added glucose and an artificial root exudate mixture (both spiked with 14C‐glucose) in intact soil samples from a deep subsoil (5–6 m) over a 10‐week incubation period, where the temporal respiration of CO2 and 14CO2 were quantified. We found that mineralization was co‐limited by nitrogen and phosphorus, but the cumulative amount of CO2 emitted was significantly larger from artificial root exudates than glucose, suggesting that the nitrogen carried in amino acids in root exudates (here, L‐arginine) was sufficient to overcome the nitrogen limitation in this subsoil.Highlights Labile C substrates and nutrients from deep‐rooted crops may affect the potential for C sequestration in subsoil. Deep subsoil was incubated with glucose and artificial root exudates amended with N, P, and S. C mineralization was co‐limited by N and P, but less so in soil amended with glucose. Amino acid derived‐N in exudates from deep‐rooted crops may alleviate the N limitation in deep subsoils.

Numerical Modelling of Oedometer Test

Abstract The oedometric test is a test widely used in civil engineering. The main objective of this article has been to investigate the primary consolidation behaviour of the intact soil samples by comparing the results obtained from finite element analysis computations in PlAXIS2D with the experimental result of the soil samples obtained from the site of the Al-Ahdab oil field in the east of Iraq. Three different material models were utilized during the finite element analysis, comparing the performance of the more advanced constitutive Soft Soil material model against the modified Cam Clay and Mohr-Coulomb material models. Numerical results of Oedomter test show that the Soft Soil model behaviour is the most appropriate model to describe the observed behaviour.

Performance of Raft Foundation under Static Vertical Loading in Contaminated Soil

This study focuses on studying the impacts of residues oil on the geotechnical properties of soil and the performance of raft footing rested on oil contaminated soil and subjected to vertical loads. The contaminant used in the present study is residues oil, which is by product disposed of diesel engine oils. The soil samples are contaminated artificially by soaking with two percentage of disposed engine oil of contaminant consist of (disposed engine oil and gasoline) of 20% weight of dried of intact soil samples to obtain different concentrations of contaminant absorbed by soil samples for 30 days to complete the saturation. The mechanical model manufactured to investigate the behavior of raft footing under vertical static loading rested on intact and contaminated soils. The obtained results detected contaminant content have notable impacts on the physical soil characteristics such as the fine particles, specific gravity, plasticity index, and maximum dry unit weight decreased with the increase of contaminant content than that of intact soil. The mechanical soil properties of soil indicated the increase of the compressibility of soil with increase of residues oil percentage, but the soil strength and stiffness are decreased notably. In addition, the total and permanent settlement of raft footing constructed in contaminated soil samples increased by (27-43) % and by (41-58) % than that of an intact soil sample, respectively.

Changes in soil quality under conservation agriculture practices in West Nusa Tenggara, Indonesia

The main challenge for cultivating upland in semi arid environment as in West Nusa Tenggara, Indonesia is the limited availability of water resources and accelerated deterioration of soil quality. This study evaluated changes in selected soil properties and soil quality 4 years after the implementation of conservation agriculture (CA) practices. The study was conducted at the CA demonstation plots in Gunung Malang Village, Pringgabaya District, East Lombok Regency, West Nusa Tenggara Province. The surface soil texture was loam with slope ranging from 5 to 10%. Two CA Models and one farmer practice (LP) were compared. Within each model three sampling positions were sampled: within the corn planted area (Position A), 0-10 cm from the edge of the corn planted area (Position B), and 10 – 20 cm from the edge of the corn planted area (Position C). Intact soil samples (76 by 40 mm) were taken from the three positions at two depths (100-mm increments) to determine soil physical properties and bulk samples from the surface soil (0 – 15 cm) to determine soil chemical properties in the laboratory. The CA Model had significantly (&lt;em&gt;P&lt;/em&gt; &amp;lt; 0.01) lower bulk density (BD), and increase soil organic carbon (SOC) and available P (Av P), while Position had significantly affect only BD. The lowest BD (0.87 ± 0.07 Mg m-&lt;sup&gt;3&lt;/sup&gt;) and the highest SOC (1.51± 0.05%) and available pore water (AWC; 18.06 ± 0.76% vol) were found at Position A in CA with permanent pit (PIT). The highest soil quality index was found in Position A followed by Position B and the least was in C indicating that the crop rotation component in CA had relatively small effect on improving soil quality. These results suggested that there is a gradual improvement on soil quality after 4 years of the implementation of conservation agriculture and require longer time than 4 yr to achieve the best soil quality for this semi arid environment

Erosional effects on distribution and bioavailability of soil nitrogen fractions in Belgian Loess Belt

Soil erosion strongly influences the transport and fate of carbon (C) and nitrogen (N) in hillslope soils. However, in dynamic landscapes, erosional effects on soil N cycling and primary controls on N bioavailability are not well understood: particularly with respect to differences between topsoil and subsoil. Here we aim to explore the influence of erosion on (i) spatial distributions of soil N fractions and (ii) controls on N bioavailability in eroding vs. depositional sites within the Belgian Loess Belt. Soil samples were fractionated by aggregate size and density. In addition, intact soil samples were incubated to determine the influence of oxygen status (0, 5, and 20%) and labile organic matter on mineralization and nitrification of N in the context of erosion. The results showed that the deposition of eroded upslope soil materials led to N enrichment throughout entire soil profiles. Across both eroding and depositional sites, more than 93% of the total N was associated with minerals. Increased macro-aggregate- and mineral-associated N at the depositional site indicated that aggregation and N stabilized by minerals contribute to N enrichment in the depositional soils. Inorganic N, mostly NO3−-N, was also larger at the depositional site. Oxygen concentrations were positively related to net N nitrification and mineralization rates regardless of geomorphic position. Glucose addition significantly reduced net N mineralization and nitrification rates. In conclusion, our results indicate that soil erosion might not only lead to spatial variations of N pools but also potentially affect the transformation and bioavailability of N along eroding hillslopes. Future research should consider the fate of different N species in eroding landscapes and consequences for both carbon sequestration and N leaching.