Mean Soil Organic Carbon Density Research Articles

National-scale mapping of soil organic carbon stock in France: New insights and lessons learned by direct and indirect approaches

Soil organic carbon (SOC) plays a crucial role in soil health and global carbon cycling, therefore accurate estimates of its spatial distribution are important for managing soil health and mitigating global climate change. Digital soil mapping shows its potential to provide accurate and high-resolution spatial distribution of SOC across scales. To convert SOC content to SOC density (SOCD), two inference trajectories exist for predicting SOCD in digital soil mapping: the direct approach (calculate-then-model) and indirect approach (model-then-calculate). However, there is a lack of comprehensive exploration regarding the differences in their performance in SOCD estimates, particularly in regions characterized by diverse pedoclimatic conditions. To bridge this knowledge gap, we evaluated the two approaches based on model performance of SOCD in France. Using 916 topsoils (0−20 ​cm) from the LUCAS Soil 2018 and 24 environmental covariates, random forest model and forward recursive feature selection were used to build the spatial predictive models of SOCD using direct and indirect approaches. The results show that, using random forest model and full covariates, both approaches show moderate performance (R2 ​= ​0.28−0.32). By utilizing forward recursive feature selection model, the number of predictors was reduced from 24 to 9, enhancing model performance for direct approach (R2 of 0.35), with no improvement for indirect approach (R2 of 0.28). The mean SOCD of the French topsoil was 5.29 and 6.14 ​kg ​m−2 by direct and indirect approaches, resulting in SOC stock of 2.8 and 3.3 ​Pg, respectively. We found that the direct approach clearly underestimated the high SOCD (>9 ​kg ​m−2), while the indirect approach performed much better for high SOCD. Our findings serve as a valuable reference for SOCD mapping, thereby providing a scientific basis for maintaining soil health.

Zonal patterns and driving factors of soil organic carbon density in Zhejiang Province, China

The complex topography and intensive land use and land cover change (LUCC) might shift the spatial pattern of soil organic carbon (SOC) density. However, the effects of LUCC caused by development on the distribution and driving factors of SOC density remain unclear. As one of the most developed regions in China, Zhejiang Province has experienced intensive land use change and has various vegetation types, making it an ideal location to analyse the zonal pattern and driving factors of SOC density in terrestrial ecosystems. To do that, a dataset was built with data collected from existing literature. The average SOC density in Zhejiang Province was 69.75 Mg ha−1, ranging widely from 6.44 to 301.90 Mg ha−1 depending on land and vegetation types. We found that forests had the highest mean SOC density (78.30 Mg ha−1), while cropland had the lowest (45.69 Mg ha−1). Meanwhile, the SOC density of unmanaged land was significantly higher than that of managed land (P < 0.001). Additionally, SOC density varied greatly with longitude and altitude, showing a decreasing zonal pattern from west to east and from high to low altitude. The RF model indicated that vegetation type, stand age, mean annual temperature (MAT), soil pH, and mean annual precipitation (MAP) were the five most important factors affecting SOC density in this area, but the effects differed between managed and unmanaged lands. These results aid with understanding the dynamics of SOC pools in terrestrial ecosystems and inform policy-making to mitigate global climate change. These findings provide valuable insights into the dynamics of SOC pools in terrestrial ecosystems, enabling more effective policymaking to mitigate the impact of global climate change.

Quantifying changes in soil organic carbon density from 1982 to 2020 in Chinese grasslands using a random forest model.

China has the second-largest grassland area in the world. Soil organic carbon storage (SOCS) in grasslands plays a critical role in maintaining carbon balance and mitigating climate change, both nationally and globally. Soil organic carbon density (SOCD) is an important indicator of SOCS. Exploring the spatiotemporal dynamics of SOCD enables policymakers to develop strategies to reduce carbon emissions, thus meeting the goals of "emission peak" in 2030 and "carbon neutrality" in 2060 proposed by the Chinese government. The objective of this study was to quantify the dynamics of SOCD (0-100 cm) in Chinese grasslands from 1982 to 2020 and identify the dominant drivers of SOCD change using a random forest model. The results showed that the mean SOCD in Chinese grasslands was 7.791kg C m-2 in 1982 and 8.525kg C m-2 in 2020, with a net increase of 0.734kg C m-2 across China. The areas with increased SOCD were mainly distributed in the southern (0.411kg C m-2), northwestern (1.439kg C m-2), and Qinghai-Tibetan (0.915kg C m-2) regions, while those with decreased SOCD were mainly found in the northern (0.172kg C m-2) region. Temperature, normalized difference vegetation index, elevation, and wind speed were the dominant factors driving grassland SOCD change, explaining 73.23% of total variation in SOCD. During the study period, grassland SOCS increased in the northwestern region but decreased in the other three regions. Overall, SOCS of Chinese grasslands in 2020 was 22.623 Pg, with a net decrease of 1.158 Pg since 1982. Over the past few decades, the reduction in SOCS caused by grassland degradation may have contributed to soil organic carbon loss and created a negative impact on climate. The results highlight the urgency of strengthening soil carbon management in these grasslands and improving SOCS towards a positive climate impact.

An evaluation of topsoil carbon storage in Chinese deserts

Deserts are important components of the terrestrial ecosystem, and significantly affect the terrestrial carbon cycle. However, their carbon storage is poorly understood. To evaluate the topsoil carbon storage in Chinese deserts, we systematically collected topsoil samples (to a depth of 10 cm) from 12 deserts in northern China and analyzed their organic carbon storage. We used partial correlation and boosted regression tree (BRT) analysis to analyze the factors influencing the spatial distribution of soil organic carbon density based on climate, vegetation, soil grain-size distribution, and element geochemistry. The total organic carbon pool of Chinese deserts was 4.83 × 108 t, the mean soil organic carbon density was 1.37 ± 0.18 kg C m−2, and the mean turnover time was 16.50 ± 2.66 yr. With the largest area, the Taklimakan Desert had the highest topsoil organic carbon storage (1.77 × 108 t). The organic carbon density was high in the east and low in the west, whereas the turnover time showed the opposite trend. The soil organic carbon density was >2 kg C m−2 in the four sandy lands in the eastern region, and was greater than the values for the eight deserts (0.72 to 1.22 kg C m−2). Grain-size (i.e., the silt and clay contents) had the strongest influence on the organic carbon density in Chinese deserts, followed by element geochemistry. Precipitation was the main climatic factor that affected the distribution of organic carbon density in the deserts. Based on climate and vegetation cover trends during the past 20 years, Chinese deserts have a high potential for future organic carbon sequestration.

Soil Carbon within the Mangrove Landscape in Rufiji River Delta, Tanzania

Mangroves are among the most carbon-rich terrestrial ecosystems, primarily attributable to the soil pool. There are substantial differences in soil carbon (C) and nitrogen (N) due to the disparities in geomorphic settings and ecological drivers, but this insight is drawn primarily from observational studies. An objective inventory of carbon stocks in mangroves of the Rufiji River Delta, Tanzania was conducted. Seventy-five soil cores were collected within a 12,164 ha inventory area, comprising the northern portion of the delta. Cores were collected from intact and dwarf mangroves, agricultural fields, and mudflats. The spatial mean soil organic carbon (SOC) density in mangroves was 16.35 ± 6.25 mg C cm−3. Mean SOC density in non-vegetated mudflats was 12.16 ± 4.57 mg C cm−3, demonstrating that mangroves develop on soils with a substantial soil C stock. However, long-established mangroves had had a higher C density (17.27 ± 5.87 mg C cm−3). Using a δ13C mixing model, the source of soil organic matter in mudflats was primarily marine, while long-established mangroves was predominantly mangrove. There were small differences in SOC among long-established mangrove sites in different geomorphic settings. The proportion of marine-sourced SOC increased with soil depth in mangroves. The SOC and nitrogen of agricultural sites resemble those of mudflats, suggesting those sites are developed from relatively young forests. The SOC and nitrogen density in dwarf mangrove sites were lower than others, perhaps reflecting past disturbances.

Estimation of soil organic carbon stock and its controlling factors in cropland of Yunnan Province, China

Soil organic carbon (SOC) is the most important indicators of soil quality and health. Identifying the spatial distribution of SOC and its influencing factors in cropland is crucial to understand the terrestrial carbon cycle and optimize agronomic management. Yunnan Province, characterized by mountainous topography and varied elevation, is one of the highest SOC regions in China. Yet its SOC stock of cropland and influencing factors has not been fully studied due to the lack of adequate soil investigation. In this study, the digital mapping of SOC at 1 km resolution and the estimation of total SOC stock in cropland of Yunnan Province was undertaken using 8 637 topsoil (0–20 cm) samples and a series of spatial data through Random Forest (RF) model. It was showed that across the cropland of Yunnan Province, the mean SOC density and total stock were 4.84 kg m–2 and 337.5 Mt, respectively. The spatial distribution indicated that relatively high SOC density regions resided in the northwest and northeast parts of Yunnan Province. Elevation (19.5%), temperature (17.3%), rainfall (14.5%), and Topographic wetness index (9.9%) were the most important factors which controlled spatial variability of SOC density. Agronomic practices (e.g., crop straw treatments, fertilizer management) should be optimized for the sustainable development of crop production with high SOC sequestration capacity in Yunnan Province.

Spatial prediction of soil acidity and nutrients for site-specific soil management in Bedele district, Southwestern Ethiopia

BackgroundUnderstanding the spatial variability of soil properties is useful to tailor site-specific agricultural inputs to enhance crop production on a sustainable basis. This study was aimed to assess and map the spatial patterns of soil acidity and nutrients using geostatistical methods and support site-specific lime and fertilizer recommendations in Bedele district, Southwestern Ethiopia.MethodsSoil samples were collected from agricultural land at a depth of 20 cm using grid sampling technique. The semivariogram analysis was performed for accurate spatial prediction and the kriging technique was used for interpolation of soil parameters.ResultsSoil pH varied between 4.5 and 6.8. Soil organic carbon (OC) content ranged from 0.3 to 5.6% and the mean soil OC density was 0.81 kg m−2. Available phosphorus (AvP) ranged from 0.8 to 38.6 mg kg−1 and nearly 80.23% of the soils exhibited very low to low AvP that could be due to fixation by strong acidity. Soils of the study area exhibited very high exchangeable potassium (K), but very low exchangeable calcium (Ca) and magnesium (Mg). The potassium to magnesium ratio (K:Mg) ranged from 0.2:1 to 10.9:1, while the values of calcium to magnesium ratio (Ca:Mg) varied between 0.3 and 3.4. Among the soil parameters, exchangeable Ca (CV = 54%) and K:Mg ratio (CV = 57.62%) were more variable than other soil parameters. Spatial variability was lowest for soil pH (CV = 10%).ConclusionsMajor portions of the study site were affected by strong acidity (pH ≤ 5.5). Accordingly, about 89% of the soils require lime that varied between 0.09 and 3.6 tons ha−1. In addition to soil acidity, deficiency of available P, Ca, and Mg were the major liming factors affecting crop production in the study area. Digital soil mapping was used to show the spatial variability of soil acidity and nutrients across agricultural land and applied for efficient lime and nutrients advisory works.

Prediction Potential of Remote Sensing-Related Variables in the Topsoil Organic Carbon Density of Liaohekou Coastal Wetlands, Northeast China

Wetland ecosystems contain large amounts of soil organic carbon. Their natural environment is often both at the junction of land and water with good conditions for carbon sequestration. Therefore, the study of accurate prediction of soil organic carbon (SOC) density in coastal wetland ecosystems of flat terrain areas is the key to understanding their carbon cycling. This study used remote sensing data to study SOC density potentials of coastal wetland ecosystems in Northeast China. Eleven environmental variables including normalized difference vegetation index (NDVI), difference vegetation index (DVI), soil adjusted vegetation index (SAVI), renormalization difference vegetation index (RDVI), ratio vegetation index (RVI), topographic wetness index (TWI), elevation, slope aspect (SA), slope gradient (SG), mean annual temperature (MAT), and mean annual precipitation (MAP) were selected to predict SOC density. A total of 193 soil samples (0–30 cm) were divided into two parts, 70% of the sampling sites data were used to construct the boosted regression tree (BRT) model containing three different combinations of environmental variables, and the remaining 30% were used to test the predictive performance of the model. The results show that the full variable model is better than the other two models. Adding remote sensing-related variables significantly improved the model prediction. This study revealed that SAVI, NDVI and DVI were the main environmental factors affecting the spatial variation of topsoil SOC density of coastal wetlands in flat terrain areas. The mean (±SD) SOC density of full variable models was 18.78 (±1.95) kg m−2, which gradually decreased from northeast to southwest. We suggest that remote sensing-related environmental variables should be selected as the main environmental variables when predicting topsoil SOC density of coastal wetland ecosystems in flat terrain areas. Accurate prediction of topsoil SOC density distribution will help to formulate soil management policies and enhance soil carbon sequestration.

Variation in Total Soil Organic Carbon Stocks in Relation to Some Land Use Systems in the Bamenda Highlands, Cameroon

Climate change and food security are among the pressing challenges facing humanity in the 21st century. Soil organic carbon (SOC) stocks, total nitrogen (TN), texture, and bulk density (BD) are important soil properties, which control climate change. Three land use systems (smallholder farmlands, grazing lands, and forest lands) that coexist in the Bamenda Highlands (BH) influence ecosystem services and induce soil degradation with the loss of SOC. The objective of this study was to evaluate the variation of SOC and some soil physicochemical properties as affected by the three land use systems (LUS). A total of 21 composite soil samples collected from 7 microclimatic zones of BH following “S” shape plots to the depth of 0 - 30 cm, were analysed for moisture content (MC), SOC, TN, BD, available phosphorus (Av.P), pH and texture. The results revealed that grazing land had the lowest mean sand content (40.79 ± 4.07). Mean MC, TN and SOC (%) content were significantly higher (p in forest land than those in the grazing land and smallholder farmlands. Conversely, BD and Av.P were significantly higher (p in smallholder farmlands than grazing and forest lands probably due to different litter accumulation and agricultural practices. Moisture content and TN revealed positive significant correlations (p 0.05) with SOC, while BD and Av.P revealed negative significant correlations (p 0.05). Mean SOC density in smallholder farmlands (132.91 ± 9.48 tC/ha) was the lowest among the three land use types. Losses in CO2 equivalence, as a result of land use change from forest lands to smallholder farmlands were 137.33 t/ha while that from grazing lands to smallholder farmlands were 109.13 t/ha. Total organic carbon (TOC) stocks differed significantly (p 0.05) from smallholder farmlands (10.73 Mt) to forest lands (91.13 Mt). A sustainable farming technique that enhances SOC sequestration and minimizes soil CO2 emissions is therefore recommended to replace tillage ridges formation commonly practiced by smallholder farmers.

Assessment of Retention Potential and Soil Organic Carbon Density of Agriculturally used Chernozems, Cambisols and Fluvisols

Climate change and the increasing frequency of climatic extremes have led to growing concerns over the sustainability of agriculture during recent years. In this context, soil retention and carbon storage are becoming widely discussed. The aim of this study was to evaluate the retention potential (RP) and soil organic carbon density (SOCD) of Chernozem, Cambisol and Fluvisol topsoil under agricultural management. Despite the different natural assumptions of these soil types, no significant statistical difference was found there. Mean RP values of the soil types varied from 39 to 40 mm and mean SOCD values from 23 to 28 t/ha. This finding may suggest that long-term agricultural management can suppress the naturally diverse potential for water retention and carbon storage of the individual soil types. Comparison of SOCD of the studied soils with agricultural soils in similar studies showed that most of the observed values can be considered as average. Despite this fact, a very strong local degradation has been revealed indicating poor agricultural management. Especially in such cases, there is an urgent need to adjust the management of the agricultural land fund (e.g. increased application of organic fertilizers, change in crop rotation) in order to increase carbon stocks and to improve the water retention capacity of soils.

Storage, pattern and driving factors of soil organic carbon in an ecologically fragile zone of northern China

Knowledge of the spatial pattern of soil organic carbon (SOC) and its influencing factors is important for understanding the carbon cycle. We investigated the SOC density (SOCD) to a depth of 30 cm from ground surface at 644 sites in an agro-pastoral ecotone of northern China that covered 654,564 km2. SOC storage to a depth of 30 cm was 2360 Tg, and SOCD averaged 3.78 kg·m−2 for the entire study area. SOCD to a depth of 20 cm and from 20 to 30 cm showed strong and moderate spatial dependence, with a nugget to sill ratio of 0.7% and 43.5%, respectively. Overall, SOCD increased from southwest to northeast, it was more strongly correlated with latitude than with longitude. Forest and sandy land had the highest and lowest SOCD, at 6.28 and 1.76 kg·m−2, respectively. The SOCD (kg·m−2) of grassland decreased with decreasing vegetation cover: high (4.42) > medium (3.62) > low (2.50). For the common soils in the study area, the highest mean SOCD was 9.31 kg·m−2 in Grey Forest Soils, versus 1.75 kg·m−2 in Brown Pedocals. In the study area, temperature appears to be the dominant factor that influences SOC, and SOCD decreased with increasing temperature. However, topographic factors (elevation, slope, and aspect) had a weaker effect on SOC. Our results provide a valuable baseline for future research on the long-term evolution of SOCD.

The role of check dams in retaining organic carbon and nutrients. A study case in the Sierra de Ávila mountain range (Central Spain)

Soil organic carbon plays an important role in the global carbon cycle, accounting for 70% of the Earth's carbon. However, soil erosion can have a major impact on the stocks of soil carbon and other soil nutrients, such as nitrogen and phosphorous. Soil and water conservation techniques, such as the building of check dams, are usually employed to control sediment yields and the losses of other soil components. The aim of this research is thus to quantify the soil organic carbon (SOC), soil nitrogen (SN) and soil phosphorous (SP) retained by the check dams of a hydrologic and forest restoration project in the Sierra de Ávila mountain range (Ávila, Central Spain). Soil samples were taken from the sediment wedges of 30 check dams and from 30 native soils. Soil texture, electric conductivity, pH, C, N and P were measured in all the soil samples. The volume of sediment retained by the check dams was calculated by the Sections Method, which is very accurate in estimating the real volume of the sediment wedges. The total sediment yield in the area was thus estimated at 6.40 Mg·ha−1·yr−1 and the mean SOC, SN and SP densities were respectively 13.76, 0.48 and 0.05 kg·m−2. These findings thus are very reliable and allow us to conclude that check dams constitute an important instrument for controlling losses of SOC, SN and SP, and preventing these substances from passing into watercourses downstream of the area.

Changes in surface soil organic carbon in semiarid degraded Horqin Grassland of northeastern China between the 1980s and the 2010s

Soil organic carbon (SOC) plays an important role in the global carbon cycle and in mitigating climate change. The Horqin Grassland is one of the largest grasslands in China and has undergone serious aeolian desertification in recent decades. We conducted the largest field inventory to date, with the highest density of soil sampling, and explored changes in SOC in the region over the 30-year gap between the 1980s and the 2010s. Our results indicated that the mean SOC density to a depth of 20 cm decreased from 2.58 to 2.21 kg C m−2, while the total SOC storage decreased from 311.11 to 266.70 Tg C, at an average of 12.29 g C m−2 yr−1. We ranked the SOC densities by ecosystem as woodland > grassland > cropland > sandy land. The decreased SOC storage in the Horqin Grassland can be ascribed to a combination of increasing temperature, decreasing precipitation, an expansion of the areas of extremely severely desertified land and cropland, and shrinkage of the grassland area. Our results provide an important updated regional baseline for quantifying how SOC storage will respond to future climate change and anthropogenic activities. Our results will also help policy makers determine how to achieve sustainable development of agriculture, forestry, and animal husbandry based on carbon sequestration.

Spatial variation of organic carbon density in topsoils of a typical subtropical forest, southeastern China

Spatial variation of regional soil organic carbon (SOC) stocks and the effects of environmental factors on SOC in forest soils play an essential part in modeling the global carbon cycle and climatic change. In this study, we analyzed topsoil samples (0–30 cm) from 838 plots in a typical subtropical forest of Zhejiang Province, southeastern China, using Moran's I, geostatistics and geographical information system (GIS) techniques. The results showed that the mean SOC density in the topsoils was 71.15 Mg ha−1 and the total storage in topsoils of Zhejiang Province was 0.47 Pg (Pg = 1015 g). The spatial distribution of SOC density based on kriging interpolation and local Moran's I hotspot analysis showed a decreasing trend from the southwest to northeast area, roughly in line with Zhejiang Province's topographic feature, as well as differences in land use, economic and social development. The results herein revealed that both dominant tree species and altitude (P < 0.01) have markedly affected SOC balance and accumulation in a typical subtropical forest of Zhejiang Province. Therefore, management of SOC should focus on the selection of dominant tree species (broad-leaved species), management of forest stand-age structures and implementation of sustainable practices so that the potential for carbon sequestration in forest soils can be maximized in the future.

Spatial distribution of soil organic carbon in the ecologically fragile Horqin Grassland of northeastern China

The spatial distribution of soil organic carbon (SOC) and its storage in the topmost 100 cm of the soil were investigated in the Horqin Grassland of northeastern China. Soil samples were collected at 1465 sites, covering 12.03 × 104 km2. The region had a mean SOC density of 6.84 kg C m−3, which is lower than China's mean (9.60 kg C m−3) and the world's mean (10.40 kg C m−3). The mean SOC density was much higher in the northern part of the study area (8.85 kg C m−3) than in the southern part (4.84 kg C m−3). The total SOC storage in the Horqin Grassland was 862.74 Tg. SOC storage decreased with increasing soil sampling depth. The SOC stored in the top 10, 20, 40, and 60 cm accounted for 17.7, 31.7, 53.8, and 71.3%, respectively, of the total amount in the top 100 cm. The region's extensive desertification appears to be one of the most important factors that led to the relatively low SOC content and the difference between the northern and southern parts of the Horqin Grassland. Our results provide an important baseline for evaluating past losses of SOC due to desertification, and for projecting the potential increase in SOC from the restoration of desertified land and how SOC will respond to climate change.

Quantification of carbon stocks in Mount Marsabit Forest Reserve, a sub-humid montane forest in northern Kenya under anthropogenic disturbance

The quantification of carbon stocks is vital for decision making in forest management, carbon stock change assessment and scientific applications. We applied the land degradation surveillance framework (LDSF) method with a sentinel site of (10 km × 10 km) to assess carbon stock levels and tree diversity in the Marsabit Forest Reserve (MFR). The above ground (ABG) carbon stock was estimated at 12.42 t/ha, while soil organic carbon (SOC) was 12.51 t/ha, with SOC densities increasing with increasing depth. The mean ABG carbon and SOC densities were higher in the least disturbed strata than the disturbed strata. The estimated ABG carbon and SOC stocks were significantly lower than the range observed in a typical dry tropical forest. Twenty-one tree species were recorded belonging to twelve families with the disturbed areas recording nine tree species while the least disturbed recording twelve species. Rubiaceae and Rutaceae were the richest families with four species each while Boraginaceae, Capparaceae, Flacourtiaceae, Tiliaceae, Violaceae, and Ochnaceae the least frequent with one species each. The most common tree species were, Croton megalocarpus, Drypetes gerrardii, Ochna insculpta, Strychnos henningsii and Vangueria madagascariensis. The forest recorded a basal diameter of 14.09 ± 12.15 cm, basal area of 0.016 m 2/ha with a mean height of 8.69 m. The basal size class distribution declined monotonically indicative of a stable population. Livestock grazing, selective logging, and firewood collection were the primary forms of anthropogenic activities recorded in the MFR despite the moratorium imposed on consumptive utilisation of forest products by the Marsabit County security committee. The Pearson correlation coefficient returned an inverse relationship between forest disturbance with SOC and ABG carbon in the disturbed strata suggesting that anthropogenic activities reduced carbon stocks in the MFR. Concerted efforts to mitigate anthropogenic impacts on the MFR could significantly increase its terrestrial carbon sequestration potential and the provision of critical ecosystem goods and services.

A segregated assessment of total carbon stocks by the mode of origin and ecological functions of forests: implication on restoration potential

In depth understanding of variation of biomass and carbon pools in different forest ecosystems is crucial for monitoring, reporting and verification of forest carbon stocks in the context of forest landscape restoration (FLR). The study compares carbon stocks from five carbon pools by the mode of origin (natural vs planted forests) and ecological functions (Special use, Protection and Production forests) of the forests. An intensive forest carbon inventory was conducted in six communes of Dinh Hoa district, Vietnam. Soil organic carbon (SOC) was found to be the largest carbon pool. Mean SOC densities were not significantly different between natural forests and planted forests, but were significantly different among different forest types classified based on ecological functions. When considering the total of all carbon pools, mean carbon densities were neither significantly different between natural and planted forests, nor among Special use, Protection and Production forests. Our study provides evidence that different FLR interventions may provide equivalent potentials for increasing forest carbon stocks. We link FLR with the United Nations Framework Convention on Climate Change (UNFCCC) initiative Reducing Emissions from Deforestation and Forest Degradation in developing countries (REDD+) to highlight synergies between processes of regaining ecological functionality, enhancement of human well-being across deforested or degraded forest landscapes, and contribution to the enhancement of forest carbon stocks.

Effects of land use and topography on spatial variety of soil organic carbon density in a hilly, subtropical catchment of China

A good understanding the effects of environmental factors on the spatial variety of soil organic carbon density (SOCD) helps achieve a relatively accurate estimation of the soil organic carbon stock of terrestrial ecosystems. The present study analysed the SOCD of 1033 top soil samples (0–20cm) from the Jinjing catchment located in subtropical China. Spatial variability of SOCD was estimated using a geostatistics method and a geographically weighted regression (GWR) model, and the major environmental factors affecting SOCD were also explored. In the present study, SOCD had a moderate spatial dependence and the best-fitting model was exponential with a nugget-to-sill ratio of 60.72% and a range of 182m. Land use types (woodlands, paddy fields and tea fields) and topography (elevation, slope, topographic wetness index (TWI)) affected the spatial variation of SOCD. Mean SOCD in the paddy fields was higher than in woodland and tea fields (3.50 vs 3.24 and 2.81kgCm–2 respectively; P&lt;0.05). In addition, SOCD was generally higher in the valleys of paddy fields (with low slope and high TWI) and the hills of woodland (with high elevation and increased slope). GWR generated the spatial distribution of SOCD more accurately than ordinary kriging, inverse distance weighted, multiple linear regression model, and linear mixed-effects model. The results of the present study could enhance our understanding of the effects of land use and topography on SOCD, and improve the accuracy in predicting SOCD by GWR in small catchments of complex land use and topography.

Soil organic carbon distribution in roadside soils of Singapore

Soil is the largest pool of organic carbon in terrestrial systems and plays a key role in carbon cycle. Global population living in urban areas are increasing substantially; however, the effects of urbanization on soil carbon storage and distribution are largely unknown. Here, we characterized the soil organic carbon (SOC) in roadside soils across the city-state of Singapore. We tested three hypotheses that SOC contents (concentration and density) in Singapore would be positively related to aboveground tree biomass, soil microbial biomass and land-use patterns. Overall mean SOC concentrations and densities (0–100 cm) of Singapore's roadside soils were 29 g kg−1 (4–106 g kg−1) and 11 kg m−2 (1.1–42.5 kg m−2) with median values of 26 g kg−1 and 10 kg m−2, respectively. There was significantly higher concentration of organic carbon (10.3 g kg−1) in the top 0–30 cm soil depth compared to the deeper (30–50 cm, and 50–100 cm) soil depths. Singapore's roadside soils represent 4% of Singapore's land, but store 2.9 million Mg C (estimated range of 0.3–11 million Mg C). This amount of SOC is equivalent to 25% of annual anthropogenic C emissions in Singapore. Soil organic C contents in Singapore's soils were not related to aboveground vegetation or soil microbial biomass, whereas land-use patterns to best explain variance in SOC in Singapore's roadside soils. We found SOC in Singapore's roadside soils to be inversely related to urbanization. We conclude that high SOC in Singapore roadside soils are probably due to management, such as specifications of high quality top-soil, high use of irrigation and fertilization and also due to an optimal climate promoting rapid growth and biological activity.

Impact of soil and water conservation on soil organic carbon content in a catchment of the middle Han River, China

Soil organic carbon (SOC) is essential for improving soil quality, sustaining food production and quality, and maintaining water quality, as well as for mitigating climate change. Understanding the impact of soil and water conservation on SOC content is important for the protection of soil and water quality. In this study, the impacts of soil and water conservation on SOC content and density in a small catchment of the middle Han River were studied based on a grid soil survey. A total of 583 soil samples from 207 sites were collected, primarily from 30 m × 30 m grids. The results indicated that SOC content generally decreased with increasing soil depth, and significant differences existed among the three examined soil layers (0–20, 20–40, and 40–60 cm, p terraces > grassland > sloping cropland. The spatial variability of SOC decreased as soil depth increased. The mean SOC densities of terraces, forestland, grassland, and sloping cropland at the 0–60 cm soil depth were 4.40, 4.31, 3.86, and 3.62 kg/m2, respectively. The high-value zones of SOC density were always observed in the upper slope and basin outlet. SOC storage in the 0–60 cm soil depth was 565.10 tons in the Yujiehe catchment. Land use was the main influencing factor for SOC content in the catchment. Forestland, grassland, and terraces exhibit higher SOC than does sloping cropland. In conclusion, the use of terraces can greatly increase SOC density. Much sloping cropland can be changed to terraces, forestland, or grassland to increase SOC and protect soil and water quality in the water source area of the Han River.