Soil Organic Carbon Determination Research Articles

Determination of soil organic carbon by conventional and spectral methods, including assessment of the use of biostimulants, N-fertilisers, and economic benefits

Soil organic carbon (SOC) is a very important indicator of soil quality, where even small changes can have large effects on the global carbon cycle, climate change, soil fertility and plant growth conditions. The aims of this study were to investigate changes in soil SOC using two types of biostimulants, to confirm the quality of different SOC determination methods, and to estimate fertiliser requirements and winter crop income and costs. Two methods were used to determine the concentration of SOC: the first was conventional sampling of two soil layers and laboratory analysis. The second method measured SOC using a mounted proximal soil sensor with an integrated visible and near-infrared (VIS-NIR) spectroscopic system. Experimental studies were carried out in three scenarios, of which SC1 used a biostimulant consisting of two components: one for soil (humus) and one for plants (leaf-special), SC2 used a biostimulant consisting of many bacterial species and SC3 was a control without biostimulant. The results of the 3-year experimental studies showed that the use of VIS-NIR spectroscopy in the field allows the prediction of soil SOC concentrations with sufficient accuracy. The coefficient of determination R2 ranged from 0.819 to 0.959 compared to the conventional laboratory SOC test. In the SC1 and SC2 scenarios with biostimulants, R2 was higher than in the SC3 control. The use of biostimulants significantly increased the yield of winter wheat and winter oilseed rape and reduced the need for nitrogen fertiliser per tonne of grain yield for both winter wheat (23.0–37.3 %) and winter oilseed rape (6.3–32.1 %). The economic analysis showed that the application of biostimulants increased the relative profit in all years from EUR 54 ha−1 (for winter oilseed rape) to EUR 143 ha−1 (for winter wheat) compared to the control scenario.

Forest stand and soil types determine soil organic carbon storage in the Middle Atlas region of Morocco using machine learning models

Forest stand and soil types determine soil organic carbon storage in the Middle Atlas region of Morocco using machine learning models

SOIL ORGANIC CARBON CONTENT ACROSS VARIOUS GEOMORPHIC UNITS IN MANGROVE FOREST: A CASE OF DUBLAR CHAR, SUNDARBANS

Lying at the tidally active region of the Bengal Delta, the Sundarbans act as a terrestrial carbon sink and play a crucial role in climate change mitigation. However, this forest is underrepresented in term of soil organic carbon research. The purpose of this study was to investigate the Soil Organic Carbon dynamics across various geomorphic units within a small area of mangrove forest ecosystem of Dublar char of Sundarbans. Salinity and pH trends were also examined across geomorphic units to understand their interplay with soil organic carbon dynamics. Soil samples from 25 locations across various geomorphic units were collected and analyzed to determine soil organic carbon, salinity and pH levels. The Walkley-Black wet oxidation method was employed to determine the organic carbon content. Results indicate varying degree of organic carbon concentration across geomorphic units with Highland areas having high level of soil organic carbon concentrations with average concentration level of 2.05%, followed by Creeks with 1.55%. Salinity levels also varied across different geomorphic units with values ranging from 4.8 ppt to 12.7 ppt, with creek area having high level of salinity due to its close proximity to seawater. Fringe forest areas had the highest pH levels with average value of 7.4 and the lowest average pH value (6.86) was observed in Beach areas of the study area. The study holds immense significance in understanding the organic carbon dynamics of mangrove ecosystem in the Sundarbans, providing essential insights for long term climate resilient land management and biodiversity conservation efforts.

Conservative farming systems and their effects on soil organic carbon and structural quality

Pesticides-free integrated farming systems emerge as a viable option to promote environmental protection, due to the diversification of the agroecosystem, making the soil productive and resilient. However, there is a lack of information about the influence of integration farming systems on the relationship between soil physical quality and organic matter. The objective was to determine soil organic carbon fractions, and soil structural attributes in conservative single and integrated farming systems, to verify the potential of these farming systems to increase soil organic carbon stocks and improve soil structural quality. The experiment was carried out at a pesticide-free agricultural systems. Soil samples were collected in three layers (0–0.05, 0.05–0.10, and 0.10–0.20 m) of five farming systems (Cropland - C, Livestock - L, Forestry - F, Livestock-Forestry – LF, and Crop-Livestock-Forestry - CLF) in the randomized block design. Sampling was carried out in two transects of 25 m each, collecting five samples per transect, totaling 10 samples per layer. The following soil attributes were determined: soil organic carbon (SOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC), soil organic carbon stocks (Cst), visual evaluation of soil structure (VESS), tensile strength of aggregates (TS), soil friability, weighted mean diameter (WMD), geometric mean diameter (GMD) and the aggregate stability index (ASI). At 0–0.05 m, the SOC content was up to 12% higher in the Cropland system compared to other farming systems, while at 0.05–0.10 m and 0.10–0.20 m of depth, the difference was higher, around 27% between Cropland and other farming systems. For the VESS, Cropland had the lowest score (1.35), while the higher scores were in the Forestry, and CLF systems (2.25, 2.24, respectively). Both soil organic carbon and soil physical quality were greater in all farming systems. The particulate organic carbon and weighted mean diameter were efficiently to promote changes in soil carbon inputs and structural changes. The single and integrated farming systems promoted an increase in soil organic carbon, by a rate of 3.02, 1.81, 2.17, 1.78, and 2.01 Mg ha−1 yr−1, respectively for Cropland, Livestock, Forestry, LF, and CLF. The pesticide-free farming systems, under conservative practices, were very promising in showing the increase of SOC, POC and MAOC, supporting the soil physical quality, and cooperating with the soil health.

Comparison of Determination Methods Total Organic Carbon in The Soil

Objective: This research aimed to compare two methods for determining soil organic carbon, in two soils with different textures. Method: Soil samples were collected in three locations (Dourados-MS, Chapadão do Sul-MS and Cassilândia-MS), with different textures (clayey and sandy), at a depth of 0-20 cm, to determine organic carbon . The results were subjected to statistical analysis, using the SAS version 6 software and the means were compared using the t test (p < 0.05). In the correlation study, linear regression analyzes were performed. Result and conclusion: There was variation in the soil organic carbon content (SOC) between the methods studied for both soils. Measuring soil samples by volume (spectrophotometer) modifies the results, regardless of the soil texture. There is greater variation between the data obtained in soils with a higher COS content than in soils where the COS content is lower. Furthermore, the results indicate the need for new studies in which soils from agricultural areas and under native vegetation are selected by soil classes, textures and types of land use. Research implications: Research related to comparison studies of SOC determination methods is of paramount importance, as there is a lack of information regarding the definition and recommendation of the most appropriate method. Originality/value: With this study it is possible to disseminate to the scientific community methods for determining SOC that make it possible at the same time to reduce the use of chemical reagents, without this negatively interfering with the quality of soil organic carbon determination.

Organic carbon sequestration by Fe oxides in aggregates in a Pinus massoniana conifer-broadleaf mixed forest

Stand conversion and Fe/Al oxides are potential variables that collectively determine soil organic carbon (SOC) sequestration. However, the mechanism of SOC sequestration provided by Fe/Al oxides in the conversion of Pinus massoniana plantations (PMs) into mixed conifer-broadleaf forests remains unknown. The increase in SOC content (4.08–151.80%) in PM-converted mixed forest was related to the significant increase in the content of all OC fractions. Light fraction (LF) contents were generally higher in larger aggregates and mixed forest aggregates, reflecting the greater plant C input and the driving effect of soil aggregation in mixed conifer-broadleaf forests. This plant C input to the soil as the core of aggregate formation provides physical protection from particulate organic carbon (POC), but this physical protection was achieved by the greater free Fe oxides (FeD) and amorphous Fe oxides (FeO) content in the mixed forests acting as an aggregate stabiliser. Potential processes are driven by pH-driven FeD and FeO binding to silt to improve aggregate stability and pore occlusion, which promotes physical protection of coarse intra-aggregate particulate organic carbon (c-iPOC). Moreover, this process reduces macroaggregate turnover (c-iPOC/f-iPOC ratio), allowing the transfer of c-iPOC in macroaggregates to microaggregate-associated fine intra-aggregate particulate organic carbon (f-iPOC). The higher mineral-associated organic carbon (MOC) content of conifer-broadleaf mixed forest soils was mainly derived from silt+clay and controlled by chemisorption of Fe/Al oxides (especially complex Fe oxides, FeP), but Fe/Al oxides do not provide physical protection for MOC. In addition, LF, c-iPOC and f-iPOC were significantly positively correlated with SOC content, reflecting the sensitivity of aggregate structure development and stabilization in predicting SOC sequestration, but these OC fractions will shift more towards MOC as conifer-broadleaf mixed forests develop. Overall, Fe oxides provide SOC accumulation and long-term stability by OC fractions associated with physical protection and chemisorption in the conversion of PM into mixed conifer-broadleaf forests.

Comparison of Determination Methods Total Organic Carbon in The Soil

Objective: This research aimed to compare two methods for determining soil organic carbon, in two soils with different textures. Method: Soil samples were collected in three locations (Dourados-MS, Chapadão do Sul-MS and Cassilândia-MS), with different textures (clayey and sandy), at a depth of 0-20 cm, to determine organic carbon . The results were subjected to statistical analysis, using the SAS version 6 software and the means were compared using the t test (p < 0.05). In the correlation study, linear regression analyzes were performed. Result and conclusion: There was variation in the soil organic carbon content (SOC) between the methods studied for both soils. Measuring soil samples by volume (spectrophotometer) modifies the results, regardless of the soil texture. There is greater variation between the data obtained in soils with a higher COS content than in soils where the COS content is lower. Furthermore, the results indicate the need for new studies in which soils from agricultural areas and under native vegetation are selected by soil classes, textures and types of land use. Research implications: Research related to comparison studies of SOC determination methods is of paramount importance, as there is a lack of information regarding the definition and recommendation of the most appropriate method. Originality/value: With this study it is possible to disseminate to the scientific community methods for determining SOC that make it possible at the same time to reduce the use of chemical reagents, without this negatively interfering with the quality of soil organic carbon determination.

Determination of soil organic carbon content of agricultural soils for proper soil management in Matazu and Musawa, Katsina State, Nigeria

Soil organic carbon is a significant parameter for estimating the global carbon cycle, which makes great sense in soil management and future climate scenario prediction. This work uses 30 heterogeneous soil samples from agricultural and non-agricultural farmlands and soil erosion areas in Matazu and Musawa LGAs to determine soil organic carbon content at the field level in Matazu and Musawa Local Government Areas, Katsina State, Nigeria. Soil samples were meticulously collected from the 0-10cm depth using a hand auger. These samples were obtained from three distinct clusters: agricultural and non-agricultural farmlands and soil erosion areas. The selection of sample locations considered the varied soil types, historical land use, and management practices. Ten soil samples were randomly gathered within each cluster, ensuring a representative and diverse set of samples for analysis. The Warlkey and Black and Hydrometer methods were used to determine the soils' organic carbon contents and particle size distribution, respectively. The data obtained were analyzed using SPSS 23 software. Two-sample t-tests and analysis of variance (ANOVA) were carried out. The soil organic carbon contents of the studied area were 0.29 ± 0.16 g/kg (0.16 – 0.34 g/kg) and 0.28 ± 0.14 g/kg (0.14 - 0.36 g/kg) for Matazu and Musawa, respectively. The study concludes that the organic carbon content helps improve sustainable agricultural productivity due to proper and efficient land use management practices.

Iron-removal learning machine for multicolor determination of soil organic carbon

Iron-removal learning machine for multicolor determination of soil organic carbon

Soil Quality Indicators under Different Smallholder Managed Cropping and Landuse Practices in Abuja, Nigeria

There are limited reports about the impacts of smallholder-managed cropping and land-use practices (CLUPs) on soil quality, especially in developing countries. This study investigates the impact of six different Cropping Land Use Practices (CLUPs) on soil quality parameters in Abuja, Nigeria, focusing on sesame mono-cropping (SM), guinea corn mono-cropping (GCM), yam mono-cropping (YM), maize + yam mixed cropping (MYM), maize mono-cropping (MM), and natural forest (NF). The objectives are to determine Soil Organic Carbon (SOC), Total Nitrogen (TN), and pH values in the six CLUPs and assess differences under various CLUPs and soil depths. The study conducted in the University of Abuja Permanent Site, covers 11,000 hectares and analyzes soil samples from three replicate plots per CLUP, considering topsoil (0-15cm) and subsoil (20-30cm). The results indicate slightly acidic soils with low SOC and TN contents. Significant differences in SOC, TN, and C/N ratio are observed among cropping systems, with mixed cropping (MYM) promoting higher SOC. The C/N ratio is consistently low across CLUPs, indicating accelerated decomposition. While intra-plot soil heterogeneity is low, significant declines in soil quality indicators are noted under cropping systems compared to the natural forest. The study recommends site-specific, sustainable land management practices tailored to each cropping system. Encouraging organic matter additions, such as using animal and farmyard manure, is proposed to enhance soil fertility and reverse degradation trends. The findings contribute to understanding how diverse cropping practices impact soil quality, providing valuable insights for sustainable land management in the Abuja region.

Modeling Land Use and Management Practices Impacts on Soil Organic Carbon Loss in an Agricultural Watershed in the Mid-Atlantic Region

Measuring organic carbon (OC) losses from soils presents a challenge because of the intricate interplay of human-induced and biophysical processes. This study employs SWAT-C to simulate particulate OC (POC) and dissolved OC (DOC) losses from the Upper Maurice Watershed in the Mid-Atlantic Region. Simulation outcomes reveal that surface runoff was the primary contributor to the total DOC load (65%), followed by lateral flow (30%), and then groundwater (5%). Meanwhile, POC load was linked to erosion processes induced by surface runoff. Our findings indicate that agricultural land-use types exhibited the highest annual average DOC and POC loads. Forests and grasslands displayed intermediate loads, while barren land had the lowest load. Concerning seasonal fluctuations, agricultural land-use types exhibited distinct DOC and POC load patterns when compared to forest and grassland types, indicating the dominant role of management practices in determining soil OC (SOC) losses. Additional modeling of management practices’ impact on SOC budgets indicates maximal SOC sequestration with full irrigation, no-till (NT), and full fertilization. In contrast, the largest SOC depletion arises from combining conservation tillage (CT) and no fertilization, irrespective of irrigation. This study shows that SWAT-C can be used to simulate land use and management impacts on SOC dynamics.

Estimativa do estoque de carbono no solo via espectroscopia de reflectância difusa (vis/nir) sensoriamento remoto aéreo e orbital

ABSTRACT Current procedures for determining soil organic carbon (SOC) content are costly, time-consuming, and generate polluting chemical waste. Therefore, developing new protocols using aerial and orbital remote sensing and diffuse reflectance spectroscopy (DRS) for digitally mapping the stock of soil organic carbon (CS) is essential for promoting actions of research and monitoring SOC in Brazilian soils. Given this, three areas of commercial plots in the region of the Middle North of Mato Grosso were studied, where sampling was carried out for the determination of SOC in the layer from 0 to 30 cm, evaluated by the dry combustion method and estimated through DRS in the visible to near -infrared region - Vis-NIR-SWIR/350-2500 nm). To obtain the images by aerial remote sensing, the Carcará II® Unmanned Aerial Vehicle was used, with a MicaSense® multispectral camera (RGB + NIR + RedEdge) attached. The orbital sensors used were the Sentinel 2® and Planet® satellites. This study showed that soil carbon stock values could be predicted using different modeling approaches based on field and laboratory spectral measurements. Predictive models to estimate SOC can be established using remote and near sensing, thus allowing a better understanding of spatial patterns of SOC in crop fields.

Effect of Fire-deposited Charcoal on Soil Organic Carbon Pools and Associated Enzyme Activities in a Recently Harvested Pinus massoniana Plantation Subjected to Broadcast Burning

Charcoal is a carbonaceous particulate matter with a highly aromatic structure produced by incomplete combustion, and it can cause persistent long-term effects on soil ecological functions. In this study, we determined soil organic carbon pools and associated enzyme activities following five years of different charcoal treatments[charcoal removal (B0), charcoal retained in situ (B1), and the addition of charcoal removed from B0(B2)] and the unburnt control (UB) in a recently harvested Pinus massoniana plantation subjected to broadcast burning. The results showed that dissolved organic carbon (DOC), microbial biomass carbon (MBC), coarse and fine particulate organic carbon (CPOC and FPOC), and recalcitrant carbon (RC) contents were significantly lower in B1 than those in UB soil (P<0.05). The MBC and FPOC contents of B2 soil were comparable to those of UB soil, which were significantly higher than those of B0 soil (P<0.001). There was no difference in MBC/TC between the B2 and UB soils, whereas MBC/TC was significantly lower in B0 than in UB soil (P<0.05). β-glucosidase and peroxidase activities of B0, B1, and B2 soils were significantly lower than that of UB soil (P<0.01), and polyphenol oxidase activity was significantly lower in B0 and B2 soils than in UB soil (P<0.01). No significant difference in soil TC, DOC, readily oxidized carbon (ROC), CPOC, and RC content as well as associated enzyme activities was observed among the charcoal treatments (P>0.05). Redundancy analysis showed that sucrose and polyphenol oxidase were the key drivers influencing soil organic carbon fractions, accounting for 16.3% and 12.7% of the total variance, respectively. Overall, our findings indicated that fire-deposited charcoal played a positive role in enhancing soil microbial biomass carbon recovery, soil organic carbon accumulation, and stability, highlighting the importance of charcoal in the management of subtropical plantations in the future.

Effects of Forest Management Approach on Carbon Stock and Plant Diversity: A Case Study from Karnali Province, Nepal

The mitigation of global warming and conservation of biodiversity are two significant environmental challenges today. Estimating and comparing forest carbon stock and plant diversity under different management approaches provide insight into the choice of management approaches for carbon and plant diversity management. We investigated the variation in carbon stock and diversity of plant species in two forest managements under different approaches: the Kakrebihar protection forest (PF) and Sano Surkhet community forest (CF) in Karnali Province, Surkhet, Nepal. In total, 63 sample plots (30 plots in PF and 33 plots in CF) were laid out systematically across the forests. Dendrometric measurements were carried out for trees, poles, and saplings, and representative leaf litter and herb samples were collected. Soil samples were taken at 10 cm, 20 cm, and 30 cm depths using a soil auger. The existing tree volume equations of tree species of interest were used to estimate tree volume, and species-specific wood density and conversion factors were used to obtain total biomass and carbon content. Soil samples were analyzed using the Walkley-Black method to determine soil organic carbon. PF had higher carbon stock, plant species richness, and abundance at the landscape level than CF; however, the scenario differed at the plot level. At the plot level, PF had significantly higher total carbon stock and biomass carbon stock than CF. However, PF and CF were statistically indistinguishable in term of soil carbon stock. At the plot level, PF and CF were statistically indistinguishable regarding richness, Simpson diversity, and Shannon diversity, but PF had significantly higher plant abundance than CF. In conclusion, the value of PF for carbon stock and plant diversity surpassed those of CF. This study suggests that PF might be a better strategy to enhance carbon stock in forests and maintain habitat for various plant species.

Spontaneous urban vegetation as an indicator of soil functionality and ecosystem services

AbstractQuestionsOur study focused on spontaneous vegetation in urban greenspaces in a Mediterranean city with the aim of relating plant community properties with ecological services along soil disturbance gradients. We asked which plant communities have the greatest plant biodiversity and soil carbon storage and the best‐performing nutrient cycles and water regulation.LocationMadrid City (Central Spain).MethodsWe studied four types of plant communities following soil disturbance gradients: vegetation on trampled soils, roadside vegetation, annual grasslands and perennial forbs. Regarding vegetation, we studied plant composition and productivity, plant diversity, plant growth forms and functional groups. Regarding soils, we determined soil organic carbon (TOC), available nutrients, the activity of seven enzymes relating to the main macronutrient cycles, and physical properties such as bulk density (BD) and soil water‐holding capacity (WHC). We used one‐way ANOVA to determine the influence of the plant community type on both soil and vegetation variables. Canonical correspondence analysis was performed to interpret the relationships between plant species assemblages with environmental gradients.ResultsPerennial forbs showed greater biomass and developed on soils with the greatest TOC and available phosphorus. Annual grasslands displayed the highest plant diversity. Roadside vegetation developed on soils with higher phenoloxidase activity when compared to vegetation on trampled soils and annual grasslands. Vegetation on trampled soils developed on soils with lower WHC, lower beta‐glucosidase, arylamidase and phosphatase activities and higher BD when compared to perennial forbs. Plant community distribution followed gradients most significantly associated with soil organic matter content, soil compaction and nutrient cycling performance.ConclusionsWe conclude that plant communities are good indicators of ecosystem function and services which are unevenly distributed throughout urban habitats. The management in Mediterranean unmaintained urban greenspaces should be aimed at avoiding soil compaction to promote biodiversity, carbon storage and water regulation.

Introducing the 3R Program in Teaching Laboratories to Promote Sustainability Science through Miniaturization Studies on the Spectrophotometric Determination of Organic Carbon and Phosphorus in Soil

The general assembly meeting of the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 2015 adopted the 17 Sustainable Development Goals (SDGs) aimed at achieving a better and more sustainable world by 2030. Incorporating sustainable values through a series of pedagogical strategies into university curricula to help future professionals enhance their understanding of sustainability and how they relate to it is one of the crucial steps to help achieve Sustainable Development Goals (SDGs) through education. Inspired by the principles of Green Analytical Chemistry (GAC) and the “3R” (reduce, recycle, and reuse) approach, a laboratory experiment has been developed to illustrate the basic concept of reaction miniaturization step by step. This article presents a novel experimental design consisting of 7 sessions, which includes all elements of the 3R approach. Herein, students miniaturize the conventional calorimetric determination of soil organic carbon (OC) and soil available phosphorus (P) utilizing recycled microtips and microcentrifuge tubes. Students apply their critical thinking abilities to compute and compare the waste generated, the analysis cost, and the time required for each test using the conventional approach (CA) and miniature approach (MA). They further assess the greenness of both approaches using the open-source Analytical GREEnness (AGREE) software. While students carry out these experiments, they acquire laboratory skills and reinforce their understanding of sustainability, Beer–Lambert law, how OC relates to the bioavailability of anionic nutrients such as PO43– phosphate species, and how such relationships can statistically vary based on the methods applied. Learning outcomes were assessed to evaluate the experimental design.

Integrated aggregate turnover and soil organic carbon sequestration using rare earth oxides and 13C isotope as dual tracers

The formation, stabilization and breakdown processes of soil aggregates determine soil organic carbon (SOC) sequestration, in turn, soil aggregate dynamics are mediated by SOC changes. However, the interactions between them remain elusive. Herein, three types of 13C-labelled residues were added to two textured soils. Rare earth oxides (REOs) and 13C isotope were used as dual tracers to simultaneously track aggregate transfer pathways and SOC sequestration during a 56-day incubation period. Residue-derived CO2 followed the sequence of Vetch > Maize > Decomposed maize during the first two weeks. Residue-derived CO2 was significantly negatively correlated with the aggregate turnover time in both investigated soils (P < 0.01), indicating that aggregate turnover was a controlling factor of residue decomposition in addition to its inherent features. Generally, residue addition decreased the aggregate turnover time in the sequence of Vetch < Maize < Decomposed maize. In Red clay soil, macroaggregates attained a higher turnover rate than that of microaggregates, while a similar change pattern was not observed in Sandstone soil with residue application. Aggregates turnover occurred faster in Sandstone soil than in Red clay soil under a given residue application. The aggregate turnover time was significantly reciprocally correlated with the residue-derived C sequestration rate (P < 0.01), suggesting that aggregate turnover was the key factor in C sequestration. A C flow conceptual model was proposed, residue-derived C firstly accumulated in macroaggregates in the formation process, and then relocated from macroaggregates to microaggregates with the breakdown processes at the mid-to-late stage. This study highlights the importance of aggregate turnover in SOC sequestration and demonstrates that these interactions are further affected by residue features and soil texture.

Soil nutrients shape the composition and function of fungal communities in abandoned ancient rice terraces

In recent decades, terraces abandonment has been prevalent in the hilly areas of China. Soil fungi play an important role in clarifying soil ecosystematic feedback after ancient rice terraces abandonment, but how their community composition and function shift remains unclear. Soil profiles of 0–120 cm were excavated in ancient rice terraces, dry land, and forest land (formed from ancient rice terraces abandonment), respectively. The 13C NMR and high-throughput sequencing were used to determine soil organic carbon chemical groups and fungal community, respectively, and FUNGuild was used to predict functional groups. The results showed that the soil fungal community changed from Ascomycota to Basidiomycota after ancient rice terraces abandonment. The trophic modes of dry land and forest land were transformed into pathotrophic fungi and symbiotrophic fungi, respectively. The number of nodes and edges of fungal co-occurrence networks increased by 83.8% and 644.1% in dry land, and 81.3% and 431.2% in forest land, respectively. Moreover, soil nutrients (especially DOC, TN, and TP) can more affected the variation of fungal community composition and function than soil organic carbon chemical groups. These findings indicate that soil fungal community shifts in different directions in response to ancient rice terraces abandonment, which is related to the adaptive strategies for environmental changes and may be more conducive to the acquisition and turnover of soil nutrients.

Fertilization treatments affect soil CO2 emission through regulating soil bacterial community composition in the semiarid Loess Plateau

A growing body of literature have emphasized the effects of fertilization regimes on soil respiration and microbial community in the semiarid region, however, fertilization treatment effects on the soil CO2 emission, soil bacterial community, and their relationships from long-term experiments is lacking. In the present study, we investigated the effects of long-term fertilization regimes on soil bacterial community and thereafter on soil CO2 emission. A 9-year field experiment was conducted with five treatments, including no fertilizer (NA) and four fertilization treatments (inorganic fertilizer (CF), inorganic plus organic fertilizer (SC), organic fertilizer (SM), and maize straw (MS)) with equal N input as N 200 kg hm–2. The results indicated that CO2 emission was significantly increased under fertilization treatments compared to NA treatment. The bacterial abundance was higher under MS treatment than under NA treatment, while the Chao1 richness showed opposite trend. MS treatment significantly change soil bacterial community composition compared to NA treatment, the phyla (Alphaproteobacteria and Gammaproteobacteria) and potential keystone taxa (Nitrosomonadaceae and Beijerinckiaceae) were higher, while the Acidobacteriota was lower under MS treatment than under NA treatment. CO2 emission was positively correlated with the abundance of Alphaproteobacteria, Gammaproteobacteria, and keystone taxa, negatively correlated with these of Acidobacteriota. Random forest modeling and structural equation modeling determined soil organic carbon, total nitrogen, and the composition and network module III of the bacterial community are the main factors contribute to CO2 emission. In conclusion, our results suggest that the increased CO2 emission was affected by the varied of soil bacterial community composition derived from fertilization treatments, which was related to Alphaproteobacteria, Gammaproteobacteria, Acidobacteriota, and potential keystone taxa (Nitrosomonadaceae and Beijerinckiaceae), and highlight that the ecological importance of the bacterial community in mediating carbon cycling in the semiarid Loess Plateau.

The impact of the long-term application of mineral nitrogen and sewage sludge fertilizers on the quality of soil organic matter

BackgroundSoil fertility is substantially influenced by soil organic matter quality and quantity. Much attention has also been given to glomalin content as one of the qualitative parameters of soil fertility. Glomalin content is considered an indicator of soil fertility due to its positive correlation with soil organic carbon.AimThis study aim to (i) determine the influence of different fertilization systems on maize yield and soil organic matter quality parameters, (ii) ensure that changes in total glomalin content (TG) and easily extractable glomalin (EEG) content are sensitive enough to reflect changes in the SOM quality resulting from long-term fertilization, and (iii) determine whether both forms of glomalin must be determined or if the easily extractable glomalin (EEG) content is sufficient, even for a fertile chernozem.Materials and methodsLong-term field experiments with silage maize monocultures were used to study relationships under different rates of mineral nitrogen and sewage sludge fertilization. The trials comprised 5 treatments: (i) no fertilization control (Con), (ii) and (iii) two different calcium ammonium nitrate rates (N120 and N240 at doses of 120 and 240 kg N ha−1 year−1, respectively), and iv) and v) two different sewage sludge rates (S120 and S240 corresponding to mineral N doses). Topsoil (0–30 cm) analysis was performed 28 years after the onset of the experiment to determine soil organic carbon, the fractions of humic substances, potentially mineralizable carbon and dissolved organic carbon, the potential wettability index, soil aggregate stability, EEG, and total glomalin (TG).ResultsThe control treatment, which did not include fertilization, showed significantly lower average yields (9.76 t DM ha−1 year−1) than the fertilization treatments (on average 12.3 DM ha−1 year−1). Significant differences in yields were not found between the fertilization treatments. A positive correlation between glomalin (EEG, TG) content and soil organic matter carbon content was observed. A periodic application of sewage sludge increased the content of glomalin. However, the highest quality of SOM was found in the control treatment (nonfertilized). This treatment had the highest values for the humic/fulvic acid ratio and the highest contents of humic acids and potentially mineralizable carbon. Furthermore, the Con treatment showed the highest soil aggregate stability and potential wettability index. Mineral N fertilization significantly reduced soil aggregate stability values.ConclusionsThe unfertilized control showed the highest SOM quality but the lowest yields. The data on glomalin content can be used to study soil organic matter quality. Because the EEG extraction method is easy to apply, uses lower quantities of chemicals and consumes less time, it presents a better option than TG extraction. The sensitivity of the methods for SOM quality determination decreases with increasing SOM content.Graphical