Sequestration Of Atmospheric CO2 Research Articles

Processes Determining the Sequestration and Maintenance of Carbon in Soils: A Synthesis of Research from Tropical India

Soil organic carbon (SOC) is the major determinant of soil quality, and it greatly influences global carbon cycling and climate change. This paper is a synthesis of the literature on soil carbon research in India, including soil organic and inorganic carbon stocks, in the form of thematic maps for national and regional level planning at bioclimatic systems and agroecological subregion levels in the country. The potential role of soils in mitigating the global warming effects of atmospheric CO 2 is discussed using results from Indian tropical soils. The database on Indian soils collected through natural resource inventory and soil carbon and crop modeling approaches show that sequestration of atmospheric CO 2 occurs as pedogenic carbonates and plays role as a soil modifier in enhancing soil organic carbon in the drier parts of the country through management interventions. Clearly, soils can act as a potential medium for sequestering atmospheric CO 2 to mitigate the global warming effect. Reviews

Greenhouse gas fluxes (CO2, N2O and CH4) from forest soils in the Basque Country: Comparison of different tree species and growth stages

Forest systems are considered quintessential terrestrial systems for atmospheric CO2 sequestration to mitigate the effect of global warming. Temperate forest soils also present the highest rates of methane uptake among all the natural systems, while may represent a significant source of N2O. Despite of the large area occupied by forest in the Basque Country, no data is yet available regarding greenhouse gas fluxes under these edaphoclimatic conditions. In this manuscript we present a 2-year study which determined the magnitude of CO2, N2O, and CH4 soil gas fluxes in radiata pine, beech and Douglas fir forests using a closed chamber technique. The magnitude of these gas fluxes was additionally compared between different growth stages of radiata pine and beech forest, and the edaphoclimatic parameters that control these gas fluxes in the different forest systems and growth stages were studied. Measured greenhouse gas fluxes were in a low range as already published elsewhere for temperate forest ecosystems. A nitrogen deficit appears to be responsible for these relatively low gas fluxes. Apparently, the different forest species play a key role as controllers responsible for the differences of soil gas-exchange fluxes between the three different forest type systems. The mature pine plantation soil was emitting the most CO2 (1.5 and 2.5 times more than the mature beech and the Douglas fir, respectively), while the Douglas fir forest soil was emitting the most N2O (3 and 17 times more than the mature pine and the mature beech, respectively) and the mature beech forest was the soil type showing the highest CH4 consumption rates (2 and 5.5 times more than the mature pine and the Douglas fir, respectively). The stage of growth and its usual management appear to be important concerning the soil gas-exchange behavior within one forest type. The young beech forest soil emitted 9 times more N2O than the mature, and the new pine and the mature pine plantation soils emitted 2.5 and 2 times more CO2 than the young, respectively. The ground vegetation cover percentage, the organic matter accumulation and the soil porosity seem to be factors which merit a closer look in future studies, as possibly responsible for the differences in gas fluxes among forest types and growth stages.

Engineering challenges of ocean liming

The relationship between the level of atmospheric CO2 (carbon dioxide) and the impacts of climate change is uncertain, but a safe concentration may be surpassed this century. Therefore, it is necessary to develop technologies that can accelerate CO2 removal from the atmosphere. This paper explores the engineering challenges of a technology that manipulates the carbonate system in seawater by the addition of calcium oxide powder (CaO; lime), resulting in a net sequestration of atmospheric CO2 into the ocean (ocean liming; OL). Every tonne of CO2 sequestered requires between 1.4 and 1.7 t of limestone to be crushed, calcined, and distributed. Approximately 1 t of CO2 would be created from this activity, of which >80% is a high purity gas (pCO2 > 98%) amenable to geological storage. It is estimated that the thermal and electrical energy requirements for OL would be 0.6–5.6 and 0.1–1.2 GJ tCO2−1 captured respectively. A preliminary economic assessment suggests that OL could cost approximately US$72–159 t−1 of CO2. The additional CO2 burden of OL makes it a poor alternative to point source mitigation. However, it may provide a means to mitigate some diffuse emissions and reduce atmospheric concentrations.

Sequestration of atmospheric CO2 in chrysotile mine tailings of the Woodsreef Asbestos Mine, Australia: Quantitative mineralogy, isotopic fingerprinting and carbonation rates

Since closure of the Woodsreef Asbestos Mine, located in the Great Serpentinite Belt (GSB), New South Wales, Australia, extensive carbonate-rich crusts have formed by recessive weathering of fine-grained material on the surface of the tailings pile. A relationship exists between the mode of carbonate occurrence, the mineralogy and the isotopic fingerprint of carbonates from the tailings pile. Vertical carbonate crusts, covering most of the tailings, predominantly consist of the hydrated Mg-carbonate hydromagnesite (Mg5(CO3)4(OH)2·4H2O), which has precipitated from evaporating meteoric waters incorporating atmospheric CO2, as reflected in high δ18O, δ13C and F14C signatures, respectively. Low and variable concentrations of magnesite, dolomite and calcite represent bedrock carbonate, which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high δ18O, low δ13C and F14C, a signature typical for ‘weathering-derived’ magnesite deposits in the GSB. The carbonate fraction of deep cement samples, collected from 70 to 120cm below the surface, representing the bulk tailings material at depth, predominantly consists of pyroaurite (Mg6Fe2(CO3)(OH)16·4H2O) and, despite stable isotope signatures similar to bedrock, contains significant radiocarbon. This indicates that pyroaurite, forming under different conditions as hydromagnesite, may represent an additional trap for atmospheric CO2 in the Woodsreef mine tailings. The distribution of carbonates and quartz, together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric-derived carbonate, strongly indicates that dissolution and re-precipitation of bedrock carbonate is not a dominant process in the Woodsreef tailings. The cations for carbonate formation are instead derived from the dissolution of serpentine minerals (lizardite and chrysotile) and brucite.The internal standard method and the reference intensity method have been used with X-ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite, respectively. Considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that, between 1400 and 70,000t of atmospheric CO2 have been sequestered in the mine tailings since closure of the mine 29a ago. Carbonation rates of 27gCm−2y−1 and 1330gCm−2y−1 are significantly higher than background rates of CO2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of CO2 in carbonate minerals.

Sequestration of atmospheric CO2 in a weathering-derived, serpentinite-hosted magnesite deposit: 14C tracing of carbon sources and age constraints for a refined genetic model

The Attunga magnesite deposit is texturally and geochemically distinct from other spatially associated, serpentinite-hosted magnesite deposits in the Great Serpentinite Belt, New South Wales, Australia, such as the hydrothermal Piedmont magnesite deposit or widespread silica–carbonate alteration zones. Cryptocrystalline magnesite at Attunga predominantly occurs in nodular masses and irregular, desiccated veins that occupy pre-existing cracks and pore spaces resulting from fracturing and weathering of the host rock. Incipient weathering of the serpentinite host rock is accompanied by a decrease in volume and the mobilisation of MgO and CaO from the serpentinite. Pore spaces and permeability created during weathering and fracturing of the host rock provide access for CO2-, MgO- and CaO-bearing meteoric waters which led to an increase of volume during carbonation. SiO2 is only mobilised during more advanced stages of weathering and late stage infiltration of SiO2-bearing waters and precipitation of opal-A lead to local silicification of the serpentinite.Stable carbon and oxygen isotope signatures show that nodular magnesite at Attunga has formed under near-surface conditions incorporating carbon from C3-photosynthetic plants and oxygen from meteoric waters. Radiocarbon concentrations in the magnesite preclude subducted carbonaceous sediments as the source of carbon and, together with distinct stable carbon and oxygen isotope signatures, indicate that magnesite at Attunga precipitated from low temperature, supergene fluids. Even though there is no direct geochemical and isotopic evidence, some textural observations and field relationships for weathering-derived magnesite deposits suggest the prior existence of a possibly Early Triassic, hydrothermal magnesite deposit at Attunga. The presence of a pre-existing magnesite deposit may entail the localised formation of the weathering-derived magnesite at Attunga, but the predominance of weathering-related textures and geochemical signatures indicate that weathering is the integral magnesite mineralisation process at Attunga. Conventional radiocarbon ages of about 50ka represent a maximum age constraint for the formation of the magnesite deposit during Quaternary weathering. A significant amount of atmospheric CO2 has been sequestered via the biosphere and carbonation of serpentinite at Attunga.

The production and accumulation of phytolith-occluded carbon in Baiyangdian reed wetland of China

Phytolith, the opal of amorphous silica formed in plant tissues, is present in most plants (mainly Poaceae, Cyperaceae and so on). The carbon bio-sequestration within the phytoliths of plants, one of the most promising approaches of long-term CO2 sequestration, is a significant mechanism of long-term biogeochemical carbon sequestration. This study analyzed the production and accumulation of phytolith-occluded-carbon (PhytOC) in Baiyangdian reed wetland of China. The plant phytolith extraction was undertaken with microwave digestion procedures and the soil phytolith extraction was based on the method of heavy liquid separation. The determination of the carbon content of phytoliths was based on phytolith-Si dissolution methods. The production flux of PhytOC for aboveground reed was 3.7–4.2gCO2m−2a−1 and the accumulation flux of PhytOC for soil layer (0–15cm) of soil deposition was 0.03gCO2m−2a−1. The results imply that PhytOC content in reed dry biomass mainly depends on the content of the silicon taken up by the plant and the occluded carbon content of phytoliths during the plant growth. In Baiyangdian reed ecosystems, the rate of PhytOC for aboveground reed is about 6.77–7.69×108geCO2a−1, and the accumulation rate of PhytOC for 0–15cm soil layer is around 5.49×106gCO2a−1. Assuming the plant-area (5.7×108ha) of global wetland with the similar maximum flux (0.054teCO2ha−1a−1) of reed PhytOC sequestration of atmospheric CO2, about 3.08 107 tone CO2 every year would be sequestrated by wetland ecosystem. The appropriate management of reed wetlands to maximize ANPP and select plant species with high-phytolith content or high-efficiency of phytolith occlusion of carbon has the potential to result in considerable production and accumulation quantities of PhytOC in reed wetland ecosystems.

Potential role of giant marine diatoms in sequestration of atmospheric CO2 during the Last Glacial Maximum: δ13C evidence from laminated Ethmodiscus rex mats in tropical West Pacific

Giant marine diatoms, blooming or aggregating within deep chlorophyll maxima under stratified conditions, can generate substantial production and a large export flux of organic carbon from surface waters. However, their role in regulating glacial-interglacial variation in atmospheric pCO2 remains unclear. Here, we report the organic carbon isotopic compositions of Ethmodiscus rex diatoms (δ13CE. rex) and bulk sediments (δ13Corg) from a sediment core in the eastern Philippine Sea dated to ~19.5–31.0kyr B.P. and consisting of (from youngest to oldest) (1) laminated E. rex diatom mats (LDM), (2) diatomaceous clay (DC), and (3) pelagic clay (PC). Our results suggest that δ13CE. rex provides a better record of palaeoceanographic processes during LDM and DC deposition than δ13Corg because of reduced differential vital effects in near-monospecific E. rex fractions. We used the isotopic composition of the coarse E. rex fraction (δ13CE. rex (>154μm)) to calculate the CO2 partial pressure of eastern Philippine Sea surface waters (pCO2-sw) during the Last Glacial Maximum (LGM). Our pCO2-sw records suggest that the eastern Philippine Sea switched from being a strong CO2 source during DC deposition to a weak CO2 sink during LDM deposition. The role of the eastern Philippine Sea as a CO2 sink during the LGM was promoted by elevated primary production and, to a lesser extent, intensified water-column stratification. These observations highlight the potential role of giant marine diatoms in the sequestration of atmospheric CO2 during the LGM and, hence, support changes in biogenic silica fluxes as a potential cause of lower glacial atmospheric CO2. Our findings are consistent with an eolian source of silica, as proposed by the ‘silica hypothesis’ and the ‘silicon-induced alkalinity pump hypothesis’ but not by the ‘silicic acid leakage hypothesis.’

Iron fluxes to Talos Dome, Antarctica, over the past 200 kyr

Abstract. Atmospheric fluxes of iron (Fe) over the past 200 kyr are reported for the coastal Antarctic Talos Dome ice core, based on acid leachable Fe concentrations. Fluxes of Fe to Talos Dome were consistently greater than those at Dome C, with the greatest difference observed during interglacial climates. We observe different Fe flux trends at Dome C and Talos Dome during the deglaciation and early Holocene, attributed to a combination of deglacial activation of dust sources local to Talos Dome and the reorganisation of atmospheric transport pathways with the retreat of the Ross Sea ice shelf. This supports similar findings based on dust particle sizes and fluxes and Rare Earth Element fluxes. We show that Ca and Fe should not be used as quantitative proxies for mineral dust, as they all demonstrate different deglacial trends at Talos Dome and Dome C. Considering that a 20 ppmv decrease in atmospheric CO2 at the coldest part of the last glacial maximum occurs contemporaneously with the period of greatest Fe and dust flux to Antarctica, we confirm that the maximum contribution of aeolian dust deposition to Southern Ocean sequestration of atmospheric CO2 is approximately 20 ppmv.

Phylogenetic aspects of the sulfate assimilation genes from Thalassiosira pseudonana

Diatoms are unicellular algae responsible for approximately 20% of global carbon fixation. Their evolution by secondary endocytobiosis resulted in a complex cellular structure and metabolism compared to algae with primary plastids. In the last years the interest on unicellular algae increased. On the one hand assessments suggest that diatom-mediated export production can influence climate change through uptake and sequestration of atmospheric CO2. On the other hand diatoms are in focus because they are discussed as potential producer of biofuels. To follow the one or other idea it is necessary to investigate the diatoms biochemistry in order to understand the cellular regulatory mechanisms. The sulfur assimilation and methionine synthesis pathways provide S-containing amino acids for the synthesis of proteins and a range of metabolites such as dimethylsulfoniopropionate (DMSP) in order to provide basic metabolic precursors needed for the diatoms metabolism. To obtain an insight into the localization and organization of the sulfur metabolism pathways, the genome of Thalassiosira pseudonana-a model organism for diatom research-might help to understand the fundamental questions on adaptive responses of diatoms to dynamic environmental conditions such as nutrient availability in a broader context.

Analysis of Interfacial Debonding of Geopolymer Annular Sealing in CO2 Geo-sequestration Wellbore

For the geological sequestration of atmospheric CO2 to be viable, it is important that leakage of stored gas back to the atmosphere is prevented for a long period. Apart from other modes of failure, damage of the bond between interfaces can open up migratory pathways for leakages of CO2 to occur. A stress induced debonding mechanism for well bore interfaces has been studied. A numerical modelling approach was used to investigate a wellbore composite cylinder system using finite element software. Analysis was performed for the wellbore annular cement sheath, both for static pressure and temperature increase/decrease. In addition, geopolymer, a novel acid resistant cementitious binder, has been considered as an annular cement system. From analysis, it has been observed that debonding can occur at discrete locations for the wellbore pressure and/temperature increase. However, for the wellbore pressure and/temperature decrease, it was found that stress-slip failure occurs when tensile normal stresses along interfaces equal the interfacial bond strength. In addition to that, for pressure and/temperature decrease, shear stresses developed in the circumferential direction appeared insignificant in debonding failure. Thermal dilation of wellbore material can help preventing discrete debonding of wellbore interfaces in the case of wellbore pressure and temperature increase. Conversely, a wellbore temperature decrease contributes to microannular formation along interface because of the material shrinkage effect.

The production of phytoliths in China's grasslands: implications to the biogeochemical sequestration of atmospheric CO2

AbstractAmong the most promising approaches of long‐term atmospheric CO2 sequestration is terrestrial biogeochemical carbon sequestration. One of the most promising terrestrial biogeochemical carbon sequestration mechanisms is the occlusion of carbon within phytoliths, the silicified features that deposit within plant tissues. Using phytolith content‐biogenic silica content transfer function obtained from our investigation, in combination with published silica content and above‐ground net primary productivity (ANPP) data of China's grasslands, we estimated the production of phytoliths and phytolith‐occluded carbon (PhytOC) in grasslands. The results show that the average above‐ground phytolith production rates of China's grasslands (10.9 106 t yr−1 or 1.45% of world grasslands) are much lower than those of other grasslands (e.g. North American nonwoody grasslands) mainly because of much lower ANPP. Assuming a median content of PhytOC of 1.5%, the average above‐ground PhytOC production rates of China's grasslands and world grasslands are estimated to be 0.6 106 t CO2 yr−1 and 41.4 106 t CO2 yr−1, respectively. The management of grasslands to maximize ANPP has the potential to result in considerable quantities of phytoliths and securely bio‐sequestered carbon.

Life cycle assessment of eucalyptus short rotation coppices for bioenergy production in southern France

AbstractShort rotation coppices (SRC) are considered prime candidates for biomass production, yielding good‐quality feedstock that is easy to harvest. Besides technical, social and economical aspects, environmental issues are important to be taken into account when developing SRC. Here, we evaluated the environmental impacts of delivering 1 GJ of heat from eucalyptus SRC using life cycle assessment (LCA), based on management scenarios involving different rotations lengths, fertilizer input rates, stem densities and harvest methods. Compared to equivalent fossil chains, all eucalyptus scenarios achieved savings of fossil energy and greenhouse gas (GHG) emissions in the 80–90% range, and had generally lower impacts, except for eutrophication. The 3 year rotation scenario was the most energy and GHG‐intensive, whereas manual felling for the longer rotations resulted in twofold larger photochemical ozone impacts compared to the other scenarios. Transportation of wood chips and fertilization were the top two contributors to the impacts, the latter being more important with the shorter rotation lengths due to the evergreen character of eucalyptus. The possibility of including ecosystem carbon dynamics was also investigated, by translating the temporary sequestration of atmospheric CO2 in the above and belowground biomass of eucalyptus as CO2 savings using various published equivalence factors. This offset the life cycle GHG emissions of heat provision from eucalyptus SRC by 70–400%.

In situ sequestration of atmospheric CO2 at low temperature and surface cracking of serpentinized peridotite in mine shafts

The investigation of carbonate formation at low temperature during weathering of ultramafic rocks has become increasingly important as it represents an analog study for a cost-efficient carbon disposal strategy. Here we present new insight into carbonate formation under subarctic surface conditions obtained from extensively carbonated chromite mine shafts in the Feragen ultramafic body, E Norway. Carbonation proceeded by formation of mm- to cm-thick carbonate surface coatings on the serpentinized peridotite host rock. The surface coatings consist in most cases of pure lansfordite (MgCO3·5H2O) and sometimes nesquehonite (MgCO3·3H2O). Heavy O- and C-isotopes are strongly enriched in the carbonate coatings relative to drip water samples from the mines and water samples from subaerial ponds. The major element composition of the water samples reveal that infiltrating rainwater reacts rapidly with the peridotite mainly due to brucite dissolution. Within the mines, discharging alkaline water forms thin films on walls and ceilings that evaporate upon circulation of cold, dry air. In mines with only one opening the carbonation is limited to the entrance area. In mines with a more efficient air circulation due to multiple entrances carbonation is found throughout the mine. Evaporation of the mine water results in lansfordite saturation and precipitation and is accompanied by a Rayleigh-type distillation effect causing enrichment of the heavy C- and O-isotopes in the liquid from which the carbonates precipitate. Formation of the carbonate coatings involved fragmentation of the underlying serpentinite substrate. Fragmentation proceeded by subcritical cracking, i.e. by a combination of substrate weakening due to brucite dissolution and stress build-up due to lansfordite precipitation in fractures close to the surface. Reaction-induced fracturing represents a positive feedback mechanism as it creates additional reactive surface area during the carbonation. Mining operations in the area ceased in the mid 1920s indicating that the described carbonation occurs on a time-scale relevant for the disposal of anthropogenic CO2.

Algal Biogeography: Metagenomics Shows Distribution of a Picoplanktonic Pelagophyte

How can we determine the distribution of uncultured marine microorganisms? Targeted metagenomics has provided the complete chloroplast genome sequence, and the distribution, for a picoplanktonic pelagophyte alga.

Sequestrated Carbon: Organic Carbon Pool in the Soils under Different Forest Covers and Land Uses in Garhwal Himalayan Region of India

Sequestration of atmospheric CO<SUB>2</SUB> in the soil, as stable soil organic matter, provides a long lasting solution to decrease the CO<SUB>2</SUB> in the atmosphere. The soil organic carbon pool was estimated in forests, tree plantations, horticulture and grasslands in the Garhwal area of Himalayan region which has wide variety of land uses and land cover. The forestry species included <i>Shorea robusta</i>, <i>Cedrus deodara</i>, <i>Quercus leucotrichophora</i>, <i>Pinus roxburghii</i>, <i>Picea smithiana</i> & <i>Abies pi</i><i>n</i><i>drow</i>, <i>Pinus wallichiana</i> and Miscellaneous species. <i>Pyrus malus</i>, <i>Psidium guava</i>, <i>Mangifera indica</i>, <i>Citrus spp</i>. and <i>Lichee chinensis</i> were the major fruit crops and the tree plantations comprised of <i>Eucalyptus spp</i>., <i>Tectona grandis</i>, <i>Dalbergia si</i><i>s</i><i>soo</i> and <i>Pinus roxburghii</i>. SOC pool was<b> </b>the<b> </b>maximum in the forest lands followed by grass lands, orchards and plantation areas. Differences in SOC pool under different land uses were statistically significant (p < 0.05). The forests had 15.84 million tons (78.49 t ha<SUP>-1</SUP>) soil organic carbon pool in this region and <i>P. smithiana</i> & <i>A. pindrow</i> forests had higher mitigation potential as they can store more than double SOC pool as compared to <i>S. robusta</i>. The<i> </i>soils under orchards contained 1.40 million tons SOC pool which is 13.05% of the total SOC pool of the orchards of Uttarakhand state. <i>P. malus</i> had the mitigation potential of 2.71 which indicates that it can have more than double SOC pool as compared to <i>P. guava</i>. SOC Pool in the grasslands was 75.76 t ha<SUP>-1</SUP>.

Climatic and geomorphic controls on the erosion of terrestrial biomass from subtropical mountain forest

Erosion of particulate organic carbon (POC) occurs at very high rates in mountain river catchments, yet the proportion derived recently from atmospheric CO2 in the terrestrial biosphere (POCnon‐fossil) remains poorly constrained. Here we examine the transport of POCnon‐fossil in mountain rivers of Taiwan and its climatic and geomorphic controls. In 11 catchments we have combined previous geochemical quantification of POC source (accounting for fossil POC from bedrock), with measurements of water discharge (Qw) and suspended sediment concentration over 2 years. In these catchments, POCnon‐fossil concentration (mg L−1) was positively correlated with Qw, with enhanced loads at high flow attributed to rainfall driven supply of POCnon‐fossil from forested hillslopes. This climatic control on POCnon‐fossil transport was moderated by catchment geomorphology: the gradient of a linear relation of POCnon‐fossil concentration and Qw increased as the proportion of steep hillslopes (&gt;35°) in the catchment increased. The data suggest enhanced supply of POCnon‐fossil by erosion processes which act most efficiently on the steepest sections of forest. Across Taiwan, POCnon‐fossil yield was correlated with suspended sediment yield, with a mean of 21 ± 10 tC km−2 yr−1. At this rate, export of POCnon‐fossil imparts an upper bound on the time available for biospheric growth, of ∼800 yr. Over longer time periods, POCnon‐fossil transferred with large amounts of clastic sediment can contribute to sequestration of atmospheric CO2 if buried in marine sediments. Our results show that this carbon transfer should be enhanced in a wetter and stormier climate, and the rates moderated on geological timescales by the regional tectonic setting.

Sustaining agronomic productivity and quality of a Vertisolic soil (Vertisol) under soybean–safflower cropping system in semi-arid central India

Srinivasarao, Ch., Venkateswarlu, B., Lal, R., Singh, A. K., Kundu, S., Vittal, K. P. R., Sharma, S. K., Sharma, R. A., Jain, M. P. and Chary, G. R. 2012. Sustaining agronomic productivity and quality of a Vertisolic Soil (Vertisol) under soybean-safflower cropping system in semi-arid central India. Can. J. Soil Sci. 92: 771–785. Enrichment of soil organic carbon (SOC) stocks through sequestration of atmospheric CO2 in agricultural soils is important because of its impacts on improving soil quality and agronomic production, and also for adaptation to and mitigation of climate change. Thus, a 15-yr soil fertility management experiment was conducted in the semi-arid tropical region of central India to evaluate the impact of crop residue C input on soybean (Glycine max L.)–safflower (Carthamus tinctorius L.) cropping sequence and SOC sequestration in soils of Vertisolic order (Vertisols). Retention of crop residues of soybean/safflower, and application of farmyard manure (FYM) at 6 Mg (t) ha−1 alone or in co...

Passive Sequestration of Atmospheric CO2 through Coupled Plant-Mineral Reactions in Urban soils

Photosynthetic removal of CO(2) from the atmosphere is an important planetary carbon dioxide removal mechanism. Naturally, an amount equivalent to all atmospheric carbon passes through the coupled plant-soil system within 7 years. Plants cycle up to 40% of photosynthesized carbon through their roots, providing a flux of C at depth into the soil system. Root-exuded carboxylic acids have the potential to supply 4-5 micromoles C hr(-1)g(-1) fresh weight to the soil solution, and enhance silicate mineral weathering. Ultimately, the final product of these root-driven processes is CO(2), present in solution as bicarbonate. This combines with Ca liberated by corrosion associated with silicate mineral weathering to enter the soil-water system and to produce pedogenic calcium carbonate precipitates. Combining understanding of photosynthesis and plant root physiology with knowledge of mineral weathering provides an opportunity to design artificial soils or to plan land use in ways that maximize removal and sequestration of atmospheric CO(2) through artificially enhanced pedogenic carbonate precipitation. This process requires relatively low energy and infrastructure inputs. It offers a sustainable carbon dioxide removal mechanism analogous to the use of constructed wetlands for the passive remediation of contaminated waters, and is likely to achieve wide public acceptance.

Critical carbon inputs to maintain soil organic carbon stocks under long‐term finger‐millet (Eleusine coracana [L.] Gaertn.) cropping on Alfisols in semiarid tropical India

AbstractEnrichment of soil organic carbon (SOC) stocks through sequestration of atmospheric CO2 in agricultural soils is important because of its impacts on adaptation to and mitigation of climate change while also improving crop productivity and sustainability. In a long‐term fertility experiment carried out over 27 y under semiarid climatic condition, we evaluated the impact of crop‐residue C inputs through rainfed fingermillet (Eleusine coracana [L.] Gaertn.) cropping, fertilization, and manuring on crop yield sustainability and SOC sequestration in a Alfisol soil profile up to a depth of 1 m and also derived the critical value of C inputs for maintenance of SOC. Five treatments, viz., control, farmyard manure (FYM) 10 Mg ha–1, recommended dose of NPK (50 : 50 : 25 kg N, P2O5, K2O ha–1), FYM 10 Mg ha–1 + 50% recommended dose of NPK, and FYM 10 Mg ha–1 + 100% recommended dose of NPK imposed in a randomized block design replicated four times. Application of FYM alone or together with mineral fertilizer resulted in a higher C input and consequently built up a higher C stock. After 27 y, higher profile SOC stock (85.7 Mg ha–1), C build up (35.0%), and C sequestration (15.4 Mg C ha–1) was observed with the application of 10 Mg FYM ha–1 along with recommended dose of mineral fertilizer and these were positively correlated with cumulative C input and well reflected in sustainable yield index (SYI). For sustenance of SOC level (zero change due to cropping) a minimum quantity of 1.13 Mg C is required to be added per hectare per annum as inputs. While the control lost C, the application of mineral fertilizer served to maintain the priori C stock. Thus, the application of FYM increased the C stock, an effect which was even enhanced by additional amendment of mineral fertilizer. We conclude that organic amendments contribute to C sequestration counteracting climate change and at the same time improve soil fertility in the semiarid regions of India resulting in higher and more stable yields.

Long‐Term Effects of Soil Fertility Management on Carbon Sequestration in a Rice–Lentil Cropping System of the Indo‐Gangetic Plains

Enrichment of soil organic carbon (SOC) stocks through sequestration of atmospheric CO2 in agricultural soils is important because of its impacts on soil quality, agronomic production, and adaptation to and mitigation of climate change. In a 21‐yr field experiment conducted under subhumid tropical conditions in India, the impacts of crop residue C inputs were assessed for the rice (Oryza sativa L.)–lentil (Lens esculenta Moench) cropping sequence. These impacts were evaluated in an experiment involving mineral fertilizers and manuring treatments on crop yield sustainability with reference to critical biomass requirements for maintenance of SOC in an Inceptisol. Application of farmyard manure (FYM) without and with mineral fertilizers increased C input and SOC concentration and stock. In comparison with the control, the 100% organic (FYM) treatment had significantly higher profile SOC (27.5 Mg ha−1), and more C build up (55.0%) and C sequestration (6.6 Mg C ha−1) to 1‐m depth vis‐à‐vis the antecedent values in 1986. These parameters were also higher in 100% FYM treatment at a rate providing equivalent amount of the recommended dose of N followed by conjunctive use of FYM and mineral fertilizers. The SOC stock and rate of sequestration were positively correlated with cumulative C input, and with sustainable yield index (SYI) of upland rice and lentil. Higher grain yield (1.95 and 1.04 Mg ha−1 of rice and lentil, respectively) was obtained with the application of 50% organic (FYM)+50% recommended dose of fertilizer (RDF). In comparison, higher SOC sequestration rate was measured with the application of 100% organic (FYM). For every Mg increase in SOC stock in the root zone there was 0.16 and 0.18 Mg ha−1yr−1 yield increase of rice and lentil, respectively. For maintaining a stable SOC level (zero change due to cropping), a minimum quantity of 2.47 Mg C ha−1 yr−1 is required for this soil, climate, cropping system, and fertilization treatments. To achieve this quantity of C, 7.1 Mg of biomass is required to be produced every year vs. average rice and lentil yields of 1.6 and 0.7 Mg ha−1, respectively. The sole application of mineral fertilizers at 50 or 100% of the RDF did not maintain the SOC stock. Thus, application of FYM (or other organics) in conjunction with mineral fertilizers is essential to maintaining and enhancing the SOC stock in the rice‐based cropping systems.