Carbon in the soil is important for the soil structure and improves the water holding capacity and other soil properties which are important for the agricultural productivity. Furthermore it becomes apparent that the maintenance of intact ecosystems is necessary to store as much carbon as possible. Usually the soil is the part of an ecosystem that stores the largest amount of carbon. For example 73% of the total carbon of the ecosystem are stored in the soil of the mangrove forests in Sofala Bay.
The carbon sequestration of soils depends substantially on the accordant ecosystems such as forests, grasslands, deserts and also arable land. Soils of grasslands and forests usually contain more carbon than soils of arable land.
But also the climate and the management of these ecosystems are important influencing factors. On a global scale, the soil carbon content increases with decreasing average temperatures. Hence cold and humid regions have carbon rich soils.
The carbon sequestration in soils of arable land can be approved by applying certain management practices such as no-tillage techniques, cover crops and crop rotations. Furthermore a change from intensive to extensive grazing or afforestation can lead to increased carbon sequestration of the soils.
This article provides a good overview of the measurements of carbon in soils, of the modelling of carbon and of measures to enhance the stored amount in the soils. mehr
Soil contains approximately 2344 Gt (1 gigaton = 1 billion tonnes) of organic carbon globally and is the largest terrestrial pool of organic carbon. Small changes in the soil organic carbon stock could result in significant impacts on the atmospheric carbon concentration. The fluxes of soil organic carbon vary in response to a host of potential environmental and anthropogenic driving factors.
Scientists worldwide are contemplating questions such as: ‘What is the average net change in soil organic carbon due to environmental conditions or management practices?’, ‘How can soil organic carbon sequestration be enhanced to achieve some mitigation of atmospheric carbon dioxide?’ and ‘Will this secure soil quality?’.
These questions are far reaching, because maintaining and improving the world’s soil resource is imperative to providing sufficient food and fibre to a growing population. Additional challenges are expected through climate change and its potential to increase food shortages. This review highlights knowledge of the amount of carbon stored in soils globally, and the potential for carbon sequestration in soil. It also discusses successful methods and models used to determine and estimate carbon pools and fluxes. This knowledge and technology underpins decisions to protect the soil resource.
The carbon stock in deep soils and its role in the carbon cycle are analysed in this study. mehr
Despite their low carbon (C) content, most subsoil horizons contribute to more than half of the total soil C stocks, and therefore need to be considered in the global C cycle. Until recently, the properties and dynamics of C in deep soils was largely ignored. The aim of this review is to synthesize literature concerning the sources, composition, mechanisms of stabilisation and destabilization of soil organic matter (SOM) stored in subsoil horizons. Organic C input into subsoils occurs in dissolved form (DOC) following preferential flow pathways, as aboveground or root litter and exudates along root channels and/or through bioturbation. The relative importance of these inputs for subsoil C distribution and dynamics still needs to be evaluated.
Due to climate warming the melting of permafrost soils and the vegetation growth are enhanced, which leads to two counteracting effects on the carbon balance. mehr
Climate warming affects permafrost soil carbon pools in two opposing ways: enhanced vegetation growth leads to higher carbon inputs to the soil, whereas permafrost melting accelerates decomposition and hence carbon release. The spatial and temporal dynamics of these two processes under scenarios of climate change are studied and their influence on the carbon balance of the permafrost zone are evaluated.
The dynamic global vegetationmodel LPJmL was used, which simulates plant physiological and ecological processes and includes a newly developed discrete layer energy balance permafrost module and a vertical carbon distribution within the soil layer. The model is able to reproduce the interactions between vegetation and soil carbon dynamics as well as to simulate dynamic permafrost changes resulting from changes in the climate. Vegetation responds more rapidly to warming of the permafrost zone than soil carbon pools due to long time lags in permafrost thawing, and that the initial simulated net uptake of carbon may continue for some decades of warming. However, once the turning point is reached, if carbon release exceeds uptake, carbon is lost irreversibly from the system and cannot be compensated for by increasing vegetation carbon input.
The analysis highlights the importance of including dynamic vegetation and long-term responses into analyses of permafrost zone carbon budgets.
This study deals with the carbon storage in organic soils in Scotland and Wales. mehr
New estimates have been derived for the amount of carbon stored in organic soils in Scotland and Wales. The data illustrate the huge pool of carbon in the organic soils of Scotland and Wales. Stock estimates have increased by over 30% for Scotland and 20% for Wales with the inclusion of organic material below 1 m depth and the improved estimates of bulk density.
Some uncertainty remains over soil C stocks and further validation is required to reduce this uncertainty. Remote sensing techniques may potentially be useful to update our knowledge of soil C stocks, particularly in the uplands of Scotland and Wales. It is important to have a reliable estimate for the carbon held in soils in order to be able to monitor and predict the consequences of global change on GHG emissions.
Measurements of greenhouse gases fluxes from organic soils (carbon dioxide, methane and nitrous oxide) at three sites in Scotland and Wales over the course of the project have provided invaluable data for developing the ECOSSE model, as well as revealing some of the key factors controlling greenhouse gas emissions at each site.
Forest soils contain a lot of carbon and certain management practices can even enhance their capacity to store carbon. mehr
Soils in equilibrium with a natural forest ecosystem have high carbon (C) density. The ratio of soil:vegetation C density increases with latitude. Land use change, particularly conversion to agricultural ecosystems, depletes the soil C stock. Thus, degraded agricultural soils have lower soil organic carbon (SOC) stock than their potential capacity. Consequently, afforestation of agricultural soils and management of forest plantations can enhance SOC stock through C sequestration.
The rate of SOC sequestration, and the magnitude and quality of soil C stock depend on the complex interaction between climate, soils, tree species and management, and chemical composition of the litter as determined by the dominant tree species. Increasing production of forest biomass per se may not necessarily increase the SOC stocks. Fire, natural or managed, is an importantperturbation that can affect soil C stock for a long period after the event. The soil C stock can be greatly enhanced by a careful site preparation, adequate soil drainage, growing species with a high NPP, applying N and micronutrients (Fe) as fertilizers orbiosolids, and conserving soil and water resources.
Climate change may also stimulate forest growth by enhancing availability of mineral N and through the CO2fertilization effect, which may partly compensate release of soil C in response to warming. There are significant advances in measurement of soil C stock and fluxes, and scaling of C stock from pedon/plot scale to regional and national scales. Soil C sequestration in boreal and temperate forests may be an important strategy to ameliorate changes in atmospheric chemistry.
Cumulic Anthroposols (soils influenced by humans) were compared with non-Anthroposols in terms of their carbon content. mehr
Soils developed on the sites of Australian Aboriginal oven mounds along the Murray River in SE Australia, classified as Cumulic Anthroposols under the Australian Soil Classification, are shown to have traits similar to the Terra Preta de Indio of the Amazon basin. Seven such sites were characterised and compared with adjacent soils. The Cumulic Anthroposols contained significantly (p < 0.05) more soil carbon (C), compared to adjacent non-Anthroposols.
Solid-state 13C NMR spectroscopy showed that the C in the Cumulic Anthroposols was predominantly aromatic, especially at depth, confirming the presence of charcoal. Radiocarbon analysis carried out on charcoal collected from two of these sites showed that it was deposited 650±30 years BP at one site and 1609±34 years BP at the other site, demonstrating its recalcitrance in soil. The charcoal originated from plant material, as shown by SEM, and had high levels of Ca agglomeration on its surfaces. The Cumulic Anthroposols were shown to have altered nutrient status, with total N, P, K and Ca being significantly greater than in the adjacent soils throughout the profile. This was also reflected in the higher mean CEC of 31.2 cmol (+) kg−1 and higher pH by 1.3 units, compared to the adjacent soils. Based on the similarity of these Cumulic Anthroposols with the Terra Preta de Indio of the Amazon, these Cumulic Anthroposols can be classified as Terra Preta Australis.
The existence of these soils demonstrates that Australian soils, in temperate climates, are capable of storing C in much higher quantities than has been previously recognised, and that this capability is founded on the unique stability and properties of charred organic matter.
Different management practices and their impact on the carbon content in the soil, especially in deeper layers, are analysed in this study. mehr
Soil C sequestration research has historically focused on the top 0 to 30 cm of the soil profile, ignoring deeper portions that might also respond to management. In this study soils along a 10-treatment management intensity gradient to a 1-m depth were sampled to test the hypothesis that C gains in surface soils are off set by losses lower in the profile.
Treatments included four annual cropping systems in a corn (Zea mays)–soybean (Glycine max)– wheat (Triticum aestivum) rotation, perennial alfalfa (Medicago sativa) and poplar (Populus x euramericana), and four unmanaged successional systems. Th e annual grain systems included conventionally tilled, no-tillage, reducedinput, and organic systems. Unmanaged treatments included a 12-yr-old early successional community, two 50-yr-old mid-successional communities, and a mature forest never cleared for agriculture. All treatments were replicated three to six times and all cropping systems were 12 yr post-establishment when sampled.
Surface soil C concentrations and total C pools were significantly greater under no-till, organic, early successional, never-tilled mid-successional, and deciduous forest systems than in the conventionally managed cropping system (p 0.05, n = 3–6 replicate sites). No consistent differences in soil C at depth, despite intensive sampling (30–60 deep soil cores per treatment). Carbon concentrations in the B/Bt and Bt2/C horizons were lower and two and three times more variable, respectively, than in surface soils. We found no evidence for C gains in the surface soils of no-till and other treatments to be either off set or magnifi ed by carbon change at depth.
The number of sheeps per hectar has a meaningful impact on the carbon storage in the soils of grasslands in northern China. mehr
Recent studies have underscored the importance of grasslands as potential carbon (C) sinks. A grazing experiment with seven stocking rates (SR0, SR1.5, SR3.0, SR4.5, SR6.0, SR7.5, and SR9.0 for 0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep /ha, respectively) was performed to investigate the effect of increasing grazing pressure on soil C and nitrogen (N) storage in the temperate grasslands of northern China.
The results revealed that C and N storage in both 0–10 cm and 10–30 cm soil layers decreased linearly with increasing stocking rates. Carbon storage in the 0–10 cm soil layer was significantly higher in lightly grazed grasslands than in heavily grazed grasslands after a 5-yr grazing treatment. Findings suggest an underlying transformation from soil C sequestration under light grazing to C loss under heavy grazing, and that the threshold for this transformation is 4.5 sheep /ha (grazing period from June to September).
Results confirmed that grasslands used for grazing in northern China have the capacity to sequester C in the soil under appropriate grazing pressure, but that they lose C under heavy grazing. Therefore, appropriate grazer densities will promote soil C sequestration in the grasslands of northern China.
This study investigates the change in carbon sequestration as a result of a reorientation from conventional to less intensive tillage and addition of organic material. mehr
Results from the UK were reviewed to quantify the impact on climate change mitigation of soil organic carbon (SOC) stocks as a result of (1) a change from conventional to less intensive tillage and (2) addition of organic materials including farm manures, digested biosolids, cereal straw, green manure and paper crumble.
The average annual increase in SOC deriving from reduced tillage was 310 kg C ±180 kg C ha−1 yr−1. Even this accumulation of C is unlikely to be achieved in the UK and northwest Europe because farmers practice rotational tillage. N2O emissions may increase under reduced tillage, counteracting increases in SOC. Addition of biosolids increased SOC (in kg C ha−1 yr−1 t−1 dry solids added) by on average 60±20 (farm manures), 180±24 (digested biosolids), 50±15 (cereal straw), 60±10 (green compost) and an estimated 60 (paper crumble). SOC accumulation declines in long-term experiments (>50 yr) with farm manure applications as a new equilibrium is approached.
Biosolids are typically already applied to soil, so increases in SOC cannot be regarded as mitigation. Large increases in SOC were deduced for paper crumble (>6 t C ha−1 yr−1) but outweighed by N2O emissions deriving from additional fertiliser. Compost offers genuine potential for mitigation because application replaces disposal to landfill; it also decreases N2O emission.
An article about the carbon storage in different ecosystems in Minnesota and about possible increases of stored carbon due to land use changes. mehr
Results suggest a three-step program to policymakers. It is importan to preserve existing large carbon stocks in peatlands and forests by identifying and protecting areas vulnerable to conversion, fire, and other preventable threats.
Promote land use and land cover changes most certain to cause carbon sequestration by including them in local, regional, and statewide conservation, renewable energy, and sustainable development priorities.
Invest in monitoring and demonstration programs to build public, practitioner, and investor confidence in terrestrial carbon sequestration as a viable emission reduction strategy.
Carbon sequestered in soils provides a further regulating ecosystem service, valued as the avoided damage from global climate change. mehr
Soil resources underpin all ecosystem service categories and as a critical natural capital they are vital for regulating biophysical processes and ultimately human wellbeing. But human pressures, including population growth, climate change, urbanisation and food demand, are depleting soil stocks and undermining the flows of the valuable services they provide. These services include the climate mitigation and adaptation functions, the importance of which is now becoming more fully appreciated by policymakers.
There are many reasons to maintain soil, but this paper focuses on the regulating service provided by carbon (C) sequestration, which can provide a compelling economic reason for soil conservation and management.
Natural vegetation restoration and tree plantation are the two most important measures for ecosystem restoration. mehr
The Loess Plateau of China is a unique geographical unit characterized by extensive loess distribution, serious soil erosion, low vegetation coverage and high soil carbonate content. Since the 1950s, the Chinese government has made great efforts to control soil erosion and restore vegetation, including large-scale tree plantation in the 1970s, integrated soil erosion control in the 1980s and 1990s, and the “Grain for Green Project” in the 2000s.
Currently, the ecological restoration of the Loess Plateau has produced remarkable achievements: increasing vegetation coverage, decreasing soil erosion and enhanced ecosystem services. Soil carbon sequestration is a critical index for evaluating the eficiency of ecological restoration. Since 1954, Natural Vegetation Restoration Is More Beneficial to Soil Surface Carbon Sequestration on Loess Plateau vegetation restoration has been conducted in one of these watersheds and tree plantation in the other. The watersheds have now formed completely different vegetation landscapes (DZG: grassland; YJG: forestland).