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Plant litter is a well-defined pool of organic matter (OM) in which the influence of manganese (Mn) on decomposition (both decomposition rate and the mix of compounds ultimately transferred to soil OM) has been clearly demonstrated in temperate forests. However, no similar study exists on grasslands and the effect of foliar Mn versus soil-derived Mn on litter decomposition is poorly known. We used a 5-month and 12-month field, and 10-month laboratory experiments to evaluate litter decomposition on the Kohala rainfall gradient (Island of Hawai‘i) in areas with different foliar and soil Mn abundances, and on which a single plant species (Pennisetum clandestinum) dominates primary production and the litter pool. The chemical imaging analyses of decomposed litter revealed that Mn2+ oxidized to Mn3+ and Mn4+ on grass litter during decompositions—hallmarks of Mn-driven litter oxidation. However, these transformations and Mn abundance did not predict greater litter mass loss through decomposition. These observations demonstrate that the importance of Mn to an ecosystem’s C cycle does not rely solely on the metal’s abundance and availability. [ABSTRACT FROM AUTHOR]

Organic matter has a very important function in soil, without which, soil formation processes cannot take place properly. It can be divided and classified based on several aspects; the most general division is between the living and non-living parts of organic matter. The results presented in this paper specifically refer to the living microbial part of organic matter. This research was carried out in the years 2021–2024 in the South Bohemia region located in the Czech Republic. Two types of land use (four permanent grassland areas, two forest areas) were evaluated. Based on laboratory soil analyses, some significant dependencies were found. For example, in grasslands with statistically identical pH, there was a dependence (p-value 0.05) between soil organic carbon (SOC), carbon of microbial biomass (MBC) and microbial basal respiration (MBR). Additionally, coniferous forest experimental locations had a lower pH, which, in turn, slowed the activity of microorganisms and promoted the accumulation of SOC in the soil. The results from this experiment support the current knowledge of organic matter and are important for a better understanding of the soil organic matter cycle. [ABSTRACT FROM AUTHOR]

Turbidity currents carve the deepest canyons on Earth, deposit its largest sediment accumulations, and break seabed telecommunication cables. Powerful canyon‐flushing turbidity currents break sensors placed in their path, making them notoriously challenging to measure, and thus poorly understood. This study provides the first remote measurements of canyon‐flushing flows, using ocean‐bottom seismographs located outside the flow's destructive path, revolutionizing flow monitoring. We recorded the internal dynamics of the longest sediment flows yet monitored on Earth, which traveled >1,000 km down the Congo Canyon‐Channel at 3.7–7.6 m s−1 and lasted >3 weeks. These observations allow us to test fundamental models for turbidity current behavior and reveal that flows contain dense and fast frontal‐zones up to ∼400 km in length. These frontal‐zones developed near‐uniform durations and speeds for hundreds of kilometres despite substantial seabed erosion, enabling flows to rapidly transport prodigious volumes of organic carbon, sediment, and warm water to the deep‐sea. Plain Language Summary: Seafloor avalanches of sediment, called turbidity currents, transport huge volumes of sediment and organic carbon to the deep‐sea, and they break critical seabed telecommunication cables that underpin global data transfer. However, turbidity currents are very difficult to measure directly as they often damage sensors placed in their flow path, so they are poorly understood. Here we show that turbidity currents generate ground vibrations that can be measured using ocean‐bottom seismographs placed outside the flow's destructive path, revolutionizing flow monitoring. These seismographs recorded the longest sediment flows yet measured in action on Earth, which traveled >1,000 km along the submarine Congo Canyon‐Channel offshore West Africa. We use these observations to test fundamental models of turbidity current flow behavior. Our measurements show that the front of the flows contain a fast frontal‐zone with high sediment concentrations, which can be up to ∼400 km long, whilst the whole duration of the flow can last for more than 3 weeks. These frontal‐zones develop near‐uniform durations and speeds, despite extensive seabed erosion that adds sediment into the flow. New information on flow durations shows how turbidity currents rapidly deliver prodigious volumes of organic carbon, sediment, and warm water to the deep‐ocean floor. Key Points: Remote seismic monitoring reveals the duration, internal structure, and evolution of powerful canyon‐flushing turbidity currentsFlows contain dense and fast frontal‐zones (up to ∼400 km long) that maintain uniform durations and speeds despite huge seabed erosionCanyon‐flushing flow frontal‐zones can bring substantial fluxes of organic carbon, sediment, and warm water to the deep‐sea in <24 hr [ABSTRACT FROM AUTHOR]

Minute particles within the soil can normally possess charges and predominantly concentrate on the soil colloids. These charges on the soil surface can contribute to a variety of physical, chemical, and physiochemical characteristics of the soil. Key property parameters of soil colloidal particles can include the surface potential, surface charge density, surface electric field intensity, specific surface area, and surface charge number. The objective of this study was to investigate the impacts of prolonged utilization of organic fertilizer and straw on these electrochemical characteristics of the soil surface. Furthermore, the primary influencing factors were determined to enhance the fertility of arable land. A long-term experiment was conducted at the Shuitou experimental base in Yuncheng City, Shanxi Province since in 2007. Four treatments were set as the exclusive application of chemical fertilizer (F), a combination of organic and chemical fertilizer (MF), the integration of straw returning with chemical fertilizer (SF), and a comprehensive application of organic fertilizer, straw returning, and chemical fertilizer (MSF). The electrochemical properties of the soil surface were examined, including surface potential, surface charge density, surface electric field intensity, specific surface area, and surface charge number. Additionally, organic carbon fractions were also analyzed, such as soluble organic carbon, particulate organic carbon, mineral-associated humus, fulvic acid, and humic acid. Furthermore, the investigation was conducted on the structural characteristics of mineral-associated humus. The results indicated that the application of organic fertilizer and straw returning treatments (MF, SF, and MSF) was substantially enhanced the electrochemical characteristics of the soil surface, compared with the F treatment (P<0.05). Among them, the MSF treatment exhibited the highest values, with the respective measurements of 17.07 cmol/kg, 67.02 m² /g, 0.25 c/m², 5.12×108 V/m, and -91.14 mV, respectively. Compared with the F treatment, the MF, SF, and MSF treatments were significantly enhanced the quantities of total soil organic carbon and organic carbon fractions, including the soluble organic carbon, particulate organic carbon, mineral-associated humus, fulvic acid, and humic acid. Additionally, there was also an increase in the ratio of humic acid to fulvic acid (P<0.05). Specifically, the MSF treatment exhibited the highest contents and ratio, with the values of 21.5, 0.1, 12.1, 5.5, 3.3, 2.2 g/kg and 1.5. Meanwhile, the organic fertilizer and straw returning treatments were resulted in the a significant reduction in the E4/E6 and △lgK values of mineral-associated humus (P<0.05). There was the an increase in the relative abundance of C=O/C(O)N group within the mineral-associated humus. The comprehensive analysis revealed that there was the a significant positive correlation between soil surface electrochemical characteristics and various factors, including the total soil organic carbon, organic carbon fractions, clay content, and the ratio of humic acid to fulvic acid. Notably, there were the most substantial influences on the soil surface electrochemical characteristics by the mineral-associated humus, clay content, and the ratio of humic acid to fulvic acid, with the interpretation rates of 67.0%, 5.9%, and 4.8% respectively. And the E4/E6, △lgK, and C=O/C(O)N groups of humus were strongly associated with the soil surface electrochemical characteristics. In summary, the prolonged use of organic fertilizer and straw were substantially enhanced the electrochemical properties of the soil surface, in terms of the soil organic carbon fraction and the structural characteristics of humus. Consequently, these findings can also provide the theoretical foundation for the microscopic and macroscopic processes in soil. [ABSTRACT FROM AUTHOR]

Organic carbon (OC) and elemental carbon (EC) play a significant role in aerosol mass and atmospheric processes. This study is focused on the eastern part of the Great Northern Plains of India, namely the Brahmaputra Plains, to understand the influence of regional and local contribution on the carbonaceous fraction of PM2.5. Mean annual PM2.5 concentrations exceeded the National Ambient Air Quality Standards (NAAQS), with values of 46.6 ± 30.0 μg/m3 in the rural area and 50.4 ± 34.4 μg/m3 in the semi-urban area. The range in monsoon-winter was found to be 22.7–71.9 μg/m3. OC and EC contribute 44–50% of the PM2.5 mass concentration. The OC/EC ratios ranged from 3.3 to 9.3 in the rural area and from 4.3 to 6.9 in the semi-urban area, indicating significant secondary organic aerosol (SOA) formation, especially during the high photochemical period of the pre-monsoon season. Lower δ13C values were observed during winter (-27.5‰ rural, -27.3‰ semi-urban), pre-monsoon (-28.1‰ rural, -27.6‰ semi-urban), and post-monsoon (-28.2‰ rural, -28.1‰ semi-urban) periods, suggesting influences from biomass burning, fossil fuel combustion, and aged aerosols. The study employs cluster analysis of air mass trajectory, and Moderate Resolution Imaging Spectroradiometer (MODIS) fire data to determine the influence of the hotspot Indo-Gangetic Plain (IGP) and long-range transport on aerosol carbonaceous content during most seasons except the monsoon period June–September in the Brahmaputra Plains. [ABSTRACT FROM AUTHOR]

Data on the content and composition of hydrocarbons, like aliphatic and polycyclic aromatic hydrocarbons, in Holocene sediments (undisturbed cores 0–30 cm) are presented. The samples were collected in the southwestern region of the Kara Sea during the first part of cruise 89 of the R/V Akademik Mstislav Keldysh in September 2022. It has been established that the distribution of hydrocarbons, unlike organic carbon, does not depend on the lithotype of bottom sediments, because, along with methane, high molecular weight hydrocarbons are formed in the gas-saturated zone. This leads to an increase in the proportions of aliphatic (>1%) and polycyclic aromatic hydrocarbons (>1 × 10–3%) in the organic carbon composition, as well as to the change in their distribution and composition within the sedimentary sequence. In the lower horizons of columns, the HC composition becomes more autochthonous due to the growth of low molecular weight alkanes and naphthalenes. Changes in the redox potential in the sedimentary sequence also affect the concentrations and composition of hydrocarbons. [ABSTRACT FROM AUTHOR]

Biochar plays an important role in agricultural production as it can improve soil fertility, promote nutrient adsorption and enhance plant growth. However, the distribution of biochar in the soil significantly impacts its application effect. In order to investigate the impact of non-uniform biochar distribution on soil nutrient uptake, root shape, peanut development, and the makeup of soil microbial communities, we carried out greenhouse peanut pot studies. This experiment followed a completely randomised design with four treatments, each with three replications. The four treatments were as follows: no biochar application (B0); concentrated biochar application near seeds (B1); relatively concentrated surface application of biochar (B2), and uniformly dispersed application of biochar (B3). The findings demonstrated that, compared to the no-biochar scenario, the aboveground and root nitrogen uptake was significantly (P < 0.05) improved by the B2 treatment, increasing by 42.79% and 51.39%, respectively, compared to the control group. Additionally, it reduced the concentrations of NO3--N and NH4+-N in the soil. The B2 treatment also significantly (P < 0.05) increased the net photosynthetic rate and aboveground dry matter weight, increasing by 196.85% and 53.96%, respectively, compared to the B0 treatment. The B1 and B3 treatments also demonstrated a higher promoting effect. The growth of the root system and the quantity of root nodules were promoted by the addition of biochar. The number of root nodules in the B2 treatment was 72.22% higher than that in the control group. In terms of microbial and bacterial communities, the addition of biochar increased the number of nitrogen--fixing bacteria to a certain extent, while the relative abundance of soil bacterial communities showed no significant differences. In general, the non-uniform distribution of biochar in the soil significantly affected peanuts' vegetative growth and developmental effects. The relatively concentrated surface application of biochar treatments contributes to improving plant nutrient uptake and root system development. This provides a more effective application method for agricultural personnel to apply biochar fertiliser in the future. [ABSTRACT FROM AUTHOR]

To examine the mechanisms of organic carbon transformation and sequestration by biochar in citrus orchard soil, a 100-day organic carbon mineralization test was conducted using citrus orchard soil from a 5-year-old forest. Calcium-modified citrus peel biochar (OBC-Ca) was applied at rates of 0%, 1%, 2%, and 4%. The results indicated that different percentages of OBC-Ca significantly influenced the mineralization processes in citrus orchards. Specifically, the cumulative mineralization of soil organic carbon was notably reduced by 8.68% and 17.00% with the application of 2% and 4% OBC-Ca, respectively, compared to the control group. Random forest analysis revealed that microbial biomass carbon (MBC), readily oxidizable carbon (ROC), and dissolved organic carbon (DOC) were critical indicators for predicting the cumulative mineralization of soil organic carbon. MBC and ROC were found to inhibit the cumulative mineralization, while DOC promoted it. As the proportion of OBC-Ca applications increased, MBC rose by 2.63% to 10.46%, ROC increased by 16.41% to 108.59%, and DOC increased by 0.48% to 11.67%. Correlation analysis demonstrated a significant negative correlation between the cumulative mineralization rate of soil organic carbon and soil enzyme activity, with soil sucrase content increasing significantly by 216.42% to 393.44% compared to the control. The application of calcium-modified biochar effectively reduces carbon dioxide emissions from citrus orchard soils, with a 4% application yielding the most favorable outcomes for enhancing soil carbon sinks, thereby positively impacting the carbon sequestration potential of citrus orchard soil. [ABSTRACT FROM AUTHOR]

The research was carried out to determine the potential effect of microbiota, organic carbon, percentage of moisture content, and microbial biomass concentration as an evaluator of variation in basal soil respiration rate. Relative distribution and composition of the microbial population were estimated from six different chronosequence manganese mine spoil (MBO0, MBO2, MBO4, MBO6, MBO8, MBO10) and forest soil (FS). The variation was seen in moisture content (6.494±0.210-11.535±0.072)%, organic carbon (0.126±0.001-3.469± 0.099)%, MB-C (5.519±1.371-646.969± 11.428) µg.g-1 of soil. A positive correlation was shown between OC with MB-C (r = 0.938; p< 0.01) and moisture content (MC) (r = 0.962; p< 0.01). Variation in the basal soil respiration (BSR) and microbial metabolic quotients (MMQ) was shown to range between 0.352 ± 0.007-0.958 ±0.014µg CO2-C.g-1 and 6.5× 10-3 - 1.481×10-3 µg CO2-C.g-1 microbial-C.h-1 with BSR: OC from (2.793-0.276)% respectively. This result shows that there is a gradual increase in OC, MC, MB-C, and BSR across seven different sites due to progressive enhancement in soil fertility that leads to the initialization of succession. Stepwise multiple regression analysis further confirms the degree of variability added by microbial biomass C, moisture content, organic carbon, and microbial population on basal soil respiration in microbes. Principal component analysis enables the differentiation of seven different soil profiles into independent clusters based on cumulative variance given by physico-chemical and microbial attributes that indicate the level of degradation of land and act as an index to restore soil fertility. [ABSTRACT FROM AUTHOR]

We investigated the total sediment O2 uptake (TOU), sulfate reduction rate (SRR), and benthic nutrient flux (BNF) at the Yellow Sea cold water mass (YSCWM) sediments (N3509 and N3507) and the coastal sediment (N3503) in the southern Yellow Sea. The organic carbon (OC) content increased from coarse- to fine-grained sediment, which was by far the highest at N3503 (0.89% and 6.1 Ø), followed by N3509 (0.72% and 4.5 Ø) and N3507 (0.15% and 3.0 Ø). The bottom water temperature at N3503 (16.0°C) was 6‒7°C higher than N3509 (10.2°C) and N3507 (9.0°C). The TOU and SRR at N3503 were 24.5 ± 5.0 mmol O2 m–2 d–1 and 6.5 mmol S m–2 d–1, 3‒6 times higher than the values measured at N3509 and N3507 (5.5 ± 0.2 and 4.2 ± 0.3 O2 mmol m–2 d–1 and 0.9 and 0.7 mmol S m–2 d–1, respectively). TOU showed a positive correlation with both the OC content and the bottom water temperature (R = 0.71, p < 0.001). The BNF at N3503 (3.4 mmol N m–2 d–1, 0.5 mmol P m–2 d–1, 3.8 mmol Si m–2 d–1) was 3‒37 times higher than the values measured at N3509. The BNF contributed 72–179% of the nutrients required for primary production at N3503, whereas the contribution was less than 30% at N3509. [ABSTRACT FROM AUTHOR]

This study investigated carbon sequestration potential in reforesting agricultural lands with prevalence of Scots pine (Pinus sylvestris L.) in the "Nasibash" site of the Eurasian Carbon Polygon, located in the Republic of Bashkortostan, Russia. The research focused on analyzing carbon stocks in different ecosystem components (tree stand, herbaceous layer, litter, and soil) across various stages of succession, including fallow land, hayfield, and four stages of Scots pine reforestation. We found that needles during the first stage of succession were characterized by the highest carbon sequestration, while the lowest was in underground phytomass (roots). The tree stand exhibited a higher potential for carbon sequestration in stem wood, branches, and needles compared to other components. The highest carbon accumulation in the tree layer was observed in the stem phytomass at the fourth stage of reforestation, while the highest phytomass accumulation in the herbaceous layer was in the root mass at the fourth stage of succession. The study revealed that the highest organic carbon content in the topsoil layer was observed in areas dominated by herbaceous vegetation, with a decrease in carbon content as the stage of succession increased. The highest carbon content was found in tree pines at the first stage of succession. The research highlighted the importance of considering conversion factors for different stages of reforestation, as the average carbon content in vegetation was 20% higher than the approved conversion factors for young tree stands. Overall, the study demonstrates the significant potential of Scots pine reforestation on former agricultural lands for carbon. The findings suggest that these territories play a decisive role in future environmental and climate projects, contributing to the decarbonization efforts. [ABSTRACT FROM AUTHOR]

Introduction: Seagrass sediments are important 'blue carbon' reservoirs which store climatically significant quantities of organic carbon (Corg) at the global scale. Seagrass meadows that overly these sediments also provide a range of critical ecosystem services including shoreline stabilization, storm surge protection, and fisheries nursery grounds. However, the controls over accumulation and the sources of organic C to these sediments beds are highly variable and poorly understood with the relative importance of hydrodynamic setting, species composition and canopy density being unclear. Methods: Here we address these questions using the first observation-based estimates of Corg stocks and provenance on Turneffe Atoll, Belize, made via remotely-sensed habitat extent, local Corg data and isotopic data. Sedimentary Corg was highest in sediments underlying the most sheltered meadows and decreased with increasing exposure to wind and wave energy with the seagrass meadows in the central lagoon containing an extensive deposit of mangrove derived organic carbon, stabilized and protected by the overlying seagrass meadow. Results: The influence of species composition appeared weak with the ubiquitous species T. testudinum occurring across a wide range of hydrodynamic regimes ranging from the most sheltered to the most energetic and being associated with a wide range of sedimentary organic C concentrations. Importantly from the perspective of remote sensing, org C concentrations were unrelated to canopy density. We hypothesize that this decoupling of organic C concentration from seagrass canopy cover reflects a much longer timescale for carbon storage in the sediments than the lifespan of the seagrass plants themselves and/or a substantial non seagrass derived organic C burden in seagrass sediments. Overall, we conservatively estimate that the top 30cm of sediments underlying the seagrass meadows overlying carbonate sediments on the atoll exterior store 0.58 x 106 Mg Corg, most of which is seagrass-derived, whilst the sediments underlying the meadows within the central lagoon store an additional 1.28 x 106 Mg Corg. When the maximum possible extent of seagrass is considered, this estimate increases to 3.54 x 106 Mg Corg. Substantial Corg stocks extending >1m depth were observed across all sites, and so these inventories are considered conservative. Discussion: A preliminary 'cost of loss' for sedimentary Corg in the top 30 cm of Turneffe Atoll's seagrass meadows, based on a carbon trading value of €60 tCO2 (eq), is estimated at €42 million for the outer atoll, increasing to €136 million when the mangrove-derived sediments of the central atoll are considered and €260 million when turbid areas are assumed to contain seagrass. [ABSTRACT FROM AUTHOR]

In response to the degraded soil health and lack of improvement in the yield of rice–wheat cropping systems in South Asia's Indo-Gangetic Plains, an experiment was formulated in a split-plot design. Four rice residue management practices were the primary factor, alongside two nitrogen levels (150 and 180 kg/ha) and two nitrogen split levels (two and three splits) as sub-treatments. The findings revealed a notable increase in soil organic carbon (SOC), microbial count, and enzymatic activity in plots subjected to conservation tillage and residue treatment compared to those in plots subjected to partial residue (anchored stubbles) and conventional methods (residue incorporated with chopping). The collective analysis demonstrated a significant influence of rice residue management practices and nitrogen application levels on wheat yield attributes and productivity. Specifically, zero tillage with full residue (unchopped) in wheat exhibited a 5.23% increase in grain yield compared to conventional tillage with full residue (chopped), concurrently boosting the soil microbial count by 19.80–25%, the diazotrophic count by 29.43–31.6%, and the actinomycete count by 20.15–32.99% compared with conventional tillage. Moreover, applying nitrogen in three splits (at sowing, before the 1st irrigation, and after the 1st irrigation) led to a 6.25% increase in grain yield than that in two splits (at sowing and after the 1st irrigation), significantly impacting wheat productivity in the soil. Furthermore, the zero tillage-happy seeder with full residue elevated dehydrogenase activity from 77.94 to 88.32 μg TPF/g soil/24 h during the study year, surpassing that in the conventional plot. This increase in enzymatic activity was paralleled by a robust positive correlation between the microbial population and enzymatic activity across various residue retention practices. In conclusion, the results underscore the efficacy of crop residue retention following conservation tillage, in tandem with nitrogen optimization and scheduling, in enhancing wheat yield within the rice–wheat cropping system. [ABSTRACT FROM AUTHOR]

Investigating carbon (C), nitrogen (N) and phosphorus (P) contents and ecological stoichiometric characteristics in leaf litter from tropical rainforests is crucial for elucidating nutrient cycling and energy flow in forest ecosystems. In this study, a 60-ha tropical montane rainforest dynamic monitoring plot in Jianfengling, was selected as the research site and 60 subplots were selected for detailed study. Leaf litter was collected monthly throughout 2016, branches of similar height were placed atthe four corners of each sample square to support a nylon cloth (1 m× 1 m) with 1 mm apertures. The collected plant leaves were sorted,placed into envelopes, labelled, and transported to the laboratory and samples from various plant species were identified, resulting in a total of 107 samples collected and analyzed. For the 31 dominant species, the leaf litter had C, N and P contents of 312.71 ± 28.42, 4.95 ± 0.46 and 0.40 ± 0.03 g/kg, respectively. The C:N, C:P and N:P ratios were 63.61 ± 7.50, 790.91 ± 82.30 and 12.49 ± 1.00, respectively, indicating moderate variability. The C, N and P contents exhibited greater variability among the plant groups, indicating significant heterogeneity among the samples. In contrast, the data from the subplots exhibited less variability, highlighting significant homogeneity. Overall, the mean carbon, nitrogen and phosphorus contents in the leaf litter from tropical montane rainforests were lower than those observed at national and global scales. The N:P ratios in leaf litter below 14 indicated that nitrogen limited litter decomposition in Jianfengling. However, no significant correlations were observed between the C, N and P contents and their stoichiometric ratios in leaf litter and those in soil. The above results provide important reference data and scientific basis for the nutrient cycling and energy flow processes, and in the future, we can explore the limiting role and mechanism of nitrogen in the decomposition process of leaf litter. [ABSTRACT FROM AUTHOR]

The purpose of this work is to study the structure of microbial communities, the physicochemical characteristics of the burozems' profiles, and the soil material infilling the humus pockets. Burozems (Cambisols) in the south of the Vitim Plateau are characterized by specific morphological features: presence of frost cracks, which form wedge-shaped humus pockets, sharply narrowing down the profile. Humus pockets are filled with dark brown humus-enriched material with black stripes that are sharply contrasting in color and properties with the enclosing soil. Compared to the profile of burozems at corresponding depths, the soil mass from humus pockets is less compacted. An increase in total porosity results in greater water permeability of the soil material in the frost cracks. Specific features of the microbial cenosis structure and of the microbial biomass carbon in the soil profile and in the soil material of pockets were revealed. The organic carbon and the absorbed bases are rather evenly distributed in the soil material of the pockets and their contents sharply decrease down the soil profile. The experimental data obtained during the study will replenish the database of the properties and status of microbial cenosis in burozems and in the soil material of their humus pockets in the south of the Vitim Plateau. [ABSTRACT FROM AUTHOR]

Aim: To identify the main factors affecting Al mobilization in soils from different climate zones. Methods: XRD and 27Al NMR were used to analyse clay minerals and the relative contents of four- and six-coordination Al. Soil acidification and Al mobilization were studied by constant pH automatic potentiometric titrator. Results: The relative content of tetrahedral Al (AlIV) in the soils increased gradually from low to high latitude, and an opposite trend was observed for soil octahedral Al (AlVI). The larger organic carbon (OC) content in surface soils (0–20 cm) effectively inhibited both soil acidification and Al mobilization compared with subsurface soils (20–40 cm). The content of mobilized Al followed the order: Inceptisol > Alfisol > Mollisol > Ultisol in both surface and subsurface soils, which determined by soil CEC, the contents of OC and clay and relative contents of AlIV and AlVI. After removal of OC from soil colloids, the amounts of mobilized Al were consistent with the relative contents of AlIV in soil colloids and followed Mollisol > Inceptisol > Alfisol > Ultisol, suggesting that the solid Al in the soils from temperate and north subtropical regions was readily mobilized during soil acidification. Conclusions: Al mobilization in different soils mainly depended on the CEC, the contents of OC and clay, and the coordination nature of Al in the soils. A larger CEC, a lower OC content, a greater clay content, and a higher content of AlIV led to a greater amount of mobilized Al during soil acidification. [ABSTRACT FROM AUTHOR]

Soil pores are dominated in various soil functions, including water infiltration and retention, soil permeability, nutrient availability, as well as aeration and mechanical impedance to root elongation. The dynamic behavior of soil pores is primarily influenced by tillage practices, the presence of crop roots, and the return of soil organic matter. In this research, a systematic investigation was implemented to explore the impacts of the long-term application of organic fertilizers and straw on the soil pore structure. An analysis was also made to elucidate the relationship between soil organic carbon and soil pore structure. The data was collected from a 16-year long-term field experiment located in Shui Tou agricultural experimental base, Shanxi Agricultural University (Shanxi Academy of Agricultural Sciences), Yuncheng, Shanxi Province. Four treatments were set as sole chemical fertilizer (F), organic fertilizer + chemical fertilizer (MF), straw returning + chemical fertilizer (SF), and organic fertilizer + straw returning + chemical fertilizer (MSF). The soil pore structure was examined using X-ray computed tomography (CT) and advanced image processing. While the soil organic carbon was assessed to determine the physical fraction contents (free particulate organic matter (FPOM), occluded particulate organic matter (OPOM), and mineral-associated organic matter (MOM)). Additionally, the structural properties of the organic carbon were qualitatively and quantitatively analyzed by Fourier transform infrared (FTIR) spectroscopy. The results indicated that all organic amendment treatments significantly enhanced the total porosity and porosity of >0.5 mm aperture, compared with the F treatment (P<0.05). the MSF treatment exhibited the highest values. Additionally, the porosity ranging from 0.5 to 0.2 mm in the MF and MSF treatments was significantly higher than that in the F treatment (P<0.05). However, there was no significant difference in porosity ranging from 0.2 to 0.06 mm among all treatments. Furthermore, MSF treatment significantly enhanced the connectivity and complexity of soil pores, with increases of 33.2% and 17.9%, respectively, compared with the F treatment P<0.05). The organic fertilizer and straw returning treatments (SF, MF, and MSF) achieved a significant increase (P<0.05) in the contents of total soil organic carbon, FPOM, OPOM, and MOM. MSF also exhibited the highest values among these treatments, with concentrations of 21.5, 7.1, 4.2, and 10.2 g/kg, respectively. The long-term straw incorporation and the application of organic fertilizers (MSF) were performed better to accumulate the polysaccharide and lipid organic carbon in the soil, while concurrently reducing the content of aromatic organic carbon. The Pearson correlation analysis revealed that there was a positive and significant relationship between soil total porosity, porosity of >0.5 mm aperture, as well as the connectivity and complexity of soil pores with the contents of total soil organic carbon, FPOM, OPOM, MOM, and polysaccharide and lipid organic carbon (P<0.05). These findings suggested that the application of organic fertilizer and straw incorporation enhanced the content of soil organic carbon to accumulate the polysaccharide and lipid organic carbon, which facilitated the formation and modification of soil pores. Consequently, the enhanced physical properties of the soil were attributed to the regulation of soil structure by the organic amendment. An optimal distribution of soil pores was achieved to increase the soil complexity and pore connectivity. Accordingly, the organic amendment can be an effective strategy to optimize the soil pore structure. Future studies should also examine the response of soil pore structure and pore size distribution to the decomposition of incorporated organic manure. [ABSTRACT FROM AUTHOR]

Machine learning approaches are utilized to identify patterns in behavior and generate predictions across various applications. The objective of this work is to create a highly efficient model for accurately measuring and analyzing the levels of soil organic carbon (SOC) in the Chambo river subbasin, which is situated in the province of Chimborazo. The model evaluation entails the application of diverse machine learning algorithms and approaches to determine the most efficient regression model. Regression models are improved using techniques such as Artificial Neural Networks, Support Vector Machines, and Decision Trees. The Resilient Backpropagation method yields the most precise model, as it accounts for a greater proportion of the variability in SOC content for the test data. This aligns with the findings from the training data, demonstrating a relatively low mean absolute error and a processing time that is approximately 400 times faster than that of the Multilayer Perceptron algorithm. The evaluation of estimating models is an objective procedure that considers not only the findings and precise metrics derived from the model's design, but also other relevant elements. The effectiveness of the Random Forest approach, specifically the quantile regression forests technique, has been established for estimating SOC contents in the Chambo river sub-basin data. [ABSTRACT FROM AUTHOR]