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on October 14, 2008 at 11:53:09 am

Welcome to a Gardening with Biochar FAQ!

... a work in progress...


When gardeners add biochar to garden soil, we are, in effect attempting to follow in the footsteps of the originators of Terra Preta. Because we don't know exactly how that process worked, nor how we can best adapt it outside its area of origin, we are left to discover much of this by experimenting with our own gardens and comparing observations within our own communities.


1.0 What is Biochar?

Biochar is charcoal formed by low temperature pyrolysis.  Higher temperature pyrolysis produces a more traditional charcoal.  Ideally biochar is made in a way that achieves maximal bio-oil condensate retention. When used broadly, the term biochar simply refers to charcoal made from any biomass waste, and may or may not have a significant bio-oil condensate component.  In this broader context biochar is simply charcoal used for agricultural purposes.


1.01 What are the benefits of using biochar in the garden?

The following benefits occur with additions of biochar

  • Enhanced plant growth
  • Suppressed methane emission
  • Reduced nitrous oxide emission (estimate 50%) (see 5.10 below)
  • Reduced fertilizer requirement (estimate 10%)
  • Reduced leaching of nutrients
  • Stored carbon in a long term stable sink
  • Reduces soil acidity: raises soil pH (see 5.01 below)
  • Reduces aluminum toxicity
  • Increased soil aggregation due to increased fungal hyphae
  • Improved soil water handling characteristics
  • Increased soil levels of available Ca, Mg, P, and K
  • Increased soil microbial respiration
  • Increased soil microbial biomass
  • Stimulated symbiotic nitrogen fixation in legumes
  • Increased arbuscular mycorrhyzal fungi
  • Increased cation exchange capacity


1.02 How much biochar do I need to apply to achieve these benefits?

This is the subject of ongoing studies. The degree of benefit clearly increases with the application rate.  If you are satisfied with a very rough estimate, we would venture that a target application rate of 5 kg/m2 (1 lb/ft2) would be sufficient to achieve these results in most gardens. However, there are substantial benefits related to soil biology at rates well below 1 kg/m2. This FAQ includes information on how to use small amounts of biochar in your garden to best advantage. [peer review requested on target application rate statement]


1.03 How long does it take for these benefits to become apparent?  How long do they persist?

Some effects, such as lowering soil acidity, occur immediately.  Other effects depend on soil biology and take time to develop.  Increased cation exchange capacity will take several years to develop fully. The good news is that these effects are very persistent.


1.04 How does biochar relate to agrichar and to Terra Preta?

 Biochar is sold under a range of brand names such as the well-known global brand name and US registered trademark Agrichar™ which relates to Biochar produced from the BEST Energies proprietary slow pyrolysis process. Biochar was fundamental to the creation of Terra Preta de Indio, as it is to creating its modern equivalent, Terra Preta Nova. Terra Preta "Classic" was made by adding charcoal, broken pottery shards, along with organic fertilizer amendments. This, in conjunction with the microbial ecology occurring in these soils, resulted in an incredibly fertile soil, and a reputation for self-regeneration. The effects of adding biochar in Terra Preta de Indio have persisted for millenia. Initial studies indicate we should not expect biochar to instantly recreate the full effect of Terra Preta de Indio, however, persistent partial effects are readily apparent for the duration of longer term studies. The degree to which Terra Preta de Indio is dependent on a community of soil biology unique to the Amazon is not known. In some ways, this is what you, the gardener, is going to attempt to discover. It is conceivable that the full effect of biochar in your garden will be seen by your grandchildren, but not by you.


1.05 What is pyrolysis?

Pyrolysis is the chemical decomposition of organic materials by heating in the absence of oxygen.  This yields combustible gases (called syngas), tars and charcoal. The charcoal produced is a combination of black carbon, along with small amounts of bio-oil condensates, tars and ash.


1.06 What temperature range is considered "low temperature" in the context of biochar?

The theoretical low end of the range approaches 120 deg C, the lowest temperature at which wood will char, (Reference) thus the temperature at the pyrolysis front.  A more practical low end is to use the piloted ignition temperature of wood, typically 350 deg C. (Reference) The theoretical high end, between biochar and more traditional charcoal, depends on the process and feedstock used, but is seldom indicated in excess of 600 deg C. This temperature range is more relevant to woody charcoal than to charcoal made from bamboo, or other high cellulose fuels.  Woody charcoal has an interior layer of bio-oil condensates that microbes consume and is equal to glucose in its effect on microbial growth (Christoph Steiner, Energy with Agricultural Carbon Utilization (EACU) Symposium, June, 2004) High temperature char loses this layer and consequently may not promote soil fertility as well. (Source)


1.07 Can I substitute other forms of charcoal for biochar?

Absolutely. While the bio-oil condensates in biochar definitely play a role in soil fertility, charcoal without bio-oil condensates has been demonstrated to produce excellent results.  It is normally advisable to avoid industrial charcoal briquettes because the binders used during manufacture can add undesirable constituents. On the other hand, briquette binder can be innocuous See below (5.08) for information on how to receive some standardized rice-hull charcoal to conduct your own home research pot trials, and compare your results with others. 


1.08 Does charcoal break down in soil?

Charcoal is highly stable, however soil microbes do break it down, although at a very slow rate.  (More...)


1.09 Where can I join in with this community of Terra Preta enthusiasts?

  1. Bioenergy lists: Terra Preta: the intentional use of charcoal in soils.
  2. Bioenergy lists: Terrapreta -- Discussion of terra preta, the intentional placement of charcoal in soil.
  3. Hypography Science Forums: Terra Preta
  4. Yahoo! Tech Group: Biochar


2.0 How do I Get Biochar?

You can purchase charcoal from a biochar manufacturer, you can purchase any of a wide range of charcoal products suitable for amending soil, or you can make charcoal yourself. Hopefully when you do, you can pick up the knack of making charcoal which retains that condensate goodness.


2.01 Where can I purchase biochar?

Currently manufactured biochar is in short supply and is fully utilized for academic research projects.


The alternative is to purchase charcoal safe for use in the soil, which by broader difinitions, can also be regarded as biochar. In Britain charcoal is widely available in nurseries. In Australia, you can ocassionally buy "redhead" brand bamboo charcoal from supermarkets, or small bags of Horticultural Charcoal. Much cheaper is to ask your Charcoal BBQ Chicken shop for a 20K bag of Mulga charcoal for about $(AUD)30. This will need to be ground a little in a motar and pestle before use. It is excellent mixed in rough chunks in native orchids potting mixes.  It usually has a pH of 6 so can be used on acid loving plants.  Cowboy brand hardwood charcoal is available in the United States in 20 pound bags by the pallet, about 600 pounds, for less than US $ 0.7/lb.  For larger amounts, as in a shipping container, consider coconut shell charcoal, available for less than US $ 300/mt. Worth repeating: It is normally advisable to avoid charcoal briquettes because the binders used during manufacture can add undesirable constituents.


2.02 What can I grow to make my own charcoal?

In Britain commercially available charcoal and is made from fuel produced by "coppicing" as has been done in British forests for more than 2,000 years. This is an ecologically sustainable use of forests and may contribute to the health and longevity of some British  forests.


2.03  Can I burn to bones to make charcoal for my garden?

Yes.  It appears that char derived from bones, along with char derived from other types of food wastes, was a component in Terra Preta de Indio.


2.04 How do I make my own charcoal?

While colliers the world over normally use either a covered pit [Example] or a covered mound (earth kiln) [Example] to make charcoal, most gardeners will want to start with an easier method that works at a smaller scale.  Home pyrolysis is pretty easy to accomplish and a simple burn barrel is a common starting point. A bottom ventilated, bottom lit burn barrel is a popular variation. [Example] If you have some basic tools for cutting metal, you can make barrel into a higher yielding kiln [Example].


If you live in a jurisdiction where its illegal to produce smoke, you will need to be highly selective in your fuel. No matter what technique you use to make charcoal, choosing uniformly sized, dry woody material produces the highest yields. Uniformity is one reason that colliers will routinely use coppiced hardwoods


If you want to use the heat generated to cook with, consider Robert Flanagan's Biochar Stove. [Example1] [Video] or Folke Günther's simple two barrel system.  The inner can in Folke's system acts as a retort, restricting the air supply to the target feed stock for the duration of the burn.  An outside heat source pyrolyzes the retort contents, small openings in the retort allow wood gas to escape, but restrict the flow of oxygen in.  Retorts are capable of very high yield efficiency.


2.05 What are some higher volume approaches to making charcoal for the garden?

 A Large Drum Retort. [Expand] Use a drum with a fairly tight lid.  Place it on a stand over the hearth, and perforate the bottom of the drum to use the volatile gasses to fire the retort. [Example] The alternative is to run a piece of perforated pipe from the top of the drum to the firebox underneath.  [Example1] [Example2] [Example3] With the right fuel choice a large drum retort adapted to use the smoke will not only have a higher overall yield, it will also cut back dramatically on the smoke produced. 


The Wood Vinegar Kiln. [Expand] Not sure this is going to be a low smoke opacity alternative, but I would hope so.


2.06 How do I make charcoal that achieves biochar structure and chemistry?

Structure is a mostly of a function of the fuel type.  Hardwoods are currently preferred in this regard, but the understanding in this area is in flux.  The chemistry is better defined. The burn process should be controlled to retain condensates.  The tools to achieve this in a home-based setting are limited but also blessedly simple.  In all approaches it means restricting the air supply to slow the burn rate and achieve a low enough pyrolysis temperature that all the tars and volatiles produced don't gas off. Being willing to tolerate the inefficent combustion of smoke production, even if only near the end of the burn, certainly makes it easier to retain this volatile liquid component.  Being willing to dowse or damping off the burn before it makes the transition from a wood gas fire to a coal gas fire also helps. That can result in some brown char mixed in with the black char, but when it comes to garden soil, its all good. 


2.07 How much charcoal yield can I expect?

On a dry matter weight basis, as well as an energy basis, between 20 percent, for a Top Lit Updraft (TLUD) gasifier with low superficial velocity (Source - PDF), and 60 percent, for a retort under ideal conditions. 40 percent is a reasonable goal. [Sources needed] 


2.08 What refractory materials can I use to make a kiln? a retort?


2.09 What gases does pyrolysis produce?

The dominant combustible gases produced are carbon monoxide and hydrogen, along with a small amount of methane.  Carbon dioxide is also produced, especially with higher fuel moisture content. (Source)  Methane (CH4), a powerful GHG, comprises 2-3% pf the produced gas. Flaring the producer gas eliminates the methane component (More).


2.10 How much heat does pyrolysis produce?

Pyrolysis itself is endothermic, thus requires an input of heat to be sustained. Heating value of the gas produced is 5,000 - 5,900 kJ/m³. (Source)  Comparatively less than the heating value of natural gas, 33,320 to 42,000 kJ/m³ (Source - PDF), it is still substantial.


2.13 Is charcoal worth more as a fuel than as a soil amendment?

This can certainly occur. Its value as a soil amendment is highest when it is used in small amounts for carrying inoculate, or side dressing with starter fertilizer.  It is also of high value on those high value crops that are responsive to high fertilizer inputs. A basic spreadsheet can help in evaluating this.


2.14 Is charcoal worth more as a fuel than its value for offsetting greenhouse gases?

Maybe yesMaybe no.


3.0 What do I do with the charcoal once I've made it?

You can use freshly made charcoal as is, especially in small amount. For larger amounts, the choices are to crush, screen, add liquids, add dry materials, and to compost it. (Photos)

3.01 Why would I need to prepare the biochar, as opposed to applying it as is?

There are several reasons that might apply to your situation. [Expand, obviously]

3.02 What size should the biochar be?

Finer is better from a soil and plant views, but finer is worse from a dust control and air quality view. Considering that charcoal naturally degrades in soil to a fine size, the level of effort exerted to make fine charcoal is really driven by the application sytem employed: banding fine charcoal down the seed row will require fine sand grain sized particles, but there is no fundamental reason to prevent incorporating gravel sized pieces.

3.03 What are some ways to crush and screen biochar?

For crushing, I am leaning to a mortor and pestle approach: a 5 cm dia tree branch and something like a 20 liter bucket with a plywood insert in the bottom.

For screening, I think a sloped screen works better than a horizontal screen for higher volumes.]3.04 What can I do to make the biochar easier to crush?

Wetting and drying it seems to help.  Be aware that soaking separates the soluble ash largely responsible for the calcium carbonate equivalency (CCE, the liming effect) and the salinity which can be a net benefit to acidic soils.  Crushing it with a little moisture in it helps to control dust without removing the soluble ash content.

3.05 Besides water, what else can I soak the biochar in?

You would want to choose materials that would mitigate stalling [ See 5.04]: Compost tea, MiracleGro (Calculation), fish emulsion, urine, more on urine, ....

3.06 Can I add biochar to compost?

Yes. This will help fill the biochar with biology and humic substances. For the added benefit of odor control, consider topping off each addition to the household kitchen scrap collector with a healthy layer of biochar.

3.07 Will biochar affect the compost process?

Casual observation indicates that adding fine, freshly made biochar may accelerate the composting process.

3.05  Will biochar harm the worms in my compost?

Composting worms have been observed to be unaffected below 50% charcoal content, above which reduced worm activity could occur.

3.08  Can I use biochar in my composting toilet?

Yes. Again, the added benefit of odor control is compelling.


4.0 How do I apply Biochar?

4.01 What is the target application rate to achieve the effects of biochar?

From the data available to date, it appears that crops respond positively to biochar additions up to at least 50 Mg C ha-1, provided sufficient fertilizer is provided to prevent charcoal induced stalling (see 5.04). This is equivalent to 5 kg/m2 (1 lb/sf) and works out to a loose charcoal depth of about 5 cm or 2 in. (Calculation) Crops may show growth reductions at higher applications. For most plant species and soil conditions studied to date, this growth reduction did not occur even with 140 Mg C ha-1.

4.01 What materials combine well with biochar for application?

4.02 How is biochar generally used?

[normally , mixed in much the way you would prepare a planting bed by mixing in compost and other bulk organic amendments]

4.03 What is the normal application rate for biochar?

This is not well established

4.04 Are there benefits to deeper placement?

[better prevent leaching loss, mycorrhyzal highway below normal cultivation]

4.05 Are there benefits to using biochar as a mulch?

[better prevent denitrification loss of nitrous oxide, methane emmisions.  Heat up seedbed in spring]

4.06 I have a very limited supply of biochar, what is its highest and best use?

[Expand. seedball, sidedress with starter fertilizer, fungi innoculate]



5.0 What happens after biochar is in the soil?

5.01 Does biochar affect soil pH?

Raising soil pH is charcoal's most important contribution to influencing soil quality. (Source) Soil pH mostly influences the relative availability of nutrients.  At low pH, aluminum toxicity is particularly harmful to plant growth.  Aluminum toxicity is an extensive and severe soil problem and biochar is the most available and obvious solution that we have to combat it.


The ash content of most biochars has a slight liming effect: it tends to increase a neutral or acidic soil pH to a more alkaline pH.  Ash tends to have a pH of 12 - 13, and charcoal tends to have a minimum ash content of 2-10%. At 10% ash, the effect a tonne of charcoal might be equivalent to as much as 1/10 tonne of lime.  At the high end of the target biochar application range (50 MG/ha) (see 4.01), soil pH would increase equivalent to lime applied at 5 tonnes/ha, enough in some cases to increase soil pH by 1.0 unit.  If you are applying substantial amounts of biochar you should test your soil pH and compare it to the ideal for your plants.


If your soil pH is below 6.0, and you are not trying to grow plants that need sub-6 pH (examples: Aechmea, Aspidistra, Camelia, Hydrangea (Blue), Orchid) you can rest assured that your soil's acidity level will improve quite significantly from the addition of biochar. At higher pH levels, the addition of thoroughly matured compost to the soil can enable so-called acid-loving plants to thrive in a soil of pH 7.  This is because the natural chelating effect of the organic matter allows it to maintain the availability of trace elements to plant roots. (Hendreck, 2002, Growing Media..)


Accordingly, adding so much biochar that you take your soil pH above the ideal range for the plant may not be a problem if 1) soil nutrients are abundant and 2) the soil contains a substantial amount of thoroughly mature compost.  Visible symptoms of nutrient deficiencies can be most informaticve in this regard.


In my experience, the most visible symptom of elevated soil pH is iron chlorosis:  Unlike the more common nitrogen chlorosis, iron chlorosis affects new growth first, turning it pale green, then yellow-green, and finally to almost white. Leaves showing iron chlorosis often retain green veins. Even in mild cases where yellowing is slight, growth is noticibly reduced. 


Another visible symptom of elevated soil pH is phosphorus deficiency.  Plant development is slow, growth is stunted with very limited root growth. Many plants develop dark green leaves with purplish or reddish hues in the leaves and petioles.  Other nutrient deficiency symptoms associated with high soil pH are yellow mottling on young leaves (manganese deficiency) and rosetted new growth.  Both boron and zinc deficiency can cause rosetted new growth. Boron deficiency can also cause the plant to become a dark green.  Copper can be deficient in high pH soils: new shoots won't open, the whole plant is pale colored and young leaves are thin and yellow.


If it looks as if increased soil pH is a concern in your garden, you might consider waiting it out: the caustic (ie alkaline) contituents in ash are reactive, that is, they are not persistent.  If your soil has a high buffering capacity, associated with high clay, high calcium, and/or high organic matter content then you should see soil pH moderate with time.  Otherwise, there are several steps you can take to mitigate biochar's lime effect:

  • Use a reduced alkalinity feedstock for your biochar. Little has been published in this area, however, biochar derived from pine-needles is purported to have an acidifying effect on alkaline soil.
  • Use a high bio-oil condensate content biochar. This implies a lower temperature biochar as well as an effort to recover bio-oil condensates (example: wood vinegar) from the producer gas and returning it to the charcoal.
  • Water processing can eliminate liming characteristic of charcoal: the alkaline constuents of charcoal are soluble. The downside is that ash-based  nutrients (especially Ca, K, and S) are also removed.
  • Increase applied organic matter. Peat can be especially effective in this regard. Peat applied at 2.5 lbs per square yard is capable of reducing pH by 1.0 unit in some soils.
  • Apply an acid-effect fertilizer, an approach which is more effective in combination with applied organic matter. Examples of acid-effect fertilizer are ammonium sulphate, urea, or an ammonium phosphate.
  • Apply sulfur, an approach that requires time and microbial activity. To reduce pH by 1.0 unit, apply 1.2 oz per square yard on sandy soils, or 3.6 oz per square yard on other soil types.  Elevated soil sulfur causes onions to taste "hot"


5.02 Does biochar increase soil CEC and Base Saturation?

5.03 Does biochar improve soil moisture characteristics?

5.04 Can adding biochar cause stalled growth?

Adding charcoal to soil can cause growth to stall where soil nitrogen levels are low. That is probably not the case in most garden situations which have the advantage of compost, manure and kitchen scraps.

 The combination of returning bio-chars with high C/N ratios and abiotic buffering of mineral N may in some situations lead to low N availability to crops (Lehmann and Rondon 2005). In experiments in northern Sweden, however, increased nitrification and decreased ammonification was found after the addition of activated C to a pine forest (Berglund et al. 2004). It appears that the effects of bio-char on N dynamics in soils is not entirely understood. In a greenhouse study in Colombia, leguminous plants were able to compensate for low N availability with increased biological N2 fixation which is actually stimulated by bio-char additions (Rondon et al. 2004). Non-legumes, however, may require additional N fertilization to compensate for the immobilization. This is an undesirable effect as more N applications require more production of N fertilizers which is very energy-demanding (West and Marland 2002). (Source - PDF)



5.05 What can be done to prevent stalled growth ?

Three solutions are possible which are not mutually exclusive: (i) bio-chars are only applied to leguminous plants until sufficient N has built up to allow economically satisfactory production of non-legumes without a net increase of N fertilization; (ii) bio-chars are fortified with N for example in a composting step or during the production of bio-char in an energy production process (Lee and Li 2003); (iii) the amounts of applied bio-char are adjusted at a sufficiently low level to allow for N to accumulate and plant productivity to optimize. (Source - PDF)


5.05 Does biochar affect soil ecology?

The structure of the charcoal provide a refuge for small beneficial soil organisms from large grazers like earthworms.

Charcoal increases activity by mycorhizal fungi. It doesn't appear that this effect changes with the manufacturing temperature of the charcoal.

There is a long tradition in Japan of using charcoal as a soil improver. Nishio (1996) states “the idea that the application of charcoal stimulates indigenous arbuscular mycorrhiza fungi in soil and thus promotes plant growth is relatively well-known in Japan, although the actual application of charcoal is limited due to its high cost”. The relationship between mycorrhizal fungi and charcoal may be important in realising the potential of charcoal to improve fertility. Nishio (1996) reports that charcoal was found to be ineffective at stimulating alfalfa growth when added to sterilised soil, but that alfalfa growth was increased by a factor of 1.7-1.8 when unsterilised soil containing native mycorrizal fungi was also added. Warnock et al (2007) suggest four possible mechanisms by which biochar might influence mycorrhizal fungi abundance. These are (in decreasing order of currently available evidence supporting them): “alteration of soil physico-chemical properties; indirect effects on mycorrhizae through effects on other soil microbes; plant–fungus signalling interference and detoxification of allelochemicals on biochar; and provision of refugia from fungal grazers. (Source - PDF)

Low temperature woody charcoal (more so than grass or high cellulose) has an interior layer of bio-oil condensates that microbes consume and is equal to glucose in its effect on microbial growth (Christoph Steiner, Energy with Agricultural Carbon Utilization (EACU) Symposium, June, 2004) (Source)

Steiner et al (2008) observed that basal respiration (BR), microbial biomass, population growth and the microbe's efficiency (expressed by the metabolic quotient) increased linearly and significantly with increasing charcoal concentrations (50, 100 and 150 g kg-1 soil).  Application of smoke condensates (pyroligneous acid, PA) causes a sharp increase in all these, plus in substrate-induced respiration (SIR), as well as an exponential increase in population. We suppose that the condensates from smoke contain easily degradable substances and only small amounts of inhibitory agents, which could be utilized by the microbes for their metabolism. (Source)

Aggregation is improved:

The presence of bio-char in soils actively promotes the formation of aggregates through a greater abundance of fungal hyphae. Bio-char is able to serve as a habitat for extraradical fungal hyphae that sporulate in their micropores due to lower competition from saprophytes (Saito and Marumoto, 2002). (Source - PDF)


5.06 Does biochar improve plant growth?

5.07 How much improved plant growth can I expect?

You can expect that harvested weight will be, in most cases, observeably higher with a combination of char+fertilizer than you will achieve with the same amount of fertilizer alone. In some cases, the observed effect will be dramatic. Steiner (2007) reported a doubling of maize grain yield with fertilizer+char compared to fertilizer alone. Yields subsequently declined over the course of four cropping cycles, however, the decline was less with char than with without. Significantly, soil P, K, Ca, Mg remained higher in the char amended soil despite greater harvest removal. (Source - PDF). Considering the few places that biochar has been tried, it should not come as a tremendous surprise to find that your actual results may turn out to be less than dramatic than this.


Data on the effect of charcoal on crop yields is still rudimentary – only a limited number of crops grown on a limited number of soils have been investigated. The interactions between crop, soil type, local conditions, and biochar feedstock, production method and application rate will have to be studied in far more detail before large scale deployment of biochar as a soil amendment can be contemplated. Nonetheless, there is evidence that at least for some crop/soil combinations, addition of charcoal may be beneficial. (Source - PDF)



5.08 Is there a way for me to perform my own yield studies in a way that will be useful to others?

Certainly: CharDB, the international online open-source database of biochar soil amendment trials.

You will now be able to register your biochar soil amendment trials in a uniform format "CharML" that should facilitate comparisons between the different entries. This will hopefully lead to interesting new conclusions and a better knowledge on the fascinating world of biochar! (Source)


5.09 How much carbon dioxide does sequestered biochar offset?

One kg charcoal, at 5% ash, offsets 3.3 kg carbon dioxide.  On a home and garden scale, assuming that a gallon of gasoline releases 2.4kg of carbon and assuming that one wants to get to a negative carbon value then utilizing a 4kg bag of Cowboy brand charcoal as biochar comfortably offsets the carbon dioxide produced, with room to accomodate tha carbon footprint of delivering the charcoal to the garden.  The production of the charcoal itself has no carbon footprint assuming the fuel used to make the charcoal was diverted from fate of decomposition. (Nod to Pangolin)


5.10 How much nitrous oxide formation does biochar prevent?

Soil scientist Lucas Van Zweiten has observed a 5 to 10 fold reduction in nitrous oxide emmissions with some of the biochars he is working with in an agricultural setting. Generally, soil with elevated soil nitrate levels in the presence of sufficient moisture and robust soil organic matter will have higher nitrous oxide production, and thus will be more likely to benefit at the levels observed by Van Zweiten. However,


The effect of biochar production on nitrous oxide emissions is largely an unknown factor. Although there is a possibility that biochar additions may reduce N2O direct emissions from soils, and may also reduce indirect N2O emissions by reducing nitrate run-off, neither of these possibilities has been adequately demonstrated under a range of different agricultural conditions. (Source - PDF)






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