Increase Soil Organic Carbon Stocks Research Articles

How do soil organic carbon pool, stock and their stability respond to crop residue incorporation in subtropical calcareous agricultural soils?

Crop residue incorporation as general cropland management practice notably improves soil organic carbon (SOC) stock. However, the effects of crop residue input rate incorporation on SOC stability remain uncertain. Here, we conducted a 12-year field experiment to evaluate the long-term effects of crop residue incorporation on SOC stocks, stabilities, and their abiotic and biotic controls in subtropical calcareous soil under a maize-wheat rotation. Four experimental treatments, including no crop residue incorporation (control), 30% of harvested crop residue incorporation (CR30), 50% of harvested crop residue incorporation (CR50), and 100% of harvested crop residue incorporation (CR100), were implemented. Our results showed that the CR100 treatment significantly increased SOC stock by 25.6%, as compared with the control. Soil dissolved organic carbon (DOC) and particulate organic carbon (POC) contents for CR100 treatment were also significantly greater than those for the control, while no significant difference in soil microbial biomass carbon (MBC) content across different experimental treatments were found. POC content for CR50 was significantly lower than the other treatments. It is noteworthy that the relative abundance of Thaumarchaeota related to microbial SOC decompositions for CR100 was significantly lower than other experimental treatments. The temperature sensitivity (Q10) of SOC mineralization for CR50 treatment was significantly higher, as compared with other treatments. Nevertheless, the partial least squares path modeling analysis (PLS-PM) illustrated that soil aggregation and DOC content were the main regulators of Q10 for SOC mineralization thereby regulating the stability of SOC. Our results suggest that the practice of 100% of harvested crop residue incorporation is effective to increase the magnitude and the stability of SOC stocks in subtropical calcareous agricultural soils, in particular on a long-term basis.

Assessing Soil Organic Carbon, Soil Nutrients and Soil Erodibility under Terraced Paddy Fields and Upland Rice in Northern Thailand

Terracing is the oldest technique for water and soil conservation on natural hilly slopes. In Northern Thailand, terraced paddy fields were constructed long ago, but scientific questions remain on how terraced paddy fields and upland rice (non-terraced) differ for soil organic carbon (SOC) stocks, soil nutrients and soil erodibility. Therefore, this study aims to evaluate and compare SOC stocks, soil nutrients and soil erodibility between terraced paddy fields and upland rice at Ban Pa Bong Piang, Chiang Mai Province, Thailand. Topsoil (0–10 cm) was collected from terraced paddies and upland rice fields after harvest. Results showed that SOC stocks were 21.84 and 21.61 Mg·C·ha−1 in terraced paddy and upland rice fields, respectively. There was no significant difference in soil erodibility between terraced paddies (range 0.2261–0.2893 t·h·MJ−1·mm−1) and upland rice (range 0.2238–0.2681 t·h·MJ−1·mm−1). Most soil nutrients (NH4-N, NO3-N, available K, available Ca and available Mg) in the terraced paddy field were lower than those in the upland rice field. It was hypothesized that the continuous water flows from plot-to-plot until lowermost plot caused dissolved nutrients to be washed and removed from the flat surface, leading to a short period for accumulating nutrients into the soil. An increase in soil erodibility was associated with decreasing SOC stock at lower toposequence points. This study suggested that increasing SOC stock is the best strategy to minimize soil erodibility of both cropping systems, while proper water management is crucial for maintaining soil nutrients in the terraced paddy field.

Spring pasture renewal involving full inversion tillage and a summer crop can facilitate soil C storage, improve crop yields and lower N leaching

Soil organic carbon (SOC) sequestration in pastoral soils could offset net greenhouse gas emissions by reducing global atmospheric carbon dioxide (CO2) concentrations and, thereby, slow climate warming. Long-term pastures typically have topsoils (0–10 cm) rich in SOC, with subsoils (10–30 cm) storing less than half as much SOC. In New Zealand, lowland farmers are advised to renew (reseed) their pastures every 7–10 years to improve pasture production. Renewal typically involves desiccating the old pasture followed by shallow tillage (or direct drilling) to establish a short season forage crop as a weed break, then direct drilling new pasture species. Minimum till at renewal maintains the vertical stratification of SOC, limiting the scope to increase SOC stocks under new pasture. During the spring of 2016 and 2017, two independent trials were established, on an Alfisol (trial 1) and on an Andisol (trial 2), to assess the effects of establishing a summer Brassica crop with either full inversion tillage (FIT; 30 cm furrow depth, as a one-off or infrequent (every 25–30 years) management), shallow tillage or no-till (direct drill) on SOC stocks and crop/pasture agronomic performance. In autumn, new pasture species were direct drilled into the stubble of the summer forage crop. Changes in SOC vertical distribution, plant growth, herbage quality (at both trials) and nitrogen (N) leaching (trial 1 only) were monitored. At both trials, FIT effectively buried SOC below 0–10 cm depth and increased crop yields compared to no-till treatment. After re-grassing pasture production was similar among all treatments. In trial 1, N leaching losses were 42% lower under FIT than under no-till. These results highlight the potential agronomic and environmental benefits of pasture renewal including FIT. Economic and N cycling benefits depend on the timely inclusion of a crop phase.

Can Regenerative Agriculture increase national soil carbon stocks? Simulated country-scale adoption of reduced tillage, cover cropping, and ley-arable integration using RothC

Adopting Regenerative Agriculture (RA) practices on temperate arable land can increase soil organic carbon (SOC) concentration without reducing crop yields. RA is therefore receiving much attention as a climate change mitigation strategy. However, estimating the potential change in national soil carbon stocks following adoption of RA practices is required to determine its suitability for this. Here, we use a well-validated model of soil carbon turnover (RothC) to simulate adoption of three regenerative practices (cover cropping, reduced tillage intensity and incorporation of a grass-based ley phase into arable rotations) across arable land in Great Britain (GB). We develop a modelling framework which calibrates RothC using studies of these measures from a recent systematic review, estimating the proportional increase in carbon inputs to the soil compared to conventional practice, before simulating adoption across GB. We find that cover cropping would on average increase SOC stocks by 10 t·ha−1 within 30 years of adoption across GB, potentially sequestering 6.5 megatonnes of carbon dioxide per year (MtCO2·y−1). Ley-arable systems could increase SOC stocks by 3 or 16 t·ha−1, potentially providing 2.2 or 10.6 MtCO2·y−1 of sequestration over 30 years, depending on the length of the ley-phase (one and four years, respectively, in these scenarios). In contrast, our modelling approach finds little change in soil carbon stocks when practising reduced tillage intensity. Our results indicate that adopting RA practices could make a meaningful contribution to GB agriculture reaching net zero greenhouse gas emissions despite practical constraints to their uptake.

Defining Quantitative Targets for Topsoil Organic Carbon Stock Increase in European Croplands: Case Studies With Exogenous Organic Matter Inputs

The EU Mission Board for Soil Health and Food proposed a series of quantitative targets for European soils to become healthier. Among them, current soil organic carbon (SOC) concentration losses in croplands (0.5% yr−1 on average at 20 cm depth) should be reversed to an increase of 0.1–0.4% yr−1 by 2030. Quantitative targets are used by policy makers to incentivize the implementation of agricultural practices that increase SOC stocks. However, there are different approaches to calculate them. In this paper, we analyzed the effect of exogenous organic matter (EOM) inputs on the evolution of SOC stocks, with a particular focus on the new European targets and the different approaches to calculate them. First, we illustrated through two case-study experiments the different targets set when the SOC stock increase is calculated considering as reference: 1) the SOC stock level at the onset of the experiment and 2) the SOC stock trend in a baseline, i.e., a control treatment without EOM addition. Then, we used 11 long-term experiments (LTEs) with EOM addition in European croplands to estimate the amount of carbon (C) input needed to reach the 0.1 and 0.4% SOC stock increase targets proposed by the Mission Board for Soil Health and Food, calculated with two different approaches. We found that, to reach a 0.1 and 0.4% increase target relative to the onset of the experiment, 2.51 and 2.61 Mg C ha−1 yr−1 of additional C input were necessary, respectively. Reaching a 0.1 and 0.4% increase target relative to the baseline required 1.38 and 1.77 Mg C ha−1 yr−1 of additional input, respectively. Depending on the calculation method used, the estimated amounts of additional C input required to reach each quantitative target were significantly different from each other. Furthermore, the quality of C input as represented by the C retention rate of the additional organic material (EOM and crop residue), had a significant effect on the variation of SOC stocks. Our work highlights the necessity to take into consideration the additional C input required to increase SOC stocks, especially for soils with decreasing SOC stocks, when targets are set independently of the baseline.

Fungi determine increased soil organic carbon more than bacteria through their necromass inputs in conservation tillage croplands

Stover mulching over no-till soil is regarded as a promising practice to increase soil organic carbon (SOC) in croplands against climate change. Microbial necromass is a significant source of SOC stock and unequivocally controlled by the microbial community. Yet, a complete link that spans from agricultural practices to microbial community features, to soil necromass C, and eventually to SOC is poorly understood. Here, we conducted a 10-y corn field experiment with five treatments, which included conventional tillage (CT), no-tillage without stover (NT–0), and no-tillage with low, medium, and high amounts of stover mulching (NT–low, NT–medium, and NT–high) in a Molisol of northeastern China. We investigated the stocks and changes in total SOC and its microbial necromass C along a soil depth down to 40 cm, and we evaluated how SOC dynamics and stabilization processes were associated with microbial community features. We characterized microbial community diversity and structure using 16S rRNA and internal transcribed spacer (ITS) sequencing, and we characterized microbial biomass and necromass using phospholipid fatty acid and amino sugar biomarkers. Compared with conventional tillage, no-tillage with medium and high amounts of stover mulching increased SOC stocks in the upper 0–40 cm of soil by > 0.4% per year. No-tillage treatments (without and with stover) had almost no effect on the proportion of total microbial necromass C to SOC, but greatly modified the ratio of fungal necromass C to bacterial necromass C, which increased in top layers (0–5 cm) and decreased in deep layers (10–40 cm). SOC was governed mainly by fungal necromass C, which was correlated positively with fungal biomass. Fungal necromass C, not bacterial necromass C, was more closely associated with microbial community composition. Our results suggested that no-tillage with medium stover mulching was the optimal treatment to achieve the best trade-off between stover input and SOC storage. Differentiating microbial C pools from total SOC and, notably, separating fungal and bacterial necromass C pools can refine our mechanistic understanding of SOC storage as well as its association with microbial biota.

Impact of crop establishment and residue management on soil properties and productivity in rice‐fallow ecosystems in India

AbstractThe degradation of agricultural land, both chemical and biological, is a big concern all over the world. Crop cultivation practices that are distinctive to each location have negative consequences for agricultural production. Therefore, there is an urgent need for better crop and soil management techniques. This experiment was conducted for 5 years (2016–2020) to identify the best crop establishment‐cum‐residue management (CERM) practices and suitable crops for succession after the rice harvest in rice‐fallow ecosystems of India. Experimentation was conducted in the split‐plot design and each treatment was replicated thrice, having CERM in main‐plot and post‐rainy season/winter crops in sub‐plot. All the CERM treatments had two variants, with crop residue (R+) and without crop residue (R−). Rice yields were markedly higher (19.1%–32.2%) in transplanted puddled rice with residue (TPR‐R+) over conventional‐till direct seeded rice (CTDSR) and zero‐till DSR (ZTDSR) treatments. However, TPR adversely impacted the performance of all the post‐rainy pulses/oilseed crops. Post‐rainy season crop yields under ZTDSR/CTDSR were 14.9%–45.8% higher leading to higher system productivity as compared to TPR. ZTDSR with residue retention showed higher soil aggregation. The practice of ZTDSR increased the soil dehydrogenase activity (46.2%), urease activity (29.8%), soil microbial biomass carbon (65.4), and fluorescein diacetate activity (9.0%) in the crop root zone with 3.3‐ and 4.47‐times higher earthworm population and earthworm biomass, respectively. The rice‐pulse system showed 1.74‐times more earthworm population over rice‐oilseed sequences. Total soil organic carbon (SOC) stock in ZTDSR was 21.8% higher over TPR in 0–45 cm soil profile. Thus, the adoption of ZTDSR practices and diversification of rice‐fallows with pulses crops is recommended for enhancing the crop productivity, increasing SOC stock, and improving soil biological properties in the rice‐fallow ecosystems of India.

Mixed plantations enhance more soil organic carbon stocks than monocultures across China: Implication for optimizing afforestation/reforestation strategies

Forests play an essential role in mitigating climate change by sequestering carbon dioxide from the atmosphere. The establishment of mixed plantations is a promising way to store carbon (C) in soil compared with monocultures. However, monoculture forests largely dominate the rapid increase in forest areas in China. To optimize afforestation strategies and maximize the subsequent potential of C sequestration, we conducted a meta-analysis with 427 observations across 176 study sites in China. The goal was to quantify changes in the stocks of soil organic carbon (SOC) in mixed plantations compared with monocultures and to identify the predominant drivers for the stocks of SOC, including geological location, climatic factors, land use history, edaphic properties, plantation age, the inclusion of nitrogen-fixing trees, mixing proportion, and mixed plant types. The results showed that mixed plantations significantly increased the SOC stocks by 12% compared with monocultures, and the mixing proportion should not exceed 55% to produce higher SOC stocks in mixed plantations compared with monoculture. Additionally, mixed plantations in barren land are the most likely to increase the SOC stocks with limited water or low temperatures for growth. Additional measures instead of mixed plantations should be explored to increase SOC stocks in north, central, and northwest China. The data from this study demonstrated the spatiotemporal variability on the storage of SOC driven by mixed trees and has valuable implications for the establishment and management of afforestation.

Effects of straw and biochar amendment on hydrological fluxes of dissolved organic carbon in a subtropical montane agricultural landscape

Straw and biochar amendments have been shown to increase soil organic carbon (SOC) stocks in arable land; however, their effects on hydrological fluxes of dissolved organic carbon (DOC), which may offset the benefits of C sequestration amounts remain uncertain. Therefore, we conducted a three-year field study that included four treatments (CK, control with no fertilizer; NPK, synthetic N fertilizer; RSDNPK, synthetic N fertilizer plus crop residues; BCNPK, synthetic N fertilizer plus biochar of crop straw) to investigate the effects of straw and biochar amendment on DOC losses through hydrological pathways of overland flow and interflow from a wheat-maize rotation system in the subtropical montane agricultural landscape. We detected substantial intra- and inter-annual variations in runoff discharge, DOC concentration, and DOC fluxes for both overland flow and interflow pathways, which were primarily attributed to variations in rainfall amount and intensity. On average, the DOC concentrations for interflow (2.98 mg C L−1) were comparable with those for overland flow (2.71 mg C L−1) throughout the three-year experiment. However, average annual DOC fluxes for interflow were approximately 2.60 times greater than those for overland flow, which probably related to higher runoff discharges of interflow than overland flow. Compared to the control, on average, the N fertilization treatments significantly decreased the annual DOC fluxes of overland flow and significantly increased annual DOC fluxes of interflow. Relative to the application of synthetic N fertilizer only, on average, crop straw amendment practice significantly increased annual DOC fluxes of interflow by 28.7%, while decreasing annual DOC fluxes of overland flow by 12.0%; in contrast, biochar amendment practice decreased annual DOC fluxes of interflow by 25.3% while increasing annual DOC fluxes of overland flow by 44.6%. Overall, considering both overland flow and interflow, crop straw amendment significantly increased hydrological DOC fluxes, whereas biochar had no significant effects on hydrological DOC fluxes throughout the three-year experiment. We conclude that crop straw incorporation strategies that aim to increase SOC stocks may enhance hydrological losses of DOC, thereby in turn offsetting its benefits in the subtropical montane agricultural landscapes.

Soil organic carbon content and stock change after half a century of intensive cultivation in a chernozem area

Soil organic carbon (SOC) is a significant soil parameter controlling soil quality and productivity and also playing an essential role in the global carbon cycle. Assessment of long-term SOC content and stocks changes is only possible by comparing historical and present data. The Czech Republic holds a national database of agricultural soils completed during the 1960s, which we used to assess SOC changes. SOC content and stock changes were detected after more than 50 years of intensive cultivation in a rolling chernozem landscape prone to soil erosion by re-sampling soil profiles from the 1960s and assessing these changes in relation to local topography. Each re-sampled soil profile was classified based on its position within the terrain, into one of three distinct slope positions namely shoulder slope (SH), backslope (BS), and foot slope (FS) which refers to a predisposition to soil erosion (SH, BS) or deposition (FS). Despite previous studies reporting SOC content decline over the past several decades, our results showed an increase in SOC content in all slope positions, being the most pronounced at FS position. However, median value for the SOC stock significantly decreased at SH positions primarily due to intensive erosion (decreased by 2.82 kg·m−2). At the FS positions, the median value for the SOC stock increased but not significantly (increased by 5.51 kg·m−2). Changes in the SOC stock were primarily driven by changes in the topsoil depth, which significantly decreased at the SH positions by 22 cm; the opposite result was found for the FS position. The local topography as a driver of SOC stock changes was further supported by the significant correlation between SOC stock changes and topographical attributes (predominantly with Multiresolution Valley Bottom Flatness index, Topographic position index or Topographic wetness index) showing increasing SOC stocks in terrain depressions or valley bottoms due to soil accumulation. We concluded that soil erosion is a dominant process in our study area, explaining the long-term changes in SOC stock.

Increasing soil organic carbon pools and wheat yields by optimising tillage and fertilisation on the Loess Plateau in China

AbstractThe effect of conservation tillage on soil organic carbon (SOC) sequestration and crop production is controversial in semi‐arid areas. In addition, fertilisation is another essential factor affecting soil carbon pool and crop yields. We sought to explore the changes of SOC pool and crop productivity after optimising fertilisation and tillage. An 11‐year field experiment on the Loess Plateau in China was conducted to evaluate the effects of (i) fertilisation (balanced fertilisation, low fertilisation, conventional fertilisation) and (ii) tillage (no‐tillage, subsoiling, ploughing) on input‐C, SOC stocks, labile C fractions, C pool management index (CMI) and wheat yield. SOC stock accumulation at 0–35 cm depth under balanced fertilisation increased by 59% compared to conventional fertilisation due to the larger amount and stabilisation efficiency of input‐C. Simultaneously, balanced fertilisation increased labile C contents and CMI at 0–10 cm depth. For tillage, no‐tillage and subsoiling improved input‐C and its stabilisation efficiency, and increased SOC stocks compared to ploughing. Balanced fertilisation combined with no‐tillage or subsoiling produced greater SOC stocks at 0–35 cm depth compared to other treatments. No‐tillage increased labile C contents and CMI at 0–10 cm depth, while subsoiling increased labile C contents and CMI at 0–10 and 35–50 cm depths. Wheat yield and sustainable yield index (SYI) were positively correlated with SOC, and the effect of SOC contributed to SYI largely through indirect effects of dissolved organic C and particulate organic C. Wheat yield and SYI were increased by optimising fertilisation and tillage, and the greatest yield was under balanced fertilisation combined with the subsoiling treatment. Our findings suggested that balanced fertilisation combined with subsoiling was an effective practice for increasing SOC sequestration, soil quality, wheat yields and had great potential application on the Loess Plateau in China.Highlights C sequestration under conservation tillage and fertilisation are controversial in semi‐arid areas. Balanced fertilisation promoted SOC sequestration in no‐tillage and subsoiling treatments. Subsoiling improved soil quality at 0–10 and 35–50 cm depths due to the greater SOC and labile C. Subsoiling was superior to no‐tillage and ploughing in maintaining crop productivity.

Soil carbon-food synergy: sizable contributions of small-scale farmers

BackgroundBenefits to agricultural yield improvement, soil degradation prevention, and climate mitigation are central to the synergies of soil organic carbon (SOC) build-up. However, the contributions of small-scale farmers, the main target of recent agricultural and rural development policies, to SOC enhancement are understudied. Here, we present a global analysis of small-scale farmers’ contributions to the potential of additional SOC stocks and the associated increase in crop production.MethodsWe applied random forest machine learning models to global gridded datasets on crop yield (wheat, maize, rice, soybean, sorghum and millet), soil, climate and agronomic management practices from the 2000s (n = 1808 to 8123). Using the established crop-specific SOC-yield relationships, the potentials of additional SOC build-up and crop production increase were simulated. The estimated SOC increase was converted into global decadal mean temperature change using the temperature sensitivity to cumulative total anthropogenic CO2 emissions from preindustrial levels. The amount of inorganic nitrogen (N) input that would result in the same yield outcome as the SOC build-up was derived from the crop-specific N-yield relationships.ResultsSOC contributes to yields in addition to management and climatic factors. Additional SOC sums up to 12.78 GtC (11.55–14.05 GtC) of global SOC stock, which earns 38.24 Mt (22.88–57.48 Mt) of additional crop production and prevents warming by 0.030 °C (0.019–0.041 °C). This production increase equates to what would be achieved by an inorganic N input of 5.82 Mt N (3.89–7.14 Mt N). Small-scale farmers account for 28% (26–30%) of the additional SOC build-up and 17% (15–20%) of the production increase. Key crops and regions in terms of small-scale farmers’ contributions include Sub-Saharan African maize and rice, Latin American and Caribbean soybean and maize, and South Asian rice and wheat.ConclusionsThe contribution of small-scale farmers to the potential increase in SOC stock and crop production is sizable, which in theory further leads to saving inorganic N input. These findings emphasize the importance of linking soil management to sustainable land and climate mitigation with institutions and policy for small-scale farmers. Such a joint policy would assist multiple development goals.

Optimization of tillage rotation and fertilization increased the soil organic carbon pool and crop yield in a semiarid region

AbstractTillage and mineral fertilization are important strategies for maintaining crop production, but their effects on soil organic carbon (SOC) and labile fractions in semiarid regions are controversial. A 10‐year field experiment was conducted to evaluate the effects of fertilization and tillage on SOC stock, labile fractions, soil quality and crop yields in a wheat–maize cropping system at the Loess Plateau. Results showed that balanced fertilization could provide comprehensive nutrition for crops and increase the crop residue input carbon, thereby increasing the SOC, readily oxidizable carbon, particulate organic carbon and dissolved organic carbon contents. In 0–50 cm layers, the SOC stock was increased by 3% under balanced fertilization compared to conventional fertilization. For tillage, no‐tillage (zero tillage) and subsoiling rotation with less soil disturbance and higher stabilization rate of input carbon was the most effective tillage practice for increasing SOC stock. This tillage technique increased the labile carbon contents by 41%–63%, 5%–19% and 26%–67% compared to ploughing in 0–10 cm, 20–35 cm and 35–50 cm layers, respectively. Balanced fertilization combined with no‐tillage and subsoiling rotation (BF + NS) increased carbon pool management index due to higher SOC and labile carbon contents, which contributed to the improvement of soil quality and the promotion of crop growth. Among all treatments, BF + NS treatment produced the highest SOC stock as well as wheat and maize yields. Therefore, BF + NS is the best strategy to increase SOC sequestration and to improve soil quality and productivity in semiarid regions.

Soil carbon stocks and water stable aggregates under annual and perennial biofuel crops in central Ohio

Biofuels have the potential to mitigate global warming by partially replacing fossil fuels. Long-term cultivation of bioenergy crops may affect soil quality and C exchange between the soil-plant-atmosphere continuum depending upon crop type and duration of cultivation. Thus, studies are needed to compare the impact different bioenergy crops have on soil organic carbon (SOC) stocks to estimate the net C mitigation potential of these crops. This study reports on changes in soil properties and C stocks after eight years of annual no-till (NT) corn (Zea mays L.), sorghum (Sorghum bicolor L.), perennial switchgrass (Panicum virgatum L.), miscanthus (Miscanthus x giganteus), and polyculture prairie cultivation in central Ohio. Perennial biofuel crops (PBCs) improved soil health by reducing soil bulk density, increasing soil porosity, and improving soil aggregate stability compared to those under annual bioenergy crops (ABCs). Changes were most prominent in the surface 0–10 cm soil layer. Bulk density decreased by 14.4% and 12.8% under PBCs and 6.0% and 5.7% under ABCs in the 0–10 cm and 10–20 cm depths, respectively. Water stable aggregate values in the PBC systems were 29.6% (0–10 cm) and 23.0% (10–20 cm) greater than those in the ABC systems with maximum and the minimum values observed under miscanthus (95.1%) and corn (70.2%). PBC systems retained 71% of overall aggregates within the > 4.75 mm size fraction after wet sieving and 2% in the < 0.25 mm size fraction, compared to ABCs retaining 20% and 28% of total aggregates within these two aggregate size fractions, respectively. C and N accumulation were greater in macroaggregates (>0.25 mm) compared to microaggregates (<0.25 mm). The SOC stock within the first eight years of the study decreased by 8.25 Mg C ha−1 (annual rate of −1.03 Mg C ha−1 y−1) for the ABC systems. In contrast, the SOC stock under PBCs for the first eight years increased by 7.94 Mg C ha−1 at an annual rate of 0.99 Mg C ha−1 y−1. These data indicate that PBCs enhanced SOC stocks and provided the dual benefit of increasing SOC stock and improving soil properties. The rate and cumulative amount of SOC sequestration were the highest under miscanthus and the least under sorghum. However, more information is needed on the C life-cycle of biofuel crops and profile C changes to evaluate the net C mitigation potential.

Can Wet Aggregate Stability and Texture Regulate Organic Carbon Stock in Alluvial Soils of East Champaran (Bihar)?

Aims: Here in this experiment, the investigation was done for the relationship among the various soil health parameters i.e., soil organic carbon (SOC), soil texture, and wet aggregate stability (WAS).&#x0D; Place and Duration of Study: Sample: Collection of soil samples were done from 0-15 cm depth from East Champaran is situated in Bihar and is located at 26038’N and 84054’E in the year 2019-2020.&#x0D; Methodology: Soil texture: 14g (+/- 0.1g) of sieved soil was added to a 50 ml centrifuge tube holding 42 ml of a dispersant 3% sodium hexametaphosphate solution follwed by 2 hr shaking and 0.053 mm sieved. Water stable aggregates: Each 0.25-mm sieve contained 4g of air-dried, 2-mm aggregate soil. Each sample's precise weight was recorded. The soil samples were dispersed for 3 minutes with 100 mL distilled water and then for 10 minutes with a 2 g/L sodium hexametaphosphate solution. Pre-weighed filter sheets were used to filter both solutions. Each filter paper was weighed after being oven-dried at 105°C.&#x0D; Soil organic carbon: The amount of soil organic carbon (SOC) was calculated using the Walkley and Black technique (1934).&#x0D; Results: Wet aggregate stability and soil organic carbon storage were shown to have a strong positive connection. Soil carbon stock in soils of East Champaran varied between 5.27-19.60 Mg ha-1 with an average of 12.98 Mg ha-1. WAS ranged from 3.82 to 36.43% with a mean of 16.11%. The results revealed that WAS increased with increase in SOC stock. This experiment also revealed that clay (%) and silt (%) directly affect WAS and hence enhance SOC storage.&#x0D; Conclusion: So, it can be concluded that WAS and soil texture directly and positively impact SOC storage in soils of East Champaran, Bihar.

Factors shaping soil organic carbon stocks in grass covered orchards across China: A meta-analysis

Orchard grass coverage has been widely adopted to increase fruit yield by improving soil fertility. However, the impact of the environment on the changes in soil organic carbon (SOC) stocks consecutive to orchard grass coverage remain poorly quantified at a large scale. The present study aimed to examine the responses of SOC stocks to grass coverage at a soil depth of 0–30 cm in orchards compared to clean tillage. A total of 342 observations across China from 139 peer-reviewed publications were subjected to meta-analysis. Aggregated boosted tree analysis was performed, evaluating the determinants of SOC stocks, such as plant traits (e.g., fruit tree type, grass type, orchard age, and grass age), edaphic variables (e.g., initial SOC and nitrogen concentration, soil pH, and soil clay content), climatic factors (e.g., mean annual precipitation (MAP) and mean annual temperature (MAT)), and management practices (e.g., grass source, grass growing mode, fertilization, grass mowing, placement of mowed residues, and irrigation). On average, orchard grass coverage significantly enhanced SOC stocks by 21.47% (percentage change) compared to clean tillage. Biotic and abiotic factors influenced this increase in SOC stocks following grass coverage in orchards to different extents. Grass age and soil clay content were the main determinants driving the variation in the SOC stocks following grass coverage in orchards. Thus, we propose an efficient way to optimize C sequestration in grass covered orchards, regarding plant traits, climatic factors, edaphic variables, and management practices. Longer than 12 months of surface grass coverage with cultivated grass species in mature deciduous fruit orchards (≥5 years) efficiently increased SOC stocks. This is particularly the case for acidic (pH < 6.5) soils with low C content (SOM < 15 g kg−1) in areas with suitable rainfall and temperature conditions (MAP ≥ 400 mm, MAT ≥ 10 °C). Collectively, this meta-analysis identified orchard grass coverage as a promising practice for significantly increasing SOC stocks at 0–30 cm across large geospatial locations in China.

Positive Effects of Legumes on Soil Organic Carbon Stocks Disappear at High Legume Proportions Across Natural Grasslands in the Pyrenees

Soil is the largest terrestrial carbon pool, making it crucial for climate change mitigation. Soil organic carbon (SOC) is suggested to depend on biodiversity components, but much evidence comes from diversity-function experiments. To disentangle the relationships of plant guild diversity with SOC storage (kg m−2) at broad spatial scales, we applied diversity-interaction models to a regional grassland database (n = 96) including wide environmental conditions and management regimes. The questions were: (1) Are the effects of plant guilds on SOC stocks in natural grasslands consistent with those found in experimental systems? (2) Are plant guild effects on SOC stocks independent of each other or do they show interactive—synergistic or antagonistic—effects? (3) Do environmental variables, including abiotic and management, modify guild effects on SOC stocks? Among our most novel results we found, legume effects on grassland SOC vary depending on legume proportion consistently across broad spatial scales. SOC increased with legume proportion up to 7–17%, then decreased. Additionally, these effects were strengthened when grasses and forbs were codominant. Grazing intensity modulated grass proportion effects on SOC, being maximum at relatively high intensities. Interpreting our results in terms of existing contrasted ecological theories, we confirmed at broad spatial scales and under wide-ranging environmental conditions the positive effects of plant guild diversity on SOC, and we showed how legumes exert a keystone effect on SOC in natural grasslands, probably related to their ability to fix inorganic N. Niche complementarity effects were illustrated when codominance of forbs and grasses at optimum legume proportions boosted SOC storage, whereas grass dominance increased SOC stocks at medium–high grazing intensities. These findings can facilitate the preparation of regional and local strategies to ameliorate the soil capacity to absorb carbon.

Livestock Increase Soil Organic Carbon in the Northern Great Plains

Managing grasslands to sequester carbon is of global importance, but effects of grazing on soil organic carbon (SOC) stocks remain uncertain. We quantified effects of livestock grazing (grazed or not for 9−26 yr) and soil texture on SOC stocks (kg × m−2) of 20 sites in a temperate grassland. We also quantified the effects of livestock grazing on SOC concentration and bulk density. Percent sand explained a considerable amount of the variation in SOC stock (r2 = 0.45 to 0.59). In addition, SOC stocks were 12% less in areas rested from livestock grazing (i.e., not grazed) than annually grazed. Soil carbon concentrations were also 10% less in rested than grazed areas. Bulk density was 2% less in areas rested from grazing, but bulk density was greater at sites with longer periods of rest. We also detected a grazing treatment and rest duration interaction, indicating that bulk density differences between grazing treatments tended to be greater at sites with longer periods of rest. Compared with no grazing, moderate grazing tended to increase SOC stocks and concentrations. Although compaction (i.e., increase in bulk density) is generally regarded as an indicator of declining soil health, minor compaction may help reduce mineralization of SOC and ultimately increase SOC stocks. We discuss methodological improvements needed for a next generation of grazing land experiments to better resolve how best to manage livestock and sequester carbon.

Responses of soil organic carbon stock to animal manure application: A new global synthesis integrating the impacts of agricultural managements and environmental conditions.

Enhancing soil organic carbon (SOC) through applying animal manure is of interest for both sustaining cereal production and mitigating greenhouse gas (GHG) emissions. Previous syntheses showed that manuring-induced SOC changes varied substantially with agricultural managements and environmental conditions, while their significance and relative importance to such variability are still largely uncertain. Here, we presented a new synthesis using an updated and balanced database integrating the manuring-induced SOC stock changes and their plausible explanatory factors in 250 observations at global 120sites. Manure application increased SOC stock by 7.41±1.14 (95% confidence interval, CI) and 8.96±1.83 (95% CI) MgCha-1 , respectively, compared to their mineral fertilized (REF-min) and unfertilized (REF-zero) references. Of which approx. 72% and 34% were directly contributed by manure-C input, respectively. Following the IPCC (Intergovernmental Panel on Climate Change) approach, these changes corresponded to the manuring-induced SOC change factors of 1.27±0.04 (95% CI) and 1.40±0.08 (95% CI), respectively. Basing on a balanced database, we identified the amount of manure-C input as the most important factor to the global variations in the resultant SOC stock changes. More importantly, our integrative analysis distinguished the significance of soil properties (e.g., soil pH and initial SOC content) in regulating the efficiency of manure application in enhancing SOC stock. These results indicate that, at the similar rate, applying manure could sequestrate much more carbon in alkaline soils than in neutral and acidic soils. By integrating the impacts of agricultural managements and environmental conditions, our findings would help to develop region-specific tailor-made manure application measures in agriculture and to refine the SOC change factors for regional GHG inventories.

No changes in soil organic carbon and nitrogen following long-term prescribed burning and livestock exclusion in the Sudan-savanna woodlands of Burkina Faso

Fire and overgrazing reduce aboveground biomass, leading to land degradation and potential impacts on soil organic carbon (SOC) and total nitrogen (TN) dynamics. However, empirical data are lacking on how prescribed burning and livestock exclusion impact SOC in the long-term. Here we analyse the effects of 19 years of prescribed annual burning and livestock exclusion on tree density, SOC and TN concentrations in the Sudanian savanna ecoregion at two sites (Tiogo and Laba) in Burkina Faso. Results revealed that neither livestock exclusion nor prescribed burning had significant impact on SOC and TN concentrations. The results at both sites indicate that 19 years of livestock and fire exclusion did not result in a significant increase in tree density compared to grazing and annual prescribed burning. The overall mean (± SEM) of SOC stocks in the 0–50 cm depth increment in the unburnt (53.5 ± 4.7 Mg C ha−1) and annually burnt (56.4 ± 4.3 Mg C ha−1) plots at Tiogo were not statistically different. Similarly, at Laba there was no significant difference between the corresponding figures in the unburnt (37.9 ± 2.6 Mg ha−1) and in the annually burnt plots (38.6 ± 1.9 Mg ha−1). Increases in belowground inputs from root turnover may have countered changes in aboveground biomass, resulting in no net change in SOC and TN. We conclude that, contrary to our expectation and current policy recommendations, restricting burning or grazing did not result in increase in SOC stocks in this dry savanna ecosystem.