Equivalent Soil Research Articles

Long-term tillage and crop rotation effects on soil carbon and nitrogen stocks in southwestern Ontario

Conservation tillage and crop rotation diversification have been promoted to increase soil C and N storage; however, the interactive effects of tillage and crop rotation on soil C and N dynamics remain contradictory. Using a long-term (24-yr) experiment established at a clay loam site (Orthic Humic Gleysol) at Ridgetown, Ontario, Canada, the interactive effects of five crop rotations and two tillage systems were tested on soil organic C (SOC) and total N storage in soil depth increments and in the full soil profile (0-0.6 m) in 2019. While crop rotation influenced SOC and total N concentration in top 0.2 m, these effects were minimized when storage was expressed on an equivalent soil mass basis. Over the 0-0.6 m depth, no-tillage had 24 Mg SOC ha-1 and 4.7 Mg total N ha-1 greater content, respectively, than conventional tillage, supporting the value of no-tillage on increasing soil C and N in the long-term. Interestingly, no interactive effects of crop rotation and tillage on soil C and N storage in 0-0.6 m were observed. While the type of crop species and amount of C and N inputs under different crop rotations are important variables impacting the soil C and N storage, our results suggest that the crop rotation diversity was not a major driver of soil C and N in this study. Future mechanistic investigations exploring the persistence and linkage of soil C and N with crop rotation diversity in the tested production systems are needed.

Surface soil sampling underestimates soil carbon and nitrogen storage of long-term cover cropping

Cover cropping is a promising management practice for soil health and climate change mitigation by improving soil organic carbon (SOC) and total nitrogen (TN) stocks. However, limited studies focused on deeper soil layers (>30 cm depth) where soil C is more stable than that in surface soil (≤30 cm depth). Here, deep soil sampling was conducted in a 15-year cover cropping experiment, in a horticulture-grain system on sandy loam soil. The SOC and TN stocks were expressed on an equivalent soil mass basis using a cubic spline model. Overall, long-term cover cropping had significantly greater SOC and TN stocks by 22 % (95 %CI: 5–43 %) and 26 % (95 %CI: 6–49 %), respectively in the 0–120 cm depth, compared to no cover cropping. Additionally, the mean SOC and TN sequestration rate (0–30 cm depth) was 0.53 Mg C ha−1 yr−1 and 0.06 Mg N ha−1 yr−1, respectively. However, if only 0–15 cm depth was evaluated, long-term cover cropping did not significantly affect SOC and TN stocks. These results indicated that shallow sampling (<15 cm depth) may not provide comprehensive information on the effect of long-term cover cropping on soil C and N storage. To better understand the mechanism of bulk soil C and N storage, we investigated their distribution between particulate and mineral-associated organic matter pools (POM and MAOM). We found POM pool was the main store of bulk SOC and TN stocks in surface soils while it was the MAOM pool in deeper soil layers, without soil texture change with soil depth. These findings indicated that soil C and N sources for bulk SOC and TN accrual differed in surface and deeper soils. Our study demonstrated that long-term cover cropping can facilitate SOC accumulation in the soil below 15 cm deep, which calls into question carbon capture protocols that focus on shallow soil depths.

Enhancing pyromorphite formation through hydroxyapatite application in lead-contaminated, water-unsaturated soils: influence of low percolation velocity and high soil porosity

Abstract Purpose Chemical immobilization using hydroxyapatite (HAP) is a cost effective and environmentally sound strategy for remediating lead-contaminated soils, such as shooting range soils. Understanding the combined impact of soil chemical and physical properties on enhancing the formation of pyromorphite, a lead-insoluble phase, is crucial for mitigating environmental risks associate with contaminated soil. This study aimed to elucidate the relationship between percolation velocity and lead leaching as well as pyromorphite transformation to optimize pyromorphite formation in water-unsaturated soils. Methods Two up-flow suction percolation tests were performed: one varying percolation velocity with soil porosity achieved by incorporating clay minerals, and the other varying percolation velocity while keeping soil porosity constant. Results Application of HAP substantially suppressed lead leaching in both percolation tests. Enhanced pyromorphite formation was observed with higher percolation velocities relative to soil porosity. Pyromorphite formation was more pronounced at lower percolation velocities compared to higher velocities at equivalent soil porosity level. The percentages of lead formed as pyromorphite in HAP-treated soil were higher than those of lead leached in non-HAP-treated soil among the lower percolation velocities. Conclusions This study provides experimental evidence indicating pyromorphite formation is favored in soils with lower percolation velocities and higher soil porosities. Therefore, considering both soil chemical and physical properties is essential for understanding immobilization mechanisms in contaminated soils.

Soil carbon stocks and nutrient stratification in a volcanically active coffee-dominated landscape in south-central Guatemala

The volcanoclastic mountains of Central America offer elevations ideal for coffee production. Both vulcanism and land use can have significant impacts on soil formation and properties. We evaluated how the interactive impacts of soil formation and coffee-dominated land use modulate soil storage and vertical distribution of organic carbon and nutrient elements in a volcanically active landscape dominated by coffee agriculture in south-central Guatemala. Thirty-seven pedons under coffee production (n = 29), forest cover (n = 5) and pasture (n = 3) were characterized and classified, and concentrations and stocks of organic carbon and macronutrient and micronutrient elements were quantified across genetic horizons. Additionally, soil organic carbon (SOC) stock values calculated using the fixed depth (FD) and equivalent soil mass (ESM) methodologies were compared. The active stratovolcano in the region had a strong effect on the development of andic properties and soil horizon burial, with thirty-one pedons classified as Andisols, three as Inceptisols and three as Entisols. Land use management practices and soil horizon burial by deposition of volcanic material were partly reflected in the vertical distribution of SOC concentrations and stocks. The vertical distribution of macronutrients was generally more sensitive to land use than the vertical distribution micronutrients, which could potentially reflect differences in inputs via fertilizers and vegetation cover and in outputs with biomass harvest. Soil organic carbon stocks were similar when calculated by FD and ESM, reflecting relatively consistent depth-wise bulk density. These results demonstrate that in volcanically active landscapes, land use should be considered in concert with soil-forming factors to comprehensively understand organic carbon and nutrient element storage in soils.

Forest soil carbon storage in 10‐year‐old Douglas‐fir plantations of western Oregon and Washington remains similar to pre‐harvest

AbstractForests around the world, and in the case of this study, the coastal Pacific Northwest United States, store large amounts of carbon, both above ground in the trees and below ground in soils. Understanding the effects of forest disturbance, including timber harvesting, is important in order to evaluate the role that forestry plays in the global carbon cycle. Soil carbon can be difficult to assess with enough precision to detect the kinds of changes that are expected, yet a series of small changes over time in the same direction could have important cumulative effects. In this study, eight randomly selected Douglas‐fir forest stands in Oregon and Washington were sampled at 300 points each using a fixed‐depth sampling approach to attempt to detect a 5% or higher change in soil carbon storage to 1 m, longitudinally from pre‐harvest to 10 years post‐harvest. There was moderate variability in results over time at individual sites, with some sites decreasing slightly and others increasing slightly. Only two sites achieved lower than the 5% minimum detectible difference target. The remaining six sites were able to detect 5.7%–10.7% differences. In one case, an unexpectedly large increase in mineral soil carbon 10 years post‐harvest occurred without clear explanation. On average, forest floor carbon stores were 20% larger 10 years post‐harvest than pre‐harvest. Even with the large increases excluded, both the fixed‐depth approach and equivalent soil mass correction showed there was no significant change in mineral soil carbon stores to 1 m at 10 years post‐harvest in the region.

Validation and Parametric Study of a Soil–Structure Interaction Nonlinear Simplified Model

This paper established a numerical model for the structure system in a soil–structure interaction using MATLAB 23.2 and ANSYS 24.1 software and validated the effectiveness and accuracy of a simplified nonlinear calculation model for soil–structure interaction through the numerical simulation results. Meanwhile, a list of key parameters was identified according to their influence on the simplified model, including the free field area, site soil parameters, equivalent soil area, superstructure size and number of stories, and input seismic waves. On this basis, a series of parametric investigations were carried out with the validated simplified model, by varying the selected key parameters. The research findings demonstrated that the simplified calculation model exhibited excellent accuracy and efficiency, and was capable of reflecting the nonlinear response of the structural system. It is applicable to the field of dynamic response analysis of the superstructure, considering soil–structure interaction.

Potential of conservation tillage, cover crops, and digestate application as integrated C farming practices for processing tomato

Conventional soil management — based on intensive tillage and low input of organic material – negatively impacts soil quality via carbon (C) losses as carbon dioxide emissions (CO2), exacerbating the effect of climate change on agriculture. Carbon farming practices (CFPs), such as minimum tillage (MT) and strip tillage (ST), offer promising solutions to maintain soil fertility, sustain crop yields, and mitigate environmental impacts. However, applying CFPs in processing tomato (Solanum lycopersicum L.) cropping presents unique challenges due to specific crop and tillage characteristics. Our two-year field study investigated the effects of conservation tillage practices (i.e., MT and ST), both combined with cover crops and digestate application, on soil quality parameters and processing tomato yield. The field studies were conducted in fields with varying soil textures (i.e., clay and silty clay loam), and aimed to evaluate responses in terms of soil C sequestration, nutrient concentrations, soil structure, and abundance of earthworms. We hypothesized that both MT and ST would enhance soil quality parameters also in tomato cropping systems, with ST potentially outperforming MT in C sequestration. Results revealed that CFPs significantly increased soil organic matter, total nitrogen, and available phosphorous compared with conventional tillage. Both MT and ST increased soil C sequestration (up to 1.06 Mg C ha−1 y−1 and 1.21 Mg C ha−1 y−1, respectively) compared with conventional tillage (CT), which lost around 0.88 Mg C ha−1 y−1 under silty-clay loam soil, and had negligible C sequestration (+0.02 Mg C ha−1 y−1) under clay soil. We found no significant difference between MT and ST when using the equivalent soil mass method for calculating C sequestration. Noteworthy, CFPs enhanced fertility parameters without a negative impact on yields, underscoring their potential for enhancing soil C sequestration, improving nutrient availability, and supporting processing tomato yield under adaptation scenarios to climate change.

РОЗРАХУНОК АРКОВОЇ ДОРОЖНЬОЇ СПОРУДИ З ГОФРОВАНОГО МЕТАЛУ З УРАХУВАННЯМ ФОРМИ ГОФРУ

Introduction. The issue of calculation of an arched road structure made of corrugated metal on the basis of numerical modeling using the finite element method (FEM) using the actual cross-sectional parameters of metal corrugated structures (MCS) is considered. Problem Statement. In past years, for the calculations and tests of road constructions from MCS, a simple rectangular cross-section, equivalent in terms of bending stiffness to a corrugated profile, was considered. This was adopted to simplify calculations and research. Such an approach is also used in modern norms for the design of buildings with MCS. But this is not quite a correct simplification. Purpose. To show the possibility to avoid unnecessary convention and simplification of the calculation scheme and to obtain more correct and more informative results of the calculation of structures with MCS. Research methods and results. The purpose and tasks are realized by calculation-theoretical analysis and numerical modeling according to FEM using a specific example of calculating a road structure (small bridge) from the MCS. The calculation model is made according to the actual shape of the corrugations, without switching to the conventional simple rectangular cross-section of the arch elements, which are equivalent in terms of bending stiffness. The main design condition for strength in this work is the condition that the design load does not exceed the bearing capacity of the arch, as a component of the «building-soil» system.The bearing capacity of the structure in this work is considered as the sum of the arch's own bearing capacity (outside the soil) and the addition, which is provided by the elastic support of the embankment soil in response to the movement of the arch toward the soil. To determine the addition of bearing capacity due to soil resistance, the arch model is adopted as a «mechanism» with full hinges in the places of the greatest stresses and deformations of the arch. The geometric stability of the "mechanism" is ensured by additional rods that simulate the soil support by moving the arch. The forces in these rods must be corresponding to the equivalent resistance of the soil. The bearing capacity supplement is defined as the load on the arch, at which the forces in the additional rods are equal to the equivalent soil resistance of the embankment by the permissible movement of the arch toward the soil.

Analysis of Soil Improvement Through PVD and Vacuum Preloading with Several Equivalent Permeability Methods

Vacuum preloading combined with prefabricated vertical drain (PVD) is one of the common soft soil improvement methods. Soft soils often pose significant problems in construction projects due to their low shear strength and high compressibility, leading to settlement issues and potential structural instability. The PVD combined with vacuum preloading method addresses these problems by accelerating the consolidation process and minimizing settlement during service period. The acceleration occurs due to the presence of PVD, allowing dissipation of excess pore water in horizontal direction towards the PVD. Thereafter, the water in the PVD is drained to the surface. When modelled in 2D, PVD behaves as a continuous drain in the plane strain direction, causing the flow conditions to deviate from the actual conditions. To address this issue, equivalent soil permeability values is required, allowing the 2D model to produce results closely resembling the actual conditions. This research explores the improvement of PVD vacuum preloading through three equivalent permeability approaches. Utilizing field monitoring data, which includes settlement measurements from settlement plates, changes in pore water pressure recorded by piezometers, and lateral deformation data captured by inclinometers, the study evaluates the effectiveness of these approaches. Comparative analyses with field monitoring data reveal that Indraratna equivalent permeability method has the best fit. The integration of PVD and vacuum preloading, coupled with the refinement of equivalent permeability methodologies, offers a promising solution for addressing soft soil problems in geotechnical engineering. This research contributes to the practical application of these methods in construction projects, emphasizing their potential to enhance soil stabilization and reduce settlement-related risks.

Effect of padeye offset ratio on keying behaviours and capacity of square plate anchors in clay

This paper reports the effect of padeye offset ratio on the keying behaviours and capacity of square plate anchors in clay. The investigation is conducted through three-dimensional large deformation finite element analyses using the Remeshing and Interpolation Technique with Small Strain in ABAQUS. Strain rate dependency of the undrained shear strength and soil remoulding are accounted for adopting an extended Tresca model. The results from LDFE analyses are compared with existing analytical solutions, centrifuge test data, and numerical results; with reasonable agreement obtained. Parametric analyses are then carried out varying several critical factors including initial embedment depth, load eccentricity, padeye offset ratio, soil sensitivity, and soil strength heterogeneity. It is seen that the padeye offset has significant influence on the ultimate loss of embedment and capacity under vertical loading. To assess the keying behaviour of square plate anchors in clay, an equivalent soil strength incorporating strain rate dependency and remoulding is adopted. A combined factor defined as a function of the initial embedment depth and equivalent soil strength is used to estimate the ultimate loss of embedment. An equivalent ultimate bearing capacity factor is shown to be a function of the initial embedment depth, padeye offset ratio, and load eccentricity.

No tillage and leguminous cover crop improve soil quality in a typical rainfed Mediterranean system

Soil and crop management influence soil organic carbon (SOC), chemical composition, and overall soil quality. In a Mediterranean region, a study initiated in 1994 examined the long-term effects of conventional tillage (CT) versus no-tillage (NT) practices. Initially focusing on continuous durum wheat cultivation until 2009, the experiment later introduced a 2-year rotation of durum wheat and Vicia faba L. cover crops in half of the CT and NT fields. SOC was monitored from 2008 to 2018, while microbial biomass (as dsDNA), soluble nitrogen (N), and enzyme activities (EAs) were monitored from 2011 to 2014 to evaluate the rotation’s impact. Between 2009 and 2018, CT yields were on average 15% higher than NT, especially during high rainfall years. NT significantly increased SOC content in the 0–30 cm soil layer, along with higher levels of soluble N, dsDNA, and EAs at 0–10 cm depth. NT led to a 23% and 10% increase in SOC stock and SOC stock per equivalent soil mass compared to CT. EAs increased by over 50% under NT, indicating enhanced biological activity. The SOC increase due to NT was limited to the top 10 cm, with a decrease at deeper depths (up to 50 cm). Introducing cover crops over 4 years did not yield significant impacts, suggesting the need for a longer period to observe noticeable effects. Overall, adopting NT practices resulted in higher SOC concentration, enhanced soil biological activity, and improved biogeochemical cycles, emphasizing the positive impact of NT on soil health and sustainability.

Assessing belowground carbon storage after converting a temperate permanent grassland into a bamboo (Phyllostachys) plantation

AbstractBamboo (Phyllostachys sp.) is considered a sustainable resource that can replace fossil fuel‐based products. Its additional ability to sequester organic carbon in the soil (SOC) makes it a promising nature‐based solution for combating climate change. However, bamboo's soil C storage potential may vary considerably between species or growing conditions and needs to be better quantified, especially in temperate climates where data are lacking. In the present research, the SOC dynamics of plots converted from grassland to plantations of three bamboo species (i.e. Phyllostachys nigra, Phyllostachys aurea and Phyllostachys aureosulcata), planted 12 years ago on podzol (World Reference Base classification) in the Belgian Campine region, have been studied. Soil and root samples were taken until a depth of 40 cm using a 10 cm interval. Besides, the total belowground C stability (mgCO2‐C g−1 C h−1) was assessed by measuring during 3 months the carbon dioxide (CO2) efflux relative to the belowground C stock. Based on an equivalent soil mass, only P. aureosulcata, the species with the highest culm basal area, had a significant (p &lt; .001) SOC increase of 5.0 kg C m−2 (relative increase of +94%) as compared with grassland. Considering the sum of C stocks in the soil, roots and leaf litter, all bamboo species showed significant (p &lt; .001) C storage, i.e. +3.6 kg C m−2 (+64%), +5.3 kg C m−2 (+94%) and +8.6 kg C m−2 (+151%) for P. nigra, P. aurea and P. aureosulcata, respectively. In addition, bamboo's relative basal CO2 efflux (0.007, 0.006 and 0.008 mgCO2‐C g−1 C h−1, respectively) was remarkably lower than in the grassland (0.012 mgCO2‐C g−1 C h−1), though it was only significant for P. aurea. This study highlights that converting temperate permanent grassland into Phyllostachys bamboo plantation can result in net and rapid organic C storage by increasing the total belowground C stability and C input. Further research regarding the net CO2 balance of bamboo‐derived products is still required to fully assess its climate change mitigation potential.

Mulch application as the overarching factor explaining increase in soil organic carbon stocks under conservation agriculture in two 8-year-old experiments in Zimbabwe

Abstract. Conservation agriculture (CA), combining reduced or no tillage, permanent soil cover, and improved rotations, is often promoted as a climate-smart practice. However, our understanding of the impact of CA and its respective three principles on top- and subsoil organic carbon stocks in the low-input cropping systems of sub-Saharan Africa is rather limited. This study was conducted at two long-term experimental sites established in Zimbabwe in 2013. The soil types were abruptic Lixisols at Domboshava Training Centre (DTC) and xanthic Ferralsol at the University of Zimbabwe farm (UZF). The following six treatments, which were replicated four times, were investigated: conventional tillage (CT), conventional tillage with rotation (CTR), no tillage (NT), no tillage with mulch (NTM), no tillage with rotation (NTR), and no tillage with mulch and rotation (NTMR). Maize (Zea mays L.) was the main crop, and treatments with rotation included cowpea (Vigna unguiculata L. Walp.). The soil organic carbon (SOC) concentration and soil bulk density were determined for samples taken from depths of 0–5, 5–10, 10–15, 15–20, 20–30, 30–40, 40–50, 50–75 and 75–100 cm. Cumulative organic inputs to the soil were also estimated for all treatments. SOC stocks at equivalent soil mass were significantly (p&lt;0.05) higher in the NTM, NTR and NTMR treatments compared with the NT and CT treatments in the top 5 cm and top 10 cm layers at UZF, while SOC stocks were only significantly higher in the NTM and NTMR treatments compared with the NT and CT treatments in the top 5 cm at DTC. NT alone had a slightly negative impact on the top SOC stocks. Cumulative SOC stocks were not significantly different between treatments when considering the whole 100 cm soil profile. Our results show the overarching role of crop residue mulching in CA cropping systems with respect to enhancing SOC stocks but also that this effect is limited to the topsoil. The highest cumulative organic carbon inputs to the soil were observed in NTM treatments at the two sites, and this could probably explain the positive effect on SOC stocks. Moreover, our results show that the combination of at least two CA principles including mulch is required to increase SOC stocks in these low-nitrogen-input cropping systems.

Study on the Influence of Water Erosion on the Bearing Capacity and Function of the High Pile Foundation of the Wharf

High-pile foundation is a common form of deep foundation commonly used in ocean environments, such as docks and bridge sites. Aiming at the problem of bearing capacity of high pile foundations, this paper proposes the calculation of bearing capacity and the analysis of scour depth of high pile foundations under the action of scour based on the modified p-y curve. In this paper, three kinds of scour mechanisms—natural evolution scour, general scour, and local scour—are described; and the calculation methods of scour widely used at present are compared and analyzed. The solution of the vertical stress of soil around the pile under local scour is solved and applied to the β method to solve the lateral resistance of the pile under local scour. The local erosion is equivalent to the whole erosion, and the expression of the ultimate soil resistance before and after the equivalent is calculated, respectively, according to the principle that the ultimate soil resistance at a certain point above the equivalent pile end remains unchanged. The distance from the equivalent soil surface to the pile end can be obtained simultaneously, and then the equivalent erosion depth, p-y curve of sand at different depths, and high pile bearing capacity can be obtained. Finally, it is found that the bending moment of a single pile body varies along the pile body in the form of a parabola, and the maximum bending moment of the pile body is below the mud surface and increases with the increase in horizontal load. When the scouring depth is 30 m, the horizontal load is 25 KN, and the maximum bending moment of the pile body is about 150 N·m. The data with a relative error greater than 10% accounted for only 16.6% of the total data, and the error between the calculated value and the measured value was small. The formula can predict the erosion depth more accurately.

The importance of accounting method and sampling depth to estimate changes in soil carbon stocks

BackgroundAs interest in the voluntary soil carbon market surges, carbon registries have been developing new soil carbon measurement, reporting, and verification (MRV) protocols. These protocols are inconsistent in their approaches to measuring soil organic carbon (SOC). Two areas of concern include the type of SOC stock accounting method (fixed-depth (FD) vs. equivalent soil mass (ESM)) and sampling depth requirement. Despite evidence that fixed-depth measurements can result in error because of changes in soil bulk density and that sampling to 30 cm neglects a significant portion of the soil profile’s SOC stock, most MRV protocols do not specify which sampling method to use and only require sampling to 30 cm. Using data from UC Davis’s Century Experiment (“Century”) and UW Madison’s Wisconsin Integrated Cropping Systems Trial (WICST), we quantify differences in SOC stock changes estimated by FD and ESM over 20 years, investigate how sampling at-depth (> 30 cm) affects SOC stock change estimates, and estimate how crediting outcomes taking an empirical sampling-only crediting approach differ when stocks are calculated using ESM or FD at different depths.ResultsWe find that FD and ESM estimates of stock change can differ by over 100 percent and that, as expected, much of this difference is associated with changes in bulk density in surface soils (e.g., r = 0.90 for Century maize treatments). This led to substantial differences in crediting outcomes between ESM and FD-based stocks, although many treatments did not receive credits due to declines in SOC stocks over time. While increased variability of soils at depth makes it challenging to accurately quantify stocks across the profile, sampling to 60 cm can capture changes in bulk density, potential SOC redistribution, and a larger proportion of the overall SOC stock.ConclusionsESM accounting and sampling to 60 cm (using multiple depth increments) should be considered best practice when quantifying change in SOC stocks in annual, row crop agroecosystems. For carbon markets, the cost of achieving an accurate estimate of SOC stocks that reflect management impacts on soils at-depth should be reflected in the price of carbon credits.

Long‐term soil organic carbon changes after cropland conversion to grazed grassland in Southern Sweden

AbstractThere is growing awareness of the potential value of agricultural land for climate change mitigation. In Sweden, cropland areas have decreased by approximately 30% over recent decades, creating opportunities for these former croplands to be managed for climate change mitigation by increasing soil organic carbon (SOC) stocks. One potential land‐use change is conversion of cropland to grazed grasslands, but the long‐term effect of such change in management is not well understood and likely varies with soil type and site‐specific conditions. Through sampling of mineral and peatland soils within a 75‐year chronosequence of land converted from crop production to grazed grassland, we assessed how time since conversion, catenary position, and soil depth affected SOC storage. The SOC stocks calculated at an equivalent soil or ash mass increased through time since conversion in mineral soils at all topographic positions, at a rate of ~0.65% year−1. Soils at low topographic positions gained the most carbon. Peat SOC stock gains after conversion were large, but only marginally significant and only when calculated at an equivalent ash mass. We conclude that the conversion of mineral soil to grazed grassland promotes SOC accumulation at our sites, but climate change mitigation potential would need to be evaluated through a full greenhouse gas balance.

Improving soil thickness estimations and its spatial pattern on hillslopes in karst forests along latitudinal gradients

Soils provide storage space for nutrients and water, which governs many hydrological processes and functions in the natural ecosystems. Due to the complex soil-rock structures and localized climate, soil thickness and stock vary distinctly in different karst areas in southwest China. The difficulties of soil detection and the non-transparent underground soil-rock structures limit a deeper understanding of the spatial distribution of soils and their ecological functions. In this study, we employed electrical resistivity tomography (ERT) combined with soil probes to detect the spatial distribution of soils on hillslopes in karst forests in southwest China. The ERT surveys were conducted at six sites with 19 plots (20 × 30 m2) along latitudinal gradients. The results show that the ERT method performs well in visualizing the complex soil–bedrock interfaces and patchy distribution of soils in karst hillslopes, with remarkable consistency with the observed soil thickness and rock outcrops. Soil probes often hit rocks in soils (which we call a “rock barrier effect”), resulting in an underestimation of the mean soil thickness within the one-meter exploration depth by ∼0.18 m. This indicates that soil stock estimates derived from soil probes may be obviously underestimated in karst areas where the rock barrier effects are widespread. Meanwhile, the concept of equivalent soil thickness is proposed to remove the impact of scattered bedrock on soil stock estimation. For the six selected sites, the ERT-inferred mean soil thickness, equivalent soil thickness, and stock are 0.86 m, 0.60 m, and 0.10 m3/m3 respectively, with a trend of decreasing from high to low latitudes. Moreover, the rock outcrop coverage rate explains 52 % (60 %) of the variation in soil thickness (stock), followed by the annual mean temperature. This study emphasizes the importance of considering bedrock topography and its distribution in improving the detection of soil distribution, and the implications of the findings in this study are perhaps most profound for soil thickness-related soil erosion, soil water storage, and carbon storage in karst critical zones.

Effects of soil remoulding on keying behaviours of strip plate anchors with padeye offset

This paper reports the effect of soil remoulding on embedment loss and pullout capacity of strip plate anchors with padeye offset in normally consolidated clay during keying through large deformation finite element (LDFE) analysis. The effects of strain rate and soil remoulding are considered during keying process of plate anchors. First, the LDFE results are compared with theoretical solutions, centrifuge test results, and LDFE data available in the literature, which shows a good agreement. Then, the influences of initial embedment depth, load eccentricity, padeye offset and soil sensitivity on the embedment loss and pullout capacity of strip plate anchors during keying are investigated. The LDFE results show that the padeye offset and the soil remoulding have significant effects on the ultimate embedment loss and pullout capacity. To assess the keying behaviour of plate anchors, an equivalent soil strength is introduced. A combined factor and an equivalent ultimate pullout capacity are adopted to estimate the embedment loss and ultimate pullout capacity of strip plate anchors in normally consolidated clay, respectively.

Pedogenic controls of soil organic carbon stocks and stability beneath montane Norway spruce forests along a precipitation gradient

Reliable data on SOC stocks in forest soils is required in the context of climate change and soil health assessments but still limited by input data availability (e.g., bulk density) and methods used for stock calculation. Relatively few studies have investigated the stability of SOC in forest soils. We investigated SOC stocks and fractionation in soils beneath Norway spruce forests and grasslands in the montane zone along a gradient of mean annual precipitation (MAP). We sampled soil cores volumetrically to 40 cm depth and measured SOC in the fractions <2 mm (fine earth), >200 μm and 200–20 μm (coarse and fine POM), and <20 μm (MAOM) along with potential pedogenic controls. Total SOC stocks beneath forests in the study region, calculated by the equivalent soil mass (ESM) approach to 40 cm depth, amount to 79.0 ± 29.9 (mean ± standard deviation) Mg ha−1 (n = 20) in the mineral soil, and to 92.9 ± 30.6 Mg ha−1 including the litter layer, with a share of 55 % associated with POM. MAOM makes up ∼41 % of SOC in the uppermost mineral layer (0–5 cm) and increases to 71 % in the subsoil (20–40 cm). Multiple regression models show that MAOM is largely controlled by ammonium oxalate extractable Al (Alo) in the forest subsoils (20–40 cm), and increases with MAP in the topsoil layers (0–20 cm). Soils on carbonate rock stand out with ∼80–100 % larger shares of MAOM in the uppermost soil layers (0–10 cm) which is likely connected to higher soil pH and MAP, supporting microbial transformation and subsequent stabilisation of organic matter, which is reflected in narrower C:N ratios in MAOM and SOC.Including the litter layers, ESM-based total SOC stocks in forest soils tend to exceed those beneath grassland (80.2 ± 21.9 Mg ha−1; n = 31) by 16 %, but only by 6.4 % if calculated by the conventional fixed-depth (FD) approach. In contrast to the forest soils, SOC stocks beneath grasslands are dominated by MAOM (75.6 %).We conclude that (coniferous) forest soils are a poor reference for establishing sequestration potentials for stable SOC. The observed large proportion of POM in forest topsoils and its increase with declining MAP (indicating water availability) suggests a risk of SOC losses in response to increasing droughts due to climate change.

Short term effects of digestate and composted digestate on soil health and crop yield: Implications for sustainable biowaste management in the bioenergy sector

Composting mitigates environmental risks associated with using solid digestate as fertilizer. However, evidence is lacking on benefits of using composted digestate as fertilizer in enhancing soil health and increasing agronomic yield compared to non-composted digestate (hereafter, digestate). A field study was conducted consisting of digestate, composted digestate, co-composted digestate with biogas feedstocks (corn [Zea mays L.] silage, poultry litter, corn silage + poultry litter or food processing by-product), inorganic nitrogen fertilizer, and control (no treatment applied) on soil microbial biomass, enzyme activities (EA), soil organic carbon (SOC), bioavailable P (P), total nitrogen (TN), soil health index (SHI), and sunflower (Helianthus annuus L.) yield. The Partial Least Square Path Model (PLS-PM) was used to predict: 1) nutrient cycling in response to changes in microbial growth and EA and 2) agronomic yield in response to SHI and soil nutrients dynamics. Composted digestate had equivalent soil health benefits with most of co-composted materials and digestate, albeit agronomic yield was greatest with composted digestate, which was 40 % and 100 % greater than with inorganic nitrogen fertilizer and digestate, respectively, indicating composted digestate's potential to replace the synthetic N fertilizer. Moreover, composts from a sole digestate, rather than the ones from co-composted with fresh feedsstocks, can be promising organic amendments and fertilizers for growing sunflower. The PLS-PM model identified that triggered microbial biomass growth and EA, following digestate and composted digestate applications, catalyzed organic matter decomposition, resulting in enhanced nutrients contents and soil health. However, the model revealed that improved SHI did not predict agronomic yield, as opposed to P and TN, suggesting agronomic performance may have been more sensitive to changes in specific soil nutrients status than the overall soil health condition. We conclude that the benefits of composted digestate as fertilizer hint the significance of digestate valorization via post-digestate composting and compost utilization for sustainability of the bioenergy sector.