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Frequently Asked Questions

  • What is Biochar?

    Biochar is produced by burning organic matter in the absence of oxygen. Biochar adds critical carbon to the soil, which in turn helps promote healthy microbial growth, water retention, and soil fertility. Miller Soils diverts biomass waste from forests and sawmills to our facilities in the Pacific Northwest and Rocky Mountain West where it’s converted into biochar. The material (biochar) is then blended with rich soil at varying levels to create the perfect mix based on specific plant requirements. By using eradicated trees that would normally act as fuel waiting for a fire we actively promote forest restoration and fire mitigation, which we see as highly beneficial to our shared ecology. The benefits of Miller’s Soils’ use of biochar begin to take effect long before our soil even reaches pots, gardens, and fields across the country.

  • What are the benefits?

    Consumers today are undoubtedly more conscious of how their food is grown and what goes into it, but it all starts with the quality of the soil in which it’s grown. Simply put, biochar absorbs water and holds essential nutrients in the soil, effectively reducing the number of additives needed to promote healthy plants and strong yields. Acting like a sponge, carbon-rich biochar helps keep nutrients and water close to plant roots all while actively enhancing soil oxygenation. Additionally, biochar acts as a natural filter, capturing nitrogen and limiting the amount leached into our groundwater through runoff. So what you’ll see a reduction in water and nutrient needs. You’ll also find that you will save time with the consistency of our product.

  • What are some common mistakes you see with new growers using your soil?

    Common mistakes that we see a lot of are overwatering and over-nutrition. Remember that biochar acts like a sponge, so it holds more water than you would normally see in other traditional and commercial soils.

  • Is Biochar safe?

    Every available ingredient and mineral you can find in our soils is also listed on all of our product pages. We also do extensive soil analysis testing (batch testing) and look for things like consistency, e. coli, salmonella, metals, etc. Don’t believe us, contact us and we can send our reporting. We care just as much as you do about what we put in our bodies, especially since we use the soil ourselves.

  • How much should I use?

    Given the variability in biochar materials and soils, users of biochar should consider testing several rates of biochar application on a small scale before setting out to apply it to large areas.

    Experiments have found that rates between 5 – 50 t/ha (0.5 – 5 kg/m2) have often been used successfully.

  • How is Biochar produced?

    Carbonization is the process of converting a feedstock into biochar through reductive thermal processing. The process involves a combination of time, heat, and pressure exposure factors that can vary between processors, equipment, and feedstocks.

    There are two main processes: pyrolysis or gasification.

    Energy products in the form of gas or oil are produced along with the biochar. These energy products may be recoverable for another use, or may simply be burned and released as heat. Also, biochar can be made from a wide variety of biomass feedstocks. As a result, different biochar systems emerge on different scales. These systems may use production technologies that do or do not produce recoverable energy as well as biochar and range from small household units to large bioenergy power plants.

  • How can Biochar help farmers?

    Biochar provides a unique opportunity to improve soil fertility for the long term using locally available materials. Used alone, or in combinations, compost, manure, and/or agrochemicals are added at certain rates every year to soils, to realize benefits. Application rates of these can be reduced when nutrients are combined with biochar. Biochar remains in the soil, and single applications can provide benefits over many years.

    Farmers can also receive an energy yield when converting organic residues into biochar by capturing energy given off in the biochar production process.

    In both industrialized and developing countries, soil loss and degradation is occurring at unprecedented rates, with profound consequences for soil ecosystem properties. In many regions, loss in soil productivity occurs despite the intensive use of agrochemicals, concurrent with adverse environmental impacts on soil and water resources. Biochar can play a major role in expanding options for sustainable soil management by improving upon existing best management practices, not only to improve soil productivity but also to decrease nutrient loss through leaching by percolating water.

  • How do we know that Biochar helps increase crop yields?

    There is a large body of peer-reviewed literature quantifying and describing the crop yield benefits of biochar-amended soil. Field trials using biochar have been conducted in the tropics over the past several years. Most show positive results on yields when biochar was applied to field soils and nutrients were managed appropriately.

    There is also evidence from thousands of years of the traditional use of charcoal in soils. The most well-known example is the fertile Terra Preta soils in Brazil, but Japan also has a long tradition of using charcoal in soil, a tradition that is being revived and has been exported over the past 20 years to countries such as Costa Rica. The Brazilian and Japanese traditions together provide long-term evidence of positive biochar impact on soils. To read more about field trials and biochar, please see the IBI publications page.

    While the larger questions concerning overall biochar benefits to soils and climate have been answered in the affirmative, significant questions remain, including the need for a better understanding of some of the details of biochar production and characterization. Work is ongoing to develop methods for matching different types of biochar to soils for the best results.

  • How does Biochar affect soil biology?

    Decades of research in Japan and recent studies in the U.S. have shown that biochar stimulates the activity of a variety of agriculturally important soil microorganisms, and can greatly affect the microbiological properties of soils. The pores in biochar provide a suitable habitat for many microorganisms by protecting them from predation and drying while providing many of their diverse carbon (C), energy, and mineral nutrient needs. With the interest in using biochar for promoting soil fertility, many scientific studies are being conducted to better understand how this affects the physical and chemical properties of soil and its suitability as a microbial habitat. Since soil organisms provide a myriad of ecosystem services, understanding how adding biochar to soil may affect soil ecology is critical for assuring that soil quality and the integrity of the soil subsystem are maintained.

  • How does Biochar affect soil properties like PH & CEC?

    Biochar reduces soil acidity which decreases liming needs, but in most cases does not add nutrients in any appreciable amount. Biochar made from manure and bones is the exception; it retains a significant amount of nutrients from its source. Because biochar attracts and holds soil nutrients, it potentially reduces fertilizer requirements. As a result, fertilization costs are minimized and fertilizer (organic or chemical) is retained in the soil for longer. In most agricultural situations worldwide, soil pH (a measure of acidity) is low (a pH below 7 means more acidic soil) and needs to be increased. Biochar retains nutrients in the soil directly through the negative charge that develops on its surfaces, and this negative charge can buffer acidity in the soil, as does organic matter in general.

    CEC stands for Cation Exchange Capacity and is one of many factors involved in soil fertility. “Cations” are positively charged ions, in this case, we refer specifically to plant nutrients such as calcium (Ca2+), potassium (K+), magnesium (Mg2+), and others. These simple forms are those in which plants take the nutrients up through their roots. Organic matter and some clays in soil hold on to these positively charged nutrients because they have negatively charged sites on their surfaces, and opposite charges attract. The soil can then “exchange” these nutrients with plant roots. If the soil has a low cation exchange capacity, it is not able to retain such nutrients well, and the nutrients are often washed out with water.

  • Can you add Biochar to alkaline soils?

    Most biochar trials have been done on acidic soils, where biochars with a high pH (e.g. 6 – 10) were used. One study that compared the effect of adding biochar to an acidic and an alkaline soil found greater benefits on crop growth in the acidic soil, while benefits on the alkaline soil were minor. In another study, adding biochar to soil caused increases in pH which had a detrimental effect on yields, because of micronutrient deficiencies which occur at high pH (>6). Care must be taken when adding any material with a liming capacity to alkaline soils; however, it is possible to produce biochar that has little or no liming capacity that is suitable for alkaline soils.

  • What kind of Biochar should I add to your soil, and how much should I use?

    It is important to note that not all biochar is the same. Biochar is made by pyrolyzing biomass—pyrolysis bakes the biomass in the absence of oxygen, driving off volatile gases and leaving behind charcoal. The key chemical and physical properties of biochar are greatly affected by the type of feedstock being heated and the conditions of the pyrolysis process. For example, biochar made from manure will have a higher nutrient content than biochar made from wood cuttings. However, the biochar from the wood cuttings may have a greater degree of persistence over time. The two different biochars will look similar but will behave quite differently. The IBI Biochar Standards provide more clarity on the characteristics of biochar.

    Some biochar materials, for example, those made from manures and bones, are mainly composed of ashes (so-called “high mineral ash biochars”), and thus can supply considerable amounts of nutrients to crops. Keep in mind that this fertilizer effect will likely be immediate and short-lived, just as is the case with synthetic fertilizers. Conversely, the carbon content of high mineral ash biochars is low (e.g. < 10%), and thus longer-term nutrient retention functions will be less for a given amount of material.

  • Why is Biochar persistence in soils important?

    The persistence of biochar when incorporated into soils is of fundamental importance in determining the environmental benefits of biochar for two reasons: first, it determines how long carbon in biochar will remain sequestered in soil and contribute to the mitigation of climate change; and second, it determines how long biochar can provide benefits to soil and water quality.

  • How is Biochar carbon persistence measured?

    The fused carbon ring structure of biochar can be measured in the laboratory using a range of established techniques, some low cost and relatively easy to conduct, others more sophisticated and requiring high-tech equipment that analyzes nano-structural properties. In combination with empirical (measurement-based) modeling exercises that show how biochar carbon mineralizes over time using field and laboratory incubation trials for validation, the degree of carbon aromaticity can be used to predict how much biochar would remain in soils over discrete periods, for example, 100 years or 1,000 years. Persistence is then quantified as mean residence time (MRT)—the average time that biochar is present in the soil.

  • How long does Biochar persist in the soil?

    Biochar is a spectrum of materials, and its characteristics vary depending upon what it is made from and how it is made. One unifying characteristic of biochars, however, is that it mineralizes in soils much more slowly than its uncharred precursor material (feedstock). Most biochars do have a small labile (easily decomposed) fraction of carbon but there is typically a much larger recalcitrant (stable) fraction. Scientists have shown that the mean residence time (the estimated amount of time that biochar carbon will persist in soils) of this recalcitrant fraction ranges from decades to millennia.

  • Why does Biochar persist in soils longer than the original biomass from which it was made?

    The carbon lattice structure made up of fused polyaromatic carbon rings is hypothesized to be the key property that confers resistance to mineralization (conversion from organic carbon to carbon dioxide via respiration) by soil microbes that utilize organic matter i.e., hydrocarbons, as food (Lehmann et al, 2015). The energy required by microbes to access the carbon in biochar appears to be greater than that acquired when it is released. In contrast, carbon compounds in the original biomass (feedstock) are net positive energy sources and are more readily mineralized by soil microbes.

    Compost is a stable, nutrient-rich, living form of soil organic material essential to agriculture. It is primarily made up of humus, a complex combination of materials dominated by humic and fulvic acids, and it is intensely populated with soil organisms and high in nutrient content. In all agricultural soils, humus is the keystone of soil biochemistry, and it is a product of that same biochemistry.

    The humic and fulvic acids are complex carboxylic acids released from decaying bacterial cell envelopes. Bacteria, in turn, play a large part in decomposing dead (and live) plant and animal matter. As the bacterial cell-envelope fragments accumulate, humus builds and interacts with the surrounding environment (especially in solution and/or in rhizospheres), adsorbing additional minerals and acting as an exchange site for microbes to attain minerals. And, as humic acids accumulate they mix with bits and pieces of refusia from the activity of bacteria, fungi, including decomposing dead and dying organisms, forming enough mass to provide habitat for soil organisms ranging from viri to bacteria, fungi, and protozoa to nematodes and chollembola. The result is humus.

    Farmers have known about humus and compost for millennia, and it remains a well-studied topic in modern science. We continue to learn the interesting characteristics of humus and compost.

    • Inoculates the soil with a rich assortment of soil organisms that contribute to the complex of nutrient-pathways and cycles.

    • Nutrient release. Compost is a great source of nitrogen, potassium, phosphorus, calcium, and pretty much anything that was in the feedstock. Our composts come from the high-quality, vegetative feedstock. No Human Manures.

    • Phyto-hormonal effect on plants and interaction with or simulation of growth regulators.

    • Is Colloidal, meaning that it suspends in solution, making it readily accessible to all the biochemical and nutrient pathways.

    • Improves soil texture. Compost reduces soil bulk density and improves porosity and it helps break-up clay soils.

    • Improves water holding capacity. Compost sucks it up and holds on to it for gradual use by microbes.

    • Can improve cation exchange capacity. Compost contributes much to the CEC of container soil-mixes.

    • pH buffering. Cured biochar can buffer soil pH, though raw biochar can increase pH due to high surface Calcium Carbonate.

    • Resides in the soil for the long-term – in some cases a century.

    Why does compost do all these wonderful things?

    • Compost has an enormous surface-to-volume ratio due to its complex surface, due to humic acids’ complex chemical structure, which involves multiple complex R-groups.

    • The chemical configurations result in a large cation-exchange capacity, making nutrients readily available to soil microbes and soil solution.

    • Chemical complexity and evolutionary co-existence have resulted in complex interactions between various plant protein functions (for example, proton pump regulation).

  • Where does compost come from?

    When we mix together materials to create humus, we are composting. For container soil-mixes, the best composts come from thermophilic composts and from composting-worms. The processes involved create the rich, earthy humus that makes plant life as we know it possible. Plants love it and the more the better. In fact, in the field, most plants require humus to survive.

  • How can Biochar mitigate climate change?

    Large amounts of forestry and agricultural residues and other biomass are currently burned or left to decompose thereby releasing carbon dioxide (CO2) and/or methane (CH4)—two main greenhouse gases (GHGs)—into the atmosphere. Under biochar conversion scenarios, easily mineralized carbon compounds in biomass are converted into fused carbon ring structures in biochar and placed in soils where they persist for hundreds or thousands of years. When deployed on a global scale through the conversion of gigatonnes of biomass into biochar, studies have shown that biochar has the potential to mitigate global climate change by drawing down atmospheric GHG concentrations (Woolf et al, 2010).

  • How much carbon can Biochar potentially remove from the atmosphere?

    According to one prominent study (Woolf et al, 2010), sustainable biochar implementation could offset a maximum of 12% of anthropogenic GHG emissions on an annual basis. Over 100 years, this amounts to a total of roughly 130 petagrams (106 metric tons) of CO2-equivalents. The study assessed the maximum sustainable technical potential utilizing globally available biomass from agriculture and forestry. The study assumed no land clearance or conversion from food to biomass-crops (though some dedicated biomass-crop production on degraded, abandoned agricultural soils was included), no utilization of industrially treated waste biomass, and biomass extraction rates that would not result in soil erosion.

  • How does Biochar work to reduce emissions of greenhouse gases other than CO2?

    Recent studies have indicated that incorporating biochar into soil reduces nitrous oxide (N2O) emissions and increases methane (CH4) uptake from soil. A: Methane is over 20 times more effective in trapping heat in the atmosphere than CO2, while nitrous oxide has a global warming potential that is 310 times greater than CO2. Although the mechanisms for these reductions are not fully understood, a combination of biotic and abiotic factors are likely involved, and these factors will vary according to soil type, land use, climate, and the characteristics of the biochar. An improved understanding of the role of biochar in reducing non-CO2 greenhouse gas (GHG) emissions will promote its incorporation into climate change mitigation strategies, and ultimately, its commercial availability and application.

  • Could Biochar impact climate through changes in soil albedo?

    After centuries of agriculture, soils globally have become depleted of carbon, compared to pre-agricultural conditions. Agricultural development goals include restoring carbon to carbon-depleted soils. Unavoidably, adding carbon to soils darkens them, changing their albedo (a measure of sunlight reflectance). Fortunately, darker, carbon-rich soils are more fertile and will be more easily re-vegetated. Vegetation has a lighter albedo, so the albedo problem is very temporary in nature and is not a significant issue.

  • Is it true that most of the Biochar added to soils is exported to rivers & oceans?

    A study published in the April 19, 2013 issue of Science magazine titled “Global Charcoal Mobilization from Soils via Dissolution and Riverine Transport to the Oceans” examined the proportion of benzene polycarboxylic acids (BPCA) as a proxy for black (pyrogenic) carbon (BC) in dissolved organic carbon (DOC) of several rivers. While the paper makes an important contribution to the global knowledge base on DOC fluxes in the environment, IBI believes there are some clarifications needed to reduce the propagation of erroneous conclusions about biochar behavior in soil.

    We concur with the finding that the export of BC to terrestrial ecosystems via rivers is significant. This should not be interpreted, however, as being greater than the export of uncharred material. The export of BC is only 10% of the total export of organic carbon, which is on the same order of magnitude or even smaller than the proportions that the authors cite for BC contents in soils of 5 – 40%. Therefore, BC in the soil is not preferentially exported from watersheds.

    Based on citations the authors conclude that production rates of BC exceed decomposition rates and thus “a relatively labile BC pool must exist, allowing for considerable losses from soils.” However, the studies cited acknowledge high uncertainty in the rates of BC production, and, in the case of BC degradation, do not support inferences about BC degradation via microbial metabolization—rather just total losses from the soil, be it via erosion, leaching, or mineralization. Based on uncertainty in both production and decomposition of BC, we believe that further research is warranted to understand BC fluxes in the environment.

    Finally, the article concludes by implying that the use of biochar may reduce DOC bioavailability with cascading effects on microbial and aquatic food webs. This, however, would only be correct if all biochar were made from biomass where the baseline scenario is an accumulation in soil. Most biochar proponents—including IBI—advocate for use of biomass feedstocks that are currently burnt, landfilled, or disposed of in ways other than returning them to soils. Furthermore, even aggressive scenarios of biochar addition would still only be a fraction of total annual biomass residues that are already returned to soils and the impact on DOC bioavailability would thus be small.

  • Could black dust from Biochar have an impact on climate?

    Small particles of black carbon are produced from the incomplete combustion of fossil and biomass fuels. When deposited on snow and ice, they can absorb heat and energy. The smallest black carbon particles associated with biochar production and application are much larger, in the millimeter range than the particles associated with global warming, in the nanometer range. Thus the application of biochar would result in little opportunity for long-range transport and deposition into the sensitive Arctic and mountain regions.

  • What about human health concerns from dust created during Biochar production & application?

    Dust is certainly a concern with biochar application, but best practices require that biochar applications be done during periods of low wind to prevent the blowing of fines. Agricultural techniques already exist to apply powdered fertilizers and other amendments. Several techniques are available to help keep wind losses to a minimum: biochar can be pelleted, prilled, mixed into a slurry with water or other liquids, mixed with manure and/or compost, or banded in rows. The optimization of biochar application to soil is important, and the farm technology and methods are available to do the job.

  • Does IBI advocate adding carbon derived fro coal, old tires, or municipal solid waste to soils?

    No. Coal is not a renewable resource. Biochar refers specifically to materials made from present-day biomass, not fossil carbon. Tires and other potentially toxic waste materials are not appropriate as sources of biochar for soil improvement.

  • What are the costs & benefits of producing and using Biochar?

    The benefits that potentially flow from biochar production and use include waste reduction, energy co-production, improved soil fertility and structure, and climate change mitigation. Not all of these benefits are accounted for under current economic systems, but under the carbon-constrained economies of the future, the climate mitigation benefit is likely to be accounted for as an economic benefit. Biochar benefits are partly offset by the costs of production, mainly hauling and processing feedstocks. The profitability of biochar systems will be especially sensitive to prices for energy and greenhouse gas reductions and offsets.

  • Can I use Biochar immediately after producing it?

    Biochar straight out of the pyrolysis unit might take some time to reach its full potential in soil because it needs its surfaces to “open up”, or “weather”. This happens naturally in soil, but the process can be sped up by mixing biochar with compost, for example. Nutrient retention with biochar is thought to improve with time, along with crop benefits. Mixing biochar with compost is a great idea since apart from the ash (and there might only be small amounts of it in biochar), biochar is not a fertilizer in itself so the compost can provide nutrients that the biochar can help retain.

  • Is Biochar production sustainable?

    Biochar production and use comprise a complex system and its sustainability must be parsed out into various components. Of all the key factors that will support the fastest commercialization of the biochar industry, feedstock supply, and sustainable yield issues are by far the most important, from both a broad sustainability perspective and the financial and commercial points of view. This will require the sources of biomass selected for biochar production to be appropriate and be able to withstand a comprehensive life cycle analysis. Biochar can and should be made from waste materials. Large amounts of agricultural, municipal, and forestry biomass are currently burned or left to decompose and release CO2 and methane back into the atmosphere. These include crop residues (both field residues and processing residues such as nutshells, fruit pits, etc), as well as yard, food, and forestry wastes, and animal manures. Making biochar from these materials will entail no competition for land with any other land-use option.

    Biochar can be a tool for improving soils and sequestering carbon in the soil. However, this technology as any other must be implemented in a way that respects the land rights of indigenous people and supports the health of natural ecosystems. The goal of biochar technology as IBI envisions it is to improve soil fertility and sequester carbon, taking into consideration the full life cycle analysis of the technology. Properly implemented, biochar production and use should serve the interests of local people and protect biodiversity.

  • Does a successful Biochar industry depend on carbon markets?

    Biochar offers direct, present-day benefits to farmers of all sizes in the form of greater crop productivity as well as numerous other quantifiable environmental benefits, among them climate change mitigation. While efforts are underway to develop mechanisms to quantify and monetize the climate benefits of biochar—chiefly in the form of carbon offset methodologies—these would only add to the existing financial incentives for farmers and other stakeholders to adopt biochar.

  • Can biochar be patented?

    While some biochar producers may be able to patent a specific biochar production process or method, there exist several open-source, low-cost, clean technologies that can make biochar at the home or village level, and more are being developed.

  • Where can you buy Biochar?

    At Miller Soils, we can provide high-quality biochar to suit your needs. Click Here to learn more about our Raw Biochar!

  • Can I order a bag of soil?

    Absolutely! You can view all of our products here, or view our Science of Soil page to learn more about custom orders. We look forward to helping your garden grow!

  • How much does soil cost?

    Prices are based on quantity ordered. Please contact us for more information.

  • How much will the delivery or freight cost be?

    Freight costs are dependent on zip code, location type, and if unloading equipment is available. Please contact us for more information.

  • Can I place a custom order?

    Yes, absolutely! Please see our Science of Soil page for more information.