Search Results (263)

Biochar can increase soil carbon (C) and nutrient retention, but application of raw biochar may reduce inorganic nitrogen (N) availability and crop yields. As a result, biochar is sometimes co-applied with organic fertilizers, though the efficacy of this practice for preventing decreases in inorganic N remains unclear. We examined how applications of hardwood, hay, and softwood biochars (25 Mg ha⁻¹), with and without blood meal co-application, affected C and N dynamics in a Southwest Virginia pasture soil. All biochars increased soil C pools initially and after 11 months. Biochar C accumulated in the coarse particulate organic matter fraction, with hay and softwood biochar C also accumulating in the fine particulate and mineral-associated fractions, respectively. Immediately after application, inorganic N was increased by blood meal co-application, but biochar had no short-term effect on inorganic N. Conversely, nitrate levels were ~81% lower in biochar-amended plots after 11 months, regardless of blood meal co-application and biochar feedstock. These findings suggest that co-application with organic fertilizer may only provide short-term N benefits, highlighting the need to monitor crop yield and N status in seasons following biochar application, as soil test nitrate alone is not a reliable predictor of crop yield in biochar-amended soils. Full article

Land-use change (LUC) and salinization interact synergistically to regulate depth-dependent fractionation and biological mediation of soil organic carbon (SOC) in vulnerable agroecosystems. Unlike previous syntheses addressing these drivers separately, the present review integrates them within a depth-resolved biological framework to reveal their combined effects on fraction-specific distribution under contrasting anthropogenic and ionic regimes. In the topsoil (0–30 cm), LUC and salinity synergistically collapse fungal networks, suppress carbon use efficiency, and restructure microbial communities to accelerate particulate organic matter (POM) turnover and impair mineral-associated organic matter (MAOM) formation. In the subsoil (>30 cm), salinity-driven clay dispersion and pore occlusion restrict oxygen diffusion and carbon accessibility, while LUC-induced loss of deep-rooting vegetation reduces carbon supply to mineral-associated pools. These depth-decoupled mechanisms render subsoil MAOM relatively resilient to direct ionic stress but highly vulnerable to land-use legacy, a distinction rarely represented in existing conceptual models. The evidence highlights key management implications, including restoring biological complexity in topsoil through reduced tillage, mycorrhizal re-establishment, and osmotic stress alleviation; conserving subsoil carbon by restoring deep-rooting vegetation and maintaining favorable ionic conditions for organo-mineral stabilization; and using depth-specific biomarkers, including enzymatic stoichiometry, fungal-to-bacterial ratios to detect SOC vulnerability before measurable losses occur. Future research should prioritize depth-explicit monitoring and integrated biological–physicochemical approaches to improve predictions of SOC dynamics. The resulting framework provides a mechanistic basis for depth-differentiated carbon management in salinizing landscapes. Full article

Under changing environmental conditions, soil buffering capacity is a key soil-related component of terroir functional stability and vineyard resilience. We assessed the effects of sheep wool and alfalfa hay under-vine mulches during the first two years after treatment establishment in four vineyards with contrasting volcanic and loess-derived soil in the Tokaj Wine Region. Soil responses were evaluated using soil organic carbon (SOC), permanganate oxidizable carbon (POXC), fluorescein diacetate (FDA) hydrolytic activity, easily extractable glomalin-related soil protein (EE-GRSP), and the relationships of EE-GRSP with SOC and clay fraction. Mulch effects were site-specific rather than uniform. SOC values remained close to or above baseline levels in several vineyard–treatment combinations. POXC relative variability decreased in mulch-treated plots, with the proportion of highly variable units declining from 75% to 25% in both mulch treatments by autumn 2025, while this category remained dominant in the control. FDA activity was mainly associated with soil depth and vineyard-specific conditions. EE-GRSP showed positive relationships with both SOC and clay fraction. Neither mulch material showed consistent superiority across all indicators during the first two years. These findings suggest that soil buffering capacity was best interpreted as the outcome of multiple biological, organic matter-related, and mineral-associated processes operating at different temporal scales. Natural under-vine mulches may support soil stability, although longer-term monitoring is needed to assess the persistence of these responses. Full article

River sediments act not only as important sinks for heavy metal pollution in watersheds, but also as potential secondary sources under changing environmental conditions. Heavy metals can enter river systems through industrial wastewater discharge, agricultural non-point runoff, urban stormwater and sewage inputs, mining and smelting activities, and atmospheric deposition. During adsorption onto suspended particles, sedimentation, and resuspension, metals such as Cd, Pb, Cr, Cu, Zn, Ni, As, and Hg progressively accumulate in sediments. Because heavy metals are persistent, non-degradable, and bioaccumulative, contaminated sediments can record historical watershed pollution while also releasing metals back into overlying water under hydrodynamic disturbance, pH and redox fluctuations, organic matter mineralization, benthic bioturbation, and dredging activities, thereby threatening aquatic ecosystem stability and human health. Using a global methodological framework with particular emphasis on Chinese river basins, this review systematically summarizes key issues in the study of heavy metal pollution in river sediments, including spatial–temporal distribution and operationally defined fractionation, pollution levels and ecological risk assessment, source apportionment, and remediation and management technologies. Current evidence indicates that heavy metal contamination in river sediments exhibits pronounced spatial heterogeneity and watershed-specific characteristics. Its distribution is jointly controlled by geological background, land use patterns, source input intensity, hydrodynamic conditions, sediment particle size composition, and organic matter content. Methodologically, the field has evolved from single total concentration monitoring and exceedance-based evaluation toward integrated assessment systems that combine total concentrations, operationally defined fractionation, bioavailability, ecological risk, health risk, and source contribution. The joint use of BCR sequential extraction, the geoaccumulation index (Igeo), the pollution load index (PLI), the potential ecological risk index (RI), the risk assessment code (RAC), sediment quality guidelines (SQGs), receptor models, isotope tracing, and machine learning has substantially improved pollution identification, risk zoning, and source apportionment. Overall, research on heavy metal pollution in river sediments has shifted from descriptive judgments of whether contamination exists toward mechanistic and management-oriented questions concerning pollution sources, risk evolution, and remediation strategies. However, important gaps remain in compound pollution transformation mechanisms, regional background values and evaluation benchmarks, uncertainty in model parameters, long-term dynamic monitoring, and engineering-scale verification of remediation technologies. Future studies should strengthen multi-media, multi-scale, and long-term monitoring and further integrate fractionation analysis, toxicological effects, source apportionment models, and remediation technologies to provide a scientific basis for watershed ecological security and precision management of contaminated sediments. Full article

Agricultural lands in Russia are increasingly being converted into fallow areas, making the study of potentially mineralizable carbon (PMC) in fallow soils essential for understanding post-agrogenic ecosystem functioning. This study provides a comparative assessment of the spatial and temporal dynamics of PMC in soils of the Leningrad and Novgorod regions (Bankovo, Belogorka, and Borovichi sites) under different land-use types, including fallows of various ages, arable, garden, pasture, hayfield soils, and secondary forests. Total carbon content was determined by high-temperature dry combustion, while basal respiration was measured using a standard incubation method. PMC parameters were estimated using biokinetic fractionation of soil organic matter (SOM), and cumulative carbon release was calculated as the sum of emissions over the incubation period. The highest basal respiration values among the studied fallow soils were observed in fallow soils at the Bankovo site (1.44–1.66 µg CO₂–C g⁻¹ h⁻¹). Carbon stocks in most fallow soils were lower than those of the corresponding background soils, although the magnitude of differences varied among sites. Both the size of the PMC pool and its mineralization rate varied among fallow soils depending on post-agrogenic succession, vegetation type, and site-specific environmental conditions. The highest cumulative C-CO₂ production was recorded in degraded pasture soils and secondary forests at Borovichi. Restorative ecosystems generally showed higher carbon-mineralizing activity than arable and garden soils, although turnover characteristics varied among sites. Region-specific patterns related to parent material and environmental conditions were identified. Even after long-term fallowing (up to 120 years), several soil properties remained different from background conditions, indicating prolonged and site-dependent recovery of organic matter dynamics. Full article

This study evaluates the performance of an indigenous microalgae-assisted aerobic digestion process for sewage sludge stabilization in a pilot-scale photobioreactor (20 L) operated over 20 days without external aeration. The system achieved 53% volatile solids reduction, exceeding the 38–40% threshold required by European stabilization guidelines, alongside 34% total nitrogen and 75% total phosphorus removal. Indigenous microalgal biomass increased substantially from 1.6% to 17% of total biomass, with photosynthetically generated oxygen serving as the primary driver of aerobic bacterial activity and organic matter mineralization. Sludge settleability improved markedly (SVI from 154 to 54 mL/g), accompanied by significant floc size reduction (220 to 33 µm); however, this was accompanied by a clear deterioration in dewaterability, with CST increasing from 16 to 27 s and SRF rising approximately 4-fold, representing a practical trade-off that must be addressed for full-scale application. Extracellular polymeric substances (EPS) analysis showed a clear shift from tightly bound to soluble and loosely bound fractions during treatment, and Pearson correlations indicated that soluble EPS was linked to poorer settling and dewatering, while tightly bound EPS was associated with larger flocs and better sludge structure, confirming EPS restructuring as a key mechanism behind the observed changes in sludge properties. These findings highlight both the strong stabilization potential of this process and the need for targeted dewatering mitigation strategies to support its scale-up. Full article

The increasing generation of municipal waste and the depletion of natural mineral resources have intensified the search for sustainable alternatives for construction materials within the framework of the circular economy. While waste glass, industrial residues, and selected municipal waste fractions have been extensively investigated individually as raw materials for lightweight aggregates, their simultaneous incorporation into a single ceramic matrix remains largely unexplored. To address this research gap, the present study investigates the feasibility of producing lightweight ceramic aggregates through the simultaneous incorporation of three municipal waste streams street sweeping waste (SSW), waste glass, and bulky waste into a clay-based ceramic matrix. Three ceramic mixtures containing different proportions of these waste materials were prepared, pelletized, and fired at 1100 °C. The produced aggregates were characterized in terms of loose bulk density, water absorption, total heavy metal concentrations, and heavy metal leachability, while the bulky waste was additionally characterized by loss on ignition to determine its organic matter content. All produced aggregates satisfied the requirements of PN-EN 13055-1 for lightweight aggregates, with loose bulk densities ranging from 442.9 to 543.1 kg m⁻³, comparable with commercially available expanded clay lightweight aggregates. Water absorption varied between 32.93% and 56.61%, with mixture composition explaining approximately 88% of the observed variance (one-way ANOVA, p < 0.001). Loss-on-ignition analysis revealed that bulky waste contained approximately 98.8 wt.% organic matter, confirming its effectiveness as a pore-forming additive during firing. Environmental assessment of the optimum mixture indicated limited mobility for most investigated heavy metals after thermal treatment; however, chromium leachability slightly exceeded the adopted reference value, indicating the need for further optimization of the ceramic composition. Overall, the developed lightweight aggregate represents a promising alternative to conventional lightweight aggregates and contributes to resource recovery, waste valorization, and the implementation of circular economy principles in the construction sector. Future research should focus on chromium speciation, mechanical performance, long-term durability, life cycle assessment, and pilot-scale production to support future industrial application. Full article

Coastal riparian zones are important transitional areas for carbon cycling between terrestrial and aquatic ecosystems. However, the associations among litter-derived dissolved organic matter (DOM), soil DOM composition, and soil organic carbon (SOC) fractions across habitats remain insufficiently understood. This study aimed to clarify SOC fraction distribution in woody and herbaceous habitats and evaluate its associations with litter-derived DOM, soil DOM composition, and soil environmental factors in different seasons from a coastal riparian zone. In this study, woody habitats had higher SOC content in March, whereas herbaceous habitats showed greater SOC content in November. Particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) were generally higher in different habitats. MAOC accounted for a large proportion of the measured SOC-related pools and showed a consistent positive association with SOC content. Soil DOM consisted of protein-like and humic-like components, with herbaceous habitats showing a stronger protein-like component and woody habitats showing a stronger humic-like component in March. Woody litter showed greater DOC and DON release potential than herbaceous litter leachates, while litter-derived humic-like DOM was closely associated with a soil humic-like component. The labile SOC pool was mainly associated with vegetation type and electrical conductivity, whereas MAOC was positively associated with soil moisture content and total phosphorus. Overall, the distribution of SOC fractions in coastal riparian habitats is shaped by habitat-specific environmental factors, including vegetative carbon inputs, litter leaching and soil physicochemical properties. This finding is critical for developing targeted management strategies to facilitate SOC accumulation in coastal zones. Full article

The sustainability of agricultural systems is linked to soil organic carbon (SOC) and nitrogen (N) dynamics, both of which are influenced by fertilization management. To investigate the long-term effects of pig slurry, a 10-year field experiment was conducted in a Mediterranean semi-arid rainfed cereal system. Four N treatments were compared: mineral fertilizer (MN), slurry from fattening pigs (FS), slurry from gestating sows (SS), and a zero-N control. Grain and straw yields, SOC and its fractions, microbial biomass and activity, and N mineralization were measured after the final cropping season. Slurry increased grain yield by 21% compared with MN. The FS treatment also increased SOC by 24% compared with the MN treatment, mainly through the mineral-associated organic matter fraction (<0.05 mm). Soil basal respiration dynamics (Gompertz model) and the N mineralization rate (0.04382 day^–1; Stanford–Smith model) did not differ among N-fertilized treatments. However, the potentially mineralizable N pool increased under N fertilization, from 19% in MN to 51% in FS relative to the control. These results indicate that repeated applications of pig slurry can replace mineral fertilizer while maintaining or improving crop productivity and soil C storage. Incorporating N mineralization models into fertilization planning could further optimize slurry application rates and timing. Full article

This study investigates the interrelationships between soil organic matter (SOM) quality characteristics and key mercury species in two sites in Czech Republic under historical Hg contamination. SOM properties derived from DRIFT spectral analysis including the aromaticity index (iAR), potential wettability index (PWI), decomposability index (DI), and organic matter quality index (OMQ) along with additional SOM quantity and quality indicators were evaluated against several key Hg fractions (Total Hg (HgT), potentially mobilizable Hg (HgPM), potentially mobilizable Hg ions (Hg²⁺), methylmercury (MeHg), and water-soluble Hg (HgWS)). Neural network analysis revealed that type of horizon (organic or mineral) as well as SOM quality characteristics play an important role in Hg mobility and methylation processes. The results show the difference in relevant SOM quality properties that affect Hg mobility and methylation that can also be opposite based on the soil horizon type for the same soil, potentially forcing different pathways for the mobilization and methylation, and indicating that the state of transformation of organic matter and its quality characteristics along with the environmental conditions are some of the key attributes influencing mobility and methylation processes of Hg in the soil. Full article

Chinese fir (Cunninghamia lanceolata) is one of the most important fast-growing timber species in southern China and plays a critical role in regional carbon sequestration and timber production. Soil organic carbon (SOC) is a key component of the terrestrial ecosystem carbon pool, and its content, composition, and stability directly affect soil fertility, ecosystem service functions, and the ability to cope with climate change. This review summarizes the mechanisms by which density regulation and conifer–broadleaf mixed forest management affect the content, fractions and stability of SOC in Chinese fir plantations. Density regulation changes stand structure, litterfall, and roots, which can impact soil microbial activity, litter decomposition, and mineralization of soil organic matter. Conifer–broadleaf mixed planting and broader mixed-forest reconstruction, through introducing functionally distinct tree species, can optimize stand microenvironments, increase species diversity, improve litter quantity and quality, and diversify root exudates. These changes further regulate soil organic carbon (SOC) accumulation and its physicochemical stability. Based on the latest literature reports, we demonstrate that mixed-species stands with a moderate broadleaf proportion significantly enhance SOC sequestration relative to pure stands, driven by improved litter quality and soil pH neutralization that promote microbial necromass formation and aggregate-associated carbon stabilization. Optimal density regulation complements these benefits by facilitating understory development and root carbon input. Current research indicates that both density reduction and species mixing, as two independent silvicultural measures, can individually enhance soil organic carbon (SOC) stability in Chinese fir plantations. This review identifies key research gaps and provides theoretical foundations for carbon-oriented sustainable management of Chinese fir plantations. Full article

This study investigates nitrogen sources and biogeochemical pathways in a highly urbanized shallow aquifer in Shinagawa Ward, Tokyo, using an integrated approach combining hydrochemical analysis, multivariate statistics (PCA and K-means cluster analysis), and stable nitrogen isotopes (δ¹⁵N-NH₄⁺, δ¹⁵N-NO₃⁻, δ¹⁵N-DON, and dual δ¹⁵N–δ¹⁸O-NO₃⁻). K-means clustering (K = 2, silhouette = 0.54) partitioned all 41 samples into a background group (n = 34) and an ion-enriched group (n = 7; wells sbi 1, 2, 3, 4, 5, 13, and 19), with the latter exhibiting hydrochemical signatures consistent with localized sewage leakage. The convergence of hydrochemical, multivariate, and isotopic evidence suggests that soil organic matter may represent the dominant diffuse background source of nitrogen across the study area. DON constitutes the dominant fraction of total dissolved nitrogen (TDN), while the linear correlations between TDN and DON concentrations (r = 0.77, p < 0.001) and between δ¹⁵N-TDN and δ¹⁵N-DON (r = 0.88, p < 0.001) indicate a common primary source. The dominance of DON combined with the theoretical inverse relationship between δ¹⁵N-DON and DON concentration is consistent with active soil DON mineralization, supported by an isotope fractionation factor (ε = −4.4 ± 0.78‰). Dual isotope analysis of NO₃⁻ (δ¹⁵N–N–δ¹⁸O slope = 0.51) points towards denitrification as an ongoing process in the aquifer. Taken together, the isotopic variations among nitrogen species suggest a transformation sequence from soil organic nitrogen → DON → NH₄⁺/NO₃⁻ → N₂, though each step in this sequence is supported to varying degrees of confidence. These findings highlight the value of δ¹⁵N-DON as a tracer for nitrogen source attribution and cycling in urban groundwater systems, and underscore the importance of considering all dissolved nitrogen fractions in contamination assessments. Full article

Anaerobic digestion (AD) of agro-industrial residues supports the green energy transition by converting organic matter into renewable biogas. Sugar beet pulp is a highly fermentable feedstock, although its process response may vary with chemical composition. This study examined how chemical composition affects mesophilic biogas-production kinetics of sugar beet pulp prepared under laboratory conditions from surplus sugar beet roots. The roots represented ten sugar beet varieties (A–J), and the prepared pulp was characterised for pH, dry matter, organic dry matter, mineral composition, and the relative shares of simple sugars, polysaccharides, protein, and fibre. Batch digestion tests were performed at 39 °C for 30 days. Production curves were analysed using complementary kinetic models (modified Gompertz and a two-fraction first-order model) to capture the lag phase and the contributions of rapidly and slowly degradable substrate pools. Biogas yields ranged from 126 to 141 m³ Mg⁻¹ fresh matter with 50–55% CH₄, corresponding to 64.3–76.1 m³ CH₄ Mg⁻¹ organic dry matter, while organic matter conversion reached 71.2–82.4%. Varieties enriched in simple sugars exhibited a higher share of the fast-degradable fraction and shorter lag phases, indicating faster onset and stronger methane formation. In contrast, higher fibre contents reduced the slow-fraction rate constant and lowered overall conversion, consistent with hydrolysis-limited degradation of the structural carbohydrate matrix. The mineral ion background, particularly K and Na, indicated moderate ionic buffering and stable operation without inhibition. The novelty of this work lies in integrating detailed compositional profiling with dual kinetic modelling to translate chemical fingerprints into tentative process-relevant implications. These implications include feeding strategy, organic loading control and hydraulic retention time selection, and they require further validation in continuous or semi-continuous AD systems. Full article

Agricultural soils worldwide are facing escalating contamination by heavy metals, which present high risks for health due to their persistence, being non-biodegradable, accumulating across the soil profile, and being easily transferred into edible plant tissues, thus propagating through the food chain, with serious consequences for human health and ecosystem integrity. Conventional physical and chemical remediation approaches are costly, ecologically disruptive and operationally complex for the extent of contamination of agricultural land. Thus, there is an urgent need for sustainable and scalable alternatives. This review addresses the need by providing an integrated, mechanistically grounded synthesis of plant-based bioremediation strategies for heavy metal contamination removal, emphasizing the links between soil chemistry, plant physiology, and soil microbiology. First, the principal contamination pathways and controls on metal speciation and bioavailability are summarized, highlighting how parameters such as pH, organic matter, clay minerals, and redox conditions govern the metal fraction available for the plants. The molecular basis of plant heavy metal uptake, translocation and detoxification is examined in detail, including transporter-mediated root uptake, xylem loading and long-distance transport, and chelation by phytochelatins and metallothioneins. The performance and limitations of the main phytoremedation strategies are evaluated across representative hyperaccumulator species, then two major enhancement solutions are discussed: chemical enhancement using synthetic and biodegradable agents, and biological enhancement through plant growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, and mycoremediation fungi. Integrating these perspectives, this review provides a critical assessment of when and how phytoremediation can offer a realistic and agronomically compatible route for managing heavy metal contamination in agricultural soils. Full article

Soil pH is a key regulator of soil chemical processes, organic matter transformation, and ecosystem functioning in acid soils. This study examines how pH gradients induced by long-term liming affect soil chemical properties, aluminum dynamics, and soil organic carbon (SOC) stabilization in Retisols under plant-derived organic inputs. The study was conducted at six soil pH levels (pH_KCl from 3.9–4.0 to 6.5–6.7), which reflect a gradient of acidity conditions. Soil chemical parameters, SOC content and fractions, humic substance composition, aluminum forms, and soil respiration (CO₂ release under laboratory conditions) were analysed. Increasing soil pH significantly reduced aluminum concentrations (by up to 59%) and improved nitrogen and phosphorus availability, indicating a gradual reduction in chemical limitations associated with soil acidity. Soil pH strongly controlled both SOC content and quality. The highest SOC content was observed at pH 6.0–6.1, and strongly acidic conditions favored the accumulation of more labile carbon forms. As the pH increased, there was a clear shift towards more stable organic matter, as indicated by higher humic acid content, an increased HA/FA ratio, and a threefold increase in the organic carbon stability index. At the same time, the reduced water-extractable organic carbon content indicated reduced carbon mobility and improved physicochemical stabilization. Microbial activity increased with increasing pH, but showed a nonlinear response, reflecting a balance between increased mineralization and carbon stabilization processes. These data indicate that soil pH primarily determines SOC stabilization pathways, rather than just total carbon accumulation. These results suggest that soil pH may influence SOC stabilization through changes in aluminum dynamics, organo-mineral interactions, and microbial processes, supporting previously reported mechanisms of carbon stabilization in acid soils. The optimal pH range of 5.5–6.1 promotes favorable interactions between nutrient availability, microbial processes, and organic–mineral associations, supporting long-term soil functionality. This study highlights liming as a key strategy for regulating soil biogeochemical processes and improving the sustainability of acid soil management. Full article