Changes In Organic Carbon Research Articles

Balancing grain yield and environmental performance by optimizing planting patterns of rice-wheat cropping systems

To alleviate the adverse consequences of conventional planting of the rice–wheat cropping system and achieve long-term sustainability, a 3-cycle experiment (2019–2022) was conducted to investigate the effects of six planting patterns (PPs) on the grain yield and environmental performance. PP1 entailed annual rotary tillage (RT) without straw returning but without fertilization for rice and wheat seasons. PP2 was the same as PP1 but involved fertilization. PP3 was the same as PP2 but included straw return. PP4 entailed rice planting the same as in PP3, but with innovative zero-tillage (ZT) seeding technology for wheat planting. PP5 entailed wheat planting the same as in PP4, but with rice planting involving direct paddy seeding under RT. PP6 entailed wheat planting the same as in PP4, but rice planting followed dry direct seeding under ZT. The results showed that the average total yield under PP2, PP3, PP4, PP5, and PP6 was 64 %, 54 %, 69 %, 51 %, and 54 % higher than that under PP1, respectively. The highest methane and nitrous oxide emissions occurred under PP4 and PP6, respectively. When soil organic carbon changes were included in the calculations, the carbon footprint per unit area (CFA) was sharply reduced under PP4 and PP6, and the highest CFA was achieved under PP1, followed by PP2. Implementing annual RT promoted soil mineral nitrogen accumulation under PP2 and PP3 after wheat harvest, increasing the risk of mineral nitrogen leaching and the nitrogen footprint per unit area than that under the other PPs. PP4 exhibited the highest ammonia volatilization, which was offset by reduced mineral nitrogen leaching. Overall, PP4 exhibited a yearly increase in the comprehensive scores obtained via Z-score analysis and yielded the highest score in the last year due to the highest annual grain yield, steady SOC increase, and lower nitrogen loss.

Continuous crop rotation increases soil organic carbon stocks in river deltas: A 40-year field evidence

River deltas, as important food production centers, support 66 % of the world's population, together with other coastal areas. However, agriculture in river deltas is negatively affected by soil salinization and agricultural intensification. Improving the soil carbon pool is a mutually beneficial solution for maximizing crop production and improving climate resilience to secure food production. In this study, long-term croplands in the Yellow River Delta (YRD), with a wheat-maize (WM) rotation system and a single cotton (SC) cropping system, were selected to explore the changes in soil organic carbon (SOC) stocks and the driving mechanisms at 0–20 cm depth from 1980 to 2020. We found that, over the past 40 years, the SOC stocks in WM and SC croplands had increased by 10.05 Mg C ha−1 and 7.44 Mg C ha−1, respectively. The Random forest model revealed that in the WM croplands, soil N stock and available K were the most important driving factors of SOC stocks, while in SC croplands, soil type and salinity were the most important driving factors of SOC stock dynamics. An increase in soil salinity to 2.0 ‰ caused a 17.5 % loss in SOC stocks in SC croplands. Our results show that, in the long run, croplands with a WM rotation system have stronger carbon sequestration potential. Depending on the planting system, promoting crop carbon input under high soil nutrients and affecting SOC decomposition by soil salinity are two different pathways of SOC sequestration in delta croplands. We propose that nutrient management and organic fertilizer application are crucial for increasing SOC stocks in the WM and SC croplands, respectively. This study confirms that it is of practical significance to take measures to promote soil carbon sequestration at the farmland scale and to provide scientific guidance for the sustainable development of river delta agriculture.

Effects of Straw Returning with Lime on SOC and Carbon Pool Management in Acidic Paddy Soil

Soil acidification and low SOC are the main limiting factors in acidic paddy soils. Straw returning with lime is an effective measure to alleviate soil acidification and improve soil fertility; however, its interaction effects on SOC and carbon pool management are still unclear. To investigate the impact of straw returning with lime on the organic carbon pool of acidic paddy soil, field experiments were conducted on acidic paddy soil in Baiyun District and Huiyang District of Guangdong Province. The changes in soil total organic carbon (TOC), water-soluble organic carbon (DOC), active organic carbon (LOC), particulate organic carbon (POC), microbial biomass carbon (MBC), carbon pool index (CPI), stable organic carbon (IOC), carbon pool activity (L), carbon pool activity index (CPAI), and carbon pool management index (CPMI) were analyzed under three treatments (CK, conventional fertilization; RS, straw returning+conventional fertilization; RS+L straw returning with lime+conventional fertilization). The results demonstrated that compared with that in CK, the TOC, LOC, POC, and MBC in the RS+L treatment were significantly increased by 10.24%-17.79%, 34.49%-44.37%, 19.27%-23.59%, and 33.36%-43.26%, respectively (P<0.05). Compared with that in CK, the RS+L treatment significantly increased the DOC content during the early growth stage (15-45 days after transplanting) of rice (P<0.05) but had no significant influence on the DOC content during the late growth stage of rice. Compared with that in RS, the TOC, LOC, POC, and MBC in the RS+L treatment were increased by 2.15%-6.95%, 1.17%-17.90%, 4.27%-8.65%, and 12.99%-14.53%, respectively. Compared with that in CK, the RS+L treatment significantly increased IOC and CPI by 8.32%-15.57% and 14.00%-20.00%, respectively (P<0.05). Compared with that in the CK treatment, the RS treatment significantly increased CPI by 14.00%-18.00% (P<0.05). No significant differences in L, CPAI, or CPMI were detected among the different treatments. The soil pH in the RS+L treatment was significantly higher than that in the CK treatment (P<0.05). No significant differences in rice yield were detected among the different treatments. Principal component analysis demonstrated that rice yield was primarily correlated with DOC, LOC, CPAI, and CPMI but its contribution to SOC and carbon pool management index was low. Principal component analysis also indicated that straw returning with lime could improve soil pH and nutrient contents of acidic paddy soil, driving the formation and accumulation of organic carbon fraction such as MBC and POC, thus boosting the increase in SOC. In conclusion, straw returning with lime is beneficial to the accumulation of MBC, POC, LOC, and IOC in acidic paddy soil to improve the content and stability of soil total organic carbon, which is an effective way to improve the carbon sequestration of acidic paddy soil.

Changes in soil organic carbon and its response to environmental factors in the Yarlung Tsangpo River basin

The distribution of terrestrial soil organic carbon changes with climate and substrate conditions. This study investigated the spatial and temporal distribution of soil organic carbon and its influencing elements in the Yarlung Tsangpo River Basin using meteorological, subsurface, and remotely sensed data over the past 39 years, combined with random forests and geodetector. The results of the study showed that soil organic carbon has been increasing in the study area over the past 39 years, and this change has been concentrated in the central part of the watershed. Among the environmental factors, precipitation, temperature, and leaf area index were the main contributors to the soil organic carbon changes, and the effects of the three factors were more significant at higher altitudes, with a 33 % increase in the significance level. Notably, the interactions among the factors exceeded their individual effects, and the combination of climate and leaf area index showed a significant two-factor enhancement effect, with q-value enhancements generally ranging from 0.15 to 0.3. The two-factor enhancement effect was more pronounced below 3000 m above sea level, where the topography of the study area concentrates soil organic carbon in the gently sloping areas of the catchment.

Soil carbon storage capacity of drylands under altered fire regimes

The determinants of fire-driven changes in soil organic carbon (SOC) across broad environmental gradients remains unclear, especially in global drylands. Here we combined datasets and field sampling of fire-manipulation experiments to evaluate where and why fire changes SOC and compared our statistical model to simulations from ecosystem models. Drier ecosystems experienced larger relative changes in SOC than humid ecosystems—in some cases exceeding losses from plant biomass pools—primarily explained by high fire-driven declines in tree biomass inputs in dry ecosystems. Many ecosystem models underestimated the SOC changes in drier ecosystems. Upscaling our statistical model predicted that soils in savannah–grassland regions may have gained 0.64 PgC due to net-declines in burned area over the past approximately two decades. Consequently, ongoing declines in fire frequencies have probably created an extensive carbon sink in the soils of global drylands that may have been underestimated by ecosystem models.

Changes in soil organic carbon and nitrogen stocks in organic farming practice and abandoned tea plantation

BackgroundThe restoration of conventional tea plantations and the adoption of organic farming practices could impact soil organic carbon (SOC) and nitrogen (N) stocks. This study investigated the soil properties, SOC and N contents and stocks, and their vertical distributions of a secondary forest restored from an abandoned conventional tea plantation and a converted organic tea plantation. An adjacent conventional tea plantation employing similar intermediate farming served as a comparison.ResultsWithin a 50-cm depth, the secondary forest exhibited a higher SOC stock of 115.53 ± 7.23 Mg C ha− 1 compared to 92.1 ± 8.54 Mg C ha− 1 for the conventional tea plantation. No significant differences in N stocks were seen between the two land uses. Significantly high SOC and N contents and stocks were found in the 0–10 cm layer of the secondary forest compared to the conventional tea plantation. No significant disparities in SOC and N stocks were found between the conventional and organic tea plantations within the 50 cm depth (92.1 ± 8.54 Mg C ha− 1 and 10.06 ± 1.01 Mg N ha− 1 vs. 97.47 ± 1.53 Mg C ha− 1 and 9.70 ± 0.10 Mg N ha− 1). However, higher levels of SOC and N contents and stocks were observed at a depth of 10 cm in the conventional tea plantation and below 10 cm in the organic tea plantation.ConclusionsThe C and N inputs derived from high litter production at the top soil strongly contributed to higher SOC and N contents and stocks in the secondary forest. The application of soybean amendments in the conventional tea plantation and the longer tea plantation age of the organic tea plantation influenced their distribution of SOC and N contents and stocks, respectively. Reverting a conventional tea plantation into a secondary forest contributed to C recovery and reaccumulation. The conventional tea plantation, employing similar intermediate farming practices, increased SOC and N contents and stocks in the surface soil compared to the organic tea plantation. However, adopting organic farming did not significantly increase SOC stocks compared to the conventional tea plantation.

Spatiotemporal variability of organic carbon in streams and rivers of the Northern Hemisphere cryosphere

The earth's cryosphere is the outpost of climatic warming, which leads to rapid changes of organic carbon (OC) transport from terrestrial to aquatic ecosystems. OC in the cryosphere rivers plays vital roles in the carbon cycle and river ecosystem health. Yet, we still lack a comprehensive assessment of the spatiotemporal patterns of riverine OC across the Northern Hemisphere cryosphere. Here, we compiled OC concentration, radiocarbon (14C), and the specific ultraviolet absorbance (SUVA) of dissolved OC (DOC) at 254 nm data from 1007 unique sites, extracted from 138 published literature between 1972 and 2022. Overall, the average DOC and particulate OC (POC) concentrations are 6.34 and 2.61 mg C L−1, respectively, with the average age of DOC and POC being ~1100 and ~4300 years BP, respectively, indicating the release of aged carbon pools. Seasonal variations in DOC and POC concentrations, Δ14C-DOC and SUVA254 were observed, with distinct spatial variations closely linked to specific watershed characteristics. We found permafrost-impacted watersheds displayed significantly higher DOC concentrations, younger OC ages but lower POC concentrations compared to glacier-impacted watersheds. Meanwhile, in boreal forest watersheds, DOC is the most concentrated and youngest in varied ecoregions. Additionally, in permafrost regions characterized by higher permafrost extent, ground ice content, or lowlands with thick overburden cover, riverine DOC is more concentrated and aromatic. We estimated that specific OC fluxes in glacier rivers are higher than that in permafrost rivers (4.77 and 1.86 g C m−2 yr−1, respectively). Our results highlight the complex and variable spatiotemporal patterns of riverine OC in the northern cryosphere, which are essential for assessing the impact of OC on the global carbon cycle and climate warming.

Adaptations of soil microbes to stoichiometric imbalances in regulating their carbon use efficiency under a range of different grazing intensities

Grazing has a profound impact on the availability of soil resources like carbon (C), nitrogen (N), and phosphorus (P) in grasslands. These changes can potentially make it difficult to meet microbial elemental demands, thus affecting microbial C use efficiency (CUE) and soil C dynamics. Nevertheless, it remains unclear how soil microbes respond to stoichiometric imbalances and their consequent effect on microbial CUE. In this study, we investigated the stoichiometry of soil labile resources, microbial biomass, extracellular enzymes, as well as the microbial community composition and microbial CUE, microbial respiration, microbial quotient (qMB), and soil organic carbon (SOC) changes, at sites with four grazing intensities (no grazing, light, medium, and heavy grazing) in a temperate steppe of northern China. Grazing led to decreased stoichiometric imbalances between soil labile resources and microbial biomass, thereby exacerbating limitations of available C on soil microbes. To alleviate this limitation of C, microbes raised the microbial threshold elemental ratios and microbial biomass, and increased fungi dominance rather than increased activities of C-, N-, and P- acquiring enzymes due to increased microbial own growth. Microbes also improved microbial CUE, qMB, and microbial respiration while decreasing SOC under increasing grazing intensity. These integrated adaptations denote that grazing can reduce SOC which is closely affected by soil microbial C utilization induced by resource change conditions despite the increased microbial biomass contribution to SOC. These findings illustrate the regulation of stoichiometric imbalances in soil C dynamics driven by microbes under grazing and improve our understanding of how stoichiometric changes influences soil C flows in semi-arid grassland.

Synergistic effect on soil health from combined application of biogas slurry and biochar

Biogas slurry and biochar, as typical by-products and derivatives of organic waste, have been applied in agricultural production to improve the soil carbon (C) pool. However, whether the combined application of biogas slurry and biochar produces synergistic effects on the soil C pool and soil health requires quantitative clarification. In this study, we performed a pot experiment to analyze the changes of soil organic carbon (SOC), potassium permanganate-oxidized carbon (POXC), mineralizable carbon (MC), soil β-glucosidase (S-β-GC), and soil protein (SP) in different treatments at the flowering and fruit-setting stages, and full fruit stage of tomato by establishing two base fertilizer modes (base fertilizer N and base biogas slurry N), three topdressing modes (topdressing chemical fertilizer N, topdressing 50% biogas slurry N + 50% chemical fertilizer N, and topdressing biogas slurry N), and two biochar levels (no addition and 3% biochar addition). During the full fruit period, the SOC content of bottom applications of biogas slurry and topdressings of biogas slurry significantly increased by 9.92–15.52% and 13.02–18.26%, respectively (P < 0.05), when compared to chemical fertilizer bottom applications and topdressings of chemical fertilizer. When compared to non-biochar treatment, the SOC content of the biochar considerably increased by 52.56–58.94% (P < 0.05). Moreover, biogas slurry treatment increased the MC, steady-state C, and C pool index, and decreased the S-β-GC, C pool efficiency, C pool activity, and C pool activity index. Application of biogas slurry initially reduced POXC, SP, the C pool management index, and the soil quality index; nonetheless, these indicators eventually recovered or even exceeded the result of single application chemical fertilizer. Overall, the combined application of biogas slurry and biochar strongly increases the soil C pool, improves soil health, and reduces the short-term negative effects of using only biogas slurry.

Soil organic carbon changes in China's croplands: A newly estimation based on DNDC model

Soil Organic Carbon (SOC) in cropland represents a significant facet of the terrestrial ecosystem's carbon reservoirs, playing a pivotal role in global climate change mitigation efforts. Within the specific context of China, cropland SOC not only extends its implications beyond environmental impact but also serves as a critical factor in ensuring the stability and security of the nation's food supply. However, there is an ongoing argument about the changes in SOC and their spatial and temporal distribution patterns within China's croplands. In this study, we constructed a new county-level DNDC database for 2020, building upon 2003 research that quantified SOC stock in China's cropland using the DNDC model. Our aim was to assess the SOC storage and temporal changes of China's cropland in 2020 using same methodology to enhance estimation accuracy. The simulation results of the validated DNDC model revealed that the average SOC storage of China's croplands (0–30 cm) in 2020 was 6.02 Pg C, with the Northeast region contributing 23 % (1.37 Pg C). The SOC density in China varied from 18.55 to 152.57 t C ha−1, averaging at 49.65 t C ha−1. In 2020, China's cropland transitioned from a net loss of SOC in 2003 to a carbon sink, with cropland SOC density and SOC storage increased by 18.2 % and 21.6 % respectively. Notably, despite experiencing a loss of SOC compared to 2003, the Northeast region had the highest average SOC density in China. This study highlights that despite the increase in SOC density and storage in China's croplands over the last 17 years, there remains substantial potential for carbon sequestration given the current spatial distribution of SOC density's significant heterogeneity within China. The findings of this study offer data support for China's strategy to achieve food security and carbon neutrality.

Improvement of Active Organic Carbon Distribution and Soil Quality with the Combination of Deep Tillage and No-Tillage Straw Returning Mode

During the initial period of straw return, a suitable straw return technology can lay the foundation for long-term soil fertility improvement. This study focused on the issues of backward straw return technology and blind fertilizer application in the southern part of the maize-producing area in the Northeast Plain of China. In this study, two straw return modes (2-year no-tillage straw cover + 1-year deep loosening and burying straw returning mode, NPT; 3-year rotary tillage and burying straw returning mode, RT), with RT mode as a control, were combined with different N fertilizer application rates (0, 192, 240 kg/ha). The changes in soil organic carbon (SOC) and its active components (MBC, DOC, and LOC) in the 0–40 cm soil layer were analyzed, and the carbon stratification rate, carbon pool index (CPI), SOC storages of each component, and maize yield were calculated to evaluate the short-term (3-year) differences in soil organic carbon quantity and quality in order to find suitable straw return methods and nitrogen application rate combinations. The results showed that the NPT mode increased the SOC and MBC content in the 20–30 cm soil layer, with an increase of 16.2% to 37.8% and 23.0% to 50.3%, respectively, compared with the RT mode. Under the NPT mode, the carbon pool stability was higher after nitrogen fertilizer addition, with a CPI value of 10.2% to 37.8% higher in the 20–40 cm soil layer compared with the RT mode. The differences in maize yield were not significant (p &lt; 0.05) between the nitrogen application rates of 192 kg/ha and 240 kg/ha, but the SOC storages did not show significant changes. The MBC storage had the highest value under the nitrogen application rate of 192 kg/ha. Therefore, we thought that, in the early stage of straw return, the organic carbon priming effect caused by increased microbial activity was higher under the nitrogen application rate of 192 kg/ha. Considering the aspects of not affecting maize yield and improving SOC stability, it is recommended to use the NPT mode with the application of a 240 kg/ha nitrogen fertilizer rate for straw return.

Changes in soil organic carbon and nitrogen stocks following revegetation in a semi-arid grassland of North China

Long-term restoration practices have been often reported to enhance soil organic carbon (SOC) and nitrogen (N) stocks in grassland ecosystems. However, there is a limited understanding of how vegetation restoration affects SOC and N stocks at different soil depths over short timescales in semi-arid grassland of North China. To address this problem, we conducted a field study to investigate the effects of plant properties on the SOC and N stock changes during a nine-year period of grassland restoration practices (natural recovery; shallow ploughing; harrowing) in a semi-arid grassland of North China. The results revealed that three restoration practices had a positive contribution to SOC and N stocks following nine years of recovery, however, the rates of SOC and N stock changes under mechanical disturbance were lower across the 0–60 cm soil depth when compared with the natural recovery. The biomass of litter, roots, and dominant plant species were the major factors contributing to SOC and N stock changes. Our findings from the nine-year restoration experiment suggested that short-duration natural recovery is likely to be a beneficial strategy for the restoration of both the plant community and the soil nutrients. Our findings elucidate the regulatory mechanisms of dominant plant species on SOC and N stock changes following revegetation and suggest that the overcompensatory growth of dominant species should be fully considered in grassland restoration.

Temporal and Spatial Changes in Soil Organic Carbon in a Semi-Arid Area of Aohan County, Chifeng City, China

Soil organic carbon (SOC) plays a crucial role in arid zones, while land-use change could lead to changes in the balance of SOC. Therefore, the aim of this study was to determine the impact of land-use change on the temporal and spatial variability in SOC at the county scale. A semi-arid zone (Aohan County, Northeast China) covering a surface of 3800 km2 was selected for this study. SOC data for 65 and 182 soil samples from 1985 and 2021, respectively, were collected for major land-use types (forestland, farmland, grassland, and sandy land) across Aohan County to a depth of 20 cm. The impacts of different land-use types and land-use changes on SOC were evaluated. The results showed that land-use change enhanced the spatial variability in SOC over the last 36 years. The mean SOC in 2021 (7.49 g kg−1) was significantly higher than that in 1985 (6.91 g kg−1). Converting sandy land into grassland and farmland into forest or grassland would lead to significant accumulation of SOC, while the depletion of SOC occurred after grassland afforestation. The balance between aboveground biomass inputs and SOC decomposition was the determining reason that affected the accumulation of SOC. Vegetation restoration due to land-use change could alter both soil texture and the C/N ratio and could have positive effects on ecosystem recovery.

Patterns and driving factors of soil organic carbon sequestration efficiency under various manure regimes across Chinese croplands

The carbon sequestration efficiency of manure (CSE-manure) is critical for the accurate estimation of manuring-induced changes in soil organic carbon (SOC). However, the mechanisms of large-scale spatiotemporal changes in CSE-manure and their crucial drivers are unclear. To investigate these under various manure regimes, we performed field observation and collected relevant data using 1023 fields across China’s main cropland, as well as collected data on high-resolution climate and soil properties. The experimental durations significantly (P < 0.001) affected CSE-manure. The CSE-manure values were 31.4% ± 13.4 (mean ± SD), 19.2% ± 10.3%, and 16.1% ± 9.4 at the experimental durations of < 10, 10–20, and > 20 years, respectively. In addition, the manure sources significantly affected CSE-manure. The CSE-manure values of the manures from horse (27.9% ± 19.0) and sheep (26.9% ± 11.0) and farmyard manure (25.7% ± 14.8) were higher than those of the manures from pig (19.8% ± 15.4), poultry (19.1% ± 10.58), and cattle (23.1% ± 13.1). The CSE-manure values varied as per the region; the values were higher in North China than in South China. Of all the investigated variables, carbon and nitrogen input from manure, soil bulk density, annual average air temperature and precipitation, and initial SOC and soil clay content were the most important drivers of CSE-manure. The results suggested that carbon sequestration potential was higher in the northeast region. The spatiotemporal CSE-manure values under various climate conditions were predicted using trained machine learning models. Simulation results suggested that by 2100, the rate of decrease in CSE-manure will be higher at RCP (Representative Concentration Pathways) 8.5, and climate change will have a great impact on CSE-manure due to high warming effects.

Effects of Hydraulic Erosion on the Spatial Redistribution Characteristics of Soil Aggregates and SOC on Pisha Sandstone Slope

Under the long-term effects of hydraulic erosion, soil particles and nutrients are continuously lost and enriched in the process of runoff and sediment movement, leading to a change in soil organic carbon (SOC) in different spatial positions on the slope, which is closely related to the carbon balance of the ecosystem. Therefore, the changes in slope erosion intensity and the spatial redistribution characteristics of soil aggregates and SOC under water erosion conditions were quantitatively analyzed by combining field runoff plots with three-dimensional (3D) laser scanning technology. The results showed that: (1) After rainfall, the slope erosion intensity successively declined from the upper to the lower parts of the slope, and the content of soil aggregates in each soil layer changed obviously. The loss of 1–2 mm soil aggregates was the largest in the sedimentary area of the 2–4 cm soil layer, at 0.38 g/kg. The concentration of 0.5–1 mm soil aggregates was the largest in the micro-erosion area of the 2–4 cm soil layer, at 0.36 g/kg. (2) After rainfall, the overall SOC on the slope showed a loss state in the 0–2 cm soil layer and an enrichment state in the 2–4 cm soil layer. Among them, the loss of SOC in the medium erosion area of the 0–1 cm soil layer was the largest, and its content decreased by 57.58%. The enrichment in the 2–4 cm soil layer was the maximum in the micro-eroded area, with a content increase of 79.23%. (3) Before and after rainfall, the SOC of each soil layer was positively correlated with small aggregates, and the correlation gradually tended to be negative with the increase in the particle size of soil aggregates, and the SOC showed a negative correlation with large aggregates (&gt;2 mm).

Assessing human impacts on soil organic carbon change in the Lower Namoi Valley, Australia

Assessing human impacts on soil organic carbon change in the Lower Namoi Valley, Australia

Microbial pathways driving stable soil organic carbon change in abandoned Moso bamboo forests in southeast China

Mineral-associated organic carbon (MOC) is a stable component of the soil carbon (C) pool, critical to realize carbon sequestration and coping with climate change. Many Moso bamboo (Phyllostachys edulis) forests in subtropical and tropical areas that used to be intensively managed have been left unmanaged. Still, studies on MOC changes occurring during the transition from intensive management to unmanagement are lacking. Besides, the understanding of the role of microorganisms in MOC accumulation is far from satisfactory. Based on the combination of field investigation and laboratory analysis of 40 Moso bamboo forest sampling plots with different unmanaged chronosequence's in southeast China, we observed the MOC content in Moso bamboo forests left unmanaged for 2–5 years had decreased, whereas that in forests left unmanaged for 11–14 years had increased compared with that in intensively managed forests. Specifically, the MOC contents in forests left unmanaged for 11–14 years were significantly higher than in those under intensive management or unmanaged for 2–5 years. Moreover, we found that microorganisms drove MOC change through two different pathways: (i) more microorganisms led to more soil nutrients, which led to more amino sugars, ultimately resulting in the accumulation of MOC, and (ii) microorganisms promoted the accumulation of MOC by influencing the content of metal oxides (poorly crystalline aluminum oxides and free aluminum oxides). We believe that ignoring the interaction between microorganisms and metal oxides may lead to uncertainty in evaluating the relative contribution of microbial residues to MOC.

Estimation of Carbon Stocks and Carbon Sequestration Rates in Abandoned Agricultural Soils of Northwest Russia

The fallow agricultural soils of Northwest Russia represent an evolutionary model of the development of ecosystem components in time and space with multidirectional dynamics of agrogenic impact during the long history of agricultural land development. There has been both large-scale land development and uncontrolled conversion of arable lands to a fallow state along with their removal in recent times. All this has led to the formation of a chrono-series of different-age soils with varying degrees of exposure of agrogenic factors. This paper presents a current review of the humus state of fallow soils in Northwest Russia, and examines the main factors (self-restoration, humus transformation, acidification) influencing the transformation of the soil cover under the process of post-agrogenesis. Effective farming techniques aimed at fixing carbon in soils as part of increasing the sequestration potential to mitigate the impact of climate change are considered. The ongoing process of the transition of lands into a fallow state could lead to organic carbon losses and changes in the main physical and chemical parameters, which negatively affects the self-restoration of fallow lands. We offer some recommendations for the effective rewetting of fallow lands in Northwest Russia with the purpose of carbon sequestration in the soil cover.

Mung Bean Is Better Than Soybean in the Legume–Wheat Rotation System for Soil Carbon and Nitrogen Sequestration in Calcareous Soils of a Semiarid Region

Small changes in soil aggregates-associated organic carbon and soil nitrogen (N) can induce huge fluctuations in greenhouse gas emissions and soil fertility. However, there is a knowledge gap regarding the responses to long-term continuous rotation systems, especially in N-fixing and non-N-fixing crop wheat in terms of the distribution of soil aggregates and the storage of soil carbon (C) and N in aggregates in the semiarid calcareous soil of Central China. This information is critical for advancing knowledge on C and N sequestration of soil aggregates in rainfed crop rotation systems. Our aim was to determine which legume (soybean (Glycine max)– or mung bean (Vigna radiata)–wheat (Triticum aestivum) rotation practice is more conducive to the formation of good soil structure and C and N fixation. A 10-year field experiment, including a soybean (Glycine max)–winter wheat (Triticum aestivum) rotation (SWR) with yield increments of 2020 compared to 2010 achieving 18.28% (soybean) and 26.73% (wheat), respectively, and a mung bean (Vigna radiata)–winter wheat rotation (MWR) achieving 32.66% (mung bean) and 27.38% (wheat), as well as farmland fallow, was conducted in Henan Province, China. The soil organic carbon (SOC), N content in the soil, and the soil aggregates were investigated. Legume–wheat rotation cropping enhanced the proportion of the &gt;2 mm soil fractions and reduced the &lt;0.053 mm silt + clay in the 0–40 cm soil profile. In the 0–30 cm soil layer, the SWR had a greater increment of the &gt;2 mm aggregate fractions than the MWR. Two legume–winter wheat rotations enhanced the C and N sequestration that varied with soil depths and size fractions of the aggregate. In contrast, the MWR had greater SOC stocks in all fractions of all sizes in the 0–40 cm soil layers. In addition, the greater storage of N in the macro-, micro-, and silt + clay fractions was observed in the 0–30 cm layers; the MWR enhanced the C/N ratios in most of the size aggregates compared with the SWR. The MWR cropping system is more beneficial to the formation of good soil structure and the increasement of C and N reserves in soil. Thus, these findings show that mung bean, in contrast with soybean in the legume–wheat rotation system of a semiarid temperate zone, may offer soil quality improvement.

Long-term Influence of Crop Residue Management and Tillage Practices on Distribution of C and N within Aggregate Size Fractions in Alluvial Soils

Aims: The goal of this experiment is to observe the variations in soil aggregate fractions and the change in percentage of carbon and nitrogen stored in the fractions due to the effect of crop residue management and tillage practices in Rice-Wheat cropping system.&#x0D; Study Design: An experiment was set up in Randomized Block Design with five treatments, i.e, T0-control, T1- zero-tillage+ no residue application, T2- zero-tillage+ residue application, T3- conventional tillage + no residue application, T4- conventional tillage+ residue application.&#x0D; Place and Duration of Study: It was conducted in a long-term experimental plot situated in University Research Farm at Pundibari in Coochbehar district of West Bengal. The data was taken in the 9th and 10th year of the experiment, i.e, 2018 and 2019.&#x0D; Methodology: Samples were collected from three different depths, i.e., 0-5 cm, 5-15 cm and 15-30 cm from four cropping seasons, i.e., wheat 2018, rice 2018, wheat 2019 and rice 2019 and were prepared and analyzed for physico-chemical factors. Dry stable aggregates were obtained by the method of sieving and change of carbon, nitrogen and C/N ratios in various fractions were observed.&#x0D; Results: Mostly for all the soil depths the total organic carbon content was highest for the treatment with zero-tillage and application of residues (T2). Total nitrogen content also followed the similar trend. Whereas in most of the crop seasons, the C/N ratio was observed to be higher in the treatment where conventional tillage was followed along with residue incorporation (T4). Within the short span of two years positive changes in total organic carbon and total nitrogen content was observed for almost all the treatments, across the depths.&#x0D; Conclusion: The optimum percentage of decrease in C/N ratio of the control as well as the treatment with zero-tillage and residue application (T2) in the large aggregate fractions (&lt;2mm) indicates the suitability of the soil for higher productivity.