Biochar is the carbon-rich product obtained when biomass (such as wood, manure or crop residues) is heated in a closed container with little or no available air. It can be used to improve agriculture and the environment in several ways, and its stability in soil and superior nutrient-retention properties make it an ideal soil amendment to increase crop yields. Biochar has been shown to serve as a habitat for microorganisms and increase soil microbial diversity, reduce emissions of non-CO2 greenhouse gasses from soil (notably CH4, NOx), reduce soil nutrient leaching (notably N, P, and K), and increase soil water retention. In addition to agronomic benefits, biochar sequestration, in combination with sustainable biomass production, can be carbon-negative and therefore used to actively remove carbon dioxide from the atmosphere, with major implications for mitigation of climate change. Biochar production can also be combined with bioenergy production through the use of the gases and liquids that are given off in the pyrolysis process.
Biochar impacts to soil
NOTE: Not all biochars and not all soils behave the same way! The above table is a representation of what SOME biochars can do to SOME soils. Flux Farm is in the process of determining how biochar interacts with soils commonly found in the Intermountain West.
Sustainable Biochar to Mitigate Global Climate Change
Production of biochar (the carbon (C)-rich solid formed by pyrolysis of biomass) and its storage in soils have been suggested as a means of abating climate change by sequestering carbon, while simultaneously providing energy and increasing crop yields. Substantial uncertainties exist, however, regarding the impact, capacity and sustainability of biochar at the global level. In this paper we estimate the maximum sustainable technical potential of biochar to mitigate climate change. Annual net emissions of carbon dioxide (CO2), methane and nitrous oxide could be reduced by a maximum of 1.8 Pg CO2-C equivalent (CO2-Ce) per year (12% of current anthropogenic CO2-Ce emissions; 1 Pg=1 Gt), and total net emissions over the course of a century by 130 Pg CO2-Ce, without endangering food security, habitat or soil conservation. Biochar has a larger climate-change mitigation potential than combustion of the same sustainably procured biomass for bioenergy, except when fertile soils are amended while coal is the fuel being offset. FIND ARTICLE HERE
Biochar, Climate Change, and Soil: A Review to Guide Future Research
Biochar is the charred by-product of biomass pyrolysis, the heating of plant-derived material in the absence of oxygen in order to capture combustible gases. The objective of this report was to review and evaluate published studies with regard to what evidence and arguments currently exist that assess the application of biochar to soil to a) sequester carbon and b) produce secondary agronomic benefits. Current analyses suggest that there is global potential for annual sequestration of atmospheric CO2 at the billion-tonne scale (109 t yr-1) within 30 years. So far, however, the underlying published evidence arises mainly from small-scale studies that do not currently support generalization to all locations and all types of biochar.
From the available published and peer-reviewed literature the following general findings can be made for eight key questions. It is noted that for each of these key questions there remains major research questions that require the attention of researchers. This summary provides these outstanding research issues along side the major findings:
1) Is all biochar the same? 2) How stable is it? 3) Is it safe to use? 4) What are the agronomic benefits? 5) Is it economically viable? 6) What are the environmental and societal benefits? 7) Are the benefits of biochar in mitigating greenhouse gases widely accepted? 8) What are the research gaps and future challenges?
Energy Balance and Emissions Associated with Biochar Sequestration and Pyrolysis Bioenergy Production
The implications for greenhouse gas emissions of optimizing a slow pyrolysis-based bioenergy system for biochar and energy production rather than solely for energy production were assessed. Scenarios for feedstock production were examined using a life-cycle approach. We considered both purpose grown bioenergy crops (BEC) and the use of crop wastes (CW) as feedstocks. The BEC scenarios consider switching from production of winter wheat to miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum L.), or forage corn (Zea mays L.), while the CW scenarios consider both corn stover and winter wheat straw as feedstocks. FIND ARTICLE HERE
Mycorrhizal Responses to Biochar in Soil - Concepts and Mechanisms
Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both biochar and mycorrhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon sequestration and hence mitigation of global climate change. As both biochar and mycorrhizal associations are subject to management, understanding and exploiting interactions between them could be advantageous. Here we focus on biochar effects on mycorrhizal associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four mechanisms by which biochar could influence mycorrhizal abundance and/or functioning.
These mechanisms are (in decreasing order of currently available evidence supporting them): (a) alteration of soil physico-chemical properties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant–fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses. FIND ARTICLE HERE
Biochar Sequestration in Terrestrial Ecosystems - A Review
The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. Apart from positive effects in both reducing emissions and increasing the sequestration of greenhouse gases, the production of bio-char and its application to soil will deliver immediate benefits through improved soil fertility and increased crop production. Conversion of biomass C to bio-char C leads to sequestration of about 50% of the initial C compared to the low amounts retained after burning (3%) and biological decomposition (<10–20% after 5–10 years), therefore yielding more stable soil C than burning or direct land application of biomass. This efficiency of C conversion of biomass to bio-char is highly dependent on the type of feedstock, but is not significantly affected by the pyrolysis temperature (within 350–500 C common for pyrolysis).
Existing slash-and burn systems cause significant degradation of soil and release of greenhouse gases and opportunities may exist to enhance this system by conversion to slash-and-char systems. Our global analysis revealed that up to 12% of the total anthropogenic C emissions by land use change (0.21 Pg C) can be off-set annually in soil, if slash-and-burn is replaced by slash-and-char. Agricultural and forestry wastes such as forest residues, mill residues, field crop residues, or urban wastes add a conservatively estimated 0.16 PgCyr^1.
Biofuel production using modern biomass can produce a bio-char by-product through pyrolysis which results in 30.6 kgC sequestration for each GJ of energy produced. Using published projections of the use of renewable fuels in the year 2100, bio-char sequestration could amount to 5.5–9.5 PgCyr^1 if this demand for energy was met through pyrolysis, which would exceed current emissions from fossil fuels (5.4 PgC yr^1). Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable. FIND ARTICLE HERE
The Charcoal Vision
Processing biomass through a distributed network of fast pyrolyzers may be a sustainable platform for producing energy from biomass.
This article offers a vision for an integrated agricultural biomass-bioenergy system that could make a significant contribution to domestic energy production while mitigating global climate change and enhancing soil and water quality.
Many agricultural scientists, farmers, and conservationists are concerned about the potential impacts associated with industrialized biomass harvesting systems. Poorly designed agricultural systems would require the input of massive amounts of fertilizer and water, further reducing the net-energy gain from biofuels production.
The author illustrates the importance of proper crop residue management to ensure soil structure and shifts the debate from "how much can be harvested without doing too much damage" to "how to design integrated agricultural systems so that both food and bioenergy crops can be sustainably harvested."
Much of the article focuses on the prospects of fast pyrolyzers that rapidly heat dry biomass to 500 °C thermally transforming the biomass into bio-oil (60% of mass), syngas (20% of mass), and charcoal (20% of mass). The energy required to operate the fast pyrolyzer amounts to 75% of the generated syngas. The produced bio-oil can be burned to generate heat or further processed into transportation fuels. The charcoal could also be used to generate energy; however, application of the charcoal co-product to soils may be key to sustainability.
The economics of scalable fast pyrolyzers are discussed along with potential obstacles and opportunities for carbon sequestration credits. FIND ARTICLE HERE
Impact of Biochar Amendments on the Quality of a Typical Midwestern Agricultural Soil
Biochar, a co-product of thermochemical conversion of lignocellulosic materials into advanced biofuels, may be used as a soil amendment to enhance the sustainability of biomass harvesting. We investigated the impact of biochar amendments (0, 5, 10, and 20 g-biochar kg− 1 soil) on the quality of a Clarion soil (Mesic Typic Hapludolls), collected (0–15 cm) in Boone County, Iowa. Repacked soil columns were incubated for 500 days at 25 °C and 80% relative humidity. On week 12, 5 g of dried and ground swine manure was incorporated into the upper 3 cm of soil for half of the columns. Once each week, all columns were leached with 200 mL of 0.001 M CaCl2. Soil bulk density increased with time for all columns and was significantly lower for biochar amended soils relative to the un-amended soils. The biochar amended soils retained more water at gravity drained equilibrium (up to 15%), had greater water retention at − 1 and −5 bars soil water matric potential, (13 and 10% greater, respectively), larger specific surface areas (up to 18%), higher cation exchange capacities (up to 20%), and pH values (up to 1 pH unit) relative to the un-amended controls. No effect of biochar on saturated hydraulic conductivity was detected. The biochar amendments significantly increased total N (up to 7%), organic C (up to 69%), and Mehlich III extractable P, K, Mg and Ca but had no effect on Mehlich III extractable S, Cu, and Zn. The results indicate that biochar amendments have the potential to substantially improve the quality and fertility status of Midwestern agricultural soils. FIND ARTICLE HERE
Biochar Impact on Nutrient Leaching From a Midwestern Agricultural Soil
Application of biochar to highly weathered tropical soils has been shown to enhance soil quality and decrease leaching of nutrients. Little, however, is known about the effects of biochar applications on temperate region soils. Our objective was to quantify the impact of biochar on leaching of plant nutrients following application of swine manure to a typical Midwestern agricultural soil. Repacked soil columns containing 0, 5, 10, and 20 g-biochar kg− 1-soil, with and without 5 g kg− 1 of dried swine manure were leached weekly for 45 weeks. Measurements showed a significant decrease in the total amount of N, P, Mg, and Si that leached from the manure-amended columns as biochar rates increased, even though the biochar itself added substantial amounts of these nutrients to the columns. Among columns receiving manure, the 20 g kg− 1 biochar treatments reduced total N and total dissolved P leaching by 11% and 69%, respectively. By-pass flow, indicated by spikes in nutrient leaching, occurred during the first leaching event after manure application for 3 of 6 columns receiving manure with no biochar, but was not observed for any of the biochar amended columns. These laboratory results indicate that addition of biochar to a typical Midwestern agricultural soil substantially reduced nutrient leaching, and suggest that soil–biochar additions could be an effective management option for reducing nutrient leaching in production agriculture. FIND ARTICLE HERE
Biological Nitrogen Fixation by Common Beans (Phaseolus vulgaris L.) Increases with Biochar Additons
This study examines the potential, magnitude, and causes of enhanced biological N2 fixation (BNF) by common beans (Phaseolus vulgaris L.) through bio-char additions (charcoal, biomass-derived black carbon). Biochar was added at 0, 30, 60, and 90 g kg−1 soil, and BNF was determined using the isotope dilution method after adding 15N-enriched ammonium sulfate to a Typic Haplustox cropped to a potentially nodulating bean variety (CIAT BAT 477) in comparison to its non-nodulating isoline (BAT 477NN), both inoculated with effective Rhizobium strains.
The proportion of fixed N increased from 50% without biochar additions to 72% with 90 g kg−1 bio-char added. While total N derived from the atmosphere (NdfA) significantly increased by 49 and 78% with 30 and 60 g kg−1 bio-char added to soil, respectively, NdfA decreased to 30% above the control with 90 g kg−1 due to low total biomass production and N uptake. The primary reason for the higher BNF with bio-char additions was the greater B and Mo availability, whereas greater K, Ca, and P availability, as well as higher pH and lower N availability and Al saturation, may have contributed to a lesser extent. Enhanced mycorrhizal infections of roots were not found to contribute to better nutrient uptake and BNF. Bean yield increased by 46% and biomass production by 39% over the control at 90 and 60 g kg−1 bio-char, respectively. However, biomass production and total N uptake decreased when biochar applications were increased to 90 g kg−1. Soil N uptake by N-fixing beans decreased by 14, 17, and 50% when 30, 60, and 90 g kg−1 bio-char were added to soil, whereas the C/N ratios increased from 16 to 23.7, 28, and 35, respectively. Results demonstrate the potential of biochar applications to improve N input into agroecosystems while pointing out the needs for long-term field studies to better understand the effects of bio-char on BNF. FIND ARTICLE HERE
Influence of Biochars on Nitrous Oxide Emission and Nitrogen Leaching from Two Contrasting Soils
The influence of biochar on nitrogen (N) transformation processes in soil is not fully understood. This study assessed the influence of four biochars (wood and poultry manure biochars synthesized at 400°C, nonactivated, and at 550°C, activated, abbreviated as: W400, PM400, W550, PM550, respectively) on nitrous oxide (N,O) emission and N leaching from an Alfisol and a Vertisol. Repacked soil columns were subjected to three wetting-drying (W—D) cycles to achieve a range of water-filled pore space (WFPS) over a 5-mo period. During the first two W-D cycles, W400 and W550 had inconsistent effects on N2O emissions and the soils amended with PM400 produced higher N,O emissions relative to the control. The initially greater N2O emission from the PM400 soils was ascribed to its higher labile intrinsic N content than the other biochars. During the third W—D cycle, all biochar treatments consistently decreased N2O emissions, cumulatively by 14 to 73% from the Alfisol and by 23 to 52% from the Vertisol, relative to their controls. In the first leaching event, higher nitrate leaching occurred from the PM400-amended soils compared with the other treatments. In the second event, the leaching of ammonium was reduced by 55 to 93% from the W550- and PM550-Alfisol and Vertisol, and by 87 to 94% from the W400- and PM400-Vertisol only (cf control). We propose that the increased effectiveness of biochars in reducing N,O emissions and ammonium leaching over time was due to increased sorption capacity of biochars through oxidative reactions on the biochar surfaces with ageing. FIND ARTICLE HERE
A Comparison of Variable Economic Costs Associated With Two Proposed Biochar Application Methods
The addition of biochar to agricultural soils has been shown to improve crop productivity and sequester carbon in soils over a millennial timeline. However, little formal research has assessed the logistics or economics of transitioning to a biochar economy. This paper examines the problem of biochar application to soil. Specifically, we look at two methods of application-broadcast-and-disk and trench-and-fill and provide cost estimates for each under varying rates of saturation. Our findings show that the broadcast process is generally cheaper; however, we consider a trench-and-fill method to be more suitable for storing large quantities of biochar in soil. For broadcast application, we found that at saturation rates of 2.5, 5, 10, 25, and 50 tons per acre, a respective cost per acre is $29, $44, $72, $158, and $300. Our examination of the trench-and-fill process revealed that cost depended on several variables, including saturation rate, trench depth, and operator efficiency. We found that at saturation rates of 5, 10, 25, 50, and 75 tons per acre, with trenches 2 feet deep, and at trenching and application rates of 15 feet per minute, a respective cost per acre of applied biochar is $34, $85, $171, $341, and $512. In both methods, we found results that suggest biochar application could constitute a considerable cost, many times greater than typical agricultural processes. Although our findings offer only a basic guide to calculating the cost of application, the intent of this paper is to serve as a launching pad for the much-needed additional research into the costs and other potential constraints of biochar application to agricultural soils. FIND ARTICLE HERE
Life Cycle Assessment of Biochar Systems: Estimating the Energetic, Economic, and Climate Change Potential
Biomass pyrolysis with biochar returned to soil is a possible strategy for climate change mitigation and reducing fossil fuel consumption. Pyrolysis with biochar applied to soils results in four coproducts: long-term carbon (C) sequestration from stable C in the biochar, renewable energy generation, biochar as a soil amendment, and biomass waste management. Life cycle assessment was used to estimate the energy and climate change impacts and the economics of biochar systems. The feedstocks analyzed represent agricultural residues (corn stover), yard waste, and switchgrass energy crops. The net energy of the system is greatest with switchgrass (4899 MJ t−1 dry feedstock). The net greenhouse gas (GHG) emissions for both stover and yard waste are negative, at −864 and −885 kg CO2 equivalent (CO2e) emissions reductions per tonne dry feedstock, respectively. Of these total reductions, 62−66% are realized from C sequestration in the biochar. The switchgrass biochar-pyrolysis system can be a net GHG emitter (+36 kg CO2e t−1 dry feedstock), depending on the accounting method for indirect land-use change impacts. The economic viability of the pyrolysis-biochar system is largely dependent on the costs of feedstock production, pyrolysis, and the value of C offsets. Biomass sources that have a need for waste management such as yard waste have the highest potential for economic profitability (+$69 t−1 dry feedstock when CO2e emission reductions are valued at $80 t−1 CO2e). The transportation distance for feedstock creates a significant hurdle to the economic profitability of biochar-pyrolysis systems. Biochar may at present only deliver climate change mitigation benefits and be financially viable as a distributed system using waste biomass. FIND ARTICLE HERE
Impacts of Woodchip Biochar Additions on Greenhouse Gas Production and Sorption/Degradation of Two Herbicides in a Minnesota Soil
A potential abatement to increasing levels of carbon dioxide (CO2) in the atmosphere is the use of pyrolysis to convert vegetative biomass into a more stable form of carbon (biochar) that could then be applied to the soil. However, the impacts of pyrolysis biochar on the soil system need to be assessed before initiating large scale biochar applications to agricultural fields. We compared CO2 respiration, nitrous oxide (N2O) production, methane (CH4) oxidation and herbicide retention and transformation through laboratory incubations at field capacity in a Minnesota soil (Waukegan silt loam) with and without added biochar. CO2 originating from the biochar needs to be subtracted from the soil–biochar combination in order to elucidate the impact of biochar on soil respiration. After this correction, biochar amendments reduced CO2 production for all amendment levels tested (2, 5, 10, 20, 40 and 60% w/w; corresponding to 24–720 t ha−1 field application rates). In addition, biochar additions suppressed N2O production at all levels. However, these reductions were only significant at biochar amendment levels >20% w/w. Biochar additions also significantly suppressed ambient CH4 oxidation at all levels compared to unamended soil. The addition of biochar (5% w/w) to soil increased the sorption of atrazine and acetochlor compared to non-amended soils, resulting in decreased dissipation rates of these herbicides. The recalcitrance of the biochar suggests that it could be a viable carbon sequestration strategy, and might provide substantial net greenhouse gas benefits if the reductions in N2O production are lasting. FIND ARTICLE HERE
Dairy-Manure Derived Biochar Effectively Sorbs Lead and Atrazine
Biochar (BC) produced from agricultural crop residues has proven effective in sorbing organic contaminants. This study evaluated the ability of dairy-manure derived biochar to sorb heavy metal Pb and organic contaminant atrazine. Two biochar samples were prepared by heating dairy manure at low temperature of 200 °C (BC200) and 350 °C (BC350). The untreated manure (BC25) and a commercial activated C (AC) were included as controls. Sorption of Pb by biochar followed a dual Langmuir−Langmuir model, attributing to Pb precipitation (84−87%) and surface sorption (13−16%). Chemical speciation, X-ray diffraction, and infrared spectroscopy indicated that Pb was precipitated as β-Pb9(PO4)6 in BC25 and BC200 treatment, and as Pb3(CO3)2(OH)2 in BC350. Lead sorption by AC obeyed a single Langmuir model, attributing mainly to surface sorption probably via coordination of Pb d-electron to CC (π-electron) and OPb bonds. The biochar was 6 times more effective in Pb sorption than AC, with BC200 being the most effective (up to 680 mmol Pb kg−1). The biochar also effectively sorbed atrazine where atrazine was partitioned into its organic phase, whereas atrazine uptake by AC occurred via surface sorption. When Pb and atrazine coexisted, little competition occurred between the two for sorption on biochar, while strong competition was observed on AC. Results from this study indicated that dairy manure can be converted into value-added biochar as effective sorbent for metal and/or organic contaminants. FIND ARTICLE HERE
Characterization of Designer Biochar Produced at Different Temperatures and Their Effects on a Loamy Sand
Biochar additions to degraded soils have the potential to improve crop yield and soil quality. We hypothesize that the biochar production process can be tailored to form designer biochars that have specific chemical characteristics matched to selective chemical and/or physical issues of a degraded soil. We produced biochars from peanut hulls, pecan shells, poultry litter, and switchgrass at temperatures ranging from 250ºC to 700ºC. Biochars were characterized by % mass recovery and by their physical and chemical distinctiveness. These were mixed at 2% w/w with a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults) and were laboratory incubated to examine changes in the Norfolk’s soil properties. Higher pyrolysis temperatures resulted in lower biochar mass recovery, greater surface areas, elevated pHs, higher ash contents, and minimal total surface charge. Removal of volatile compounds at the higher pyrolysis temperatures also caused biochars to have higher percentages of carbon (C) but much lower hydrogen (H) and oxygen (O) contents. 13C NMR spectral analyses confirmed that aliphatic structure losses occurred at the higher pyrolysis temperatures, causing the remaining structures to be composed mostly of poly-condensed aromatic moieties. Biochars produced at higher pyrolysis temperatures increased soil pH values, while biochar made from poultry litter feedstock grossly increased Mehlich-1 extractable phosphorus (P) and sodium (Na) concentrations. Water-holding capacity varied after biochar incorporation. Biochars produced from different feedstocks and under different pyrolysis conditions influenced soil physical and chemical properties in different ways; consequently, biochars may be designed to selectively improve soil chemical and physical properties by altering feedstocks and pyrolysis conditions.FIND ARTICLE HERE
Impact of Two Different Biochars on Earthworm Growth and Survival
Interest in the use of biochar as a soil amendment to increase soil fertility and sequester carbon is increasing. However, the effects of biochar on the survival and reproduction of earthworms are unknown. The toxicity of two different biochars (pine chip and poultry litter char) on Eisenia fetida applied to an artificial soil (70% sand, 20% kaolin, and 10% sphagnum) was investigated at five different application rates of 0, 22.5, 45, 67.5, and 90 Mg ha-1. Earthworm mortality and weight loss reached 100% at the two highest application rates of poultry litter biochar, whereas mortality and weight loss with pine chip biochar did not differ from control treatments. Soil pH, which also increased in controls and pine chip biochar treatments over the course of the incubation, was the most likely cause of earthworm mortality in all treatments. However, it was apparent that poultry litter biochar provided a more stressful environment to earthworms since many worms died in the first five days of incubation. This stressful environment was most likely due to the presence of ammonia gas in addition to high pH, which increased from 7.2 to 8.9 with increasing application rates of poultry litter biochar (pH 10.3). Potentially toxic micronutrients, including As, Zn, Cu, Fe, and Al, present at sub-toxic levels in poultry litter biochar treatments on an individual basis were not likely to have contributed to earthworm mortality; additive effects, however, were not established. Poultry litter biochar also had high Na and Mg content, which could have led to high salinity. As biochar characteristics depend on the feedstock and conditions of pyrolysis, toxicity screening of biochars, particularly those likely to increase soil pH, prior to land application is recommended. FIND ARTICLE HERE
Effect of Banded Biochar on Dryland Wheat Production and Fertiliser Use in South-Western Australia: An Agronomic and Economic Perspective
Effects of banded biochar application on dryland wheat production and fertiliser use in 4 experiments in Western Australia and South Australia suggest that biochar has the potential to reduce fertiliser requirement while crop productivity is maintained, and biochar additions can increase crop yields at lower rates of fertiliser use. Banding was used to minimise wind erosion risk and place biochar close to crop roots. The biochars/metallurgical chars used in this study were made at relatively high temperatures from woody materials, forming stable, low-nutrient chars. The results suggest that a low biochar application rate (~1 t/ha) by banding may provide significant positive effects on yield and fertiliser requirement. Benefits are likely to result from improved crop nutrient and water uptake and crop water supply from increased arbuscular mycorrhizal fungal colonisation during dry seasons and in low P soils, rather than through direct nutrient or water supply from biochars. Financial analysis using farm cash flow over 12 years suggests that a break-even total cost of initial biochar use can range from AU$40 to 190/ha if the benefits decline linearly to nil over 12 years, taking into account a P fertiliser saving of 50% or a yield increase of 10%, or both, assuming long-term soil fertility is not compromised. Accreditation of biochar for carbon trading may assist cost reduction. FIND ARTICLE HERE