Soil Layer Research Articles

A novel semi-analytical model for laterally loaded piles

A new model for laterally loaded piles is proposed, consisting of a linear part and a non-linear iterative part. The linear part is based on the Green's function method, which strictly satisfies the displacement and stress continuity conditions at the pile-soil interface and leads to a rigorous solution. The non-linear iterative part assumes that the shear modulus of the soil around the pile decreases with the average strain of the soil layer. Only two soil parameters need to be calibrated, including the initial shear modulus of the soil and the reference shear strain at half the initial modulus. Compared to the finite element model, the advantage of this model is that it converges quickly while maintaining accuracy, which greatly improves computational efficiency. The advantage of this model over the p-y curve model is that it does not have the difficulty of selecting p-y spring parameters, especially for monopiles. The accuracy of this model is verified by comparison with three-dimensional finite element models and nine existing studies, including numerical models, field tests and centrifuge tests. These cases cover various piles with diameters of D∼0.273–10 m and aspect ratios of L/D∼3–40, installed in sand or clay by driving, jacking or vibration.

Nutrients Status of Citrus Orchards of District Multan, Punjab, Pakistan

Citrus is important and leading fruit crops across Pakistan now facing the decline qualitatively and quantitatively which directly affecting the total production per unit area. The major reason for these changes seems to be improper fertilization of nutrients. In this regard, an experiment has been conducted on the citrus orchards of district Multan, to evaluate the present condition of nutrients in soil and citrus plants. The relationship between soil properties, available nutrients in soil, and plants were also investigated. In 24 orchards, the soil samples at three different soil depths (0-15cm, 15-30cm, 30-45 cm) with 4–6-month-old leaves of the plant were collected. In soils, the N (100%), P (50%), B (70.83%), Fe (16.67%) and Zn (33.33%) were deficient at upper soil layer (0-15cm). The deficiency of these nutrients decreases with increasing soil depth. The leaf analysis of citrus plants showed that there was a deficiency of N (70.83%), P (66.66%), K (12.5%), Zn (66.6%) and B (50%). Among soil properties, the pH is negatively and significantly related to N, P, Fe, and Mn, while CaCO3 and EC showed a negatively significant correlation to P and B respectively at upper soil layer. Organic matter was positive and significantly related to P and Cu at upper soil layer. The significant correlation between soil properties and nutrients decreases with increasing soil depth. The K and Fe in the soil are directly associated with increasing its contents in the leaf.

Interpretable baseflow segmentation and prediction based on numerical experiments and deep learning

Baseflow is a crucial water source in the inland river basins of high-cold mountainous region, playing a significant role in maintaining runoff stability. It is challenging to select the most suitable baseflow separation method in data-scarce high-cold mountainous region and to evaluate effects of climate factors and underlying surface changes on baseflow variability and seasonal distribution characteristics. Here we attempt to address how meteorological factors and underlying surface changes affect baseflow using the Grey Wolf Optimizer Digital Filter Method (GWO-DFM) for rapid baseflow separation and the Long Short-Term Memory (LSTM) neural network model for baseflow prediction, clarifying interpretability of the LSTM model in baseflow forecasting. The proposed method was successfully implemented using a 63-year time series (1958–2020) of flow data from the Tai Lan River (TLR) basin in the high-cold mountainous region, along with 21 years of ERA5-land meteorological data and MODIS data (2000–2020). The results indicate that: (1) GWO-DFM can rapidly identify the optimal filtering parameters. It employs the arithmetic average of three methods, namely Chapman, Chapman-Maxwell and Eckhardt filter, as the best baseflow separation approach for the TLR basin. Additionally, the baseflow significantly increases after the second mutation of the baseflow rate. (2) Baseflow sources are mainly influenced by precipitation infiltration, glacier frozen soil layers, and seasonal ponding. (3) Solar radiation, temperature, precipitation, and NDVI are the primary factors influencing baseflow changes, with Nash-Sutcliffe efficiency coefficients exceeding 0.78 in both the LSTM model training and prediction periods. (4) Changes in baseflow are most influenced by solar radiation, temperature, and NDVI. This study systematically analyzes the changes in baseflow and response mechanisms in high-cold mountainous region, contributing to the management of water resources in mountainous basins under changing environmental conditions.

One-dimensional infiltration in a layered soil measured in the laboratory with the mini-disk infiltrometer

Abstract Layered soils can consist of a thin little permeable upper layer over a more permeable subsoil. There are not many experimental data on the influence of this upper layer on infiltration. The mini-disk infiltrometer set at a pressure head of –3 cm was used to compare infiltration of nearly 40 mm of water in homogeneous loam and clay soil columns with that in columns made by a thin layer (1 and 3 cm) of clay soil over the loam soil. For each run, the Horton infiltration model was fitted to the data and the soil sorptivity was also estimated by considering the complete infiltration run. For the two layered soils, the estimates of initial infiltration rate and decay constant were similar but a thicker upper layer induced 2.4 times smaller final infiltration rates. Depending on the infiltration parameter and the thickness of the upper layer, the layered soils were characterized by 2.2–6.3 times smaller values than the loam soil and 2.2–6.6 higher values than the clay soil. Sorptivity did not differ between the homogeneous clay soil and the layered soil with a thick upper layer and a thin layer was enough to induce a decrease of this hydrodynamic parameter by 2.5 times as compared with that of the homogeneous loam soil. Even a thin upper layer influences appreciably infiltration and hydrodynamic parameters. Layering effects vary with the thickness of the upper layer and the considered parameter. The applied experimental methodology could be used with other soils and soil combinations.

Adaptive grazing enhances plant species richness and density in the soil seed bank in a semi-arid grassland

The soil seed bank plays a key role in vegetation resilience under environmental disturbances, and is especially important for the restoration of degraded vegetation. However, the responsive dynamics of the soil seed bank to animal grazing and its potential in the restoration of grazing degraded steppe grassland remain unclear. Here we examined the changes in plant species diversity and density in both the soil seed bank and the aboveground vegetation of a natural grassland along an experimental gradient of four grazing intensities (nil, light, moderate and heavy grazing) in an adaptive grazing management system that ensures grassland residual cover was always above a certain criteria. The grassland is a typical steppe dominated by Leymus chinensis, Stipa grandis, and Cleistogenes squarrosa in central Inner Mongolia, China. We found that (i) plant species richness and density of the seed bank in the top 10 cm soil layer increased with grazing intensity, though the density of the seed bank in the top 5 cm soil layer showed an decrease. (ii) Moderate and heavy grazing significantly decreased the density of perennial but increased annual and biennial plants in the top 5 cm soil layer, which dominate the changes in the top 10 cm soil layer. (iii) Plant species richness and density in the aboveground vegetation also increased with grazing intensity, so did the similarity between the species composition of the soil seed bank and aboveground vegetation in the top 10 cm. The increase in the richness and density of annual and biennial species dominated the responsive changes to grazing of the soil seed bank and aboveground vegetation in the studied grassland. Our results provide a reference basis for grazing management in the region from the perspective of the soil seed bank, and suggest that the adaptive grazing system with grassland residual height controlled above a criterion benefits to the soil seed bank thus the re-generation of vegetation.

Soil health indicators in oil palm agroforestry systems in the eastern Amazon, Brazil

Agroforestry systems (AFSs) are generally recognized for improving soil health and increasing soil carbon (C) stock. In the Amazon region, oil palm AFSs have been promoted as a productive strategy and may offer an additional benefit of recovering degraded areas. Our objective was to evaluate whether the management practices adopted in oil palm AFSs affect soil health indicators and C stock. We carried out a study in Tomé-Açu, state of Pará, eastern Amazon, through which we evaluated two oil palm AFSs that differed in species diversity: higher diversity (AFShigh) and lower diversity (AFSlow). We used a regenerating forest (FOR) to compare with the oil palm AFSs, as regenerating forests are also a model of environmental recovery in the eastern Amazon. In the 0–10, 10–20 and 20–30 cm soil layers, we evaluated chemical indicators (active acidity (pH), calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), and aluminum (Al)), (b) physical indicators (density (SD) and stability of aggregates (AGGRE)), and (c) biological indicators (permanganate oxidizable carbon (POXC), particulate organic carbon (POC), total soil carbon (SOC content) and root stock (ROOT)). We also evaluated the total soil carbon stock (SOC stock). The values of the biological indicators in the most superficial layer, especially the C indicators, were higher in the AFSlow (C content: 1.63 ± 0.13%, POXC: 568 ± 17 mg kg−1, POC: 0.63 ± 0.10 g kg−1) and the AFShigh (C content: 1.84 ± 0.04%, POXC: 656 ± 24 mg kg−1, POC: 0.83 ± 0.06 g kg−1) than in FOR (C content: 1.35 ± 0.09%, POXC: 336 ± 10 mg kg−1, POC: 0.44 ± 0.03 g kg−1). In general, the values of chemical indicators were higher in the AFSs than in FOR, except for the Al content, which was higher in FOR than in the AFSs. The physical indicators did not show a specific pattern of variation between the AFSs and FOR; aggregate stability was higher in FOR (range throughout the soil profile: 5.57 ± 0.09 to 5.38 ± 0.24 mm) than in the AFSlow (5.41 ± 0.03 to 3.79 ± 0.07 mm) and the AFShigh (5.07 ± 0.01 to 3.79 ± 0.11 mm) in all the soil layers, and soil density was higher in the AFShigh and FOR than in the AFSlow in most subsurface layers. Therefore, oil palm AFSs improve the chemical and biological health of the soil, especially in the more superficial layers, but it does not improve the physical health of the soil when compared to the forest.

Influence of cultivation methods on the soil aggregate state in the context of weed development in winter wheat plantations

Weed control in winter wheat crops is an important issue. There is a risk of increasing populations of certain weed species that are resistant to some of herbicides used for winter wheat crops. This could be controlled by a combination of agronomic, mechanical, chemical, and biological methods. After introducing winter wheat into the rotation and improving tillage, the weediness of regular black soils with perennial root and emerged weeds were significantly reduced. The formation of nodal and rudimentary roots had a significant effect on the productivity of winter wheat under different soil moisture conditions. The highest yield of winter wheat was obtained when sown at the optimum time, with higher stem density and ear productivity due to better grain fullness. We studied what effects did the tillage methods have on the aggregate state of the soil in relation to weed development in winter wheat crops, finding that the structural and aggregate composition of the soil played an important role in winter wheat crops, influencing both the development of the crop root system and the water-physical balance of the chernozem, as well as naturally influencing the course of erosion processes in the experimental plots, and having a universal dynamic in terms of adaptation of aggregation and disaggregation processes. Prolonged mechanical stress on soil can cause destruction of its structure. For instance, continuous ploughing or moldboardless tillage with little or no manure application may permanently reduce soil fertility by increasing humus mineralisation. Subsequently, these factors may cause a significant decline in the soil's structural and aggregate composition, resulting in larger amounts of dusty particles smaller than 0.25 mm and cloddy particles larger than 10–12 mm. The soil's structural condition before sowing winter wheat in early September, on average for 2011–2016, indicates increased dispersion of the tilth layer (0–10 cm) in the experimental variants where shallow disc tillage of 10–12 cm was applied. Increase in the number of clods larger than 10 mm in the areas where moldboardless tillage had been applied can be attributed to significant soil drainage. The soil's aggregate state was rated as good, with 8.7% in the 0–10 cm soil layer and 1.7% of clods > 10 mm in the 0–30 cm layer. In 2014–2016, it was rated as satisfactory, with 7.4% and 9.8% of clods > 10 mm, respectively. Shallow disc cultivation resulted in slightly worse indicators: 6.6% and 8.3% of clods > 10 mm in soil layer 0–10 cm and 0–30 cm, respectively, in 2011–2013; and 7.2% and 6.9% of clods > 10 mm, respectively, in 2014–2016. In general, the parameters of optimal structural condition were positive. The tillage method used had a considerable effect on weed growth and development, particularly for those with a root and rhizome structure. It also affected the prevalence and development of pests and diseases in winter wheat. Agrotechnical methods of weed control do not guarantee complete destruction of weeds. Mechanical moldboardless tillage to the depth of 14–16 cm and disc tillage to the depth of 10–12 cm left the fields with 4.1 to 8.8 annual weeds per square meter and 1.3 to 3.3 specimens of harmful root weeds such as Convolvulus arvensis, Lactuca tatarica and Cirsium arvense. Mechanical moldboardless tillage to the depth of 14–16 cm and disc tillage to the depth of 10–12 cm left the fields with 4.1 to 8.8 annual weeds per square meter and 1.3 to 3.3 specimens of harmful root weeds such as Convolvulus arvensis, Lactuca tatarica and Cirsium arvense. Post-harvest residues (4–5 t/ha) can provide almost complete protection against weeds by covering the soil surface. However, pests and diseases may spread more easily due to preservation of fungal spores on the surface of plant residues and preservation of pest larvae in the straw and soil. The distribution of weed seeds in the soil was altered when the rotational tillage of common chernozems in winter wheat cultivation technology had been replaced with energy–saving minimum tillage (shallow flat-cutting disc tillage). This resulted in the concentration of most of the weed seeds (85–90%) in the upper soil layer (0–10 cm).

NUMERICAL ANALYSIS OF A SINGLE-VAULT STATION OF THE SHALLOW CONTOUR INTERVAL OF THE KHARKIV METRO

Purpose. The development of the Kharkiv metro is characterized by the development of new structures and technologies for their construction. The extensive metro system in the city of Kharkiv and the presence of deep and shallow underground stations require scientific substantiation of these complex underground objects. The method of the scientific article is the numerical analysis of a single-vaulted shallow contour interval station, the vault of which has a special design (perforated reinforced concrete blocks). Methodology. To achieve the goal, the design of the station with a prefabricated vault and "slurry wall" was analyzed, as well as the engineering and geological conditions of its construction. A finite-element model of a single-vault station of a shallow contour interval was created. The model reproduces the geometric dimensions of the real structure of the Kharkiv metro, the layers of soil in which it is laid, the conditions of adjacency of "slurry wall", as well as perforated vault blocks. The model is based on volumetric finite elements and more fully reflects the interaction of the station with the surrounding massif. The calculation of the finite-element model for the joint effect of the self-weight of the model and the moving load of the NK-80 (combined loading) was carried out. Findings. The value of the stress-strain state of a single-vault station of the shallow contour interval was obtained. Analysis of displacements and stresses at concentration points was carried out. The situation of overstressing of the station structure and the appearance of cracking zones in the case of combined load action was revealed. Originality. The value of the stress-strain state was obtained with a combination of self-weight and moving load of NK-80, as well as with the separation of the portion of the latter. The obtained results indicate the need to revise the design of the shallow contour interval station, the vault of which has a special design (perforated reinforced concrete blocks). Practical value. It consists of the obtained results, which show the vector of development of station structures of the Kharkiv metro.

Inverse modeling of frequency domain-based one-dimensional soil water flow in layered soils

Soils are heterogeneous at multiple scales. Estimates of spatially varying saturated hydraulic conductivity (Ks) of soils dictate the resolution of modeling water flux based on the Richardson-Richards equation (RRE), but direct measurements of Ks everywhere in a field are practically impossible. As a result, this study develops an inverse approach to estimate spatially varying Ks utilizing soil moisture observations driven by periodic weather variability at different frequencies. Using a numerical solution to vertical, one-dimensional RRE based on Gardner-Kozeny (GK) model in a heterogeneous soil with periodic flux, we investigate the spatial cross-correlation between Ks and observations (the amplitude or phase shift) of soil moisture fluctuation at different frequencies without high computational cost in the conventional time-domain model. These correlation patterns vary with the spatial location and frequency, suggesting that soil moisture fluctuations at different frequencies at one monitoring location carry non-redundant information about the heterogeneous distribution of Ks. Guided by cross-correlation maps, several inverse experiments reveal the effectiveness of multi-frequency data of soil moisture fluctuation for mapping the heterogeneous distribution of Ks. Monte Carlo simulations suggest that multi-frequency data can provide non-redundant and useful information about the estimation of heterogeneous Ks. Synthetic data based on a commonly-applied nonlinear van Genuchten-Mualem (VG) model is then tested in our inversion algorithm. The results indicate that the spatial pattern of the inverted GK Ks is very similar to that of the VG Ks, although these two parameters are inherently not identical since they are used in two different models. In addition, the inverted GK Ks can successfully predict the soil moisture fluctuation of frequencies that were not used in the inversion. Despite having no field experiments to validate this model, we believe this is the first attempt to conduct frequency-domain inverse modeling in vadose zone hydrology using soil moisture fluctuation.

Decrease in fertility of typical chernozem due to long-term anthropogenic pressure in grain-beet crop rotations

The saturation of sugar beet rotations under different fertilizer application systems and long-term cultivation induces significant changes in soil properties, leading to decreases in humus content, mineral nitrogen, phosphorus, and potassium. The study was conducted in a stationary multifactorial experiment in grain-beet crop rotations: crop rotation, row-crop, and grain-row crop rotations with the application of 40 t/ha of manure under sugar beets + NPK 100:90:90 and a variant without fertilizers. The paper presents the results of monitoring changes in humus content during each rotation, reduction of humus reserves in the plow layer, and physicochemical and agrochemical soil indicators. In the variants without fertilizers, we observed 0.24–0.41% decline in humus content in all crop rotations during 3 rotations of ten-field crop rotations (30 years). Overall, there occurred 0.89–1.00% decrease over 50 years of anthropogenic influence, equivalent to 31.8–35.7 t/ha, or 23.1–26.1% of initial reserves per hectare. Despite application of 40 t/ha of manure + NPK 100:90:90 under sugar beets, humus loss was 27.5 t/ha in the row-crop rotation and 16.8 t/ha in the grain-row crop rotation. Fertilizer application led to increase in exchangeable and hydrolytic soil acidity. With the application of 6.7 t/ha of manure + NPK 53:42:42 per 1 ha of crop rotation area, there was a tendency towards increase in mineral nitrogen content, mobile phosphorus doubled to 280.1–302.8 mg/kg compared to the variant without fertilizers, and exchangeable potassium decreased regardless of the fertilization system, which was associated with its utilization by plants. Sugar-beet yield increased to 44.76 t/ha in the crop-rotation under the organo-mineral-fertilizer application system, exceeding the spring wheat rotation by 4.63 t/ha and the variants without fertilizers by 2.45–2.72 times. Therefore, the modern fertilizer application system under sugar beets did not ensure stabilization of humus content in the soil and increased its acidity. It is necessary to more broadly use cover crops in crop rotations, incorporate crop residues, and apply biological preparations to improve soil fertility.

Variability of soil organic carbon and nutrient content across land uses and agriculturally induced land use changes in the forest-savanna transition zone of Cameroon

Data expressing the effects of land use change on soil attributes is still very scarce in Cameroon as in most of Africa. In this regard, this study aimed to assess soil organic carbon (OC), nitrogen (N), phosphorus (P), and potassium (K) content across land uses and agricultural-induced land use changes in the forest-savanna transition zone of Cameroon. Nine land uses were identified in the study area showing five directions of land use changes namely the change from the native forest to cocoa agroforestry, native savannah to cocoa agroforestry, native savannah to cropland, savannah fallow to cropland, and transition zone fallow to cropland. The soil was sampled at 0–10 cm (upper layer) and 10–30 cm (lower layer) depths in three replicates for each land use and analyzed for physicochemical properties. There were significant differences across the land uses for OC (p < 0.02), N (p < 0.01), C/N (p < 0.01), pH (p < 0.02), soil organic carbon stocks (SOCS) (p < 0.01), and soil nitrogen stocks (SNS) (p < 0.01), with a relatively higher magnitude in the upper soil layer. Higher magnitudes of OC (26.1 to 22.5 g kg−1), N (2.5 to 1.6 g kg−1), SOCS (32.1 to 27.8 Mg ha−1), and SNS (2.9 to1.9 Mg ha−1) were observed in native lands and cocoa agroforestry with the highest in the native forest and the forest-based cocoa agroforestry. Meanwhile, the effect of land use change on soil properties was mainly significant in the change from native savannah to croplands at p < 0.05 for OC, N, SOCS, and SNS, and p < 0.02 for P. Therefore, agroforestry is an alternative to enhance the ecological resilience of lands affected by land use changes.

Effects of Application of Different Organic Materials on Phosphorus Accumulation and Transformation in Vegetable Fields

Presently, the improvement of soil organic matter is the basis to ensure food security, but the accumulation and transformation characteristics of soil phosphorus (P) as affected by organic matter remain unclear. The accumulation, transformation, and migration characteristics of soil P in different soil layers of vegetable fields were researched under the application of organic materials. Six treatments were set up in the experiment:control (no fertilization), traditional fertilizer application by farmers, biochar, chicken manure, food waste, and straw application. Available phosphorus (Olsen-P), water-soluble phosphorus (CaCl2-P) content, soil phosphorus forms, soil organic matter (SOM), and pH were determined during the pepper harvest period. In the 0-5 cm and 5-10 cm soil layers, the available phosphorus content of traditional fertilization of farmers was higher, and the available phosphorus content of the four organic materials was in the order of straw &gt; biochar &gt; chicken manure &gt; food waste. Compared to that with food waste, the straw and biochar treatments increased soil available phosphorus by 59.6%-67.3% and 29.1%-36.9%, respectively. The straw treatment could easily enhance the soil labile P pool, and soil labile P in the 0-5 cm soil layer increased by 47.3% and 35.1% compared with that under the chicken manure and food waste treatments, respectively. With the increase in soil depth, the proportion of available phosphorus in the chicken manure treatment decreased the least, and available phosphorus of the 20-30 cm soil layer accounted for 55.9% of the topsoil layer but only accounted for 16.0%-34.0% under treatment with the other three materials. Compared with that under the traditional fertilization of farmers, the pH significantly increased by 0.18-0.36 units after the application of organic fertilizer, and the pH of the chicken manure and food waste treatments was significantly higher than that of biochar and straw (P &lt; 0.05). SOM content under the biochar treatment significantly increased by 7.7%-17.6% compared to that under the other three organic materials. Among the four organic materials, the straw treatment boosted the labile P pool the most, which was conducive to the rapid increase in plant-available P. Phosphorus was most likely to migrate downward under the chicken manure treatment. In the field management based on soil fertility enhancement, the application of biochar could not only improve soil pH and SOM but also avoid excessive accumulation of phosphorus in the surface layer, which decreases environmental risks.

Study on Early Identification of Rainfall-Induced Accumulation Landslide Hazards in the Three Gorges Reservoir Area

The early identification of potential hazards is crucial for landslide early warning and prevention and is a key focus and challenging issue in landslide disaster research. The challenges of traditional investigation and identification methods include identifying potential hazards of landslides triggered by heavy rainfall and mapping areas susceptible to landslides based on rainfall conditions. This article focuses on the problem of early identification of rainfall-induced accumulation landslide hazards and an early identification method is proposed, which is “first identifying the accumulation that is prone to landslides and then determining the associated rainfall conditions”. This method is based on identifying the distribution and thickness of accumulation, analyzing the rainfall conditions that trigger landslides with varying characteristics, and establishing rainfall thresholds for landslides with different accumulation characteristics, ultimately aiming to achieve early identification of accumulation landslide hazards. In this study, we focus on the Zigui section of the Three Gorges Reservoir as study the area, and eight main factors that influence the distribution and thickness of accumulation are extracted from multi-source data, then the relative thickness information extraction model of accumulation is established by using the BP neural network method. The accumulation distribution and relative thickness map of the study area are generated, and the study area is divided into rocky area (less than 1 m), thin (1 to 5 m), medium (5 to 10 m), and thick area (thicker than 10 m) according to accumulation thickness. Rainfall is a significant trigger for landslide hazards. It increases the weight of the sliding mass and decreases the shear strength of soil and rock layers, thus contributing to landslide events. Data on 101 rainfall-induced accumulation landslides in the Three Gorges Reservoir area and rainfall data for the 10 days prior to each landslide event were collected. The critical rainfall thresholds corresponding to a 90% probability of landslide occurrence with different characteristics were determined using the I-D threshold curve method. Prediction maps of accumulation landslide hazards under various rainfall conditions were generated by analyzing the rainfall threshold for landslides in the Three Gorges Reservoir area, serving as a basis for early identification of rainfall-induced accumulation landslides in the region. The research provides a method for the early identification of landslides caused by heavy rainfall, delineating landslide hazards under different rainfall conditions, and providing a basis for scientific responses, work arrangements, and disaster prevention and mitigation of landslides caused by heavy rainfall.

Soil Arthropods: An Unsung Heroes of Soil Fertility

Soils are crucial elements of ecosystems, and their fertility is maintained mainly by the actions of their living organisms. The fertility of soil depends on its ability to provide plants with vital nutrients needed for their growth and reproduction. Additionally, soil acts as a physical medium that facilitates root growth and respiration while also maintaining its structural integrity against erosive forces. Arthropods play a significant role in enhancing the decomposition of plant litter in two ways. Firstly, they directly turn it into their tissues. Secondly, they indirectly alter it physically and chemically, turning it into substrates that can further be decomposed. Termites have higher assimilation efficiencies compared to other soil arthropods, which means they can convert a greater proportion of ingested litter into biomass directly. On the other hand, collembola, oribatid, myriapods, and Isopoda contribute to nutrient cycling indirectly as secondary decomposers. They condition litter for further breakdown by the microflora through comminution and passage through the gut. Arthropods, such as insects, can create tunnels and burrows in soil, which help to allow air and water to penetrate deeper into the soil. These tunnels also help to mix organic materials into the upper layers of soil. In addition, arthropod faeces serve as the starting point for the creation of soil aggregates that are necessary for maintaining the soil structure and integrity. Soil arthropods play a crucial role in the formation of humus, which helps to retain water and nutrients in the soil. In addition, they provide important ecosystem services, including provisional, supporting, and regulating services. Unfortunately, these tiny creatures' contributions to the environment are often undervalued and neglected.

Crop management strategies shape the shared temporal dynamics of soil food web structure and functioning

In recent decades, there has been growing interest in exploring the soil biota, highlighting the significance of soil organisms' networks in soil functioning. Here, we use a modeling approach to investigate how changes in cropping practices influence the soil food web dynamics and it relates to that of soil functioning. In an experimental trial, we tested for change in topsoil food webs after shift from conventional to alternative practices (changes in tillage intensity, amount of residues returned and N fertilization rate). Samplings were made in 16 plots of a randomized complete block design during spring of year 0, 2 and 4 after the onset of the trial. Microorganisms, microfauna, mesofauna and macrofauna were sampled, identified and grouped into trophic groups. We built a general soil food web describing plausible carbon flows between these trophic groups and computed several network indices. At the same dates, soil functions linked to C and N dynamics were measured from soil samples. We used a COSTATIS analysis to investigate relationships between temporal sequences of soil functions and soil food web indices. Significant interactive effects of the date and of agricultural systems were found on the mean and the maximum trophic level, the bacterial-to-fungal path ratio, the total biomass and the way biomass accumulates across trophic levels, the number of trophic groups and the functional redundancy in trophic groups. Similarly, organic matter transformations and enzymatic activities showed differences across date and agricultural systems. Results show that temporal changes in soil food web structure and in soil processes related to N and C cycling co-vary following changes in agricultural management practices. Management practices related to tillage exerted stronger effects on soil food web functioning than those related to the export of crop residues or reduction in mineral N fertiliser. For instance, reduced tillage lead to more complex food webs, with increased C and N mineralization in the upper soil layer (0–5 cm), in which most of the residues accumulate. Our results provide insights on soil food webs temporal dynamics, even within a restricted panel of agricultural practices. Our results suggest that changes in agricultural practices influence feedbacks between organisms and the functions they perform, so that a temporal co-structure can be observed in the studied site. Such work could help better understand the mechanisms of resistance or ecological debt during agroecological transition, which could limit or delay expected Nature-based solutions.

Tracing the contribution and fate of synthetic nitrogen fertilizer in young apple orchard agrosystems

Excessive synthetic nitrogen (N) inputs in intensive orchard agrosystems of developing countries are a growing concern regarding their adverse impacts on fruit production and the environment. Quantifying the distribution and contribution of fertilizer N is essential for increasing N use efficiency and minimizing N loss in orchards. A 15N tracer experiment was performed in a young dwarf apple orchard over two growing seasons to determine the fertilizer N transformation and fate. Fertilizer N primarily contributed to 25 % to 75 % of soil nitrate in the top 60 cm, but the contribution to soil microbial biomass N and fixed ammonium was <8 %, with the contribution to plant N ranging from 9 % to 19 %. In most growth periods, soil nitrate and fixed ammonium contents derived from native soil with N fertilization were higher than those not receiving N fertilizer. The N use efficiency of plants was only 2.6 % and 4.9 % in the first and second seasons, respectively, in contrast to 56.6 % and 54.0 % of N recovered in soil. Meanwhile, N assimilated into microbial biomass accounted for 0.8 %, and the proportion fixed by clay minerals was 3.5 %–5.2 %. One season after N fertilization, the nitrate below the 1 m soil layers accounted for 4.6 % of the applied N fertilizer, and the proportion increased to 22.5 % after two seasons. The N loss rate via N2O emission was 0.4 % over two years. The application of N fertilizer facilitated indigenous soil N mineralization, and abiotic ammonium fixation more efficiently retained synthetic N than microbial immobilization. These findings provide new insight into orchard N cycling, and attention should be given to the improvement of soil N retention and turnover capacity regulated by soil microbial and abiotic processes, as well as the potential environmental impacts of additional soil N mineralization resulting from prolonged chemical N fertilization.

Different Land-Use Effects on Soil Aggregates and Aggregate-Associated Organic Carbon in Eastern Qinghai–Tibet Plateau

Land use changes modify soil properties, including aggregate structure, and thus, profoundly affect soil quality and health. However, the effects of land use changes originating from alpine grassland on soil aggregates and aggregate-associated organic carbon have received little attention. Soil aggregate fraction, aggregate-associated organic carbon and relevant influencing factors were determined at 0–20, 20–40 cm soil layers for alpine grassland, cropland and abandoned land in the eastern Qinghai–Tibet Plateau (QTP), and their relationships were analyzed by partial least square regression (PLSR). Results showed the following: (1) conversion from alpine grassland to cropland resulted in a significant decline macroaggregate fraction (R0.25), mean weight diameter (MWD), mean weight diameter (GMD), soil organic carbon (SOC), and microaggregate-associated SOC; (2) almost all aggregate stability indexes, SOC, and aggregate-associated SOCs were significantly positively correlated with silt and glomalin, suggesting that the binding of fine particles (silt) with the organic cementing agent (glomalin) was probably a key mechanism of SOC formation and aggregate stability in the studied region; (3) compared with biotic factors such as SOC, glomalin and root biomass, abiotic factors including silt and sand can better predict aggregate stability and SOC fraction using the PLSR model. The above results indicated that the conversion of alpine grassland to other land use types in high altitude areas would destroy soil structure and decrease soil organic carbon content, and then reduce soil quality.

Physical properties and organic carbon in no-tilled agricultural systems in silty Pampas soils of Argentina

Context Under continuous long-term no-till farming, many silty soils develop platey and massive compacted structures in topsoil, ascribed to low crop diversification and intense agricultural traffic. Aims We hypothesise that agricultural scenarios of greater diversification and cropping intensity should increase carbon (C) inputs and total and particulate organic C, resulting in the disappearance of these platey and massive compacted structures and soil compaction. Methods The hypothesis was tested in 55 selected production fields (lots or macro-plots of trials with a cultivated area greater than 15 ha) and five non-cultivated sites across the Rolling Pampas of Argentina. The whole area was covered by fine, illitic, thermal, silty loams (Typic Argiudolls, US Soil Taxonomy; Typic Phaeozems, FAO Soil Map). Based on estimations of the crop intensity index (CII; proportion of days in the year with active crop growth) and recent agricultural history of crop sequences, sampled fields were grouped into five categories: soybean (Glycine max) monoculture (CII &lt; 0.45; mean CII = 0.39); low intensity cropping sequence (CII = 0.45–0.60; mean CII = 0.50); high intensity cropping sequence (CII = 0.60–0.80; mean CII = 0.66); pastures for hay bale production (CII = 1.0); and quasi-pristine situations (areas with non-implanted and non-grazed grass vegetation or with negligible stocking rate, CII = 1.0). Key results Total C inputs to soil varied within ~1400–7800 kg C ha−1 year−1 and were significantly and positively related to crop intensity index (P &lt; 0.0001, r = 0.83). The highest (P &lt; 0.05) soil organic C levels were observed in the first 0.05 m of soil and quasi-pristine conditions (even higher than under pasture), and the lowest (P &lt; 0.05) under soybean monoculture. In the 0.05–0.20 m soil layer, quasi-pristine conditions had significantly (P &lt; 0.05) higher soil organic C levels; the other situations did not differ. Soil organic C and particulate organic C levels (0–0.05 m layer) were related to both CII and annual C input. Platey structures and clods &gt;0.1 m (0–0.2 m layer) were negatively related to CII (r = −0.59 and −0.45, respectively; P &lt; 0.0001) and C inputs from crops (r = −0.60 and −0.29, respectively; P &lt; 0.01). Nevertheless, this did not result in soil compaction alleviation, as shown by soil bulk density, maximum penetration resistance and water infiltration variations. About 92% of the samples with soil bulk density above the threshold (1.35 Mg m−3), and about 32% of the total records, presented levels of maximum penetration resistance, aeration porosity and/or water infiltration beyond the values suggested as critical. Conclusions Although soil organic C in topsoil varied as hypothesised, the studied soil physical properties did not. This partially rejects our hypothesis. Implications This study underscores the intricate interplay between crop intensity, SOC enhancement, soil structure improvement and the persistent challenge of subsoil compaction.

Kinetics of soil re-acidification under no-tillage system

The rate and amount of Al3+ released from re-solubilization of the Al-containing polymers and minerals due to the increase in proton activity in the soil solution in subtropical regions is scarce in the literature. The objective of the present study was to track the Al3+ reappearance following its neutralization during the switch from a conventional tillage system to a no-till (NT) system. For this purpose, we evaluated a long-term lime experiment under NT on a subtropical Ultisol. The treatments included varying lime rates, with different historic of lime reapplication. Soil samples were taken at the 0–5, 5–10, and 10–15 cm depth in 1988, 1994, 1995, 1996, 2001, 2003, 2006, 2012, and 2022. The re-solubilization of Al-containing soil polymers and minerals in the 0–15 cm soil layer proceeds slowly in the first 10 years; afterwards, the rate and amount of Al3+ released increased. However, regardless of the lime treatment, the soil never returns its natural acidic state, even after 34 years of the first liming operation. A decrease in the intensity of reappearance of exchangeable Al3+ in the soil profile is clearly observed, compared to the treatment without reapplication of surface lime. We have observed that it takes 7–9 years for 10% of the effective cation exchange capacity to be occupied by Al3+ if limestone is not reapplied on the soil surface; if underdoses are reapplied this level can be maintained for 13–15 years. Furthermore, if larger and more frequent lime doses are used, a low Al3+ saturation (<10%) can be maintained permanently. These findings emphasize the importance of an appropriate liming process at the start of NT, followed with surface limestone reapplication, to ensure a very low Al3+ saturation over a long period of time in the 0–15 cm soil layer.

Experimental and numerical settlement analysis of railway track over geogrid reinforced ballast

PurposeThe main objective of the present research is to investigate the benefits of using geogrid reinforcement in minimizing the rate of deterioration of ballasted rail track geometry resting on soft clay and to explore the effect of load amplitude, load frequency, presence of geogrid layer in ballast layer and ballast layer thickness on the behavior of track system. These variables are studied both experimentally and numerically. This paper examines the effect of geogrid reinforced ballast laying on a layer of clayey soil as a subgrade layer, where a half full scale railway tests are conducted as well as a theoretical analysis is performed.Design/methodology/approachThe experimental tests work consists of laboratory model tests to investigate the reduction in the compressibility and stress distribution induced in soft clay under a ballast railway reinforced by geogrid reinforcement subjected to dynamic load. Experimental model based on an approximate half scale for general rail track engineering practice is adopted in this study which is used in Iraqi railways. The investigated parameters are load amplitude, load frequency and presence of geogrid reinforcement layer. A half full-scale railway was constructed for carrying out the tests, which consists of two rails 800 mm in length with three wooden sleepers (900 mm × 90 mm × 90 mm). The ballast was overlying 500 mm thick clay layer. The tests were carried out with and without geogrid reinforcement, the tests were carried out in a well tied steel box of 1.5 m length × 1 m width × 1 m height. A series of laboratory tests were conducted to investigate the response of the ballast and the clay layers where the ballast was reinforced by a geogrid. Settlement in ballast and clay, was measured in reinforced and unreinforced ballast cases. In addition to the laboratory tests, the application of numerical analysis was made by using the finite element program PLAXIS 3D 2013.FindingsIt was concluded that the settlement increased with increasing the simulated train load amplitude, there is a sharp increase in settlement up to the cycle 500 and after that, there is a gradual increase to level out between, 2,500 and 4,500 cycles depending on the load frequency. There is a little increase in the induced settlement when the load amplitude increased from 0.5 to 1 ton, but it is higher when the load amplitude increased to 2 ton, the increase in settlement depends on the geogrid existence and the other studied parameters. Both experimental and numerical results showed the same behavior. The effect of load frequency on the settlement ratio is almost constant after 500 cycles. In general, for reinforced cases, the effect of load frequency on the settlement ratio is very small ranging between 0.5 and 2% compared with the unreinforced case.Originality/valueIncreasing the ballast layer thickness from 20 cm to 30 cm leads to decrease the settlement by about 50%. This ascertains the efficiency of ballast in spreading the waves induced by the track.