Soil Organic Carbon Content Research Articles

Glucoproteins in particulate and mineral-associated organic matter pools during grassland restoration

Glomalin related soil proteins (GRSP) produced by arbuscular mycorrhizal fungi are important stabilizing components of soil aggregates, and consequently helping to entrap organic matter and encapsulate it from microbial decomposition. Grasslands provide excellent opportunity to study GRSP effects because arbuscular mycorrhiza responsible for GRSP production is well development on roots of grasses. Fast GRSP production will accelerate soil organic carbon (SOC) accumulation, but the contribution of GRSP to particulate organic C (POC) and mineral-associated organic C (MAOC) pool remain unclear. We investigated GRSP content and thermal stability of POC and MAOC in topsoil (0–10 cm) as dependent on grassland restoration. SOC content had a nonlinear rise tendency with grassland restoration, and SOC changes were largely dependent on MAOC (>64 %). The POC content decreased by 58 %, while the MAOC content increased by 34 % after 40 years of restoration, microbial transformation of POC plays important role for MAOC formation. The GRSP content contributed 1.7 times more to MAOC (15 %) content than to POC (9 %), but the potential accumulation of GRSP in POC was higher than that in MAOC. The GRSP in the POC pool (less protected) is more sensitive to grassland restoration than in the MAOC pool (more protected). Thermally easily decomposable and refractory organic matter was quantified in POC and MAOC. Thermal stability of MAOC was higher than POC, and GRSP contribute to increase in SOC thermal stability. The GRSP content and thermal stability of POC pool gradually decreased with grassland restoration, reflecting production of more organic matter available for microorganisms and with fast turnover. In conclusion, we must account for the role of GRSP in maintaining SOC thermal stability, and the potential for GRSP sequestration during grassland restoration.

Ecosystem carbon accumulation of Sonneratia apetala mangroves along an afforestation chronology in Bangladesh

Coastal plantation ecosystems play a vital role in the protection of coastal regions, biodiversity conservation, and the provision of valuable ecosystem services. These ecosystems have been recognized for their capacity to sequester carbon, making them instrumental in mitigating global warming. In this study, we assessed ecosystem carbon (EC) density levels in Sonneratia apetala planted coastal ecosystems in the Char Kukri-Mukri and Montaz mangrove reserves in the south-central Bangladesh. Using 48 representative plots from four stand ages (8–32 years), carbon density changes in trees and soil (0–15 and 15–30 cm) were evaluated. Results showed significant differences in vegetation carbon (VC) density, soil organic carbon (SOC) concentration, SOC density, and EC density among different stand ages, soil depths and mangroves. The increased EC density in Char Kukri Mukri (12.21 t ha−1 yr−1) and in Char Montaj (12.62 t ha−1 yr−1) with advancing stand ages (year-8 to year-32) provides empirical evidence of the effectiveness of afforestation in enhancing EC density in S. apetala planted mangroves. Regardless of stand age, the higher SOC density found in the upper soil layer (51 t ha−1 in year-32 stand) compared to the lower layer (38 t ha−1 in year-32 stand) in both mangroves highlights that the majority of soil carbon is concentrated in the top 15 cm of the forest floor. Within the 0–30 cm soil layer, SOC density demonstrated an increasing trend, with rates of 1.30 t ha−1 yr−1 in Char Montaj, and 1.33 t ha−1 yr−1 in Char Kukri Mukri mangroves between year-8 and year-32 stands. This study provides valuable insights for policymakers, land managers, and conservation practitioners, emphasizing the significance of coastal plantation ecosystems in carbon sequestration and the need for informed management strategies to optimize their climate mitigation potential.

Enhancing soil organic carbon prediction of LUCAS soil database using deep learning and deep feature selection

The main terrestrial carbon (C) fraction is soil organic carbon (SOC), which has a considerable effect on climate change and greenhouse gas emissions through the absorption and sequestration of carbon dioxide (CO2). This has made SOC assessment very important from both economic and environmental viewpoints. The growing count of soil spectral libraries (SSLs) from regional to global scales has brought a tremendous opportunity for the quantification of SOC through developing spectral-based prediction models. Hence, there is a need to take advantage of big data analytics for spectral data processing. The unique ability of deep learning (DL) techniques to leverage important features of high-dimensional large-scale SSLs has made them top-demanding for more sophisticated modeling. The core objective of the present study was to assess the ability of two different DL algorithms, i.e., one-dimensional convolutional neural network (1DCNN) and fully connected neural network (FCNN) coupled with stacked autoencoder (SAE) feature extraction for SOC prediction based on the data from the land use/cover area frame statistical survey (LUCAS) database. SAE extracted the high-level deep features from the visible–near-infrared–shortwave infrared (Vis–NIR–SWIR) spectra of 11441 soil samples, which were then considered as inputs to the 1DCNN and FCNN models for predicting the SOC content. Both SAE-DL feature-selected models yielded higher accuracy than those the DL developed on the entire spectra and a random forest (RF) model was constructed for comparison. The best prediction was achieved by SAE-1DCNN (R2= 0.78, RMSE = 3.94%, RPD = 4.88, RPIQ = 3.91) followed by 1DCNN (R2= 0.73, RMSE = 5.43%, RPD = 3.67, RPIQ = 2.84) proving the superiority of 1DCNN over FCNN in this study. These results supported the applicability of combined deep features extraction and regression methods for predicting SOC using high dimensional large-scale SSLs.

Drivers of denitrification and nitrification in a dryland agroecosystem: The role of abiotic and biotic factors

Agricultural practices such as tillage and fertilization impact soil nitrogen (N) cycling processes, but how they alter the coupling between the activity, abundance and diversity of N-cycling microbes remains to be understood. Here, we used a fifteen-year trial in a dryland agroecosystem on the Loess Plateau of China (two tillage regimes crossed with six fertilization treatments) to understand how (de)nitrification potentials are determined by soil abiotic conditions and the abundances and compositions of the (de)nitrifier communities. We measured the abundances of bacterial (AOB) and archaeal (AOA) ammonia oxidizers and nirK- and nirS-nitrite reducers, their community compositions, potential nitrification (PNA) and denitrification (PDA), and soil abiotic conditions. PNA and PDA across the 12 treatments were positively correlated to AOB abundance and nirS abundance, respectively. Co-occurrence network analysis revealed the presence of dominant ecological modules of (de)nitrifiers sensitive to agricultural treatments, and more complex network under no-tilled than tilled conditions as well as under multiple fertilizers than unfertilized conditions. Path analysis and random forest analysis both showed that PNA was explained by AOB abundances and the relative abundance of one module of (de)nitrifiers driven by soil ammonium concentration, while PDA was most related to soil organic carbon concentration, pH and to a lesser extent nirS abundance. These findings demonstrate that, in agricultural soils, the potential of denitrification –a facultative activity for denitrifiers– is mainly predicted by abiotic conditions, while the potential of nitrification –an obligate activity for nitrifiers– is determined by biotic variables, here AOB abundances and a particular cluster of microbial populations.

Determination of Organic Carbon Content of the Soils within the Greenhouses Built on Pyroclastic Deposits in Isparta Settlement Area

Soil organic carbon (SOC) is an important indication of soil health and helps to sustain soil fertility. As a result, determining its composition and the factors that influence it is critical for long-term soil nutrient management, especially in controlled conditions such as greenhouses. This study utilizes machine learning to classify SOC content in greenhouses built on pyroclastic deposits in the Isparta region. A dataset of 276 samples and eight variables—clay (%), silt (%), sand (%), soil electrical conductivity (EC), pH, elevation, slope, and aspect—were used to model SOC values. SOC content was classified into five classifications: very low (2.3%). In this study, five machine learning models—Logistic Regression (LR), K-Nearest Neighbors (KNN), Support Vector Machine (SVM), Decision Tree (DT), and Random Forest (RF)—were evaluated using cross-validation to determine their classification accuracy, precision, recall, F-score, and ROC area. Random Forest (RF) and Decision Tree (DT) outperformed the other models, with RF achieving the highest overall accuracy (76.4%), precision (77.3%), and AUC (0.904), followed by DT at 75.4% and AUC of 0.874. This study shows the practicality of machine learning models in categorizing SOC content, highlighting their importance for long-term soil health and fertility control in greenhouse conditions. To improve model efficacy, future studies should include more auxiliary variables, such as soil physical and chemical qualities and lithological data, as well as a wider range of soil types.

Prediction of soil organic carbon and total nitrogen affected by mine using Vis-NIR spectroscopy coupled with machine learning algorithms in calcareous soils.

The utilization of visible-near infrared (Vis-NIR) spectroscopy presents a nondestructive, fast, reliable and cost-effective approach to predicting total nitrogen (TN) and organic carbon (OC) levels. This study employed a combination of Vis-NIR spectroscopy, partial least-squares regression (PLSR), and support vector machine (SVM) models to investigate the effects of mining on TN and OC stocks in both the topsoil (0-10 cm) and subsoil (10-40 cm). 105 soil samples were collected from agricultural areas near an iron mine, polluted, moderately-polluted, and non-polluted sites. Results indicated that soils at the non-polluted site had the highest of soil OC stocks (7.5 kg m-2) and total nitrogen (2.5 kg m-2), followed by the moderately-polluted site. Furthermore, it was observed that soils from the polluted site displayed the highest spectral reflectance. The spectral bands in the range of 500-700 nm showed the strongest correlation with soil organic carbon content. Notably, the SVM method utilizing Vis-NIR spectroscopy provided superior predictions for both subsoil and topsoil organic carbon and total nitrogen compared to the PLSR methods. Additionally, SVM demonstrated better performance in predicting topsoil soil organic carbon (R2 = 0.87, RMSE = 0.13%, and RPD = 2.8) and total nitrogen (R2 = 0.91, RMSE = 0.13%, and RPD = 2.4) compared to the subsoil, owing to the larger OM content in the topsoils.

Evaluating Wheat Cultivation Potential in Ethiopia Under the Current and Future Climate Change Scenarios

Land suitability analyses are crucial for identifying sustainable areas for agricultural crops and developing appropriate land use strategies. Thus, the present study aims to analyze the current and future land suitability for wheat (Triticum aestivum L.) cultivation in Ethiopia. Twelve variables including soil properties, climate variables, and topographic characteristics were used in the evaluation of land suitability. Statistical methods such as Rotated Empirical Orthogonal Functions (REOF), Coefficient of Variation (CV), correlation, and parametric and non-parametric trend analyses were used to analyze the spatiotemporal variability in current and future climate data and identified significant patterns of variability. For future projections of land suitability and climate, this study employed climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) framework, downscaled using regional climate model version 4.7 (RegCM4.7) under two different Shared Socioeconomic Pathway (SSP) climate scenarios: SSP1 (a lower emission scenario) and SSP5 (a higher emission scenario). Under the current condition, during March, April, and May (MAM), 53.4% of the country was suitable for wheat cultivation while 44.4% was not suitable. In 2050, non-suitable areas for wheat cultivation are expected to increase by 1% and 6.9% during MAM under SSP1 and SSP5 climate scenarios, respectively. Our findings highlight that areas currently suitable for wheat may face challenges in the future due to altered temperature and precipitation patterns, potentially leading to shifts in suitable areas or reduced productivity. This study also found that the suitability of land for wheat cultivation was determined by rainfall amount, temperature, soil type, soil pH, soil organic carbon content, soil nitrogen content, and elevation. This research underscores the critical importance of integrating spatiotemporal climate variability with future projections to comprehensively assess wheat suitability. By elucidating the implications of climate change on wheat cultivation, this study lays the groundwork for developing effective adaptation strategies and actionable recommendations to enhance management practices. The findings support the county’s commitment to refining agricultural land use strategies, increasing wheat production through suitability predictions, and advancing self-sufficiency in wheat production. Additionally, these insights can empower Ethiopia’s agricultural extension services to guide farmers in cultivating wheat in areas identified as highly and moderately suitable, thereby bolstering production in a changing climate.

Variation in microbial communities and network ecological clusters driven by soil organic carbon in an inshore saline soil amended with hydrochar in Yellow River Delta, China.

Char materials (e.g., hydrochar) can enhance carbon sequestration, improve soil quality and modulate soil microbial communities to recuperate soil health. However, little is known about the soil organic carbon (SOC) content, as well as the microbial communities and co-occurrence networks in response to hydrochar amendment in an inshore saline soil. Here, the effect of Sesbania cannabina (a halophyte) straw derived hydrochar (SHC) amendment on SOC and labile organic carbon (LOC) fractions and the potential associations among SOC content change, soil C-cycling enzyme activities and microbial communities were illustrated using a pot experiment. SHC effectively improved the contents of SOC and LOC, particularly particulate organic carbon (POC), and stimulated the activities of C-cycling enzymes. Furthermore, SHC induced shift in microbial community compositions and co-occurrence networks, result in decrease in relative abundance of Actinobacteriota and its corresponding ecological cluster, which may favor SOC accumulation. Functional annotation of prokaryotic taxa (FAPROTAX) analysis also revealed a decrease in microbial ecological function related to carbon degradation. These findings provided a deeper insight about the hydrochar-induced SOC enhancement and suggested an efficient approach to improve C sequestration and improve soil health in the coastal salt-affected soil.

Micro-CT Analysis of Pore Structure in Upland Red Soil Under Different Long-Term Fertilization Regimes

This study hypothesized that long-term fertilization alters the pore structure and aggregate stability in upland red soil. A long-term fertilization experiment in Qiyang, Hunan, was conducted with three treatments: no fertilization (CK), nitrogen–phosphorus–potassium fertilization (NPK), and nitrogen–phosphorus–potassium combined with pig manure (NPKOM). X-ray computed tomography (CT) scanning technology was used to assess three-dimensional pore structures at both the soil column (50 mm diameter and 50 mm height) and aggregate scales (diameter 3–5 mm), alongside the evaluation of the soil’s physical and chemical properties. Results showed that the soil organic carbon content (SOC) increased by 44.8% in NPK and 112.5% in NPKOM compared to CK. NPKOM improved the aggregate stability by 51.6%, whereas NPK had no significant effect. At the soil column scale, NPK increased the total porosity by 13.7% but reduced larger pores (>0.06 mm), whereas NPKOM decreased the total porosity by 7.8% and increased larger pores. At the aggregate scale, NPKOM increased the porosity for pores >0.098 mm by 7.6 times compared to CK and 9.5 times compared to NPK. In conclusion, long-term NPKOM significantly enhances the SOC and aggregate stability and promotes larger pore formation, unlike NPK, which mainly increases SOC but does not improve the soil structure.

Long-term garlic‒maize rotation maintains the stable garlic rhizosphere microecology.

Crop rotation is a sophisticated agricultural practice that can modify the demographic structure and abundance of microorganisms in the soil, stimulate the growth and proliferation of beneficial microorganisms, and inhibit the development of harmful microorganisms. The stability of the rhizosphere microbiome is crucial for maintaining both soil ecosystem vitality and crop prosperity. However, the effects of extended garlic‒maize rotation on the physicochemical characteristics of garlic rhizosphere soil and the stability of its microbiome remain unclear. To investigate this phenomenon, soil samples from the garlic rhizosphere were collected across four different lengths of rotation in a garlic-maize rotation. There were notable positive associations between the total nitrogen and total phosphorus contents in the soil and the duration of rotation. Prolonged rotation could increase the maintenance of microbiome α diversity. The number of years of rotation and the soil organic carbon (SOC) content emerged as principal determinants impacting the evolution of the bacterial community structure, with the SOC content playing a pivotal role in sculpting the species diversity within the garlic rhizosphere bacterial community. Additionally, SOC remains predominant in shaping the root-associated bacterial community's β-nearest taxon index. However, these factors do not have a notable effect on the fungal community inhabiting the garlic rhizosphere. In comparison with monoculture, rotation can amplify the interconnectivity and intricacy of microbial ecological networks. Long-term rotation can further maintain the stability of both microbial ecological networks and interactions between bacterial and fungal communities. It can enlist a plethora of beneficial Bacillus species microorganisms within the garlic rhizosphere to form a biological barricade that aids in safeguarding garlic against encroachment by the pathogenic fungus Fusarium oxysporum, consequently diminishing disease incidence. This study provides a theoretical foundation for the sustainable development of garlic through long-term crop rotation with maize. Our research results indicate that long-term garlic‒maize rotation maintains stable garlic rhizosphere microecology. Our study provides compelling evidence for the role of long-term crop rotation in maintaining microbiota and community stability, emphasizing the importance of cultivating specific beneficial microorganisms to enhance rotation strategies for garlic farming, thereby promoting sustainability in agriculture.

Characteristics of soil organic carbon fractions and influencing factors in different understory mosses in karst urban parks.

The impact of different vegetation types on soil organic carbon (SOC) is a key focus in global warming research. Bryophytes, commonly found in karst urban forests, significantly contribute to carbon accumulation in surface soil. However, the changes in soil organic carbon fractions under moss and the influencing factors remain unclear. To address this knowledge gap, the study examined the organic carbon content, soil physicochemical properties, and associated environmental factors in both moss-covered soil and bare soil under six different forest species within an urban park. The results showed that the SOC contents under moss cover in evergreen coniferous forest (127.28g/kg), bamboo forest (144.70g/kg), deciduous broad-leaved forest (87.63g/kg), and evergreen shrub (109.28g/kg) were significantly higher compared to bare soil. Moss cover also had a significant impact on soil readily oxidizable carbon (ROC), particulate organic carbon (POC), mineral-associated organic carbon (MOC), and heavy fraction organic carbon (HFOC) (P < 0.01). The soil under moss had a higher content of stable organic carbon fraction, which is conducive to the stability of the soil organic carbon pool. The interaction between moss cover and stand type had the most significant effect on soil organic carbon, especially in bamboo forests. Canopy density, moss biomass, and soil moisture were the main environmental factors affecting the content of soil organic carbon and its fractions, while soil organic carbon content was mainly affected by soil nitrogen and phosphorus. This study establishes a theoretical framework for investigating the carbon cycle in karst urban underforest ecosystems, offering a scientific basis for the management and preservation of urban green space ecosystems. Future studies should include bryophytes in the assessment of dynamic factors affecting the soil carbon pool under forest cover and further explore the function and ecological significance of bryophytes in understory ecosystems.

Edge Influence in a Semi‐Deciduous Tropical Forest: An Investigation of Soil Organic Carbon Fractions

ABSTRACTRecent studies have proven the sensitivity of soil organic carbon (SOC) in responding to variations imposed by tropical forest fragmentation, which may reflect changes in both its quantity and quality. Despite this, studies evaluating soil carbon fractions as an edge effect indicator are still non‐existent. We developed this work asking: How do the oxidizable fractions of soil organic carbon (OFSOC) respond to the edge effect in fragments of semi‐deciduous seasonal forest? Is this response influenced by the size of the forest fragment? The study was conducted in Vitória da Conquista, Bahia, Brazil, in three forest fragments with different sizes. Thus, three sampling sections were defined in each fragment: edge (0–10 m), transition (40–50 m), and interior. Soil samples were collected at a depth of 0–10 cm. The SOC was divided into three fractions (LC—labile carbon, MLC—moderately labile carbon, and LLC—low labile carbon), adopting the chemical method based on oxidation degrees. Reductions in the SOC (28.2%), LC (17.4%), and MLC content (66.7%) were observed at the edge in the small fragment. There was a reduction of SOC (21.3%) and LLC (39.0%) at the edge in the medium fragment, while MLC showed an increase at the edge (70.4%). The OFSOC were able to respond to the changes imposed by the edge effect, with emphasis on the LC and MLC fractions in smaller fragments. The forest fragment size influenced the level of changes caused by the edge effect in OFSOC, showing greater susceptibility in smaller fragments.

Plants and microorganisms both contribute to soil organic matter formation through mineral interactions: Evidence from a subtropical forest succession

Understanding the formation and stabilization of soil organic carbon (SOC) is essential for predicting SOC dynamics. Traditionally, it was believed that SOC accumulates primarily through the selective retention of recalcitrant plant lignin components. However, an emerging hypothesis suggests that microbial necromass adsorbed onto mineral-associated soil fractions play a more significant role in promoting SOC formation. In this study, we tested the above hypothesis by investigating SOC content, particulate fraction (LF + POC) vs. mineral-associated fraction (MAOC), along with microbial necromass (amino sugars as biomarker) and plant lignin component (lignin phenols as biomarker) in the topsoil (0–20 cm) and subsoil (20–40 cm) across three successional stages: early coniferous forest, middle mixed forest and climax broadleaved forest in southern China. Results showed that SOC content increased with forest succession, accompanied by increasing contributions of MAOC in both soil layers. Interestingly, the contribution of microbial necromass to SOC increased throughout the succession only in the subsoil, whereas in the topsoil, it increased from the early to the middle stage, then slightly decreased at the climax stage. Additionally, the contributions of lignin phenols or LF + POC to SOC decreased in both soil layers with forest succession. A partial least squares path model further revealed that MAOC played a dominate role in governing SOC accumulation, driven by active mineral content combined with plant-derived dissolved organic matter in the topsoil and microbial necromass in the subsoil. Collectively, our findings suggest that plants and microorganisms contribute to SOC formation through interactions with minerals, unveiling an intricate interactive mechanism of plant–microbe-mineral continuum in SOC stabilization.

Microbial necromass in soil profiles increases less efficiently than root biomass in long-term fenced grassland: Effects of microbial nitrogen limitation and soil depth

Grassland fencing is acknowledged as a crucial initiative to enhance biodiversity and to increase soil organic carbon (SOC) content in ecologically fragile regions or barren systems. Theoretical perspectives propose that fencing induced an increase in root biomass, and its penetration into the soil profile introduced organic matter that facilitated SOC formation through microbial necromass and root residues. It is hypothesized that long-term grassland fencing increases root biomass, thereby enhancing SOC formation within the soil profile through microbial residues in badland ecosystems. To test this hypothesis, we selected grasslands subjected to varying durations of fencing post-grazing (i.e., 10, 15, 20, 30, and 40 y). Our investigation aimed to clarify microbial necromass dynamics in 0–100 cm soil profiles after fencing and to identify the influencing factors. Long-term grassland fencing (i.e., >30 y) increased root biomass by 160 %, SOC by 69 %, and necromass by 41 % compared to grazed grassland within the 0–40 cm horizon; in contrast, increased root biomass by 870 %, SOC by 111 %, and necromass by 46 % in the 40–100 cm horizon. Necromass in deep soil (40–100 cm) accounted for about 50 % of total residues in the 0–100 cm profile. Increased root and living microbial biomass stimulated the necromass accumulation, with a more pronounced increase in fungal residues compared with bacterial residues. Nonetheless, microbial nutrient limitation increases C or N-acquisition enzyme coefficients, which subsequently reduced fungal and bacterial residues and stimulated their recycling. Despite substantial increases in root biomass within the soil profile after fencing, limitation of microbial N and depth reduced the effectiveness of enhancing SOC and necromass. In conclusion, although microbial residues were the important source of SOC in grasslands of the Loess Plateau, microbial N limitation impeded necromass accumulation, and the interplay of root biomass, soil depth, and nutrient limitation regulated the dynamics of necromass following grassland fencing.

Influence of Different Sources and Levels of Phosphorus on Nutrient Use Efficiency (NUE) and Properties of Low Calcareous Soil

A field experiment was conducted during kharif season of 2023 at Post Graduate Instructional Farm, College of Agriculture, Pune to study the impact of different phosphorus sources and levels on soybean growth and nutrient uptake in low calcareous soil. The experiment was laid out in randomized block design having eight treatments with three replications. The treatments comprised T1 - Absolute control, T2 - RDF (50:75:45 kg ha-1 N: P2O5: K2O), T3 - 50% P2O5 through PROM, T4 - 75% P2O5 through PROM, T5 - 100% P2O5 through PROM, T6 - 100% P2O5 through DAP + FYM @12.5 t ha-1, T7 - 100% P2O5 through SSP + FYM @12.5 t ha-1 and T8 - 100% P2O5 through vermicompost. The soil of experimental site was clay loam in texture. The findings of the present investigation revealed that the higher nutrient use efficiency was registered in treatment 100% P2O5 through SSP + FYM @12.5 t ha-1 (16.25 kg kg-1). The application of 100% P2O5 through PROM recorded higher nutrient use efficiency (13.31 kg kg-1) over RDF (11.52 kg kg-1). In respect of agronomic nutrient use efficiency, 100% P2O5 through SSP + FYM @12.5 t ha-1 registered higher nitrogen (40 kg grain kg nutrient-1), phosphorus (26 kg grain kg nutrient-1) and potassium efficiency (44 kg grain kg nutrient-1) to soybean crop. The agronomic efficiency of nitrogen, phosphorus and potassium was observed higher in treatment 100% P2O5 through PROM over treatment RDF. After harvest of crop the soil pH was remained unaffected while the electrical conductivity of soil was significantly higher in 100 % P2O5 through vermicompost and PROM to soybean crop. The application of 100% P2O5 either through vermicompost or PROM recorded at par organic carbon content in soil (0.66% and 0.64% respectively). The application of 100% P2O5 through PROM significantly reduced calcium carbonate (6.29%) in soil. The 100% P2O5 through SSP + FYM @12.5 t ha-1 showed higher available nitrogen in soil (297.33 kg ha-1) while the application of 100% P2O5 through DAP + FYM @12.5 t ha-1 exhibited higher level of available phosphorus and potassium content in soil (41.33 and 745.33 kg ha-1, respectively). Further, the application of 100% P2O5 through vermicompost was also significantly superior in available micronutrients like iron (5.7 mg kg-1), manganese (9.9 mg kg-1), zinc (4.6 mg kg-1) and copper (10.4 mg kg-1). The application of 100% P2O5 through PROM registered significantly higher available nitrogen (287.33 kg ha-1), available phosphorus (37.33 kg ha-1), available potassium (737.67 kg ha-1), available micronutrients viz. iron (5.4 mg kg-1), manganese (9.2 mg kg-1), zinc (4.4 mg kg-1) and copper (10.4 mg kg-1) over recommended dose of fertilizers. In general, the integration of organic fertilizers, FYM, PROM and vermicompost, with chemical fertilizers can significantly enhance nutrient use efficiency, soil nutrient content, improve soil health and increase soybean yield in low calcareous soils.

Litter and Root Removal Modulates Soil Organic Carbon and Labile Carbon Dynamics in Larch Plantation Ecosystems

Plant detritus plays a crucial role in regulating belowground biogeochemical processes in forest ecosystems, particularly influencing labile carbon (C) dynamics and overall soil C storage. However, the specific mechanisms by which litter and roots affect soil organic carbon (SOC) and its components in plantations remain insufficiently understood. To investigate this, we conducted a detritus input and removal treatment (DIRT) experiment in a Larix principis-rupprechtii Mayr plantation in the Taiyue Mountains, China, in July 2014. The experiment comprised three treatments: root and litter retention (CK), litter removal (LR), and root and litter removal (RLR). Soil samples were collected from depths of 0–10 cm and 10–20 cm during June, August, and October 2015 to evaluate changes in soil pH, water content (SW), SOC, dissolved organic carbon (DOC), readily oxidizable organic carbon (ROC), and microbial biomass carbon (MBC). The removal of litter and roots significantly increased soil pH (p &lt; 0.05), with pH values being 8.84% and 8.55% higher in the LR and RLR treatments, respectively, compared to CK treatment. SOC levels were significantly reduced by 26.10% and 12.47% in the LR and RLR treatments, respectively (p &lt; 0.05). Similarly, DOC and MBC concentrations decreased following litter and root removal, with DOC content in August being 2.5 times lower than in June. Across all treatments and sampling seasons, SOC content was consistently higher in the 0–10 cm depth, exhibiting increases of 35.15% to 39.44% compared to the 10–20 cm depth (p &lt; 0.001). Significant negative correlations were observed between SOC and the ratios of ROC/SOC, pH, DOC/SOC, and MBC/SOC (R = −0.54 to −0.37; p &lt; 0.05). Path analysis indicated that soil pH had a significant direct negative effect on SOC (p &lt; 0.05), with a standardized path coefficient (β) of −0.36, while ROC had a significant direct positive effect on SOC (β = 0.66, p &lt; 0.05). Additionally, pH indirectly affected SOC by significantly influencing ROC (β = −0.69), thereby impacting SOC indirectly. Random forest analysis also confirmed that the ROC/SOC ratio plays a critical role in SOC regulation. This study reveals the complex interactions between litter and root removal and soil C dynamics in larch plantations, identifying soil pH and ROC as crucial regulator of SOC content. However, the short-term duration and focus on shallow soil depths limit our understanding of long-term impacts and deeper soil C storage. Future research should explore these aspects and consider varying climate conditions to enhance the applicability of our findings. These insights provide a scientific foundation for developing effective forest management strategies and forecasting changes in soil C storage in the context of climate change.

The influence of tree species on small scale spatial soil properties and microbial activities in a mixed bamboo and broad-leaved forest

Soil enzyme activity and microbial biomass play a critical role in myriad ecological processes. Bamboo and broad-leaved mixed forests have received widespread attention as important forestry models for ecological restoration and sustainable development; however, our understanding the influences of broad-leaved tree species in mixed bamboo forests on soil properties and microbial activity remains unclear. Here we sampled twenty-seven spatially interspersed stands of bamboo-Castanopsis chinensis Hance mixed forest (CCB), bamboo-Alniphyllum fortune (Hemsl.) Makino mixed forest (AFB), and bamboo-Choerospondias axillaris mixed forest (CAB), with different mixing ratios (0–10 %, 10–20 %, 20–40 % canopy proportions) in subtropical China, to examine the effects of tree species and mixed ratio on soil nutrients, microbial biomass, and enzyme activity. We found that the different forests exhibited variations in soil nutrient levels. CAB forests exhibit notably higher mean C, N, and P contents than AFB and CCB, particularly at a 10–20 % mixing ratio where SOC concentration reached 46.50 g/kg. CAB forests demonstrated significantly higher activities of invertase (mean 701.83U/g), urease (8393.44U/g), and catalase (501.73U/g) compared to AFB and CCB forests, with peak enzyme activities observed at a 10–20 % mixing ratio. Soil microbial biomass C and N were notably greater in CAB and CCB forests than in AFB forests. CAB forests also exhibited the highest soil microbial biomass P (mean 48.68 mg/kg), which rose consistently with an increased mixing ratio. Multiple factor analysis revealed that the enzyme activities were significantly correlated with the annual growth of fine roots in the forest and were positively correlated with resident C, total N, total P, C: N, and C: P. Overall, the results provide insights into the importance of tree species and crown size in bamboo and broadleaved tree mixed forest in soil features and the microbial activity while providing management guidance for the selection of mixed tree species for sustainable management of bamboo forest soil microenvironment.

Comparative assessment of SoilGrids system with regional soil data for advancing ecosystem reporting in Bulgaria

The aim of this study is to test the suitability of the SoilGrids system for ecosystem reporting, research and monitoring. The study is conducted in the Rila Mountains in Bulgaria, an area characterised by diverse ecological factors. We propose a methodological approach to compare SoilGrids predictions with independent point observations, addressing issues of inconsistency across survey layers when combining data from different sources. The comparative analysis is discussed in respect to point data, soil type, altitude and climate. The results show that the SoilGrids represents the main soil parameters well in terms of their dynamics over the altitudinal range. There is a good agreement between the observed and predicted values for the averages of the parameters - bulk density, coarse fraction, soil organic carbon (SOC) content and SOC stock. The average measured SOC stock (0-30 cm) is 58.54 t/ha, while the average predicted SOC stock (0-30 cm) is 55.38 t/ha. However, the study also showed that the predicted values for nitrogen content are almost two times higher than the observed figures and the pH values from the SoilGrids are less acidic than those measured in the field.

Iron-bound organic carbon declined after estuarine wetland reclamation into paddy fields

Iron-bound organic carbon (Fe-OC) is a main pathway for the long-term maintenance of soil organic carbon (SOC), but research on its mechanism is still relatively weak. We investigated the coupling relationships among iron (Fe), carbon (C) and Fe-reducing bacteria (FeRB) in the soil of a reclaimed paddy field in comparison with natural Phragmites australis wetland in the Minjiang River estuary in southeastern China. The results showed that conversion of P. australis wetland to paddy cultivation changed the soil redox process. After reclamation, soil Fe(II), Fe(III), HCl-Fet, free iron oxide (Fed) and amorphous iron (Feo) contents and Fe(III)/Fe(II) decreased significantly (p < 0.05), while the content of complexed iron (Fep) increased. Nonmetric multidimensional scaling analysis (NMDS) demonstrated variability in FeRB across soil types (r = 0.900, p = 0.001). The lower Fe-OC concentration in soil after wetland reclamation may be the result of Fe reduction by dissimilatory FeRB (e.g., Bacillus, Anaeromyxobacter). On average, both Fe-OC and SOC contents decreased significantly (p < 0.05), while the contribution of Fe-OC to total SOC (fFe-OC) increased significantly (p < 0.05), after conversion to paddy cultivation. Structural equation modeling (SEM) showed that SOC, dissolved organic C, and Fe-OC were affected by FeRB and the speciation of Fe. In addition, Fe (III) concentration affected SOC concentration (r = 0.60, p < 0.05) and DOC concentration (r = 0.58, p < 0.05), and Fed affected DOC concentration (r = 0.69, p < 0.05). We conclude that after rice field reclamation in estuarine wetlands, Fe-reducing bacteria can mediate iron-bonded organic C decoupling, affecting SOC stabilization.

The Fungal Community Structure Regulates Elevational Variations in Soil Organic Carbon Fractions in a Wugong Mountain Meadow

Soil organic carbon (SOC) fractions are vital intrinsic indicators of SOC stability, and soil fungi are the key drivers of soil carbon cycling. However, variations in SOC fractions along an elevational gradient in mountain meadows and the role of the fungal community in regulating these variations are largely unknown, especially in subtropical areas. In this study, an elevation gradient experiment (with experimental sites at 1500, 1700, and 1900 m) was set up in a Miscanthus sinensis community in a meadow on Wugong Mountain, Southeast China, to clarify the effects of elevation on soil fungal community composition, microbial residue carbon, and SOC fractions. The results showed that the contribution of soil microbial residue carbon to SOC was only 16.1%, and the contribution of soil fungal residue carbon to SOC (15.3%) was far greater than that of bacterial residue carbon (0.3%). An increase in elevation changed the fungal community structure and diversity, especially in the topsoil (0–20 cm depth) compared with that in the subsoil (20–40 cm depth), but did not affect fungal residue carbon in the two soil layers. When separating SOC into the fractions mineral-associated organic carbon (MAOC) and particulate organic carbon (POC), we found that the contribution of MAOC (66.6%) to SOC was significantly higher than that of POC (20.6%). Although an increased elevation did not affect the SOC concentration, it significantly changed the SOC fractions in the topsoil and subsoil. The soil POC concentration and its contribution to SOC increased with an increasing elevation, whereas soil MAOC showed the opposite response. The elevational variations in SOC fractions and the POC/MAOC ratio were co-regulated by the fungal community structure and total nitrogen. Our results suggested that SOC stabilization in mountain meadows decreases with an increasing elevation and is driven by the fungal community structure, providing scientific guidance for SOC sequestration and stability in mountain meadows in subtropical areas.