Soil Organic Carbon Sequestration Potential Research Articles

Fine resolution map of top- and subsoil carbon sequestration potential in France

Although soils have a high potential to offset CO2 emissions through its conversion into soil organic carbon (SOC) with long turnover time, it is widely accepted that there is an upper limit of soil stable C storage, which is referred to SOC saturation. In this study we estimate SOC saturation in French topsoil (0–30cm) and subsoil (30–50cm), using the Hassink equation and calculate the additional SOC sequestration potential (SOCsp) by the difference between SOC saturation and fine fraction C on an unbiased sampling set of sites covering whole mainland France. We then map with fine resolution the geographical distribution of SOCsp over the French territory using a regression Kriging approach with environmental covariates. Results show that the controlling factors of SOCsp differ from topsoil and subsoil. The main controlling factor of SOCsp in topsoils is land use. Nearly half of forest topsoils are over-saturated with a SOCsp close to 0 (mean and standard error at 0.19±0.12) whereas cropland, vineyard and orchard soils are largely unsaturated with degrees of C saturation deficit at 36.45±0.68% and 57.10±1.64%, respectively. The determinant of C sequestration potential in subsoils is related to parent material. There is a large additional SOCsp in subsoil for all land uses with degrees of C saturation deficit between 48.52±4.83% and 68.68±0.42%. Overall the SOCsp for French soils appears to be very large (1008Mt C for topsoil and 1360Mt C for subsoil) when compared to previous total SOC stocks estimates of about 3.5Gt in French topsoil. Our results also show that overall, 176Mt C exceed C saturation in French topsoil and might thus be very sensitive to land use change.

Matching policy and science: Rationale for the ‘4 per 1000 - soils for food security and climate’ initiative

At the 21st session of the United Nations Framework Convention on Climate Change (UNFCCC, COP21), a voluntary action plan, the ‘4 per 1000 Initiative: Soils for Food Security and Climate’ was proposed under the Agenda for Action. The Initiative underlines the role of soil organic matter (SOM) in addressing the three-fold challenge of food and nutritional security, adaptation to climate change and mitigation of human-induced greenhouse gases (GHGs) emissions. It sets an ambitious aspirational target of a 4 per 1000 (i.e. 0.4%) rate of annual increase in global soil organic carbon (SOC) stocks, with a focus on agricultural lands where farmers would ensure the carbon stewardship of soils, like they manage day-to-day multipurpose production systems in a changing environment. In this paper, the opportunities and challenges for the 4 per 1000 initiative are discussed. We show that the 4 per 1000 target, calculated relative to global top soil SOC stocks, is consistent with literature estimates of the technical potential for SOC sequestration, though the achievable potential is likely to be substantially lower given socio-economic constraints. We calculate that land-based negative emissions from additional SOC sequestration could significantly contribute to reducing the anthropogenic CO2 equivalent emission gap identified from Nationally Determined Contributions pledged by countries to stabilize global warming levels below 2 °C or even 1.5 °C under the Paris agreement on climate. The 4 per 1000 target could be implemented by taking into account differentiated SOC stock baselines, reversing the current trend of huge soil CO2 losses, e.g. from agriculture encroaching peatland soils. We further discuss the potential benefits of SOC stewardship for both degraded and healthy soils along contrasting spatial scales (field, farm, landscape and country) and temporal (year to century) horizons. Last, we present some of the implications relative to non-CO2 GHGs emissions, water and nutrients use as well as co-benefits for crop yields and climate change adaptation. We underline the considerable challenges associated with the non-permanence of SOC stocks and show how the rates of adoption and the duration of improved soil management practices could alter the global impacts of practices under the 4 per 1000 initiative. We conclude that the 4 per 1000 initiative has potential to support multiple sustainable development goals (SDGs) of the 2030 Agenda. It can be regarded as no-regret since increasing SOC in agricultural soils will contribute to food security benefits that will enhance resilience to climate change. However, social, economic and environmental safeguards will be needed to ensure an equitable and sustainable implementation of the 4 per 1000 target.

Carbon Sequestration Potential Promoted by Oxalate Extractable Iron Oxides through Organic Fertilization

Core Ideas Organic fertilization increased the oxalate extractable iron oxides. Oxalate extractable iron oxides contributed to soil organic carbon sequestration. Soil organic carbon from 20 to 40 cm was more labile than that from 0 to 20 cm. Oxalate extractable iron oxides preferentially preserved aromatic compounds. Carbon sequestration in paddy soils through organic fertilization is of great importance for soil quality improvement in subtropical Asia. This study explored the effect of oxalate extractable iron oxides (Feo) on soil organic carbon (SOC) sequestration in response to different fertilization treatments. Soil samples were collected from 0‐ to 10‐cm, 10‐ to 20‐cm, and 20‐ to 40‐cm depth intervals in June 2016 after a wheat (Triticum aestivum L.) harvest. This study involved five treatments: control with no fertilizer (CK), chemical fertilizer (NPK), 50% chemical fertilizer plus manure (NPKM), 100% chemical fertilizer plus straw (NPKS), and 30% chemical fertilizer plus manure organic‐inorganic compound fertilizer (NPKMOI). Organic fertilization significantly (P < 0.05) increased the SOC content and the Feo concentration compared with chemical fertilization alone. The specific C mineralization rate (SCMR, rate per unit SOC) increased with increasing soil depths, suggesting that SOC at the 20‐ to 40‐cm depth was more labile than that from 0 to 20 cm. The percentage of SOC present as microbial biomass carbon (MBC) was significantly (P < 0.001) positively correlated with SCMR, indicating that soil microorganisms influenced the potential SOC mineralization. Furthermore, the alternation of drying and wetting in paddy soils drives the biogeochemical cycles of iron and SOC, during which organic fertilization promotes the accumulation of Feo possibly by forming organo‐iron complexes as indicated by the higher Feo content in NPKM than in NPK. The Feo was significantly (P < 0.001) positively correlated with SOC and the percentage of aromatic C, indicating that Feo may play an important role in preserving SOC, especially the aromatic compounds. Therefore, the enhancement of Feo by organic fertilization, especially organic manure that is enriched in aromatic compounds, improved the SOC sequestration potential in the rice (Oryza sativa)–wheat rotation system.

Soil carbon sequestration potential of permanent pasture and continuous cropping soils in New Zealand.

Understanding soil organic carbon (SOC) sequestration is important to develop strategies to increase the SOC stock and, thereby, offset some of the increases in atmospheric carbon dioxide. Although the capacity of soils to store SOC in a stable form is commonly attributed to the fine (clay+fine silt) fraction, the properties of the fine fraction that determine the SOC stabilization capacity are poorly known. The aim of this study was to develop an improved model to estimate the SOC stabilization capacity of Allophanic (Andisols) and non-Allophanic topsoils (0-15cm) and, as a case study, to apply the model to predict the sequestration potential of pastoral soils across New Zealand. A quantile (90th) regression model, based on the specific surface area and extractable aluminium (pyrophosphate) content of soils, provided the best prediction of the upper limit of fine fraction carbon (FFC) (i.e. the stabilization capacity), but with different coefficients for Allophanic and non-Allophanic soils. The carbon (C) saturation deficit was estimated as the difference between the stabilization capacity of individual soils and their current C concentration. For long-term pastures, the mean saturation deficit of Allophanic soils (20.3mg C g-1 ) was greater than that of non-Allophanic soils (16.3mg C g-1 ). The saturation deficit of cropped soils was 1.14-1.89 times that of pasture soils. The sequestration potential of pasture soils ranged from 10t C ha-1 (Ultic soils) to 42t C ha-1 (Melanic soils). Although meeting the estimated national soil C sequestration potential (124Mt C) is unrealistic, improved management practices targeted to those soils with the greatest sequestration potential could contribute significantly to off-setting New Zealand's greenhouse gas emissions. As the first national-scale estimate of SOC sequestration potential that encompasses both Allophanic and non-Allophanic soils, this serves as an informative case study for the international community.

Do land use change and check-dam construction affect a real estimate of soil carbon and nitrogen stocks on the Loess Plateau of China?

Land use change and check-dam construction have been widely considered as the major measures to reduce soil and water loss. However, whether catchments behave as sources or sinks of soil carbon and nitrogen based on the combined performance of land use change and check-dam construction in sub-catchment systems are still poorly known. To quantitatively assess the effect of land use change and check-dam construction on soil organic carbon (SOC) and total soil nitrogen (TSN) stocks, and to explore the dominate factor influencing SOC and TSN sequestration potential, three sub-catchments controlled by check-dams were selected in the small catchment on the loess plateau of China. The SOC and TSN content and soil physic-chemical properties were analyzed under different land use types (farmland, grassland, shrubland, forestland, and check-dam land). Results clearly showed that the conversion from farmland to grassland and forestland induced an increase of SOC and TSN (1.32-fold C and1.36-fold N increase in grassland and 1.24-fold C and1.20-fold N increase in forestland, respectively). Comparing sediments to the corresponding source soil, the average enrichment ratios (ER) for SOC and TSN in sediments trapped behind check-dams were lower than 1 (0.56±0.10 and 0.65±0.12, respectively), and check-dam construction induced a net C and N loss (19.38% and 10.61%, respectively). The amount of SOC and TSN in three sub-catchments showed a significant positive correlation with the controlled watershed area (P<0.05). High proportion of forestland and years after construction contributed positively to SOC and TSN stocks per unit area in check-dam (P<0.05), indicating that the controlled watershed area, forestland fraction, and years after construction other than soil erosion were also the dominate influencing factors to affect carbon and nitrogen sequestration potential. The results indicated that, although erosion-induced soils and associated SOC and TSN were redistributed at the landscape scale, land use change and check-dam construction might still cause the catchment to behave as soil C and N sinks within the soil erosion subsystem since the 1999s.

Soil organic carbon sequestration by shelterbelt agroforestry systems in Saskatchewan

Carbon (C) sequestration through the implementation of agroforestry practices is identified as one of the major strategies in the reduction of carbon dioxide (CO2) emissions from the agricultural sector. The objective of this study was to examine the soil organic carbon (SOC) sequestration potential of major shelterbelt species, including green ash (Fraxinus pennsylvanica), hybrid poplar (Populus spp.), Manitoba maple (Acer negundo), white spruce (Picea glauca), Scots pine (Pinus sylvestris), and caragana (Caragana arborescens), ranging in age from 5 to 63 yr. Soil samples (0–50 cm) were collected for six major shelterbelt species and adjacent agricultural fields, and SOC concentration was determined. Shelterbelts had a significantly higher amount of SOC compared with adjacent agricultural fields, with an average difference of 18.6 Mg C ha−1 in the top 50 cm soil. An additional 3–8 Mg C ha−1 was contained in the tree litter layer. Younger shelterbelts (age less than 20 yr) tended to lose SOC in the early ...

Future C loss in mid-latitude mineral soils: climate change exceeds land use mitigation potential in France.

Many studies have highlighted significant interactions between soil C reservoir dynamics and global climate and environmental change. However, in order to estimate the future soil organic carbon sequestration potential and related ecosystem services well, more spatially detailed predictions are needed. The present study made detailed predictions of future spatial evolution (at 250 m resolution) of topsoil SOC driven by climate change and land use change for France up to the year 2100 by taking interactions between climate, land use and soil type into account. We conclude that climate change will have a much bigger influence on future SOC losses in mid-latitude mineral soils than land use change dynamics. Hence, reducing CO2 emissions will be crucial to prevent further loss of carbon from our soils.

Spatio-temporal variations in organic carbon density and carbon sequestration potential in the topsoil of Hebei Province, China

Reliable prediction of soil organic carbon (SOC) density and carbon sequestration potential (CSP) plays an important role in the atmospheric carbon dioxide budget. This study evaluated temporal and spatial variation of topsoil SOC density and CSP of 21 soil groups across Hebei Province, China, using data collected during the second national soil survey in the 1980s and during the recent soil inventory in 2010. The CSP can be estimated by the method that the saturated SOC content subtracts the actual SOC associated with clay and silt. Overall, the SOC density and CSP of most soil groups increased from the 1980s to 2010 and varied between different soil groups. Among all soil groups, Haplic phaeozems had the highest SOC density and Endogleyic solonchaks had the largest CSP. Areas of soil groups with the highest SOC density (90 to 120 t C ha−1) and carbon sequestration (120 to 160 t C ha−1) also increased over time. With regard to spatial distribution, the north of the province had higher SOC density but lower CSP than the south. With respect to land-use type, cultivated soils had lower SOC density but higher CSP than uncultivated soils. In addition, SOC density and CSP were influenced by soil physicochemical properties, climate and terrain and were most strongly correlated with soil humic acid concentration. The results suggest that soil groups (uncultivated soils) of higher SOC density have greater risk of carbon dioxide emission and that management should be aimed at maximizing carbon sequestration in soil groups (cultivated soils) with greater CSP. Furthermore, soils should be managed according to their spatial distributions of SOC density and carbon sequestration potential under different soil groups.

Long‐term manure amendments and chemical fertilizers enhanced soil organic carbon sequestration in a wheat (Triticum aestivum L.)–maize (Zea mays L.) rotation system

The carbon sequestration potential is affected by cropping system and management practices, but soil organic carbon (SOC) sequestration potential under fertilizations remains unclear in north China. This study examined SOC change, total C input to soil and, via integration of these estimates over years, carbon sequestration efficiency (CSE, the ratio of SOC change over C input) under no fertilization (control), chemical nitrogen fertilizer alone (N) or combined with phosphorus and potassium fertilizers (NP, NK, PK and NPK), or chemical fertilizers combined with low or high (1.5×) manure input (NPKM and 1.5NPKM). Results showed that, as compared with the initial condition, SOC content increased by 0.03, 0.06, 0.05, 0.09, 0.16, 0.26, 0.47 and 0.68 Mg C ha-1 year-1 under control, N, NK, PK, NP, NPK, NPKM and 1.5NPKM treatments respectively. Correspondingly, the C inputs of wheat and maize were 1.24, 1.34, 1.55, 1.33, 2.72, 2.96, 2.97 and 3.15 Mg ha-1 year-1 respectively. The long-term fertilization-induced CSE showed that about 11% of the gross C input was transformed into SOC pool. Overall, this study demonstrated that decade-long manure input combined with chemical fertilizers can maintain high crop yield and lead to SOC sequestration in north China. © 2016 Society of Chemical Industry.

Total soil organic carbon and carbon sequestration potential in Nigeria

This study aimed to quantify SOC stocks and potential C sequestration for Nigeria using legacy soil data. Mass preserving splines were fitted to legacy SOC and bulk density (BD) pedon data based on GlobalSoilmap soil depths. SOC concentrations (g kg−1) were predicted using Random Forest model (RFM), Cubist and Boosted regression tree (BRT). Thereafter, the soil carbon density (MgCha−1) was calculated from the SOC concentration and BD (Mgm−3). The information was combined with land use/land cover (LULC) map and agro-ecological zone (AEZ) digital maps to estimate SOC sequestration. The mean SOC concentration ranged between 4.2 and 23.7gkg−1 in the top 30cm and between 2.6 and 9.2gkg−1 at the lower soil depth. Total SOC stock in the top 1m was 6.5Pg with an average density of 71.60MgCha−1. Almost half of the SOC stock was found in the 0–30cm layer. SOC stocks decreased from the southwest to the northeast of Nigeria, and increased from Sahel to Humid forest agro-ecological zones. Restoration of the various land use types has the potential to sequester about 0.2 to 30.8MgCha−1 depending on the AEZ. The Derived Guinea Savannah presents a potential hotspot for targeted carbon sequestration projects in Nigeria. Knowledge of SOC stock and sequestration is vital for framing appropriate management regimes to increase soil carbon stocks, for C accounting and environmental monitoring purposes.

Crop establishment techniques affect productivity, sustainability, and soil health under mustard-based cropping systems of Indian semi-arid regions

Indian mustard [Brassica juncea (L.) Czern & Coss] is the predominant oilseed crop in semi-arid India, conventionally grown by repeated plowings during the rainy seasons to conserve soil moisture in fallow fields. To evaluate the effect of establishment methods on productivity, soil health and economics of mustard under various cropping systems, a field experiment was conducted for four years from 2009–2010 to 2012–2013 at the Directorate of Rapeseed-Mustard Research, Bharatpur, India. Conventional tillage (CT), reduced tillage (RT), zero tillage (ZT), and permanent furrow irrigated raised beds (FIRB) treatments were evaluated for five mustard-based cropping systems, viz., fallow–mustard, green manure–mustard, brown manure–mustard, cluster bean–mustard, and pearl millet–mustard, in split-plot design with three replications. The variable tillage practices significantly affected seed, stover, and biological yields, production efficiency, and the economics of mustard along with the bulk density and soil organic carbon dynamics. After four years of the experimentation, the highest mustard seed yield was obtained under FIRB (2765kgha−1) which was 23.6% higher over CT. The seed yield obtained under ZT (2533kgha−1) was 17.5% higher over CT. The seed yield recorded under RT was found similar with ZT, but significantly higher over CT due to higher dry matter accumulation, higher translocation efficiency, and greater sink/source potential at the seed filling stage. Among the cropping systems, highest yield was obtained under the green manure-mustard system followed by the cluster bean–mustard system. The seed yield enhancement with the green manure–mustard cropping system was 13.9% over the fallow-mustard system. The highest assimilate supply (0.33gsiliqua−1) was recorded under ZT. Sustainability parameters, including harvest index (0.29), sustainability yield index (0.85), and production efficiency (16.1kgha−1day−1) were also found highest under ZT after four years of the experiment. Soil organic carbon increased to 0.39% and 0.36% in ZT and FIRB, respectively, from 0.26% in CT. A higher mass of soil organic carbon and carbon sequestration potential rate was recorded under ZT. The bulk density under ZT and FIRB decreased over CT. The soil organic carbon, the mass of soil organic carbon, and the carbon sequestration potential rate were highest in the green manure–mustard system. These parameters were similar between the pearl millet–mustard system and fallow-mustard system, indicating that an additional pearl millet crop can be successfully grown without exhausting the soil organic carbon. The net returns, profitability, and the benefit-cost ratio were highest under FIRB, followed by ZT.

Erratum to: Optimization of method to quantify soil organic matter dynamics and carbon sequestration potential in volcanic ash soils

Erratum to: Optimization of method to quantify soil organic matter dynamics and carbon sequestration potential in volcanic ash soils

Comparison of sampling schemes for the spatial prediction of soil organic matter in a typical black soil region in China

Data on the spatial distribution of soil organic matter (SOM) are important for the spatio-temporal modeling of soil organic carbon dynamics and soil carbon sequestration potential estimates. A total of 175 topsoil samples (0–20 cm) were collected from a typical black soil area in central Hailun County in northeastern China. Seven sampling design schemes, ordinary kriging (OK), and regression kriging (RK) were applied to the re-sampled SOM data for predicting the spatial distribution of SOM. The results showed that single sampling designs, such as simple random, stratified random (STR), and conditional Latin hypercube (CLH), produced poor estimates of SOM, while hybrid sampling designs, such as uniform distribution of point pairs for variogram estimation combined with spatial coverage, STR combined with spatial coverage (STRC), and CLH combined with spatial coverage (CLHC), had a higher predicting accuracy when the sample size was relatively small (≤262). For square grid sampling, a higher predicting accuracy could be achieved only when the sample size was sufficiently large (i.e., ≥402). The inclusion of prior knowledge or SOM-related secondary data in the sampling design and the trade-off between the even and uneven distribution of sampling points are especially important for designing a small-size sampling scheme. Moreover, although the SOM-predicting accuracy of RK was not as good as OK in this study, increasing the sample size may improve the predicting accuracy of SOM. Therefore, the optimal sampling design and spatial predicting method are both important for the predictive mapping of SOM spatial distribution in this area.

The legacy of cropping history reduces the recovery of soil carbon and nitrogen after conversion from continuous cropping to permanent pasture

Enhancing soil organic carbon (SOC) and total nitrogen (N) is considered an important step in mitigating greenhouse gas emissions and improving soil fertility. The loss of SOC and N generally observed during cropping may be reversed by converting such land use to permanent pasture. However, large uncertainties remain around the processes that govern how much C and N may be sequestered from this conversion in soils worldwide. Here, we sampled soils across 10 paddocks on 20-year old grass pasture sites with a chronosequence of cropping history in order to quantify changes in SOC and N after the conversion of long-term cropping to pasture land use in a semi-arid region of southwest Queensland, Australia. The average rate of change in SOC stocks under pasture in the top 0–0.1m soil layer was approximately 0.1tCha−1yr−1, consisting of an increase in SOCC4 (pasture) of 0.2tCha−1yr−1 and a decrease in SOCC3 (pre-pasture) of 0.1tCha−1yr−1. The decrease in SOCC3 was enhanced at sites with greater years under cropping, indicating a reduced potential for SOC sequestration at sites with longer duration under cropping. The loss of total nitrogen (N) under cropping was also partially recovered with the introduction of permanent perennial pastures. A significant, positive correlation between soil aggregation and mineralisable N under cropping suggested that soil structure has a strong influence over N stability in the soil. However, soil aggregation and mineralisable N did not improve under pastures, indicating that the loss of soil fertility and structure under cropping remained a residual effect that was not recovered within 20 years of permanent pastures in this semi-arid subtropical environment. We suggest here that the resilience of ecosystems to recover soil fertility under pastures declines with greater years under cropping.

Cover crop and tillage systems effect on soil CO2 and N2O fluxes in contrasting topographic positions

Soils are important sources of CO2 and N2O emissions to the atmosphere. Introducing cover crop and conservation tillage are among the strategies to improve soil organic carbon (SOC) and nitrogen (N) sequestration potentials with potential to reduce the amounts of greenhouse gases (GHG) emitted from soil. The objectives of the study were to evaluate CO2 and N2O emissions in rye cover crop and tillage system treatments in contrasting topographical positions. Two replicated field experiments were established in 2011 at Kellogg Biological Station and Mason Research Farm sites, located in Southwest and Central Michigan, respectively. At each site, two replications of three contrasting topographical positions, namely depression, slope and summit were used. The two studied factors were tillage system (chisel plow and ridge tillage) and winter rye cover crop (present and absent). Topographical positions significantly affected the performance of rye cover crop with above ground biomass ranged from 80 to 200kgha−1 and 120 to >500kgha−1 in depressions and summits, respectively. The presence of rye cover tended to increase CO2 emissions across all topographical positions. However, the amount of increases in the CO2 emissions was ∼15mgm2h−1 and <5mgm2h−1 in depressions and summits, respectively, which were inversely proportional to the amount of rye biomass inputs. Ridge tillage had significantly higher CO2 emissions than chisel tillage in depressions and showed increasing trends at the slopes and summits. Neither the effect of cover crop nor tillage system was found to be statistically significant across the whole study period on N2O emissions. Regression analysis indicated that both CO2 and N2O emissions were positively associated with soil temperature. The effect of temperature on CO2 emissions was most pronounced in management treatments with cover crops and in topographical depressions. Per a unit increase in the soil temperature was a greater increase in the CO2 emission in depression areas than other parts of the landscape. The results of the present study highlight existence of complex interactive influences among cover crop presence, tillage, and topography driven variations in soil properties on the resulting soil GHG emissions.

Carbon storage capacity of semi-arid grassland soils and sequestration potentials in northern China.

Organic carbon (OC) sequestration in degraded semi-arid environments by improved soil management is assumed to contribute substantially to climate change mitigation. However, information about the soil organic carbon (SOC) sequestration potential in steppe soils and their current saturation status remains unknown. In this study, we estimated the OC storage capacity of semi-arid grassland soils on the basis of remote, natural steppe fragments in northern China. Based on the maximum OC saturation of silt and clay particles <20μm, OC sequestration potentials of degraded steppe soils (grazing land, arable land, eroded areas) were estimated. The analysis of natural grassland soils revealed a strong linear regression between the proportion of the fine fraction and its OC content, confirming the importance of silt and clay particles for OC stabilization in steppe soils. This relationship was similar to derived regressions in temperate and tropical soils but on a lower level, probably due to a lower C input and different clay mineralogy. In relation to the estimated OC storage capacity, degraded steppe soils showed a high OC saturation of 78-85% despite massive SOC losses due to unsustainable land use. As a result, the potential of degraded grassland soils to sequester additional OC was generally low. This can be related to a relatively high contribution of labile SOC, which is preferentially lost in the course of soil degradation. Moreover, wind erosion leads to substantial loss of silt and clay particles and consequently results in a direct loss of the ability to stabilize additional OC. Our findings indicate that the SOC loss in semi-arid environments induced by intensive land use is largely irreversible. Observed SOC increases after improved land management mainly result in an accumulation of labile SOC prone to land use/climate changes and therefore cannot be regarded as contribution to long-term OC sequestration.

Soil organic carbon sequestration potential of artificial and natural vegetation in the hilly regions of Loess Plateau

The objectives of this study were (i) to determine the stock and distribution of soil organic carbon (SOC) and the quantity and quality of fine root; and (ii) the correlation between SOC stock and fine root quantity and quality in soils of artificial and natural vegetation in the Loess Plateau. Three vegetation types (grassland, shrubland and woodland) and two restoration approaches (artificially and naturally restored from cropland) were investigated in the Yangou watershed of the Loess Plateau. SOC stock, fine root biomass and root C/N ratio at the 0–20, 20–40, 40–60, 60–80, and 80–100cm depths were determined. The mean SOC stock of natural vegetation at the 0–100cm depth was significantly greater than that of artificial vegetation, with an increase of 100% for woodland, 15% for shrubland, and 23% for grassland. Natural vegetation restoration led to a significantly greater SOC stock up to a depth of 100cm for woodland, 40cm for shrubland, and 40cm for grassland. The fine root biomass of natural vegetation at the 0–100cm depth was also significantly greater than that of artificial vegetation, with an increase of 170% for woodland, 140% for shrubland, and 20% for grassland. Natural vegetation restoration led to a significantly greater fine root biomass up to a depth of 100cm for woodland, 60cm for shrubland, and only 20cm for grassland. There was a significant linear correlation between SOC stock and fine root biomass. Thus, natural vegetation restoration could lead to a significantly greater SOC stock, fine root biomass, and fine root C/N ratio than the artificial vegetation restoration. Fine root was an important factor influencing the differences in the SOC stock between artificial and natural vegetation.

Soil organic carbon fractions and sequestration across a 150-yr secondary forest chronosequence on the Loess Plateau, China

Restoration of natural vegetation is recommended as an effective approach to restore soil function and rebuild degraded ecosystems. Information is lacking about the long-term results of secondary forest succession on the Loess Plateau with respect to soil organic carbon (SOC) fractions and sequestration in the root-zone soil profile. We investigated the differences in SOC fractions down to 100cm depths along a 150-yr chronosequence, including cropland (control) and five successional stages (pioneer weeds, herbage, shrub, early forest, and climax forest). Total, labile, and non-labile SOC concentrations increased rapidly at early successional stages (before shrub, <50-yr) and then gradually leveled off. Total SOC stock was highest at the climax forest stage (64.3Mgha−1) and lowest in cropland (39.9Mgha−1). Nearly half (~44.8%) of total SOC stock was stored in surface soils (0–20cm) and the majority (76.4%) existed in the non-labile fraction. The ratio of labile to non-labile fraction decreased with depth but remained stable across successional stages. The mean SOC sequestration potential and rate relative to cropland were 20.5Mgha−1 and 0.73Mgha−1yr−1, respectively. Although the SOC sequestration potential decreased with depth (64.7% for 0–20cm vs. 35.3% for 20–100cm), it decreased by 3.1Mgha−1 in the surface and increased by 3.4Mgha−1 in the subsurface from herbage to climax forest stage. This study indicated that long-term secondary forest succession played a positive role in SOC sequestration on the Loess Plateau, especially in the subsurface soil layers.

Effect of different fertilization modes on soil organic carbon sequestration in paddy fields in South China: A meta-analysis

Evidences have shown that fertilizer application could affect soil organic carbon (SOC) content in cropland. South China is the main production region of rice, in which many different fertilization practices have been widely used during the last several decades, but the effect of different fertilization modes on SOC sequestration in paddy fields in this region was scarcely studied. Based on 274 samples taken from 44 paddy field experimental sites in South China, a meta-analysis was performed to quantify the relative annual change of SOC content (RAC) and SOC sequestration duration in paddy fields under five fertilization modes (inorganic nitrogen fertilization, N; inorganic nitrogen and phosphorus fertilization, NP; inorganic nitrogen, phosphorus, and potassium fertilization, NPK; organic fertilization, O; and inorganic combined with organic fertilization, OF). The results showed that the RAC under the five fertilization modes was 0–0.4gkg−1yr−1, with increments of 0.19 and 0.23gkg−1yr−1 in double cropping systems and triple cropping systems, respectively. The RAC under the O and OF treatments was higher than that under the N, NP and NPK treatments and was the highest (0.32gkg−1yr−1) under OF among the five treatments. The SOC accumulation rate decreased with time, and the SOC sequestration duration under N, NP, NPK, O and OF was approximately 23, 28, 46, 64 and 55 years, respectively. The accumulation enhancement rate of SOC over the whole SOC sequestration period under the N, NP, NPK, O and OF treatments was approximately 12.9%, 23.4%, 29.3%, 47.2% and 55.1%, respectively. The OF treatment performed the largest potential for SOC sequestration in paddy fields in South China under long-term conditions.

Carbon sequestration potential in perennial bioenergy crops: the importance of organic matter inputs and its physical protection

AbstractTo date, only few studies have compared the soil organic carbon (SOC) sequestration potential between perennial woody and herbaceous crops. The main objective of this study was to assess the effect of perennial woody (poplar, black locust, willow) and herbaceous (giant reed, miscanthus, switchgrass) crops on SOC stock and its stabilization level after 6 years from plantation on an arable field. Seven SOC fractions related to different soil stabilization mechanisms were isolated by a combination of physical and chemical fractionation methods: unprotected (cPOM and fPOM), physically protected (iPOM), physically and chemically protected (HC‐μs + c), chemically protected (HC‐ds + c), and biochemically protected (NHC‐ds + c and NHC‐μs + c). The continuous C input to the soil and the minimal soil disturbance increased SOC stocks in the top 10 cm of soil, but not in deeper soil layers (10–30; 30–60; and 60–100 cm). In the top soil layer, greater SOC accumulation rates were observed under woody species (105 g m−2 yr‐1) than under herbaceous ones (71 g m−2 yr‐1) presumably due to a higher C input from leaf‐litter. The conversion from an arable maize monoculture to perennial bioenergy crops increased the organic C associated to the most labile organic matter (POM) fractions, which accounted for 38% of the total SOC stock across bioenergy crops, while no significant increments were observed in more recalcitrant (silt‐ and clay‐sized) fractions, highlighting that the POM fractions were the most prone to land‐use change. The iPOM fraction increased under all perennial bioenergy species compared to the arable field. In addition, the iPOM was higher under woody crops than under herbaceous ones because of the additional C inputs from leaf‐litter that occurred in the former. Conversion from arable cropping systems to perennial bioenergy crops can effectively increase the SOC stock and enlarge the SOC fraction that is physically protected within soil microaggregates.