Agronomic values of biochar
The needs to develop more sustainable agriculture systems and improve weak rural
economies necessitate major changes in agriculture management. Soil degradation,
including decreased fertility and increased erosion, is a major concern in agriculture.
Long term cultivation of soils could result in degradation, containing soil acidification,
soil organic matter depletion, and severe soil erosion. Furthermore, the decrease in
soil organic matter decreases the aggregate stability of soil, therefore, it is crucial to
remediate the degradation soils by simple and sustainable methods.
The thermal process that produces biochar is called pyrolysis, pyro, meaning fire and lysis,
meaning separation. During pyrolysis, the crucial trace elements found in plants (over 50
metals) become part of the carbon structure, thereby preventing them from being leached
out while making them available to plants via root exudates and microbial symbiosis.
A range of organic chemicals are produced during pyrolysis. Some of these remain stuck to
the pores and surfaces of the biochar and may have a role in stimulating a plant’s internal
immune system, thereby increasing its resistance to pathogens. The effect on plant defense
mechanisms was mainly observed when using low temperature biochars.This potential use
is, however, only just now being developed and still requires a lot of research effort.
Soil mineral depletion is a major issue due mainly to soil erosion and nutrient leaching. The
addition of biochar is a solution because biochar has been shown to improve soil fertility, to
promote plant growth, to increase crop yield, and to reduce contaminations. We review here
biochar potential to improve soil fertility. The main properties of biochar are the following:
high surface area with many functional groups, high nutrient content, and slow-release
fertilizer.
Biochar is much too valuable for it to be just added to soil without using it at least once for
other beneficial purposes. Basic uses include: drinking water filtration, sanitation of human
and kitchen wastes, and as a composting agent. All of these uses have been documented in
many different pre-industrial cultures. In the modern world, the uses multiply: adsorber in
functional clothing, insulation in the building industry, as carbon electrodes in capacitors for
energy storage, food packaging, waste water treatment, air cleaning, silage agent or feed
supplement. All those uses could be part of more complex cascades when, after extended
up- and down cycling, biochar can be used in a farmer’s manure slurry pit or in a sewage
treatment plant, before being composted and thus finally becoming a soil amendment.
Biochar should only be worked into the soil at the end of such cascades, keeping in mind
that some biochar uses, for cleaning up metal or chemical contamination, would render the
biochar unsuitable for agricultural soils and need different recycling pathways.
At present some 40% of the biochar used in Croatia goes into animal farming.
Different to its application to Croatian fields, a farmer will notice its effects within a few days.
Whether used in feeding, litter or in slurry treatment, a farmer will quickly notice less smell.
Used as a feed supplement, the incidence of diarrhea rapidly decreases, feed intake is
improved, allergies disappear, and the animals become calmer. In Germany, researchers
conducted a controlled experiment in a dairy that was experiencing a number of common
health problems: reduced performance, movement disorder, fertility disorders, inflammation
of the urinary bladder, viscous salivas, and diarrhea. Animals were fed different
combinations of charcoal, sauerkraut juice or humic acids over periods of 4 to 6 weeks.
Experimenters found that oral application of charcoal (from 200 to 400 g/day), sauerkraut
juice and humic acids influenced the antibody levels to C. botulinum, indicating reduced
gastrointestinal neurotoxin burden. They found that when the feed supplements were ended,
antibody levels increased, indicating that regular feeding of charcoal and other supplements
had a tonic effect on cow health.
20% of the biochar used in Croatia goes into soil.
The application of biochar into soils has great potential for improving soils fertility and
promoting plant growth. The choice of biochar managing various soils is flexible, because
diverse biomass materials could be used as feedstocks of biochars and the feedstocks could
be pyrolyzed at different temperatures. Moreover, biochar has huge surface area,
well-developed pore structure, amounts of exchangeable cations and nutrient elements, and
plenty of liming. Because of these properties, soil properties could be improved after biochar
treatment. For instance, the huge surface area and well-developed pore structure may
increase the water holding capacity and microbial abundance. The cation exchange capacity
and availability of nutrients could be increased due to the amounts of exchangeable cations
and nutrient elements. The increased pH of soils should be attributed to the plenty of liming
contained in biochar. Therefore, improvements of soil physical, chemical, and biological
properties promote the productivity of plant through increasing the amount of nutrient
elements, enhancing availability of nutrient elements, reducing nutrient leaching, and
mitigating gaseous nutrients losses.
These results of characterization analyses, column experiments and some field trials
indicated that biochar could be designed or may have the potential to manage specific soil
purposefully, through controlling the feedstock and pyrolysis conditions. Biochar can be a
novel and feasible fertilizer directly or indirectly. This is not only because of the biochars
fertility but also their environmental and economic benefits. Despite the interests of using
biochars to manage soils is increasing, some studies are also reported the negative effects
and a number of research gaps as well as uncertainties still exist as discussed above in this
review. In order to clear these knowledge gaps, further relevant investigations are inevitable
in the following research, especially long-term experiments.
References
Schmidt HP, Wilson K:
‘The 55 uses of biochar’
Yang Ding, Yunguo Liu:
‘Biochar to improve soil fertility’
Zeljko Serdar:
‘Agronomic values of biochar’
Aciego Pietry:
‘Relationships between soil pH and microbial properties in a UK arable soil’
Croatian Center of Renewable Energy Sources (CCRES)