Assessment Of Soil Organic Carbon Stocks Research Articles

Soil Organic Carbon Stock Assessment for Volunteer Carbon Removal Benefit: Methodological Approach in Chestnut Orchard for Fruit Production

The implementation of a protocol for supporting a reliable soil C market is needed. This paper aims to propose a methodology for evaluating soil organic C (SOC) stock changes for the C credit market. A 15-year-old chestnut orchard (CO) and a chestnut coppice (CC) as reference land were selected in the northern part of the Apennine chain (Italy). The CO is the result of the CC conversion carried out in 2005. The soil sampling by pedogenetic horizons till parent material was carried out in 2005, 2010, 2015 and 2020 in CO and in 2005 and 2020 in CC. For each sample, the concentration and stock of the total SOC and of the most recalcitrant SOC form were estimated. Unlike the CC, in CO, an increase over time of SOC stocks was observed throughout the entire soil profile indicating the suitability of CO for C credit gaining. Most of the SOC was stored within the deepest soil horizon. The methodology can be considered eligible for the C credit market because, replicable, the CO was intentionally realized by humans after 1990, and the additionality was evaluated. Moreover, soil functionality was considered through the evaluation of SOC forms and of the pedogenetic horizons.

A simple soil mass correction for a more accurate determination of soil carbon stock changes

Agricultural soils can act as a sink for large quantities of soil organic carbon (SOC) but can also be sources of carbon to the atmosphere. The international standard for assessing SOC stock and measuring stock change stipulates fixed depth sampling to at least 30 cm. The tendency of bulk density (BD) to decrease with decreasing disturbance and increasing SOC concentration and the assumption of constant SOC and BD within this depth profile promotes error in the estimates of SOC stock. A hypothetical but realistic change in BD from 1.5 to 1.1 g cm−3 from successive fixed depth sampling to 30 cm underestimates SOC stock change by 17%. Significant effort has been made to evaluate and reduce this fixed depth error by using the equivalent soil mass (ESM) approach, but with limited adoption. We evaluate the error in SOC stock assessment and change generated from fixed depth measurements over time relative to the ESM approach and propose a correction that can be readily adopted under current sampling and analytical methods. Our approach provides a more accurate estimate of SOC stock accumulation or loss that will help incentivize management practice changes that reduce the environmental impacts of agriculture and further legitimize the accounting practices used by the emerging carbon market and organizations that have pledged to reduce their supply chain greenhouse gas (GHG) footprints.

Best practice for upscaling soil organic carbon stocks in salt marshes

Calculating the amount of soil organic carbon (SOC) stored in coastal environments, including salt marshes, is needed to determine their role in mitigating the Climate Crisis. Several techniques exist to calculate the SOC content of a unit of land from the upscaling of soil cores. However, no comprehensive assessment has been made on the performance of commonly used SOC upscaling techniques until now. We measured the SOC content of soil cores gathered from two Scottish salt marshes. Two SOC values were used for upscaling; SOC content for a 1 m standardised depth (as recommended by the IPCC), and SOC content of the modern marsh deposit (identified in the stratigraphy as a transition from organic-rich (marsh) to mineral-rich (intertidal flat) soil. Twenty-two upscaling techniques were used (SOC content × area, interpolative, and regression-based extrapolative calculations). Leave-one-out cross-validation procedures and prediction interval widths were used to assess the accuracy of each technique. Digital Terrain Models and Normalized Difference Vegetation Indices were used as covariate surfaces in the regression models. We found that marsh-scale SOC stocks varied by as much as fifty-two times depending on which sampling depth and upscaling technique was used. The largest differences emerged when comparing SOC stocks upscaled from 1 m deep and modern marsh deposits. Using the IPCC recommended 1 m sampling depth inflated the SOC stocks of salt marshes, as intertidal flat environments were included in the calculation. Ensemble regression models from the weighted average of seven machine learning algorithm outputs produced the highest upscaling accuracies across marshes and sampling depths. Simple SOC content × area calculations produced marsh-scale SOC stocks that were comparable to stock values produced by more advanced ensemble regression models. However, regression models produced detailed maps of SOC distribution across a marsh, and the associated uncertainty in the SOC values. Our findings are broadly applicable for other environments where large-scale SOC stock assessments and uncertainty are needed.

Monitoring changes in global soil organic carbon stocks from space

Soils are under threat globally, with declining soil productivity and soil health in many places. As a key indicator of soil functioning, soil organic carbon (SOC) is crucial for ensuring food, soil, water and energy security, together with biodiversity protection. While there is a global effort to map SOC stock and status, SOC is a dynamic soil property and can change rapidly as a function of land management and land use. Here, we introduce a semi-mechanistic model to monitor SOC stocks at a global scale, underpinned by one of the largest worldwide soil database to date. Our model generates a SOC stock baseline for the year 2001, which is then propagated through time by keeping track of annual landcover changes obtained from remote sensing products with loss and gain dynamics dependent on temperature and precipitation, which finally define the magnitude, rate and direction of the SOC changes. We estimated a global SOC stock in the top 30 cm of around 793 Pg with annual losses due to landcover change of 1.9 Pg SOC yr−1 from 2001 to 2020, 20% larger than the annual production-based emissions of the United States in 2018. The biggest losses were found in the tropic and sub-tropical regions, accounting for almost 50% of the total global loss. This is a considerable contribution to greenhouse gas emissions but it also has a direct impact on agricultural production with more than 16 million hectares yr−1 falling below critical SOC limits. The proposed modelling framework is flexible, allowing it to be updated as more remote sensing and soil data becomes available, offering a first-of-its-kind global spatio-temporal SOC stock assessment and monitoring system.

Soil organic carbon stock assessment in forest ecosystems through pedogenic horizons and fixed depth layers sampling: What's the best one?

AbstractIn soil organic carbon (SOC) survey, the role of sampling approach is crucial and should not be underestimated. In this sense, the appropriateness of soil sampling by pedogenic horizons (PGH) and fixed depth layers (FDL) in forest is still a field of debate. The present work aimed to: (a) study the spatial variability of SOC concentrations and C stocks through PGH and FDL samplings in uneven‐aged sweet chestnut, European beech and Norway spruce forests of the Apennine chain (Italy); (b) clarify the major advantages and drawbacks of sampling by PGH and FDL. In a representative area (18 × 18 m) of each forest, a soil profile was investigated and eight additional sampling points were selected. The sampling was performed both by PGH and FDL (0–15 and 15–30 cm). For each forest, no SOC content and C stock differences in 0–30 cm soil depth were found between PGH (58.8 ± 5.3 g kg−1 and 103 ± 7 g ha−1, respectively) and FDL (52.7 ± 4.3 g kg−1 and 117 ± 9 Mg ha−1, respectively) sampling. However, under Norway spruce, PGH sampling pointed‐out that C was mainly stored in Oe and Oa horizons (51.1 vs. 146 Mg ha−1 in the 0–30 cm layer). The higher coefficient of variation obtained when soil horizons were considered (from 19.2% to 72.8% for PGH and from 16.5% to 25.7% for FDL) suggested that PGH sampling preserved the information about the spatial variability within an ecosystem. The information loss about SOC vertical and spatial distribution would indicate the inability of FDL sampling to support decision‐making plans addressed for sustainable use of soil resource.

Quantifying organic carbon stocks using a stereological profile imaging method to account for rock fragments in stony soils

Accounting for soil organic carbon (SOC) in stony soils is critical for estimating global SOC stocks. However, accurate and cost-effective assessments of SOC stocks in stony soil profiles remain challenging due to the difficulties in accurately determining the rock fragment volume. The objective of this study was to develop a stereological profile imaging method for rock fragment volume fraction estimation and SOC stock assessment in stony soil profiles. Three soil profiles with different rock fragment lithologies, concentrations, and distributions were imaged and quantitatively sampled. The stereological profile imaging method reproduced consistent estimation of the 3-dimensional rock fragment number density distribution and volume fraction compared to the direct measurement. The SOC stocks of the three stony profiles estimated by visual estimation, profile imaging, and stereological profile imaging methods were also assessed and compared to direct measurement. The average difference in total SOC stock between direct measurement and visual estimation, profile imaging, and stereological profile imaging methods was 0.32, 0.17, and 0.09 kg m−2, respectively. The total profile (0–100 cm) SOC stock for profile 2 differed among the visual estimation and profile imaging methods, but estimated SOC stock from the proposed method did not differ from direct measurement for the three profiles. Results also showed that the differences in SOC stock assessment between rock fragment estimation methods increased with rock fragment concentration. The proposed method was less affected by rock fragment concentration and was more stable compared to the visual and profile imaging methods. The stereological profile imaging method was demonstrated to be a reasonably accurate method for the quantification of rock fragment number density distribution, volume fraction, and SOC stock in stony soil profiles.

Evaluating soil organic carbon stock changes induced by no-tillage based on fixed depth and equivalent soil mass approaches

It is controversial whether no tillage (NT) should be regarded an effective agro-ecosystem management to increase soil organic carbon (SOC). Some studies suggest NT leads to a notable accumulation of SOC stock across the whole sampling profile over the long-term, whereas other studies argue that the effect of duration on SOC stock increase is limited. Similar controversy is common with respect to the role of climatic conditions in SOC changes. In addition, despite the gradual recognition of the importance of equivalent soil mass (ESM) compared to fixed depth (FD) approach, in terms of SOC stock evaluation, the ESM approach mainly focuses on the direct impact of bulk density but ignores the potential indirect effect on SOC concentration. To further understand the SOC sequestration mechanisms under NT, responses of SOC stock after the adoption of NT were investigated based on FD and ESM approaches. The results showed that NT significantly changed the SOC stock distribution in different soil depths according to both FD and ESM, but no significant changes were observed when soil sampling deeper than 50 cm. Notably, the results illustrated that the use of FD overestimated the SOC stock in the soil surface due to the increased bulk density under NT, but underestimated the SOC stock in 30–70 cm soil layers compared to ESM. Consequently, the overestimate of SOC based on FD may not be as high as previously assumed across the sampling depth. Mean annual temperature and mean annual rainfall did not lead to any significant changes in SOC stock of the overall soil profile or different layers, indicating the limited impacts of climatic conditions on carbon sequestration after the adoption of NT. Long-term NT resulted in a significant accumulation in SOC stock in the top 5 cm of the surface soil, but SOC stock changes with time in soil layers deeper than 5 cm was not significant in both FD and ESM approaches. The overall changes in SOC stock as time increased were not significant across the whole profile based on FD, but was weakly significant based on ESM. The results illustrate that using the overall SOC stock change of the whole sampling soil profile deeper than 30 cm masks the beneficial change in SOC stock in the 0–5 cm soil over long-term adoption of NT. The biased interpretation of depth factor is the main reason that fuels the debate over whether long-term NT is beneficial for the accumulation of SOC stock, and hence must be properly considered. Overall, the data illustrate that the depth factor is not only important in terms of assessing total SOC stock changes under NT, but also critical when evaluating the effectiveness of FD and ESM, as well as the impact of experimental duration on SOC increase. The depth factor should thus be comprehensively considered in SOC stock assessment and more field experiments sampling to deeper depth are urgently needed to clarify whether NT is beneficial for SOC sequestration and climate mitigation.

Spatial heterogeneity of soil organic carbon in a karst region under different land use patterns

AbstractUsing the grid‐based sampling method, 2755 soil profiles consisting of 22,057 soil samples were sampled and analyzed to study the spatial distribution and storage of soil organic carbon (SOC) in the Houzhai River Basin in Guizhou Province, a typical karst region in southwestern China. The results suggest that the total levels of SOC stored in the 0–10, 0–20, 0–30, and 0–100 cm soil layers of the Houzhai River Basin are approximately 1.48 × 108, 2.65 × 108, 3.44 × 108, and 5.39 × 108 kg C, respectively. SOC content and soil bulk density levels were found to vary depending on the land use. In the 0–50 cm soil layer, forest SOC content levels (including arbor forests, arbor–shrub mixed forests, shrubland, and shrub grassland) are generally higher than those of uncultivated land, followed by grassland and cropland (including paddy fields, arid land, sloping cropland, and abandoned cropland), gardens, and orchard. It is believed that land use is a vital factor directly affecting carbon storage patterns in the study area. Soil thickness, rock outcrop, and slope gradients are the main factors in arrangement of land use by local governments and peasants. This study has established a feasible method for assessment of SOC stock in karst mountainous areas. The findings of this study are applicable to other karst mountainous regions globally.

The devil is in the detail: Discrepancy between soil organic carbon stocks estimated from regional and local data sources in Flanders, Belgium

AbstractStorage of soil organic carbon (SOC) is an essential function of ecosystems underpinning the delivery of multiple services to society. Regional SOC stock estimates often rely on data collected during land‐use‐specific inventory schemes with varying sampling depth and density. Using such data requires techniques that can deal with the associated heterogeneity. As the resulting SOC assessments are not calibrated for the local scale, they could suffer from oversimplification of landscape processes and heterogeneity. This might especially be the case for sandy regions where typical historical land use practices and soil development processes determine SOC storage. The aims of this study were (a) to combine four land‐use‐specific SOC stock assessments to estimate the total stock in Flanders, Belgium, and (b) to evaluate the applicability of this regional‐scale estimate at the local scale. We estimated the SOC stock in the upper 100 cm of the unsealed area in Flanders (887,745 ha) to be 111.67 Mt OC, or 12.6 ± 5.65 kg OC m−2 on average. In general, soils under (semi‐) natural land‐use types, for example forests, store on average more organic carbon than under agriculture. However, overall agricultural soils store the largest amounts of SOC due to their vast spatial extent. Zooming in on a sandy location study (13.55 km2) revealed the poor performance of the regional estimates, especially where Histosols occurred. Our findings show that a greater spatial sampling density is required when SOC stock estimates are needed to inform carbon‐aware land management rather than to provide for regional reporting.

Soil Organic Carbon Stock Assessment in a Grassland and a Polyculture Tree Plantation

Polyculture tree plantations are generally characterized by the sustainability to resist disturbance, potential for higher yield and better ecological services. A study was conducted in a polyculture tree plantation and a grassland site inside the main campus of Visayas State University, Baybay City, Leyte to (1) estimate and compare the soil organic carbon (SOC) stocks between the two land uses, and (2) find relationships between soil physicochemical properties, and SOC in the polyculture tree plantation and grassland. In each land use, soil samples were collected at depth intervals of 0-10 cm, 10-30 cm, and 30-50 cm. Higher SOC stocks in the 10 – 30 cm and 30 – 50 cm depths and the whole profile of the polyculture tree plantation (23.02, 43.28, 45.18, 111.47 Mg C ha-1 , respectively) compared to the grassland site (27.53, 35.70, 28.93, 82.14 Mg C ha-1 ) were observed. Thus, this polyculture tree plantation significantly improved some soil physicochemical characteristics and increased SOC stock after conversion from grassland.

The soil organic carbon stock and its influencing factors in a mountainous karst basin in P. R. China

Soil organic carbon represents a major carbon pool in terrestrial ecosystems. Currently, in karst areas, there is considerable uncertainty regarding the estimation of soil organic carbon pools due to limited profile numbers and heterogeneity. Using a grid-based sampling method, 2755 soil profiles consisting of 22,057 soil samples were analyzed to determine the spatial distribution and storage of soil organic carbon (SOC) in the Houzhai River Basin in the Guizhou Province in southwest China. The results suggest that the total SOC storages in the 0–20 and 0–100 cm soil horizons of the Houzhai River Basin are approximately 2.65 × 108 and 5.39 × 108 kg C, respectively. The differences in the soil bulk density between different soil types were considerable. The average soil bulk density of large mud field loam, which ranged from 1.25 to 1.52 g/cm3, was significantly higher than that of the other soil types. The differences in soil organic carbon content were obvious as well. As soil depth increased, the organic carbon content gradually decreased. At a depth of 0–50 cm, the soil organic carbon content significantly decreased. In contrast, soil organic carbon content decreased slowly from 50 to 100 cm, indicating that a depth of 50 cm is the turning point for organic carbon content. The different degrees of soil organic carbon storage in different soil types were mainly caused by differences in organic carbon density. In karst regions, the soil parent material limits the spatial distribution of soil organic carbon, and soluble rock is the base development material. Soil thickness, slope gradient, and rock exposure are the primary factors leading to differences in SOC storage in different soil types. In addition, this study also suggests that increased attention should be paid to rock exposure in the assessment of SOC stocks in karst mountainous areas, such as the Houzhai River Basin.

Carbon losses from prolonged arable cropping of Plinthosols in Southwest Burkina Faso

The ongoing conversion of natural ecosystems of the tropics into agricultural land usually results in a loss of soil organic carbon (SOC), the extent of which being largely affected by climate and soil order. We assumed that i) SOC losses are not restricted to the surface soil but extend into the subsoil, but that ii) the rate of SOC losses is controlled by interactions of SOC with Fe oxides. Hence, we sampled Plinthosols down to one meter (if feasible) that had been converted from native savannah into cropland 0 to 29 years ago in the Dano district (Southwest Burkina-Faso). Beside the assessment of SOC stocks, we also determined the proportion of surface (0–10cm) SOC remaining after Fe oxide removal as well as its distribution among the following particle-size fractions: 2000–250μm (coarse sand-sized SOC; POM1), 250μm–53μm (fine-sand-sized SOC; POM2), 53μm–20μm (very fine sand-sized SOC; POM3), and <20μm (nonPOM). We found that the soils lost 24tCha−1 from the upper 10cm and 49tCha−1 from the upper 30cm, respectively, after 29 years. SOC losses extended also into the subsoil, and, on the average, 0.7–19.5tCha−1 was lost from the 30–100cm depth interval. The loss rates of SOC were similar to those reported for other soil types. Rapid losses of SOC occurred from all POM fractions as well as from the Fe-oxide pool, which, on average, contained about 16% of total SOC stock. We conclude that even if Fe oxides as well as other silt- and clay-sized organomineral complexes delay losses of SOC relative to POM, they failed to efficiently protect SOC from decomposition in these Plinthosols.

Sampling designs for soil organic carbon stock assessment of soil profiles

We investigated four sampling designs for soil organic carbon (SOC) stock assessment of soil profiles: (i) sampling by horizons, (ii) vertical transect sampling, (iii) depth-based stratified random sampling, (iv) fuzzy c-means sampling in which we explored the use of vis-NIR spectroscopy, image analysis and color models. An Alfisol and Mollisol profile wall (1×1m) was divided into a 10×10cm raster and 100 samples (about 200g each) were collected at the centers of grid cells for SOC analysis. Bulk density samples were collected from each 10-cm depth interval along a single vertical transect and the SOC stock was calculated using 100 points in the profile wall. Horizon-based sampling for the Mollisol (5 horizons) ranged from 231 to 262MgCha−1, whereas it ranged from 69 to 99MgCha−1 in the Alfisol (3 horizons). The SOC stocks obtained by 1 to 7 vertical transects ranged from 68 to 81MgCha−1 in the Alfisol, and 239 to 246MgCha−1 in the Mollisol. Depth-based stratified random sampling resulted in the SOC stocks ranging from 77 to 82MgCha−1 in the Alfisol and 234 to 257MgCha−1 in the Mollisol, and the standard errors decreased with increasing sample size from 10 to 70. Fuzzy c-means clustering created clusters similar to the field delineated horizons. A sample size of 7 in both profiles was sufficient to estimate the mean profile SOC stock by fuzzy c-means sampling. The CIE L*a*b* color model resulted in more accurate estimation in the Alfisol, but the vis-NIR spectra resulted in more accurate estimation in the Mollisol. Soil depth improved the performance of vis-NIR spectra. It is concluded that in these soils, at least two or three vertical transects are required to capture the horizontal variation for estimating profile SOC stock. Depth-wise stratified random sampling reduces the number of samples and is suitable when horizontal variation is high. Fuzzy c-means sampling is useful to determine the minimum sample size for profile SOC stock assessment but requires ancillary data and processing before sampling the soil profile.

Effect of Vegetation Communities and Altitudes on the Soil Organic Carbon Stock in Kotli Bhel‐1A Catchment, India

As per international policy agendas on mitigation of greenhouse gas emission, the impact change in land use on soil organic carbon (SOC) stocks is of major concern. There has been no systematic study carried out to estimate SOC pool in the catchment of hydroelectric reservoirs. An assessment of SOC stock along altitudinal gradient was carried out in the catchment of proposed Kotli Bhel 1A hydroelectric reservoir located in Uttarakhand, India. The SOC stocks were found to be decreasing with altitude, (i.e. soil under high altitude forests having more SOC and vice versa). The SOC map developed from the normalized difference vegetation index also verified the results and allowed for spatially explicit targeting of potential climate change mitigation efforts through soil carbon sequestration. The results also revealed that the alpine forest soil has a greater potential of C sequestration compared to devdar, oak, and chir species found in the catchment. This information will help policymakers or environmentalists to take preventive measures for afforestation of forest species that can sequester more C.

Soil carbon stock assessment in the tropical dry deciduous forest of the Sathanur reserve forest of Eastern Ghats, India

ABSTRACTClimate change and carbon mitigation through forest ecosystems are some of the important topics in global perspective. Tropical dry forests are one of the most widely distributed ecosystems in tropics, which remain neglected in research. The soil organic carbon (SOC) stock was quantified on a large scale (30 1-ha plots) in the dry deciduous forest of the Sathanur reserve forest of Eastern Ghats. The SOC stock ranged from 16.92 to 44.65 Mg/ha with a mean value of 28.26 ± 1.35 Mg/ha. SOC exhibited a negative trend with an increase in soil depth. A significant positive correlation was obtained between SOC stocks and vegetation characteristics viz. tree density, shrub basal area, and herb species richness, while a significant negative correlation was observed with bulk density. The variation in SOC stock among the plots obtained in the present study could be due to differences in tree abundance, herb species richness, shrub basal area, soil pH, soil bulk density, soil texture etc. The present study generates a large-scale baseline data of dry deciduous forest SOC stock, which would facilitate SOC stock assessment at the national level as well as to understand its contribution on a global scale.

Soil Organic Carbon Stocks in a Large Eutrophic Floodplain Forest of the Southeastern Atlantic Coastal Plain, USA

Anthropogenic land use has significantly altered sediment and nutrient dynamics at watershed-scales, resulting in significant redeposition within large floodplain ecosystems. Some upland land uses have had documented negative effects on soil carbon (C) stocks, although the specific impacts of these disturbances on soil organic carbon (SOC) dynamics in depositional environments are poorly understood. Assessment of SOC stocks in floodplain environments will allow for more precise estimates of C distribution at watershed and regional scales. In this study, we measured SOC pools to depths of 100 and 200 cm in four distinct floodplain landscapes (natural levee, flats, mineral wetlands, organic wetlands) in a large bottomland forest within Congaree National Park, South Carolina, USA. Mean SOC stocks to a depth of 100 cm were 108–109 Mg C ha−1 in flats and levees, 193 Mg C ha−1 in mineral wetlands, and 533 Mg C ha−1 in organic wetlands. In addition, hydric soils contained significantly more SOC in deep horizons (100–200 cm depths). At a regional scale, similar alluvial soils within large floodplains were estimated to store approximately 0.l Pg of SOC. These results highlight the importance of inclusion of deep SOC storage in alluvial settings when estimating watershed C budgets.

Soil Organic Carbon Stock Assessment in Two Temperate Forest Types of Western Himalaya of Jammu and Kashmir, India

Soil organic carbon (SOC) in the temperate forests of the Himalayas is important to estimate their contribution to regional, national and global carbon stocks. This information however is poor and fragmented in regards to the western Himalayas of India. No published information is available on SOC stock in this region. Carbon stocks were assessed at different soil depths (0-10, 10-20 and 20-30 cm) in Pinus wallichiana (PW) and Abies pindrow (AP) forest types in the western Kashmir Himalayas of India. SOC stocks in these temperate forests were relatively low ranging from 50.37 to 55.38 Mg C ha-1 in the top 30 cm of soils. Significantly greater SOC stock was observed in PW forest type compared to AP forest type. Tree density, shrub density, shrub biomass, herb biomass and forest floor litter were greater in the PW forest type as compared to AP forest type, which could be the reason for greater accumulation of organic carbon in soil. The present study revealed that tree species composition and its associated underground vegetation alter SOC accumulation in the moist temperate forest ecosystems. In addition, environmental parameters such as soil moisture and soil biological activity change soil carbon sequestration potential in moist temperate forest ecosystems.

Soil carbon stocks and their variability across the forests, shrublands and grasslands of peninsular Spain

Abstract. Accurate estimates of C stocks and fluxes of soil organic carbon (SOC) are needed to assess the impact of climate and land use change on soil C uptake and soil C emissions to the atmosphere. Here, we present an assessment of SOC stocks in forests, shrublands and grasslands of peninsular Spain based on field measurements in more than 900 soil profiles. SOC to a depth of 1 m was modelled as a function of vegetation cover, mean annual temperature, total annual precipitation, elevation and the interaction between temperature and elevation, while latitude and longitude were used to model the correlation structure of the errors. The resulting statistical model was used to estimate SOC in the ∼8 million pixels of the Spanish Forest Map (29.3 × 106 ha). We present what we believe is the most reliable estimation of current SOC in forests, shrublands and grasslands of peninsular Spain thus far, based on the use of spatial modelling, the high number of profiles and the validity and refinement of the data layers employed. Mean concentration of SOC was 8.7 kg m−2, ranging from 2.3 kg m−2 in dry Mediterranean areas to 20.4 kg m−2 in wetter northern locations. This value corresponds to a total stock of 2.544 Tg SOC, which is four times the amount of C estimated to be stored in the biomass of Spanish forests. Climate and vegetation cover were the main variables influencing SOC, with important ecological implications for peninsular Spanish ecosystems in the face of global change. The fact that SOC was positively related to annual precipitation and negatively related to mean annual temperature suggests that future climate change predictions of increased temperature and reduced precipitation may strongly reduce the potential of Spanish soils as C sinks. However, this may be mediated by changes in vegetation cover (e.g. by favouring the development of forests associated to higher SOC values) and exacerbated by perturbations such as fire. The estimations presented here provide a baseline to estimate future changes in soil C stocks and to assess their vulnerability to key global change drivers, and should inform future actions aimed at the conservation and management of C stocks.

Assessment of SOC Stock, Their Changes Overtime and Prediction of SOC Stock Using Roth-C Model for Benchmark Soils of Different Agro-climatic Zones of Tamil Nadu

A study was conducted in different agroclimatic zones of Tamil Nadu with the objective of assessment of Soil Organic Carbon (SOC) stock and its changes overtime, prediction of SOC stock under existing and alternate cropping pattern using Roth C model. Fifteen benchmark soils were selected in different agroclimatic zones of Tamil Nadu based on their land use and areal extent to assess SOC level and its changes overtime. Results revealed that, during 1997 and 2007 SOC was higher in forest ecosystem of pedon 15 (Ooty series) and in pedon 14 (Pechiparai series) of horticultural land use. Among seven agroclimatic zones of Tamil Nadu soil series in five agroclimatic zones viz., Periyanaickenpalayam series (Western zone), Peelamedu series (Southern zone), Vallam series (North eastern zone), Vannappatti series (North western zone) and Padugai series (Cauvery delta zone) were selected to predict SOC stock for the year 2025 and 2050 except hilly and high rainfall zone due to high organic carbon content in these agroclimatic zones. Results showed that, among the soil series selected for the study, Vannappatti and Padugai series registered the highest Total Organic Carbon (TOC), Biomass Carbon (BIO) and Humified Organic Carbon (HUM) under existing cropping pattern while Periyanaickenpalayam, Peelamedu and Vallam series had high TOC, BIO and HUM under alternate cropping pattern. Among five selected soil series, Periyanaickenpalayam, Peelamedu and Padugai series recorded 7.5 g kg-1 TOC during 2025 and 2018, 2100 and 2035, 2013 and 2014 under existing and alternate cropping pattern respectively.

Soil organic carbon stock assessment for the different cropland land uses in Italy

The aim of this work was to quantify the soil organic C (SOC) stock in the top 30 cm of mineral soil for the whole Italian territory, according to the different land use types of the Intergovernmental Panel on Climate Change (IPCC) cropland category (arable land, agroforestry, vineyards, olive groves, orchards and rice fields), as a basis for future land use scenarios and to address mitigation policy at country level. A database for SOC stock was created with the data from the national project denominated SIAS and partly from regional map reports. All data were referred to the year 2000 since they were derived from surveys conducted from 1995 to 2005. The data were stratified according to the Italian climatic regions, the landscape position and the IPCC cropland subcategories. Taking into account the uncertainty in the estimate, the mean SOC stock values of the different subcategories show significant differences (p < 0.05) among climatic regions and landscapes, ranging from 41.9 ± 15.9 Mg C ha−1 in the vineyards to 63.3 ± 27.9 Mg C ha−1 in the rice fields. Generally, a small decrease of the SOC stock from the temperate regions toward the Mediterranean ones is observed. Taking into account the mean value of each subcategory and the country area they occupied in 2000, the total C stored in the upper 30 cm of soil was estimated at 490.0 ± 121.7 Tg C. The resulting estimate represents the 17% of the value reported by another study for the soil of the whole country down to 50 cm depth, suggesting the importance of preserving this large C pool. Considering the cropland category as a whole, the estimated mean SOC stock is 52.1 ± 17.4 Mg C ha−1, similar to that reported for other European countries, 50–60 Mg C ha−1. In conclusion, the assessment of the mean SOC stock of the different cropland land uses, landscape position and climate regions could notably help when assessing the impact of different agricultural practices and future stock change evaluation.