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• DSM of SOC using different remote sensing data was reviewed. • Majority of studies were conducted on mixed land-use types followed by cropland. • Machine learning techniques were used more than (geo)statistical ones. • Terrain variables as predictors had the largest contribution to map SOC. • Data acquired by satellite sensors was employed more than the other types. Soil organic carbon (SOC) has attracted a lot of attention in the soil science community. Freely available remote sensing data combined with advanced digital soil mapping (DSM) techniques has led to a better understanding and management of SOC. This paper has considered the published literature with a focus on digital mapping of SOC using remote sensing data within 2010 to 2023 intervals. The objective was to consider all the important aspects of SOC prediction and mapping, including different land-use types, DSM algorithms, environmental variables, and remote sensing data sources. According to this review conducted on the 217 papers, cropland was the most popular type of land use. Regarding the DSM algorithms, random forest (RF) appeared in the largest number of studies. The terrain and spectral variables derived from the digital elevation model (DEM) and remote sensing images, were the highest demanding among all those used as input predictors. In addition, satellite platforms provided the largest portion of the remote sensing data used for the calibration of DSM models. This review provides quantitative insight into recent trends of SOC digital mapping using remote sensing technology while suggesting some directions for future development of the topic. [ABSTRACT FROM AUTHOR]

• Tree richness and mycorrhizal-symbionts effects on SOC, GRSP-C, Rh, Q 10, Hs and GHGs were studied. • High tree richness induced 16–126.6% higher SOC, TG-C, Rh, and in situ N 2 O flux. • AM dominant plots had 34–39% higher SOC and Rh than the ectomycorrhizal plots. • Richness and AM's effects in 0–1 m soils were more evident than 0–20 cm soils. • Richness directly improved stability, while richness-AM-decreased-CAZymes favoured storage accrual. • Six types of CAZymes of GHs, PLs, CEs, GTs, AAs and CBMs cooperatively worked in the regulation. Biodiversity loss and tree alternations often occurred in high-latitude Northern Hemisphere forests owing to climatic changes and human disturbance, while their effects on soil carbon sequestration remain unclear. In this paper, tree richness and arbuscular mycorrhizal (AM)-tree dominance experiments were settled in an experimental forest, and soil organic carbon (SOC) and glomalin-related soil protein carbon (Total, TG-C and easily extracted, EEG-C), stability (heterotrophic respiration, Rh, temperature sensitivity, Q 10 and humidity sensitivity, Hs), in situ soil CO 2 , CH 4 , N 2 O fluxes, and CAZymes activities from the microbial metagenome technique were measured to identify their impacts and underlying mechanism. Both analysis of variance (ANOVA) and linear regression found tree richness and AM tree loss accompanied by soil carbon sequestration loss of total SOC storage, their mycorrhizal components (TG-C) and Rh. In 0–20 cm soils, high tree richness quadrats had 16–126.6 % higher SOC, TG-C, Rh, and in situ N 2 O flux, while AM-dominated stands had 34–39 % higher SOC and Rh than the EcM-dominated stands. In the 1 m soil profile, the effect size from tree richness and AM trees were more evident than the 0–20 cm soils. Compared with the richness gradient, much significant differences occurred between AM- and EcM-dominated stands. Structural equation modeling found that tree richness directly improved C stability, while the SOC accrual from the tree richness enrichment and AM-tree dominance were indirectly achieved by their decreasing in multiple CAZymes activities. Of CAZymes, glycoside hydrolases, polysaccharide lyases, carbohydrate esterases, glycosyl transferases, auxiliary activities, and carbohydrate-binding modules cooperated in their regulation of the soil C accrual. Our findings support carbon sequestration via biodiversity conservation and proper forest management related to tree mycorrhizal symbionts. [ABSTRACT FROM AUTHOR]

Abstract Soil organic carbon (OC) plays a vital role on physico-chemical and biological properties of soils and on climate change regulation. The use of pedo-transfer functions from easily available soil properties for estimating soil OC could be fast and cheap when considering field and laboratory work implications especially in Sub Saharan Africa including Tanzania. This paper attempts to develop a model for estimating soil OC contents under maize croplands ecosystem using pedo-transfer functions from soil texture. A total of 100 epipedon data entries were randomly collected from the previous soil sampling works that were conducted under maize croplands in coastal plains of Tanzania. Eighty percent of the collected data were used for training the model by using multiple regression analysis while the remained 20% were used to validate the model. The results indicated that, clay and silt had significant (p < 0.001) positive correlation with soil OC while sand contents in soils had negative (p < 0.001) correlation with soil OC. All together clay, sand and silt were revealed powerful predictors (p < 0.001, R2 = 0.82) of OC content in soils. On validation, the soil OC predicted agreed by 81.2% with the soil OC determined by laboratory test. These results imply that pedo-transfer functions for predicting soil OC based on soil texture is not only fast and cheap but also is an effective option for estimating OC content in soils. Highlights • Soil organic carbon contents differed significantly between the studied soils types. • Strong correlation exist between sand, silt and clay with soils OC contents. • Soil texture predicted significantly the contents of soil OC in the studied soils. [ABSTRACT FROM AUTHOR]

Abstract The soil organic carbon (SOC) and total nitrogen (TN) of topsoil could be greatly affected by the conversion of grassland to cropland (CGC) due to vegetation harvesting and soil erosion. However, few studies have evaluated the effects of these changes in the subsoil and distinguished its main controls at the regional scale. This paper investigated the total changes in the SOC stock (SOC S) and TN stock (TN S) of soils from 0 to 30 cm and 0–100 cm in depth over the past three decades in the Songnen Plain, China, a typical Mollisol region. The CGC resulted in a moderate loss of topsoil C and N but an increase in subsoil C and N, and the soil mapping results showed that approximately 7.47 × 1011 kg C and 1.51 × 1011 kg N were accumulated during the past three decades. Prediction uncertainty was assessed by 100 model runs with random jackknife partitions, and high uncertainty was found in the areas with rapidly changing SOC S and TN S levels. Our findings indicated that subsoil should be considered in the estimation of the SOC S and TN S at the regional scale. The SOC S and TN S of the CGC areas were anticipated to increase after long-term cultivation. In view of ongoing cropland expansion, up-to-date land use and soil type data are vital for selecting monitoring sites and understanding long-term soil evolution at the regional scale. Highlights • Conversion of grassland to cropland led to a moderate loss of topsoil C and N, but an increase in C and N in subsoil. • Subsoil should be considered for the estimation of SOC and TN stocks at the regional scale. • The SOC and TN stocks of recent cultivated soils were anticipated to increase after a long term cultivation. [ABSTRACT FROM AUTHOR]

The carbon cycle is being altered as a result of human-induced changes in the Earth's system. Therefore, ecosystems such as wetlands, authentic CO 2 sinks, are becoming especially important. Little information exits on the soil organic carbon (SOC) stock for the middle east-countries man-made wetlands making wadis permanent with the outflow of wastewater treatment plants. This paper presents the vertical distribution of SOC content, soil bulk density (SBD) and SOC density in soil of vegetated and bare sites in Wadi Al-Thulaima, one of the artificial wetlands in central Saudi Arabia. The mean distribution of SBD in the vegetated and bare sites increased significantly with depth. Inversely, the SOC content declined significantly with depth, from 17.1 g C kg −1 at 0–3 cm depth to 3.3 g C kg −1 at 15–18 cm depth in vegetated sites and from 4.7 g C kg −1 at 0–3 cm depth to 0.7 g C kg −1 at the 15–18 cm depth in bared sites. Vegetation significantly affected the SOC pool, the total mean SOC pool of the vegetated sites (2.0 kg C m −2 ) was higher than that of the bare sites (0.5 kg C m −2 ). Therefore, arid regions could contribute to carbon sequestration with appropriate management, which would result in the enhancement of soil quality. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic carbon (SOC) dynamics affect soil quality, agricultural productivity and atmospheric CO2 concentration. Despite the need for spatial assessments of SOC content over time, reliable estimates from traditional field survey methods are limited by data availability; where measurements are often made at discrete point locations, at a coarse sample spacing or over a limited spatial extent. Remote sensing (RS) is in a strong position to provide spatially distributed, reproducible, scale-appropriate and resource-efficient measurements of SOC content and fluxes at field, landscape and regional scales. This paper provides a critical review of optical RS techniques for such applications. The first part of the paper reviews the methods, instruments and techniques used for developing predictive models for monitoring spatial SOC content. Secondly, sources of spatio-temporal SOC variations are examined, including the lateral transfer of SOC by erosion, soil structural breakdown and land management practices, in the context of RS data and techniques. The key challenges of using RS to monitor SOC contents are discussed along with opportunities for improving SOC predictions within a spatial framework. Such opportunities include the use of ancillary data, scale-specific methods, improved development of spectral libraries and better integration of RS technologies into empirical and simulation SOC models. This paper aims to provide a transparent assessment and practical guide to RS techniques and products in order to further advance and better incorporate the use of RS methods within soil science. [Copyright &y& Elsevier]

For mapping soil properties in three dimensions the simplest option is to choose a series of depth intervals, and to calibrate a two-dimensional (2-D) model for each interval. The alternative is to calibrate a full three dimensional (3-D) model that describes the variation in lateral and vertical direction. In 3-D modeling we must anticipate possible changes with depth of the effects of environmental covariates on the soil property of interest. This can be achieved by including interactions between the environmental covariates and depth. Also we must anticipate possible non-stationarity of the residual variance with depth. This can be achieved by fitting a 3-D correlation function, and multiplying the correlation between two points by the residual standard deviations at these two points that are a function of depth. In this paper various 3-D models of the natural logarithms of SOC are compared with 2-D depth-interval specific models. Five environmental covariates are used as predictors in modeling the lateral trend. In the 3-D models also depth was used as a predictor, either categorical, with categories equal to the depth intervals (3-Dcat), or continuous (3-Dcon). The covariance of the residuals in 3-D is modeled by a sum-metric covariance function. Both stationary and non-stationary variance models are fitted. In the non-stationary variance models the residual standard deviations are modeled either as a stepwise function or as a linear function of depth. In the 2-D models the regression coefficients differed largely between the depth intervals. In the 3-Dcat model extreme values for the regression coefficients were leveled out, and in the 3-Dcon model only the coefficients of NDVI and aspect changed with depth. The 3-Dcon model with a residual standard deviation that is a stepwise function of depth had the largest residual log-likelihood and smallest AIC among all 3-D models. Based on the cross-validation root mean squared error (RMSE) there was no single best model. Based on the mean and median of the standardized squared error (MSSE, MedSSE) the 2-D models outperformed all 3-D models. Overestimation of the prediction error variance by the kriging variance was less strong with the non-stationary variance models compared to the stationary variance models. 3-D modeling is required for realistic geostatistical simulation in spatial uncertainty analyses. [ABSTRACT FROM AUTHOR]

[Display omitted] • We estimate SOC sequestration by the fixed-depth (FD) and equivalent-mass (EM) approaches. • SOC sequestration rates are similar in both, but the amounts of sequestered SOC may strongly differ. • FD approach mostly underestimates SOC sequestration compared to the EM approach. • Changes in soil compaction are the main driver of the errors in SOC sequestration by the FD approach. • EM better quantifies SOC sequestration, but FD is preferable for comparison of SOC stocks worldwide. Soil organic carbon (SOC) sequestration is often quantified through the comparison of SOC stocks down to a fixed depth, usually 30 cm. This approach gives biased estimates because SOC sequestration changes soil bulk density. To account for these biases, the comparison of SOC stocks on an equivalent mass basis is recommended. How big are the biases due to the use of a fixed-depth approach (either under- or overestimations of SOC sequestration), and whether these biases imply that the current estimates of SOC sequestration worldwide need an overhaul, are the two questions addressed in this work. We collected from literature 140 pairs (initial-final) of plots affected by land use changes: crop to forest, crop to grassland, etc. Peatlands were excluded. The datasets were detailed enough to calculate SOC sequestration by both approaches: fixed-depth (down to 30 cm) and equivalent-mass (amount of fine mineral earth at the top 30 cm of the initial stage). Differences between both approaches were often small, but relevant in many cases: namely, when changes in soil compaction were relevant too. The fixed-depth approach overestimates SOC sequestration when soil compaction occurs, and underestimates it when soil expands. However, the average error is low, because over- and underestimations of sequestered SOC partly compensate: the fixed-depth approach underestimates SOC sequestration by about 0.326 ± 1.016 kg SOC m−2 (overall amount), or 14 g SOC m−2 yr−1 (rate). This suggest that the corrections needed by current estimates of SOC sequestration worldwide—at least, those related to the problem studied in this paper—would be low. From our data, the equivalent-mass approach is compulsory in studies about SOC sequestration. Nevertheless, it seems less adequate than fixed-depth as an approach to compare SOC stocks worldwide. Both approaches should not be considered as opposite views, but as complementary tools for the study of carbon cycle in soils. [ABSTRACT FROM AUTHOR]

The Mediterranean mountainous landscapes have undergone large-scale exploitation for millennia. In the Central Pyrenees, land abandonment has occurred since the 1950s, leading to a process of woody encroachment. The main objective of this paper is to shed light on the effects of different land use and land covers (LULCs) on soil organic carbon (SOC) and nitrogen (N) stocks, and on the composition of soil organic matter (SOM) after land abandonment in the Central Pyrenees. Five LULCs (8 specific sites) were selected through detailed land use change mapping. Soil and litter samples (n = 160) were collected and analyzed, including Tetramethylammonium hydroxide pyrolysis–gas chromatography. Organic carbon (Corg)/N ratios, Carbon Preference Index and Average Chain Length indices were calculated based on the distribution of fatty acids in order to determine the molecular composition and degradation of SOM. The results showed: (i) an increase in the dominance index and forest cover, at the expense of shrublands and agricultural fields, and a decrease in Shannon's Diversity and Evenness indexes; (ii) LULC and depth had significant effects on SOC and N contents and stocks; (iii) SOC and N contents and stocks were higher in the meadows and young forests; (iv) significant differences were observed between meadows and young forests and the first stages of land abandonment considering the soil profile; (v) total decomposition of lignins and an omnipresence of unsaturated and saturated straight-chain fatty acids; and (vi) Corg/N values indicate that the origin of SOM is microbial. This study confirms that SOC accumulation after abandonment is a slow process, and the first stages of the woody encroachment decrease SOC stocks. Woody encroachment should be managed with measures based on scientific knowledge, but also considering the historic adaptation of agro-pastoral activities to the environment to ensure the proper functioning of ecosystem services and promote SOC storage in Mediterranean mountain soils. [ABSTRACT FROM AUTHOR]

• Elevated CO 2 in the atmosphere and soil affects soil inorganic carbon (SIC) stock. • Natural and anthropogenic factors influence SIC dynamics at elevated CO 2. • Soil pH, pCO 2 , water content, and precipitation are critical factors for SIC pool. • High CO 2 has short- and long-term consequences on soil acidification. • Weathering of soil carbonates may be enhanced by acidification in future. Soil inorganic carbon (SIC) is the largest pool (≈950 Pg of soil carbonate + 1404 Pg of bicarbonate in groundwater; i.e., 1 Pg = 1015 g = 1 gigaton) of the global carbon cycle at a 100 cm depth, and it might be a significant carbon source and sink in arid and semi-arid regions. The knowledge of the impacts of changing climatic conditions on this important soil structural component is minimal. This review paper provides an inclusive compilation of the available information on potential natural and anthropogenic factors triggering soil acidification and weathering mechanisms under elevated CO 2. Furthermore, the consequences of elevated atmospheric CO 2 on the SIC pool, soil quality, and compromised ecosystem services have been explored. Soil water content and precipitation are critical factors that influence the effects of elevated CO 2 in the SIC pool. Soil microbiological properties, respiration, depth, weathering, precipitation, acidity, and fertilization are emphasized here owing to the high degree of interrelationship between these factors on influencing overall soil quality. These phenomena are then outlined together with comments about possible short and long-term consequences in SIC stock. [ABSTRACT FROM AUTHOR]

• Contour tillage reduced runoff and sediment yield compared to traditional tillage. • Topography and management practices affected the effectiveness of contour tillage. • Climate affected the capacity of contour tillage in reducing runoff. • Soil properties affected the benefits of contour tillage in reducing sediment yield. Contour tillage is a widely practiced conservation tillage in China. The beneficial effects of contour tillage in controlling water erosion have been recognized, further researches are needed to quantify the effectiveness of contour tillage in reducing water erosion and identify the influencing factors in China. We conducted a nationwide meta-analysis based on 229 runoff and 290 sediment paired observations from 47 published papers from national and international literatures. The results showed that compared to traditional tillage, the benefits of contour tillage in China with respect to runoff and sediment reduction were 35.86% and 49.02%, respectively. Sediment yield reduction by contour tillage was greater under simulated rainfall than under natural rainfall. Runoff reduction by contour tillage decreased with the increasing mean annual precipitation and temperature, while sediment yield reduction was not affected by climate factors. Contour tillage in loamy soils and soils with organic carbon content > 1% showed the greatest benefits in reducing sediment yield (64.26% and 52.52%, respectively). The greatest runoff and sediment yield reduction (61.04% and 67.24%, respectively) occurred at slope length > 20 m. The greatest runoff reduction by contour tillage was found for tillage duration > 10 years (44.08%), while the greatest sediment yield reduction occurred at tillage duration ≤ 5 years (52.89%). The effectiveness of contour tillage under cereals was better for runoff and sediment yield reduction compared to legumes and rotation as consequence of the high biomass quantity and lower mineralization rate of cereal straw. Our results conclude that contour tillage is an effective measure for controlling water erosion, and its benefits in reducing runoff and sediment yield are different according to the climate, soil properties, topography and management practices. [ABSTRACT FROM AUTHOR]