Higher Soil Organic Carbon Stocks Research Articles

The changes in soil organic carbon stock and quality across a subalpine forest successional series

Soil organic carbon (SOC) affects the function of terrestrial ecosystem and plays a vital role in global carbon cycle. Yet, large uncertainty still existed regarding the changes in SOC stock and quality with forest succession. Here, the stock and quality of SOC at 1 m soil profile were investigated across a subalpine forest series, including shrub, deciduous broad-leaved forest, broadleaf-conifer mixed forest, middle-age coniferous forest and mature coniferous forest, which located at southeast of Tibetan Plateau. The results showed that SOC stock ranged from 9.8 to 29.9 kg·m–2, and exhibited a hump-shaped response pattern across the forest successional series. The highest and lowest SOC stock was observed in the mixed forest and shrub forest, respectively. The SOC stock had no significant relationships with soil temperature and litter stock, but was positively correlated with wood debris stock. Meanwhile, the average percentages of polysaccharides, lignins, aromatics and aliphatics based on FTIR spectroscopy were 79.89%, 0.94%, 18.87% and 0.29%, respectively. Furthermore, the percentage of polysaccharides exhibited an increasing pattern across the forest successional series except for the sudden decreasing in the mixed forest, while the proportions of lignins, aromatics and aliphatics exhibited a decreasing pattern across the forest successional series except for the sudden increasing in the mixed forest. Consequently, the humification indices (HIs) were highest in the mixed forest compared to the other four successional stages, which means that the SOC quality in mixed forest was worse than other successional stages. In addition, The SOC stock, recalcitrant fractions and HIs decreased with increasing soil depth, while the polysaccharides exhibited an increasing pattern. These findings demonstrate that the mixed forest had higher SOC stock and worse SOC quality than other successional stages. The high proportion of SOC stock (66% at depth of 20–100 cm) and better SOC quality (lower HIs) indicate that deep soil have tremendous potential to store SOC and needs more attention under global change.

Exploring the best nutrient management options for improving the maize yield for future climate change scenario with DSSAT crop simulation model in century old Permanent Manurial Experiment

Increasing the C sequestration potential and higher soil organic carbon stocks with the application of organic manures will reflect in the improvement of crop productivity. Long-term monitoring approach is essential to evaluate these impacts, especially given the escalating effects of climate change on agriculture. Recognizing this, a 112-year-long Permanent Manurial Experiment (PME) at Tamil Nadu Agricultural University, Coimbatore, India, investigates the influence of application of organic manures. Utilizing the DSSAT crop simulation model, the study assessed the impact of organic manure, specifically NPK + FYM (Farm Yard Manure), on maize yield over 25 years on a sandy-loam Alfisol. Data collected from the field experiment including crop growth parameters, management options, weather, and soil data were used for simulations. Results showed a 93.8% agreement between simulated and observed yields, endorsing NPK + FYM treatment with a 20% increase in grain yield by 2032 compared to using 100% NPK alone. Furthermore, the study explored future climate change scenarios’ impact on maize yield. It highlighted that NPK + FYM consistently outperformed other treatments, emphasizing its efficacy in increasing the yields under changing climatic conditions. This approach emerges as promising for enhancing carbon sequestration, elevating soil organic carbon stocks, and significantly improving crop productivity. In conclusion, adopting the NPK + FYM treatment is recommended to achieve optimal maize yield outcomes, surpassing the effects of using NPK or FYM independently. This research signifies the potential of combining organic manures with synthetic fertilizers in sustainable agriculture amid evolving climate challenges.

Urbanization-induced soil organic carbon loss and microbial-enzymatic drivers: insights from aggregate size classes in Nanchang city, China.

Soil microorganisms and enzymes play crucial roles in soil organic carbon (SOC) sequestration by promoting soil aggregate formation and stability and by participating in SOC cycling and accumulation. However, the effects by which soil microorganisms and enzymes act as mediators driving dynamic changes in SOC during rapid urbanization remain unclear. Therefore, this study selected the built-up area of Nanchang City, China (505 km2), as the study area. Sampling surveys were conducted using 184 sample plots stratified based on the proportion of impermeable surface area to distinguish different urbanization levels. The driving factors of dynamic changes in SOC of different aggregates during the process of urbanization were analyzed using the soil microbial community and enzyme activities. The results demonstrated that with an increase in urbanization intensity, both SOC content and stock exhibited a significant decline (p < 0.05). The highest SOC stock and contribution rate were observed in the 0.25-1 mm aggregates, and they were significantly influenced by urbanization (p < 0.05). In addition, the biomass of gram-positive bacteria (G+) and actinomycetota, and the activities of N-acetylglucosaminidase and acid phosphatase (AP) were significantly higher in low-urbanization areas than in high-urbanization areas (p < 0.05). SOC of each aggregate was positively correlated with fungi, arbuscular mycorrhizal fungi, G+, gram-negative bacteria, actinomycetota, protozoa, β-1,4-glucosidase, N-acetylglucosaminidase, AP, urease, and catalase. Compared to soil enzymes, soil microorganisms exhibited a greater role in SOC sequestration (22.7%). Additionally, a structural equation model indicated that urbanization can directly or indirectly lead to a decrease in SOC of aggregates by altering soil physicochemical properties and affecting microbial and enzyme dynamics. However, the larger vegetation characteristics index mitigate the negative impacts of urbanization on SOC. Overall, urbanization had a negative impact on soil carbon storage. In the future, it is important to consider strategies that focus on improving soil nutrients, maintaining soil structure, protecting existing urban trees, and enhancing plant diversity during the urbanization process. These measures can help increase soil microbial biomass and enzyme activity, thereby improving soil and aggregate-related SOC content. The study could contribute to enhancing carbon sequestration in urban greenspaces.

İzmir Yöresi Zeytin Bahçe Topraklarının Karbon ve Azot Stokları

Soil organic carbon (SOC) and total nitrogen (TN) have a very important role in sustainable soil quality, crop production, and environmental impacts, and determining of carbon nitrogen ratio (C: N ratio) is very important for creating data banks in terms of ecosystem functions. Plants influence the interaction of SOC and TN, as well as ecosystem yield and the continental carbon cycle. Climate, atmosphere, and land-use change are all included in numerical models of the carbon (C) and nitrogen (N) cycles. This study was conducted to determine the SOC and TN stocks, the C: N ratio and their relationships with the soil properties of olive orchards in Aliaga, Bayindir, Bergama, Dikili, Foca, Karaburun, Kemalpasa, Menderes, Menemen, Odemis, Seferihisar, Selcuk, Tire, Torbali and Urla provinces of Izmir in Turkey. For this purpose, 129 soil samples were taken from 0-30 cm depth. The texture, pH, EC, lime, OM, SOC and TN content and stocks, Bulk density (Db) was determined. Db and C: N ratio varied between 0.84-1.31 g cm-3, 5.17-80.50, and SOC density and stocks changed between 4.00-53.00 mg cm-3, 1.25-1.59 kg m-2, N density and stocks between 0.09-2.66 mg cm-3, 0.03-0.80 kg m-2, respectively. The highest BD was obtained from Tire, the highest SOC stocks from Karaburun, the highest TN from Seferihisar and Karaburun. The very small bulk density which is negatively associated with OM and clay is an important feature. The SOC contents were higher in relatively heavy rainfall regions. SOC and soil texture have a strong relationship. As a result, texture, precipitation, temperature, soil depths, and regeneration of soil affect the SOC and TN stocks. The results may be effective in terms of sustainable soil quality and ecosystem functions for olive cultivation.

Space-time mapping of soil organic carbon stock and its local drivers: Potential for use in carbon accounting

The measurement and tracking of changes in soil organic carbon (SOC) stocks and its underpinning drivers are important in greenhouse gas accounting and carbon trading schemes. While repeated direct measurement of a location over time is the ‘gold standard’ for SOC stock change estimation, this is currently unfeasible at scale due to sample collection and analysis costs. Here, we used a data-driven, space–time digital soil mapping modelling approach (ST-DSM) coupled with an interpretive machine learning (IML) technique to both predict and quantify the relative contributions of covariates to annual SOC stocks and their uncertainty at 0–30 cm depth and at a 90 m spatial resolution for Australia between 1990 and 2018. A quantile regression forest model was calibrated using data from a datacube comprising of SOC stock values collected over the prediction years and a suite of dynamic and static environmental covariates. The evaluation of the ST-DSM model on a test set was satisfactory. Long-term annual mean (Mg C/ha), and total (Pg C) topsoil SOC stock were 37.6 (12.3 – 101.1, 90 % PI) and 28.3 (9.25 – 83.1, 90 % PI) respectively. The mean annual rate of SOC stock change over the Australian continent was 0.11 (±0.22) Mg C/ha yr−1 and the total net change was 23.5 Tg C yr−1, indicating Australia’s soils were a net sink of SOC over the 29-year period. However, SOC stocks declined in the montane ecoregion, a great concern given its fragility and high SOC stock. The long-term mean fraction of photosynthetic vegetation was the most important individual local contributor to SOC stock prediction in many parts of Australia. The aggregated effect of covariates based on the soil forming factors indicates vegetation as the principal local driver of SOC stock across most of the Australian continent, followed by climate. The evaluation of our results against independent, temporally paired field data and estimates from a nationally accepted SOC process-based model yielded promising results. Our approach demonstrates the use of readily available and inexpensive covariates to estimate SOC stock changes, as well as the underlying drivers over a larger area but at a spatial resolution suitable for decision making. This approach presents a new monitoring and verification possibility for carbon projects and national carbon accounting especially with the growing number of existing profile observations in soil databases.

Enhancing soil water, carbon, and nitrogen by partially substituting chemical fertilizer with organic fertilizer integrated with a rainwater collection system in rainfed orchards

Rainfed apple orchards, particularly in loess hilly regions of China, face significant challenges due to water scarcity and declining soil fertility, necessitating their restoration for sustainable apple production. This study investigated the impact of partially substituting chemical fertilizers with organic fertilizers integrated with a rainwater collection system on restoring soil water storage (SWS), soil organic carbon (SOC) stocks, and total nitrogen (TN) stocks and their relationship with apple production. Three orchard management practices were evaluated: (1) OSCR: partially substituting chemical fertilizer with organic fertilizer (60% N from organic fertilizer) integrated with a rainwater collection system; (2) CR: chemical fertilizer integrated with a rainwater collection system; and (3) CK: chemical fertilizer alone without a rainwater collection system. Averaged across five years, the OSCR treatment (457.83 mm) substantially enhanced SWS from 0 to 280 cm profile by 19.12% compared to the CK (384.34 mm). OSCR system outperformed CR treatment in terms of the 0–280 cm SWS compensation index (SWSCI). The OCSR and CR treatments had higher SWSCI values in 2016 (dry year) than the other years, indicating more effective SWS restoration in dry years. Average across five years, OSCR treatment had 55.26% and higher SOC stock (214.1 Mg ha–1) and 45.91% higher TN stock (5.72 Mg ha−1) from 0 to 280 cm than the CK; and the OSCR treatment positively restored SOC and TN stocks, while the CR treatment decreased SOC stock and restored TN stock from 0 to 200 cm profile. Compared to 2016, OSCR, CR and CK treatments increased SOC stock by 36.84%, −5.78% and −6.98%, and TN stock by 36.31%, 37.88 and −3.36% in 2020, respectively. Average across five years, the OSCR treatment had the highest mean apple yield (24.61 Mg ha−1) and crop water production (CWP, 48.64 kg ha−1 mm−1), 64.62% and 66.69% higher than the CK treatment across five years; no significant differences in fruit size or shape index occurred between treatments. The difference in apple yield is unfavorably connected with SWSCI and favorably connected with SOC and TN stock restoration. Overall, the OSCR system successfully restored SWS, SOC, and TN stocks, increasing apple yield and CWP, making it a promising management strategy for rainfed apple orchards.

Effects of land use/cover changes on soil organic carbon stocks in Qinghai-Tibet plateau: A comparative analysis of different ecological functional areas based on machine learning methods and soil carbon pool data

Understanding the process of land use/cover changes (LUCC) can provide experience on the enhancement of soil organic carbon (SOC) stocks and carbon sequestration potential for different areas. This study is uniquely to divide different ecological functional areas, and originally combine the machine learning method and soil carbon pool dataset for regional comparative analysis, to compare and quantitatively analyze the drivers of LUCC and the changes in SOC stocks effected by LUCC over 30 years. The results show that topography and climate changes are the main drivers affecting LUCC in four natural areas, while soil factors and population changes do not cause significant effects. The total SOC stocks in Qinghai was increased by 71.18 Tg C and 107.19 Tg C in 0–30 cm and 0–300 cm layers, respectively, and the highest SOC stocks within 0–300 cm were in Pastoral area. Desert and Gobi area had the lowest SOC stocks in both 0–30 cm and 0–300 cm layers. SOC stocks increased in both 0–30 cm and 0–300 cm layers only in Sanjiangyuan Natural Reserve, while the Desert and Gobi area showed a decrease in both over 30 years. This study emphasizes the significant impact of grassland changes on SOC stocks, indicating the importance of considering these changes in land management and ecological protection policies. The initial and original SOC stocks of pre-LUCC may influence the SOC stocks in post-LUCC. The response of SOC stocks changes to LUCC was varies in different areas. The heterogeneity of different ecological functional areas is affected by multiple factors and SOC stocks will become more complex among these areas in the future. These findings contribute to the development of ecological protection policies and the enhancement of regional land management strategies.

Carbon Storage Potential of Soil in Diverse Terrestrial Ecosystems

Soil is one of the largest carbon reservoirs sequestering more carbon than vegetation and atmosphere. Due to the enormous potential of soil to sequester atmospheric CO2, it becomes a feasible option to alleviate the current and impending effects of changing climate. Soil is a vulnerable resource globally because it is highly susceptible to global environmental problems such as land degradation, biodiversity loss, and climate change. Therefore, protecting and monitoring worldwide soil carbon pools is a complicated challenge. Soil organic carbon (SOC) is a vital factor affecting soil health since it is a major component of SOM and contributes to food production. This review attempts to summarize the information on carbon sequestration, storage, and carbon pools in the major terrestrial ecosystems and underpin soil carbon responses under climate change and mitigation strategies. Topography, pedogenic, and climatic factors mainly affect carbon input and stabilization. Humid conditions and low temperature favor high soil organic carbon content. Whereas warmer and drier regions have low SOC stocks. Tropical peatlands and mangrove ecosystems have the highest SOC stock. The soil of drylands stores 95% of the global Soil Inorganic Carbon (SIC) stock. Grasslands include rangelands, shrublands, pasturelands, and croplands. They hold about 1/5th of the world’s total soil carbon stocks.

Grassland vegetation decline is exacerbated by drought and can be mitigated by soil improvement in Inner Mongolia, China

Grassland activity is highly susceptible to drought while drivers from climate and soil attributes can largely affect drought propagation. However, understanding how these drives regulate the risk of vegetation decline under drought conditions remains limited, potentially impeding the adoption of appropriate adaptation strategies. To address this knowledge gap, we conducted a case study focusing on grassland activity in Inner Mongolia, China. In this study, we applied copula theorem to estimate the conditional probabilities of vegetation decline under drought conditions. Additionally, we utilized a structural equation model and a machine learning approach to identify the relative contributions of external drivers to the risk of vegetation decline. Our findings demonstrated a positive correlation between anomalies in vegetation activity and the status of water balance, and grassland vegetation in drier regions exhibited a more rapid response to water deficit. Increasing water deficit continuously reduced vegetation activity with risks of 77.27 %, 83.83 %, and 88.35 % under moderate, severe, and extreme drought conditions, respectively. Furthermore, the risks of vegetation decline under drought conditions were primarily governed by climate attributes, followed by soil properties and topography. Soil with high soil organic carbon stock content contributed significantly to mitigating the adverse effects of drought on grassland vegetation. In addition, we detected nonlinear patterns among environmental drivers and vegetation decline risks caused by drought. These findings highlight the importance of climate, soil properties, topography, and their intricate interconnections in regulating vegetation decline. This knowledge provides valuable insights into drought risk management for vegetation in advance and offers potential solutions to enhance vegetation resistance in the face of extreme drought events.

The response of crop yield, carbon sequestration, and global warming potential to straw and biochar applications: A meta-analysis

Organic materials play an important role in improving crop yield. However, due to variations in natural and field management practices, the impact of straw incorporation (NS) and biochar addition (NB) on soil organic carbon (SOC) sequestration and global warming potential (GWP) remains uncertain. This meta-analysis synthesizes the findings from 112 published studies, encompassing 897 samples, to assess the effects of NS and NB on crop yield, SOC, and GWP. The results reveal that Northeast China has the highest SOC stocks (40.80 Mg ha−1) and annual SOC sequestration (4.27 Mg ha−1 yr−1) compared to other regions. Notably, the NS and NB differ in their effect sizes on improving crop yield (7.68 % and 8.23 %, respectively) and SOC (6.92 % and 30.72 %, respectively), with opposing effects on GWP (increasing by 37.69 % in NS and decreasing by 23.94 % in NB). Following organic material application, climatic conditions, crop and field type, and soil properties affected SOC content and GWP. The main factors influencing variations in crop yield, SOC, and GWP were mean annual temperature and precipitation, initial SOC content, and soil pH, accounting for 57.46 %–60.29 %, 54.75 %–58.52 %, and 61.81 %–65.11 %, respectively. Considering the need to balance food demand, soil fertility and environmental benefits, biochar emerges as a recommended strategy for advancing future agriculture goals. In summary, this study quantitatively assessed the impact of organic material on crop yield, SOC, and greenhouse gas emissions, offering a scientific foundation for optimizing these factors under diverse regional conditions.

Soil Carbon and Biochemical Indicators of Soil Quality as Affected by Different Conservation Agricultural and Weed Management Options

Burning of agricultural residues, cultivation of single crop varieties such as rice (Oryza sativa L.) and wheat (Triticum aestivum L.), and traditional soil tillage practices collectively contribute to the degradation of environmental quality, water systems, and soil resources. To address these issues, conservation agriculture (CA)-based crop management practice has emerged as one of the viable options. The current study was conducted with the aim to evaluate the effect of CA and weed management (WM) practices on carbon dynamics and biochemical properties of soil. The experiment included two factors, viz., CA and WM practices. The CA levels vary from conventional agriculture to partial CA (pCA1, pCA2, and pCA3) and full CA, while WM had three levels consisting of chemical control, integrated weed management, and weedy check. The results demonstrated that soil organic carbon (SOC) under the full CA treatment, was 30.6, 23.5, and 20.6 percent higher than conventional agriculture (T1), partial CA1, and partial CA2 practices, respectively. Similarly, labile fractions of carbon, KMnO4-C MBC, WSOC, and POC, in full CA increased by 46.3, 52.3, 152.4, and 15.6 percent, respectively, over conventional agriculture. Nonetheless, the total organic carbon exhibited no significant impact. The highest SOC stock was sequestered under full CA treatment, which was higher by 26.5 to 40.6 per cent than the rest of the CA treatments. Among biological properties, full CA resulted in 104.3 and 40.6 percent higher dehydrogenase and alkaline phosphatase activity than conventional agriculture. The impact of weed management practices was significant for KMnO4-C, with very labile carbon and alkaline phosphatase activity only in the surface soil layer. Soil quality index (SQI) followed the decreasing order as full CA (0.94) &gt; partial CA3 (0.88) &gt; partial CA2 (0.78) partial CA1 (0.77) &gt; conventional agriculture (0.67) under different CA treatments, whereas WM followed herbicide (0.82) &gt; weedy check (0.81) &gt; IWM (0.80). The current study offered incredible information on soil carbon and biological indicators to monitor soil quality changes in rice–wheat cropping systems in response to conservation agriculture practices.

Forest carbon stock variation with altitude in bolale natural forest, Western Ethiopia

This study was initiated to assess forest carbon stock variation with altitude. A systematic sampling technique was used to select sample plots. A total of 36 (12 plots from each altitude class) square plots with size of 20 m × 20 m were obtained. Diameter at breast height (DBH) and height of individual trees of DBH > 5 cm were measured from all the selected sample plots. A total of 216 soil samples, 108 for analysis of soil organic carbon (SOC) fraction (% C), and 108 for bulk density determination (BD), were collected. Altitude had a significant effect on above and belowground tree biomass, and litter carbon stock, but not on deadwood, and soil organic carbon stock. The aboveground and belowground biomass and litter carbon were higher at lower altitudes, which were attributed to higher biomass production due to higher photosynthesis and higher net primary production. Soil organic carbon varied significantly with depth. A higher soil organic carbon stock was observed at the upper soil depth (0–10 cm). At lower soil depths, carbon stocks were smaller due to less plant residue and less biological activity in the deeper soil. In general, the study found that carbon density is high at lower altitudes and lower at higher altitudes. Therefore, altitude should be given due consideration for forest development and management for climate change mitigation. The result suggests that different governmental and nongovernmental organizations have to give due attention for forest conservation to reduce the CO2 emmission.

Impact of land use/cover change and slope gradient on soil organic carbon stock in Anjeni watershed, Northwest Ethiopia.

Today's agri-food systems face the triple challenge of addressing food security, adapting to climate change, and reducing the climate footprint by reducing the emission of greenhouse gases (GHG). In agri-food systems, changes in land use and land cover (LULC) could affect soil physicochemical properties, particularly soil organic carbon (SOC) stock. However, the impact varies depending on the physical, social, and economic conditions of a given region or watershed. Given this, a study was conducted to quantify the impact of LULC and slope gradient on SOC stock and C sequestration rate in the Anjeni watershed, which is a highly populated and intensively cultivated area in Northwest Ethiopia. Seventy-two soil samples were collected from 0-15 and 15-30cm soil depths representing four land use types and three slope gradients. Soil samples were selected systematically to match the historical records (30years) for SOC stock comparison. Four land use types were quantified using Landsat imagery analysis. As expected, plantation forest had a significantly (p < 0.05) higher SOC (1.94Mgha-1) than cultivated land (1.38Mgha-1), and gentle slopes (1-15%) had the highest SOC (1.77Mgha-1) than steeper slopes (> 30%). However, higher SOC stock (72.03Mgha-1) and SOC sequestration rate (3.00Mgha-1year-1) were recorded when cultivated land was converted to grassland, while lower SOC stock (8.87Mgha-1) and sequestration rate (0.77Mgha-1year-1) were recorded when land use changed from cultivation to a plantation forest. The results indicated that LULC changes and slope gradient had a major impact on SOC stock and C sequestration rate over 30years in a highly populated watershed. It is concluded that in intensively used watersheds, a carefully planned land use that involves the conversion of cultivated land to grassland could lead to an increase in soil C sequestration and contributes to reducing the carbon footprint of agri-food systems.

Small, Coastal Temperate Rainforest Watersheds Dominate Dissolved Organic Carbon Transport to the Northeast Pacific Ocean

AbstractThe northeast Pacific Coastal Temperate Rainforest (NPCTR) extending from southeast Alaska to northern California is characterized by high precipitation and large stores of recently fixed biological carbon. We show that 3.5 Tg‐C yr−1 as dissolved organic carbon (DOC) is exported from the NPCTR drainage basin to the coastal ocean. More than 56% of this riverine DOC flux originates from thousands of small (mean = 118 km2), coastal watersheds comprising 22% of the NPCTR drainage basin. The average DOC yield from NPCTR coastal watersheds (6.20 g‐C m−2 yr−1) exceeds that from Earth's tropical regions by roughly a factor of three. The highest yields occur in small, coastal watersheds in the central NPCTR due to the balance of moderate temperature, high precipitation, and high soil organic carbon stocks. These findings indicate DOC export from NPCTR watersheds may play an important role in regional‐scale heterotrophy within near‐shore marine ecosystems in the northeast Pacific.

Factor contribution to soil carbon and nitrogen accumulation after vegetation restoration on the Loess Plateau, China

Unraveling the distributions and controls of soil carbon (C) and nitrogen (N) accumulation is conducive to providing guidance for sustainable ecosystem management. Although the factors that affect soil C and N accumulation have been widely investigated, the relative importance of these factors and whether they confer direct or indirect effects remain unclear. Herein, we examined the distributions of soil organic carbon (SOC), soil inorganic carbon (SIC), and total nitrogen (TN) stocks across the 0–200 cm soil profiles in grasslands, forestlands, and shrublands on the Loess Plateau. Moreover, we determined the relative contributions of land use, topography, and soil properties (texture, water, phosphorus, and available nitrogen) to their variations. The results showed that with increasing soil depth, SOC and TN stocks decreased, while SIC stocks fluctuated. However, large amounts of SOC, SIC, and TN were stored in the deep soil layers (100–200 cm), with values of 3.06, 26.63, and 0.50 kg/m2, respectively. In the 0–200 cm soil layers, the total SIC stock was 53.40 kg/m2 and was 6.8 times higher than the total SOC stock. Among different plant communities, grasslands had the highest SIC stock (54.83 kg/m2), while Armeniaca sibirica and Robinia pseudoacacia had the highest SOC stock (10.06 kg/m2) and TN stock (1.49 kg/m2), respectively. Furthermore, approximately 85% of the variations in SOC, SIC, and TN stocks were jointly affected by land use, topography, and soil properties, in which soil properties acted as the most important driving factors, followed by topography and land use. In particular, topography affected SOC, SIC, and TN stocks mainly through its effects on soil texture and water. Overall, vegetation restoration scenarios incorporating grasslands and Robinia pseudoacacia are highly recommended and should be tailored according to specific topographic features.

Grazing in a megagrazer‐dominated savanna does not reduce soil carbon stocks, even at high intensities

Recent studies suggest that wild animals can promote ecosystem carbon sinks through their impacts on vegetation and soils. However, livestock studies show that intense levels of grazing reduce soil organic carbon (SOC), leading to concerns that rewilding with large grazers may compromise ecosystem carbon storage. Furthermore, wild grazers can both limit and promote woody plant recruitment and survival on savanna grasslands, with both positive and negative impacts on SOC, depending on the rainfall and soil texture contexts. We used grazing lawns in one of the few African protected savannas that are still dominated by megagrazers (&gt; 1000 kg), namely white rhinoceros Ceratotherium simum, as a model to study the impact of prolonged and intense wild grazing on SOC stocks. We contrasted SOC stocks between patches of varying grazing intensity and woody plant encroachment in sites across different rhino habitat types. We found no differences in SOC stocks between the most‐ and least grazed plots in any of the habitats. Intermediately grazed plots, however, had higher SOC stocks in the top 5 cm compared to most and least grazed plots, but only in the closed‐canopy woodland habitat and not in the open habitats. Importantly, we found no evidence to support the hypothesis that wild grazing reduces SOC, even at high grazing intensities by the world's largest megagrazer. Compared to the non‐encroached reference plots, woody encroached plots had higher SOC stocks in soils with low clay content and lower SOC stocks in soils with high clay content, although only in the top 5 cm. Accordingly, our study highlights that wild grazers may influence SOC indirectly through their impact on tree‐grass ratios in grassy ecosystems. Our study thus provides important insights for future natural climate solutions that focus on wild grazer conservation and restoration.Keywords: fire, grazing impact, rewilding, soil carbon, white rhinoceros, woody encroachment

JumpStart of soil organic matter with highly stabilized organic amendment: Implication for climate-smart agriculture

Rebuilding soil organic matter (SOM) to regionally specific targets for high quality soil that are likely maintained in the long term, here defined as “SOM JumpStart”, can unlock soil's potential for increased productivity, enhanced resilience and reduced emission as the main components for climate-smart agriculture (CSA). A field experiment was established in 2013 at Fulton County, western Illinois to use highly stabilized organic amendment (HSOA) at a rate, potentially raising surface SOM of cultivated Alfisol (low quality soil) to the level of cultivated Mollisol (high quality soil for US Midwest). Treatments included one-time application of lagoon-aged air-dried biosolids at 165 Mg ha−1, one-time application of vegetative compost at 165 Mg ha−1, chemical fertilizer at 225–50–85 kg ha−1 yr−1 (N-P-K) as control, and grass fallow as reference. In every year following the HSOA application, fertilizer (N and K) rate was reduced by 25%, and no P was applied for most years. Corn was planted annually. The HSOA JumpStart application dramatically increased SOM, leading to soil organic carbon (SOC) at 2–2.5% after biosolids and about 3% after compost for 2013–2019, as that of Mollisol, while that in chemical fertilizer control remained unchanged at 1–1.2%. For the first seven years, HSOA JumpStart increased corn grain yield by a mean of 19.8% (biosolids) and 7.1% (compost) above the control, with greater increase at precipitations-abnormal (low/high) years. The SOM JumpStart caused the shift of soil microbial physiology to high C utilization efficiency, as evident by reduced microbial metabolic quotient for CO2, leading to the decrease in CO2 emission from agricultural crop residues by 19.6% (biosolids) and 20.0% (compost). Our modeling revealed the promising soil C sequestration (excluding residual C from HSOA) over next 50 years at 10.6 Mg C ha−1 by biosolids application and 13.9 Mg C ha−1 by compost application, higher than 6.8 Mg C ha−1 anticipated by “4 per 1000″ international initiative. A simple but straightforward model suggests JumpStarted soil still contain 50% higher SOC stocks as compared to control after 50 years. Our results suggest the SOM JumpStart by HSOA such as biosolids and compost can transform conventional corn production to CSA.

Impacts of land use conversions on soil organic carbon in a warming-induced agricultural frontier in Northern Ontario, Canada under historical and future climate

Land conversion from forest to agriculture in higher latitude regions such as the Great Clay Belt of northern Ontario, Canada is expected to intensify due to warming. It is critical to minimize soil organic carbon (SOC) loss, but there is limited understanding of best land management practices for these Northern agricultural frontiers. We conducted a measurement campaign to assess changes in SOC after land conversion from native forest to either permanent pasture or to arable cropping by measuring SOC content (0–60 cm) at six farms with different land uses over the past 68 years (1950–2018). The Denitrification-Decomposition (DNDC) model was validated for historical SOC trends and then used to assess the impacts of future climate change on crop yields, SOC stocks, and SOC sequestration rates from 1954 to 2070 under three Shared Socio-economic Pathways (SSPs) scenarios from the Coupled Model Intercomparison Project Phase 6. Three land uses (1) continuous barley-oats (BO), (2) continuous Legume hay-BO, (3) continuous Pasture; and two land use conversions (4) pasture from 1954 to 2014 and then converted to BO from 2015 to 2070 (Pasture » BO) and (5) BO from 1954 to 2014 and then converted to pasture from 2015 to 2070 (BO » Pasture) were considered. Averaged across all six farms, the measured SOC stocks 68 years after conversion from forest were 22.7 and 25.3% higher under pasture than under forest and arable cropping, respectively. The DNDC demonstrated good performance in simulating yields of annual crops, legume hay and pasture as well as SOC stocks across all sites. Under future climate scenarios, higher SOC stocks were predicted for all land use conversions relative to the historical period, except for Pasture » BO. Under different land use, predicted SOC stocks were highest for continuous pasture, followed by BO » Pasture, Pasture » BO, Legume hay-BO and lowest for continuous BO. The DNDC predicted that the SOC sequestration rate would decrease for all land uses in the period 2015–2070 relative to 1954–2014, except for BO » Pasture. The predicted change declined from 0.35 to 0.22–0.28 Mg C ha−1 yr−1 for continuous pasture, but when change in management occurred from BO to pasture the rate of SOC gain increased. This underscores the potential role of pasture and crop diversification in avoiding SOC losses in agricultural frontiers induced by climate-warming.

Changes in soil organic carbon fractions in abandoned croplands of Nepal

Cropland abandonment in Nepal is an emerging land use change that has significant impacts on ecosystem functions, particularly soil organic carbon (SOC) pools and stocks. Information relating to SOC is limited for the mountainous terrain of Nepal that is subject to either SOC loss from erosion or SOC accumulation from secondary succession after cropland is abandoned. The rate of cropland abandonment is accelerating in Nepal but the impact of the abandoned duration on SOC, fractions, and SOC stock has not yet been investigated. We used a space-for-time substitution approach to assess the impacts of abandonment on SOC concentrations, stocks and associated pools of carbon across abandoned cropland (<5, 5–10, and > 10 years) compared with forest, pasture, and currently cropped land. Soil samples were collected at four depth increments (0–10, 10–20, 20–40, 40–60 cm). The change in SOC and stock was found to be significantly higher in the surface (0–20 cm) compared with sub-surface soil (20–60 cm) and consistently decreased with increasing soil depth under all land uses. Change in soil nitrogen concentration followed a similar pattern to that of SOC at all land uses and depths. Among the SOC fractions, particulate organic carbon increased significantly by a greater proportion compared to mineral-associated organic carbon and dissolved organic carbon after 10 years of cropland abandonment. Abandoned cropland >10 years had a higher SOC stock (64.19 Mg ha−1) in the soil profile (0–60 cm) compared with cropped land (58.76 Mg ha−1) although it remained lower than forest (66.56 Mg ha−1) and pasture (66.60 Mg ha−1) soils. Although there was a decrease in the first five years, there was a significant accumulation of SOC, associated fractions, and SOC stock after ten years of abandonment and colonisation by vegetation indicating the inception of ecosystem regeneration in abandoned croplands in the mountainous region of Nepal.

Slash and burn management and permanent or rotation agroforestry systems: A comparative study for C sequestration by century model simulation

Understanding the effects of agroforestry systems (AFs) on soil organic carbon (SOC) requires long-term experiments, but scenarios simulations can anticipate the potential of these systems to sequester or lose carbon (C). This study aimed to simulate the SOC dynamics in slash and burn management (BURN) and AFs using the Century model. Data from a long-term experiment implemented in the Brazilian semiarid region were used to simulate SOC dynamics under BURN and AFs situations, and the natural vegetation (NV) “Caatinga” as a reference. BURN scenarios considered different fallow periods (0, 7, 15, 30, 50 and 100 years) among cultivation of the same area. The two types of AFs (agrosilvopastoral-AGP and silvopastoral-SILV) were simulated in two contrasting conditions: (i) each one of the AFs and also NV area were permanently conducted with no rotation among these areas; and (ii) the two AFs and NV rotated among them every 7 years. The correlation coefficients (r), coefficients of determination (CD) and coefficients of residual mass (CRM) showed adequate performance, meaning that the Century model is able to reproduce the SOC stocks in the slash and burn management and AFs situations. The equilibrium points of NV SOC stocks stabilized around 30.3 Mg ha−1, as similar to the measured average of 28.4 Mg ha−1 at field conditions. The adoption of BURN without a fallow period (0 years) resulted in a reduction of 50% of SOC, approximately 20 Mg ha−1, after the first 10 years. Permanent (p) and rotating (r) AFs management systems recovered (in 10 years) fast to the original SOC stocks, resulting in higher SOC stocks than NV SOC at equilibrium. The fallow period of 50 years is necessary to recovery SOC stocks in the Caatinga biome. The simulation shows that the AFs systems increase more SOC stocks than observed in natural vegetation in long-term.