Soil Zone Research Articles

Accumulation and Distribution of Heavy Metals in Soils and Medicinal Plants in the Impact Zone of Novocherkassk Power Station

Accumulation and Distribution of Heavy Metals in Soils and Medicinal Plants in the Impact Zone of Novocherkassk Power Station

Non‐Stationary Flash Drought Analysis and Its Teleconnection With Low‐Frequency Climatic Oscillations

ABSTRACTFlash droughts, characterised by their rapid onset and significant impacts on local communities and agriculture, pose challenges for monitoring and mitigation efforts due to their unpredictable nature. Therefore, this study aims to investigate the occurrence, characteristics and influencing factors of flash droughts in the Ganga River Basin (GRB) for the period 1981–2020. Flash droughts are identified using the pentad averaged root zone soil moisture (PRZSM). The Mann‐Kendall trend test is used to determine the spatial and temporal pattern of flash drought characteristics. Furthermore, a multivariate flash drought index (MFDI) is developed to account for the combined effects of flash drought characteristics. Finally, wavelet coherence analysis evaluates the relationship between climatic oscillations and MFDI at the sub‐basin scale. Utilising a revised flash drought identification approach incorporating non‐stationary cumulative distribution functions (CDFs), the study identifies flash droughts in the GRB, particularly emphasising higher occurrences in the Chambal and Upper Yamuna Sub‐basins. Analysis of flash drought characteristics under stationary and non‐stationary conditions reveals increased frequency, severity and decline rates, highlighting the impact of evaporation and latent heat flux. Furthermore, the Upper Ganga Sub‐basin demonstrates coherence with the DMI at shorter time scales (1 to 4‐year time scales), while the Lower Ganga Sub‐basin displays a pronounced association with the NINO3.4 index (5.65‐year time scale), indicating the impact of climate oscillations on flash drought dynamics in these regions. These findings provide valuable insights for drought monitoring, prediction and management strategies in a changing climate, emphasising the need for integrated approaches to address the complex interplay between climate variability and flash drought occurrences in the GRB.

Dynamics of meteorological and hydrological drought: The impact of groundwater and El Niño events on forest fires in the Amazon

Over recent decades, anthropogenic forest fires have significantly altered vegetation dynamics in the Amazon region. While human activities primarily initiate these fires, their escalation is intricately linked to climatic conditions, particularly droughts induced by the warm El Niño phase. This study investigates the impact of meteorological and hydrological drought on forest fires in the Amazon, focusing on the role of groundwater and El Niño events. Utilizing comprehensive drought indicators at various soil depths and standardized precipitation indexes, the research spans from 2004 to 2016, revealing a consistent decrease in humidity conditions across surface soil moisture, root zone soil moisture, and groundwater storage levels. With its slower response to precipitation changes, groundwater emerges as a crucial factor influencing hydrological drought patterns in the Amazon. The spatial distribution of drought conditions is explored, highlighting areas with lower humidity concentrations in the northeast and a correlation between forest fires and positive rates of change in burned area fraction during El Niño events. Notably, the study underscores the substantial increase in burned area during the 2015–2016, characterized by a very strong El Niño. This nuanced understanding of groundwater dynamics and its interplay with El Niño events provides critical insights for developing a tailored fire risk index in the ecologically significant and vulnerable Amazon basin, subsidizing strategies for mitigating fire risk and enhancing preparedness.

Spatial-temporal simulation and prediction of root zone soil moisture based on Hydrus-1D and CNN-LSTM-Attention in the Yutian Oasis, Southern Xinjiang, China

Root zone soil moisture (RZSM) plays a critical role in land-atmosphere hydrological cycles and serves as the primary water source for vegetation growth. However, the correlation between RZSM and its associated variables, including surface soil moisture (SSM), often exhibit nonlinearities that are challenging to identify and quantify using conventional statistical techniques. Therefore, this study presents a CNN-LSTM-Attention (CLA) model for predicting RZSM. Owing to the scarcity of soil moisture observation data, the physical model Hydrus-1D was employed to simulate a comprehensive dataset of spatiotemporal vertical soil moisture. Meteorological data and MODIS vegetation characterization parameters were used as predictor variables for the training and validation of the CLA model. The results of the CLA model for soil moisture prediction within the root zone were significantly enhanced compared with those of the traditional LSTM and CNN-LSTM models. This was particularly notable at depth of 80–100 cm, where the coefficient of determination (R²) reached nearly 0.9298. Moreover, the RMSE was reduced by 49% and 57% compared with those of the LSTM and CNN-LSTM models, respectively. This study demonstrates that the integration of physical modeling and deep learning techniques provides a more comprehensive and accurate understanding of spatial and temporal soil moisture variations in the root zone.

Natural radionuclide and <sup>137</sup>Cs activity concentration in soils of the Brazilian State of Sergipe and their correlation with environmental characteristics

Radionuclides occur naturally in the environment, exposing living organisms to ionizing radiation. In addition, human activities have introduced artificial radionuclides such as 137Cs, among others, into the environment. To better understand the occurrence and behaviour of radionuclides in soil, several countries have developed radiological studies and constructed maps. An effort has been made in Brazil to assess the radioactivity in the soils of the country. In this study, the activity concentrations of natural radionuclides 40K, 226Ra and 228Ra, and artificial 137Cs were determined in samples at a depth of 20 cm collected from the soils of the Brazilian State of Sergipe, in a regular grid of 25 km x 25 km. Samples were analysed by gamma-ray spectrometry with the use of hyperpure germanium detectors. The results were correlated with the type of soil, geology, and climate characteristics of the State. The median activity concentrations of 40K, 226Ra, and 228Ra were 210.4 Bq.kg-1, 12.33 Bq.kg-1, and 18.69 Bq.kg-1, respectively. The results are lower than those reported for soils from other Brazilian States in the same region. The activity concentration of 137Cs was lower than the minimum detectable activity. The activity concentration of 40K in young soils of the semi-arid region was higher than that found in most weathered soils of the rainy regions due to the very low pluviometry of the semi-arid area. Higher activity levels of 226Ra were found in Planosol and for 228Ra it was found in the weathered soils (Acrisol) of the coastal zone. Maps of the distribution of the studied radionuclides were designed. The median value of the outdoor absorbed dose rate in air (Dnat) calculated for the soils of the State of Sergipe is lower when compared with other Brazilian States and the UNSCEAR’s worldwide median value.

Климатические и палеоклиматические факторы почвообразования на территории Крымского полуострова

The article provides data on the peculiarities of climate dynamics on the territory of the Crimean Peninsula during the Holocene. Taking into account paleoclimatic data is necessary to predict the direction of evolution of soils and soil cover of the peninsula. It is especially important to take into account the presence of relict properties of soils, taking into account the progressive anthropogenic interference in the processes of modern soil formation. Attention is focused on the need to take into account features unusual for zonal soils when developing Soil management strategies. After all, most often, for objective reasons, a changed or inherited trait disappears forever from the current natural environment and cannot be restored.

Опыт изучения трансформации подзолистых почв в условиях городской среды Севера

The results of soil studies of one of the medium-sized cities of the Russian European Northeast – Syktyvkar (Russia, Komi Republic, middle taiga subzone) are presented in the article. The series from a podzolic soil with a microprofile of podzol (Albic Retisol (Loamic, Protospodic)) typical for the region to various variants of its human transformation in urban conditions – cultivated agrodernovo-podzolic soil (Eutric Albic Retisol (Loamic, Aric, Humic)), represented on the site of the Botanical Garden, to urbodernovo-podzolic soil (Eutric Albic Retisol (Loamic, Humic, Transporti-Novic, Thaptoaric)) and urbostratozem (Urbic Technosol (Loamic, Eutric, Humic Transport)) described in the central part of the city, included in the urban development in the first half of the XX century is considered. In urbo-soil and urbanostratozem the thickness of urbogenic horizons is approximately 40 and 70 cm. It is shown the first stages of the development of the territory of Syktyvkar city are associated with the agricultural impact. Subsequently, the arable horizons overlap with the horizons of the urban cultural layer. In the considered series of soils, weak alkalinization, an increase in the absorbed bases and the total mineralization of the soil solution were found. A noticeable increase in the concentration of organic carbon in modern arable and urban horizons, as well as the thickness of horizons with the organic carbon content of more than 0.6% was revealed. An indirect evidences of changes in the composition of iron and manganese minerals (due to an increase in the pH) with partial preservation of zonal soil formation trends has been found. The revealed direction of soil evolution is consistent with the one previously described in the cities of the European part of Russia.

Characteristics and Drivers of Soil Ecological Stoichiometry in Saline–Alkali Areas of Western Jilin Province, Northeast China

ABSTRACTSoil ecological stoichiometry (SES) provides an important approach in exploring chemical element balance relationships and ecosystem structure and function, but the characterization, significance, and drivers of SES in saline–alkali areas have not been well studied. Soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) were measured and their SES ratios were calculated from 155 soil samples collected at a depth of 20 cm in the saline–alkali soil zone of western Jilin Province, China. The results showed that SOC, TN, and TP contents and SES ratios (52:4:3) were lower in this region than in terrestrial ecosystems both in China as a whole and globally. The distribution of SOC, TN, and TP in saline–alkali soil varied significantly across land use types, with high concentrations mainly in woodland, grassland, and cropland. SOC, TN, and TP were tightly coupled, with significant positive correlations (p < 0.01), and C:N was significantly negatively correlated (p < 0.01) with the other SES ratios, indicating that saline–alkali soils are susceptible to carbon and nitrogen limitation. The distribution patterns of SOC, TN, TP, and their eco‐chemometrics on the environmental gradient were variable, mainly in the form of significant decreases with increasing mean annual precipitation, mean annual temperature, and elevation. Cropland was most affected by environmental factors, and all SES except TP were affected by environmental factors. Soil nutrient (44.9%) and soil texture (9.8%) contributed the most to explaining SES in the saline–alkali soil zone, while climate (1.6%) and vegetation (0.4%) contributed the least to the explanation. All land use types were most explained by AN, except for woodland SES, which was most explained by AP. Elevation (17.4%) possessed a high degree of explanation for SES on underutilized land, except for the soil itself. Grassland is the land category most affected by climatic factors (12.7%). By applying biochar, nitrogen fertilizer, and planting saline‐tolerant crops such as Leymus chinensis, the soil structure can be effectively improved and the content of carbon and nitrogen in the soil can be increased, which has a positive effect on the improvement of saline–alkali soil. The results of the study provide information that can be used to help saline–alkali areas cope with environmental and climate change and restore degraded ecosystems.

Assessment of soil pollution with polycyclic aromatic hydrocarbons in Ulan-Ude

: For the first time, polycyclic aromatic hydrocarbons (PAH) contamination of the soil cover of Ulan-Ude, the capital of the Republic of Buryatia, was studied. The content of 16 individual polyarenes was analyzed in the upper horizon of background chestnut and urban soils, sampled during soil and geochemical survey in July–August 2022. The average concentration of total PAHs in the soil cover of Ulan-Ude was 735 ng/g, which was 8 times as much as the concentration in the background soils (87 ng/g). The PAH amount in the soil of various functional zones decrease in the following order: railway transport > motor traffic > industrial > one-story residential > multi-story residential > recreational. At the same time, the amount of PAHs in the railway transport zone was 2.6–5.2 times higher than in other functional zones, which indicates that railway transport is the most powerful source of PAHs in the city. Contamination of soils with polyarenes in all functional zones is determined primarily by medium- (46%) and high-molecular-weight (41%) compounds. Among PAHs with low molecular weight, phenanthrene prevailed (9% of the total PAHs), but medium-molecular-weight fluoranthene (18%) and pyrene (13%) showed higher share; high-molecular-weight compounds dominated by benzo(ghi)perylene (12%), benzo(b)fluoranthene (10%), indeno(1,2,3-cd)pyrene (8%) and benzo(a)pyrene (6%). The total amount of 16 PAHs in the soil cover of the city varied within the range of 17–9 540 ng/g. The highest levels of pollution (3 226–9 540 ng/g) were recorded at 9 sampling points (4% of the city), which form the most contrasting local PAH anomalies. In more than half of the territory of Ulan-Ude, the total amount of PAHs did not exceed 500 ng/g. The indicator ratios of individual PAHs made it possible to determine the dominant types of sources, which include railway transport and coal combustion. The contribution to the environmental hazard of soil contamination with PAHs in Ulan-Ude was mainly made by benzo(a)pyrene (64%) and, to a lesser extent, by benzo(b)fluoranthene (9.6%), indeno(1,2,3-cd)pyrene (7.2%), dibenzo(ah)anthracene (6.5%) and benzo(a)anthracene (6.1%).

Differential insights into the distribution characteristics of archaeal communities and their response to typical pollutants in the sediments and soils of deep-water reservoir

This study focused on the Fengshuba deep-water reservoir in South China, and systematically explored the distribution characteristics of archaeal communities in the sediment and soil in water level fluctuation zones and their response mechanisms to typical pollutants. The results show that Euryarchaeota and Bathyarchaeota are the dominant phyla in sediment archaeal communities, while Thaumarchaeota dominates in soil. The absolute abundance of archaea in the sediments was lower than that in the soils, but the diversity and richness of archaeal communities were higher than those in the soils. Seasonal changes affected the composition of sediment archaeal communities, and the archaeal compositions in the two habitats also showed significant differences. The neutral community model indicates that the assembly of archaeal communities in sediments is mainly governed by stochastic processes, while deterministic processes dominate in soils. The responses of archaeal communities to pollutants in the two habitats were significantly different. Among them, the carbon-nitrogen ratio and tetracycline concentration are the key factors driving seasonal changes in the archaeal communities in the sediment. Structural equation modeling further showed that the archaeal community in the sediment was positively correlated with organochlorine pesticides and antibiotics, while the archaeal community in the soil showed an opposite trend. This study provides new insights into the complexity of interactions between archaeal communities and typical contaminants in reservoir systems.

A "love match" score to compare root exudate attraction and feeding of the plant growth-promoting rhizobacteria Bacillus subtilis, Pseudomonas fluorescens, and Azospirillum brasilense.

The rhizosphere is the zone of soil surrounding plant roots that is directly influenced by root exudates released by the plant, which select soil microorganisms. The resulting rhizosphere microbiota plays a key role in plant health and development by enhancing its nutrition or immune response and protecting it from biotic or abiotic stresses. In particular, plant growth-promoting rhizobacteria (PGPR) are beneficial members of this microbiota that represent a great hope for agroecology, since they could be used as bioinoculants for sustainable crop production. Therefore, it is necessary to decipher the molecular dialog between roots and PGPR in order to promote the establishment of bioinoculants in the rhizosphere, which is required for their beneficial functions. Here, the ability of root exudates from rapeseed (Brassica napus), pea (Pisum sativum), and ryegrass (Lolium perenne) to attract and feed three PGPR (Bacillus subtilis, Pseudomonas fluorescens, and Azospirillum brasilense) was measured and compared, as these responses are directly involved in the establishment of the rhizosphere microbiota. Our results showed that root exudates differentially attracted and fed the three PGPR. For all beneficial bacteria, rapeseed exudates were the most attractive and induced the fastest growth, while pea exudates allowed the highest biomass production. The performance of ryegrass exudates was generally lower, and variable responses were observed between bacteria. In addition, P. fluorescens and A. brasilense appeared to respond more efficiently to root exudates than B. subtilis. Finally, we proposed to evaluate the compatibility of each plant-PGPR couple by assigning them a "love match" score, which reflects the ability of root exudates to enhance bacterial rhizocompetence. Taken together, our results provide new insights into the specific selection of PGPR by the plant through their root exudates and may help to select the most effective exudates to promote bioinoculant establishment in the rhizosphere.

Reducing the Sodium Adsorption Ratio Improves the Soil Aggregates and Organic Matter in Brackish-Water-Irrigated Cotton Fields

The assessment of soil health relies on key parameters such as soil aggregates and organic matter content. Therefore, examining the impact of irrigation water ion composition and variations in salinity on soil aggregates and organic matter is imperative, which is key to developing a theoretical basis for the sustainable utilization of saline water resources, particularly in extremely arid regions. This experiment was conducted to investigate the impact of different irrigation water salinity treatments (T3: 3 g/L, T5: 5 g/L, and T7: 7 g/L) on the root zone soil of cotton fields. Each salinity treatment included three variations of the sodium adsorption ratio (SAR) at S10: 10 (mmol/L)1/2, S15: 15 (mmol/L)1/2, and S20: 20 (mmol/L)1/2. Local freshwater irrigation served as the control, resulting in a total of 10 treatments. Our findings show that the soil Ca2+ and Mg2+ content increased with higher irrigation water salinity but decreased with increasing irrigation water SAR. The relative macroaggregate stability and the content of water-stable macroaggregates and soil organic matter (SOM) decreased as the irrigation water salinity and SAR increased. In comparison to T3S20, T5S10 did not improve the soil Na+ content but significantly increased the soil Ca2+ content by 147.76%, while the water-stable aggregate and SOM saw a notable increase of 7.66% and 9.86%, respectively. Reducing the SAR in brackish water lessens its negative impact on soil aggregates in cotton fields. This is primarily because Ca2+ counteracts the dispersive effect of high Na+ concentrations and promotes aggregate formation. Irrigation water with a salinity of 3 g/L and an SAR of 10 (mmol/L)1/2 positively affected the stabilization of soil aggregates and organic matter.

Phosphorus fertilization promotes carbon cycling and negatively affects microbial carbon use efficiency in agricultural soils: Laboratory incubation experiments

Soil organic carbon (SOC) loss from intensive agriculture represents a major global concern. Consequently, strategies to improve soil management to mitigate or abate SOC losses and enhance carbon (C) sequestration are urgently needed. Nutrient availability, especially nitrogen (N) and phosphorus (P), regulates soil C cycling and storage. While N effects are well studied, less is known about how soil P status and different fertilizer types affects SOC dynamics. This laboratory incubation assessed how two common P fertilizers, diammonium phosphate (DAP) and single superphosphate (SSP), affected microbial activity and C immobilization in the zone of soil directly around the fertilizer granule (prillosphere) across three contrasting agricultural soils (Inceptisol, Vertisol, Alfisol). Soils were amended with DAP or SSP granules and C turnover assessed with 14C-labeled glycine, malic acid or glucose, alongside unfertilized controls. After three weeks, soil pH, electrical conductivity (EC), Olsen-P and microbial C use efficiency (CUE) were measured. DAP increased pH in the Inceptisol (acidic soil), while SSP decreased pH in all soils. Both fertilizers increased EC and Olsen-P, but SSP enhanced Olsen-P more than DAP. Cumulative 14CO2 emissions were 19–20 % higher with P fertilizers compared to the control, with DAP stimulating faster initial C mineralization rates than SSP, except in the Alfisol. P addition reduced microbial CUE by 23–34 % across all soils and substrates versus the unfertilized control. We ascribe this reduction in CUE to an alleviation of nutrient limitation or a fertilizer-induced osmotic stress. The co-addition of N either in DAP or glycine did not alter the P-induced CUE response suggesting that P was more important than N in regulating microbial CUE in these soils. We conclude that P fertilization increased short-term C turnover and may lead to reduced C storage in soil, however, further long-term (>1 year) research is needed to identify optimum P management strategies to minimize C losses in agricultural soils.

Soil Respiration Under a Short–Term Drought on the Example of Typical West Siberian Bogs (Middle Taiga)

Cumulative (June–August) soil respiration (Rsoil(cum)), obtained based on field measurements and mathematical modeling, increased from wet areas of the oligotrophic bog to drained ones – “Hollow E.”, “Hollow Sh.” (hollows, dominated by Eriophorum vaginatum and Scheuchzeria palustris, respectively), “Open bog” (sphagnum bog with sparse low pine trees), “Ridge” (oligotrophic ridges covered with low pine trees), “Tall ryam” and “Ryam” (forested pine-shrub-sphagnum bog): 135 ± 2.3, 139 ± 2.4, 275 ± 7.8, 279 ± 7.5, 466 ± 16.4, 510 ± 18.5 g C/ (m2 season), respectively (mean ± std). An important factor of seasonal and annual variability of Rsoil was the water table level (WTL): the extremely low amount of precipitation (6 mm) that fell in July 2022 led to a sharp drop of WTL in August, an increase of the aerated soil zone. As result, total Rsoil(cum) over the summer in the studied biotopes increases by 29–54% compared to the same period in 2021. At the same time, the most intensive growth of Rsoil during the drop of the WTL was on the edge of the bog (“Tall ryam”, “Ryam” and “Open Bog”), in contrast to its central area.

Soil Formation on Loamy Deposits in Technogenic Landscapes of the Taiga Zone in the North-Eastern Part of European Russia

The paper highlights the influence of moisture on the soil formation process on loamy deposits during the primary vegetation succession. The study was carried out in the north-eastern part of European Russia (Komi Republic) in the middle taiga subzone. The authors analyzed young soils on the territory of a quarry for extraction of loamy grounds and background soils in the vicinity of it. Planting the Siberian spruce cultures on the territory of the quarry activated formation of the tree layer and thereby accelerated formation of the zonal type soils. The third succession decade in drained conditions saw formation of organic soil horizons (litters), a decrease in soil density in the upper profile part, a tendency to redistribute and differentiate the silty fraction by one-and-a-half oxides, indicating the beginning of selective podzolization. The rise in soil moisture content increased conservation of organic residues (peat formation) and made gley formation active. The quarry soils, like background soils, increased in acidity, carbon and nitrogen reserves along with the soil moisture content increase. In automorphic soil formation conditions, the rate of organic carbon accumulation in the upper 0–20-cm layer is 0.4 t· ha–1·year1; the excessive soil moisture content further increased it (1.0–1.2 t·ha–1·year1). The reserves of Corg in the upper 20-cm soil layer of young soils are by 2–4 times less than those in background soils.

Ecological State of Environmental Facilities in the Zone of Influence of the Lipetsk Industrial Agglomeration

It has been found that the accumulation of heavy metals (HM) in environmental facilities of the Lipetsk industrial agglomeration varies significantly and may depend on the technological mode of the companies, the composition of aerosol fallout, soil properties, distance and direction from the emission plume, biological characteristics of plants and other factors. In the area where the Novolipetsk Iron and Steel Works (NLMK) is located, the excess levels of kerosene, gasoline and hydrocarbons in the atmospheric air were detected, as well as increased dust concentrations in the area of the Lipetsk Tractor Plant. At that, the concentrations of gaseous hazardous chemicals in the air of other areas of Lipetsk and agricultural lands at different distances and directions from NLMK did not exceed the established maximum values. The maximum content of HM was recorded in the upper layers of virgin undisturbed soils in the near zone of influence of industrial companies. It was noted that on arable soils the content of HM does not exceed the standard values, with the exception of a number of cases where the content of Fe, Cr, Ni in the grass stand exceeds the permissible level. It was concluded that the research carried out made it possible to identify the main patterns and factors influencing the pollution of environmental facilities, including components of agroecosystems.

Using Pseudo-Color Maps and Machine Learning Methods to Estimate Long-Term Salinity of Soils

Soil salinity assessment methods based on remote sensing data are a common topic of scientific research. However, the developed methods, as a rule, estimate relatively small areas of the land surface at certain moments of the season, tied to the timing of ground surveys. Considerable variability of weather conditions and the state of the earth surface makes it difficult to assess the salinity level with the help of remote sensing data and to verify it within a year. At the same time, the assessment of salinity on the basis of multiyear data allows reducing the level of seasonal fluctuations to a considerable extent and revealing the statistically stable characteristics of cultivated areas of land surface. Such an approach allows, in our opinion, the processes of mapping the salinity of large areas of cultivated lands to be automated considerably. The authors propose an approach to assess the salinization of cultivated and non-cultivated soils of arid zones on the basis of long-term averaged values of vegetation indices and salinity indices. This approach allows revealing the consistent relationships between the characteristics of spectral indices and salinization parameters. Based on this approach, this paper presents a mapping method including the use of multiyear data and machine learning algorithms to classify soil salinity levels in one of the regions of South Kazakhstan. Verification of the method was carried out by comparing the obtained salinity assessment with the expert data and the results of laboratory tests of soil samples. The percentage of “gross” errors of the method, in other words, errors when the predicted salinity class differs by more than one position compared to the actual one, is 22–28% (accuracy is 0.78–0.72). The obtained results allow recommending the developed method for the assessment of long-term trends of secondary salinization of irrigated arable land in arid areas.

Enhanced root zone soil moisture monitoring using multitemporal remote sensing data and machine learning techniques

Accurate root zone soil moisture (RZSM) estimation using remote sensing (RS) in areas with dense vegetation is essential for real-time field monitoring and precise irrigation scheduling. Traditional methods often face challenges due to the dense crop cover and the complexity of soil and climate interactions. These challenges include the coarse spatial resolution of available soil moisture products, the influence of vegetation and surface roughness, and the difficulty of estimating RZSM from surface data. Aiming to overcome these limitations, two RZSM estimation methods were developed by combining synthetic aperture radar (SAR) data from Sentinel-1 (VV and VH polarizations) and optical and thermal RS data from Landsat-8. These data sources were used in conjunction with various machine learning (ML) models such as M5-pruned (M5P), support vector regression (SVR), extreme gradient boosting (XGBoost), and random forest regression (RFR) to improve the accuracy of soil moisture estimation. In addition to RS data, soil physical and hydraulic properties, meteorological variables, and topographical parameters were selected as inputs to the ML models for estimating the RZSM of sugarcane crops in Khuzestan, Iran. This study identified the temperature vegetation dryness index (TVDI) as a critical parameter for estimating RZSM in combination with the Sentinel-1 SAR data under high vegetation conditions. In both methods, the RFR algorithm outperformed, with similar performance, the XGBoost, SVR, and M5P algorithms in estimating soil surface moisture (R2 = 0.89, RMSE = 0.04 cm3cm−3). However, the accuracy of the RFR algorithm decreased with increasing depth for both the optical-thermal and combined SAR and optical-thermal RS data. This decrease was more pronounced in the combined approach, particularly for the root zone, where the RMSE reached approximately 0.073 cm3cm−3. Accordingly, the key findings demonstrated that the optical-thermal RS data outperformed the SAR RS data for retrieving RZSM in high-vegetated areas. However, combining TVDI with SAR data is a substantial improvement that opens a new path in radar-based RZSM estimation methods under high vegetation conditions.

Species-Specific Root Distribution and Leaf Iso/Anisohydric Tendencies Shape Transpiration Patterns Across Heterogeneous Karst Habitats.

The driving forces of transpiration are not only atmospheric evaporation but also root zone water supply and stomatal regulation among species. However, the biophysiological drivers of transpiration remain incompletely understood in heterogeneous karst habitats. This study investigated the commonly coexisting tree species Mallotus philippensis and Celtis biondii in two typical karst habitats: rock-dominated (RD) habitat and control soil-dominated (SD) habitat. Over 2 years, soil moisture, transpiration, root distribution, and leaf water potential were measured. The results showed that soil moisture in the RD habitat was significantly lower than in the SD habitat. Transpiration patterns also differed between habitats, with species-specific distinctions driven by biophysiological traits. M. philippensis showed small hydroscape areas and its root system mainly distributed in the soil zone in both habitats. The isohydric behaviour and lower root density in the RD habitat drove M. philippensis to reduce transpiration in response to soil water deficiency. Conversely, C. biondii had large hydroscape areas and roots capable of penetrating bedrock. It transpired higher relying on ample accessible water through anisohydric behaviour and having a more robust root system both in soil and bedrock zones in the RD habitat. Our study highlights the critical role of root water accessibility and leaf iso/anisohydric tendencies in driving transpiration.

Graph-Analytical Method for Calculating Settlement of a Single Pile Taking into Account Soil Slippage

Most of the existing methods of pile settlement calculation, including normative methods, do not fully take into account the processes occurring in the soil when loads are transferred to them and the changes in the properties of the contact zone soils. This leads to underutilisation of the bearing capacity of the soil, and the calculated settlement value may differ several times from the real values. In this paper, a graph-analytical solution to the problem of interaction of a single pile with a three-layer soil foundation is proposed to determine the settlement, taking into account the complex nature of the pile operation and the processes occurring in the soil when loads are transferred to them. The proposed method allows to use the non-linear behaviour of the soil on the lateral surface and under the tip of the pile, the possibility of its detachment and slippage after reaching the ultimate strength of the soil, changes in the properties of the contact zone soils, and the load distribution on the pile between its lateral surface and the tip. To verify the proposed graph-analytical solution, a comparative analysis was performed with the numerical method in the Plaxis 2d software (version 21.00.01.7) and with the results of static tests of piles at the construction site. To determine the strength reduction factor at the contact of soils with concrete, laboratory tests were carried out on a direct shear apparatus. Based on the results of the performed calculations, graphs of the dependence of settlements on loads were plotted, conclusions were drawn about the possibility of using the graph-analytical method, and prospects for further development and improvement of the graph-analytical method were proposed.