Effects of vegetation restoration on soil organic carbon sequestration at multiple scales in semi-arid Loess Plateau, China

Abstract:Revegetation is vital for enhancing soil carbon sequestration. However, the impacts of revegetation and terracing measures on soil organic carbon (SOC) and SOC sequestration (SOCS), and the differences in the effects of revegetation on SOC and SOCS when implemented on sloped fields versus terraced fields, are still unclear. Thus, we conducted a field survey on cropland (CL), grassland (GL), and forestland (FL) on both sloped fields and terraced fields in Wuqi county, China’s Loess Plateau. The results showed that SOC content in FL at 0–10 cm, 10–20 cm, 20–40 cm, 40–60 cm depths were 1.70, 1.28, 1.28, and 1.19 times respectively higher than in CL. Similarly, SOC content in GL at the same depths were 1.30, 1.13, 1.18, and 1.20 times higher than in CL. In terraced, SOC content at 40–60 cm, 60–80 cm, 80–100 cm depths were 1.22, 1.28, and 1.20 times respectively higher than on sloped fields. Revegetation primarily significantly affected SOC at 0–10 cm depth on sloped fields (GL: p = 0.04; FL: p < 0.01), and more deeply (0–100 cm) on terraced fields (GL at 40–80 cm: p < 0.05; FL: p < 0.01). Furthermore, revegetation on sloped fields generated the highest SOCS at 0–40 cm depth, with a subsequent decrease as depth increased to 40–100 cm depth. Conversely, on terraced, SOCS increased with soil depth within the 0–100 cm depth. These results indicated that revegetation primarily enhanced SOCS in the surface soil (0–40 cm), and terracing measures stabilized the SOCS in the surface soil and further enhanced them in deeper soil horizons (0–100 cm). Therefore, in the context of soil erosion control and ecological restoration, the combined implementation of vegetation restoration and engineering measures can effectively stabilize and enhance SOCS, thereby fully leveraging the role of soil in mitigation climate change.Keywords: Soil and water conservation measures; Carbon sequestration; Land use change；Vegetation restoration; Engineering measures; Deep soil organic carbon

In order to clarify the differences in the effects of vegetation restoration strategies on soil carbon sequestration and aggregate stability under different water-eroded environments, we collected experimental data from 91 papers and evaluated the response of soil organic carbon (SOC) stock and aggregate stability to vegetation restoration based on Meta-analysis. The results showed the following:① compared with cropland or bare land, forestland/grassland restoration was beneficial to increase SOC stock and improve aggregate stability, but the dominant functions of the two were different. The effect of forestland restoration on carbon sequestration was stronger than that of grassland reforestation, and the effect of grassland restoration on aggregate stability was stronger than that of forestland restoration. ② Multi-factor Meta-analysis showed that the factors that significantly affected SOC were restoration year, soil clay content, vegetation coverage, mean annual precipitation (MAP), mean annual temperature (MAT), and soil depth. The positive effect of vegetation restoration on SOC stock increased with the increase in vegetation coverage rate. Grassland restoration had a more significant effect on SOC stock when soil clay content was 20%-32%, it was more likely to promote the carbon sequestration effect of grassland when MAP>800 mm or MAT<15℃, and there was no significant change in SOC stock under different restoration years. However, the effect of forestland restoration on SOC stock was more significant when soil clay content was>32%. Climate conditions had no limited effect on SOC stock in forestland, and there was a positive effect between SOC stock under forestland restoration and restoration years. ③ Vegetation restoration had stronger significant positive effects on mean weight diameter (MWD) and mean geometric diameter (GMD) when the clay content was 20%-32%, and MWD and GMD increased with the increase in vegetation coverage. ④SOC stock growth could explain 25% and 24% of the variation in the effect value of MWD and GMD, respectively. These results indicated that the formation of SOC was the result of multiple factors, and soil aggregate stability was limited only by vegetation coverage and soil clay content. The increase in SOC stock could promote the improvement of water stability MWD and GMD. These results can clarify the carbon sequestration effect of different vegetation restoration measures in water-eroded environments and provide theoretical reference for the restoration and reconstruction of degraded ecosystems.

The duration of soil organic carbon (SOC) sequestration in agricultural soils varies according to soil management, land-use history and soil and climate conditions. Despite several experiments have reported SOC sequestration with the adoption of no-tillage (NT) in Mediterranean dryland agroecosystems scarce information exists about the duration and magnitude of the sequestration process. For this reason, 20 years ago we established in northeast Spain a NT chronosequence experiment to evaluate SOC sequestration duration under Mediterranean dryland conditions. In July 2010 we sampled five chronosequence phases with different years under NT (i.e., 1, 4, 11, and 20 years) and a continuous conventional tillage (CT) field, in which management prevailed unchanged during decades. Soil samples were taken at four depths: 0–5, 5–10, 10–20 and 20–30 cm. The SOC stocks were calculated from the SOC concentration and soil bulk density. Furthermore, we applied the Century ecosystem model to the different stages of the chronosequence to better understand the factors controlling SOC sequestration with NT adoption. Differences in SOC stocks were only found in the upper 5 cm soil layer in which 4, 11 and 20 years under NT showed greater SOC stocks compared with 1 year under NT and the CT phase. Despite no significant differences were found in the total SOC stock (0–30 cm soil layer) there was a noteworthy difference of 5.7 Mg ha−1 between the phase with the longest NT duration and the phase under conventional tillage. The maximum annual SOC sequestration occurred after 5 years of NT adoption with almost 50% change in the annual rate of SOC sequestration. NT sequestered SOC over the 20 years following the change in management. However, more than 75% of the total SOC sequestered was gained during the first 11 years after NT adoption. The Century model predicted reasonably well SOC stocks over the NT chronosequence. In Mediterranean agroecosystems, despite the continuous use of NT has limited capacity for SOC sequestration, other environmental and agronomic benefits associated to this technique may justify the maintenance of NT over the long-term.

Enhancing soil organic carbon (SOC) stocks through fertilization and crop rotation will contribute to sustaining crop productivity and mitigating global warming.&amp;#160;Although it is known that cropping systems may affect SOC stocks by influencing the balance between C input and C decomposition, only few studies focused on the impact of different rice cropping systems on SOC stock changes in paddy soils.&amp;#160;In this study, we analyzed the differences in SOC stocks and their driving factors in the topsoil (0&amp;#8211;20 cm) with various fertilization measures in two rice-based cropping systems (i.e. rice-wheat rotation and double rice rotation systems) over the last four decades from seven long-term experiments in the Yangtze River catchment. The treatments include no fertilizer application (CK), application of chemical nitrogen, phosphorus and potassium fertilizers (NPK) and a combination of NPK and manure (NPKM). Results showed that during the last four decades, the topsoil SOC stock significantly increased by 8.6 t ha-1&amp;#160;on average under NPKM treatment in rice-wheat system and by 2.5&amp;#8211;6.4 t ha-1&amp;#160;on average under NPK and NPKM treatments in double rice system as compared with CK. A higher SOC sequestration rate and a longer SOC sequestration duration were found in NPKM treatment than that in NPK treatment in both cropping systems. The highest relative SOC stock percentage (SOC stock in fertilized treatments to CK) was observed under the NPKM treatment in both cropping systems, though no significant difference was found between these two cropping systems. However, the fertilization-induced relative increase of the SOC stock was 109.5% and 45.8% under the NPK and NPKM treatments, respectively in the rice-wheat system than that in the double rice system. This indicates that the rice-wheat system is more conducive for SOC sequestration. RF and SEM analyses revealed that the magnitude and influencing factors driving SOC sequestration varied between two systems. In the double rice system, continuous flooding weakens the influence of precipitation on SOC sequestration and highlights the importance of soil properties and C input. In contrast, soil properties, C input and climate factors all have important impacts on SOC sequestration in rice-wheat system. This study reveals that the rice-wheat system is more favorable for SOC sequestration despite its lower C input compared to the double rice system in China&amp;#8217;s paddies.

Estimates of regional and national topsoil soil organic carbon (SOC) stock change may help evaluating the soil role in mitigation of greenhouse gas (GHG) emissions through carbon (C) sequestration in soils. However, understanding of the exact mitigation role is often constrained by the uncertainty of the stock estimation associated with different methodologies. In this paper, a soil database of topsoil (0–20 cm) SOC measurements of Jiangsu Province, China, obtained from a soil survey in 1982, and from a geological survey in 2004, was used to analyze the variability of topsoil SOC among soil groups and among soil regions, and to estimate the change in SOC stocks that have occurred in the province over the last two decades. The soil survey data was obtained from measurements of 662 690 randomly collected samples, while the geological survey data was from 24 167 samples taken using a 2 km × 2 km grid. Statistical analysis was conducted on SOC values for 1982 and 2004 for different categories of soil groups, soil regions, and administrative municipalities, respectively. Topsoil SOC storage was then calculated and the provincial topsoil SOC stock was estimated for each sampling time. There were remarkable differences in SOC levels between soil groups and soil regions and different municipalities. The grid sampling with the geological survey in 2004 yielded smaller variability of topsoil SOC averages, both with soil groups and with soil spatial distribution than the random sampling method used in 1982. Variation of SOC was greater with soil groups than with soil regions in both sampling times, although it was less variable across soil taxonomic categories than within a spatial category. Little variance of the SOC level with soil groups could be explained by clay content. However, the prevalence of paddy fields in the total cropland area governed the regional and municipal average SOC levels. The average provincial topsoil SOC content increased from 9.45 g kg−1 in 1982 to 10.9 g kg−1 in 2004, and the total provincial topsoil SOC stock was enhanced from 149.0±58.1 Tg C in 1982 to 173.2±51.4 Tg C in 2004, corresponding to a provincial average SOC sequestration rate of 0.16±0.09 t C ha−1 yr−1. The SOC sequestration trend for the last two decades could be, in part, attributed to the enhanced agricultural production, symbolized by the grain yield per hectare. The results of SOC stock changes suggest a significant C sequestration in soils of Jiangsu, China, during 1980–2000, with paddy management playing an important role in regional SOC storage and sequestration capacity.

Afforestation changes soil organic carbon stocks on sloping land: The role of previous land cover and tree type

Vegetation restoration is widely recognized as a way to improve soil organic carbon (SOC) stock. However, whether these recovered carbons are stable is yet largely uncertain. Thus, we determined the sequestration and stability of SOC in soils with three different types (Caragana korshinskii (CA) aged for 10, 20, 36, and 47 years, Hippophae rhamnoides (HR) aged for 5, 10, 20, and 30 years, and Robinia pseudoacacia (RP) aged for 5, 10, 20, 37, and 56 years) to compare their SOC sequestration and stability in different depths in this study. The SOC content, SOC stock, very labile fraction of oxidizable carbon (C1), labile fraction of oxidizable carbon (C2), and carbon management index (CMI) in 0–30 cm depths of the three types increased over the chronosequence. The SOC stocks increased by 1.40–3.19 Mg ha−1 in CA during the 47‐year restoration, by 5.76–10.01 Mg ha−1 in HR during the 30‐year restoration and by 1.88–8.93 Mg ha−1 in RP during the 56‐year restoration, respectively, in 0–30 cm depths. The carbon stability index (SI) in 0–10 cm depth of CA, 0–30 cm depths of HR, and 0–50 cm depths of RP decreased with recovery time. Over the recovery time, SOC content, SOC stock, CMI, and SI were lower than those of nature forest (NF aged more than 100 years) in all restored sites at the later stage of recovery. SOC sequestration decreased, but its stability increased, with the soil depths. Overall, HR had a higher SOC sequestration rate and lower SI (0–30 cm) than CA and RP. Our results revealed that although the SOC sequestration appears enhanced over the restoration, but the SOC stability becomes lower, so that the recovery of these site to the level of NF may meet difficulties in this semiarid Loess Hilly Region.

The sustainable land management program (SLMP) of Ethiopia aims to improve livelihoods and create resilient communities and landscape to climate change. Soil organic carbon (SOC) sequestration is one of the key co-benefits of the SLMP. The objective of this study was to estimate the spatial dynamics of SOC in 2010 and 2018 (before and after SLMP) and identify the SOC sequestration hotspots at landscape scale in four selected SLMP watersheds in the Ethiopian highlands. The specific objectives were to: 1) comparatively evaluate SOC sequestration estimation model building strategies using either a single watershed, a combined dataset from all watersheds, and leave-one-watershed-out using Random Forest (RF) model; 2) map SOC stock of 2010 and 2018 to estimate amount of SOC sequestration and potential; 3) evaluate the impacts of SLM practices on SOC in four SLMP watersheds. A total of 397 auger composite samples from the topsoil (0–20 cm depth) were collected in 2010, and the same number of samples were collected from the same locations in 2018. We used simple statistics to assess the SOC change between the two periods, and machine learning models to predict SOC stock spatially. The study showed that statistically significant variation (P < 0.05) of SOC was observed between the two years in two watersheds (Gafera and Adi Tsegora) whereas the differences were not significant in the other two watersheds (Yesir and Azugashuba). Comparative analysis of model-setups shows that a combined dataset from all the four watersheds to train and test RF outperform the other two strategies (a single watershed alone and a leave-one-watershed-out to train and test RF) during the testing dataset. Thus, this approach was used to predict SOC stock before (2010) and after (2018) land management interventions and to derive the SOC sequestration maps. We estimated the sequestrated, achievable and target level of SOC stock spatially in the four watersheds. We assessed the impact of SLM practices, specifically bunds, terraces, biological and various forms of tillage practices on SOC using partial dependency algorithms of prediction models. No tillage (NT) increased SOC in all watersheds. The combination of physical and biological interventions (“bunds + vegetations” or “terraces + vegetations”) resulted in the highest SOC stock, followed by the biological intervention. The achievable SOC stock analysis showed that further SOC stock sequestration of up to 13.7 Mg C ha--1 may be possible in the Adi Tsegora, 15.8 Mg C ha-1 in Gafera, 33.2 Mg C ha-1 in Azuga suba and 34.7 Mg C ha-1 in Yesir watersheds.

Estimating temporal and spatial changes in soil organic carbon stocks and its controlling factors in moraine landscapes in Denmark

Soil Organic Carbon (SOC) dynamics study in arable land use at different agro-ecological zones is important for recommendation of sustainable land use management practices against detrimental practices. This will provide insight on how to enhance SOC sequestration, improve soil quality and mitigate impact of climate change in different agro-ecological zones. This study was conducted at two agro-ecological zones of Nigeria; upland rainforest (Ado-Ekiti) and southern guinea savanna (Kabba) to evaluate SOC sequestration under arable land use. From the two agro-ecological zones, 1 ha (ha) of land was marked out, five soil samples were randomly collected at four different depths (0–15, 15–30, 30–45, and 45–60 cm) for SOC sequestration study. Higher SOC concentration and stock were observed at Ado-Ekiti site over Kabba site was due to best soil management practices like soil organic and inorganic fertilizers application and incorporation of crop residues. SOC concentration distribution varied greatly (%CV > 35%) and decreased with depth at the two agro-ecological zones. SOC stocks ranged from 6.59 t ha −1 to 24.97 t ha −1 and decreased with depth in similar trend with SOC concentration. Generally, at both sites, soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) decrease with increasing depth especially to 45 cm depth while soil pH increase with increasing depth. Both SOC concentration and stock were observed to have significant positive correlation ( P < 0.01; P < 0.05) with SOM ( r = 1.000** and 0.996**; and r = 0.991** and 0.707**) and TN ( r = 0.936** and 0.934**; and r = 0.992** and 0.691**) at Ado-Ekiti and Kabba sites respectively. This indicated that increase in SOM and TN were associated with increase in SOC stock and concentration. Maximum value (20.33%) of exchangeable sodium percentage (ESP) of above critical value of 15% was recorded at Ado-Ekiti site which requires that soil be managed against sodicity. There was significant difference ( t = 2.975**) between the overall mean SOC stocks (14.83 and 9.15 t ha −1 at Ado-Ekiti and Kabba sites respectively) at two agro-ecological zones. Thus, adoption of better soil management practices will enhance SOC sequestration and soil quality at the two agro-ecological zones.

Organic farming (OF) enhances top soil organic carbon (SOC) stocks in croplands compared with conventional farming (CF), which can contribute to sequester C. As farming system differences in the amount of C inputs to soil (e.g. fertilization and crop residues) are not enough to explain such increase, shifts in crop residue traits important for soil C losses such as litter decomposition may also play a role. To assess whether crop residue (leaf and root) traits determined SOC sequestration responses to OF, we coupled a global meta‐analysis with field measurements across a European‐wide network of sites. In the meta‐analysis, we related crop species averages of leaf N, leaf‐dry matter content, fine‐root C and N, with SOC stocks and sequestration responses in OF vs. CF. Across six European sites, we measured the management‐induced changes in SOC stocks and leaf litter traits after long‐term ecological intensive (e.g. OF) vs. CF comparisons. Our global meta‐analysis showed that the positive OF‐effects on soil respiration, SOC stocks, and SOC sequestration rates were significant even in organic farms with low manure application rates. Although fertilization intensity was the main driver of OF‐effects on SOC, leaf and root N concentrations also played a significant role. Across the six European sites, changes towards higher leaf litter N in CF also promoted lower SOC stocks. Our results highlight that crop species displaying traits indicative of resource‐acquisitive strategies (e.g. high leaf and root N) increase the difference in SOC between OF and CF. Indeed, changes towards higher crop residue decomposability was related with decreased SOC stocks under CF across European sites. Synthesis and applications. Our study emphasizes that, with management, changes in crop residue traits contribute to the positive effects of organic farming (OF) on soil carbon sequestration. These results provide a clear message to land managers: the choice of crop species, and more importantly their functional traits (e.g. leave and root nitrogen), should be considered in addition to management practices and climate, when evaluating the potential of OF for climate change mitigation.

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

Soil organic carbon content and stock change after half a century of intensive cultivation in a chernozem area

Optimizing organic amendment applications to enhance carbon sequestration and economic benefits in an infertile sandy soil

China’s Loess Plateau is both the largest and deepest loess deposit in the world, and it has long been one of the most severely eroded areas on Earth. With the implementation of the Grain-for-Green Project in 1999, the Loess Plateau has become the most successful ecological restoration zone, and soil organic carbon (SOC) sequestration has greatly increased. However, little is known about the balance of SOC sequestration and vegetation restoration on the Loess Plateau. Thus, this review focused on the SOC sequestration from vegetation restoration in this region. Firstly, the current situations and principal aspects of vegetation restoration processes were reviewed, and the effects of vegetation restoration on SOC sequestration were summarized. Secondly, based on the new technologies and methods for soil carbon (C) sequestration, the mechanism of soil microbial C sequestration was described from the molecular level of genes, and some management measures for SOC sequestration were summarized. Finally, we pointed out the main directions in C sequestration mechanisms for vegetation restoration depending on the basic process of the C cycle, which should integrate into physics, chemistry, and biology. Overall, this review will help us understand the SOC sequestration function and the ecological benefits of vegetation restoration on the Loess Plateau.