Subsurface Soil Research Articles

Unveiling the soil physicochemical dynamics of bare soils in Southeast Kazakhstan: A comprehensive study in the Akdala Massif

This study addresses desertification in Kazakhstan's Akdala region, aiming to propose sustainable solutions by examining the effects of various plants on soil properties and nutrient dynamics. Desertification poses a threat to land productivity in arid areas, and this research aims to determine its impact on soil and identify plants for mitigation. Field experiments over three years in the Akdala region utilized crops such as rice, corn, soybean, sudan grass, and sorghum to assess their influence on key soil parameters. Results revealed diverse effects on soil bulk density, agronomically valuable aggregates, water-stable aggregates, labile and total organic carbon, easily hydrolyzable nitrogen, nitrate, available phosphorus, and exchangeable potassium. While no significant differences in bulk density were observed among crops, variations in surface and subsurface soil layers emphasized the importance of depth-specific considerations. Sorghum stood out as a particularly influential crop, significantly increasing labile and total organic carbon levels, highlighting its potential role in enhancing soil quality. The experiments were conducted on the fields of "Birlik" LLP in the Balkhash district of the Almaty region from 2015 to 2017. The chosen crops, each with distinct characteristics, provided a comprehensive understanding of their impact on soil dynamics. Advanced techniques for soil sampling and analyses ensured accurate measurements of various soil parameters. The study site's sharply continental climate, marked by temperature variations, snowy winters, and hot, dry summers, added complexity to the investigation due to its influence on plant growth and soil interactions. In conclusion, this comprehensive study offers valuable insights into the intricate relationships between different crops and soil parameters for combating desertification. The findings contribute significantly to the development of sustainable soil management practices, providing a foundation for identifying suitable crops for soil improvement in arid regions. By understanding how different plants impact soil properties, this research supports informed decision-making in agricultural practices, promoting the long-term sustainability of farming in regions vulnerable to desertification.

Study on the accelerated biodegradation of PAHs in subsurface soil via coupled low-temperature thermally treatment and electron acceptor stimulation based on metagenomic sequencing

In situ anoxic bioremediation is a sustainable technology to remediate PAHs contaminated soils. However, the limited degradation rate of PAHs under anoxic conditions has become the primary bottleneck hindering the application of this technology. In this study, coupled low-temperature thermally treatment (<50 °C) and EA biostimulation was used to enhance PAH removal. Anoxic biodegradation of PAHs in soil was explored in microcosms in the absence and presence of added EAs at 3 temperatures (15 °C, 30 °C, and 45 °C). The influence of temperature, EA, and their interaction on the removal of PAHs were identified. A PAH degradation model based on PLSR analysis identified the importance and the positive/negative role of parameters on PAH removal. Soil archaeal and bacterial communities showed similar succession patterns, the impact of temperature was greater than that of EA. Soil microbial community and function were more influenced by temperature than EAs. Close and frequent interactions were observed among soil bacteria, archaea, PAH-degrading genes and methanogenic genes. A total of 15 bacterial OTUs, 1 PAH-degrading gene and 2 methanogenic genes were identified as keystones in the network. Coupled low-temperature thermally treatment and EA stimulation resulted in higher PAH removal efficiencies than EA stimulation alone and low-temperature thermally treatment alone.

Soil health implications of some d-block metals in selected agricultural soils in Southeast Nigeria.

Soil fertility, soil health and environmental management through the estimation of background concentration of potentially toxic elements is required for environmental safety. This study aims at investigating the concentration, fertility and potential health risks of some d-block metals (Ti, V, Fe, Mn, and Mo) in some agricultural soils, and establishes the relationship between the metals and some soil properties. Eight elevation ranges resulted from the digital elevation models of the study area; two in Ishibori (NG1, NG2), three each in Agoi-Ibami (CG1, CG2, CG3) and Mfamosing (SG1, SG2 and SG3). One soil profile pit was sunk along each of the elevations. Thirty-five composite soil samples were collected at 0-30, 30-60, 60-90, 90-120, 120-150, 150-180 and 180-200cm depending on soil depth. Only the profile means of Mn (660.82 ± 612.89mg/kg) and Mo (2.61 ± 0.73mg/kg) exceeded permissible concentrations and would pose threats to the environment. Also, the concentrations of the d-block metals exceeded permissible values in Ishibori making them prone to toxicity. The metals were irregularly distributed with depth; however, Mn and Fe were concentrated in the subsurface soils. Clay and sand contents correlated positively and negatively, respectively with all the d-block metals at p < 0.05. The linear model was more efficient in estimating V and Mo via soil properties with adjusted R2 of 33 - 67% for the metals. In conclusion, agricultural activities and geology may influence the accumulation of d-block metals, hence the call for environmental monitoring to curtail metals' assimilation by crops. HIGHLIGHTS: • Mn and Mo threaten the environment the most. • Soils in the Southern Guinea Savannah are most prone to d-block metals contamination. • BD, pH, Mg, and CEC are the best predictors of d-block metals in the soils. • The linear model was best performing in the estimation of V and Mo, respectively.

Ground settlement prediction for open caisson shafts in sand using a neural network constrained by empiricism

Accurate prediction of soil settlements induced by open caisson construction in sand is essential for safe and reliable delivery of critical underground urban infrastructure. This paper presents a novel prescriptive design approach using a neural network (NN) constrained by empirical relationships, referred to as an ’empiricism-constrained neural network’. The proposed approach is benchmarked using a traditional closed-form empirical expression. Both methods are calibrated using experimental data from reduced-scale laboratory testing for the prediction of surface and subsurface settlement trough shape and magnitude. The outcomes demonstrate that while both methods accurately capture the primary effect of caisson depth on surface and subsurface soil settlements, the NN approach exhibits superior prediction accuracy. These methods are developed in a form amenable for routine design use in industry and have the potential for broader applicability in other design scenarios, such as building damage assessment and risk-assessment exercises.

Geophysical research on the interplays between soil–rock variability and hydrogeological structures: a case study

Understanding the spatial variations in soil–rock profiles is crucial for identifying weathered rock layers and mapping geological structures, particularly in the complex feldspar-rich granitic terrain of Penang Island, Malaysia. This study employs a combination of electrical resistivity and seismic refraction tomographic techniques, along with borehole lithological data, in three distinct areas on the island. Its goal is to provide insights into surficial and subsurface soil–rock characteristics and water-bearing structures within the North Penang Pluton (including a part of the Sungai Ara axis) for sustainable groundwater development, addressing the needs of the region's growing population. The research identifies three distinct geological units at the near-surface: residual soils, highly to moderately weathered/fractured granitic layers and fresh bedrock, each with its hydrogeological properties. Promisingly, the weathered layers offer significant groundwater development potential, with deep weathered and potentially fractured zones exceeding depths of 30 m in the study area. These findings have substantial implications for sustainable groundwater development, especially in tropical hard-rock terrains. In addition, the study underscores the limitations of small geophysical spacings when probing deeper groundwater resources. This knowledge is essential for informed decision-making in water resource management and infrastructure development, addressing the ongoing global challenge of ensuring access to clean water resources amid population growth.

Effect of soil management practice on soil phosphorus dynamics: A meta‐analysis

AbstractSoil phosphorus (P) is pivotal for crop health and growth. We collated a dataset spanning 65 studies from 19 countries to quantify the effects of both natural and anthropogenic factors on P dynamics (dataset provided). Our meta‐analysis encompassed five variables: the type of fertilizer (chemical or organic fertilizer), tillage practices (tillage or no‐till), land use (cultivated or forest), soil texture (either loam soil or sandy loam soil) and soil depth (surface or subsurface). The interplay between soil management strategies, especially those encompassing fertilizer application and tillage, and soil phosphorus dynamics is well established. Our quantitative data suggests the use of organic fertilizers relates to a significant 82% increase in soil Olsen‐P content. Additionally, while the no‐till method has resulted in only a slight 1.6% increase in Total‐P, it has brought about a remarkable 60% increase in organic phosphorus, especially NaHCO3‐Po, in contrast to conventionally tilled soils. Further, we found that the concentrations of Total‐P and Olsen‐P in surface loam soils is elevated, being 24.8% and 1023.6% higher, respectively, compared with subsurface loam soils. In sandy loam soils, these values are 35.3% and 872.2% higher, respectively. These meta‐analysis data highlight how soil management practices can cause variation in P species in soil. They not only underscore potential strategies for refined phosphorus use in diverse farming contexts but also pave the way for further research focusing on agricultural P management.

Responsive characteristics of soil water regimes to rainfall events in a boreal larch forest in China: Dynamic processes and decoupling effects

Investigating the soil water dynamics in relation to rainfall events is of great importance for enhancing our understanding of eco-hydrological processes and improving soil hydrological models. However, the lack of long-term, in-situ observational data and the neglect of soil moisture decoupling have hindered the study of dynamic responses in soil water regimes to rainfall events in China’s boreal forests with permafrost. This study utilized soil water content monitoring and rainfall observational data from the Xing’an larch (Larix gmenilii) forest in Northeast China during the growing seasons of 2015–2021 to evaluate the dynamic response of soil water regimes to rainfall events. The results show a significant increase in the decoupling strength between soil water and rainfall with increasing soil depth. The thresholds of rainfall amount (RA), duration (RD), and intensity (RI) for triggering soil wetting events also increased. Soil water dynamic processes exhibited inconsistent and complex patterns in response to the hierarchical effects of RA, RD, and RI along the vertical soil profile. However, the dominant controls on soil water dynamic responses to RA, RD, and RI varied depending on specific response metrics, such as the accumulated soil water content increments (ASMI), duration time (DT), and the mean slope of the soil wetting curve (Sm). Interestingly, the dominant factor for affecting response time (RT) changed from RI to RD as soil depths increased. Importantly, the decoupling of soil moisture led to a substantial reduction in the responsiveness of these metrics of subsurface soil water to rainfall, and the role of the decoupling effect diminished with increasing soil depths. These findings highlight the complexity of the dynamic response of soil water to rainfall events and provide new insights into the relationship between soil water dynamics and rainfall features through the introduction of the decoupling of soil moisture in boreal forests.

Viral metagenomics reveals diverse virus-host interactions throughout the soil depth profile.

Soil viruses can moderate the roles that their host microbes play in global carbon cycling. However, given that most studies investigate the surface layer (i.e., top 20 cm) of soil, the extent to which this occurs in subsurface soil (i.e., below 20 cm) is unknown. Here, we leveraged public sequencing data to investigate the interactions between viruses and their hosts at soil depth intervals, down to 115 cm. While most viruses were detected throughout the soil depth profile, their adaptation to host microbes varied. Nonetheless, we uncovered evidence for the potential of soil viruses to encourage their hosts to recycle plant-derived carbon in both surface and subsurface soils. This work reasons that our understanding of soil viral functions requires us to continue to dig deeper and compare viruses existing throughout soil ecosystems.

Improving evapotranspiration computation with electrical resistivity tomography in a maize field

AbstractHydrogeophysical methods have been increasingly used to study subsurface soil–water dynamics, yet their application beyond the soil compartment or the quantitative link to soil hydraulic properties remains limited. To examine how these methods can inform model‐based evapotranspiration (ET) calculation under varying soil water conditions, we conducted a pilot‐scale field study at an experimental maize plot with manipulated irrigation treatments. Our goal was to develop a workflow for (1) acquiring and inverting field electrical resistivity tomography (ERT) data, (2) correlating ERT to soil hydraulic properties, (3) spatially characterizing soil water stress that feeds into ET modeling (the FAO‐56 model), and (4) evaluating the performance of ERT‐based ET computation. Our results showed that ERT was able to capture decimeter‐scale soil water content (SWC) dynamics from root water uptake and irrigation manipulation and the contrast of soil water stress between deficiently and fully irrigated maize. We also demonstrated the flexibility of using ERT to spatially integrate soil water stress in the soil volume of interest, which could be adjusted based on different crops and plot layouts. The integration of the ERT datasets into ET modeling provided insights into the spatial heterogeneity of the subsurface that has been challenging for point‐based sensing, which can further our understanding of the hydraulic dynamics in the soil‐plant‐atmosphere continuum.

Effect of Long-Term Application of Inorganic Fertilizers, Organic Manure, and Lime on Different Forms of Potassium in Soil under Maize-Wheat Cropping System

The field study was undertaken with the major emphasis on potassium fractionation and its contribution in acid alfisol soils as affected by adoption of continuous cropping, fertilization, and manuring under maize-wheat cropping system in same field over 62 years of crop cycles. The experiment consisted of fourteen treatments, replicated thrice times in a randomized block design, out of which nine treatments were selected for the present study. The selected treatments were as follows - control, T2-100% N, T3- FYM, T4-100% NP, T5-100% NPK, T6- 1/2(N+FYM) + P(A-X/2) + K(B-Y/2) (INM), T7-100% NPK + Lime where the lime application in LR once in 4 years, T8-Lime+ FYM+ P(A-X) + K(B-Y), T9-Lime+N. Surface soil (0-15cm) and subsurface soil (16-30 cm) samples were collected after the harvest of wheat in 2017-18 to observe the initial Physico-chemical properties. Different fractions of potassium, viz., water-soluble K, exchangeable K, available K, 1NHNO3K, non-exchangeable K, Lattice K, and Total K were analyzed for the study. There was a significant difference among the different treatments with respect to potassium fractions in 0-15 cm, and 16-30 cm layers. Moreover, K fractions were significantly decreased with increasing depth of soil. Results showed that the percentage contribution of different forms of K with regard to the total K in surface soil and subsurface soil followed as: Lattice K (68.75-78.11%) &gt; Non – Exchangeable K (19.15-25.49%) &gt; Exchangeable K (1.65-2.45%) &gt;Water soluble K (0.18-0.62%). Application of N and P without K caused depletion of soil, water-soluble K, available K, exchangeable K, non-exchangeable K, and lattice K because of continuous omission of potassium content during the all crop growing stages or the simultaneous leaching nature of residual potassium under same field of the experiment. Therefore, the present investigation stresses the vital importance of the inclusion of organic manure and lime in the fertilizer schedule to maintain soil K dynamics over the long run under the maize-wheat cropping system.

Co-evolution among soil thickness, epikarst weathering degree, and runoff characteristics on a subtropical karst hillslope

Carbonate landscapes make up one-fifth of the terrestrial land area, a better understanding of the coupling relationship between the soil–epikarst form and hydrological function is imperative for hydrology and landscape evolution modeling. In this study, we monitored a total of 158 rainfall-runoff events on a karst slope between 2019/4 and 2022/5 in southwest China, while simultaneously examining the soil–epikarst architecture (924 pairs of soil thickness and epikarst weathering degree). The results indicated that soil thickness increased with the underlying epikarst weathering degree, and soil thickness was positively correlated with epikarst thickness (P<0.001). Additionally, a significant positive relationship (P<0.001) was observed between surface runoff (SR) and soil thickness, as well as a significant negative relationship (P=0.0018) between subsurface runoff (SSR) and soil thickness. These findings imply the dominance of SR and SSR (under normal rainfall conditions) in runoff plots with deep soil layers and thin soil layers, respectively. The soil thickness threshold at which the hillslope discharge shifted from being SSR-dominated to SR-dominated was approximately 50 cm. Nonetheless, a positive relationship was found between SR and SSR under extreme rainfall events, indicating the establishment of hydrological connectivity between the surface and subsurface. Moreover, the hillslope discharge when the rainfall depth is lower than 50 mm is primarily composed of either SR or SSR from different plots. In other words, the hillslope discharge is typically influenced by both SR and SSR when the rainfall depth exceeds 50 mm. We finally proposed a positive feedback loop among soil thickness, epikarst weathering degree, and the hydrological function of the soil–epikarst system (water storage and release). These findings enhance our understanding of the complex interactive relationships in hillslope hydrology by illuminating the physical links between critical zone structures and hydrological processes on the karst slope.

Degree of compaction, aeration, and soil water retention indices of a sugarcane field without soil disturbance after initial tillage

Soil compaction after initial soil tillage for crop establishment has been a major problem in crop fields because of its deleterious effects on soil functioning and crop performance. Therefore, the study aimed to determine the degree of compaction, soil air capacity, near-surface optimum ratios, and water retention characteristics in a sandy loam. Dystrophic Paleudalf initially under different tillage methods for sugarcane crop but without tillage for two seasons in southern Brazil. Initial soil tillage systems consisted of no-tillage (NT), compacted no-tillage (NTC), conventional tillage, and chiseling of no-tillage (Ch). Disturbed and undisturbed soil was sampled from 0 to 10, 10 to 20, 20 to 40, and 40 to 60 cm layers to determine degree of compaction, air capacity, near-surface optimum ratios, soil water retention characteristics, and soil physical quality index S. Initially, NT treatment had the significantly ( p &lt; 0.05) lowest degree of compaction (87%), highest soil air capacity (0.104 cm3 cm−3), air capacity/total porosity ratio (0.261), and better water retention characteristics in the surface layer. Over time, Ch had improved the structure of the subsurface soil layers with the lowest degree of compaction (≈88%) and highest air capacity (≈0.140 cm3 cm−3), while the measured indices were poor in NTC. Irrespective of tillage, the surface layer showed resilience during the years without soil disturbance with low degree of compaction, increased water retention, and air capacity. NT could be a good soil management option for sugarcane production, while mechanical chiseling is advocated for ameliorating compacted soils.

Reexamination of a 40Ca(n,α)37Ar cross section measurement from existing literature

Background 37Ar, produced from the neutron activation of 40Ca in sub-surface rock and soil, is important for nuclear explosion monitoring. Most of the cross section measurements done for the 40Ca(n,α) 37 Ar reaction are in the fast neutron region. A thermal cross section measurement was attempted in 1989, with the assumption that the 4-8 MeV neutrons would be completely thermalized with 8-cm of water. Methods The experimental setup was modeled using Monte Carlo N-Particle code to see if the assumptions for the neutron distribution were accurate. A model of a 3.0 MeV deuteron source was used to recreate the neutron source from the experiment. Additional modeling was done using SCALE to compare the predictions of 37Ar yields when using the measured cross section from 1989 compared to current nuclear data models. Results Modeling showed the neutron distribution was closer to 10% thermal and 90% fast as opposed to entirely thermalized. The additional modeling showed how the overestimation of the thermal cross section would affect the predicted yield of 37Ar. Conclusions Based on the modeling results, the assumption that all the 4-8 MeV neutrons are thermalized with 8-cm of water is not accurate. The high fraction of fast neutrons interacting with the Ca will result in an overestimation of the thermal cross section.

Self-stabilization of Zn, Pb, Cd, and As in smelter-impacted organic-rich soil: The effect of hydrous Fe oxides and ZnCd sulfide coprecipitation

Soil constitutes a direct sink for elements mobilized due to mining and smelting activities. One of the desired pathways for reducing the bioavailability and toxicity of the contaminants is their transformation into sparingly soluble solid phases. Here, we report the formation of secondary mineral phases in extremely contaminated (up to 210 g Zn kg−1,102 g Pb kg−1, 5.68 g Cd kg−1, and 6.42 g As kg−1, respectively) organic-rich soil. Combining mineralogical techniques (SEM, XRD), a nonspecific sequential extraction (CISED) with Mössbauer and X-ray photoelectron (XPS) spectroscopies evidenced two poorly crystalline goethite components differing in crystallite size and As, Zn, Pb, Ca, Al, P substitutions and minor magnetite associated with plant roots (mainly Deschampsia caespitosa, Equisetum palustre, and Carex rostrate) directly below a layer of smelter-derived particles deposited into the soil. SEM was the only method that unambiguously documented the occurrence of ZnCd sulfide microsize aggregates incrusting plant roots and located in between the (hydrous) Fe oxides. Sequential extraction confirmed a complete As immobilization by goethite, while Cd forms a solid solution with ZnS and is lacking in the Fe hydroxides. The partitioning of Zn and Pb between the goethite and sulfide phases depends on soil water saturation. It is proposed that the coexistence of hydrous Fe oxides and nonferrous metal sulfides in the soil subsurface is possible because of redox heterogeneity of the rhizosphere and the decoupling of sulfur and iron cycles. Low mobility of biogenic sulfide ions and the protecting role of organic matter limits goethite sulfidation. The system remains active, adapting to the seasonally changeable plant roots ecology and fluctuations in water saturation. The obtained results are of value in remediation and managing strategies for contaminated soils and in reconstructing processes related to the formation and/or transformation of low-temperature sulfide deposits.

Improvement of Subsurface Thermal Characteristics for Green Parks

The ground surface of green parks in arid and semi-arid areas may not be comfortable at specific times during the day and night due to the sun and the rate at which the subsoil gains or loses heat. Knowledge of the subsurface soil’s thermal properties can provide designers with convenient and comfortable settings. Design focus is generally directed toward stability, density, and hydraulic conductivity. An assessment of the thermal properties of clay–sand mixtures of 10%, 20%, and 30% clay content is conducted. The proposed clay–sand layers are subjected to three different thermal gradients of 30, 20, and 10 degrees of magnitude. The profile of temperature changes was monitored using 5TE sensors and data loggers. The mixtures were also subjected to cooling at room temperature. The results indicate that the clay type and the clay content govern the response of subsurface clay–sand liners to temperature gain and loss. Two field sections with clay–sand layers of 15% and 20% clay were examined for temperature changes over an extended period. In winter, green areas rich in clays were found to keep heat for several hours and provide relatively warm evenings. In summer, the mixture retains a cool temperature for some time during the day.

Studies on Potassium Fractions in Central and Southern Dry Zones of Coconut Growing Areas of Hassan District of Karnataka, India

The experiment was conducted in an order to get an insight about the potassium (K) fractions in Central and Southern dry zone of coconut growing areas of Hassan district, Karnataka during 2022-23. The soil samples from surface (0-30 cm) and sub-surface (30-60 cm) were collected from the soils of selected coconut gardens of Central and Southern dry zones of Hassan district for the study. Results revealed that the average water soluble K, hot water soluble K, exchangeable K, non-exchangeable K, lattice K and total K in surface soils of coconut gardens of Central dry zone of Hassan district registered was 2.76, 9.25, 54.65, 555.35, 5896.00 and 6509.00 mg kg-1, respectively. Whereas the above potassium fractions in sub-surface soil recorded were 2.67, 7.70, 47.36, 699.66, 7282.00 and 8032.00 mg kg-1, respectively. The various forms of potassium in surface soils of Southern dry zone revealed that water soluble K, hot water-soluble K, exchangeable K, non-exchangeable K, lattice K and total K was 2.87, 8.85, 53.51, 546.61, 5603.00 and 6206.00 mg kg-1, respectively. Whereas the above potassium fractions in sub-surface soil recorded were 2.21, 7.20, 45.21, 709.20, 7431.00 and 8188.00 mg kg-1, respectively. The trend of decrease in water soluble K and exchangeable K from surface to sub-surface layers was noticed in soils of Central and Southern dry zone whereas non-exchangeable K, lattice K and total K exhibited an increasing trend with depth. The contribution of each form of potassium to total potassium was in the order of water soluble &lt; hot water-soluble K&lt; exchangeable &lt; non-exchangeable &lt; lattice K. Knowledge of different forms of potassium in soil together with their distribution has greater relevance in assessing the long-term K supplying power of soil to coconut palm and is important in formulating a sound fertilizer program for a given set of soil.

The Relationship of Soil Organic Carbon and Nutrient Contents to Maize Yield as Affected by Maize Straw Return Modes

Returning crop residues to the field after harvesting is a proven effective strategy for improving soil fertility, carbon sequestration, and crop productivity. However, the relationships between crop residue return modes, SOC and nutrient contents, and crop yields are still unclear. In this study, a field trial was conducted to investigate the effects of different maize straw return modes, i.e., straw mulching (SMU), straw deep ploughing (SDP), and control without straw return (CK), on soil organic carbon (SOC) and nutrient contents in soil layers of 0–40 cm in a Mollisol. The relationships between straw return modes, SOC and nutrient contents, and maize yield were evaluated. Compared with CK, SMU and SDP significantly increased SOC, total nitrogen (N), available N, total phosphorus (P), and available P contents in all soil layers. Relative to SMU, SOC, total N, available N, total P, and available P contents were significantly lower in soil layers of 0–10 cm, but they were significantly higher in soil layers of 20–40 cm in SDP. Redundancy analysis indicated that total N, available N, and SOC were major factors controlling maize yield. Structural equation modeling further showed that straw return modes indirectly affected maize yield by directly and preferentially affecting total N and available N contents. The results indicated that SMU and SDP were beneficial for increasing SOC and nutrient contents at the surface and subsurface soils, respectively. Optimizing a nitrogen management strategy is important to achieve high maize yield with straw return.

Interkingdom ecological networks between plants and fungi drive soil multifunctionality across arid inland river basin.

Despite the known collective contribution of above- (plants) and below-ground (soil fungi) biodiversity on multiple soil functions, how the associations among plant and fungal communities regulate soil multifunctionality (SMF) differentially remains unknown. Here, plant communities were investigated at 81 plots across a typical arid inland river basin, within which associated soil fungal communities and seven soil functions (nutrients storage and biological activity) were measured in surface (0-15 cm) and subsurface soil (15-30 cm). We evaluated the relative importance of species richness and biotic associations (reflected by network complexity) on SMF. Our results demonstrated that plant species richness and plant-fungus network complexity promoted SMF in surface and subsurface soil. SMF in two soil layers was mainly determined by plant-fungus network complexity, mean groundwater depth and soil variables, among which plant-fungus network complexity played a crucial role. Plant-fungus network complexity had stronger effects on SMF in surface soil than in subsurface soil. We present evidence that plant-fungus network complexity surpassed plant-fungal species richness in determining SMF in surface and subsurface soil. Moreover, plant-fungal species richness could not directly affect SMF. Greater plant-fungal species richness indirectly promoted SMF since they ensured greater plant-fungal associations. Collectively, we concluded that interkingdom networks between plants and fungi drive SMF even in different soil layers. Our findings enhanced our knowledge of the underlying mechanisms that above- and below-ground associations promote SMF in arid inland river basins. Future study should place more emphasis on the associations among plant and microbial communities in protecting soil functions under global changes.

The effect of short-term plants cultivation on soil organic/inorganic carbon storage in newly formed soils

Studying total soil carbon (STC), which encompasses organic (SOC) and inorganic carbon (SIC), as well as investigating the influence of soil carbon on other soil properties, is crucial for effective global soil carbon management. This knowledge is invaluable for evaluating carbon sequestration, although its scope is currently limited. Boosting soil carbon sequestration, particularly in arid regions, has direct and indirect implications for achieving over four Sustainable Development Goals: mitigating hunger, extreme poverty, enhancing environmental preservation, and addressing global climate concerns. Research into changes within SOC and SIC across surface and subsurface soils was conducted on aeolian deposits. In this specific case study, two sites sharing similar climates and conditions were chosen as sources of wind-blown sediment parent material. The aim was to discern variations in SOC, SIC, and STC storage in surface and subsurface soils between Sistan and Baluchistan Province (with rapeseed and date orchard cultivation) and Kerman Province (with maize cultivation) in southeastern Iran. The findings highlighted an opposing pattern in SOC and storage concerning soil depth, unlike SIC. The average SOC content was higher in maize cultivation (0.2%) compared to date orchard and rapeseed cultivation (0.11%), attributed to the greater evolution of these arid soils (aridisols) in comparison to the other region (entisols). Conversely, SIC content in the three soil uses demonstrated minimal variation. The mean STC storage was greater in maize cultivation (60.35 Mg ha−1) than in date orchard (54.67 Mg ha−1) and rapeseed cultivation (53.42 Mg ha−1). Within the examined drylands, SIC, originating from aeolian deposits and soil processes, assumes a more prominent role in total carbon storage than SOC, particularly within subsurface soils. Notably, over 90% of total carbon storage exists in the form of inorganic carbon in soils.

The Short-Term Effect of Olive Mill Wastewater Application on Humic Acid in Subsurface Soil Layers of the Arid Region of Tunisia

ABSTRACT Few studies have assessed the changes in soil quality based on humic acids (HA) in relation to the fresh olive mill wastewater (OMW) application. Qualitative changes to soil organic matter (SOM) under the application of OMW in real conditions have been little investigated. To make a contribution in this context, an experimental field was established in an arid Tunisian area, which included a control soil, a soil treated with 10 L m˗ 2 OMW and another amended with 10 kg m˗ 2 manure. Soil samples were collected from soil depths: 0–20 cm, 20–40 cm and 40–60 cm on the first day of OMW and manure application (day 0) and after 4 months (120 days). Results revealed that soil treated with OMW had the highest SOM content (1.42 ± 0.13%), cation exchange capacity (CEC) (3.03 ± 0.51 (cmol(c) kg−1)) and soil pH value. OMW mineralization supplied soluble ions which enhanced the electrical conductivity (EC) (1.44 ± 0.34 dS m−1). Infrared (IR) spectroscopy showed higher aliphatic, aromatic and phenolic groups in OMW amended soil than the manured soil for initial and final dates. Spreading OMW on soils provides a favorable environment for improving soil humic acids (HAs), recycling organic matter (OM) and enhancing soil properties by transferring aromatic and aliphatic structures into deeper horizons, which in turn increased the sequestration of soil organic carbon (SOC).