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Soil Organic Carbon (soil + organic_carbon)
Selected AbstractsA review of nitrogen enrichment effects on three biogenic GHGs: the CO2 sink may be largely offset by stimulated N2O and CH4 emissionECOLOGY LETTERS, Issue 10 2009Lingli Liu Abstract Anthropogenic nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application, alters biogeochemical cycling of ecosystems in a way that leads to altered flux of biogenic greenhouse gases (GHGs). Our meta-analysis of 313 observations across 109 studies evaluated the effect of N addition on the flux of three major GHGs: CO2, CH4 and N2O. The objective was to quantitatively synthesize data from agricultural and non-agricultural terrestrial ecosystems across the globe and examine whether factors, such as ecosystem type, N addition level and chemical form of N addition influence the direction and magnitude of GHG fluxes. Results indicate that N addition increased ecosystem carbon content of forests by 6%, marginally increased soil organic carbon of agricultural systems by 2%, but had no significant effect on net ecosystem CO2 exchange for non-forest natural ecosystems. Across all ecosystems, N addition increased CH4 emission by 97%, reduced CH4 uptake by 38% and increased N2O emission by 216%. The net effect of N on the global GHG budget is calculated and this topic is reviewed. Most often N addition is considered to increase forest C sequestration without consideration of N stimulation of GHG production in other ecosystems. However, our study indicated that although N addition increased the global terrestrial C sink, the CO2 reduction could be largely offset (53,76%) by N stimulation of global CH4 and N2O emission from multiple ecosystems. [source] Magnitude and sources of uncertainties in soil organic carbon (SOC) stock assessments at various scalesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2009E. Goidts Summary Uncertainties in soil organic carbon (SOC) stock assessments are rarely quantified even though they are critical in determining the significance of the results. Previous studies on this topic generally focused on a single variable involved in the SOC stock calculation (SOC concentration, sampling depth, bulk density and rock fragment content) or on a single scale, rather than using an integrated approach (i.e. taking into account interactions between variables). This study aims to apply such an approach to identify and quantify the uncertainties in SOC stock assessments for different scales and spatial landscape units (LSU) under agriculture. The error propagation method (, method) was used to quantify the relative contribution of each variable and interaction involved to the final SOC stock variability. Monte Carlo simulations were used to cross-check the results. Both methods converged (r2=0.78). As expected, the coefficient of variation of the SOC stock increased across scales (from 5 to 35%), and was higher for grassland than for cropland. Although the main source of uncertainty in the SOC stock varied according to the scale and the LSU considered, the variability of SOC concentration (due to errors from the laboratory and to the high SOC spatial variability) and of the rock fragment content were predominant. When assessing SOC stock at the landscape scale, one should focus on the precision of SOC analyses from the laboratory, the reduction of SOC spatial variability (using bulk samples, accurate re-sampling, high sampling density or stratified sampling), and the use of equivalent masses for SOC stock comparison. The regional SOC stock monitoring of agricultural soils in southern Belgium allows the detection of an average SOC stock change of 20% within 11 years if very high rates of SOC stock changes occur (1 t C ha,1 year,1). Amplitude et sources des incertitudes liées aux estimations des stocks de carbone organique dans le sol (COS) à différentes échelles Résumé Les erreurs associées aux estimations du stock de carbone organique dans le sol (COS) sont rarement quantifiées bien qu'elles puissent empêcher l'obtention de résultats significatifs. Les quelques études qui le font focalisent en général sur une seule variable nécessaire au calcul du stock de COS (concentration en COS, profondeur échantillonnée, densité apparente et contenu en fragments rocheux) ou sur une échelle spatiale particulière, sans utiliser d'approche intégrée (prenant en compte les interactions entre les variables). Cette étude a pour objectif d'utiliser une telle approche pour identifier et quantifier les incertitudes liées aux estimations de stock de COS à différentes échelles spatiales et pour diverses unités spatiales de paysages (USP) agricoles. La loi de propagation des erreurs (méthode ,) permet de quantifier la contribution relative de chaque variable et interaction à la variabilité finale du stock de COS. Les simulations de Monte Carlo sont utilisées pour la vérification croisée des résultats. Les deux méthodes ont convergé (r2= 0.78). Comme prévu, le coefficient de variation du stock de COS a proportionnellement augmenté avec l'échelle spatiale considérée (de 5 à 35%), et était plus élevé pour les cultures que pour les prairies. Bien que la principale source d'erreur sur le stock de COS soit fonction de l'échelle spatiale et du type d'USP considérés, la variabilité du contenu en COS (du fait des erreurs de laboratoire et de sa grande variabilité spatiale) et du contenu en fragments rocheux étaient prédominants. Lors de l'estimation des stocks de COS à l'échelle du paysage, l'attention devrait prioritairement porter sur la précision des analyses en COS du laboratoire, la réduction de la variabilité spatiale du COS (en utilisant des échantillons composites, un ré-échantillonnage précis, une densité d'échantillonnage élevée ou un échantillonnage stratifié), et sur l'utilisation de masses équivalentes pour comparer les stocks de COS. Le réseau régional de suivi des stocks de COS des sols agricoles dans le sud de la Belgique permet la détection d'un changement de stock de COS moyen de 20% en 11 ans pour un taux très élevé de changement en stock de COS (1 t C ha,1 year,1). [source] Sampling and analytical plus subsampling variance components for five soil indicators observed at regional scaleEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2009B. G. Rawlins Summary When comparing soil baseline measurements with resampled values there are four main sources of error. These are: i) location (errors in relocating the sample site), ii) sampling errors (representing the site with a sample of material) iii) subsampling error (selecting material for analysis) and iv) analytical error (error in laboratory measurements). In general we cannot separate the subsampling and analytical sources of error (since we always analyse a different subsample of a specimen), so in this paper we combine these two sources into subsampling plus analytical error. More information is required on the relative magnitudes of location and sampling errors for the design of effective resampling strategies to monitor changes in soil indicators. Recently completed soil surveys of the UK with widely differing soils included a duplicate site and subsampling protocol to quantify ii), and the sum of iii) and iv) above. Sampling variances are estimated from measurements on duplicate samples , two samples collected on a support of side length 20 m separated by a short distance (21 m). Analytical and subsampling variances are estimated from analyses of two subsamples from each duplicate site. After accounting for variation caused by region, parent material class and land use, we undertook a nested analysis of data from 196 duplicate sites across three regions to estimate the relative magnitude of medium-scale (between sites), sampling and subsampling plus analytical variance components, for five topsoil indicators: total metal concentrations of copper (Cu), nickel (Ni) and zinc (Zn), soil pH and soil organic carbon (SOC) content. The variance components for each indicator diminish by about an order of magnitude from medium-scale, to sampling, to analytical plus subsampling. Each of the three fixed effects (parent material, land use and region) were statistically significant for each of the five indicators. The most effective way to minimise the overall uncertainty of our observations at sample sites is to reduce the sampling variance. [source] Quantifying the relationship between soil organic carbon and soil physical properties using shrinkage modellingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2009P. Boivin Summary Changes in soil organic carbon (SOC) may strongly affect soil structure and soil physical properties, which in turn may have feedback effects on the soil microbial activity and SOC dynamics. Such interactions are still not quantitatively described and accounted for in SOC dynamics modelling. The objective of this study was to test the hypothesis that soil shrinkage curve (ShC) analysis allows the establishment of close relationships between soil physical properties and SOC. We sampled a rice-cropped vertisol, a cambisol under conventional tillage and no-tillage and a restored cambisol. Soil samples were analysed for clay and SOC content, bulk volume, hydro-structural stability and plasma and structural pore volumes changes on the full water content range using ShC analysis. Although the soils behaved differently according to their constituents and history, changes in SOC linearly affected most of the soil physical properties, with stronger effects than changes in clay content. The observed effects of increasing SOC, such as increasing hydro-structural stability, specific bulk volume and water retention, agreed well with previously reported results. However, using ShC measurement and modelling allowed the observation of all these different effects simultaneously for small changes in SOC, and in a single measurement. Moreover, the relation between SOC changes and physical properties could be quantified. ShC analysis may, therefore, be used to account for the effect of changes in SOC on soil physical properties. [source] In search of stable soil organic carbon fractions: a comparison of methods applied to soils labelled with 14C for 40 days or 40 yearsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2008S. Bruun Summary A reliable method for the isolation of a stable fraction of soil organic carbon (SOC) would be very helpful for improving our understanding of the mechanisms responsible for stabilization of SOC and the dynamics of SOC turnover. We tested acid hydrolysis, physical fractionation (particle density/size), photo-oxidation, treatment with chemical oxidants (NaOCl and NaS2O8) and thermal treatment on two soils incubated with 14C-labelled barley straw for either 40 days or 40 years. Different intensities of the treatments were included. Acid hydrolysis, photo-oxidation and treatment with a chemical oxidant consistently removed more 40-year-old C than 40-day-old C, which suggests that the isolated fractions contained a large proportion of material with a relatively rapid turnover. The clay + silt associated SOC fraction contained a small proportion of 40-day-old C and a large proportion of 40-year-old C. This is consistent with a SOC fraction with medium turnover. The thermal treatment removed more 40-year-old C than 40-day-old C. At 400°C there was still a small proportion of the 40-year-old C remaining, whereas almost all the 40-day-old C was removed. This is consistent with a stable SOC fraction. However, because only 2,3% of the C remained after this treatment, the isolated SOC fraction may be of little quantitative importance. Furthermore, the thermally resistant fraction is likely to be heavily altered by the treatment, and therefore unsuitable for further studies of the chemical nature of stable SOC. [source] Soil organic carbon in density fractions of tropical soils under forest , pasture , secondary forest land use changesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2008S. Paul Summary Our knowledge of effects of land use changes and soil types on the storage and stability of different soil organic carbon (SOC) fractions in the tropics is limited. We analysed the effect of land use (natural forest, pasture, secondary forest) on SOC storage (depth 0,0.1 m) in density fractions of soils developed on marine Tertiary sediments and on volcanic ashes in the humid tropics of northwest Ecuador. The origin of organic carbon stored in free light (< 1.6 g cm,3) fractions, and in two light fractions (LF) occluded within aggregates of different stability, was determined by means of ,13C natural abundance. Light occluded organic matter was isolated in a first step after aggregate disruption by shaking aggregates with glass pearls (occluded I LF) and in a subsequent step by manual destruction of the most stable microaggregates that survived the first step (occluded II LF). SOC storage in LFs was greater in volcanic ash soils (7.6 ± 0.6 Mg C ha,1) than in sedimentary soils (4.3 ± 0.3 Mg C ha,1). The contribution of the LFs to SOC storage was greater in natural forest (19.2 ± 1.2%) and secondary forest (16.6 ± 1.0%) than in pasture soils (12.8 ± 1.0%), independent of soil parent material. The amount of SOC stored in the occluded I LF material increased with increasing silt + clay content (sedimentary soils, r = 0.73; volcanic ash soils, r = 0.58) and aggregation (sedimentary soils, r = 0.52; volcanic ash soils, r = 0.45). SOC associated with occluded I LF, had the smallest proportion of new, pasture-derived carbon, indicating the stabilizing effect of aggregation. Fast turnover of the occluded II LF material, which was separated from highly stable microaggregates, strongly suggested that this fraction is important in the initial process of aggregate formation. No pasture-derived carbon could be detected in any density fractions of volcanic ash soils under secondary forest, indicating fast turnover of these fractions in tropical volcanic ash soils. [source] Variable carbon recovery of Walkley-Black analysis and implications for national soil organic carbon accountingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2007S. Lettens Summary There is considerable interest in the computation of national and regional soil carbon stocks, largely as the result of the provisions of the Kyoto Protocol. Such stocks are often calculated and compared without proper reference to the uncertainties induced by different analytical methodologies. We illustrate the nature and magnitude of these uncertainties with the present soil organic carbon (SOC) study in Belgium. The SOC recovery of the Walkley-Black method was investigated based on a database of 475 samples of silt loam and sandy soils, which cover different soil depths and vegetation types in northern Belgium. The organic carbon content of the soil samples was measured by the original Walkley-Black method and by a total organic carbon analyser. The recovery was computed as the ratio of these two results per soil sample. Land use, texture and soil sampling depth had a significant influence on the recovery as well as their three-way interaction term (land use × texture × sampling depth). The impact of a land use, texture and sampling depth dependent Walkley-Black correction on the year 2000 SOC inventory of Belgium was determined by regression analysis. Based on new correction factors, the national SOC stocks increased by 22% for the whole country, ranging from 18% for cropland to 31% for mixed forest relative to the standard corrected SOC inventory. The new recovery values influenced therefore not only C stocks in the year 2000, but also the expected SOC change following land use change. Adequate correction of Walkley-Black measurements is therefore crucial for the absolute and comparative SOC assessments that are required for Kyoto reporting and must be computed to take into account the regional status of soil and land use. ,Universal' corrections are probably an unrealistic expectation. [source] Corn stover feedstock trials to support predictive modelingGCB BIOENERGY, Issue 5 2010DOUGLAS L. KARLEN Abstract To be sustainable, feedstock harvest must neither degrade soil, water, or air resources nor negatively impact productivity or subsequent crop yields. Simulation modeling will help guide the development of sustainable feedstock production practices, but not without field validation. This paper introduces field research being conducted in six states to support Sun Grant Regional Partnership modeling. Our objectives are to (1) provide a fundamental understanding of limiting factor(s) affecting corn (Zea mays L.) stover harvest, (2) develop tools (e.g., equations, models, etc.) that account for those factors, and (3) create a multivariant analysis framework to combine models for all limiting factors. Sun Grant modelers will use this information to improve regional estimates of feedstock availability. A minimum data set, including soil organic carbon (SOC), total N, pH, bulk density (BD), and soil-test phosphorus (P), and potassium (K) concentrations, is being collected. Stover yield for three treatments (0%, 50%, and 90% removal) and concentrations of N, P, and K in the harvested stover are being quantified to assess the impact of stover harvest on soil resources. Grain yield at a moisture content of 155 g kg,1 averaged 9.71 Mg ha,1, matching the 2008 national average. Stover dry matter harvest rates ranged from 0 to 7 Mg ha,1. Harvesting stover increased N,P,K removal by an average of 42, 5, and 45 kg ha,1 compared with harvesting only grain. Replacing those three nutrients would cost $53.68 ha,1 based on 2009 fertilizer prices. This first-year data and that collected in subsequent years is being used to develop a residue management tool that will ultimately link multiple feedstock supplies together in a landscape vision to help develop a comprehensive carbon management plan, quantify corn stover harvest effects on soil quality, and predict regional variability in feedstock supplies. [source] Carbon sequestration under Miscanthus: a study of 13C distribution in soil aggregatesGCB BIOENERGY, Issue 5 2009MARTA DONDINI Abstract The growing of bioenergy crops has been widely suggested as a key strategy in mitigating anthropogenic CO2 emissions. However, the full mitigation potential of these crops cannot be assessed without taking into account their effect on soil carbon (C) dynamics. Therefore, we analyzed the C dynamics through four soil depths under a 14-year-old Miscanthus plantation, established on former arable land. An adjacent arable field was used as a reference site. Combining soil organic matter (SOM) fractionation with 13C natural abundance analyses, we were able to trace the fate of Miscanthus -derived C in various physically protected soil fractions. Integrated through the whole soil profile, the total amount of soil organic carbon (SOC) was higher under Miscanthus than under arable crop, this difference was largely due to the input of new C. The C stock of the macroaggregates (M) under Miscanthus was significantly higher than those in the arable land. Additionally, the C content of the micro-within macroaggregates (mM) were higher in the Miscanthus soil as compared with the arable soil. Analysis of the intramicroaggregates particulate organic matter (POM) suggested that the increase C storage in mM under Miscanthus was caused by a decrease in disturbance of M. Thus, the difference in C content between the two land use systems is largely caused by soil C storage in physically protected SOM fractions. We conclude that when Miscanthus is planted on former arable land, the resulting increase in soil C storage contributes considerably to its CO2 mitigation potential. [source] Soil organic carbon stock change due to land use activity along the agricultural frontier of the southwestern Amazon, Brazil, between 1970 and 2002GLOBAL CHANGE BIOLOGY, Issue 10 2010STOÉCIO M. F. MAIA Abstract The southwestern portion of the Brazilian Amazon arguably represents the largest agricultural frontier in the world, and within this region the states of Rondônia and Mato Grosso have about 24% and 32% of their respective areas under agricultural management, which is almost half of the total area deforested in the Brazilian Amazon biome. Consequently, it is assumed that deforestation in this region has caused substantial loss of soil organic carbon (SOC). In this study, the changes in SOC stocks due to the land use change and management in the southwestern Amazon were estimated for two time periods from 1970,1985 and 1985,2002. An uncertainty analysis was also conducted using a Monte Carlo approach. The results showed that mineral soils converted to agricultural management lost a total of 5.37 and 3.74 Tg C yr,1 between 1970,1985 and 1985,2002, respectively, along the Brazilian Agricultural Frontier in the states of Mato Grosso and Rondônia. Uncertainties in these estimates were ±37.3% and ±38.6% during the first and second time periods, respectively. The largest sources of uncertainty were associated with reference carbon (C) stocks, expert knowledge surveys about grassland condition, and the management factors for nominal and degraded grasslands. These results showed that land use change and management created a net loss of C from soils, however, the change in SOC stocks decreased substantially from the first to the second time period due to the increase in land under no-tillage. [source] The European carbon balance.GLOBAL CHANGE BIOLOGY, Issue 5 2010Part 3: forests Abstract We present a new synthesis, based on a suite of complementary approaches, of the primary production and carbon sink in forests of the 25 member states of the European Union (EU-25) during 1990,2005. Upscaled terrestrial observations and model-based approaches agree within 25% on the mean net primary production (NPP) of forests, i.e. 520±75 g C m,2 yr,1 over a forest area of 1.32 × 106 km2 to 1.55 × 106 km2 (EU-25). New estimates of the mean long-term carbon forest sink (net biome production, NBP) of EU-25 forests amounts 75±20 g C m,2 yr,1. The ratio of NBP to NPP is 0.15±0.05. Estimates of the fate of the carbon inputs via NPP in wood harvests, forest fires, losses to lakes and rivers and heterotrophic respiration remain uncertain, which explains the considerable uncertainty of NBP. Inventory-based assessments and assumptions suggest that 29±15% of the NBP (i.e., 22 g C m,2 yr,1) is sequestered in the forest soil, but large uncertainty remains concerning the drivers and future of the soil organic carbon. The remaining 71±15% of the NBP (i.e., 53 g C m,2 yr,1) is realized as woody biomass increments. In the EU-25, the relatively large forest NBP is thought to be the result of a sustained difference between NPP, which increased during the past decades, and carbon losses primarily by harvest and heterotrophic respiration, which increased less over the same period. [source] Changes in topsoil carbon stock in the Tibetan grasslands between the 1980s and 2004GLOBAL CHANGE BIOLOGY, Issue 11 2009YUANHE YANG Abstract Climate warming is likely inducing carbon loss from soils of northern ecosystems, but little evidence comes from large-scale observations. Here we used data from a repeated soil survey and remote sensing vegetation index to explore changes in soil organic carbon (SOC) stock on the Tibetan Plateau during the past two decades. Our results showed that SOC stock in the top 30 cm depth in alpine grasslands on the plateau amounted to 4.4 Pg C (1 Pg=1015 g), with an overall average of 3.9 kg C m,2. SOC changes during 1980s,2004 were estimated at ,0.6 g C m,2 yr,1, ranging from ,36.5 to 35.8 g C m,2 yr,1 at 95% confidence, indicating that SOC stock in the Tibetan alpine grasslands remained relatively stable over the sampling periods. Our findings are nonconsistent with previous reports of loss of soil C in grassland ecosystems due to the accelerated decomposition with warming. In the case of the alpine grasslands on the Tibetan Plateau studied here, we speculate that increased rates of decomposition as soils warmed during the last two decades may have been compensated by increased soil C inputs due to increased grass productivity. These results suggest that soil C stock in terrestrial ecosystems may respond differently to climate change depending on ecosystem type, regional climate pattern, and intensity of human disturbance. [source] Soil inorganic carbon storage pattern in ChinaGLOBAL CHANGE BIOLOGY, Issue 10 2008NA MI Abstract Soils with pedogenic carbonate cover about 30% (3.44 × 106 km2) of China, mainly across its arid and semiarid regions in the Northwest. Based on the second national soil survey (1979,1992), total soil inorganic carbon (SIC) storage in China was estimated to be 53.3±6.3 PgC (1 Pg=1015 g) to the depth investigated to 2 m. Soil inorganic carbon storages were 4.6, 10.6, 11.1, and 20.8 Pg for the depth ranges of 0,0.1, 0.1,0.3, 0.3,0.5, and 0.5,1 m, respectively. Stocks for 0.1, 0.3, 0.5, and 1 m of depth accounted for 8.7%, 28.7%, 49.6%, and 88.9% of total SIC, respectively. In contrast with soil organic carbon (SOC) storage, which is highest under 500,800 mm yr,1 of mean precipitation, SIC storage peaks where mean precipitation is <400 mm yr,1. The amount and vertical distribution of SIC was related to climate and land cover type. Content of SIC in each incremental horizon was positively related with mean annual temperature and negatively related with mean annual precipitation, with the magnitude of SIC content across land cover types showing the following order: desert, grassland >shrubland, cropland >marsh, forest, meadow. Densities of SIC increased generally with depth in all ecosystem types with the exception of deserts and marshes where it peaked in intermediate layers (0.1,0.3 m for first and 0.3,0.5 m for latter). Being an abundant component of soil carbon stocks in China, SIC dynamics and the process involved in its accumulation or loss from soils require a better understanding. [source] Storage, patterns and controls of soil organic carbon in the Tibetan grasslandsGLOBAL CHANGE BIOLOGY, Issue 7 2008YUANHE YANG Abstract The soils of the Qinghai-Tibetan Plateau store a large amount of organic carbon, but the magnitude, spatial patterns and environmental controls of the storage are little investigated. In this study, using data of soil organic carbon (SOC) in 405 profiles collected from 135 sites across the plateau and a satellite-based dataset of enhanced vegetation index (EVI) during 2001,2004, we estimated storage and spatial patterns of SOC in the alpine grasslands. We also explored the relationships between SOC density (soil carbon storage per area) and climatic variables and soil texture. Our results indicated that SOC storage in the top 1 m in the alpine grasslands was estimated at 7.4 Pg C (1 Pg=1015 g), with an average density of 6.5 kg m,2. The density of SOC decreased from the southeastern to the northwestern areas, corresponding to the precipitation gradient. The SOC density increased significantly with soil moisture, clay and silt content, but weakly with mean annual temperature. These variables could together explain about 72% of total variation in SOC density, of which 54% was attributed to soil moisture, suggesting a key role of soil moisture in shaping spatial patterns of SOC density in the alpine grasslands. [source] C4-derived soil organic carbon decomposes faster than its C3 counterpart in mixed C3/C4 soilsGLOBAL CHANGE BIOLOGY, Issue 10 2007JONATHAN G. WYNN Abstract The large difference in the degree of discrimination of stable carbon isotopes between C3 and C4 plants is widely exploited in global change and carbon cycle research, often with the assumption that carbon retains the carbon isotopic signature of its photosynthetic pathway during later stages of decomposition in soil and sediments. We applied long-term incubation experiments and natural 13C-labelling of C3 and C4-derived soil organic carbon (SOC) collected from across major environmental gradients in Australia to elucidate a significant difference in the rate of decomposition of C3- and C4-derived SOC. We find that the active pool of SOC (ASOC) derived from C4 plants decomposes at over twice the rate of the total pool of ASOC. As a result, the proportion of C4 photosynthesis represented in the heterotrophic CO2 flux from soil must be over twice the proportional representation of C4-derived biomass in SOC. This observation has significant implications for much carbon cycle research that exploits the carbon isotopic difference in these two photosynthetic pathways. [source] Soil greenhouse gas fluxes and global warming potential in four high-yielding maize systemsGLOBAL CHANGE BIOLOGY, Issue 9 2007M. A. A. ADVIENTO-BORBE Abstract Crop intensification is often thought to increase greenhouse gas (GHG) emissions, but studies in which crop management is optimized to exploit crop yield potential are rare. We conducted a field study in eastern Nebraska, USA to quantify GHG emissions, changes in soil organic carbon (SOC) and the net global warming potential (GWP) in four irrigated systems: continuous maize with recommended best management practices (CC-rec) or intensive management (CC-int) and maize,soybean rotation with recommended (CS-rec) or intensive management (CS-int). Grain yields of maize and soybean were generally within 80,100% of the estimated site yield potential. Large soil surface carbon dioxide (CO2) fluxes were mostly associated with rapid crop growth, high temperature and high soil water content. Within each crop rotation, soil CO2 efflux under intensive management was not consistently higher than with recommended management. Owing to differences in residue inputs, SOC increased in the two continuous maize systems, but decreased in CS-rec or remained unchanged in CS-int. N2O emission peaks were mainly associated with high temperature and high soil water content resulting from rainfall or irrigation events, but less clearly related to soil NO3 -N levels. N2O fluxes in intensively managed systems were only occasionally greater than those measured in the CC-rec and CS-rec systems. Fertilizer-induced N2O emissions ranged from 1.9% to 3.5% in 2003, from 0.8% to 1.5% in 2004 and from 0.4% to 0.5% in 2005, with no consistent differences among the four systems. All four cropping systems where net sources of GHG. However, due to increased soil C sequestration continuous maize systems had lower GWP than maize,soybean systems and intensive management did not cause a significant increase in GWP. Converting maize grain to ethanol in the two continuous maize systems resulted in a net reduction in life cycle GHG emissions of maize ethanol relative to petrol-based gasoline by 33,38%. Our study provided evidence that net GHG emissions from agricultural systems can be kept low when management is optimized toward better exploitation of the yield potential. Major components for this included (i) choosing the right combination of adopted varieties, planting date and plant population to maximize crop biomass productivity, (ii) tactical water and nitrogen (N) management decisions that contributed to high N use efficiency and avoided extreme N2O emissions, and (iii) a deep tillage and residue management approach that favored the build-up of soil organic matter from large amounts of crop residues returned. [source] Soil organic carbon stocks in China and changes from 1980s to 2000sGLOBAL CHANGE BIOLOGY, Issue 9 2007ZUBIN XIE Abstract The estimation of the size and changes of soil organic carbon (SOC) stocks is of great importance for decision makers to adopt proper measures to protect soils and to develop strategies for mitigation of greenhouse gases. In this paper, soil data from the Second State Soil Survey of China (SSSSC) conducted in the early 1980s and data published in the last 5 years were used to estimate the size of SOC stocks over the whole profile and their changes in China in last 20 years. Soils were identified as paddy, upland, forest, grassland or waste-land soils and an improved soil bulk density estimation method was used to estimate missing bulk density data. In the early 1980s, total SOC stocks were estimated at 89.61 Pg (1 Pg=103 Tg=1015 g) in China's 870.94 Mha terrestrial areas covered by 2473 soil series. In the paddy, upland, forest and grassland soils the respective total SOC stocks were 2.91 Pg on 29.87 Mha, 10.07 Pg on 125.89 Mha, 34.23 Pg on 249.32 Mha and 37.71 Pg on 278.51 Mha, respectively. The SOC density of the surface layer ranged from 3.5 Mg ha,1 in Gray Desery grassland soils to 252.6 Mg ha,1 in Mountain Meadow forest soils. The average area-weighted total SOC density in paddy soils (97.6 Mg ha,1) was higher than that in upland soils (80 Mg ha,1). Soils under forest (137.3 Mg ha,1) had a similar average area-weighted total SOC density as those under grassland (135.4 Mg ha,1). The annual estimated SOC accumulation rates in farmland and forest soils in the last 20 years were 23.61 and 11.72 Tg, respectively, leading to increases of 0.472 and 0.234 Pg SOC in farmland and forest areas, respectively. In contrast, SOC under grassland declined by 3.56 Pg due to the grassland degradation over this period. The resulting estimated net SOC loss in China's soils over the last 20 years was 2.86 Pg. The documented SOC accumulation in farmland and forest soils could thus not compensate for the loss of SOC in grassland soils in the last 20 years. There were, however, large regional differences: Soils in China's South and Eastern parts acted mainly as C sinks, increasing their average topsoil SOC by 132 and 145 Tg, respectively. In contrast, in the Northwest, Northeast, Inner Mongolia and Tibet significant losses of 1.38, 0.21, 0.49 and 1.01 Pg of SOC, respectively, were estimated over the last 20 years. These results highlight the importance to take measures to protect grassland and to improve management practices to increase C sequestration in farmland and forest soils. [source] Development of a stable isotope index to assess decadal-scale vegetation change and application to woodlands of the Burdekin catchment, AustraliaGLOBAL CHANGE BIOLOGY, Issue 7 2007EVELYN KRULL Abstract Forty-four study sites were established in remnant woodland in the Burdekin River catchment in tropical north-east Queensland, Australia, to assess recent (decadal) vegetation change. The aim of this study was further to evaluate whether wide-scale vegetation ,thickening' (proliferation of woody plants in formerly more open woodlands) had occurred during the last century, coinciding with significant changes in land management. Soil samples from several depth intervals were size separated into different soil organic carbon (SOC) fractions, which differed from one another by chemical composition and turnover times. Tropical (C4) grasses dominate in the Burdekin catchment, and thus ,13C analyses of SOC fractions with different turnover times can be used to assess whether the relative proportion of trees (C3) and grasses (C4) had changed over time. However, a method was required to permit standardized assessment of the ,13C data for the individual sites within the 13 Mha catchment, which varied in soil and vegetation characteristics. Thus, an index was developed using data from three detailed study sites and global literature to standardize individual isotopic data from different soil depths and SOC fractions to reflect only the changed proportion of trees (C3) to grasses (C4) over decadal timescales. When applied to the 44 individual sites distributed throughout the Burdekin catchment, 64% of the sites were shown to have experienced decadal vegetation thickening, while 29% had remained stable and the remaining 7% had thinned. Thus, the development of this index enabled regional scale assessment and comparison of decadal vegetation patterns without having to rely on prior knowledge of vegetation changes or aerial photography. [source] Effects of nutrient additions on ecosystem carbon cycle in a Puerto Rican tropical wet forestGLOBAL CHANGE BIOLOGY, Issue 2 2006YIQING LI Abstract Wet tropical forests play a critical role in global ecosystem carbon (C) cycle, but C allocation and the response of different C pools to nutrient addition in these forests remain poorly understood. We measured soil organic carbon (SOC), litterfall, root biomass, microbial biomass and soil physical and chemical properties in a wet tropical forest from May 1996 to July 1997 following a 7-year continuous fertilization. We found that although there was no significant difference in total SOC in the top 0,10 cm of the soils between the fertilization plots (5.42±0.18 kg m,2) and the control plots (5.27±0.22 kg m,2), the proportion of the heavy-fraction organic C in the total SOC was significantly higher in the fertilized plots (59%) than in the control plots (46%) (P<0.05). The annual decomposition rate of fertilized leaf litter was 13% higher than that of the control leaf litter. We also found that fertilization significantly increased microbial biomass (fungi+bacteria) with 952±48 mg kg,1soil in the fertilized plots and 755±37 mg kg,1soil in the control plots. Our results suggest that fertilization in tropical forests may enhance long-term C sequestration in the soils of tropical wet forests. [source] Global climate change and soil carbon stocks; predictions from two contrasting models for the turnover of organic carbon in soilGLOBAL CHANGE BIOLOGY, Issue 1 2005Chris Jones Abstract Enhanced release of CO2 to the atmosphere from soil organic carbon as a result of increased temperatures may lead to a positive feedback between climate change and the carbon cycle, resulting in much higher CO2 levels and accelerated global warming. However, the magnitude of this effect is uncertain and critically dependent on how the decomposition of soil organic C (heterotrophic respiration) responds to changes in climate. Previous studies with the Hadley Centre's coupled climate,carbon cycle general circulation model (GCM) (HadCM3LC) used a simple, single-pool soil carbon model to simulate the response. Here we present results from numerical simulations that use the more sophisticated ,RothC' multipool soil carbon model, driven with the same climate data. The results show strong similarities in the behaviour of the two models, although RothC tends to simulate slightly smaller changes in global soil carbon stocks for the same forcing. RothC simulates global soil carbon stocks decreasing by 54 Gt C by 2100 in a climate change simulation compared with an 80 Gt C decrease in HadCM3LC. The multipool carbon dynamics of RothC cause it to exhibit a slower magnitude of transient response to both increased organic carbon inputs and changes in climate. We conclude that the projection of a positive feedback between climate and carbon cycle is robust, but the magnitude of the feedback is dependent on the structure of the soil carbon model. [source] Carbon emission and sequestration by agricultural land use: a model study for EuropeGLOBAL CHANGE BIOLOGY, Issue 6 2002L. M. Vleeshouwers Abstract A model was developed to calculate carbon fluxes from agricultural soils. The model includes the effects of crop (species, yield and rotation), climate (temperature, rainfall and evapotranspiration) and soil (carbon content and water retention capacity) on the carbon budget of agricultural land. The changes in quality of crop residues and organic material as a result of changes in CO2 concentration and changed management were not considered in this model. The model was parameterized for several arable crops and grassland. Data from agricultural, meteorological, soil, and land use databases were input to the model, and the model was used to evaluate the effects of different carbon dioxide mitigation measures on soil organic carbon in agricultural areas in Europe. Average carbon fluxes under the business as usual scenario in the 2008,2012 commitment period were estimated at 0.52 tC ha,1 y,1 in grassland and ,0.84 tC ha,1 y,1 in arable land. Conversion of arable land to grassland yielded a flux of 1.44 tC ha,1 y,1. Farm management related activities aiming at carbon sequestration ranged from 0.15 tC ha,1 y,1 for the incorporating of straw to 1.50 tC ha,1 y,1 for the application of farmyard manure. Reduced tillage yields a positive flux of 0.25 tC ha,1 y,1. The indirect effect associated with climate was an order of magnitude lower. A temperature rise of 1 °C resulted in a ,0.05 tC ha,1 y,1 change whereas the rising CO2 concentrations gave a 0.01 tC ha,1 y,1 change. Estimates are rendered on a 0.5 × 0.5° grid for the commitment period 2008,2012. The study reveals considerable regional differences in the effectiveness of carbon dioxide abatement measures, resulting from the interaction between crop, soil and climate. Besides, there are substantial differences between the spatial patterns of carbon fluxes that result from different measures. [source] Determination of the soil organic carbon, nitrogen, available phosphorus and the combined aboveground plant materials in the semi-arid Mbulu District, TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2009Mligo Cosmas Abstract Soil of the semi-arid Mbulu District is part of the tropical soils, covered with sparse trees, shrubs or grasses in which domestic grazing animals have prevented the wide spread of vegetation cover. The study aimed at determining soil organic carbon (OC), total nitrogen (N), available phosphorus (P) and the combined aboveground plant materials. Six study sites were established in which soil samples were collected at the depths of 0,5, 6,10 and 11,20 cm. Soil samples were analysed for OC, N and P as well as the levels of N and P in the combined aboveground materials of Panicum coloratum and Hyparrhenia filipendula. The percentage concentrations of OC, N and P were high in the top soil than in the deeper soil horizons. However, analysis of variance showed significant differences of OC in some sites whereas no difference for N and P between soil depth classes. OC was highly related with N and P along soil depth classes. It was concluded that the availability of N and P was because of the decomposition of organic matter in the soil. Soil N and P were highly related with the same in the combined aboveground plant materials. It was concluded that the increased concentration of N and P in the soil resulted into availability of the same in P. coloratum and H. filipendula. There was a very high variation in N and P among sites with different levels of intensity of grazing. It was concluded that grazing animals contributes to the redistribution of soil elements in the rangelands because they graze upon plant parts but the excreta are dropped away from the grazed spot. Résumé Le sol du district semi-aride de Mbulu fait partie de ces sols tropicaux couverts d'arbres, de buissons et d'herbes rares où le pâturage des animaux domestiques a empêché une large dispersion du couvert végétal. L'étude visait à déterminer le carbone organique (CO) du sol, l'azote (N) total, le phosphore (P) disponible et l'ensemble combiné de la matière végétale aérienne. Six sites d'étude furent établis, où l'on a récolté des échantillons de sol à des profondeurs de 0 à 5 cm, 6 à 10 cm, et 11 à 20 cm. Les échantillons de sols ont été analysés pour le CO, le N et le P ainsi que les niveaux de N et de P dans la matière végétale aérienne composée de Panicum coloratum et Hyparrhenia filipendula. Le pourcentage des concentrations de CO, N et P était plus élevé dans la couche supérieure du sol que dans les couches plus profondes. Cependant, une analyse de variance a révélé des différences significatives du CO dans certains sites alors qu'il n'y avait pas de différences pour N ni P aux différentes profondeurs de sol. Le CO était fortement liéà N et à P selon les classes de profondeur. On en a conclu que la disponibilité de N et de P était due à la décomposition de la matière organique dans le sol. Le N et le P du sol étaient fortement liés aux mêmes éléments présents dans la matière végétale aérienne combinée. On a conclu que la concentration accrue de N et de P dans le sol résultait de la concentration de ces mêmes éléments dans P. coloratum et H. filipendula. Il y a avait une très grande variation de N et de P entre des sites où l'intensité de pâturage était différente. On a conclu que les animaux qui pâturent contribuent à la redistribution des éléments du sol dans tous les endroits fréquentés étant donné qu'ils mangent des plantes à certains endroits mais que leurs excréments peuvent être rejetés ailleurs que les zones pâturées. [source] Carbon Sequestration in Two Alpine Soils on the Tibetan PlateauJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2009Yu-Qiang Tian Abstract Soil carbon sequestration was estimated in a conifer forest and an alpine meadow on the Tibetan Plateau using a carbon-14 radioactive label provided by thermonuclear weapon tests (known as bomb- 14C). Soil organic matter was physically separated into light and heavy fractions. The concentration spike of bomb- 14C occurred at a soil depth of 4 cm in both the forest soil and the alpine meadow soil. Based on the depth of the bomb- 14C spike, the carbon sequestration rate was determined to be 38.5 g C/m2 per year for the forest soil and 27.1 g C/m2 per year for the alpine meadow soil. Considering that more than 60% of soil organic carbon (SOC) is stored in the heavy fraction and the large area of alpine forests and meadows on the Tibetan Plateau, these alpine ecosystems might partially contribute to "the missing carbon sink". [source] Labile soil organic carbon, soil fertility, and crop productivity as influenced by manure and mineral fertilizers in the tropicsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2010Siba Prasad Datta Abstract In recent years, organic agriculture has been receiving greater attention because of the various problems like deterioration in soil health and environmental quality under conventional chemical-intensive agriculture. However, little information is available on the comparative study related to the impact of use of mineral fertilizers and organic manures on the soil quality and productivity. A long-term field experiment was initiated in 2001 to monitor some of the important soil-quality parameters and productivity under soybean,wheat crop rotation. The treatments consisted of 0, 30, and 45,kg N ha,1 for soybean and of 0, 120, and 180,kg N ha,1 for wheat. The entire amount of N was supplied to both the crops through urea and farmyard manure (FYM) alone or in combination at 1:1 ratio. Results indicated that Walkley-and-Black C (WBC; chromic acid,oxidizable) exhibited a marginal increase under only organic treatments as compared to control treatment (without fertilizers and manure) after completion of five cropping cycles. In case of labile-C (KMnO4 -oxidizable) content in soil, relatively larger positive changes were recorded under organic, mixed inputs (integrated) and mineral fertilizers as compared to WBC. Maximum improvement in the values of C-management index (CMI), a measure of soil quality was recorded under organic (348,362), followed by mixed inputs (268,322) and mineral fertilizers (198,199) as compared to the control treatment after completion of five cropping cycles. Similarly there was a substantial increase in KCl-extractable N; in Olsen-P; as well as in DTPA-extractable Zn, Fe, and Mn under organic treatments. Although labile soil C positively contributed to the available N, P, K, Zn, Fe, and Mn contents in soil, it did not show any relationship with the grain yield of wheat. After completion of the sixth cropping cycle, organic treatments produced 23% and 39% lower grain yield of wheat as compared to that under urea-treated plots. Relatively higher amount of mineral N in soil at critical growth stages and elevated N content in plant under mineral-fertilizer treatments compared to FYM treatments were responsible for higher yield of wheat under mineral fertilizers. [source] Is thermal oxidation at different temperatures suitable to isolate soil organic carbon fractions with different turnover?JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2010Mirjam Helfrich Abstract Findings of previous studies suggest that there are relations between thermal stability of soil organic matter (SOM), organo-mineral associations, and stability of SOM against microbial decay. We aimed to test whether thermal oxidation at various temperatures (200°C, 225°C, 275°C, 300°C, 400°C, or 500°C) is capable of isolating SOM fractions with increasing stability against microbial degradation. The investigation was carried out on soils (Phaeozem and Luvisol) under different land-use regimes (field, grassland, forest). The stability of the obtained soil organic carbon (SOC) fractions was determined using the natural- 13C approach for continuously maize-cropped soils and radiocarbon dating. In the Luvisol, thermal oxidation with increasing temperatures did not yield residual SOC fractions of increasing microbial stability. Even the SOC fraction resistant to thermal oxidation at 300°C contained considerable amounts of young, maize-derived C. In the Phaeozem, the mean 14C age increased considerably (from 3473 y BP in the mineral-associated SOC fraction to 9116 y BP in the residual SOC fraction after thermal oxidation at 300°C). An increasing proportion of fossil C (calculated based on 14C data) in residual SOC fractions after thermal oxidation with increasing temperatures indicated that this was mainly due to the relative accumulation of thermally stable fossil C. We conclude that thermal oxidation with increasing temperature was not generally suitable to isolate mineral-associated SOC fractions of increasing microbial stability. [source] Effect of water and nitrogen management on aggregate size and carbon enrichment of soil in rice-wheat cropping system,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2004Rojalin Tripathy Abstract A study was carried out on a silty clay loam soil (Typic Haplustept) to evaluate the effect of farmyard manure (FYM) vis-à-vis fertilizer and irrigation application on the soil organic C content and soil structure. The fertilizer treatments comprised of eight different combinations of N and FYM and three water regimes. The results indicated that the application of FYM and increasing N rate increased soil organic carbon (SOC) content. Addition of FYM also increased the percentage of large sized water stable aggregates (> 5,mm) and reduced the percentage of smaller size aggregates. This was reflected in an increase in the mean weight diameter (MWD) and improved soil structure. The organic carbon content in macroaggregates (> 1,mm) was greater compared to microaggregates, and it declined with decrease in size of microaggregates. This difference in organic C content between macro- and microaggregates was more with higher N dose and FYM treated plots. The effect of residual FYM on MWD and organic C content of the soil after wheat harvest was not significant. The effect was less in deeper layers compared to surface layers of the soil. MWD was significantly correlated with the SOC content for the top two layers. [source] Change in soil organic carbon following the ,Grain-for-Green' programme in ChinaLAND DEGRADATION AND DEVELOPMENT, Issue 1 2010K. Zhang Abstract Agricultural soils are considered to have great potential for carbon sequestration through land-use change. In this paper, we compiled data from the literatures and studied the change in soil organic carbon (SOC) following the ,Grain-for-Green' Programme (GGP, i.e., conversion from farmland to plantation, secondary forests and grasslands) in China. The results showed that SOC stocks accumulated at an average rate of 36·67,g,m,2,y,1 in the top 20,cm with large variation. The current SOC storage could be estimated using the initial SOC stock and year since land use transformation (Adjusted R2,=,0·805, p,=,0·000). After land use change, SOC stocks decreased during the initial 4,5 years, followed by an increase after above ground vegetation restoration. Annual average precipitation and initial SOC stocks had a significant effect (p,<,0·05) on the rate of change in SOC, while no significant effects were observed between plantation and natural regeneration (p,>,0·05). The ongoing ,Grain-for-Green' project might make significant contribution to China's carbon sequestration. Copyright © 2009 John Wiley & Sons, Ltd. [source] Soil restorative effects of mulching on aggregation and carbon sequestration in a Miamian soil in central OhioLAND DEGRADATION AND DEVELOPMENT, Issue 5 2003G. S. Saroa Abstract Soils play a key role in the global carbon cycle, and can be a source or a sink of atmospheric carbon (C). Thus, the effect of land use and management on soil C dynamics needs to be quantified. This study was conducted to assess: (1) the role of aggregation in enhancing soil organic carbon (SOC) and total soil nitrogen (TSN) concentrations for different mulch rates, (2) the association of SOC and TSN with different particle size fractions, and (3) the temporal changes in the SOC concentration within aggregate and particle size fractions with duration of mulching. Two experiments were initiated, one each in 1989 and 1996, on a Crosby silt loam (Aeric Ochraqualf or Stagnic Luvisol) in central Ohio. Mulch treatments were 0, 8, and 16,Mg,ha,1,yr,1 without crop cultivation. Soil samples from 0,5,cm and 5,10,cm depths were obtained in November 2000; 4 and 11 years after initiating the experiments. Mulch rate significantly increased SOC and TSN concentrations in the 0,5,cm soil layer only. The variation in the SOC concentration attributed to the mulch rate was 41 per,cent after 4 years of mulching and 52 per,cent after 11 years of mulching. There were also differences in SOC and TSN concentrations among large aggregate size fractions, up to 2,mm size after 4 years and up to 0,5,mm after 11 years of mulching. There were also differences in SOC and TSN concentrations among particle size fractions. Variation in the SOC concentration in relation to particle size was attributed to clay by 45,51 per,cent, silt by 34,36 per,cent, and to sand fraction by 15,19 per,cent. Bulk of the TSN (62,67 per,cent) was associated with clay fraction and the rest was equally distributed between silt and sand fractions. The enrichment of SOC and TSN concentrations in the clay fraction increased with depth. The C:N ratio was not affected by the mulch rate, but differed significantly among particle size fractions; being in the order of sand >silt >clay. Copyright © 2003 John Wiley & Sons, Ltd. [source] Soil carbon sequestration in China through agricultural intensification, and restoration of degraded and desertified ecosystems,LAND DEGRADATION AND DEVELOPMENT, Issue 6 2002R. Lal Abstract The industrial emission of carbon (C) in China in 2000 was about 1,Pg,yr,1, which may surpass that of the United States (1,84,Pg,C) by 2020. China's large land area, similar in size to that of the United States, comprises 124,Mha of cropland, 400,Mha of grazing land and 134,Mha of forestland. Terrestrial C pool of China comprises about 35,60,Pg in the forest and 120,186,Pg in soils. Soil degradation is a major issue affecting 145,Mha by different degradative processes, of which 126,Mha are prone to accelerated soil erosion. Total annual loss by erosion is estimated at 5,5,Pg of soil and 15,9,Tg of soil organic carbon (SOC). Erosion-induced emission of C into the atmosphere may be 32,64,Tg,yr,1. The SOC pool progressively declined from the 1930s to 1980s in soils of northern China and slightly increased in those of southern China because of change in land use. Management practices that lead to depletion of the SOC stock are cultivation of upland soils, negative nutrient balance in cropland, residue removal, and soil degradation by accelerated soil erosion and salinization and the like. Agricultural practices that enhance the SOC stock include conversion of upland to rice paddies, integrated nutrient management based on liberal use of biosolids and compost, crop rotations that return large quantities of biomass, and conservation-effective systems. Adoption of recommended management practices can increase SOC concentration in puddled soil, red soil, loess soils, and salt-affected soils. In addition, soil restoration has a potential to sequester SOC. Total potential of soil C sequestration in China is 105,198,Tg,C,yr,1 of SOC and 7,138,Tg,C,yr,1 for soil inorganic carbon (SIC). The accumulative potential of soil C sequestration of 11,Pg at an average rate of 224,Tg,yr,1 may be realized by 2050. Soil C sequestration potential can offset about 20 per cent of the annual industrial emissions in China. Copyright © 2002 John Wiley & Sons, Ltd. [source] Soil organic carbon pools in a periglacial landscape: a case study from the central Canadian ArcticPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2010Gustaf Hugelius Abstract We investigated total storage and landscape partitioning of soil organic carbon (SOC) in continuous permafrost terrain, central Canadian Arctic. The study is based on soil chemical analyses of pedons sampled to 1-m depth at 35 individual sites along three transects. Radiocarbon dating of cryoturbated soil pockets, basal peat and fossil wood shows that cryoturbation processes have been occurring since the Middle Holocene and that peat deposits started to accumulate in a forest-tundra environment where spruce was present (,6000 cal yrs BP). Detailed partitioning of SOC into surface organic horizons, cryoturbated soil pockets and non-cryoturbated mineral soil horizons is calculated (with storage in active layer and permafrost calculated separately) and explored using principal component analysis. The detailed partitioning and mean storage of SOC in the landscape are estimated from transect vegetation inventories and a land cover classification based on a Landsat satellite image. Mean SOC storage in the 0,100-cm depth interval is 33.8,kg C,m,2, of which 11.8,kg C m,2 is in permafrost. Fifty-six per cent of the total SOC mass is stored in peatlands (mainly bogs), but cryoturbated soil pockets in Turbic Cryosols also contribute significantly (17%). Elemental C/N ratios indicate that this cryoturbated soil organic matter (SOM) decomposes more slowly than SOM in surface O-horizons. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||||||||