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• Soil water content (SWC) is determined as the outcomes of land use changes. • A significant correlation occurred between δ13C and δ15N values in wetlands, but underwent considerable changes after wetland conversion. • The shifts in organic matter sources over time and distinct mechanisms of degradation and preservation of SOM were underscore in wetlands following land use changes. Land use change in wetlands leads to significant losses of soil organic matter (SOM). Stable carbon (C) and nitrogen (N) isotopes offer insights into changes in C3/C4 vegetation, SOM sources, and decomposition processes. Yet, predicting the spatial–temporal dynamics of SOM contents and isotopes under land use changes remains challenging. This study delves into the effects of land use changes on soil organic carbon (SOC), total nitrogen (TN), δ13C and δ15N values, and soil physico-chemical properties and lignin phenols. Our results highlight the significance of soil water content (SWC) in determining the outcomes of land use changes. The conversion of wetland to cropland, forestland and construction land, led to notable reductions in SOC contents (8.71–56.33 %), and TN contents (7.87–37.12 %). Wetland conversion resulted in an enrichment of 13C and 15N abundance, with wetlands exhibiting the lowest δ13C (−25.57 to –22.89 ‰) and δ15N (2.66 to 6.67 ‰) values. A significant correlation occurred between δ13C and δ15N values in wetlands, but underwent considerable changes after wetland conversion. Key parameters, including bulk density (BD), C:N, the acid-to-aldehyde of vanillyl ((Ad/Al)v), lignin content (Λ 8), and total phosphorus (TP), were identified as influencing factors for both SOC and TN contents. When evaluating δ13C values, the most influential factors included silt, C:N, SOC, sand, and BD. These indicate the importance of soil chemical group (from 41 % to 21 %) in elucidating δ13C values declined, while lignin group's (from 9 % to 28 %) importance increased from topsoil to subsoil. The acid-to-aldehyde of syringyl ((Ad/Al)s), Λ 8 , C:N, BD and the cinnamyl-to-vanillyl ratio (C/V) were identified as the primary factors influencing δ15N values, with chemical group accounting for 36 % and lignin group for 48 % in topsoil, while physical group dominated 42 % in subsoil. Our findings underscore the shifts in SOM sources and distinct mechanisms of degradation/preservation of SOM following land use changes. [ABSTRACT FROM AUTHOR]

• The agri-horticulture (AH) system exhibited the highest Carbon management index (CMI). • CMI increased at higher altitude in dry temperate Himalayas. • Passive carbon pool was higher under AH system than agriculture (A) by 16.2 %. • The highest Lability index was reported in A indicating lower stability than AH. Globally, land use management consistently changes the dynamics of labile and recalcitrant (non-labile) soil organic carbon (SOC) fractions. However, the effects vary depending on altitude, soils and management practices. The dry temperate north-western Himalayan region is characterized by the presence of diverse land use systems, however the comparison of these SOC fractions across various land use regimes is not well-documented in the area. This study reported the differences in labile and non-labile SOC fractions under the major land-use systems viz., Agriculture (A), Horticulture (H), Agri-horticulture (AH) and Grass fallow (OF) land in various soil-depth classes (0–20, 20–40 and 40–60 cm) along three altitudinal ranges i.e., 2200–2500, 2500–2800 and 2800–3100 m above mean sea level (m. a.m.s.l.) across the dry temperate region of north-western Himalayas. The lability index and carbon management index of the soils were determined using these fractions. The analysis affirmed the highest accumulation of active fractions viz., very-labile (2.66 mg g−1), and labile C fraction (2.55 mg g−1) under AH, while the highest recalcitrant fractions i.e., less-labile (3.34 mg g−1) and non-labile C fraction (7.46 mg g−1) was documented under H. Moreover, the Carbon Management Index (CMI) followed the order of AH > A > H > OF. All the SOC fractions, pools and CMI significantly increased with increase in altitude but declined at lower soil depths. The Pearson correlation analysis revealed that the CMI was positively correlated with the active C fractions i.e. C frac 1 (r = 0.96; p < 0.05) and C frac 2 (r = 0.9; p < 0.05). The higher active carbon pool and CMI (6.9–16 % and 4.1–15.7 % higher, respectively) under the AH may be due to the greater organic matter inputs to the soil under the agri-horticulture land use system. The findings of this study suggest that the soil can be managed sustainably by the adoption of stable land use systems such as agri-horticulture (owing to their higher CMI values) in the highly fragile dry temperate ecosystem of the north-western Himalayas. [ABSTRACT FROM AUTHOR]

• Land-use types, seasons, slope position significantly affected SOC and SWC. • Revegetation increased SWS consumption and SOC accumulation. • There was a positive linear relationship between SOC and SWC. • Planting grass and shrubs is recommended in the semi-arid hilly and gully regions. Understanding the response of soil organic carbon (SOC) and moisture to different land-use types, slope positions, seasonal variations, and their interactions has great significance for land use and management. However, the coupling effects of SOC and soil moisture in typical hilly and gully regions are still elusive. Therefore, in this study, five different land-use types, including cropland, abandoned land, grassland, shrubland, and forestland were selected in a typical Chinese loess hilly-gully region, and soil samples were collected from 0 to 200 cm profiles at the upper, middle, and lower slope positions in four seasons. The results demonstrated that the distributions of SOC and soil moisture were jointly significantly affected by land-use types, seasons, and slope positions (P < 0.01). Average SOC content was found to be highest in the shrubland, followed by grassland, abandoned land, forestland, and cropland. SOC storage at the lower slope position was 10.97% higher than that at the upper slope position. SOC storage in winter was 45.47% higher than that in summer. SOC storages of abandoned land, grassland, shrubland, and forestland were 17.38%, 33.08%, 52.52% and 1.26% more than that of cropland, respectively. Soil moisture fluctuated greatly in 0–100 cm layers and was stable beneath the 100 cm layers, which was highest in autumn, and lowest in summer. Whereas, under different land-use types, the soil moisture of cropland was the highest, especially significantly higher than all revegetated treatments in the 60–200 cm soil layers. Compared with cropland, soil water storage at other land-use types was averagely 36.45 % lower in the entire 200 cm soil profile. SOC was positively correlated with soil moisture under different factors. Thus, we recommend planting shrub and grass in watersheds with serious soil erosion in the semi-arid hilly and gully region, because they can sequestrate more SOC and retain more soil water. [ABSTRACT FROM AUTHOR]

• Spatial variations in soil erodibility was quantified by indicators in karst hillslope. • Identify the predominant factors affecting spatial variations in soil erodibility. • Land use and slope position had great effects on near-surface soil characteristics. • CSEI varied with land use and slope position, and affected by soil characteristics. Land use type and slope position have a considerable impact on soil properties and thus likely influence soil erodibility. Soil erosion on karst hillslopes in South China is still serious due to the high intensity of human activities and fragile ecological environment. Nevertheless, the potential effects of land use type and slope position on soil erodibility indicators in karst areas are still unclear. This study was conducted to investigate the spatial variations in soil erodibility indicators, namely, the saturated hydraulic conductivity (K S), mean weight diameter (MWD), soil structural stability (SSI), soil erodibility K factor, soil organic carbon content (SOC), and a comprehensive soil erodibility index (CSEI) for three typical land uses and three slope positions on a karst hillslope. The results showed that K S , MWD , SSI , K factor, SOC and CSEI varied significantly with land use type and slope position. The measured K S , MWD , SSI , K factor and SOC at the nine tested sites displayed a similar trend with soil depth. SOC , MWD and SSI contributed more to the CSEI , with contributions of 27.9%, 25.9% and 25.9%, respectively. K S and K factor contributed less to the CSEI , with contributions of 17.7% and 2.5%, respectively. Woodland is most susceptible to erosion on upper, cropland on middle and grassland on lower slope positions according to the values of CSEI. There were significant positive correlations among sand content, bulk density and CSEI , and there were significant negative correlations among clay content, silt content, root mass density, SOC and CSEI. The changes in soil properties and soil erodibility indicators with land use type and slope position led to the differences in the CSEI. The results provide valuable information for policymakers to select appropriate land use types to mitigate soil erosion and thus improve the healthy development of the ecological environment on karst slopes. Moreover, the results have crucial implications for understanding the mechanism of the spatial variation in soil erosion of karst hillslopes in Southwest China. [ABSTRACT FROM AUTHOR]

Soil salinity poses a threat to the sustainable management of agricultural landscapes and has an effect on soil carbon storage. This study investigated land use-land cover (LULC) relations with soil organic carbon (C) in a salinity-infested landscape with inter-spun vegetated and non-vegetated land area. A sodicity infested command area (~100 ha) along Sharda Sahayak canal in Uttar Pradesh, India was selected for studying LULC effects on soil organic carbon (C) and soil properties to 60 cm soil depth. The area was divided in a grid of 100 m × 100 m, and soils were sampled and analyzed at 140 geo-referenced points representing five LULC classes. The LULC dominant in the representative area were barren-coverless (BC), barren-grass cover (BG), rice-fallow (RF), rice-wheat (RW), and rice-okra-mentha (ROM). Soil organic C decreased with depth, decreased with increase in soil pH, and decreased with an increase in exchangeable sodium percentage (ESP). The effects were highly significant in surface layers (0–0.3 m). Similarly with electrical conductivity (EC) too, soil organic C had a negative correlation. Soil organic C varied significantly with LULC. The soil organic C content decreased in the order: ROM > RW > RF > BG > BC. As the intensity of crop/plant cover increased, the soil salinity (ESP, pH and EC) decreased. The average soil ESP was maximum in BC (44%) followed by BG (30%), RF (15%), RW (8.5%), and ROM (7.0%). The cumulative probability trends indicated the probability of lesser ESP with increased vegetative cover/primary productivity. A strong (p < 0.001), a negative relationship was observed between soil organic C and pH in rice-based systems. Analysis of soil organic C stock with depth for the studied LULCs indicated 4–70% (grass cover to rice-wheat cropping sequence) increase in total soil organic C stock just by supporting vegetative cover on barren sodic land. The study was indicative of scope for soil C sequestration and reclamative effects in salt-affected areas of Indo-Gangetic region by adopting appropriate land use strategies, which may include the adoption of rice-based and grass-based cropping systems, to check the development of sodicity in soils. • Soil ESP, pH and EC have negative relationship with soil organic carbon. • Intensified land use-land cover shows ameliorative effects on salinity. • Intensive management relates to increased soil C and decreased pH, EC, ESP. • Land use management could be frontline strategy against soil salinity development. [ABSTRACT FROM AUTHOR]

• The mean soil organic carbon (SOC) content in agroecosystem of Eastern China was 18.24 g kg−1. • The SOC content of planted forest > cropland > grassland in the total study area. • The SOC value of grassland was higher than cropland in North China due to excessive mechanized operation. • The random forest hybrid model exhibited higher comprehensive performance in SOC prediction. • Our predictions were much more detailed and accurate than the existing SOC content maps. 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. [ABSTRACT FROM AUTHOR]

• Facility lands were considered to be greater carbon sinks compared to other land uses. • The most stable type of organic carbon is in facility land, and the most unstable is in grasslands. • Changes in land use have a significant impact on organic carbon fractions and carbon mineralization. Soil carbon is an essential component that influences soil health and agronomic productivity, and land-use practices significantly impact soil carbon stocks. In this study, the researchers investigated the impact of various land-use types (farmland, orchards, grasslands, and facility lands) on soil organic carbon (SOC) fractions in the Qaidam Basin of China's Qinghai-Tibet Plateau. The soil samples were taken from the 0–10 and 10–20 cm depths. The particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) fractions of various land uses have been measured. The results revealed that grasslands had the greatest POC/SOC ratio (0.59), with POC accounting for the majority of the SOC fraction. In contrast, all other land-use types (facility land, orchards, and farmland) had greater MAOC/SOC ratios than POC/SOC. The facility land had the highest SOC content (17.75 g kg−1), and orchard had the lowest (8.51 g kg−1). The grassland had the highest POC content (9.82 g kg−1) at a depth of 0–10 cm. The trend for MAOC content among the various land-use types was facility lands > farmlands > grasslands > orchards. The soil pH was also observed to be moderately alkaline, with an average of 8. The orchard has the highest bulk density (BD), measuring 1.38 g cm−3. The grasslands contained the highest amount of total nitrogen (TN) (2.2 g kg−1) while the agricultural fields contained the highest amount of total phosphorus (TP) (1.16 g kg−1). In addition, facility lands showed the highest level of microbial activity compared to other land-use types. According to the findings, SOC, POC, and MAOC fractions had considerably positive associations with TN and microbial biomass carbon (MBC), but were significantly negatively associated with metabolic CO 2. The findings imply that different land-use types can have a considerable impact on the quality and amount of soil organic carbon, which has consequences for soil health and ecosystem processes. The findings also highlight the significance of long-term land management practices that promote the preservation and enhancement of soil organic carbon in various land-use systems. [ABSTRACT FROM AUTHOR]

• Grassland had the highest soil infiltration capacity among the land use types with vegetation. • Soil infiltration capacity of anti-dip slope was significantly higher than that of dip slope. • The bedrock strata dip could be treated as an indicator of infiltration properties. • The common experience model was the most suitable for describing the soil infiltration characteristics. The dip of bedrock has a great influence on the infiltration of water into soil, and can control the spatial distribution of rainwater in fragile karst rocky desertification regions. Thus, it is necessary to scientifically assess the soil infiltration capacity of dip and anti-dip slopes in karst trough valleys. In this study, we comprehensively evaluated the soil infiltration capacity of dip and anti-dip slopes under different land use types using the cutting ring infiltration method. The results showed the following. i) Compared with the anti-dip slope, the dip slope had a higher bulk density, noncapillary porosity and pH and a lower soil water content, capillary porosity and soil organic carbon content (p < 0.05). In addition, the soil infiltration capacity of grassland was the highest among the studied land use types except for abandoned land. ii) Both the bulk density and the total soil porosity could be treated as indicators of the infiltration properties of dip and anti-dip slopes.iii) Based on the coefficient of determination, R2 , the common experience model was the most suitable for describing the characteristics of the soil infiltration rate. iv) Based on the principal component equation, the soil infiltration capacity and organic matter of the grassland on dip slopes and anti-dip slopes were higher than those of other land use types with vegetation, but not higher than those of abandoned land without vegetation. The results of this study provide a reference for the selection of the restoration method and the assessment of the soil infiltration capacity of dip and anti-dip slopes in karst trough valleys and other karst landforms with the same geological background. [ABSTRACT FROM AUTHOR]

• A meta-analysis to test rubber stand age and altitude effects on soil properties. • Forest-to-rubber conversion significantly reduced SOC pools by 24%. • Rubber monoculture-to-intercropping significantly increased SOC pools by 6%. • Improvement of intercropping occurred in 0–20 cm soil and at 500–800 m altitude. The rapid expansion of rubber plantations may have greatly influenced the carbon stocks of the ecosystem, with potential impacts on mitigating climate change and future carbon fluxes. Therefore, soil carbon pools and other properties must be reliably estimated after rubber-based land cover transitions. The aim of this meta-analysis is to understand how various land use changes based on rubber plantations affect soil physicochemical properties, especially soil organic carbon (SOC) pools. This study focuses on three land use changes: (1) forest-to-rubber conversion; (2) rubber monoculture vs. intercropping; and (3) the age and altitude of the rubber stand over a chronosequence in rubber plots. Results showed that the conversion of forest to rubber plantation significantly reduced the SOC, microbial carbon (MBC), total nitrogen (TN) and total magnesium pools by 24%, 35%, 13% and 94% respectively, whereas rubber intercropping with different crops profoundly increased the SOC and MBC pools by 6% and 24% on average, respectively. The improvement of rubber intercropping on SOC and properties mainly occurred in the surface soil at 0–20 cm and at altitudes of 500–800 m, but these effects were diminished in the subsurface soil at 20–60 cm and at altitudes higher than 800 m. Rubber intercropping plantations can significantly alleviate soil acidification. Changes in the response ratio of SOC were closely related to the variations in soil clay, bulk density, and C/N ratio. These results suggest that rubber-based land use management policies should promote intercropping plantations, especially those with woody plants, and the altitude of rubber planting should be manipulated to minimize the loss of soil C, N, and other nutrients. [ABSTRACT FROM AUTHOR]

Although the evaluation of soil organic carbon (SOC) stocks across different types of land use and major reference soil groups is essential for mitigating climate change, there remains, to date, limited comprehensive understanding of whole tropical soil profiles. Therefore, this study aimed to explain the amount of SOC stocks in different land-use systems and across various soil groups, as well as its spatial pattern in the topsoil (0–30 cm) and subsoil (30–100 cm) within the savannah zone of Burkina Faso. Roughly 70 soil profiles were considered along with additional auger sampling to account for spatial variation in both cropland (CR) and savannah (SA). The machine learning technique random forest regression (RFR) and multiple linear regression (MLR) were used for modeling the surface and subsurface SOC stocks. For model calibration, covariates including land use, topographic, texture, and climatic data were considered as surrogate for soil forming factors. The prediction maps produced by the calibrated models were validated by an independent dataset. The results indicated that about 53% of the SOC stock over 1 m depth was held in the upper 30 cm. Only a marginal difference was recorded between the topsoil SOC stock in SA (41.4 t C ha −1 ) and CR (39.1 t C ha −1 ) soils. For the subsoil, a significant difference (p < 0.05) was observed between the SOC stock of CR soils recording about 40.2 t C ha −1 and SA soils with 26.3 t C ha −1 . Among the reference soil groups, the Gleysols located at lower elevation positions revealed the highest SOC stocks over 0–30 cm (44 t C ha −1 ) and 100 cm depth (86.6 t C ha −1 ). The Stagnosols (45.2 t C ha −1 ) followed by the Gleysols (42.7 t C ha −1 ) recorded the highest SOC stocks over 30–100 cm. The variability of SOC stock in the topsoil was primarily related to site-specific elements, such as particle-size fraction and wetness index, while its distribution in the subsoil was mainly associated with the topographical orientation represented by the slope aspect. Compared to the MLR, RFR estimated mean top- and subsoil SOC stocks of the catchment fairly well, along with lower statistical error metrics, though extreme values were not covered. Nevertheless, the findings on SOC stocks reinforce the view that the semi-arid ecosystems of West Africa still offer a significant opportunity for carbon sequestration for both topsoil and subsoil, and these results represent a baseline for future modeling of SOC dynamics in the region. [ABSTRACT FROM AUTHOR]

Composition and stability of soil organic matter (SOM) affect the sustenance and productivity of soil over the long-term. This issue is particularly important for karst regions in China where the water supply and fertilizer use are limiting factors. Here, we used four indicators to evaluate changes in the composition and stability of SOM quantitatively in five main land-use types in karst area, including primary forest [PF], 15-year secondary forest [SF], grazing secondary forest [GF], abandoned farmland [AF] and farmland [FL]. We collected soil samples at a depth of 0–20 cm to conduct the analyses. Four indicators were used: soil physical and chemical properties, active organic carbon (C), humus C composition, and SOM functional groups. Our results showed that the content of SOM, total nitrogen, and easily oxidized organic C at 0–20 cm soil depth differed among the five land-use types ( P < 0.05). For humic acid C concentration, the land-use types were ordered as: SF > PF > GF > FL > AF. Solid-state 13 C NMR spectra showed that the highest ratio of Alkyl C/O-alkyl C was in AF, while the lowest was in SF. Overall, the comprehensive quality of SOM in different land-use types was PF (setting 100%) > SF (83.1%) > GF (58%) > AF (30.9%) > FL (29.9%). For karst areas, we suggest that farmlands in sloping area should be converted back to forests, with only moderate grazing being permitted, whereas farmlands in the plains should implement grain-forage rotation and grain-soybean rotation to meet the needs of the growing population and economic development. In conclusion, our findings provide a scientific basis from which to delineate rational land-use types for different land (geographical and geological) formations. [ABSTRACT FROM AUTHOR]

Soil is the largest terrestrial organic carbon pool and can act as a source or sink for atmospheric CO 2 . Although reliable soil carbon (SOC) stock measurements of major ecosystems are essential for predicting the influence of advancing climate change, comprehensive data on SOC stocks is still scarce for most ecosystems in subtropical areas. In this study, SOC and N stocks of different land use systems were investigated along a climatic gradient in Northwest Ethiopia. The land use systems ranged from dry subtropical Afromontane forest, as the baseline, to cropland as the most degraded system. In addition, we investigated the changes of SOC stocks after interventions to recover vegetation cover; these were eucalyptus plantations and an exclosure to prevent grazing. Total SOC varied between land use systems and ranged from 3.1 kg C m − 2 in croplands to 23.9 kg C m − 2 in natural forest, and average N stock ranged from 0.4 kg N m − 2 in croplands to 2.1 kg N m − 2 in natural forest. In forests, there were a clear vertical gradient in SOC and N stock down the soil profile, and 60% of the total SOC and N stocks were found in the upper 10 cm soil depth. Using the Sr/Ca and Ba/Ca ratios and the vertical distribution of the C/N ratio of the soil, the losses of SOC were shown to be due to loss of the of the upper soil layer. Afforestation of degraded croplands and grazing lands with eucalyptus increased SOC stocks to nearly 70% of the natural forest levels within 30 years. Exclosure, which removed grazing pressure and allowed regeneration of native vegetation, increased SOC in the top soil only. [ABSTRACT FROM AUTHOR]

The impact of land use on the content of labile soil organic carbon (SOC) has been studied well. However, limited information is known about its effect on the recalcitrant SOC pool, which is a key proxy for long-term carbon sequestration. We investigated the impact of land use change on the distribution of labile and recalcitrant SOC fractions in soil profiles (0–30 cm) in the Jinchuan peatland, Northeast China, where native peatland (with peat soil) and forest (with mineral soil) are converted to paddy and cropland, respectively. Peat and mineral soil profile samples were collected from 10 sites in native and cultivated land. Total organic carbon (TOC) and KMnO 4 -oxidizable carbon (KOC) defined as the labile SOC fraction were measured in both peat and mineral soils. Fibre and lignin were also determined in peat samples. The mineral-associated organic carbon (MOC) and black carbon were examined as two recalcitrant SOC fractions. In peat soil profiles, the TOC and KOC contents increased with the increasing depth across all land uses. The conversion of peatland to paddy field can affect TOC content at each peat soil depth. The KOC content was lower in cultivated soils, indicating that cultivation decreased KOC. The KOC decrease was smaller than the TOC decrease, indicating that some recalcitrant SOC fractions were decomposed because of land use change. Unlike peat soil profiles, the TOC and KOC contents decreased with depth in mineral soil profiles across all land uses. The TOC and KOC contents in surface soil decreased remarkably after cultivation to cropland but were not affected in deep soil. Interestingly, recalcitrant SOC fractions, such as MOC, increased in mineral soil profile after cultivation but showed no change in peat soil profile. This study suggests that conversion of peatland to paddy can release the recalcitrant SOC fraction. In addition, conversion of cultivated forest to cropland decreased the TOC content but prolonged the long-term storage of some recalcitrant SOC fractions, such as MOC. [ABSTRACT FROM AUTHOR]

Stoichiometry is an important indicator of the elemental balance in ecological interaction and process. However, the effect of land-use on stoichiometry of soil nutrient along soil profile remains uncertain. In this study, soil samples (0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm and 80–100 cm) were collected from six different land-uses including maize field (MZ), wheat field (WT), paddy field (PD), apple orchard (OC), grassland (GL) and wetland (WL) in a traditional agro-pastoral region of the Ili River Valley, northwest China, to evaluate the influences of land-use on contents and stoichiometry of soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K) along a 100 cm soil profile. The results showed that natural land (GL and WL) had significantly higher soil organic C (SOC), soil total nitrogen (STN) and soil available N (SAN) contents than those of croplands (MZ, WT, PD and OC) in all soil layers. However, differences in soil P and K contents between the two land-uses were not significant in most soil layers. Such characteristics of soil nutrient contents led to significant differences in soil C: P (R CP ), C: K (R CK ), N: P (R NP ) and N: K (R NK ), while no significant differences in soil C: N (R CN ) and P: K (R PK ) between cropland and natural land, indicating that nutrient stoichiometry of deep soils can be also affected by land-use. In the 0–20 cm soil layer, soil R CN of different land-uses, as well as their average in our study were similar to those on Chinese and global scales. However, since our study area has relatively lower SOC and STN contents while higher STP contents than the global averages, the average soil R CP , R NP and C: N: P (R CNP ) of our study were lower than the those on the global scale. Therefore, we suggest that more nutrient inputs, such as manure and crop residues should be applied to the croplands of the Ili River Valley to improve the levels of soil C and N. [ABSTRACT FROM AUTHOR]

The overall impact of individual environmental factors on the content of soil organic carbon (SOC) is well known, but the simultaneous impacts of natural and anthropogenic factors on the amount and diversity of SOC pools in mountain areas are still insufficiently recognized. This study has three objectives: (1) to determine SOC pools in the mountain toposequence in relation to the climate-elevation gradient and vertical vegetation zonality, largely as a result of interference caused by human activity; (2) to predict the fluctuations of SOC pools in mountain soils affected by changes in land use/forest management and expected climate warming; and (3) to verify whether the humus form is a predictor of SOC pools in mountain soil. A spatial, climate-/altitude-dependent trend of SOC pools is clearly marked on the northern slopes of the Karkonosze Mountains, SW Poland. These SOC pools gradually increase up to the altitude of ca. 1000 m a.s.l. and then decrease in the uppermost forest and subalpine zones. The SOC pools are also strongly related to land use/vegetation (arable soils < grasslands = European beech stands < Norway spruce stands) and soil type (Luvisols < Cambisols < Podzols). Humus forms reflect the differences in SOC pools (mull < moder < mor), but the recent European classification does not clearly allocate semiterrestrial sub-types among mor and moder humus forms. Expected climate warming and present changes in land use and forest management lead to similar changes in SOC pools. However, replacing spruce monocultures with mixed or broadleaf stands reduces the SOC pools in the lower forest zones, while the timberline rise and the succession of Norway spruce on grasslands increases SOC pools in the upper forest and subalpine zones. Thus, the balance of SOC pools caused by changes in land use and climate warming will be specific in particular mountain areas, depending on their maximum altitude and existing vegetation zones, the degree of anthropogenic transformation of ecosystems, and the resilience of ecosystems to climate changes. It is expected that the SOC pools in the Karkonosze Mts and similar medium-elevation mountain ranges of Central Europe will decrease due to the larger scale of phenomena which decrease SOC pools. [ABSTRACT FROM AUTHOR]

Soil carbon (C) pool contains organic carbon (SOC) and inorganic carbon (SIC). A detailed understanding of SOC and SIC is meaningful and essential for precisely assessing the effects of land-use on soil C stocks. Alpine grassland around Qinghai Lake basin has experienced extensive land-use changes due to the cultivation of native grassland and vegetation recovery on cropped land. However, limited information is available about the changes and distribution patterns of soil C pool with land-use in this region. Here, three land-use types were chosen, including natural alpine grassland (NG), and a pair of restored grassland (RG) and farmland (FL), to examine the effects of cultivation and restoration on SOC and SIC horizontal patterns and vertical distributions in the upper 30 cm soil layer. Land-use changed the ratio of SOC/SIC without affecting the net soil total C accumulation in this area. The NG had the highest SOC (96.0 Mg C ha − 1 ) and lowest SIC (19.8 Mg C ha − 1 ) stocks, while the FL had the opposite result, with the average of SOC and SIC stocks was 65.0 and 57.7 Mg C ha − 1 , respectively. After 10-year restoration, SOC stock increased to 73.2 Mg C ha − 1 , while SIC decreased to 47.8 Mg C ha − 1 in the RG. The vertical distribution of SOC and SIC changed sharply with depth in the NG but gently in the RG, and with little changes in the FL. Stepwise regression analysis manifested that soil nitrogen and pH were the main determinants for the redistribution patterns of SOC and SIC with land-use. In addition, ordinary regression analysis revealed a significant negative correlation between SIC content and aboveground biomass of the respective vegetation. The results demonstrated that land-use had affected the horizontal and vertical patterns of SOC and SIC synchronously, and indicated SIC stocks played crucial roles for estimating the C sequestration capacity in the restoration and farmland ecosystems around Qinghai Lake basin. Moreover, the results of this study provided an interesting snapshot of the compensation relationship between SOC and SIC stocks with land-use, and suggested that the changes of soil properties and plant above- and belowground biomass resulting from cultivation and restoration were potentially responsible for the transformation of soil C forms. [ABSTRACT FROM AUTHOR]

• Soil organic carbon can be predicted by land use and terrain attributes. • Soil erosion can preserve SOC by burying it at downslope deposition locations. To provide a more accurate assessment of soil organic carbon (SOC) stocks in agroecosystems, sampling strategies should be designed in a way that accounts for topographic variability and soil redistribution via erosion and deposition. While the importance of topography for influencing soil properties is long established, recent advances in digital elevation models (DEMs) permit more rapid assessment of topographic attributes. We determined primary terrain attributes from a 3 m DEM to guide sampling in cultivated fields and nearby grasslands in Southeastern Minnesota, USA. Soil samples were analyzed to quantify SOC stocks and activity of 137Cs, a radioisotope employed to track soil movement over decadal timescales. In addition to soil depth, digital terrain attribute values were important for developing predictive models in both cropland and grassland sites but contributed more to predictions in cropland soils. Profile and planform curvature were significant terms in the regression model for both cropland and grassland soils. Additionally, percent slope was also significant in models for cropland soils. Overall, regression models were able to explain 90% and 73% of variability in SOC stocks observed in grassland and cropland sites, respectively. Soil profile 137Cs inventories were correlated with SOC stocks in both land cover types and show that soil movement can explain SOC variability in upland soils. Soil erosion or deposition rates (based on 137Cs inventories) ranged from 34.8 (erosion) to −70.1 (deposition) t ha−1 yr−1 in cropland sites and from 11.7 to −17.2 t ha−1 yr−1in grassland sites. Results from this study showed that soil redistribution can result in burial of eroded OC-rich surface soil in depositional locations characterized by low slopes and concave curvature in agricultural fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thick clay-silty Luvisols in the bottom of dolines have high SOC storage capacity. • Past agricultural land-use presents long-term impact on SOC stock in dolines. • Succession plots in dolines show the highest SOC storage capacity (130 t/ha). • Soil organic carbon stock in dolines was double the amount on the levelled plateau. The soil organic carbon (SOC) was determined in soils of enclosed karst depressions (dolines) (NW Dinaric Mts.) to define their potential for organic carbon sequestration. SOC was measured in the forest, succession (scrubland), and grassland plots at the bottom of dolines at four depths (0–40 cm) and for 40 cm soil layer SOC stock was calculated. We demonstrated that the prevailing fine soil fractions, the C/N ratio and soil thickness play a positive role in the storage capacity of SOC in dolines regardless land use type. Grasslands have the lowest SOC storage capacity (106 t/ha/40 cm), while the highest SOC storage capacity is in succession plots (130 t/ha/40 cm). The last are covered by shrub communities dominated by Prunus spinosa , forming dense communities, and are typical of abandoned croplands or meadows that have been impacted by high levels of nutrients during cultivation phase. At this stage, there is no additional nutrient input in studied plots, which lowers the nutrient content and increases the C/N ratio. C/N ratio is the highest in the forest, where SOC stock capacity is 116 t/ha/40 cm. Given the trend towards the abandonment of agricultural land at Kras Plateau (SW Slovenia), we can expect more overgrowth of dolines, and thus an increase in carbon stocks and stabilization of organic carbon in forest soils. In contrary, we noticed the alarming decrease in grasslands and increase in urban land. The SOC storage in 2020 was for 12,538 t/ha/40 cm lower than in 2002. Although grasslands showed the lowest SOC storage, their contribution to total SOC storage in dolines is very important. Since there is a lack of studies on carbon stocks in doline soils, our research is of great importance and a novelty and gives an important background for further research on SOC stock in karst landscapes worldwide. [ABSTRACT FROM AUTHOR]

• Stability of SOC fractions differed among the forest types. • SOC stock was highest in a temperate forest (132.7 Mg C ha−1). • Active and passive carbon pool was highest in temperate and Quercus forests, respectively. • Conversion of natural forests to bamboo and jhum land reduced SOC stock. • Quercus forest plays a significant role in long-term carbon sequestration. Forests are among the largest terrestrial carbon pools that are most vulnerable to land use and land cover change (LULC). Therefore, it is essential to manage forest ecosystems to enhance soil organic carbon (SOC) pools and soil functionality. The present study was carried out to analyze C stability and change in SOC stock under different forest types in the eastern Himalayan region of India. Topsoil (0–15 and 15–30 cm) samples from six dominant forests i. e. tropical wet evergreen, montane subtropical, temperate, Quercus , bamboo, and shifting cultivation (Jhum) lands were collected and analyzed for selected soil properties and SOC stock. Active (very labile + labile), slow (less labile), and passive (non-labile) C fractions were also analyzed to determine the stability of the SOC pool under the LULC scenario. Results show that the percentage contribution of active C to total organic carbon in topsoil was highest in a temperate forest (74.1%) while lowest in a bamboo forest (48.1%). Unlike, slow C (18.4%) and passive C (26.6%) were highest in Quercus forest. Pearson correlation analysis shows significant positive relation of active and slow C pool with SOC and total nitrogen concentration. The estimates of SOC stock (0–30 cm) were significantly higher in temperate forests (132.7 Mg C ha−1). However, the conversion of natural forests to bamboo forest and jhum land reduced SOC stock by 29% and 68%, respectively. C lability index shows higher labile C in jhum land while recalcitrancy index was highest in a bamboo forest. Our study concluded that LULC change significantly altered the stability and stock of SOC in natural forests. Owing to a higher percentage of slow and passive C pools, Quercus forests play a major role in C sink management. [ABSTRACT FROM AUTHOR]

Land use change is the second main reason for carbon (C) emissions after fossil fuel combustion, and it is recognized as an important driving force for soil organic carbon (SOC) and soil nitrogen (N) dynamics. Conversion of the secondary forest to Chinese fir ( Cunninghamia lanceolata [Lamb.] Hook) and Moso bamboo ( Phyllostachys heterocycla [Carr] Mitford cv. Pubescens ) plantations represents one of the most important land use changes in subtropical China. However, the effects of these land use changes on the SOC and N stocks were not well documented. Therefore, in this study soil samples were collected in a secondary forest, a 17-year Chinese fir and a 18-year Moso bamboo plantation after the conversion from the secondary forest in November 2013, and total SOC and N concentrations were measured. Total SOC and N concentrations decreased with soil depth over the 0–50 cm in three land uses, and they were significantly higher in the secondary forest than those of Chinese fir and Moso bamboo plantations; however, these concentrations were not significantly different between Chinese fir and Moso bamboo plantations. Top soil (0–10 cm) stored one third of total SOC and N stocks. SOC and N stocks in the secondary forest were significantly higher than those of Chinese fir and Moso bamboo plantations with values of 203.68, 127.34 and 118.25 t·ha − 1 for SOC stock and 9.24, 5.10 and 6.35 t·ha − 1 for N stock. The results indicated that converting the secondary forest to Chinese fir and Moso bamboo plantations significantly decreased the SOC and N stocks over 0–50 cm. [ABSTRACT FROM AUTHOR]

We examined the impact of human changes in land use on the concentrations and stoichiometric relationships among soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K) in a Phragmites australis riparian wetland (Minjiang River estuary, China). We compared a natural (unaltered) wetland with five altered land uses: intertidal mudflat culture and vegetable, flower, fruit and rice cultivations. All these land uses decreased C, N and K soil concentrations relative to those in the P. australis wetland. The close relationship between total soil C and N concentrations, under all land uses, suggested that N was the most limiting nutrient in these wetlands. The lower N concentrations, despite the use of N fertilizers, indicated the difficulty of avoiding N limitation in the agricultural land. Croplands, except rice cultivation, had lower soil N:P ratios than the original P. australis wetland, consistent with the tendency of favoring species adapted to high rates of growth (low N:P ratio). The release of soil C was less and the soil C:N and C:P ratios higher in the natural P. australis riparian wetland than in the croplands, whereas C storage was more similar. The levels of soil C storage were generally opposite to those of C release, indicating that C release by respiration was the most important factor controlling C storage. Cropland soil management promotes faster nutrient and C cycles and changes in soil nutrient stoichiometry. These impacts can further hinder the regeneration of natural vegetation by nutrient imbalances and increase C-cycling and C emissions. [ABSTRACT FROM AUTHOR]

• Litter and tree roots modify the proportion of soil aggregate fractions. • Extensive agriculture implies similar soil carbon storage than agroforestry. • Agroforestry increases the carbon associated with the small soil aggregate fractions. The land use sector currently represents ∼25% of the global greenhouse gas emissions, thus this human activity is having a huge impact on climate change. Semi-arid climate areas, which are widely distributed, are particularly influenced by such climate change. In these areas, land use changes have transformed the entire landscape and increased the greenhouse gas emissions. However, in semi-arid climate areas, the information on the effect of climate change is scarce and usually centred on one single type of land use. For the land uses (forest, agricultural and agroforestry) traditionally found in the semi-arid area in South Portugal, this study aimed to evaluate (i) the soil chemical (pH) and physical properties (bulk density and percentage of different soil aggregate fractions: 250–2000; 53–250 and <53 μm) and (ii) the carbon (C) storage in whole soil and each soil aggregate fraction in land with over 100 years of the same use. The results show that after >100 years with the same land use, C storage in the whole soil was similar in the plots with extensive agriculture based on the agroecology principles to that in the agroforestry plots. However, the concentration and storage of C in the microaggregates (53–250 μm) and the silt + clay soil fraction (<53 μm) were generally higher for the forest and agroforestry land uses than for the agricultural land use due to the tree effect. This C associated with the smallest soil fractions is very stable and is retained in the soil in the long term. In this context, agroforestry systems improve the soil C storage in the long term at the same time that agricultural production is allowed compared to the traditional forest systems. Therefore, the establishment and maintenance of agroforestry systems in the semi-arid climate areas is a sustainable land use for climate change mitigation. [ABSTRACT FROM AUTHOR]

• Evaluation of different land use on SOC stock under climate change scenarios. • Both decreases and increases of SOC stocks would be possible in the future. • Under high emission scenario SOC stock increases to 6.23 million tons in cashew LUS. • RothC Model indicated cashew plantations as the most prominent sink of SOC storage. • Promotion of agroforestry systems are imperative to improve SOC storage. Soil organic carbon (SOC) is one of the significant soil components influencing soil functions and soil processes. However, little is known about the impact of land-use change on SOC dynamics on coastal agroecosystems. We, therefore, simulated the impact of land use on SOC stock using RothC model under different climate change scenarios. In the present study, natural forest and pasture lands are the native land uses, while cashew, arecanut, and coconut plantations were established about 70–80 years ago from the natural forest. Measured SOC stocks were significantly higher in cashew and forest land uses (109.5 and 88.6 t C/ha) and much lower in coconut, arecanut and pasture lands (64.1–71.0 t C/ha). The study showed that under projected climate change conditions in Goa state and depending on emission scenarios, both decreases and increases of SOC stocks would be possible. By the end of the century, SOC stock in cashew would decrease by 4.3 t C/ha (RCP 4.5) and increase by 2.4 t C/ha (RCP 8.5), in coconut the SOC change was negligible (0.2 t C/ha) in RCP 4.5 while increased by 3.2 t C/ha in RCP 8.5. Arecanut, pasture and forest land uses showed a marked SOC decrease in RCP 4.5 (ranging from 5.2 to 5.4 t C/ha) and negligible positive (0.6–0.7 t C/ha) or negative (0.6 t C/ha) changes in RCP 8.5. Overall, the model indicated cashew plantations as the most prominent sink of SOC storage, while coconut and pasture are not viable sinks of SOC in the study area. We suggest promoting cashew, arecanut, and coconut land use system integrated with tree components and pasture to improve the SOC storage and other ecosystem services in the coastal agroecosystem. [ABSTRACT FROM AUTHOR]

The release of dissolved organic carbon (DOC) from peatlands implies a loss of sequestered carbon. During the last two decades, an increase of DOC exports in Europe and North America has been reported. The influence of land use on DOC has been contradictorily discussed and a lack of knowledge exists particularly for fens in Northeastern Germany. Therefore, we aimed to investigate DOC release from fen soils with differing land use intensity. To exclude climatic influences and water level fluctuations, a lysimeter study was performed. The lysimeter vessels contained three histosols from Northeastern Germany and varied in peat quantity, substrate quality, water table depth, pH and vegetation, as these factors are strongly influenced by land use intensity. Water for DOC analysis was sampled biweekly over a two year period. DOC release ranged from 4 to 123 mg/L − 1 with a median of 32 ± 22 mg/L − 1 . Lowest DOC concentrations were found at deeply drained gleysols and at relatively slightly decomposed, acidic histosols. Highest concentrations were measured in the most degraded histosols. Degree of decomposition and pH were found to be the major driving factors for DOC release. Long-lasting rewetted lysimeters were not observed to release a lower amount of DOC than drained ones, which may be of importance when restoration of degraded peatlands is intended. As lysimeters from the same site released relatively similar amounts of DOC despite their varying management during the last 50 years, it appears that peatlands have an individual potential for DOC release. [ABSTRACT FROM AUTHOR]

Soil erosion processes play an important role in the redistribution of soil organic carbon over the landscape. The factors controlling this carbon (C) redistribution have been thoroughly studied at the plot scale, but knowledge at the landscape level is still limited. In this study, we explore the role of different factors on C export at the catchment scale. We measured the C concentration in sediment deposited behind check-dams at the outlet of catchments ranging between 7 ha and 438 ha and combined it with specific sediment yield rates (SSY, Mg ha − 1 y − 1 ) to estimate catchment specific C yields (SCY, g m − 2 y − 1 ). Correlation analysis between C concentration, SCY and morphological, lithological and land use data derived from GIS analysis and interpretation of ortophotoimages was conducted. The results showed a close relationship between SCY rates and catchment morphometric properties such as catchment area, slope gradient and lithology, while C concentration in sediments was correlated to the percentage of forest cover in a catchment. In addition, it is suggested that morphological properties such as average slope gradient, drainage area and drainage density could have implications for the fate and stability of C stored at depositional sites through changes in the in-depth variability of C concentration in sediments and in the concentration of two measured C fractions. Further research is needed in this direction. [ABSTRACT FROM AUTHOR]

Soil erosion by water and tillage are major drivers for soil degradation in the mountainous regions of NW Vietnam. Data on cumulative and recent erosion of bulk soil and soil organic carbon (SOC) are needed for carbon budgeting and to evaluate e.g. the impact of erosion on climate change, environmental services and subsequent socioeconomic consequences. Thus, the aims of the present study were (1) to quantify cumulative erosion and recent erosion rates of bulk soil (2) to quantify cumulative eroded SOC and (3) to estimate the proportions of water and tillage induced soil erosion after land use change from primary forest to continuous maize cultivation for up to 21 years. Soil erosion rates were determined by 137Cs and ranged from 12 to 89 t ha- 1 a- 1. A large part of the variation of cumulative bulk soil (R² = 0.79) and SOC loss (R² = 0.67) between the sites was simply but effectively explained by the ratio of site specific cumulative RUSLE LS factors to clay contents. The newly developed CIDE approach, which attributes SOC changes on steep slopes to either carbon input, decomposition or erosion, delivered 20% higher (up to 0.7 kg m- 2) and more reliable estimates on cumulative SOC erosion than a traditional approach, because CIDE considered the effects of soil profile truncation, decomposition and humification, which all affected SOC simultaneously to soil erosion. Tillage induced soil flux accounted for 38 ± 3 kg m- 1 per tillage pass, which was lower than found in similar studies. Soil erosion by water was higher than tillage induced erosion in middle and foot slope positions, accounting for 86 to 89% of total soil erosion. To prevent further soil degradation, erosion protection measures should be implemented. [ABSTRACT FROM AUTHOR]

The soil carbon reservoir is the largest carbon reservoir in terrestrial ecosystems and consists of soil organic and inorganic carbon stocks. Previous studies have mainly focused on the soil organic carbon (SOC) stock, and limited information is available about the soil inorganic carbon (SIC) stock. The Chinese Loess Plateau (CLP), which is located in the arid and semi-arid region of China, is an important inorganic carbon reservoir, with a thick soil layer that is rich in calcium carbonate. However, there are few reports on the SIC stock and its spatial distribution in this region. In the current study, the SIC densities and stocks for various soil types and land use patterns were evaluated based on 495 profiles with 2470 soil samples across the CLP, which were collected from the Chinese Second National Soil Survey. The results showed that in the top 1m of soil across the CLP, the average SIC density is 17.04kg/m², and the total SIC stock is approximately 10.20 Pg C (1 Pg=1015g). The SIC stock of the CLP accounts for approximately 18.4% of the total SIC stock throughout China. The average values of the SIC stock in the 0-20, 20-50 and 50-100cm depths of the CLP are 2.39, 2.92 and 4.89 Pg, respectively. Under different land use patterns, the order of the average SIC density is farmland≈grassland > forest in all soil layers. For the various soil types, the SIC density in the 0-100cm layer is the highest in alkaline soil and lowest in subalpine meadow soil, whereas the SIC stock is highest in loessial soil, eolian sandy soil and sierozem, and the lowest in subalpine meadow soil. These differences are largely a result of the area occupied by each soil type and the climate conditions. The results of this study provide basic information about carbon reservoir in China and contribute to our understanding of the SIC stock on the CLP as it relates to the carbon balance of terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Land use and topography strongly influence soil organic C (SOC) and N accumulation in eroded hilly regions. However, their combined effects and the underlying mechanism remain unclear. In this study, five land uses and three topographic positions across an eroded hilly watershed of the Loess Plateau were selected to investigate their effects on SOC and N accumulation. The restored grassland, shrubland and woodland (25 to 30years) increased SOC and total N by 32% to 119% in the slope and 17% to 81% in the gully, respectively compared with the cropland. These restored vegetation increased soil dissolved organic C (DOC) and microbial biomass C and N (MBC and MBN) by 1.1- to 3.0-fold in the slope and 30% to 108% in the gully, respectively. Similar increases were observed in soil aggregates, MBN/total N, soil C:N and microbial C:N ratios. These improvements were higher in the shrubland than in the other land uses. The SOC significantly decreased from the gully to the slope, and the magnitudes decreased in a sequence of cropland, grassland, shrubland and woodland. Soil DOC, total N, and MBN also decreased from the gully to the slope in the cropland, but remained unchanged in the grassland, shrubland, and woodland. Land use (P <0.05), topographic position (P <0.05), and their interaction (P <0.1) influenced SOC, total N, DOC, MBC, MBN, soil C:N and microbial C:N ratios. There were close relationships among soil aggregates, SOC and total N, and DOC, MBC and MBN. Therefore, land use, topographic position (erosion and deposition), and their interactions regulate SOC and N accumulation and their labile fractions in the eroded hilly region at a watershed scale. Our results suggested that converting cropland to shrubland is an initial strategy to restore degraded ecosystems and increase soil C sequestration in eroded hilly region of the Loess Plateau. [Copyright &y& Elsevier]

• Driving factors of SOC and total N were explored in 28 lucerne fields. • The SOC and total N were mainly explained by soil resources. • Soil P, moisture, and altitude were the key factors affecting SOC and total N. • Plant species diversity positively affected SOC and total N contents. • A strong interaction effect was observed among topography, vegetation and soil on SOC. Lucerne (Medicago sativa L.) is one of the most successfully introduced species for revegetation on the Loess Plateau of China and provides important ecosystem services. However, the driving mechanism of soil organic carbon (SOC) and total nitrogen (TN) in lucerne grasslands remains unclear. This study explored the controlling factors of SOC and TN in lucerne grasslands in the semiarid Loess Plateau. A total of 112 quadrats were employed in 28 lucerne fields. Vegetation characteristics, topographic factors, and soil properties at a 0–20 cm depth were measured in each quadrat. The SOC and TN contents increased with altitude and showed positive correlations with species richness, aboveground biomass of native plants, soil moisture, soil inorganic nitrogen, total soil phosphorus (P), and C:P and N:P ratios. Variations in SOC and TN contents were mainly attributed to soil resources, followed by the interaction of topography, vegetation and soil. Soil P, soil moisture, altitude, and native plant species were the main factors controlling SOC and TN contents in these lucerne grasslands. Results suggest that specific abiotic (soil P and moisture) and biotic (plant species diversity) factors controlled SOC and TN in semiarid lucerne grasslands. These factors should be included in SOC and TN evaluation models to predict the future terrestrial ecosystem carbon and nitrogen dynamics. [ABSTRACT FROM AUTHOR]

• Landscape-scale spatial variability of SOC in a temperate grassland was analyzed. • SOC presents strong and moderate spatial autocorrelation at two layers respectively. • Topography and land use have independent and combined influences on SOC. • Wind erosion and deposition both can alter SOC and increase its spatial variability. • The influence of wind erosion on SOC should be considered in carbon accounting. Understanding the spatial variability of soil organic carbon (SOC) and its main influencing factors is crucial for sustainable land use management and climate change mitigation. Existing studies mostly focus on the influence of environmental factors on the spatial variability of SOC, while little attention has been paid to the effects of wind erosion which has important influences in arid and semi-arid landscapes. In this study, spatial variability of SOC content at landscape scale and its main influencing factors were analysed at 0–1 cm and 1–6 cm in a typical temperate grassland. Results show that SOC content ranges from 0.45% to 4.11% and is higher at 0–1 cm. SOC presents strong and moderate spatial autocorrelation at 0–1 cm and 1–6 cm, respectively. SOC is high in part of the hilly area, and low in the west plain and southeast undulation. Elevation and vegetation coverage have significantly positive effects on SOC. SOC varies with land uses with the order that arable land (AL) < heavily grazed grassland (HG) < moderately grazed grassland (MG) < lightly grazed grassland (LG) < ungrazed grassland (UG) at 0–1 cm and AL < HG < MG < UG < LG at 1–6 cm. Under the same land use, SOC is generally the highest in the flatland at both layers and lowest in the leeward slope at 0–1 cm and the windward slope at 1–6 cm, respectively. Wind erosion and deposition can both alter SOC content and increase its spatial variability. SOC is high in areas without wind erosion and deposition and decreases with erosion and deposition rates due to the selective erosion and remote region sourced deposition materials which generally have low SOC. Such effects have important influence on land productivity, global carbon cycle and climate change, and it could not be neglected in carbon accounting. [ABSTRACT FROM AUTHOR]

• Land-use conversion was conducted to assess its effect on the changes of soil 13C. • Significant changes in δ13C were observed at the 0–10 cm depth after conversion. • SOC stock was largely increased in the 20–40 cm layer for grassland and forest. • New SOC was formed greater in grassland than in forest above 60 cm soil depth. Soil organic carbon (SOC) content and its 13C natural abundance along soil profile are sensitive to the changes of land use since these changes alter external carbon (C) inputs and belowground C turnover processes. A study was conducted to investigate how the conversion of cropland to forest, grassland or bare land (no vegetation) affect the distribution of SOC and its 13C values in 200-cm soil profiles. After 28 years of land conversion, the cropland that was remained as cropland (treated as control) had a significantly higher δ13C value than the bare land, grassland or forest at the top 10 cm soil depth. Regardless of the land use type, the mean soil 13C values in the subsurface soil layers depleted and δ13C signature decreased by 1%−5% compared with the top 10 cm soil layer, while the corresponded SOC content decreased by 3.5% to 91.2% as soil depth went down deeper. The SOC stock in the 0–200 cm profile was 16% and 12% higher in the grassland and forest, respectively, than in the control. The conservation of cropland to grassland and forest largely increased the SOC stock in the 20–40 cm soil layer compared with the control. The newly formed SOC was higher in the grassland than in the forest, and accounted for 15.4% and 9.7% of the SOC stock in the soil depth of 0–60 cm in the grassland and forest, respectively. Soil δ13C values and SOC contents were negatively correlated with pH and clay content, while they were positively correlated with nitrogen and C/N ratio along the soil profile. We infer that the conversion of cropland to forest or grassland is a beneficial practice for SOC storage, especially in the 0–60 cm depth. Such conversion has little impact on the SOC turnovers in deep soil layers during the study period. [ABSTRACT FROM AUTHOR]

[Display omitted] • The interactive effects of soil erosion and land use on SOC were studied. • Soil erosion rates were higher in orchard land relative to farmland. • The direct impact of soil erosion accounts for 1.5% of SOC variability in soil surface. • The direct or indirect effects of land use accounts for 89.0% for SOC variability in deeper soil. Changes in land use can result in soil erosion and the loss of soil organic carbon (SOC). However, the individual contribution of different land use types on SOC variability as well as the combined impacts of land use and soil erosion are still unclear. The aims of the present study were to: (1) evaluate soil erosion and SOC contents under different land use types, (2) identify the influences of soil depth and land use on SOC content, and (3) determine the contribution of land use and soil erosion on SOC variability. We assessed the SOC and total soil nitrogen (TSN) contents under three types of land use in the dry-hot valley in southern China. Caesium-137 (137Cs) and excess lead-210 (210Pb ex) contents were also measured to determine soil-erosion rates. Land use was found to significantly affect soil erosion, and erosion rates were higher in orchard land (OL) relative to farmland (FL), which is in contrast with previous study results. SOC and TSN contents varied significantly between the three land use types, with highest values in forest land (FRL) and lowest values in OL. SOC was found to decrease with decreasing soil depth; the highest rate of reduction occurred in the reference site (RS), followed by FRL and FL. The interaction between soil erosion and land use significantly impacted SOC in the soil surface layer (0–12 cm); the direct impact of soil erosion accounted for 1.5% of the SOC variability, and the direct or indirect effects of land use accounted for the remainder of the variability. SOC content in deep soil was mainly affected by factors related to land uses (89.0%). This quantitative study furthers our understanding on the interactive mechanisms of land use and soil erosion on changes in soil organic carbon. [ABSTRACT FROM AUTHOR]

• Post-agricultural restoration increased SOC due to the build-up of non-protected SOC. • Post-agricultural restoration shifts SOC composition towards more easily available C. • Physico-biochemically protected SOC was hampered by restoration in temperate soils. • Within SOC composition, convergent and divergent self-restoring trends coexist. Post-agricultural natural restoration is a worldwide strategy for eco-environmental sustainability. However, it is unclear how it affects soil organic carbon (SOC) pools and composition among soil types across climate gradient. Here, we investigated 23-year post-agricultural restorations of SOC in three soils: Luvic Phaeozem, Calcaric Cambisol and Ferralic Cambisol typical for mid-temperate, warm-temperate and subtropical zones, respectively. Six SOC fractions with different protection mechanisms (non-protected, physically, chemically, biochemically, physico-chemically and physico-biochemically) were separated. Compared with pre-restoration in 1990, post-agricultural restoration rebuilt SOC similarly (+68–+91%) among the three soils despite of different SOC background. Compared with continuous cultivation, post-agricultural restoration increased total SOC pools in all the three soils (+33–+60%) mainly because of the increments of non-protected pool (coarse particulate organic C, cPOC). However, the pure physically, chemically, and biochemically protected SOC fractions were less sensitive to post-agricultural restoration. The physico-biochemically protected SOC was hampered by restoration in the two temperate soils but remained stable in the subtropical soil, suggesting a divergent self-restoring trend. Positive correlations of the total SOC and most fractions with wetness (precipitation/temperature ratio) demonstrated the climate dependency of SOC. In conclusion, post-agricultural natural restoration builds up SOC pool mainly due to the cPOC increment and shifts SOC composition towards more easily available C in three soils across the climatic gradient. [ABSTRACT FROM AUTHOR]

• Thermal techniques are robust and rapid methods for determining changes in SOC. • SOC of our sites was mainly represents polysaccharides and aliphatic structures. • PA + SM and NV showed higher contribution of microbial-derived in the SOC. • The application of SM increases SOC content. • SM application combined to no-tillage practices may lead to SOC stabilization. The pool of carbon (C) present in soil systems is larger than the amount of organic C stored in living biomass and the atmosphere. Soil degradation has increased soil C emissions at the expense of C accumulation. Climate-smart management practices may be adapted to increase C sequestration as soil organic carbon (SOC). To avoid the SOC loss, different strategies have been applied, including no-tillage and organic fertilizer. Here, we investigated thermal stability of SOC after long-term manure application across land uses and tillage systems in weathered soils of Brazil. We chose five commercial areas with different land uses: pasture with swine manure (SM) application (PA + SM), conventional tillage (CT) with SM application (CT + SM), natural vegetation (NV), no-tillage with SM application (NT + SM), and no-tillage (NT). Thermal analysis revealed that SOC oxidation and CO 2 emission started around 240 °C, close to gibbsite and goethite structural collapse, suggesting preferential adsorption of SOC onto these minerals. Approximately 50% of SOC for all sites was oxidizable at lower temperature (~315 °C) which suggests the prevalence of polysaccharides, decarboxylation of acidic groups and dehydration of hydroxylate aliphatic structures, regardless of land-use. The energy content of SOC for NV (6.5) and PA + SM (10.6) were in average, 46% lower than other treatments which suggest a higher necromass contribution to SOC in these systems. However, the higher energy content in CT + SM (14.9), NT + SM (16.5), and NT (15.8), suggests a higher contribution of plant-derived compounds in SOC. Our results showed that SM application on pastureland reached similar SOC accumulation to NV and increment of ~33% when applied to no-till system. We conclude that SM could a drive higher C accumulation and stabilization if preferentially associated to soil conservative system. [ABSTRACT FROM AUTHOR]

• The number of organic phosphate-solubilizing bacteria (PSB) increased with soil TP. • The number of phosphate-solubilizing fungi (PSF) increased with soil carbon content. • The ability to solubilize phosphate was organic PSB > PSF > inorganic PSB. • The organic PSB was the best bacterial group to solubilize phosphate. Some soil bacteria and fungi are known to solubilize phosphates and play an important role in supplying phosphorus (P) to plants. In this study, we characterized the phosphate-solubilizing bacteria and fungi as well as P availability in latosols from southern China under different land use practices. Three different latosols (i.e., red soil, lateritic red soil and laterite red soil), each with four different land uses (i.e., agricultural land, grass land, forest land and orchard land), from Guangdong Province, China, were chosen to determine the amounts of phosphate-solubilizing bacteria (PSB) and phosphate-solubilizing fungi (PSF) and their phosphate solubilizing abilities. Our results show that the amount of available P (AP) increased with the amount of PSB favored in solubilizing organic P (or PSBop), while the amount of PSF increased with the content of soil organic carbon (SOC). The average rates of phosphate solubilization were 28.23% for PSBop, 6.97% for PSF, and 0.16% for PSBip (PSB favored in solubilizing inorganic P). An increase in soil pH decreased the ability of PSB to solubilize phosphate in latosols. This ability occurred in the following order: PSBop > PSF > PSBip. No significant difference in the amount of PSF was observed among the four different land uses for the lateritic red soil and laterite red soil, whereas a profound significant difference was found for the red soil, with the highest number of PSF in the grass land. Reasonable linear correlations between the PSB and the AP and between the PSF and the SOC were obtained and could provide a good reference to characterize soil PSB and PSF. Additionally, PSBop was the best bacterial species to solubilize phosphate in the latosols. [ABSTRACT FROM AUTHOR]

• Five land uses were assessed for soil organic carbon (SOC) dynamics. • Conversion of forest land to cropland declined SOC and biological activities. • Alder + large cardamom land use was a viable alternative for SOC buildup. • Alder + large cardamom land use increased the recalcitrant pool of SOC fractions. Land use management exerts a tenacious impact on soil organic carbon (SOC) dynamics; however, the impact varies with climate, soils, and management practices. Therefore, an in-depth understanding of changes in SOC pools and its fractions is necessary to reduce carbon (C) emissions and adopt efficient land use planning for sustainable soil management in the North Eastern Himalayan (NEH) region of India. The soils under five prominent land uses [e.g., alder (Alnus nepalensis) + large cardamom (Amomum subulatum), alder + turmeric (Curcuma longa), ginger (Zingiber officinale) + maize (Zea mays), ginger and undisturbed forest] were sampled down to 45 cm depth to assess the impacts of land use systems on SOC content and storage, its fractions, microbial biomass carbon (MBC) and the dehydrogenase (DHA) activities. Results demonstrated that undisturbed forest soil had the highest organic carbon (OC, 145.8 Mg ha−1), active C (AC, 73.7 Mg ha−1), passive C (PC, 72.1 Mg ha−1) pools, MBC and DHA activities followed by alder + large cardamom system (140.7 Mg OC ha−1, 70.9 Mg AC ha−1, and 69.8 Mg PC ha−1, respectively). The soils under undisturbed forest and alder + large cardamom system had a higher share of the very labile C fractions for all depths than other land uses. Conversely, soils under sole ginger and ginger + maize land uses had a greater proportion of non-labile C (NLC) fractions; however, absolute values of the NLC pool were the highest under undisturbed forest soil. Alder + large cardamom land use system had the highest AC: PC pool ratio (1.13) and C stratification (1.02–1.05) compared to the other land uses. Of the various land uses, SOC pools (0–45 cm) in six years were reduced nominally under alder + large cardamom system (4.2%), while the reduction was maximum under the ginger system (11.2%) as compared to the SOC pools of undisturbed forest. The study demonstrated that the cultivation of crops like maize and/or ginger is more degrading and will always have a negative impact on the fertility and overall health of the Himalayan soil. Hence, alder + large cardamom system may be promoted to restore the soil C in the Sikkim Himalayan region of NEH, India, and other similar regions of the world. [ABSTRACT FROM AUTHOR]

• The increase rate of active C was higher than those of intermediate and passive C. • Increased proportion of active C with the forest age led SOC to become more labile. • The increase of C:N ratio verified that SOC becomes more labile after reforestation. Land use changes have a great impact on carbon (C) cycling of terrestrial ecosystems by changing both the C inputs and mineralization rates. It not only results in variations of SOC stocks, but that the SOC properties could also change after vegetation conversions. In this study, we collected soil samples in a series of forests converted from croplands at different times in Southeast China. The effects of the reforestation on SOC pools and stabilities were investigated based on information of SOC contents, SOC fractions (active, intermediate and passive C) and C:N ratios. The organic carbon (OC) contents of the bulk soil and soil fractions increased with the forest ages in both topsoils (0–10 cm) and subsoils (40–50 cm). The increase rates of the active C were higher than those of the intermediate and passive C. As a result, the proportion of the active C increased with the forest ages, which would result in an increase of SOC instabilities. This was confirmed by the observation that the C:N ratio of the bulk soil increased with the forest ages. Our results implied that the C sink potential of the forest soil is to a large extent determined by the forest age. [ABSTRACT FROM AUTHOR]

• Here we performed a SOC distribution model in soil with different occupation. • We performed a comparison of two different SOC mapping technics. • The morphology and soil texture play the major role on SOC distribution. • Our introduction of variables related to SOC improve the interpolation results. • Soil organic carbon sequestration is the best under soil with dense vegetation. Soils of semi-arid climates undergo organic carbon loss, which in turn affects their agricultural potential. Geostatistics is often used as an interpolation tool to thoroughly describe SOC spatial distribution. To focus on soil organic carbon (SOC) depletion, the Tiffech watershed (Northeast of Algeria), an economically important agricultural area, was chosen due to intensive agricultural practices, decline of forests and occurrence of erosion. The present study aimed to predict the spatial variation of SOC in Tiffech watershed using geostatistics and a Geographical Information System (GIS) software, comparing the performance of two geostatistical methods—Ordinary Kriging (OK) and Regression Kriging (RK)—also assessing the role of auxiliary variables in improving the prediction accuracy and highlighting the role of land cover in SOC storage. The SOC content in Tiffech soils was determined on 42 soil samples from the surface layer (0–10 cm) collected all over the study area and the results were used to estimate SOC density in non-sampled locations. The prediction efficiency of the two methods was evaluated by calculating the Mean Error (ME), the Root Mean Square Error (RMSE) and the Root Mean Square Standardized Error (RMSSE). The interpolation results showed that SOC distribution in the study area was correlated to the topography, the clay index, and general landscape features. SOC content increased northwards in the area, ranging from 0.53 to 6.9 kg·m−2 in relation to land use. As expected, maps figured a good conservation status of SOC stocks in areas with dense vegetation; conversely poor SOC contents were estimated where land degradation factors take place. Cross-validation results showed an outperformance in the interpolation accuracy of RK on OK after the introduction of environmental variables, with an RMSE value of 0.02 versus 0.81. This suggests a higher efficiency of RK in predicting SOC content across the Tiffech area in comparison with OK, confirming that introducing some auxiliary data correlated to the target variable in SOC estimation, considerably improved the interpolation accuracy. [ABSTRACT FROM AUTHOR]

• Soil respiration including winter CO 2 efflux was studied in the desert-oasis region. • Annual soil CO 2 emissions varied from 176 to 918 g C m−2 across the study ecosystems. • The ratio of cold season CO 2 emissions to the annual was 6–15% across ecosystems. • Land use conversion influenced soil respiration across the desert-oasis ecoregion. Quantifying annual soil CO 2 emissions and the effects of physical and geochemical factors on soil CO 2 efflux will improve the carbon budget estimates, as well as enhance predictions of how soil CO 2 emission will response to climate change in arid areas. To data, variability in soil respiration rates caused by land use conversion in the desert-oasis ecoregion of Northwest China remains poorly characterized, especially the contribution of cold season (November-February) CO 2 emission. Soil respiration was measured in a Haloxylon ammodendron desert shrubland, a Zea mays cropland, a Populus gansuensis forest, and a Tamarix chinensis Lour wetland using a LI-COR 8100 Soil Respiration Observation System from April 2016 to March 2019. Annual soil CO 2 emissions totaled 176, 778, 918, and 397 g C m−2 in the desert shrubland, cropland, forest, and wetland, respectively. The ratio of cold season CO 2 emissions to the annual varied from 6 to 15% across ecosystems. Therefore, ignoring cold season CO 2 emissions would lead to underestimates of carbon losses in the desert-oasis ecoregion. The soil respiration rate at 10 °C was influenced by soil organic carbon content in all four ecosystems. In the cropland and forest, soil respiration rate was affected by the interaction of soil moisture and soil temperature, while in the wetland and desert shrubland, soil respiration was sensitive to a single factor, soil temperature. Land use conversion induced differences in organic matter accumulation, soil temperature, and soil moisture, and as a consequence, produced variability in soil respiration rates across the desert-oasis ecoregion. [ABSTRACT FROM AUTHOR]

The natural abundance of δ15N in soils is a simple tool for understanding ecosystem nitrogen cycling. However, the main drivers for soil δ15N in different natural land use types are not clear enough. To investigate the main drivers for soil δ15N in different land uses, we measured δ15N in the top 10 cm of the soil along a precipitation gradient with various land uses on the Loess Plateau of China, which covers a total area of 620,000 km2 and is one of the most erodible area in the world, to determine effects of climatic, soil and vegetation factors on soil δ15N and the relationships between them using the partial least squares regression (PLSR) method. Soil δ15N ranged from 1‰ to 9‰ on the Loess Plateau with an average of 5.8‰ in forest lands, 5.6‰ in shrub lands, and 4.8‰ in grasslands. Calculated variable influence on projection by PLSR showed that both soil properties (including soil organic carbon content, total nitrogen content and soil texture) and mean annual precipitation influenced soil δ15N strongly. In addition, site elevation also influenced soil δ15N strongly in forest lands. The dominant controls of soil δ15N varied among three land use types on the Chinese Loess Plateau, and PLSR would be a reasonable tool to predict soil δ15N. • Soil δ15N was analyzed on the Loess Plateau and globally in different land uses. • Precipitation, soil C and N influenced soil δ15N strongly on the Loess Plateau. • Equations between soil δ15N and the main factors were built on the Loess Plateau. • Regional equations did not work on global scale due to large precipitation range. [ABSTRACT FROM AUTHOR]

Large-scale land degradation occurs in the foothill Himalayas mainly because of soil erosion, accelerated by tillage and poor management practices in agricultural lands and encroachment of land under forest cover. Land use exerts both direct (through C additions) and indirect (through its impact on soil erosion) influence on soil carbon. Partitioning of Total Carbon (TC) in organic and inorganic forms in degraded soils was studied, and compared these with soils under agriculture, horticulture and forest systems. Highest Total Organic Carbon (TOC) was recorded in forest soils followed by horticultural systems, whereas the least was observed in degraded and agricultural systems while Inorganic Carbon (IC) decreased in the sequence of: degraded lands > forest > agriculture ≥ horticulture. TOC stocks in the upper half-a-meter layer were 163.9 Mg ha−1 in forest soils followed by horticulture (144.7 Mg ha−1) while in case of TC, the degraded lands closely followed forest soils. The contribution of IC to TC was about 39% in degraded lands, which was about twice that of its contribution in forest soils. TOC decreased with soil depth whereas IC increased with depth. The increase in IC with depth was minor for agricultural and horticultural soils, whereas it was about 84% for degraded and about 61% for forest soils. Our study highlights the impact of erosion on dynamics of soil carbon and its partitioning and suggests the need to promote better carbon sequestering land use systems towards conservation of top carbon rich soil and promoting sustainability in hill ecosystems particularly in Himalayas. • Total carbon was partitioned into organic and inorganic forms. • Highest TOC was recorded in forest soils, whereas maximum IC was in degraded. • IC was 39% of the TC in degraded lands, which was twice that of in forest soils. • Degraded soils were at par with agricultural soils with respect to TOC. • Increase in IC carbon with depth was 84% for degraded lands. [ABSTRACT FROM AUTHOR]