Offsetting global CO2 emissions by restoration of degraded soils and intensification of world agriculture and forestry

Increase in atmospheric concentration of CO₂ from 285 parts per million by volume (ppmv) in 1850 to 370 ppm in 2000 is attributed to emissions of 270 ± 30 Pg carbon (C) from fossil fuel combustion and 136 ± 55 Pg C by land‐use change. Present levels of anthropogenic emissions involve 6·3 Pg C by fossil fuel emissions and 1·8 Pg C by land‐use change. Out of the historic loss of terrestrial C pool of 136 ± 55 Pg, 78 ± 12 Pg is due to depletion of soil organic carbon (SOC) pool comprising 26 ± 9 Pg due to accelerated soil erosion. A large proportion of the historic SOC lost can be resequestered by enhancing the SOC pool through converting to an appropriate land use and adopting recommended management practices (RMPs). The strategy is to return biomass to the soil in excess of the mineralization capacity through restoration of degraded/desertified soils and intensification of agricultural and forestry lands. Technological options for agricultural intensification include conservation tillage and residue mulching, integrated nutrient management, crop rotations involving cover crops, practices which enhance the efficiency of water, plant nutrients and energy use, improved pasture and tree species, controlled grazing, and judicious use of inptus. The potential of SOC sequestration is estimated at 1–2 Pg C yr⁻¹ for the world, 0·3–0·6 Pg C yr⁻¹ for Asia, 0·2–0·5 Pg C yr⁻¹ for Africa and 0·1–0·3 Pg C yr⁻¹ for North and Central America and South America, 0·1–0·3 Pg C yr⁻¹ for Europe and 0·1–0·2 Pg C yr⁻¹ for Oceania. Soil C sequestration is a win–win strategy; it enhances productivity, improves environment moderation capacity, and mitigates global warming. Copyright © 2003 John Wiley & Sons, Ltd.     

Impact of Land Use and Land Cover Changes on Organic Carbon Stocks in Mediterranean Soils (1956–2007)

During the last few decades, land use changes have largely affected the global warming process through emissions of CO₂. However, C sequestration in terrestrial ecosystems could contribute to the decrease of atmospheric CO₂ rates. Although Mediterranean areas show a high potential for C sequestration, only a few studies have been carried out in these systems. In this study, we propose a methodology to assess the impact of land use and land cover change dynamics on soil organic C stocks at different depths. Soil C sequestration rates are provided for different land cover changes and soil types in Andalusia (southern Spain). Our research is based on the analysis of detailed soil databases containing data from 1357 soil profiles, the Soil Map of Andalusia and the Land Use and Land Cover Map of Andalusia. Land use and land cover changes between 1956 and 2007 implied soil organic C losses in all soil groups, resulting in a total loss of 16·8 Tg (approximately 0·33 Tg y⁻¹). Afforestation increased soil organic C mostly in the topsoil, and forest contributed to sequestration of 8·62 Mg ha⁻¹ of soil organic C (25·4 per cent). Deforestation processes implied important C losses, particularly in Cambisols, Luvisols and Vertisols. The information generated in this study will be a useful basis for designing management strategies for stabilizing the increasing atmospheric CO₂ concentrations by preservation of C stocks and C sequestration. Copyright © 2012 John Wiley & Sons, Ltd.     

Regional estimates of carbon sequestration potential: linking the Rothamsted Carbon Model to GIS databases

 Soil organic matter (SOM) represents a major pool of carbon within the biosphere. It is estimated at about 1400 Pg globally, which is roughly twice that in atmospheric CO₂. The soil can act as both a source and a sink for carbon and nutrients. Changes in agricultural land use and climate can lead to changes in the amount of carbon held in soils, thus, affecting the fluxes of CO₂ to and from the atmosphere. Some agricultural management practices will lead to a net sequestration of carbon in the soil. Regional estimates of the carbon sequestration potential of these practices are crucial if policy makers are to plan future land uses to reduce national CO₂ emissions. In Europe, carbon sequestration potential has previously been estimated using data from the Global Change and Terrestrial Ecosystems Soil Organic Matter Network (GCTE SOMNET). Linear relationships between management practices and yearly changes in soil organic carbon were developed and used to estimate changes in the total carbon stock of European soils. To refine these semi-quantitative estimates, the local soil type, meteorological conditions and land use must also be taken into account. To this end, we have modified the Rothamsted Carbon Model, so that it can be used in a predictive manner, with SOMNET data. The data is then adjusted for local conditions using Geographical Information Systems databases. In this paper, we describe how these developments can be used to estimate carbon sequestration at the regional level using a dynamic simulation model linked to spatially explicit data. Some calculations of the potential effects of afforestation on soil carbon stocks in Central Hungary provide a simple example of the system in use. Received: 1 December 1997     

Total carbon and nitrogen in the soils of the world

The soil is important in sequestering atmospheric CO₂ and in emitting trace gases (e.g. CO₂, CH₄ and N₂O) that are radiatively active and enhance the ‘greenhouse’ effect. Land use changes and predicted global warming, through their effects on net primary productivity, the plant community and soil conditions, may have important effects on the size of the organic matter pool in the soil and directly affect the atmospheric concentration of these trace gases. A discrepancy of approximately 350 × 10¹⁵ g (or Pg) of C in two recent estimates of soil carbon reserves worldwide is evaluated using the geo-referenced database developed for the World Inventory of Soil Emission Potentials (WISE) project. This database holds 4353 soil profiles distributed globally which are considered to represent the soil units shown on a ¹/₂° latitude by ¹/₂° longitude version of the corrected and digitized 1:5 M FAO–UNESCO Soil Map of the World. Total soil carbon pools for the entire land area of the world, excluding carbon held in the litter layer and charcoal, amounts to 2157–2293 Pg of C in the upper 100 cm. Soil organic carbon is estimated to be 684–724 Pg of C in the upper 30 cm, 1462–1548 Pg of C in the upper 100 cm, and 2376–2456 Pg of C in the upper 200 cm. Although deforestation, changes in land use and predicted climate change can alter the amount of organic carbon held in the superficial soil layers rapidly, this is less so for the soil carbonate carbon. An estimated 695–748 Pg of carbonate-C is held in the upper 100 cm of the world's soils. Mean C: N ratios of soil organic matter range from 9.9 for arid Yermosols to 25.8 for Histosols. Global amounts of soil nitrogen are estimated to be 133–140 Pg of N for the upper 100 cm. Possible changes in soil organic carbon and nitrogen dynamics caused by increased concentrations of atmospheric CO₂ and the predicted associated rise in temperature are discussed.     

Carbon and nitrogen stocks in the soils of Central and Eastern Europe

Abstract. Soil organic carbon and total nitrogen stocks are presented for Central and Eastern Europe. The study uses the soil geographic and attribute data held in a 1:2 500 000 scale Soil and Terrain (SOTER) database, covering Belarus, Bulgaria, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Moldova, Poland, Romania, the Russian Federation (west of the Urals), Slovakia, and Ukraine. Means and coefficients of variation for soil organic carbon and total nitrogen are presented for each major FAO soil grouping. The mean content of organic carbon, to a depth of 1 m, ranges from 3.9 kg C m^–2 for coarse textured Arenosols to 72.9 kg C m^–2 for poorly drained Histosols. Mean carbon content for the mineral soils, excluding Arenosols, is 15.8 kg C m^–2. The top 1 m of soil holds 110 Pg C (Pg=10¹⁵ g), which corresponds to about 7% of the global stock of soil organic carbon. About 44% of this carbon pool is held in the top 0.3 m of the soil, the layer that is most prone to be changed by changes in soil use and management. About 166 million ha in Central and Eastern Europe have been degraded by compaction, erosion of topsoil, fertility decline and crusting. The achievable level of carbon sequestration for these soils, upon adoption of 'best' management practices or restorative measures, is estimated.     

施加脱硫石膏对盐碱土固碳的影响

增加陆地生态系统碳固定能力能有效缓解大气CO 2升高引起的温室效应。以干旱区典型盐土和碱土为研究对象,通过室内土柱模拟试验,研究不同施用量脱硫石膏(0,10,20,21.78,30,40 t/hm²)对盐土和碱土生态系统碳储量(包括土壤碳储量和生物量碳储量)的影响。结果表明:与对照相比,施加脱硫石膏盐土总碳储量(C)降低8.78%~15.72%,其中以土壤有机碳储量降低为主;碱土总碳储量(C)增加5.00%~23.94%,其中以土壤无机碳增加为主。脱硫石膏施加后盐土总生物量碳储量(C)较对照平均降低23.14%,碱土总生物量碳储量(C)较对照平均增加30.44%。施用脱硫石膏碱土生态系统碳储量(C)较对照增加0.09~0.42 kg/m²,而盐土生态系统碳储量(C)较对照降低0.33~0.56 kg/m²。相关分析结果表明,脱硫石膏施加量、土壤电导率以及由脱硫石膏施加引起的土壤含水量变化是影响盐碱土生态系统固碳的主要因素。总体上,施加脱硫石膏后,盐土生态系统碳储量显著降低,碱土生态系统碳储量显著增加,其中施加量30,40 t/hm²处理对盐碱土生态系统碳储量影响效果最大。研究结果可为增加干旱区生态系统碳固定提供科学参考。     

Soil carbon sequestration in China through agricultural intensification,and restoration of degraded and desertified ecosystems

The industrial emission of carbon (C) in China in 2000 was about 1 Pg yr⁻¹, which may surpass that of the United States (1ċ84 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 5ċ5 Pg of soil and 15ċ9 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.     

不同土地利用和施肥方式下黑土碳平衡的研究

本研究进行了东北黑土不同土地利用(草地GL、裸地BL)与农田施肥管理方式(无肥NF、化肥NPK及化肥+有机肥处理NPKOM)下草本植物与作物净初级生产力(NPP)和净生态系统生产力(NEP)以及土壤碳排放的估算,目的是揭示自然与农田生态系统及经过土壤大气界面的碳收支平衡。土壤生长季碳排放总量(Rgs)、全年碳排放总量(Rann)以及全年微生物异养呼吸总量(Rm)以如下顺序递减:NPKOMGLNPKNFBL,5个处理之间存在显著差异(P0.05),但是草地与农田化肥+有机肥处理之间差异不显著(P0.05)。净初级生产力表现:GLNPKOMNPKNFBL,5个处理之间存在显著差异(P0.05)。草地总生物量及固碳量显著高于农田各处理(P0.05),草地NPP总量与农田各处理相比增加32%~96%。化肥+有机肥处理和化肥处理NPP总量比无肥处理高46%和49%。草地与农田的NEP均为正值,表明草地与农田在生态系统尺度上均是大气CO2的"汇"。对大气土壤界面碳平衡的分析表明,当前管理方式下,草地土壤是大气碳库的净汇,而裸地和农田土壤是净源。农田不同施肥处理土壤有机碳含量呈下降趋势,但增加有机肥的投入可增强土壤的固碳容量,达到新的碳平衡。     

A mass balance approach to assess carbon dioxide evolution during erosional events

The accelerated greenhouse effect and the degradation of land resources by water and wind erosion are two major, yet interrelated global environmental challenges. Accelerated decomposition of soil organic carbon (SOC) in cultivated soils results in decline in SOC stocks over time and also contributes to increased levels of CO₂ in the atmosphere. Off‐site transport of SOC in runoff waters during erosional events also contributes to SOC depletion, but there is a paucity of data in the literature documenting erosional SOC losses and the fate of eroded SOC. In this paper, we present a mass balance approach to compute CO₂ evolved from mineralization of SOC during transport and deposition of eroded soils. Erosion‐induced CO₂ emission rates ranging between 6 and 52 g C m⁻² yr⁻¹ were computed using data on SOC stocks and dynamics from a series of long‐term experiments conducted across a range of ecological regions. For the cropland of the world, we estimated an annual flux of 0.37 Pg CO₂‐C to the atmosphere due to water erosion. This flux is significant and suggests that water erosion must be taken into consideration when constructing global and regional C budgets. Through its contribution to atmospheric CO₂ increase, water erosion can have a positive feedback on the accelerated greenhouse effect. Copyright © 2001 John Wiley & Sons, Ltd.     

Tillage,fertilizer type,and plant residue input impacts on soil carbon sequestration rates on a Japanese Andosol

ABSTRACT

To identify efficient field management practices for enhanced soil carbon sequestration suited to crop rotation-based Andosol fields in northern Japan, the impacts of a combination of tillage, fertilizer type, and plant residue input on soil carbon sequestration rates were studied in a 4-year field experiment (April 2007 to March 2011). The rates of changes in soil organic carbon over the entire study period were determined by soil carbon stock change and by net ecosystem carbon budget. Across eight field management treatments and two replicates for each treatment, the rates of changes in soil organic carbon determined by net ecosystem carbon budget were positively correlated with the rates determined by soil carbon stock change (r = 0.766, n = 16). The arithmetic means of the rates determined by net ecosystem carbon budget (1.24 Mg C ha^?1 year^?1) were greater than those determined by soil carbon stock change (?0.18 Mg C ha^?1 year^?1) because decomposing crop residues and composted cattle manure in soil were included in the calculation of the net ecosystem carbon budget but were excluded in the calculation of soil carbon stock change (decomposing crop residues and composted cattle manure in soil samples were removed by sieving in measuring the soil carbon stock change). Both methods led to the same conclusion that soil carbon sequestration was significantly enhanced by composted cattle manure application and increased input of plant carbon from crop residues and green manure but was not enhanced by reduced tillage. The p values for net ecosystem carbon budget were smaller than those for soil carbon stock change in analysis of variance; therefore, the net ecosystem carbon budget was more sensitive to field management practice than the soil carbon stock change.     

After the Kyoto Protocol: Can soil scientists make a useful contribution?*

Abstract. Over 170 countries have ratified the UN Framework Convention on Climate Change (UNFCCC) which aims at ‘the stabilisation of greenhouse gases in the atmosphere at a level that will prevent dangerous anthropogenic interference with the climate system’. The Kyoto Protocol, signed in 1997, commits the developed (‘Annex 1′) countries to a reduction in gaseous emissions. The global increase in atmospheric CO₂, the main greenhouse gas, comes mainly from fossil fuels (6.5 Gt C yr^?1), together with about 1.6 Gt C yr^?1 from deforestation. The atmospheric increase is only 3.4 Gt C yr^?1, however, due to a net sink in terrestrial ecosystems of about 2 Gt C yr^?1, and another in the oceans. Increasing net carbon sequestration by afforestation of previously non-forested land is one way of reducing net national emissions of CO₂ that is permitted under the Kyoto Protocol. Future modifications may also allow the inclusion of carbon sequestration brought about by other forestry and agricultural land management practices. However, associated changes in net fluxes of two other greenhouse gases identified in the Protocol — nitrous oxide (N₂O) and methane (CH₄) — will have to be taken into account. Growth of biomass crops can increase N₂O emissions, and drainage of wetlands for forestry or agriculture also increases them, as well as emissions of CO₂, while decreasing those of CH₄. The problems of how to quantify these soil sources and sinks, to maximize soil C sequestration, and to minimize soil emissions of CH₄ and N₂O, will present a major scientific challenge over the next few years — one in which the soil science community will have a significant part to play.     

Carbon stocks in Ethiopian soils in relation to land use and soil management

The effect of soil management and land use change are of interest to the sustainable land management for improving the environment and advancing food security in developing countries. Both anthropogenic changes and natural processes affect agriculture primarily by altering soil quality. This paper reviews and synthesizes the available literatures related to the influence of soil management and land use changes on soil carbon (C) stock in Ethiopia. The review shows that topsoil C stock declines approximately 0–63%, 0–23%, and 17–83% upon land use conversion from forest to crop land, to open grazing, and to plantation, respectively. An increase of 1–3% in soil C stock was observed within 10 years of converting open grazed land to protected enclosures. However, there was a little change in soil C stock below 20 cm depth. There is a large potential of increasing SOC pool with adoption of land restorative measures. Total potential of soil C sequestration with the adoption of restoration measures ranges 0·066–2·2 Tg C y⁻¹ on rain‐fed cropland and 4·2–10·5 Tg C y⁻¹ on rangeland. Given large area and diverse ecological conditions in Ethiopia, research data available in published literature are rather scanty. Therefore, researchable priorities identified in this review are important. Copyright © 2008 John Wiley & Sons, Ltd.     

Potential for greenhouse gas emissions from soil carbon stock following biofuel cultivation on degraded lands

Consequent to the interest in converting degraded lands for cultivation of biofuel crops, concerns have been expressed about greenhouse gas (GHG) emissions resulting from changes in soil‐carbon (C) stock following land conversions. A literature‐based study was undertaken for estimating the magnitude of emission of GHGs, particularly carbon dioxide (CO₂), following an assessment of the extent and causes of land degradation and the nature of CO₂ emission from soils. The study estimated the potential for CO₂ emission resulting from changes in soil‐carbon stock following land conversions, using oil palm (Elaeis guineensis Jacq.) as a case study. The analysis indicated that, overall, the magnitude of CO₂ emission resulting from changes in soil C stock per se following opening up of degraded land would be low compared with other potential sources of CO₂ emission. However, lack of data on critical aspects such as baseline soil C status was a limitation of the study. Soil respiration is the single best measure of GHG emission from soils. Fixation of C in additional biomass will compensate, over time, for C loss through soil respiration following a change in land use or land management, unless such changes involve conversion of existing large C stocks. Therefore, any net CO₂ emission from soils resulting from changes in soil C stock following opening up of degraded land is likely to be a short‐term phenomenon. The estimations used in the study are based on various assumptions, which need to be validated by experimental field data. Copyright © 2010 John Wiley & Sons, Ltd.     

Carbon sequestration in dryland ecosystems of West Asia and North Africa

The West Asia–North Africa (WANA) region has a land area of 1.7 billion ha, and a population of 600 million. Desertification and soil degradation are severe problems in the region. The problem of drought stress is exacerbated by low and erratic rainfall and soils of limited available water holding capacity and soil organic carbon (SOC) content of less than 0.5 per cent. The SOC pool of most soils has been depleted by soil degradation and widespread use of subsistence and exploitative farming systems. The historic loss of a SOC pool for the soils of the WANA region may be 6–12 Pg compared with the global loss of 66–90 Pg. Assuming that 60 per cent of the historic loss can be resequestered, the total soil‐C sink capacity of the WANA region may be 3–7 Pg. This potential may be realized through adoption of measures to control desertification, restore degraded soils and ecosystems, and improve soil and crop management techniques that can enhance the SOC pool and improve soil quality. The strategies of soil‐C sequestration include integrated nutrient management (INM) and recycling, controlled grazing, and growing improved fodder species on rangeland. Improved technologies for cropland include use of INM and biofertilizers, appropriate tillage methods and residue management techniques, crop rotations and cover crops, and water and nutrient recycling technologies. Through adoption of such measures, the potential of soil‐C sequestration in the WANA region is 0.2–0.4 Pg C yr⁻¹. Copyright © 2002 John Wiley & Sons, Ltd.     

Re‐evaluating the biophysical and technologically attainable potential of topsoil carbon sequestration in China's cropland

To assess the topsoil carbon sequestration potential (CSP) of China's cropland, two different estimates were made: (i) a biophysical potential (BP) using a saturation limit approach based on soil organic carbon (SOC) accumulation dynamics and a storage restoration approach from the cultivation‐induced SOC loss, and (ii) a technically attainable potential (TAP) with a scenario estimation approach using SOC increases under best management practices (BMPs) in agriculture. Thus, the BP is projected to be the gap in recent SOC storage to either the saturation capacity or to the SOC storage of uncultivated soil, while the TAP is the overall increase over the current SOC storage that could be achieved with the extension of BMPs. The recent mean SOC density of China's cropland was estimated to be 36.44 t/ha, with a BP estimate of 2.21 Pg C by a saturation approach and 2.95 Pg C by the storage restoration method. An overall TAP of 0.62 Pg C and 0.98 Pg C was predicted for conservation tillage plus straw return and recommended fertilizer applications, respectively. This TAP is comparable to 40–60% of total CO₂ emissions from Chinese energy production in 2007. Therefore, carbon sequestration in China's cropland is recommended for enhancing China's mitigation capacity for climate change. However, priority should be given to the vast dry cropland areas of China, as the CSP of China is based predominantly on the dry cropland.     

Microbial assimilation of atmospheric CO2 into soil organic matter revealed by the incubation of paddy soils under 14C-CO2 atmosphere

Similar to higher plants, microbial autotrophs possess photosynthetic systems that enable them to fix CO₂. To measure the activity of microbial autotrophs in assimilating atmospheric CO₂, five paddy soils were incubated with ¹⁴C-labeled CO₂ for 45 days to determine the amount of ¹⁴C-labeled organic C being synthesized. The results showed that a significant amount of ¹⁴C-labeled CO₂ incorporated into microbial biomass was soil specific, accounting for 0.37%–1.18% of soil organic carbon (¹⁴C-labeled organic C range: 81.6–156.9 mg C kg^?1 of the soil after 45 days). Consequently, high amounts of C-labeled organic C were synthesized (the synthesis rates ranged from 86 to 166 mg C m^?2 d^?1). The amount of atmospheric ¹⁴CO₂ incorporated into microbial biomass (¹⁴C-labeled microbial biomass) was significantly correlated with organic C components (¹⁴C-labeled organic C) in the soil (r = 0.80, p < 0.0001). Our results indicate that the microbial assimilation of atmospheric CO₂ is an important process for the sequestration and cycling of terrestrial C. Our results showed that microbial assimilation of atmospheric CO₂ has been underestimated by researchers globally, and that it should be accounted for in global terrestrial carbon cycle models.     

Enhancing crop productivity for recarbonizing soil

Plants capture atmospheric carbon dioxide (CO₂) for carbon (C) assimilation through photosynthesis, with the photosynthates stored as plant biomass (above- and below-ground plant parts). The C stored as living biomass is a short-term C sequestration strategy, whereas soil organic carbon (SOC) is a long-term C sequestration strategy. In this regard, plant roots are the primary route of C entry into the SOC pool. Through establishing a recalcitrant SOC pool, long-term sequestration can potentially offset the C losses caused by soil degradation in industrial and pre-industrial eras. Over the next 50–100 years, implementing effective agricultural practices could sequester 80–130 GT (10⁹) C as SOC. Carbon, as the primary elemental component of soil organic matter, plays a significant role in shaping the soil’s physical, chemical, and biological properties, ultimately influencing soil biomass productivity. By enhancing crop productivity and biomass production, farmers can increase C sequestration, creating a positive feedback loop that contributes to overall C sequestration. Carbon sequestration has numerous co-benefits, including climate change mitigation, ecosystem health, food security, and farm profitability. Adopting conservation agriculture and site-specific practices and developing crop and pasture genotypes with high yields and C sequestration potential should significantly improve crop productivity and C sequestration simultaneously. This opinion article delves into the nexus between photosynthesis and soil C sequestration, highlighting its significance in enhancing farm productivity while mitigating climate change.     

The impact of fire on redistribution of soil organic matter on a mediterranean hillslope under maquia vegetation type

Soil organic matter (SOM) changes affect the CO₂ atmospheric levels and is a key factor on soil fertility and soil erodibility. Fire affects ecosystems and the soil properties due to heating and post‐fire soil erosion and degradation processes. In order to understand fire effects on soil organic carbon (SOC) balance research was undertaken on a fire‐prone ecosystem: the Mediterranean maquia . The spatial distribution of SOC was measured in a Burnt site 6 months after a wildfire and in a Control site. Samples were collected at two different depths (0–3 and 3–10 cm) and SOC was determined. The results show that 41·8 per cent of the SOC stock was lost. This is due to the removal of the burnt material by surface wash. No significant differences in SOC content were found for the subsurface samples between burnt and control plots. Those results show that ashes and charcoal are transported by runoff downslope and are subsequently deposited in the valley bottom and this is the key process that contributes the burial of SOC after a forest fire. SOC redistribution by water erosion is accelerated after forest fires and contribute to the degradation of soils located at the upper part of the hillslopes but causes the enrichment with SOM of the soils located at the valley bottom. Buried SOC in the bottoms valley terraces will contribute to the sequestration of carbon for longer. Conservation of abandoned terraces is a key policy to avoid land degradation and climate change. Copyright © 2010 John Wiley & Sons Ltd.     

Functional dependencies of soil CO2 emissions on soil biological properties in northern German agricultural soils derived from a glacial till

Agricultural soil CO₂ emissions and their controlling factors have recently received increased attention because of the high potential of carbon sequestration and their importance in soil fertility. Several parameters of soil structure, chemistry, and microbiology were monitored along with soil CO₂ emissions in research conducted in soils derived from a glacial till. The investigation was carried out during the 2012 growing season in Northern Germany. Higher potentials of soil CO₂ emissions were found in grassland (20.40 µg g^?1 dry weight h^?1) compared to arable land (5.59 µg g^?1 dry weight h^?1) within the incubating temperature from 5°C to 40°C and incubating moisture from 30% to 70% water holding capacity (WHC) of soils taken during the growing season. For agricultural soils regardless of pasture and arable management, we suggested nine key factors that influence changes in soil CO₂ emissions including soil temperature, metabolic quotient, bulk density, WHC, percentage of silt, bacterial biomass, pH, soil organic carbon, and hot water soluble carbon (glucose equivalent) based on principal component analysis and hierarchical cluster analysis. Slightly different key factors were proposed concerning individual land use types, however, the most important factors for soil CO₂ emissions of agricultural soils in Northern Germany were proved to be metabolic quotient and soil temperature. Our results are valuable in providing key influencing factors for soil CO₂ emission changes in grassland and arable land with respect to soil respiration, physical status, nutrition supply, and microbe-related parameters.     

Carbon sequestration in a temperate grassland; management and climatic controls

Soil management practices that result in increased soil carbon (C) sequestration can make a valuable contribution to reducing the increase in atmospheric CO₂ concentrations. We studied the effect of poultry manure, cattle slurry, sewage sludge, NH₄NO₃ or urea on C cycling and sequestration in silage grass production. Soil respiration, net ecosystem exchange (NEE) and methane (CH₄) fluxes were measured with chambers, and soil samples were analysed for total C and dissolved organic C (DOC). Treatments were applied over 2 years and measurements were carried out over 3 years to assess possible residual effects. Organic fertilizer applications increased CO₂ loss through soil respiration but also enhanced soil C storage compared with mineral fertilizer. Cumulative soil respiration rates were highest in poultry manure treatments with 13.7 t C ha^?1 in 2003, corresponding to 1.6 times the control value, but no residual effect was seen. Soil respiration showed an exponential increase with temperature, and a bimodal relationship with soil moisture. The greatest NEE was observed on urea treatments (with a CO₂ uptake of ?4.4 g CO₂ m^?2 h^?1). Total C and DOC were significantly greater in manure treatments in the soil surface (0–10 cm). Of the C added in the manures, 27% of that in the sewage pellets, 32% of that in the cattle slurry and 39% of that in the poultry manure remained in the 0–10 cm soil layer at the end of the experiment. Mineral fertilizer treatments had only small C sequestration rates, although uncertainties were high. Expressed as global warming potentials, the benefits of increased C sequestration on poultry manure and sewage pellet treatments were outweighed by the additional losses of N₂O, particularly in the wet year 2002. Methane was emitted only for 2–3 days on cattle slurry treatments, but the magnitudes of fluxes were negligible compared with C losses by soil respiration.