Increase Soil Organic Carbon Stocks Research Articles

Impacts of straw return coupled with tillage practices on soil organic carbon stock in upland wheat and maize croplands in China: A meta-analysis

Despite numerous individual studies evaluating the impact of straw return on soil organic carbon (SOC) stock in upland wheat and maize croplands in China using no-tillage (NTS), rotary tillage (RTS), and deep tillage (DTS) practices, the results have shown inconsistency. In addition, several factors influence the effects of various tillage practices with straw return on SOC stock that are not well understand. In this study, we conducted a meta-analysis of 764 comparisons to determine the combined impact of SOC stock in the topsoil (0–20 cm) and subsoil (20–40 cm) layers, while considering factors such as climate conditions, management practices, and initial soil properties. The results indicate that straw return with different tillage practices significantly improved SOC stock in both soil layers compared to straws removal. The increase in topsoil SOC stock was nearly identical for NTS (7.38 %) and DTS (7.17 %), compared to the RTS. However, the increase in subsoil SOC stock was significantly higher for DTS (28.8 %). According to subgroup analysis, NTS has been more effective in increasing topsoil SOC stock in regions with medium temperature (10–15 °C) and low precipitation (<400 mm), when used in a single cropping system. However, in regions with higher temperature (>15 °C) and precipitation (>800 mm), DTS is more effective in increasing SOC stock in both topsoil and subsoil layers in a double cropping system. Long-term (11–20 years) DTS resulted in a significant increase in SOC stock in the topsoil (19.2 %) and subsoil (18.5 %), while the increased effects of NTS on SOC stock were only in topsoil layer (17.1 %). The effects of straw return on SOC stock were also found to be associated with soil texture, with NTS having a greater impact on sandy to loam soils, and DTS having a greater impact on clay soils. Furthermore, a significant (P < 0.01) positive linear relationship was observed between annual carbon (C) input and SOC sequestration in the topsoil under NTS, as well as in both soil layers under DTS. These findings have important implications for enhancing SOC in Chinese upland wheat and maize cropland soils through optimizing straw return, given that more than 518 million tons of crop straw are produced annually.

Compost and biosolids increase long-term soil organic carbon stocks

Biobased residues derived from organic urban waste materials can be processed to produce soil amendments that enhance soil fertility and carbon sequestration. However, the extent of carbon sequestration by biobased residues depends on the interaction between their physicochemical properties, climate, and agroecosystem management practices. Our objective was to predict how different biobased residues (compost, anaerobic digestate, or biosolids), compared to nitrogen fertilizer, affect soil organic carbon stocks under continuous cropping and crop rotation in Ontario, Canada, using the Century model. The Century model was calibrated and validated with data, from a three-year field study located in Elora, Ontario, Canada, that was used to predict long-term changes in soil organic carbon. Our results showed that after 150 years, soil amended with compost and biosolids increased soil organic carbon stocks significantly ( p &lt; 0.05) compared to anaerobic digestate and nitrogen fertilizer. Soil organic carbon stocks were 1%–27% greater with crop rotation compared to continuous cropping. Model performance indicated a strong correlation between measured and simulated soil organic carbon stocks ( R2 = 0.26–0.82; RMSD = 432–727 g m−2). Our findings suggested that compost had the greatest soil carbon sequestration potential of the tested soil amendments, and this difference was due to the quantity and quality of carbon input.

Limitations of farm management data in analyses of decadal changes in SOC stocks in the Danish soil‐monitoring network

AbstractChanges in soil organic carbon (SOC) storage in agricultural land are an important part of the Land Use, Land‐Use Change and Forestry component of national greenhouse gas emission inventories. Furthermore, as climate mitigation strategies and incentives for carbon farming are being developed, accurate estimates of SOC stocks are essential to verify any management‐induced changes in SOC. Based on agricultural mineral soils in the Danish soil‐monitoring network, we analysed management effects on SOC stocks using data from the two most recent surveys (2009 and 2019). Between 2009 and 2019, the average increase in SOC stock was 1.2 Mg C ha−1 for 0–50 cm despite a loss of 1.2 Mg C ha−1 from the topsoil (0–25 cm), stressing the importance of including deeper soil layers in soil‐monitoring networks. Comparing all four national surveys (1986, 1997, 2009, 2019), the mean SOC stock of mineral soils in Denmark appears stable. The change in SOC stock between 2009 and 2019 was analysed in detail in relation to management practices as reported by farmers. We found that the effects of single management factors were difficult to isolate from co‐varying factors including soil parameters and that the use of farm management data to explain changes in SOC stocks observed in soil‐monitoring networks appears limited. Uncertainty in SOC stock estimates also arises from low sampling frequency and statistical challenges related to regression to the mean. However, repeated stock measurements at decadal intervals still represent a benchmark for the overall development in regional and national SOC storage, as affected by actual farm management.

Long-term tillage and cropping systems affect soil organic carbon components and mineralization in aggregates in semiarid regions

Examining soil organic carbon (SOC) mineralization and sequestration under different agricultural practices is pertinent to mitigate climate change and improve soil quality. Soil structure and SOC chemical components are important regulating factors for SOC dynamics. A 12-year field experiment was conducted in Northwest China to assess the effects of cropping system (wheatmaize rotation system and continuous wheat system) and tillage practice (no-tillage, subsoiling and plowing) on SOC stocks, soil aggregate stability, aggregate-associated OC concentrations, chemical components and mineralization. Results showed that wheatmaize rotation, no-tillage and subsoiling increased input-C from crop residue, thus increasing SOC, soil aggregate stability and aggregate-associated OC concentrations. The wheatmaize rotation system with subsoiling had the highest MWD at the 0–40 cm depths as well as increased SOC stock. Fourier transform infrared spectra showed that the OC hydrophobicity within aggregate classes was decreased by wheatmaize rotation system, but increased by no-tillage and subsoiling. Soil aggregates and SOC components jointly affected carbon mineralization kinetics, and the increase in MWD and OC hydrophobicity inhibited OC mineralization. The wheatmaize rotation system increased total carbon mineralization, OC mineralizability and the mineralization rate, which was related to lower OC hydrophobicity. The higher MWD and OC hydrophobicity under no-tillage and subsoiling contributed to decrease SOC mineralizability and delay the carbon mineralization rate (especially slow carbon). At the 0–20 cm depth, no-tillage and subsoiling decreased total carbon mineralization by 21% and 19% compared to plowing, respectively. Overall, the adoption of subsoiling under a wheatmaize rotation system is a promising practice to improve soil structure and SOC sequestration as well as decrease SOC mineralization in semiarid regions.

An overlooked soil carbon pool in vegetated coastal ecosystems: National-scale assessment of soil organic carbon stocks in coastal shelter forests of China

Protection and restoration of vegetated coastal ecosystems provide opportunities to mitigate climate change. Coastal shelter forests as one of vegetated coastal ecosystems play vital role on sandy coasts protection, but less attention is paid on their soil organic carbon (OC) sequestration potential. Here, we provide the first national-scale assessment of the soil OC stocks, fractions, sources and accumulation rates from 48 sites of shelter forests and 74 sites of sandy beaches across 22° of latitude in China. We find that, compared with sandy beaches, shelter forest plantation achieves an average soil desalination rate of 92.0 % and reduces the soil pH by 1.3 units. The improved soil quality can facilitate OC sequestration leading to an increase of soil OC stock of 11.8 (0.60–64.2) MgC ha−1 in shelter forests. Particulate OC (POC) is a dominant OC fraction in both sandy beaches and shelter forests, but most sites are >80 % in shelter forests. The low δ13C values and higher C:N ratios, which are more regulated by climate and tree species, together with high POC proportions suggest a substantial contribution of plant-derived OC. Bayesian mixing model indicates that 71.8 (33.5–91.6)% of the soil OC is derived from local plant biomass. We estimate that soil OC stocks in Chinese shelter forests are 20.5 (7.44–79.7) MgC ha−1 and 4.53 ± 0.71 TgC in the top meter, with an accumulation rate of 45.0 (6.90 to 194.1) gC m−2 year−1 and 99.5 ± 44.9 GgC year−1. According to coastal shelter forest afforestation plan, additional 1.72 ± 0.27 TgC with a rate of 37.9 ± 17.1 GgC year−1 can be sequestrated in the future. Our findings suggest that construction of coastal shelter forests can be an effective solution to sequester more soil carbon in coastal ecosystems.

Effects of Vegetation Restoration on Soil Organic Carbon Sequestration and Aggregate Stability in Water-Eroded Environment: A Meta-analysis

In order to clarify the differences in the effects of vegetation restoration strategies on soil carbon sequestration and aggregate stability under different water-eroded environments, we collected experimental data from 91 papers and evaluated the response of soil organic carbon (SOC) stock and aggregate stability to vegetation restoration based on Meta-analysis. The results showed the following:① compared with cropland or bare land, forestland/grassland restoration was beneficial to increase SOC stock and improve aggregate stability, but the dominant functions of the two were different. The effect of forestland restoration on carbon sequestration was stronger than that of grassland reforestation, and the effect of grassland restoration on aggregate stability was stronger than that of forestland restoration. ② Multi-factor Meta-analysis showed that the factors that significantly affected SOC were restoration year, soil clay content, vegetation coverage, mean annual precipitation (MAP), mean annual temperature (MAT), and soil depth. The positive effect of vegetation restoration on SOC stock increased with the increase in vegetation coverage rate. Grassland restoration had a more significant effect on SOC stock when soil clay content was 20%-32%, it was more likely to promote the carbon sequestration effect of grassland when MAP>800 mm or MAT<15℃, and there was no significant change in SOC stock under different restoration years. However, the effect of forestland restoration on SOC stock was more significant when soil clay content was>32%. Climate conditions had no limited effect on SOC stock in forestland, and there was a positive effect between SOC stock under forestland restoration and restoration years. ③ Vegetation restoration had stronger significant positive effects on mean weight diameter (MWD) and mean geometric diameter (GMD) when the clay content was 20%-32%, and MWD and GMD increased with the increase in vegetation coverage. ④SOC stock growth could explain 25% and 24% of the variation in the effect value of MWD and GMD, respectively. These results indicated that the formation of SOC was the result of multiple factors, and soil aggregate stability was limited only by vegetation coverage and soil clay content. The increase in SOC stock could promote the improvement of water stability MWD and GMD. These results can clarify the carbon sequestration effect of different vegetation restoration measures in water-eroded environments and provide theoretical reference for the restoration and reconstruction of degraded ecosystems.

Deep tillage enhanced soil organic carbon sequestration in China: A meta-analysis

The increasing atmospheric carbon dioxide (CO2) causes serious environmental problems, soil organic carbon (SOC) sequestration is suggested as an efficient strategy to offset global CO2 emissions. Deep tillage (DT) can change soil properties and the input and loss of OC, and then influence SOC sequestration across the whole soil profile. However, the effect of DT on SOC sequestration relative to conventional tillage (CT) under different environmental factors and management practices is unclear in China. In this study, we evaluated the response of SOC stock to DT based on collected field data (447 observations) with a meta-analysis. DT significantly increased SOC stock by 7.36% over CT, with a greater increase for subsoiling (8.76%) than for deep ploughing (DP) (5.85%). Subsoiling enhanced SOC across the 0–40 cm soil layer and the greatest increase occurred at 0–10 cm layer (11.41%); DP enhanced SOC stock at 10–40 cm layer, but had no effect on SOC of 0–10 cm layer. DP and subsoiling did not affect SOC storage below 40 cm depth. According to subgroup analysis, the high rainfall, fine soil texture, residue retained, double cropping, and high rate of N fertilization greatly promoted SOC stock compared with the low rainfall, sandy texture, residue removal, monoculture, and low N fertilizer input under DT. DT significantly enhanced SOC storage under low initial SOC (<15 g kg−1), but did not affect SOC when the initial SOC exceeded 15 g kg−1 compared with CT. However, the experiment duration, initial SOC and bulk density (BD) did not significantly affect the response of SOC to DT. Overall, this study has supplied a reference for SOC management in mitigating climate change, and the specific environmental factors and management practice should be considered when utilizing DT to enhance SOC sequestration in different regions of China.

Current and future potential soil organic carbon stocks of vegetated coastal ecosystems and their controls in the Bohai Rim Region, China

Vegetated coastal ecosystems (VCEs) have much higher organic carbon sequestration rates and storage capacities than most other earth surface ecosystems, and thus play a vital role in blue carbon sequestration for climate change mitigation. However, soil organic carbon (SOC) stock assessment in VCEs at a large regional-scale remain problematic, and the controlling mechanisms for SOC remain poorly understood. Here, we estimated current and future SOC stocks of VCEs in the Bohai Rim Region, China at a spatial resolution of 10 m, using a data-driven method based on multi-source data; and investigated the key environmental and anthropogenic controls. The total SOC stocks and SOC density of VCEs in the Bohai Rim Region were estimated to be approximately 62.7 Tg carbon and about 68.8 Mg ha−1, respectively (in the upper 1 m of soil). We found that climate and soil salinity are the most critical environmental controls of SOC stocks within VCEs in the region. Increasing temperature and soil salinity would increase SOC decomposition and decrease plant productivity, resulting in a decrease in SOC stocks. Conversely, increasing precipitation would increase SOC stocks by reducing soil salinity. We projected that the potential losses of SOC stocks due to the combined effects of climate changes, sea-level rise, and anthropogenic disturbances would be ∼ 12.2 % between 2041 and 2060 under two Shared Socioeconomic Pathway (SSP) scenarios (SSP245 and SSP585), extending to 19.3 % between 2081 and 2100. The decreases in SOC stocks would occur mainly in the higher latitude and colder regions. The study demonstrated the potential significant reduction in SOC stocks in coastal ecosystems and provided an important framework for better understanding the blue carbon ecosystems.

The potential to increase grassland soil C stocks by extending reseeding intervals is dependent on soil texture and depth

Grasslands account for ∼30% of global terrestrial carbon (C), of which most is stored in soils and provide important ecosystem services including livestock and forage production. Reseeding of temporary grasslands on a 5-year cycle is a common management practice to rejuvenate sward productivity and reduce soil compaction, but is physically disruptive and may reduce soil organic carbon (SOC) stocks. However, research to date is limited, which impacts on the ability to optimise grassland management for climate change mitigation. To determine whether extending the time interval up to 20 years between grassland reseeding can increase stable SOC stocks, a soil survey was conducted across three UK grassland chrono-sequences comprising 24 fields on contrasting soil types. We found that grassland SOC stocks (39.8–114.8 Mg C ha−1) were higher than co-located fields in arable rotations (29.3–83.2 Mg C ha−1) and the relationship with grassland age followed a curvilinear relationship with rapid SOC stock accumulation in the year following reseeding (2.69–18.3 Mg C ha−1 yr−1) followed by progressively slower SOC accumulation up to 20 years. Contrary to expectation, all grasslands had similar soil bulk densities and sward composition questioning the need for traditional 5-year reseeding cycles. Fractionation of soils into stable mineral associated fractions revealed that coarse textured grassland topsoils (0–15 cm) were near-saturated in C irrespective of grassland age whilst loam soils reached saturation ∼10 years after reseeding. Fine-textured topsoils and subsoils (15–30 cm) of all textures were under saturated and thus appear to hold the most potential to accrue additional stable C. However, the lack of a relationship between C saturation deficit and grassland age in subsoils suggests that more innovative management to promote SOC redistribution to depth, such as a switch to diverse leys or full inversion tillage may be required to maximise subsoil SOC stocks. Taken together our findings suggest that extending the time between grassland reseeding could temporarily increase SOC stocks without compromising sward composition or soil structure. However, detailed monitoring of the trade-offs with grassland productivity are required. Fine textured soils and subsoils (15–30 cm) have the greatest potential to accrue additional stable C due to under saturation of fine mineral pools.

DYNAMICS OF SOIL ORGANIC CARBON AFTER MORE THAN 25 YEARS OF FARMING IN THE DANUBE DELTA

Soil organic carbon (SOC) is an important parameter in the context of global warming, and a special attention should be given to its dynamics. The purpose of this paper is to test the existence of SOC losses from the soils taken for farming for more than 25 years in some areas of the Danube Delta. Another objective is to quantify such SOC losses if they exist. The studied soils belong to two land reclamation areas, Carasuhat and Dunavat, from the Danube Delta. Data of present-day SOC stocks were compared to the SOC stocks calculated for the period until year 1996 for the same soil units in order to assess the dynamics of SOC losses for more than 25 years. We have found that a specific process was noted for the organic soils, Histosols, which were turned into histic soils after farming, meaning that there was a significant decrease in SOC pool. Thus, SOC losses due to farming were maximum for Histosols, and SOC stocks were highly significantly lower in 2022 versus 1996, due to increasing mineralization processes of organic matter and subsequent greenhouse gas emissions that occurred in cropland areas. Relationships have been found quantifying SOC losses versus the original 1996 stocks, confirming that Histosols, containing the maximum SOC stocks, present the highest risk of degradation. Lowering of the ground water and consequently the intensified oxidation of peat are very important factors in SOC losses beside the agricultural land use works. Policy makers, decision makers and stake holders should promote conservation of the natural landscape of the Danube Delta in order to increase SOC stocks and decrease CO2 and other greenhouse gas emissions into the atmosphere. Maintaining the former SOC stock at the present-day level and enhancing new organic C sequestration in the renatured parts of the less fertile Delta soils could contribute to global warming mitigation in the future and to supply agricultural products in the cropland already in use. Future research in characteristic stationary sites of the Danube Delta, especially in the farmland area, is recommended to improve our knowledge on SOC evolution.

Soil organic carbon, total nitrogen stocks and CO2 emissions in top- and subsoils with contrasting management regimes in semi-arid environments

This study aims to investigate soil organic carbon (SOC) and total nitrogen (TN) contents and stocks, CO2 emissions and selected soil properties in croplands, grazing lands, exclosures and forest lands of semi-arid Ethiopia. Sampling was done at 0–30, 30–60 and 60–90 cm soil depths and concentration and stocks of SOC, TN and selected soil properties were determined using standard routine laboratory procedures. There were variations in distribution of SOC and TN stock over 90 cm depth across land use types and locations, decreasing from topsoils to subsoil, with average values ranging from 48.68 Mg C ha−1 and 4.80 Mg N ha−1 in Hugumburda cropland to 303.53 Mg C ha−1 and 24.99 Mg N ha−1 in Desa’a forest respectively. Forest sequestered significant higher SOC and TN stock, decreasing with depth, compared with other land use types. In Desa'a and Hugumburda, the conversion of forest to cropland resulted in a total loss of SOC stock of 9.04 Mg C ha−1 and 2.05 Mg C ha−1, respectively, and an increase in CO2 emission of 33.16 Mg C ha−1 and 7.52 Mg C ha−1 yr−1, respectively. The establishment of 10 years (Geregera) and 6 years (Haikihelet) exclosures on degraded grazing land increased SOC stock by 13% and 37% respectively.

Changes in cropland soil carbon through improved management practices in China: A meta-analysis

Recommended management practices (RMPs, e.g., manuring, no-tillage, crop residue return) can increase soil organic carbon (SOC), reduce greenhouse gas emissions, and maintain soil health in croplands. However, there is no consensus on how RMPs affect the SOC storage potential of cropland soils for climate change mitigation. Here, based on 2301 comparisons from 158 peer-reviewed papers, a meta-analysis was conducted to explore management-induced SOC stock changes and their variations under different conditions. The results show that SOC stocks in the 0–20 cm layer were increased by 31.8% when chemical fertilization combined with manure application was compared with no fertilizer; 9.98% when no-tillage was compared with plow tillage; and 10.84% when straw return was compared with removal. The RMPs favorably increased SOC stock in arid areas, and in alkaline and fine-textured soils. Initial SOC, carbon-nitrogen ratio, and experimental duration could also affect SOC storage. Compared with the initial SOC stock, RMPs increased the SOC sequestration potential by 2.6–4.5% in the 0–20 cm soil depth, indicating that these practices can help China achieve targets to increase SOC by 4.0‰. Hence, it is essential to implement RMPs for climate change mitigation and soil fertility improvement.

Studies from global regions indicate promising avenues for maintaining and increasing soil organic carbon stocks

Studies from global regions indicate promising avenues for maintaining and increasing soil organic carbon stocks

Energy cover crops for biogas production increase soil organic carbon stocks: A modeling approach

AbstractEnergy cover crops for biogas production through anaerobic digestion (AD) are inserted between two primary crops. They replace either bare soil or nonharvested cover crops, and their management is usually intensified to produce more biomass. They allow the production of renewable energy as well as digestate, used as an organic fertilizer, without directly competing with food production. Because of the increased biomass production and export and of the return of a digested biomass to the soil, the impact of energy cover crops on soil organic carbon (SOC) is questioned. The objective of this paper was to study the difference in SOC stocks induced by the introduction of energy cover crops for AD coupled with the application of the resulting amount of digestate. We used the AD model Sys‐Metha combined with the soil C model AMG to simulate SOC stocks for 13 case studies in France, with scenarios comparing different intercrop management practices, with or without cover crops, harvested or not. Our results indicated that the higher biomass production of energy cover crops (from 6.7 to 11.1 t DM ha−1) in comparison with nonharvested cover crops (2 t DM ha−1) or bare soil led to higher humified C input (belowground input and digestate), despite the high C fraction exported in AD. This resulted in an increase in SOC stocks in comparison with nonharvested cover crops or bare soil (from 0.01 to 0.12 t C ha−1 year−1 over 30 years). The uncertainties in the model parameters did not modify these results. However, in the case of equal biomass production between energy cover crops and nonharvested cover crops, SOC stocks would be lower with energy cover crops.

Effects of recultivation on soil organic carbon sequestration in abandoned coal mining sites: a meta-analysis

Opencast coal mining results in high loss of soil organic carbon (SOC), which may be restored via recultivation. Common strategies include liming, topsoil application, and phytoremediation. It remains unclear, however, which parameters determine the effectiveness of these varying recultivation strategies especially regarding SOC sequestration. This meta-analysis analyses the effect of varying recultivation strategies on SOC sequestration under different climate and soil conditions (pH, texture, depth) as well as in relation to time, based on 404 data entries from 51 studies. All included climatic regions recorded increases in SOC stocks, with tropical soils showing the highest potential for relative gains at up to 637%. We demonstrate that loamy soils sequester twice as much newly introduced SOC than sand. Strategy-wise, the highest mean rate of SOC sequestration is achieved by forest after topsoil application (3.9 Mg ha−1 a−1), agriculture after topsoil application (2.3 Mg ha−1 a−1), and agriculture with topsoil and fertiliser application (1.9 Mg ha−1 a−1) with a response ratio of 304%, 281%, and 218%, respectively. Soils analysed to less then 40 cm depth show higher SOC sequestration rates (< 10 cm: 0.6 Mg ha−1 a−1, < 20 cm: 1.0 Mg ha−1 a−1, and 20–40 cm: 0.4 Mg ha−1 a−1; response ratio of 123%, 68%, and 73%, respectively) than those analysed to a depth of 41–80 cm (0.1 Mg ha−1 a−1; response ratio of 6%). In terms of pH, strongly acidic soils (pH < 4.5) and alkaline conditions (pH > 7) offer the most beneficial environment for SOC sequestration at 0.4 Mg ha−1 a−1 and 0.8 Mg ha−1 a−1, respectively (185% and 273% response). Given comparable SOC sequestration potentials of forest after topsoil application, agriculture without amendments, and forest without amendments, we recommend to weigh these strategies against each other. Potentially decisive aspects are short- vs. long-term economic gains, food security concerns, and—in case of agriculture—the risk of overintensification leading to losses in SOC. Our data suggests that amendments exert considerable influence on SOC sequestration and need to be introduced under careful consideration.

Long‐term manure application enhances organic carbon and nitrogen stocks in Mollisol subsoil

AbstractSubsoils contain half of the total soil organic carbon (SOC) that is supposed to be relatively more persistent than that present in the topsoil. Improving SOC and total nitrogen (TN) stocks in croplands is crucial to mitigate climate change and ensuring food security. However, our insight into how the management practices and climatic variables influence stocks of SOC and TN, and crop grain yields in the soil profile is limited. In this study, we assessed the long‐term impacts of mineral and manure fertilizers on SOC and TN stocks at soil profile levels (up to 100 cm), and cropping system (wheat–maize–soybean) grain yields. Results indicated that in the top 0–40‐cm layers SOC and TN stocks were the highest in manure plus mineral fertilizers (MNPK) compared with control, that is, non‐fertilized control (CK). Conversely, compared with NPK, sole application of manure (M) clearly increased SOC stocks by 19%, 40%, and 39% and TN stocks by 51%, 105%, and 116% in 40–60, 60–80, and 80–100 cm, respectively (p &lt; 0.05). Moreover, Pearson correlation revealed that climate variables, that is, mean annual temperature (MAT) affected both SOC and TN stocks in 0–40‐cm layers only of the soil profile. Our findings implicated that the sole application of manure (M) is vital to augment SOC and TN sequestration, particularly in the subsurface layers. However, trade‐offs between SOC and TN sequestration and crop yields should also need to be considered while making recommendations for SOC and TN stocks maintenance and increasing crop productivity in terms of management strategies.

Multi‐modelling predictions show high uncertainty of required carbon input changes to reach a 4‰ target

AbstractSoils store vast amounts of carbon (C) on land, and increasing soil organic carbon (SOC) stocks in already managed soils such as croplands may be one way to remove C from the atmosphere, thereby limiting subsequent warming. The main objective of this study was to estimate the amount of additional C input needed to annually increase SOC stocks by 4‰ at 16 long‐term agricultural experiments in Europe, including exogenous organic matter (EOM) additions. We used an ensemble of six SOC models and ran them under two configurations: (1) with default parametrization and (2) with parameters calibrated site‐by‐site to fit the evolution of SOC stocks in the control treatments (without EOM). We compared model simulations and analysed the factors generating variability across models. The calibrated ensemble was able to reproduce the SOC stock evolution in the unfertilised control treatments. We found that, on average, the experimental sites needed an additional 1.5 ± 1.2 Mg C ha−1 year−1 to increase SOC stocks by 4‰ per year over 30 years, compared to the C input in the control treatments (multi‐model median ± median standard deviation across sites). That is, a 119% increase compared to the control. While mean annual temperature, initial SOC stocks and initial C input had a significant effect on the variability of the predicted C input in the default configuration (i.e., the relative standard deviation of the predicted C input from the mean), only water‐related variables (i.e., mean annual precipitation and potential evapotranspiration) explained the divergence between models when calibrated. Our work highlights the challenge of increasing SOC stocks in agriculture and accentuates the need to increasingly lean on multi‐model ensembles when predicting SOC stock trends and related processes. To increase the reliability of SOC models under future climate change, we suggest model developers to better constrain the effect of water‐related variables on SOC decomposition.Highlights The feasibility of the 4‰ target was studied at 16 long‐term agricultural experiments. An ensemble of soil organic carbon models was used to estimate the uncertainty of the predictions. On average across the sites, carbon input had to increase by 119% compared to initial conditions. High uncertainty of the simulations was mainly driven by water‐related variables.

Effects of land clearing for agriculture on soil organic carbon stocks in drylands: A meta-analysis.

Agricultural activities have been expanding globally with the pressure to provide food security to the earth's growing population. These agricultural activities have profoundly impacted soil organic carbon (SOC) stocks in global drylands. However, the effects of clearing natural ecosystems for cropland (CNEC) on SOC are uncertain. To improve our understanding of carbon emissions and sequestration under different land uses, it is necessary to characterize the response patterns of SOC stocks to different types of CNEC. We conducted a meta-analysis with mixed-effect model based on 873 paired observations of SOC in croplands and adjacent natural ecosystems from 159 individual studies in global drylands. Our results indicate that CNEC significantly (p < .05) affects SOC stocks, resulting from a combination of natural land clearing, cropland management practices (fertilizer application, crop species, cultivation duration) and the significant negative effects of initial SOC stocks. Increases in SOC stocks (in 1m depth) were found in croplands which previously natural land (deserts and shrublands) had low SOC stocks, and the increases were 278.86% (95% confidence interval, 196.43%-361.29%) and 45.38% (26.53%-62.23%), respectively. In contrast, SOC stocks (in 1m depth) decreased by 24.11% (18.38%-29.85%) and 10.70% (1.80%-19.59%) in clearing forests and grasslands for cropland, respectively. We also established the general response curves of SOC stocks change to increasing cultivation duration, which is crucial for accurately estimating regional carbon dynamics following CNEC. SOC stocks increased significantly (p < .05) with high long-term fertilizer consumption in cleared grasslands with low initial SOC stocks (about 27.2Mg ha-1 ). The results derived from our meta-analysis could be used for refining the estimation of dryland carbon dynamics and developing SOC sequestration strategies to achieve the removal of CO2 from the atmosphere.

Optimizing crop rotation increases soil carbon and reduces GHG emissions without sacrificing yields

Enhancing soil organic carbon (SOC) while concurrently reducing greenhouse gas (GHG) emissions and without compromising yield is a contemporary challenge for many agricultural sectors across the globe. In China, resolving the "carbon- food" nexus is a key pillar of government policies aimed at constraining “Carbon Peak” and delivering “Carbon Neutrality”. The present study explores the potential to increase SOC stocks while reducing GHGs emissions, without sacrificing crop yields considering crop rotation optimization under different irrigation managements in the North China Plain (NCP) based on a 6-year experiment. We found higher crop yields for the irrigated treatments compared with the rainfed treatments, demonstrating that rainfed crops were constrained by water deficit stress in the region. Yield was highest in the winter wheat-summer maize rotation (WM), followed by yields of the winter wheat-summer soybean (WS), while the average yields of winter wheat-summer maize-spring maize (WMMs) were lowest. SOC stocks in the surface soil (0–20 cm) increased for the irrigated treatments, but soil carbon sequestration (i.e. the rate of SOC stocks change over time) for the rainfed treatments decreased for all treatments. SOC stocks for WMMs was greatest of all treatments, leading to the highest carbon sustainability index (CSI) for this treatment. Nitrous oxide (N2O) emissions were 23–57% higher in the irrigated treatments than the rainfed treatments for the three rotations, which was highest in WMMs and lowest in WS. Carbon footprints (CFs) were highest in WS and lowest in WMMs. Overall, we found that increasing SOC stocks reduced CFs and increased yield. WMMs with irrigation was the most effective treatment for promoting SOC sequestration and mitigating GHG emissions with relatively high yield in this study, suggesting that crop rotations that are (1) more intensive and (2) grow more aboveground biomass are more likely to promulgate lower CFs and contribute towards national emissions abatement targets, such as those aimed at Net Zero.

Fractions, stability, and influencing factors of soil organic carbon under different land-use in sodic soils

Salt-affected soils have considerable carbon sequestration potential in aboveground biomass and soil organic carbon (SOC). However, organic carbon pool characteristics and the significant important factors affecting the land use of sodic soils have not been clearly elucidated. In this study, 252 samples were collected from 20 typical sodic soil sites across the western Songnen Plain, China. This study investigated the effects of five land-use types, that is, saline wasteland (SWL), degraded grassland (GL), forestland (FL), upland (UL), and paddy fields (PF), on sodic soil SOC fractions and stabilities to find that UL and PF decreased salinity and alkalinity, but increased soil nutrient and water stability aggregate (WSA) contents and stability. Compared with degraded natural land-use types (SWL and GL), FL and croplands (UL and PF) increased the physical protection of SOC and aggregate-associated SOC contents. Furthermore, cropland, especially PF, increased nonlabile organic carbon (NOC) (7.47 g kg−1), labile organic carbon (LOC) (3.79 g kg−1), dissolved organic carbon (DOC) (0.16 g kg−1), and mineralizable organic carbon (MOC) (0.41 g kg−1) fractions. Furthermore, compared with degraded natural lands, PF increased NOC ratios (59.65%) and carbon management index (CMI) (126.1), thus increasing organic carbon content and stability. Structural equation modelling revealed that improvements in soil properties, total nitrogen (TN), WSA, electrical conductivity (EC), and pH were the crucial factors for increasing SOC stock in sodic soils. We concluded that the positive effect that PF had on SOC content and stability were much greater than that of the other land-use types, and that PF was the optimal management practice for increasing SOC sequestration capacity in sodic soils.