Biochar in Mixtures - International Biochar Initiative

IBI Research Summary:
Biochar in Mixtures
Updated: January 2011
Author: Julie Major, PhD
Note: IBI Research Summaries are intended to provide answers about biochar science
for the general public. These summaries are based on IBI’s review of published scientific
literature. As this literature is updated, IBI will update these summaries. Please contact
IBI at info@biochar-international.org if you have questions or information to share.
The role of mixtures in biochar
Although biochar can be used to improve soils over the long term, it is not a long-term
source of nutrients. Depending on the feedstock and pyrolysis conditions, biochar can
contain varying amounts of ash which can provide nutrients for plant growth in the short
term. A significant advantage of biochar when added to soil is its recalcitrance and its
ability to retain nutrients which are present in soil, or added as fertilizer or decomposing
organic matter, over the long term. Biochar has also been shown to support soil
microorganisms through its highly porous structure which provides protection from
predators and access to water and nutrients (Thies and Rillig, 2009). Consequently, a
number of researchers in academia and industry are preparing and testing mixes of
biochar with nutrients and/or cultures of bacteria or fungi, in order to improve the
nutrient content of biochar immediately upon addition to soil.
This research summary is a review of data available in the published scientific literature
and other sources, regarding the effect of biochar on the production of compost, biochar
mixtures with manure, and the use of biochar in a microbial ferment called Bokashi.
Biochar as an ingredient in Bokashi
Bokashi is a traditional Japanese soil amendment that is now used in various places
around the world. Although there are various recipes for making Bokashi (ingredient lists
can be adapted to the materials available in each region, including locally sourced
microorganisms), it can be made by combining microbes (termed “effective
microorganisms”, or “EM”), molasses, biochar, bran and animal manure with water
(Reap Canada). Bokashi can be made either anaerobically (i.e. by fermentation in closed
vessels) or partially aerobically, similarly to normal composting (Formowitz et al., 2007),
or using a combination of both.
IBI Research Summary – Biochar in Mixtures – January 2011 page 1

Some researchers found better yield of peanuts and greater numbers and total biomass of
nitrogen-fixing nodules on peanut roots when Bokashi was used instead of synthetic
fertilizer (Yan and Xu, 2002). However, Formowitz et al. (2007) showed that the
“effective microorganisms” were not likely responsible for beneficial effects of the
material on plant growth, and similar observations were made in field crops grown over
four years in central Europe (Mayer et al., 2008). However, the Bokashi made by
Formowitz et al. (2007) did not include biochar, and the reports by Yan and Xu (2002)
and Mayer et al. (2008) do not provide details on the materials used to make Bokashi and
whether or not biochar was used. Thus while Bokashi was found to provide plant growth
benefits in these studies, and these benefits could not be attributed to EM, there are no
reports in the literature about the role of biochar in Bokashi mixtures. Nevertheless,
biochar-containing Bokashi has been used successfully for over 15 years for growing
vegetables in Costa Rica (IBI Practitioner Profile, 2010) and used by farmers in the
Philippines, as outlined in Jensen et al (2006), as one example.
Biochar as a medium for fungal inoculants
Peat is commonly used as a carrier for rhizobial inoculant. Rhizobia are bacteria used to
promote proper nodulation and biological nitrogen fixation in legume crops. However,
peat is not available in all regions and is arguably not a renewable resource since its
formation takes a very long time. Biochar can also be used as a carrier for microbial
inoculants. Stephens and Rask (2000) indicate that carriers for microbial inoculants
should, among other factors, support the growth of the target organisms, have high
moisture holding and retention capacity, and be environmentally safe. Properly produced
biochar has these characteristics. When testing the survival rate of rhizobial inoculum,
charcoal performed similarly to peat, oil and other carriers (Kremer and Peterson, 1983).
Similar results were found by Sparrow and Ham (1983), where rhizobial inoculant
survival rates were greater in peat, charcoal and vermiculite than in peanut hulls or corn
cobs. Mycorrhizae are another type of fungus which also forms symbiotic associations
with plants, and soil-applied biochar has often been demonstrated to be beneficial to
mycorrhizal fungi (reviewed by Warnock et al., 2007), although neutral effects have also
been observed (Habte and Antal, 2010).
Biochar as a “bulking agent” in compost
Studies to date show that the composting process can be accelerated by adding biochar to
poultry manure (Dias et al., 2009; Steiner et al., 2010). For example, maximum
temperatures of the compost were reached faster when biochar was applied (Steiner et al.,
2010) and the degree of humification of the resulting compost was greater (Dias et al.
2009) with biochar application. Steiner et al. (2010) assumed that biochar did not
decompose during the 42 day trial, and found that the loss of poultry manure biomass was
not different in cases where biochar was added as 0, 5 or 20% of the mixture on a dry
weight basis. Dias et al. found that total mass loss in their 1:1 by wet weight mixture of
biochar and poultry litter was intermediate compared to equivalent mixtures with coffee
husks and sawdust (coffee husks as a bulking agent caused greater losses and sawdust
caused lower losses relative to biochar), and alluded to the fact that biochar could have
IBI Research Summary – Biochar in Mixtures – January 2011 page 2

undergone decomposition, although their data did not allow this to be determined. More
research is needed on the effect of biochar on the C and mass balance during composting;
however a faster “ripening” of compost as demonstrated by both authors is desirable for
compost makers.
Total nitrogen losses over 42 days of composting sewage sludge were reduced by 64% by
adding 9% biochar to the sludge (Hua et al., 2009) as opposed to a control not receiving
biochar. Adding 20% biochar to poultry litter reduced ammonia emissions by 64% over
42 days (Steiner et al. 2010) compared to a non-amended control. Dias et al. (2009) found
that N losses when using biochar as a bulking agent were lower than when coffee husks
were used, but greater than when sawdust was used as a bulking agent. These results are
promising, especially considering the recalcitrance of biochar in soil compared to other
bulking agents, and the potential for biochar to reduce odors in compost and retain
inorganic N against leaching, after soil application. Indeed Steiner et al. (2007) found
greater yield of maize and sorghum on an acid soil after four years when biochar was
applied with compost as opposed to being applied with synthetic fertilizer.
Dr Makoto Ogawa of the Osaka Institute of Technology in Japan states: “Making
compost from litter and excretions has been common in Japan for a long time. In the
1980s, charcoal compost was made from fresh chicken dung and palm shell charcoal; the
more charcoal used, the faster the composting process. Under aerobic conditions the
Bacillus group became dominant and produced antibiotics that inhibited growth of soilborne
pathogens and suppressed root diseases. Charcoal compost is now sold in Japan as
a biological fungicide. Various other organic composts are now being been produced
from livestock excretions and charcoal and sold commercially.” (Ogawa, 2009).
Biochar and manure
In a column study, Laird et al. (2010) found that the addition of biochar to manureamended
soil reduced the leaching of nutrients. One method for mixing biochar with
manure is to feed biochar directly to animals. While there are constraints on the amount
of biochar which can be delivered to soil in this way, it can potentially provide other
advantages. It has been known for a long time that adding charcoal or various zeolite-like
materials to the feed of livestock improves their ability to utilize protein and assimilate
protein-derived nitrogen from poor-quality (tannin-rich) fodder, most probably via
control of loss of ammonia that is subsequently used for microbial protein synthesis in the
rumen. Van et al. (2006) showed that growth rate was 20% greater, and final animal
weight was 5% greater when goats fed tannin-rich Acacia sp. fodder were also fed less
than 1 g bamboo charcoal per kg animal weight per day. This trial lasted 12 weeks. As
suggested by Blackwell et al. (2009) and McHenry (2010), biochar can thus be
“ecologically delivered” to soil as part of the animals’ manure. A technical bulletin from
the Food and Fertilizer Technology Center (FFTC, year unknown) in Taiwan also
proposes feeding bamboo charcoal to cattle, pigs and poultry to reduce smells in barns as
well as providing other benefits to animal health. Similarly, the Brief Compend on
American Agriculture (an agriculture handbook published in 1847) gives the following
advice on keeping pigs: “If they are closely confined in pens give them as much charcoal
IBI Research Summary – Biochar in Mixtures – January 2011 page 3

twice a week as they will eat. This corrects any tendency to disorders of the stomach”
(Allen, 1847). Studies are needed to understand which characteristics ensure biochar is
safe for feeding to animals, the mode of action (adsorption, etc.) and which amounts are
beneficial.
Biochar could also conceivably be treated with compost tea, urine, nutrient-rich effluent,
and other products. The efficacy of such treatments and their value in “improving”
biochar materials has not yet been demonstrated.
References
Allen, R.L., 1847. A Brief Compend of American Agriculture, second edition. C. M. Saxton, New York.
Blackwell, P., Riethmuller, G., Collins, M., 2009. Biochar Application to Soil (Chapter 12). In: Lehmann,
J., Joseph, S. (Eds.), Biochar for Environmental Management: Science and Technology.
Earthscan, London, UK, p. 207.
Dias, B.O., Silva, C.A., Higashikawa, F.S., Roig, A., Sanchez-Monedero, M.A., 2009. Use of biochar as
bulking agent for the composting of poultry manure: Effect on organic matter degradation and
humification. Bioresource Technology 101, 1239-1246.
FFTC (Food and Fertilizer Technology Center), 14 Wenchow St., Taipei, Taiwan ROC
Tel.: (886 2) 2362 6239 Fax: (886 2) 2362 0478 E-mail: fftc@agnet.org Website:
www.fftc.agnet.org “Use of bamboo charcoal to remove the bad smell of manure” Livestock
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Formowitz, B., Elango, F., Okumoto, S., Muller, T., Buerkert, A., 2007. The role of "effective
microorganisms" in the composting of banana (Musa ssp.) residues. Journal of Plant Nutrition and
Soil Science-Zeitschrift Fur Pflanzenernahrung Und Bodenkunde 170, 649-656.
Habte, M., Antal, M.J., 2010. Reaction of mycorrhizal and nonmycorrhizal Leucaena leucocephala to
charcoal amendment of mansand and soil. Communications in Soil Science and Plant Analysis 41,
540-552.
Hua, L., Wu, W.X., Liu, Y.X., McBride, M., Chen, Y.X., 2009. Reduction of nitrogen loss and Cu and Zn
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Jensen, H., Guilaran, L., Jaranilla, R., and Garingalao G. 2006. APPENDIX 6
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Conference, May 17-20 2009, Gold Coast, Australia.
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Reap Canada, online information available at: http://www.reap-canada.com/bio_and_climate_3_4.htm.
Last accessed 8 February 2010.
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Steiner, C., Teixeira, W.G., Lehmann, J., Nehls, T., de Macedo, J.L.V., Blum, W.E.H., Zech, W., 2007.
Long term effects of manure, charcoal and mineral fertilization on crop production and fertility on
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