Multiple soil map comparison highlights challenges for predicting topsoil organic carbon concentration at national scale

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土丘陵区不同侵蚀环境下土壤有机碳对植被恢复的响应 DOI: 10.5846/stxb201606161168 作者: 作者单位: 西北农林科技大学水土保持研究所黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学水土保持研究所黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学水土保持研究所黄土高原土壤侵蚀与旱地农业国家重点实验室;中国科学院水利部水土保持研究所,西北农林科技大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41371280）；水利部公益性行业科研专项项目（201501045） Response of soil organic carbon to vegetation restoration in different erosion environments in the hilly-gullied region of the Loess Plateau Author: Affiliation: State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A＆F University,,State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A＆F University;Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:植被恢复是提高土壤有机碳累积和储存的重要措施。以黄土丘陵区两个典型侵蚀环境下的小流域即黄土区坊塌流域和砒砂岩区满红沟流域退耕坡面为研究对象，分析了土壤有机碳含量（SOCC）、有机碳密度（SOCD）在同一侵蚀环境不同群落下的变化以及在同一群落不同侵蚀环境间的差异，旨在探明不同侵蚀环境下土壤有机碳对植被恢复的响应。结果表明：1）同一侵蚀环境下，与坡耕地相比，自然恢复方式下退耕地植被恢复初期SOCC、SOCD均显著降低，之后随植被恢复均显著升高（P < 0.05）；人工恢复方式下退耕地20-25年柠条锦鸡儿群落和13-14年刺槐群落SOCC、SOCD均显著升高（P < 0.05），说明同一侵蚀环境内，退耕地在两种恢复方式下均能显著提高土壤有机碳累积和储存。2）同一侵蚀环境下，与相近恢复年限的自然恢复群落相比，刺槐群落SOCC、SOCD均显著高于长芒草+铁杆蒿群落（P < 0.05），砒砂岩区柠条锦鸡儿群落SOCC、SOCD均显著低于铁杆蒿群落（P < 0.05），黄土区柠条锦鸡儿群落SOCC显著低于而SOCD显著高于铁杆蒿群落（P < 0.05），说明相同恢复时间内，相对于自然恢复方式，人工刺槐造林在两种侵蚀环境下均能累积与储存较多的土壤有机碳，而柠条锦鸡儿造林在两种侵蚀环境下累积土壤有机碳的效果均不佳，在黄土区储存土壤有机碳效果好于砒砂岩区。3）同一群落下，黄土区人工和自然恢复群落SOCC均高于砒砂岩区；黄土区人工恢复群落SOCD均显著高于而自然恢复群落SOCD均低于砒砂岩区（P < 0.05），说明黄土区人工恢复累积和储存土壤有机碳及自然恢复累积土壤有机碳的效果较好，而砒砂岩区自然恢复储存土壤有机碳的效果较好。 Abstract:Vegetation restoration is one of the most important measures to improve accumulation and storage of soil organic carbon (SOC). The objective of our study was to understand the response of soil organic carbon to vegetation restoration in different erosion environments in the hilly-gullied region of the Loess Plateau. The study was thus conducted on 42 restored slopes and six sloping croplands (control) in the Fangta watershed and the Manhonggou watershed, which are located, respectively, in the Loess area and Sandstone area and is characterized by different erosion environments. Variations in soil organic carbon content (SOCC) and soil organic carbon density (SOCD) among different plant communities in each erosion environment and among different erosion environments for each plant community were analyzed. In each erosion environment, compared with sloping croplands, SOCC and SOCD decreased significantly at the preliminary stage of natural restoration while the increased significantly with the process of restoration (P < 0.05); and significant increases of SOCC and SOCD were also observed for Caragana korshinskii communities (20-25 a) and Robinia pseudoacacia communities (13-14 a). This shows that soil organic carbon could be improved using both natural and artificial means of restoration within each erosion environment. SOCC and SOCD of R. pseudoacacia communities were much higher than those of Stipa bungeana +Artemisia gmelinii communities (15 a) within each erosion environment (P < 0.05); SOCC and SOCD in C. korshinskii communities (20-25 a) were much lower than in A. gmelinii communities (30 a) in the Sandstone area (P < 0.05); and C. korshinskii communities (20-25 a) had much lower SOCC and much higher SOCD than A. gmelinii communities (30 a) in Loess area (P < 0.05). These results indicate that within the same duration of restoration, compared with natural restoration, R. pseudoacacia afforestation could accumulate and store more SOC within each erosion environment. The effectiveness of C. korshinskii afforestation for accumulating SOC was not superior within all erosion environments, however, its effectiveness in storing SOC was superior in the Loess area but not in the Sandstone area. Both artificial and natural communities had higher SOCC in the Loess area than in Sandstone area, and artificial and natural communities had higher SOCD and lower SOCD in the Loess area than in the Sandstone area, respectively. Therefore, in contrast to the Sandstone area, artificial restoration in the Loess area was more effective at accumulating and storing SOC, and natural restoration was superior in accumulating SOC, but not in storing SOC. 参考文献 相似文献 引证文献

Estuarine wetlands exhibit significant interaction between fresh and salt water, with long-term carbon sequestration capability. We set up 60 sampling sites in the reed wetlands of the fresh-salt water interaction zone of the Yellow River Estuary, covering four different zones of the weak-intensity fresh-salt water interaction zone (WIZ), medium-intensity fresh-salt water interaction zone (MIZ), high-intensity interaction fresh-salt water zone (HIZ) and strong-intensity fresh-salt water interaction zone (SIZ). We investigated how fresh-salt water interaction affected the spatial variation of soil organic carbon (SOC) storage. The results showed that the area of reed wetland accounted for 17.8% of the total area of the fresh-salt water interaction zone the Yellow River Estuary, which mainly distributed in the WIZ and MIZ. The SOC content of reed wetland in the fresh-salt water interaction zone ranged from 1.09 to 3.65 g·kg-1, the SOC density was between 1.85-5.84 kg·m-2, and the SOC storage was (17.32±3.64)×104 t. The SOC content and SOC density decreased with increasing fresh-salt water interaction. There were significant differences in surface SOC content between different subzones of the fresh-salt water interaction zone. The surface SOC content decreased significantly with the increases of fresh-salt water interaction intensity. SOC density was positively correlated with SOC, TN, NH4+-N, and biomass, but negatively correlated with salt ions, soil bulk density, pH, and EC. SOC storage in the 0-30 cm soil layer accounted for 50.9%-64.2% of that in the 0-60 cm soil layer, while SOC storage in the 0-60 cm soil layer occupied 19.1%-37.7% of that in the 0-400 cm soil layer. The results could provide a scientific basis for accurately evaluating SOC storage of estuarine wetlands, improving carbon sink function and wetland management.

The impact of different vegetation communities on soil organic carbon (SOC) in a tropical freshwater wetland in Uganda was investigated. SOC content, density and storage potential were determined under three different dominant vegetation communities: Cyperus papyrus L., Typha latifolia L. and Phragmites mauritianus Kunth. SOC content (123.7 ± 2.6 SE g C kg−1 dry soil) in C. papyrus was significantly higher (p < 0.05) than in both T. latifolia and P. mauritianus, whereas SOC density (kg C m−2) insignificantly varied (p > 0.05) among the three vegetation communities (C. papyrus = 7.2 ± 0.1, T. latifolia = 6.7 ± 0.1 and P. mauritianus = 6.2 ± 0.1). Similarly, for the entire sampled soil depth (0–50 cm), SOC storage potential was significantly higher (p < 0.05) in C. papyrus (36 118.08 ± 552.52 t C km−2), and was in the order of decreasing magnitude: C. papyrus > T. latifolia > P. mauritianus. Plant biomass density, and soil physico-chemical characteristics, bulk density, salinity, pH and temperature were significantly correlated (p < 0.05) with SOC. In conclusion, where climate change mitigation is considered as a wetland ecosystem service, restoration priorities for degraded/lost tropical freshwater wetlands need to consider C. papyrus plants. In addition, comparing SOC storage by ecosystems, Uganda’s wetlands contain three times more SOC than is contained in the country’s forests.

Marshes in high plateaus are critical in governing carbon cycle because of their huge but labile soil organic carbon (SOC) storage, which of even a small proportion of carbon contained in SOC can lead to high variations in the atmospheric CO2 levels. The Yarlung Zangbo River (YZR) is the world's highest river, flowing from west to east across Tibet. There are widespread alpine marshes and meadows along the YZR basin, with huge SOC storage but extremely vulnerable to climate change. However, few studies were carried out to explore the potential effects of environmental factors on SOC pool along the YZR. In the present work, effects of climate, plant biomass, soil nutrients, and molecular features of organic matter on SOC storage were systematically evaluated. Results indicated that SOC contents varied from 0.86% to 29.68%, with an average of 7.29%, and an estimated 5887 Gg (109g) of carbon was stored in marsh soils along the YZR. Soil accretion rates ranged from 1.66 to 2.73 mm yr−1, while carbon sequestration rates ranged from 43.65 gC m−2 yr−1 to 125.4 gC m−2 yr−1, with an average of 75.89 gC m−2 yr−1. It was estimated that 34.58 Gg of carbon was sequestrated by wetlands along the YZR every year. The abundance of lignin‐derived components, total nitrogen, and soil moisture contents (SWC) were the main drivers promoting SOC contents. SOC storage was significantly related to mean annual temperature (Temp) but decreased with the ratio of annual precipitation (Pre) to Temp. Compared with the chemical decomposition resistance of organic matter, more SOC variations arose from climate, and climate warming had adverse impacts on SOC pool. SWC were proved to be the most powerful promoter of SOC increase. Rising temperatures are expected to have a detrimental impact on SOC storage when the climate is warming in the future.

Soil organic carbon (OC) storage across regions is influenced by climate and parent materials, which determine soil properties like clay content and mineralogy. Within homogeneous soil regions, land use and management practices are further important controls for soil OC contents and turnover. Here, we studied the impact of study region, land use (forest, grassland), forest management (spruce and beech forest under age-class management, unmanaged beech forest), and grassland management (meadow, mown pasture, unmown pasture) on stocks and turnover (based on Δ14C values) of soil OC in density frations of topsoil horizons. Samples were taken from 36 plots in the regions Hainich–Dun (HAI) and the Schwabische Alb (ALB) in Germany. They were separated into two light fractions (free light fraction (LF1), occluded light fraction (LF2)) and the mineral-associated organic matter (MOM) fraction using sodium polytungstate with a density of 1.6 g cm−3. Overall most soil OC was stored in the MOM fraction (73%). Soil OC concentrations and stocks in the MOM fraction differed between study regions, probably due to larger amounts of pedogenic Al- and Fe-oxides in the ALB than in the HAI region. Within each region, forest soils stored significantly higher proportions of total OC in the two LF (33±1.9 %) than grassland soils (20±2.3 %). Different management of forests and grasslands affected the C:N ratio of density fractions, but not OC storage. While modelled soil OC turnover in the MOM was longest of all fractions, all fractions had average Δ14C values above atmospheric values, suggesting a significant fast-cycling component in all of them. Different from stocks, turnover of OC in the MOM fraction were not affected by study region or contents of pedogenic oxides. Radiocarbon contents in the LF were higher for forest than for grassland sites, indicating faster turnover of OC at grassland sites. However, some of the observed difference could originate from different average lifetimes of roots in forests and grasslands. Applying different lag-times for OC input for forests and grasslands significantly reduced the differences in modelled turnover times. Lower Δ14C values of mown pastures than pasture soils in both regions suggest a management effect on soil C turnover in grasslands.We conclude that OC storage in the MOM of topsoil layers is more affected by regional differences in soil texture and mineralogy than by land use and management, while its turnover could not be explained with the studied soil properties. Soil OC storage and turnover in the two LFs is influenced by land use (forest or grassland) and management, but ecosystem specific lag-times have to be considered for modelling OC turnover in these fractions.

BackgroundSoil aggregation and organic carbon (OC) content are important indicators of soil quality that can be improved with plant residue amendments. The extent of the effects of plant residue amendments on soil aggregation and OC content across different plant residue and soil types is not fully understood.AimIn this meta‐analysis, we evaluated the effects of plant residue amendments on soil aggregation and OC content for different plant residues (fresh, charred) and soil types varying in clay content, initial OC content, and pH.MethodsOur meta‐analysis included 50 published studies (total of 299 paired observations). We estimated the response ratios of mean weight diameter (MWD) and separate aggregate size classes, total soil OC (TSC), and aggregate‐associated OC. We also considered the effect of experimental factors (study duration, residue type, residue amount, initial soil OC, clay content, and pH).ResultsThe benefit of plant residue amendment on soil aggregation was larger in soils with initially low OC content and neutral pH. Initial soil OC content and pH were more important than soil clay content for OC storage in soil aggregates. Both fresh and charred plant residue amendments were effective in forming aggregates, whereas charred residues were more effective in increasing TSC. We found only a weak positive relationship between the response ratio of TSC and MWD indicating that other factors besides soil aggregation contributed to the increase in soil C storage.ConclusionsWhile plant residue amendments can enhance soil aggregation and TSC, these effects are likely governed by the type of plant residue and soil properties such as the initial soil pH and OC content.

Changes in soil organic carbon and aggregate stability after conversion to conservation tillage for seven years in the Huang-Huai-Hai Plain of China

Widespread adoption of conservation practices is increasingly encouraged to improve soil organic carbon (SOC) storage and mitigate climate change. However, soil texture and mineralogy cause variable SOC responses under conservation tillage. The role of minerals and organic carbon composition in soil aggregation and SOC stabilization remains insufficiently understood. This study evaluated the long‐term effects of conservation tillage (no‐tillage with straw return, NTS) versus conventional tillage (plough tillage with straw removal, CT) on carbon storage across Phaeozems, Calcaric Cambisols, and Calcic Luvisols. Compared to CT, NTS increased the annual average C sequestration rate by 15.3%–76.7% and SOC storage by 10.2%–28.4% in different soil types. NTS also increased macroaggregate percentage and mean weight diameter (MWD), resulting in 17.8%–28.3% larger macroaggregate‐associated SOC and total nitrogen (TN) contents. Notably, the aromatic‐C/aliphatic‐C ratio under NTS increased in bulk soil and macroaggregates, which were positively correlated with larger amorphous iron (Feo) content, Ca 2+ concentration, and specific surface area in different treatments. Phaeozems exhibit the largest SOC storage, along with larger Feo and Ca 2+ contents and aromatic‐C/aliphatic‐C ratio. However, NTS led to the greatest increases in MWD and SOC storage in Calcaric Cambisols, and the greatest enhancement of microbial biomass carbon in Calcic Luvisols. PLS‐PM analysis indicated that although the aromatic‐C/aliphatic ratio directly enhances aggregated stability, Feo and Ca 2+ promoted MWD indirectly by facilitating greater aromatic‐C and polysaccharide‐C. Overall, conservation tillage promoted selective binding of Feo and Ca 2+ to SOC functional groups, thus enhancing soil aggregation and SOC physico‐chemical protection, with calcareous soils showing a stronger response.

Seven artificial alfalfa grasslands (aged 3, 5, 6, 7, 8, 11, 12 a) and an abandoned land plot were selected to examine the changes in soil organic carbon content, active organic carbon content, soil organic carbon storage and active organic carbon storage in the 0–200 cm soil layer and their correlation with soil nutrients, soil water content, soil bulk density, alfalfa cover, density, height and aboveground biomass. The results show that the soil organic carbon content was between 2.02 and 4.54 g kg–1 within depths of 0–200 cm, which was higher than that in the abandoned land. The soil organic carbon storage in the 0–40 cm layers accounted for, on average, 29.50 ± 7.13% of the total storage in the 0–200 cm soil layers in the 7-year-old alfalfa grasslands and the abandoned land, and the 0–40 cm layer was the main layer of soil organic carbon storage. The soil organic carbon storage in 12 a grassland was the highest, and the abandoned land had the smallest reserve, with values of 10.22 and 5.06 kg m–2, respectively. In addition, carbon storage was, on average, 1.84 kg m–2 higher in 7-year alfalfa artificial grassland than in abandoned farmland. The proportion of soil AOC storage to SOC storage ranged from 30.24 to 58.11%; the proportion in 5-year grassland was the lowest, while it was the highest in the abandoned land. SOC storage had significant positive correlations with TN and soil active organic carbon storage, and it had negative correlations with soil bulk density at the 0.01 level (p < 0.01).

In organic farming, intensive tillage for weed control can degrade soil structure and reduce organic carbon and water retention. Organic no‐tillage with surface mulch offers a potential solution, but its long‐term effectiveness in Andosol soil remains poorly understood. This study evaluated the long‐term effects of organic no‐tillage practices combined with organic mulch on soil organic carbon (SOC) content and storage, water‐stable aggregate distribution (WSAD%), aggregate‐associated carbon, carbon stabilisation within aggregates, bulk density (BD), mean weight diameter (MWD), and soil water retention. The field experiment was conducted using a randomised complete block design with four replications, comparing two treatments: no‐tillage (NT) and conventional tillage (CT), both supplemented with organic mulch. Compared with CT, NT treatment yielded a 65.4% increase in SOC content and a 16.9% decrease in bulk density in the 0–5 cm surface layer, triggering a 16.3% improvement in SOC accumulation in the 0–20 cm soil depth. Furthermore, WSAD and MWD increased at the 0–5 cm, 5–10 cm, and 10–15 cm soil depths. Compared with CT, at all depths, aggregates exceeding 4 mm showed high SOC content and increased SOC stock within macroaggregates in NT, with field capacity and total plant available water (PAW) content also increasing. This study emphasises the critical role of SOC in enhancing PAW directly and the mean weight diameter in indirectly improving it by regulating field capacity. Overall, in organic farming, NT with residue retention markedly facilitates the overall improvement of SOC, soil structure stability, SOC stabilisation within macroaggregates, and soil water retention.

Microbial necromass contribution to soil carbon storage via community assembly processes

Soil organic carbon (SOC) is a crucial indicator of soil quality and fertility. However, excessive nitrogen (N) application, while increasing Moso bamboo yield, may reduce SOC content, potentially leading to soil quality issues. The impact of N on SOC and its active fraction in Moso bamboo forests remains underexplored. Investigating these effects will elucidate the causes of soil quality decline and inform effective N management strategies. Four N application gradients were set: no nitrogen (0 kg·hm−2·yr−1, N0), low nitrogen (242 kg·hm−2·yr−1, N1), medium nitrogen (484 kg·hm−2·yr−1, N2), and high nitrogen (726 kg·hm−2·yr−1, N3), with no fertilizer application as the control (CK). We analyzed the changes in SOC, active organic carbon components, and the Carbon Pool Management Index (CPMI) under different N treatments. The results showed that SOC and its active organic carbon components in the 0~10 cm soil layer were more susceptible to N treatments. The N0 treatment significantly increased microbial biomass carbon (MBC) content but had no significant effect on SOC, particulate organic carbon (POC), dissolved organic carbon (DOC), and readily oxidizable organic carbon (ROC) contents. The N1, N2, and N3 treatments reduced SOC content by 29.36%, 21.85%, and 8.67%, respectively. Except for POC, N1,N2 and N3 treatments reduced MBC, DOC, and ROC contents by 46.29% to 71.69%, 13.98% to 40.4%, and 18.64% to 48.55%, respectively. The MBC/SOC ratio can reflect the turnover rate of SOC, and N treatments lowered the MBC/SOC ratio, with N1 &lt; N2 &lt; N3, indicating the slowest SOC turnover under the N1 treatment. Changes in the Carbon Pool Management Index (CPMI) illustrate the impact of N treatments on soil quality and SOC sequestration capacity. The N1 treatment increased the CPMI, indicating an improvement in soil quality and SOC sequestration capacity. The comprehensive evaluation index of carbon sequestration capacity showed N3 (−0.69) &lt; N0 (−0.13) &lt; CK (−0.05) &lt; N2 (0.24) &lt; N1 (0.63), with the highest carbon sequestration capacity under the N1 treatment and a gradual decrease with increasing N fertilizer concentration. In summary, although the N1 treatment reduced the SOC content, it increased the soil CPMI and decreased the SOC turnover rate, benefiting soil quality and SOC sequestration capacity. Therefore, the reasonable control of N fertilizer application is key to improving soil quality and organic carbon storage in Moso bamboo forests.

Subsoils play an important role within the global C cycle, since they have high soil organic carbon (SOC) storage capacity due to generally low SOC contents. However, measures for enhancing SOC storage, such as no-tillage, agroforestry and application of animal manure, commonly focus on topsoils. In this dissertation, the option of actively burying SOC-rich soil material through tillage practices was studied for the first time assessing SOC sequestration in deep ploughed arable and forest soils as well as in fossil ridge and furrow cropland under forest with buried topsoils. Assessed deep-ploughed cropland soils contained on average 42±18% more SOC than the reference plots down to 100 cm. In contrast, total SOC stocks in deep ploughed forest soils were not significantly higher than in their respective reference soils. The ‘newly formed’ topsoil of the deep ploughed soils still contained less SOC than the reference topsoil, 14% and 37% under cropland and under forest, respectively. On average, the fraction of mineralised SOC assessed in one-year laboratory incubations, was 32% lower in incubated buried than in reference topsoils. Sandy cropland buried topsoil stripes and reference topsoils had the lowest mineralisable SOC fraction. Buried SOC was partly to fully preserved, most effectively in sandy cropland soils, but selective preservation of certain, most stabile SOC fractions and preferential decomposition of labile fractions, such as the commonly most easily decomposable free light fraction, could not explain SOC stability. Land use history of many of the studied sandy sites as heath was identified as an important aspect concerning SOC stabilisation. Medieval ridge-and-furrow cultivation led to the burial of former topsoil under ridges. SOC content was 0.4-0.9 g kg-1 higher at ridges than at reference positions, indicating long-term preservation of former topsoil SOC by burial under ridges, although enhanced SOC stocks at ridges due to carbon burial could not be significantly confirmed for all sites. In conclusion, deep ploughing led to enhanced subsoil SOC contents and stocks compared to a reference plot in forests and cropland. Deep ploughing increased the storage space for SOC by mechanically translocating topsoil material into the subsoil. SOC accumulation in the new topsoil horizons additionally determine the effect of deep ploughing on full profile SOC stocks.

&amp;lt;p&amp;gt;The degradation of European soils is a cause for concern. Examples are the reduction of carbon content and soil fertility. The European Commission therefore recommends further research on how to better monitor soils and their changes over time and space. Digital soil mapping (DSM) is already an established method for the use of hyperspectral information from soil samples for quantifying soil properties under laboratory conditions based on soil spectral libraries. At the remote sensing level, imaging spectroscopy has already achieved good results for the prediction of soil properties on a local scale. Major advantages of this method are that topsoil maps can be updated more frequently, spatially more accurately and with less costs.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In this study we bring together pedometric and remote sensing approaches to achieve the development of soil spectral models applicable to upcoming global hyperspectral imagery, combining DSM methods and data with Earth Observation expertise. In a first step at laboratory level, we used the EU-wide topsoil database LUCAS. We investigated whether using solely spectral data (without any covariates) and selected classification algorithms combined with PLSR could allow and improve the quantification of soil organic carbon (SOC) content. The best results were obtained for the local PLSR approach with RMSE=5.16 g kg-1, RPD=1.74 and R&amp;amp;#178;=0.67. In addition, the local PLSR approach was tested with LUCAS spectral data resampled to EnMAP satellite spectral resolution, resulting in a very similar SOC prediction model accuracy.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In the next step, the local PLSR approach was applied to airborne HySpex image data and simulated satellite EnMAP data from a test area in north-eastern Germany where local soil data are available for model validation. This area is associated with one LUCAS point. A direct application of the laboratory-based SOC model to the spectra of the airborne image was not possible due to higher variability in the image data caused by different environmental conditions (solar illumination, mixed soil-vegetation pixels, surface state -roughness, wetness-) and sensor performances different from the laboratory data resulting in an overall lower signal-to-noise ratio in the airborne image. Therefore, after reducing the effect of soil moisture, green vegetation cover, residues coverage, we used a two-step approach where (i) wet chemistry SOC analyses for a set of soil samples from the test area were replaced by the local PLSR approach using the LUCAS database. Then (ii) an airborne model was calibrated using the SOC content from (i) and the corresponding image spectra to calibrate an airborne PLSR. Preliminary results show a good airborne model accuracy for HySpex imagery with RMSE=3.33 g kg-1, RPD=1.59, R&amp;amp;#178;=0.63 and slightly lower but still good accuracy for simulated EnMAP imagery with RMSE=3.72 g kg-1, RPD=1.45, R&amp;amp;#178;=0.55. Both models were then applied to the images to produce SOC maps for bare soils and validated with existing data and previous SOC mapping works in the area based on local datasets. This approach demonstrates the possibility to replace wet chemistry by the local PLSR approach based on large scale soil spectral libraries for SOC mapping.&amp;lt;/p&amp;gt;

Soil organic carbon (SOC) storage is an important component of global carbon cycle and climate change mitigation. SOC storage depends on climate, topography and soil properties. The main objective of this research was to quantify average soil SOC content across the toposequence of a selected mountain terrain. The secondary objective was to compare the impact of microclimatic variables and slope angle on soil organic carbon content. It was hypothesized that mountainous locations with an overall high percent slope have lower SOC than the mountainous locations with lower percent slope. In this study, four slope positions across the toposequence of two tea fields (Field A and Field B) within Queensberry tea estate, Nawalapitiya were sampled for soil analyses. Measurements on micrometeorological variables (soil and air temperature, relative humidity, wind velocity, light intensity), litter and soil cores were taken in the field, and soil parameters including soil moisture, pH, texture and SOC stocks were analyzed in the laboratory. The overall average soil organic carbon stock in the studied soils was 159.85 t/ha .The overall percent slope of field A (25 percent) was higher than that of field B (21 percent). A significant difference in soil carbon stock could be seen among the slope positions considered across the toposequence of each field (P 0.05) have no significant effect on SOC stock. The SOC stock was higher at the field B (172.16 t/ha) which had the lower percent slope while SOC stock was lower at the field A (147.52t/ha) which had the higher percent slope. Therefor our hypothesis that mountainous locations with high percent slope would have lower SOC than the mountainous locations with lower percent slope was supported. Overall, the SOC stocks were significantly different with regard to the differences in slope angle (as found for the two fields) and the slope position across the toposequence (as observed within each field) in the medium-gradient tea plantation considered in the current study. Among the microclimatic variables, only the moisture had a significant influence on the SOC stock. Keywords: SOC stock, Slope position, Slope angle, Percent soil moisture, Medium-gradient tea plantation