Biochar and plant growth promoting rhizobacteria effects on switchgrass (Panicum virgatum cv. Cave-in-Rock) for biomass production in southern Québec depend on soil type and location

Switchgrass (Panicum virgatum L.) is a fast growing native C₄ perennial and a lignocellulosic biomass crop for North America. In combination with biochar, an active plant growth promoting rhizobacterial (PGPR) community can contribute to the long-term sequestration of carbon in soil, fix nitrogen, and enhance the availability of other nutrients to plants. Biochar and PGPR have the potential to improve grass biomass production, but they have not been tested together under high-latitude temperate zone field conditions. Therefore, the objective of this three-year field study was to determine whether there were effects on biomass yield and yield components of switchgrass (cv. Cave-in-Rock) due to a rhizobacterium that was able to mobilize soil phosphorus (Pseudomonas rhodesiae), a bacterial consortium that was able to supply nitrogen (Paenibacillus polymyxa, Rahnella sp., and Serrati sp.), and pine wood chip biochar applied as a soil amendment at 20 Mg ha⁻¹. The incorporation of biochar, or inoculation with the N-fixing consortium, and the combined inoculation of the experimental bacteria had positive effects on switchgrass height. At a loam soil site in Sainte-Anne-de-Bellevue, Québec, when nitrogen fertilizer was not applied, the addition of biochar had a positive effect on stand count (tillers m⁻¹ row). On the sandy soil in Sainte-Anne-de-Bellevue, when biochar was applied with 100 kg N ha⁻¹, biomass yield increased over the control but did not provide additional benefits over plots receiving only 50 kg N ha⁻¹. It remains unclear whether or not the increased C sequestration of this management system justifies increased N fertilizer usage.     

The economic value of biochar in crop production and carbon sequestration

This paper estimates the economic value of biochar application on agricultural cropland for carbon sequestration and its soil amendment properties. In particular, we consider the carbon emissions avoided when biochar is applied to agricultural soil, instead of agricultural lime, the amount of carbon sequestered, and the value of carbon offsets, assuming there is an established carbon trading mechanism for biochar soil application. We use winter wheat production in Eastern Whitman County, Washington as a case study, and consider different carbon offset price scenarios and different prices of biochar to estimate a farm profit. Our findings suggest that it may be profitable to apply biochar as a soil amendment under some conditions if the biochar market price is low enough and/or a carbon offset market exists.     

Influence of fast pyrolysis temperature on biochar labile fraction and short-term carbon loss in a loamy soil

Production of bio-oil, gas and biochar from pyrolysis of biomass is considered a promising technology for combined production of bioenergy and recalcitrant carbon (C) suitable for sequestration in soil. Using a fast pyrolysis centrifuge reactor (PCR) the present study investigated the relation between fast pyrolysis of wheat straw at different reactor temperatures and the short-term degradability of biochar in soil. After 115 days incubation 3-12% of the added biochar-C had been emitted as CO₂. On average, 90% of the total biochar-C loss occurred within the first 20 days of the experiment, emphasizing the importance of knowing the biochar labile fraction when evaluating a specific biochars C sequestration potential. The pyrolysis temperature influenced the outputs of biochar, bio-oil and syngas significantly, as well as the stability of the biochar produced. Contrary to slow pyrolysis a fast pyrolysis process may result in incomplete conversion of biomass due to limitations to heat transfer and kinetics. In our case chemical analysis of the biochars revealed unconverted cellulosic and hemicellulosic fractions, which in turn were found to be proportional with the short-term biochar degradation in soil. As these labile carbohydrates are rapidly mineralized, their presence lowers the biochar-C sequestration potential. By raising the pyrolysis temperature, biochar with none or low contents of these fractions can be produced, but this will be on the expense of the biochar quantity. The yield of CO₂ neutral bio-oil is the other factor to optimize when adjusting the pyrolysis temperature settings to give the overall greatest climate change mitigation effect.     

Biochar-mediated reductions in greenhouse gas emissions from soil amended with anaerobic digestates

This investigation examines nitrous oxide (N₂O) fluxes from soil with simultaneous amendments of anaerobic digestates and biochar. The main source of anthropogenic emissions of N₂O is agriculture and in particular, manure and slurry application to fields. Anaerobic digestates are increasingly used as a fertiliser and interest is growing in their potential as sources of N₂O via nitrification and denitrification. Biochar is a stable product of pyrolysis and may affect soil properties such as cation exchange capacity and water holding capacity. Whilst work has been conducted on the effects of biochar amendment on N₂O emissions in soils fertilised with mineral fertilisers and raw animal manures, little work to date has focused on the effects of biochar on nitrogen transformations within soil amended with anaerobic digestates. The aim of the current investigation was to quantify the effects of biochar application on ammonification, nitrification and N₂O fluxes within soil amended with three anaerobic digestates derived from different feedstocks. A factorial experiment was undertaken in which a sandy loam soil (Dunnington Heath series) was either left untreated, or amended with three different anaerobic digestates and one of three biochar treatments; 0%, 1% or 3%. Nitrous oxide emissions were greatest from soil amended with anaerobic digestate originating from a maize feedstock. Biochar amendment reduced N₂O emissions from all treatments, with the greatest effect observed in treatments with maximum emissions. The degree of N₂O production and efficacy of biochar amelioration of gas emissions is discussed in context of soil microbial biomass and soil available carbon.     

Gasification biochar as a valuable by-product for carbon sequestration and soil amendment

Thermal gasification of various biomass residues is a promising technology for combining bioenergy production with soil fertility management through the application of the resulting biochar as soil amendment. In this study, we investigated gasification biochar (GB) materials originating from two major global biomass fuels: straw gasification biochar (SGB) and wood gasification biochar (WGB), produced by a Low Temperature Circulating Fluidized Bed gasifier (LT-CFB) and a TwoStage gasifier, respectively, optimized for energy conversion. Stability of carbon in GB against microbial degradation was assessed in a short-term soil incubation study and compared to the traditional practice of direct incorporation of cereal straw. The GBs were chemically and physically characterized to evaluate their potential to improve soil quality parameters. After 110 days of incubation, about 3% of the added GB carbon was respired as CO₂, compared to 80% of the straw carbon added. The stability of GB was also confirmed by low H/C and O/C atomic ratios with lowest values for WGB (H/C 0.12 and O/C 0.10). The soil application of GBs exhibited a liming effect increasing the soil pH from ca 8 to 9. Results from scanning electron microscopy and BET analyses showed high porosity and specific surface area of both GBs, indicating a high potential to increase important soil quality parameters such as soil structure, nutrient and water retention, especially for WGB. These results seem promising regarding the possibility to combine an efficient bioenergy production with various soil aspects such as carbon sequestration and soil quality improvements.     

Black carbon sequestration as an alternative to bioenergy

Most policy and much research concerning the application of biomass to reduce global warming gas emissions has concentrated either on increasing the Earth's reservoir of biomass or on substituting biomass for fossil fuels, with or without CO₂ sequestration. Suggested approaches entail varied risks of impermanence, delay, high costs, and unknowable side-effects. An under-researched alternative approach is to extract from biomass black (elemental) carbon, which can be permanently sequestered as mineral geomass and may be relatively advantageous in terms of those risks. This paper reviews salient features of black carbon sequestration and uses a high-level quantitative model to compare the approach with the alternative use of biomass to displace fossil fuels. Black carbon has been demonstrated to produce significant benefits when sequestered in agricultural soil, apparently without bad side-effects. Black carbon sequestration appears to be more efficient in general than energy generation, in terms of atmospheric carbon saved per unit of biomass; an exception is where biomass can efficiently displace coal-fired generation. Black carbon sequestration can reasonably be expected to be relatively quick and cheap to apply due to its short value chain and known technology. However, the model is sensitive to several input variables, whose values depend heavily on local conditions. Because characteristics of black carbon sequestration are only known from limited geographical contexts, its worldwide potential will not be known without multiple streams of research, replicated in other contexts.     

生物炭应用研究进展

生物炭在碳封存剂、土壤改良剂等方面具有重要的应用价值和现实意义,是开发利用生物质能的方向之一,有利于减轻温室气体效应和农业生产对农药、化肥以及化石能源或原料的依赖。文章分析了生物炭的特性,介绍了国内外生物炭燃料研究现状,探讨了生物炭在农业、能源、环境保护、养殖、副产品等方面的影响,并与秸秆还田进行了对比,指出下一步的发展方向,以期为生物炭技术创新与产业化发展提供参考。     

Prospective life cycle carbon abatement for pyrolysis biochar systems in the UK

Life cycle assessment (LCA) of slow pyrolysis biochar systems (PBS) in the UK for small, medium and large scale process chains and ten feedstocks was performed, assessing carbon abatement and electricity production. Pyrolysis biochar systems appear to offer greater carbon abatement than other bioenergy systems. Carbon abatement of 0.7–1.3 t CO₂ equivalent per oven dry tonne of feedstock processed was found. In terms of delivered energy, medium to large scale PBS abates 1.4–1.9 t CO₂e/MWh, which compares to average carbon emissions of 0.05–0.30 t CO₂e/MWh for other bioenergy systems. The largest contribution to PBS carbon abatement is from the feedstock carbon stabilised in biochar (40–50%), followed by the less certain indirect effects of biochar in the soil (25–40%)—mainly due to increase in soil organic carbon levels. Change in soil organic carbon levels was found to be a key sensitivity. Electricity production off-setting emissions from fossil fuels accounted for 10–25% of carbon abatement. The LCA suggests that provided 43% of the carbon in the biochar remains stable, PBS will out-perform direct combustion of biomass at 33% efficiency in terms of carbon abatement, even if there is no beneficial effect upon soil organic carbon levels from biochar application.     

Sustainable gasification–biochar systems? A case-study of rice-husk gasification in Cambodia,Part I: Context,chemical properties,environmental and health and safety issues

Biochar is a carbon- and energy-rich porous material produced through slow pyrolysis of biomass, which has been proposed as a way of storing carbon in soils for the long-term (centurial to millennial timescales) but its production incurs an energy penalty. Gasification of rice husks at paddy mills combines the benefits of reasonably efficient delivery of energy with a reasonably high carbon char and ash mixture. The ca. 35% carbon content of the rice husk char is possibly a consequence of the protective shield of silica, preventing full exposure of the biomass to oxidation in the gasifier. In this paper we undertake an evaluation of the sustainability of this ‘gasification–biochar system’ (GBS) in Cambodia, where a rapid deployment of gasifiers is underway. In Part I, we describe the context and analyse (some of) the physical and chemical properties of the biochar. While there are some potential health, safety and environmental issues that require further analysis, they are problems that could be readily addressed in further research and appear to be resolvable. In Part II, we present results from field trials, summarise the data on the carbon abatement of the gasification–biochar system and present some preliminary economic data.     

Impacts of soil management on root characteristics of switchgrass

One approach to reducing the concentration of atmospheric carbon dioxide, which is a dominant greenhouse gas, is to develop renewable energy sources from biofuel crops. Switchgrass, (Panicum virgatum L.) as an energy crop, can partly mitigate potential global warming by supplementing fossil fuels and sequestering carbon (C). Although switchgrass grown for energy may impact C sequestration via the input of root biomass, information on the impact of soil management on switchgrass root growth is extremely limited. We determined the influence of row spacing, nitrogen (N) rate, switchgrass cultivar, and soil type on switchgrass root characteristics. Roots were mainly distributed in the surface soil (0–15 cm), and were 90.4 and 68.2% of the total in the intrarow and interrow profile, respectively. Nitrogen application altered root N but not C concentration, implying that any increase in C sequestration by switchgrass roots will be due to increased root biomass rather than increased C concentration. Root weight density generally decreased in the interrow with wider row width, and N application generally did not affect root weight density. Root weight density in the Pacolet soil was higher than in the other four soils, and root density was 4.1 times higher in the Pacolet soil than in the Norfolk soil. Root mass in the Pacolet soil (36,327 kg ha⁻¹) was 2.7 times greater than that found in the Norfolk soil (13,204 kg ha⁻¹) within 150 cm of the soil surface. Differences in root characteristics were found among cultivars: root weight density with ‘Cave-in-Rock’ switchgrass was 29.4 and 47.6% higher than ‘Alamo’ and ‘Kanlow’, respectively. Variations in switchgrass root biomass production owing to soil type and cultivar suggest that site and cultivar selection will be important determinants of C sequestration by switchgrass roots. A potential benefit of switchgrass is the reduced loss of nutrients associated with non-point pollution, owing to its deep root system that may extend 330 cm below the soil surface.     

Negative carbon intensity of renewable energy technologies involving biomass or carbon dioxide as inputs

Conventional fossil fuel-based energy technologies can achieve efficiency in energy conversion but they are usually completely inefficient in carbon conversion because they generate significant CO₂ emissions to the atmosphere per unit energy converted. In contrast, some renewable energy technologies characterized by negative carbon intensity can simultaneously achieve efficiency in the conversion of energy and in the conversion of carbon. These carbon negative renewable energy technologies can generate useful energy and remove CO₂ from the atmosphere, either by direct capture and recycling of atmospheric CO₂ or indirectly, by involving biofuels. Interestingly, the deployment of carbon negative renewable energy technologies can offset carbon emissions from conventional fossil fuel-based energy technologies and thus reduce the overall carbon intensity of energy systems.The current review analyzes two groups of renewable energy technologies involving biomass or CO₂ as inputs. The discussions focus on useful techniques which enable to achieve negative carbon intensity of energy while being technologically promising in near-term as well as cost-effective. These analyzes include advanced carbon sequestration concepts such as soil carbon sequestration and CO₂ recycling to useful C-rich products such as fuels and fertilizers. The 'drop-in' of renewable energy is achieved by allowing bioenergy and renewable energies in the form of renewable electricity, renewable thermal energy, solar energy, renewable hydrogen, etc. The carbon negative renewable energy technologies are analyzed and perspectives and constraints of each technology are expounded.     

我国生物质热解特性及工艺研究进展

我国秸秆和畜禽粪便等生物质原料的产量非常丰富,用这些量大而来源广泛的生物质原料热解制取生物炭,可用于燃料,替代化石能源,还可用作吸附剂以及土壤改良剂,用途广泛。本文从原料的种类,热解技术,工艺过程,以及影响因素等四方面,对生物质热解特性以及制取生物炭工艺研究现状进行梳理、分析与研究。依据现阶段的研究结果,阐明未来应在秸秆原料基础特性、秸秆热解特性、优化不同地域间的秸秆热解工艺以及畜禽粪便热解制炭等方面着手进行深入研究。     

Beneficial effects of biochar application to contaminated soils on the bioavailability of Cd,Pb and Zn and the biomass production of rapeseed (Brassica napus L.)

Phytoremediation of soils contaminated by heavy metals was tested by liming (CaCO₃) or adding biochar (1%, 5% and 10%, mass fraction) and by growing rapeseed (Brassica napus L.), a common bioenergy crop. Bioavailable metal concentrations (0.01 mol L⁻¹ CaCl₂ extraction) decreased with increasing concentrations of biochar amendment. The reduction reached 71%, 87% and 92% for Cd, Zn and Pb respectively in the presence of 10% biochar. Twelve weeks after sowing, all plants cultivated on the untreated soil and on the soil amended by biochar at 1% had died, while the plants grew normally on the soil that had the other treatments. Compared to liming, treatment with 10% biochar proved equally efficient in reducing metal concentrations in shoots but the biomass production tripled as a result of the soil fertility improvement. Thus, in addition to C sequestration, the incorporation of biochar into metal-contaminated soils could make it possible to cultivate bioenergy crops without encroaching on agricultural lands. Although additional investigations are needed, we suggest that the harvested biomass might in turn be used as feedstock for pyrolysis to produce both bioenergy and new biochar, which could contribute further to the reduction of CO₂ emission.     

Production and characterization of bio-oil and biochar from rapeseed cake

New and renewable fuels are the major alternatives to conventional fossil fuels. Biomass in the form of agricultural residues is becoming popular among new renewable energy sources, especially given its wide potential and abundant usage. Pyrolysis is the most important process among the thermal conversion processes of biomass. In this study, the production of bio-oil and biochar from rapeseed cake obtained by cold extraction pressing was investigated and the various characteristics of biochar and bio-oil acquired under static atmospheric conditions were identified. The biochar obtained are carbon rich, with high heating value and relatively pollution-free potential solid biofuel. The bio-oil product was presented as an environmentally friendly green biofuel candidate.     

Decentralised carbon footprint analysis for opting climate change mitigation strategies in India

Carbon footprint (CF) refers to the total amount of carbon dioxide and its equivalents emitted due to various anthropogenic activities. Carbon emission and sequestration inventories have been reviewed sector-wise for all federal states in India to identify the sectors and regions responsible for carbon imbalances. This would help in implementing appropriate climate change mitigation and management strategies at disaggregated levels. Major sectors of carbon emissions in India are through electricity generation, transport, domestic energy consumption, industries and agriculture. A majority of carbon storage occurs in forest biomass and soil. This paper focuses on the statewise carbon emissions (CO₂, CO and CH₄), using region specific emission factors and statewise carbon sequestration capacity. The estimate shows that CO₂, CO and CH₄ emissions from India are 965.9, 22.5 and 16.9 Tg per year, respectively. Electricity generation contributes 35.5% of total CO₂ emission, which is followed by the contribution from transport. Vehicular transport exclusively contributes 25.5% of total emission. The analysis shows that Maharashtra emits higher CO₂, followed by Andhra Pradesh, Uttar Pradesh, Gujarat, Tamil Nadu and West Bengal. The carbon status, which is the ratio of annual carbon storage against carbon emission, for each federal state is computed. This shows that small states and union territories (UT) like Arunachal Pradesh, Mizoram and Andaman and Nicobar Islands, where carbon sequestration is higher due to good vegetation cover, have carbon status >1. Annually, 7.35% of total carbon emissions get stored either in forest biomass or soil, out of which 34% is in Arunachal Pradesh, Madhya Pradesh, Chhattisgarh and Orissa.     

Carbon-negative biofuels

Current Kyoto-based approaches to reducing the earth's greenhouse gas problem involve looking for ways to reduce emissions. But these are palliative at best, and at worst will allow the problem to get out of hand. It is only through sequestration of atmospheric carbon that the problem can be solved. Carbon-negative biofuels represent the first potentially huge assault on the problem, in ways that are already technically feasible and practicable. The key to carbon negativity is to see it not as technically determined but as an issue of strategic choice, whereby farmers and fuel producers can decide how much carbon to return to the soil. Biochar amendment to the soil not only sequesters carbon but also enhances the fertility and vitality of the soil. The time is approaching when biofuels will be carbon negative by definition, and, as such, they will sweep away existing debates over their contribution to the solution of global warming.     

Review and model-based analysis of factors influencing soil carbon sequestration under hybrid poplar

The potential for soil carbon (C) sequestration under short-rotation woody crops, like hybrid poplar (Populus spp.), is a significant uncertainty in our understanding of how managed tree plantations might be used to partially offset increasing atmospheric CO₂ concentrations. Through development of a multi-compartment model, we reviewed information from studies on hybrid poplar and analyzed the potential impact of changes in plant traits and nitrogen (N) fertilization on soil C storage. For a hypothetical setting in the southeastern U.S.A., and starting from soils that are relatively depleted in organic matter (2.5 kg C m⁻²), the model predicted an increase in mineral soil C stocks (1.7 kg C m⁻²) over four 7-year rotations of hybrid poplar. However, at the end of the fourth rotation, both cumulative soil C gains and annual rates of soil C accrual (23-93 g C m⁻² yr⁻¹) varied widely depending on fertilization rate, biomass yield, and rates of dead root decomposition (three factors that were examined in a factorial model-based experiment). Our analysis indicated that processes linked to genetically modifiable poplar traits (aboveground biomass production, belowground C allocation, root decomposition) are potential controls on soil C sequestration. Key measures of model performance were sensitive to how aboveground biomass production responded to N fertilization. Site specific properties that were independent of plant traits were also important to predicted soil C accumulation and point to possible genotype x site interactions that may explain contradictory data from both empirical and theoretical studies of C sequestration under hybrid poplar plantations.     

Catalytic decomposition of methane over enteromorpha prolifera-based hierarchical porous biochar

Biochar is a potential catalyst for methane decomposition (CMD) owing to its environmental-friendly and application prospects. In this work, the hierarchical porous biochar was prepared by carbonization and H₃PO₄ activation using Enteromorpha prolifera (EP) as precursor, respectively. The results show that when the ratio of H₃PO₄/EP is 1.5, the maximum CH₄ conversion is 46%, along with hydrogen output of 396 mmol/g_cat, which is 5.8 times as that of the unactivated biochar. The characterization results by XPS, Raman, SEM and HRTEM indicate that P element is inserted in carbon layer in the form of C–O–P, resulting in lattice distortion of carbon layer and larger defect density, and C–O–P plays a dominant role in initial CH₄ conversion. The mesopores formed by H₃PO₄ activation alleviate the influence of the deposited carbon on the catalyst and decrease the deactivation rate, thereby exhibiting better performance in CMD.     

Carbon sequestration by forestation across China: Past, present, and future

Plantation forests are the most effective and ecologically friendly way of absorbing CO₂ and increasing carbon sinks in terrestrial ecosystems; mitigating global warming and beginning ecological restoration. China's forestation rate is the highest in the world, and contributes significantly to the nation's carbon sequestration. We have applied empirical growth curves, scale transformations, field sampling plots, and forest inventory data, to our carbon estimation model, to analyze the carbon sequestration in living biomass and soil organic carbon pools in past and current plantations. Furthermore, the potential carbon sinks of future plantations, 2010-2050, have been simulated. From 1950 to the present, plantations in China sequestered 1.686 Pg C by net uptake into biomass and emissions of soil organic carbon. The carbon stock of China's present plantations was 7.894 Pg C, including 21.4% of the total sequestration as forest biomass and 78.6% as SOC. We project that China's forestation activities will continue to net sequester carbon to a level of 3.169 Pg C by 2050, and that carbon stock in plantations will amount to 10.395 Pg C. Spatial patterns of carbon sequestration were dissimilar to those of planting area. On the basis of area, carbon sequestrations were highest in North China, while changes were generally greatest in the Northeast and Southwest regions.