Mean Soil Organic Carbon Content Research Articles

Soil organic carbon stocks increased across the tide-induced salinity transect in restored mangrove region

AbstractBlue carbon in mangrove ecosystems contributes significantly to the global carbon cycle. However, large uncertainties maintain in the soil organic carbon (SOC) storage throughout the tide-induced salinity and alkalinity transect in the mangrove restoration region in Southern China. Total 125 soil samples were obtained to detect the SOC content and physicochemical properties. The mean SOC content of each layer ranged from 6.82 to 7.86 g kg−1, while the SOC density ranged from 2.99 to 11.41 kg m−2, increasing with soil depths. From different land covers in the study region, the SOC content varied from 4.63 to 9.71 g kg−1, increasing across the salinity and alkalinity transect, while the SOC density fluctuated from 3.01 kg m−2 in mudflats to 10.05 kg m−2 in mangrove forests. SOC concentration was favorably linked with total nitrogen (r = 0.95), and total phosphorus (r = 0.74), and negatively correlated with Cl− (r = − 0.95), electrical conductivity (r = − 0.24), and total dissolved solids (r = − 0.08). There were significant logarithmic relationships between SOC content and the concentrations of clay (r = 0.76), fine silt (r = 0.81), medium silt (r = − 0.82), and coarse silt (r = − 0.78). The spatial patterns of SOC concentration were notably affected by soil texture, physicochemical properties, and land-cover type, providing essential reference for future investigations of blue carbon budget in restored mangrove forests.

Remote estimation of soil organic carbon under different land use types in agroecosystems of Eastern China

Soil organic carbon (SOC) plays a key role in soil function, ecosystem services, and the global carbon cycle. Large SOC stocks accumulate in agroecosystems, but the estimates of SOC distribution and magnitude in agroecosystems still have large uncertainties in global products. Based on multiple high-resolution environmental variables (terrain derived from digital elevation model, climate and organism from Landsat 8 OLI) and 369 observed soil samples from 2019 to 2021, two machine learning methods, random forest (RF) and support vector machine (SVM) models, were used to estimate the content and spatial distribution of SOC in agroecosystems of Eastern China. We proposed a hybrid model in which the optimal predictors of SOC were selected for different land use types (cropland, planted forest and grassland), and it aimed to improve the performance of machine learning. Our results showed that (1) the hybrid models performed better than the global models, and the Random forest-Hybrid (RF-Hybrid) model led to the highest prediction accuracy, with a validation R2 of 0.65 and RMSE of 5.76 g kg−1. (2) The SOC content in the agroecosystems of Eastern China among different land use types ranked in the following order: planted forest (19.92 g kg−1) > cropland (17.51 g kg−1) > grassland (17.30 g kg−1). However, in North China, the SOC content in cropland (14.04 g kg−1) was much lower than that in planted forest (17.21 g kg−1) and grassland (17.07 g kg−1), which was caused by excessive mechanized operation. (3) The agroecosystem in Northeast China presented the highest mean SOC content (26.55 g kg−1) due to low temperature. (4) Our estimations (R2 = 0.53, RMSE = 6.74 g kg−1, 30-m resolution) were more detailed and precise than the existing global SOC maps (Soil Grids: R2 = 0.26, RMSE = 12.44 g kg−1, 250-m resolution; HWSD: R2 = 0.06, RMSE = 41.07 g kg−1, 1000-m resolution). The results may improve the accuracy of agroecosystem carbon mapping and contribute to SOC assessments in agricultural ecosystems.

Regional spatial variability of soil organic carbon in 0–5 m depth and its dominant factors

Soil organic carbon (SOC) stored in deeper soils is becoming increasingly significant in carbon management and carbon cycle especially in the face of climate and land use alterations. However, spatial variability of deep SOC at a regional scale and its related dominant factors are rarely investigated. To ascertain the vertical distribution and regional spatial variations in the SOC content of deep soil, 1648 soil samples were collected from 67 sites across the Chinese Loess Plateau (CLP) at a depth of 500 cm. Results showed that the mean SOC content of three land use types were recorded as follows: cropland (2.93 ± 0.29 g kg−1) > forest (2.56 ± 0.24 g kg−1) > grassland (2.39 ± 0.29 g kg−1), and the vertical distribution of soil profile from 0 to 500 cm was similar. Furthermore, a significant alteration in SOC content was observed in the soil layer of 0–180 cm among the three land use types (p < 0.05). Spatial distribution maps of SOC content indicated that there was a central region of the northern CLP with low SOC content, which corresponds to the eolian sand area in Ordos. Both the spatial variations and influencing factors of SOC content were found to be depth-dependent, but soil texture and temperature were identified as the dominant factors affecting the 0–500 cm soil profile of the CLP. Clarifying this information is helpful for understanding content level and variation of deep SOC, which can provide a reference for carbon sequestration in deep soil and developing sustainable SOC management for the CLP and other related ecological regions.

Estimation of soil carbon pools under major cropping systems of Mayiladuthurai district of Cauvery Delta Zone, Tamil Nadu, India

Soil organic carbon (SOC) is a potential indicator of soil quality and ecosystem sustainability. The present study aimed to evaluate SOC pools under major cropping systems of Mayiladuthurai district of Tamil Nadu. The composite samples were collected from two depths (0-15 and 15-30 cm) by stratified random sampling and were analysed for pH, EC (Electrical conductivity), C fractions, inorganic carbon and permanganate oxidisable carbon by standard procedures. The SOC content under different land use was in the order of Forestry &gt; Rice – pulses &gt; Rice – cotton &gt; Sugarcane &gt; Uncultivated. The mean SOC content of the study area was 12.58 Mg ha-1, where the majority of the area falls under low to medium rating of SOC. Hence, cultivation practices should incorporate activities that increase SOC to maintain soil quality. SOC was positively correlated with fractions of carbon – CVL (r = 0.37**), CL (r = 0.65**) and CLL (r = 0.58**), indicating changes in land use would affect the carbon dynamics of the ecosystem. The root biomass, aeration status, microbial activity, nutrient reserves and inherent soil characteristics influenced SOC to decrease with depth. The PCA analysis revealed that the variation in carbon dynamics of the study area was influenced by SOC, CLC, CLL and non-labile carbon due to differences in land management practices. Therefore, such soil management practices will be a powerful tool to sequester carbon, which supplements climate change mitigation.

Responses of soil organic carbon cycle to land degradation by isotopically tracing in a typical karst area, southwest China.

The loss of soil organic carbon (SOC) under land degradation threatens crop production and reduces soil fertility and stability, which is more reflected in eco-sensitive environments. However, fewer studies simultaneously compared SOC variations and δ13CSOC compositions under diverse land uses, especially in karst areas. Soil profiles from two agricultural lands and a secondary forest land were selected to analyze SOC contents and their stable isotope composition (δ13CSOC) in a typical karst area located in southwest China to understand the response of the SOC cycle to land degradation. Moreover, the relationships between SOC contents and mean weight diameter (MWD) and soil erodibility (K) factor were comprehensively analyzed for assessing the response of SOC to soil degradation risk. The mean SOC content was found to be the lowest in abandoned cropland (6.91 g/kg), followed by secondary forest land (9.31 g/kg) and grazing shrubland (34.80 g/kg), respectively. Meanwhile, the δ13CSOC values exhibited the following trend: secondary forest land (mean: -23.79‰) ≈abandoned cropland (mean: -23.76‰) >shrubland (mean: -25.33‰). The isotopic tracing results suggested that plant litter was the main contributor to SOC in the secondary forest land. Whereas abundant nitrogen from goat feces enhanced plant productivity and resulted in additional accumulation of SOC in the grazing shrubland. Conversely, long-term cultivation led to the depletion of SOC sequestration by the loss of calcium. In surface soils, the fractionation of δ13CSOC were considerably affected by the decomposition of SOC by soil microorganisms and covered vegetation rather than agricultural influences. The findings indicate that the cycling of SOC and soil stability in the calcareous soil of southwest China are largely regulated by different land uses and the presence of vegetation cover. The depletion of SOC and soil physical degradation pose significant challenges for abandoned cropland, particularly in the karst area, where land degradation is inevitable. Nevertheless, moderate grazing enhances SOC levels, which is beneficial to the land fertility maintenance in the karst region. Therefore, more emphasis should be placed on the cultivation methods and management strategies for abandoned cropland in the karst area.

Subsoiling for planting trees in dehesa system: long-term effects on soil organic carbon

Incorporating trees into agricultural systems, including grasslands, increases the soil organic carbon sequestration and contributes to climate change mitigation. Site preparation for tree establishment is a common practice that can involve a variety of techniques and agricultural implements such as subsoiling. This study aimed to evaluate the long-term effects of subsoiling on soil organic carbon (SOC) concentrations and stocks in a Mediterranean grassland afforested with holm oaks 22 years ago and now converted into a Dehesa agroforestry system. The study was conducted in a dehesa farm in Southwest Spain. Soil samples were taken at six depths under 10 tree canopies within and outside the original subsoiling line. Subsoiling significantly decreased SOC concentration. Mean SOC concentration in the first 20 cm was 30% lower at the subsoiling line. SOC stocks for the first 60 cm were 2660 g m−2 within the subsoiling line and 4320 g m−2 outside the line. There was a clear reduction in SOC concentration and stock with increasing depth. Root abundance and deeper rooting increased with subsoiling but did not translate into sufficient carbon accumulation in the soil, which is moderate even after 22 years. This study reveals that, in the long term, there is a trade-off in CO2 sequestration between tree planting and soil subsoiling, highlighting the need for further research into the potential benefits and detriments of subsoiling.

Assessment of water quality with comparative study of soil organic carbon stock in Nagdaha Lake and its adjacent agricultural land of Lalitpur, Nepal

Abstract. Bhatta M, Joshi R. 2023. Assessment of water quality with comparative study of soil organic carbon stock in Nagdaha Lake and its adjacent agricultural land of Lalitpur, Nepal. Intl J Bonorowo Wetlands 13: 9-16. The lakes are an important component of the terrestrial Carbon (C) cycle. Estimates of global C burial by lakes suggest burial rates ranging from 0.03-0.07 Pg C yr?1. In the present study, the water quality of Nagdaha Lake and comparative analysis of Soil Organic Carbon (SOC) in Nagdaha Lake and its adjoining agricultural area has been studied. Water quality was determined following APHA (1998); SOC was determined by the Walkey and Black (1934) Titration Method. The present study results show that the mean N-nitrate and P-phosphate concentration in the waters of Nagdaha Lake is 0.135 mg/L and 0.123 mg/L, respectively, and the mean SOC concentration of Nagdaha Lake (71.39±42.58g kg-1) is higher than the adjacent agricultural land (14.36±8.38g kg-1). The t-test result also shows that there is a significant difference in SOC concentration in lakes (t = 9.18) and agricultural (t = 7.66) for agricultural land (p &lt; 0.0001). Nagdaha Lake's area decreased from 52 ropani to 42 ropani between 1964 and 2022. Despite the decrease in area, Nagdaha Lake has more carbon per unit area than agricultural land. Since the conversion of lake land to agricultural land can release a large amount of carbon into the atmosphere, it is imperative to preserve the lakes to mitigate increasing atmospheric CO2 concentration.

Long-term subsoiling and straw return increase soil organic carbon fractions and crop yield

Conservation tillage has been adopted worldwide as an attractive alternative to conventional tillage. However, suitable conservation tillage for increasing soil organic carbon (SOC) and crop yield simultaneously is still limited. Two conservation tillage methods, subsoiling to the 40 cm depth (ST) and no-tillage (NT), were combined with three straw return treatments (i.e., no return [−0], return of whole wheat (<i>Triticum aestivum</i> L.) straw and 1 m high maize (<i>Zea mays</i> L.) stubble [−1], and return of whole wheat and maize straw [-a]) to study their impacts on SOC content, labile C fractions, and crop yields, with conventional tillage (CT) used as a control in a 15-year field experiment. Subsoiling with 1 m high maize stubble return (ST–1) increased the mean annual grain yields by 18% and the mean SOC content by 39% at the 0 to 100 cm depth compared with conventional tillage with no maize straw return (CT–0) in 2016 and 2017. The mean SOC at the 0 to 100 cm depth of the NT treatment was lower than those of ST and CT because of the reduced transformation from straw to SOC and labile C fractions. One meter high maize stubble return can maintain high SOC content, C fractions, and crop yield compared with whole maize straw return. Thus, subsoiling combined with 1 m high maize stubble return was an effective conservation tillage to increase the SOC content and crop yield.

Soil texture influences soil bacterial biomass in the permafrost-affected alpine desert of the Tibetan plateau.

Under warm climate conditions, permafrost thawing results in the substantial release of carbon (C) into the atmosphere and potentially triggers strong positive feedback to global warming. Soil microorganisms play an important role in decomposing organic C in permafrost, thus potentially regulating the ecosystem C balance in permafrost-affected regions. Soil microbial community and biomass are mainly affected by soil organic carbon (SOC) content and soil texture. Most studies have focused on acidic permafrost soil (pH < 7), whereas few examined alkaline permafrost-affected soil (pH > 7). In this study, we analyzed soil microbial communities and biomass in the alpine desert and steppe on the Tibetan plateau, where the soil pH values were approximately 8.7 ± 0.2 and 8.5 ± 0.1, respectively. Our results revealed that microbial biomass was significantly associated with mean grain size (MGS) and SOC content in alkaline permafrost-affected soils (p < 0.05). In particular, bacterial and fungal biomasses were affected by SOC content in the alpine steppe, whereas bacterial and fungal biomasses were mainly affected by MGS and SOC content, respectively, in the alpine desert. Combined with the results of the structural equation model, those findings suggest that SOC content affects soil texture under high pH-value (pH 8-9) and that soil microbial biomass is indirectly affected. Soils in the alpine steppe and desert are dominated by plagioclase, which provides colonization sites for bacterial communities. This study aimed to highlight the importance of soil texture in managing soil microbial biomass and demonstrate the differential impacts of soil texture on fungal and bacterial communities in alkaline permafrost-affected regions.

Spatial Variation of Soil Organic Carbon from Bamen Bay Mangrove in Southern China

Mangrove forests are large pools of soil organic carbon (SOC) found across the world, and play a vital role in global carbon (C) cycling. In this study, to investigate the effects of spatial factors on SOC in mangrove forests, soil samples at different depth layers from upper estuary (UE), lower estuary (LE), and tidal inlet (TI) in the Qinglangang mangrove forest in Southern China were collected and the differences in SOC among the layers and geomorphological settings were compared. The mean SOC content showed a pattern of LE (4.63 ± 1.28%) &gt; UE (2.94 ± 0.73%) &gt; TI (1.44 ± 0.33%). SOC content and storage decreased with soil depth in TI, but increased in UE. The total SOC storages (0–80 cm) of sites TU, UE, and LE, were 104.41 ± 16.63, 207.14 ± 44.83, and 228.78 ± 19.37 Mg/ha, respectively. The results suggested that top- and subsoil organic C content and storage were largely dependent on their specific location, which underwent different river-sea interactions and human activities. The SOC of the soil profile varied at different sites, implying that the current C storage of mangrove ecosystems can be accurately estimated by quantifying the C of sediments at sites.

Organic carbon rich-soils in the brazilian semiarid region and paleoenvironmental implications

Soil organic carbon (SOC) contents are commonly high in the mountainous tropical soils with wet climates in Southeastern and Southern Brazil, but high SOC soils in the Brazilian semiarid zone are poorly known. The Borborema Plateau represent a complex core of folded and uplifted crystalline rocks with the highest altitudes in the Brazilian semiarid. The present study objetived to describe unusual SOC-rich soils from the semiarid Borborema Plateau, discussing past and present, soil-forming processes, and landscape evolution. We described and characterized 11 Late Quaternary soils in the Borborema Plateau, emphasizing chemical and physical properties, soil carbon stock, and water behavior, allowing us to know about the soil diversity of the semiarid highlands. Five Umbrisols and one Cambisol were described in concave slopes and summits above 1,000 m, under relicts of semideciduous forest and Rupestrian Grassland vegetation; downslope, we found Planosols, Leptosols, Regosols, Luvisols, and Arenosols in partially dissected pediments below 600 m, representing typical soils of the Caatinga (Dry forest). Borborema highland soils with high SOC are acidic, dystrophic, moderately developed, whereas soils from the Caatinga range from moderately acid to moderately alkaline, hypereutrophic, and poorly to moderately developed. The Umbrisols and Cambisols have a mean SOC content of up to 94% higher than typical Caatinga soils. Water retention and availability are similar between acidic soils with high SOC and typical dry forest soils. Radiocarbon analysis of humic fraction of soil indicated the dominance of C3 plants since the start of pedogenesis of Umbrisols, at ∼ 6,900 cal yr BP. The stabilization of high amounts of organic carbon in highland semiarid soils was attributed to P, acidity, and fine particles. These small relicts of soils with high SOC represent hotspots of SOC stocks in the Brazilian semiarid, and they protect “islands” of relict vegetation from past wetter Late Quaternary paleoenvironments.

Modelling and prediction of soil organic carbon using digital soil mapping in the Thar desert region of India

In the present study, the distribution of soil organic carbon (SOC) was investigated using digital soil mapping for an area of ~29 lakhs ha in Bikaner district, Rajasthan, India. To achieve this goal, 187 soil profiles were used for SOC estimation by Quantile regression forest (QRF) model technique. Landsat data, terrain attributes and bioclimatic variables were used as environmental variables. 10-fold cross-validation was used to evaluate model. Equal-area quadratic splines were fitted to soil profile datasets to estimate SOC at six standard soil depths (0–5, 5–15, 15–30, 30–60, 60–100 and 100–200 cm). Results showed that the mean SOC concentration was very low with values varied from 1.18 to 1.53 g kg−1 in different depths. While predicting SOC at different depths, the model was able to capture low variability (R2 = 1–7%). Overall, the Lin's concordance correlation coefficient (CCC) values ranged from 0.01 to 0.18, indicating poor agreement between the predicted and observed values. Root mean square error (RMSE) and mean error (ME) were 0.97 and 0.16, respectively. The values of prediction interval coverage probability (PICP) recorded 87.2–89.7% for SOC contents at different depths. The most important variables for predicting SOC concentration variations were the annual range of temperature, latitude, Landsat 8 bands 2, 5 and 6. Temperature-related variables and remote sensed data products are important for predicting SOC concentrations in arid regions. We anticipate that this digital information of SOC will be useful for frequent monitoring and assessment of carbon cycle in arid regions.

Coffee plantations can strongly sequester soil organic carbon at high altitudes in Brazil

Context Soil organic carbon (SOC) affects all soil-based environmental services, and can be readily depleted upon cultivation. SOC concentrations are often higher in mountains than in lowlands due to lower temperatures slowing microbial activity and organic decomposition. However, the effects of altitudinal differences on SOC changes upon cultivation are mostly unknown. Aims We posed the question: when cultivated, are high-SOC mountain soils more likely to be depleted or are more stable under lower temperatures? Methods We assessed SOC concentrations and stocks (to a 40 cm depth) under comparable native forest and coffee (Coffea arabica L.) stands, both at two different altitudes (940 and 1260 m a.s.l.) along a mountain range in Brazil. The two soils were Inceptisols with similar 11° slope, and under native forests showed strong acidity, low fertility and cation exchange capacity. Key results Mean SOC concentrations under forests were relatively high, varying between 4.3% (0–5 cm depth) and 1.05% (20–40 cm depth) and were not significantly affected by altitude. The effects of cultivation varied with altitude: at 940 m, SOC concentrations decreased under coffee at the 0–5 cm depth, but increased below 10 cm depth at 1260 m, when compared to the native forest control. Conclusions SOC stocks under native forest and coffee stands were similar at 940 m, but the SOC stock under coffee stands at 1260 m increased by ca. 30 Mg ha−1. Implications These results are a promising indication that well-managed coffee stands can preserve or sequester SOC in higher altitudes, thus suggesting tropical mountain range soils are not highly susceptible to SOC losses upon conversion to perennial crops.

Grassland soil organic carbon and the effects of irrigated cropping in Alberta, Canada

AbstractHigh heterogeneity in the spatial distribution of soil organic carbon (SOC) in grasslands causes uncertainty in estimating its content and storage. In this study, we investigated the spatial distribution of SOC content and storage in the prairies of southern Alberta, Canada, and how it is affected by land use such as irrigated cropping and other environmental conditions such as cattle grazing, slope landscape position and dominant plant species. The mean SOC content was determined to be 11.5 g kg–1 (range: 8.9 to 22.4 g kg–1) in the 0–10 cm layer and 6.8 g kg–1 (range: 4.0 to 13.3 g kg–1) in the 10–30 cm layer; mean SOC storage was 1.59 kg C m–2 (range: 1.23 to 2.78 kg C m–2) in the 0–10 cm layer and 2.07 kg C m–2 (range: 1.21 to 3.62 kg C m–2) in the 10–30 cm layer. The SOC content was significantly affected by slope position in both the 0–10 and 10–30 cm layers, in the following order: bottom &gt;middle &gt; top position. Moreover, SOC storage was higher in sites dominated by shrubs than graminoid/forb communities. Thus, SOC content and storage had distinctly clustered spatial patterns throughout the study area and were significant differences between the 0–10 and 10–30 cm soil layers. Prior land‐use change from arid grassland to irrigated cropland increased SOC content and storage in bulk soils.

Differences in organic matter properties and microbial activity between bulk and rhizosphere soil from the top- and subsoils of three forest stands

The distribution of soil organic carbon (SOC) in subsoil is much more heterogeneous than in topsoils. This is largely caused by more localized inputs of fresh substrates and nutrients that mainly derive from rhizodeposition creating hotspots of microbial activity.To elucidate the role of rhizosphere soil as an important input path for substrates into deeper soil layers, we investigated differences of organic matter distribution and microbial degradation in the rhizosphere soil and the surrounding bulk topsoil as well as in the subsoil. In addition, we considered the effect of different parent materials on SOC dynamics by analyzing soils developed in pleistocene sand, triassic sandstone and loess all covered with similarly aged beech forest within the same climatic region. Besides basic soil parameters, basal respiration, microbial biomass (Cmic) and 14C content were determined. Further, extracellular enzymes involved in C-, N- and P-cycling were analyzed. Differences in the microbial community were investigated using a taxon-specific real time qPCR approach. The results revealed significant differences of the microbial community composition between bulk and rhizosphere in top- and subsoil at the investigated sample sites. The mean SOC contents were 322% and 475% higher in the rhizosphere soil in both the top- and subsoil, respectively. The microbial biomass (Cmic) in the rhizosphere was up to 80% higher in the topsoil and on average 200% higher in the subsoil (SOC normalized), compared to the respective bulk soil. The qPCR results for all samples showed a higher diversity and abundance in the rhizosphere compared to the respective bulk samples and a shift in community composition with increasing soil depth. Total activity of the analyzed extracellular enzymes involved in different nutrient cycles differed significantly between bulk and rhizosphere soil and revealed that the microbial community in the rhizosphere subsoil can effectively utilize substrates even under scarce availability. The SOC normalized basal respiration at the Pleistocene sand and Loess sites and K2SO4-extractable C were higher in the subsoil compared to the topsoil showing more labile C in deeper soil layers with younger 14C in the rhizosphere. These results show that the rhizosphere at the investigated forest sites is a hotspot for microbial activity, which is more pronounced in the subsoil where the relevance of these hotspots is important for C turnover.

Influence of Slope Gradient and Aspect on Soil Organic Carbon Content in the Region of Niš, Serbia

Topography-induced microclimate differences determine the local spatial variation of soil characteristics as topographic factors may play the most essential role in changing the climatic pattern. The aim of this study was to investigate the spatial distribution of soil organic carbon (SOC) with respect to the slope gradient and aspect, and to quantify their influence on SOC within different land use/cover classes. The study area is the Region of Niš in Serbia, which is characterized by complex topography with large variability in the spatial distribution of SOC. Soil samples at 0–30 cm and 30–60 cm were collected from different slope gradients and aspects in each of the three land use/cover classes. The results showed that the slope aspect significantly influenced the spatial distribution of SOC in the forest and vineyard soils, where N- and NW-facing soils had the highest level of organic carbon in the topsoil. There were no similar patterns in the uncultivated land. No significant differences were found in the subsoil. Organic carbon content was higher in the topsoil, regardless of the slope of the terrain. The mean SOC content in forest land decreased with increasing slope, but the difference was not statistically significant. In vineyards and uncultivated land, the SOC content was not predominantly determined by the slope gradient. No significant variations across slope gradients were found for all observed soil properties, except for available phosphorus and potassium. A positive correlation was observed between SOC and total nitrogen, clay, silt, and available phosphorus and potassium, while a negative correlation with coarse sand was detected. The slope aspect in relation to different land use/cover classes could provide an important reference for land management strategies in light of sustainable development.

A meta‐analysis of carbon content and stocks in Technosols and identification of the main governing factors

AbstractTechnosols, which are soils strongly impacted by human activity, are becoming increasingly common. To date, there has been little study of the share of the global soil carbon budget made up of carbon in Technosols or the contribution of Technosols to climate mitigation. A meta‐analysis is proposed based on the analysis of 130 articles and consisting of the extraction of 953 observations on soil organic carbon (SOC) content of Technosols and related factors (e.g., climate, land use, nitrogen and bulk density). The mean SOC content of Technosols is 4.3% and SOC stock is 73.2 t C ha−1 for the 0–30‐cm layer. The SOC content does not decrease significantly with depth and it shows high variability, even within the same depth layers. Climate has a significant effect on SOC content, especially in the upper soil layer. Land use (mainly urban, mining or industrial) shows a significant effect when considering all depths and is related to the nature of the constitutive artefacts. Unlike natural and agricultural soils, no correlation is observed with the depth nor the nature and presence of vegetation. This meta‐analysis highlights the strong originality and diversity of Technosols, compared to other soils. Compared to other existing Reference Soil Groups, they are undoubtedly among the soils with the highest carbon stocks per unit area in the pedosphere.Highlights Technosols appear to be among the soils with the largest organic carbon stocks Mean value of soil organic carbon content in Technosols is 4.3% As for natural soils, the soil organic carbon in Technosols is influenced by climate Artefacts appear to be a major driver of organic carbon in Technosols

Long-term vegetation restoration increases deep soil carbon storage in the Northern Loess Plateau

Afforestation plays an important role in soil carbon storage and water balance. However, there is a lack of information on deep soil carbon and water storage. The study investigates the effect of returning farmland to the forest on soil carbon accumulation and soil water consumption in 20-m deep soil profile in the hilly and gully region of the Chinese Loess Plateau. Four sampling sites were selected: Platycladus orientalis (Linn.) Franco forest (PO: oriental arborvitae), Pinus tabulaeformis Carr. Forest (PT: southern Chinese pine), apple orchard (AO) and farmland (FL, as a control). Soil organic carbon (SOC) and soil inorganic carbon (SIC) content were measured in 50-cm sampling intervals of 20-m soil profiles, as well as the associated factors (e.g. soil water content). The mean SOC content of PT was the highest in the 1–5 m layer and that of FL was the lowest (p < 0.05). Compared with FL, the SOC storages of PO, PT and AO increased by 2.20, 6.33 and 0.90 kg m−2 (p > 0.05), respectively, in the whole profile. The SIC content was relatively uniform throughout the profile at all land-use types and SIC storage was 9–10 times higher than SOC storage. The soil water storage of PO, PT and AO was significantly different from that of FL with a decrease of 1169.32, 1161.60 and 1139.63 mm, respectively. After the 36-yrs implementation of the “Grain for Green” Project, SOC in 20 m soil profiles increased as a water depletion cost compared with FL. Further investigation is still needed to understand the deep soil water and carbon interactions regarding ecological restoration sustainability in the Northern Loess Plateau.

Distribution characteristics and controls of soil organic carbon at different spatial scales in China′s Loess Plateau

Understanding the variations and controls of soil organic carbon (SOC) at different spatial scales can help in selecting edaphic and environmental covariates that enables us to model SOC more accurately. The present study investigated the distribution characteristics and controls of SOC content at various spatial scales, including a deep soil core (204.5 m) taken from land surface down to bedrock (plot scale), two toposequences with different slope aspects (slope scale), and eighty-six soil profiles along a north-south transect under different land uses (regional scale) in China's Loess Plateau. The results showed that SOC content at different spatial scales decreased exponentially with increasing soil depth, but the rate of reduction differed at various spatial scales and in soil layers at different depths. For the deep soil core, the SOC content and the average rate of reduction with depth in the 0–15.5 m soil layer were significantly higher than the corresponding values of the 15.5–34.5 m and 34.5–204.5 m soil layers (p < 0.05). For the toposequences with varying slope aspects, SOC content in the 0–50 cm soil layer declined rapidly with increasing depth; while SOC content in the 50–200 cm soil layer showed relatively no change. There was no significant difference of average SOC content at depths of 0–200 cm for forestland and grassland considering slope aspects that differed or were the same (p > 0.05) due to the similar climatic conditions. However, SOC content within 0–500 cm soil profile under different land uses along the north-south transect exhibited a significant difference (p < 0.05), following the order of farmland (4.94 ± 1.23 g kg−1) > forestland (3.01 ± 1.45 g kg−1) > grassland (2.03 ± 0.68 g kg−1); moreover, the mean SOC content of the 0–500 cm soil profile generally decreased from south to north following the decreasing rainfall and temperature gradient. The average rates of reduction of SOC content in the 0–50 cm soil layer under different land uses (0.0807–0.1756 g kg−1 cm−1) were higher than the values of the 50–200 cm (0.0021–0.0154 g kg−1 cm−1) and 200–500 cm soil layers (0.0001–0.0017 g kg−1 cm−). The SOC content at the plot scale at different depths positively correlated with total nitrogen content. The SOC content at the slope scale was mainly affected by soil water content and saturated hydraulic conductivity, while that at the regional scale was impacted by climate, topography and soil water/clay content. Pedotransfer functions were applied to adequately simulate and predict SOC content at different spatial scales in the studied area, which could provide a foundation to build SOC prediction models and extrapolate the various spatial scales to other loess regions worldwide. Our findings demonstrate the importance of considering the scale effects for efficiently predicting the spatial patterns of SOC and can help in devising better policy to protect or enhance existing SOC stocks.

Modeling the Spatial Dynamics of Soil Organic Carbon Using Remotely-Sensed Predictors in Fuzhou City, China

Assessing the spatial dynamics of soil organic carbon (SOC) is essential for carbon monitoring. Since variability of SOC is mainly attributed to biophysical land surface variables, integrating a compressive set of such indices may support the pursuit of an optimum set of predictor variables. Therefore, this study was aimed at predicting the spatial distribution of SOC in relation to remotely sensed variables and other covariates. Hence, the land surface variables were combined from remote sensing, topographic, and soil spectral sources. Moreover, the most influential variables for prediction were selected using the random forest (RF) and classification and regression tree (CART). The results indicated that the RF model has good prediction performance with corresponding R2 and root-mean-square error (RMSE) values of 0.96 and 0.91 mg·g−1, respectively. The distribution of SOC content showed variability across landforms (CV = 78.67%), land use (CV = 93%), and lithology (CV = 64.67%). Forestland had the highest SOC (13.60 mg·g−1) followed by agriculture (10.43 mg·g−1), urban (9.74 mg·g−1), and water body (4.55 mg·g−1) land uses. Furthermore, soils developed in bauxite and laterite lithology had the highest SOC content (14.69 mg·g−1). The SOC content was remarkably lower in soils developed in sandstones; however, the values obtained in soils from the rest of the lithologies could not be significantly differentiated. The mean SOC concentration was 11.70 mg·g−1, where the majority of soils in the study area were classified as highly humus and extremely humus. The soils with the highest SOC content (extremely humus) were distributed in the mountainous regions of the study area. The biophysical land surface indices, brightness removed vegetation indices, topographic indices, and soil spectral bands were the most influential predictors of SOC in the study area. The spatial variability of SOC may be influenced by landform, land use, and lithology of the study area. Remotely sensed predictors including land moisture, land surface temperature, and built-up indices added valuable information for the prediction of SOC. Hence, the land surface indices may provide new insights into SOC modeling in complex landscapes of warm subtropical urban regions.