Bio-char or Agri-char: the new frontier
Inspired by the fascinating properties of Terra Preta de Indio, bio-char is a soil amendment that has the potential to revolutionize concepts of soil management. While “discovered” may not be the right word, as bio-char (also called charcoal or biomass-derived black carbon, recently in context of agricultural application also named agri-char) has been used in traditional agricultural practices as well as in modern horticulture, never before has evidence been accumulating that demonstrates so convincingly that bio-char has very specific and unique properties that make it stand out among the opportunities for sustainable soil management.
The benefits of bio-char rest on two pillars:
1- The extremely high affinity of nutrients to bio-char
2- The extremely high persistence of bio-char
These two properties (which are truly extraordinary – see details below) can be used effectively to address some of the most urgent environmental problems of our time:
1- Soil degradation and food insecurity
2- Water pollution from agro-chemicals
3- Climate change
“Soils with bio-char additions are typically more fertile, produce more and better crops for a longer period of time.”
THE TWO PILLARS OF BIO-CHAR PROPERTIES
Nutrient Affinity
All organic matter added to soil significantly improves various soil functions, not the least the retention of several nutrients that are essential to plant growth. What is special about bio-char is that it is much more effective in retaining most nutrients and keeping them available to plants than other organic matter for example common leaf litter, compost or manures. Interestingly, this is also true for phosphorus which is not at all retained by ‘normal’ soil organic matter.
Persistence
It is undisputed that bio-char is much more persistent in soil than any other form of organic matter that is commonly applied to soil. Therefore, all associated benefits with respect to nutrient retention and soil fertility are longer lasting than with alternative management. The long persistence of bio-char in soil also make it a prime candidate for the mitigation of climate change as a potential sink for atmospheric carbon dioxide. The success of effective reduction of greenhouse gases depends on the associated net emission reductions through bio-char sequestration. However, a net emission reduction can only be achieved in conjunction with sustainable management of biomass production. During the conversion of biomass to bio-char about 50% of the original carbon is retained in the bio-char, which offers a significant opportunity for creating such a carbon sink.
LAND-USE SYSTEMS AND BIO-CHAR USE
Bio-energy production through low-temperature pyrolysis
“Combining bio-energy production with bio-char application to soil offers one of the most exciting perspectives of future land-based production technologies.”
Terra Preta
“The knowledge that we can gain from studying the Amazonian dark earths, found throughout the Amazon River region, not only teaches us how to restore degraded soils, triple crop yields and support a wide array of crops in regions with agriculturally poor soils, but also can lead to technologies to sequester carbon in soil and prevent critical changes in world climate,” said Johannes Lehmann, assistant professor of biogeochemistry in the Department of Crop and Soil Sciences at Cornell University, speaking today (Feb. 18) at the 2006 meeting of the American Association for the Advancement of Science.
Lehmann, who studies bio-char and is the first author of the 2003 book “Amazonian Dark Earths: Origin, Properties, Management,” the first comprehensive overview of the black soil, said that the super-fertile soil was produced thousands of years ago by indigenous populations using slash-and-char methods instead of slash-and-burn. Terra preta was studied for the first time in 1874 by Cornell Professor Charles Hartt.
Whereas slash-and-burn methods use open fires to reduce biomass to ash, slash-and-char uses low-intensity smoldering fires covered with dirt and straw, for example, which partially exclude oxygen.
Slash-and-burn, which is commonly used in many parts of the world to prepare fields for crops, releases greenhouse gases into the atmosphere. Slash-and-char, on the other hand, actually reduces greenhouse gases, Lehmann said, by sequestering huge amounts of carbon for thousands of years and substantially reducing methane and nitrous oxide emissions from soils.
“The result is that about 50 percent of the biomass carbon is retained,” Lehmann said. “By sequestering huge amounts of carbon, this technique constitutes a much longer and significant sink for atmospheric carbon dioxide than most other sequestration options, making it a powerful tool for long-term mitigation of climate change. In fact we have calculated that up to 12 percent of the carbon emissions produced by human activity could be offset annually if slash-and-burn were replaced by slash-and-char.”
In addition, many biofuel production methods, such as generating bioenergy from agricultural, fish and forestry waste, produce bio-char as a byproduct. “The global importance of a bio-char sequestration as a byproduct of the conversion of biomass to bio-fuels is difficult to predict but is potentially very large,” he added.
Applying the knowledge of terra preta to contemporary soil management also can reduce environmental pollution by decreasing the amount of fertilizer needed, because the bio-char helps retain nitrogen in the soil as well as higher levels of plant-available phosphorus, calcium, sulfur and organic matter. The black soil also does not get depleted, as do other soils, after repeated use.
“In other words, producing and applying bio-char to soil would not only dramatically improve soil and increase crop production, but also could provide a novel approach to establishing a significant, long-term sink for atmospheric carbon dioxide,” said Lehmann. He noted that what is being learned from terra preta also can help farmers prevent agricultural runoff, promote sustained fertility and reduce input costs.
What the soil scientists, working with microbiologists, discovered was that a community of bacteria exists in symbiosis with the root hairs of plants. The bacteria produce enzymes that release the mineral ions trapped by the heat stabilized plant resins in the charcoal and make it available to the root hairs of the plant as nutrients. In return, the plants secrete nourishment for the bacteria. Not only that, but the resins within the charcoal act like an ion exchange resin, adsorbing traces of mineral ions onto the charcoal particle surfaces from the rain water, and trapping it within the charcoal’s molecular structure, where it can be held for centuries – until the soil bacteria associated with a root hair come along and secrete the enzymes necessary for it to be released once again. So the trace minerals always present in rainwater actually act as a fertilizer – providing the nutrients needed by the crops, year after year. The secret of the soil fertility of the terra preta was finally understood. And it was understood how the indigenous farmers were able to produce bumper crops year after year, decade after decade without a single application of chemical fertilizer and without wearing out the soil. . .
This discovery also solves a mystery that has puzzled farmers in tropical regions for years. It has long been known that growing sugar cane increases soil fertility. Over the years, soil in which sugar cane has been grown can become quite fertile – the opposite of what happens with nearly all other crops, which tend to exhaust soil. We now know the reason why – sugar cane fields are normally set alight before harvesting. The flames sweep through the field, burning off the thicket of leaves and leaving only the cane behind, making it much easier to harvest. What is left behind also includes a small amount of charcoal, which finds its way into the soil, gradually adding to its fertility, year after year. Where I live in Costa Rica, sugar cane, which is a low-value crop, is often grown simply to keep the farm alive and sustain the soil, while the farmer tries to find an alternative use for his land. It is a sad situation, but now there is an alternative. It is to make the land economically productive once again, by doing deliberately what the cultivation of sugar cane does accidentally.
We have two pressing problems – the need for energy and the need for food. With energy we can develop nations and with food we can feed growing populations. It’s not automatic or simple, but with these two problems conceptually solved the difficult details of owning and operating a civilization can receive our full attention.
So why aren’t we already doing this on a large scale? Gardeners have been doing it for ages in some places. But char is highly alkaline (high pH) and rich in potassium salts so it may exacerbate problems in some soils already too alkaline. Still, there are lots of acidic soils that need potassium salts. It may not work everywhere but it seems like it would in lots of places. Lehmann, the Cornell guy, is still doing studies. Maybe it’s just early days.
This research explores the opportunities and constraints to combining a bio-char soil management with energy production using novel low-temperature pyrolysis. Three real-world issues justify this approach: (1) The ever increasing pressure on rural land users to generate sufficient income from their land with decreasing market prices for food; (2) the necessity to provide sustainable production systems that minimize on- and off-site pollution and soil degradation; and (3) the demand for solutions to global warming. . .
The proposed technology is low-temperature pyrolysis that yields bio-oil, hydrogen or directly electricity as the energy carrier (including valuable co-products), with bio-oil being the more advanced and more wide-spread technology (Meier and Faix 1999; Bridgwater et al. 2002). The biomass feedstock may include a wide variety of biomass (Yaman 2004) such as wood chips or pellets, bark, crop residues such as nut shells or rice husks, and grass residues such as bagasse from the sugarcane industry. More importantly, however, planted energy crops can be used with the sole purpose of producing bio-fuels, such as short-rotation woody plants (e.g. willow), grasses (e.g. Miscanthus spp.), or herbaceous plants. The key for securing environmental benefits is the production of a bio-char by-product during pyrolysis which can be applied to soil.
I can’t find the flaw. Other bio-fuel systems degrade soil, use nutrients and water, compete with food for arable land and are just hide-the-pea games anyway since they don’t sequester carbon, they just move it around. This system makes more and better farmland by sequestering carbon long term in the soil, which makes for better cation exchange capacity, and so requires less nutrients to achieve high yields, and improves nutrient and water retention in soil!
I have some acidic land weathered from granite mountains. I’ve been using calcium carbonate to get some of the benefits noted above, as well as calcium, but I have access to charcoal as well. It isn’t the fancy low-temperature pyrolysis type mentioned above, and it’s home made to boot, but I may learn something by trying it.
Update:
Bio-char seems to have another interesting property: it seems to “stimulate” AMF.
The idea that the application of charcoal stimulates indigenous arbuscular mycorrhizal fungi (AMF) 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 concept originated in the work of M. Ogawa, a former soil microbiologist in the Forestry and Forest Products Research Institute in Tsukuba. He and his colleagues applied charcoal around the roots of pine trees growing by the seashore, and found that Japanese truffles became plentiful. He also tested the application of charcoal to soybean with a small quantity of applied fertilizer, and demonstrated the stimulation of plant growth and nodule formation (Ogawa 1983). His findings with regard to legumes were taken up for further study by the National Grassland Research Institute (Nishio and Okano 1991).
That implies that rhizobia as well as AMF benefit.
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The Biomass Advisory Council to the U.S. DOE and USDA recommended in July 2004 that a biomass-based hydrogen strategy be elevated due to its “unique carbon sequestration capabilities”.[7] Extraction of energy from biomass (in the form of hydrogen) and production of a solid carbon matrix for agricultural use can offer a primary storage system for billions of tons of biologically-produced carbon as well as CO2 derived from fossil fuel combustion. The returned carbon provides inherent trace minerals and has been proven to restore degraded topsoil.
Recent developments have taught us how to produce charcoal plus a hydrogen-rich “syngas” for ammonia synthesis and fuel production. The charcoal is used as a modified selective catalytic reactor (SCR) scrubbing media for cleaning up power plant exhaust. While removing CO2, SOx and NOx from coal power plant exhaust, the charcoal is enriched with nitrogen creating a soil amendment fertilizer. This compound has very long-lasting sequestration capabilities[8],[9], [10], [11]. An economic analysis performed by the University of Kentucky and in press for The International Journal of Energy shows that this method of energy production and carbon sequestration can be a profitable method of reducing atmospheric carbon levels. This approach offers a long-term solution to our global climate change dilemma. [12]
The use of charcoal as a soil amendment has been known for thousands of years. Indigenous peoples of the Amazon were using charcoal to enrich their soil over 2,000 years ago. [13],[14] Since then, this technology has been lost or forgotten in the Americas. However, Japan has a long continuous history of charcoal use in agriculture. Agricultural research work in the mid 1990’s led the Japanese government to approve charcoal as an authorized land management practice.[15],[16],[17],[18]
The research work on combined charcoal and fertilizer shows very practical benefits. Charcoal addition has been shown to increase water holding capacity, decrease nutrient leaching, increase cation exchange capacity (i.e. nutrient uptake), increase tilth, increase microbial response (i.e. soil fertility), increase nitrogen uptake, decrease nitrogen runoff, and increase crop and biomass yields.[19], [20], [21] Its stability as a safe and natural carbon sink offers a sequestration life of geologic times. [22]
Soils offer new hope as carbon sink
Trials of agrichar using pyrolysis
The huge potential of agricultural soils to reduce greenhouse gases and increase production at the same time has been reinforced by new research findings at NSW Department of Primary Industries’ (DPI) Wollongbar Agricultural Institute.Trials of agrichar – a product hailed as a saviour of Australia’s carbon-depleted soils and the environment – have doubled and, in one case, tripled crop growth when applied at the rate of 10 tonnes per hectare.
Agrichar is a black carbon byproduct of a process called pyrolysis, which involves heating green waste or other biomass without oxygen to generate renewable energy. Tim Flannery, Australian of the Year and renowned scientist, conservationist, writer and explorer, is a major advocate of agrichar and pyrolysis. In The Bulletin magazine, Flannery recently ranked “fostering pyrolysis-based technologies” fourth among his five steps for saving the planet, because they convert crop waste into fuel and agrichar which can be used to enhance soil fertility and store carbon long-term.
NSW DPI senior research scientist Dr Lukas Van Zwieten said soils naturally emit about 10 times more greenhouse gas on a global scale than the burning of fossil fuels. “So it is not surprising there is so much interest in a technology to create clean energy that also locks up carbon in the soil for the long term and lifts agricultural production,” he said. The trials at Wollongbar have focused on the benefits of agrichar to agricultural productivity. “When applied at 10t/ha, the biomass of wheat was tripled and of soybeans was more than doubled,” said Dr Van Zwieten. “This percentage increase remained the same when applications of nitrogen fertiliser were added to both the agrichar and the control plots. “For the wheat, agrichar alone was about as beneficial for yields as using nitrogen fertiliser only. “And that is without considering the other benefits of agrichar.”
Regarding soil chemistry, Dr Van Zwieten said agrichar raised soil pH at about one-third the rate of lime, lifted calcium levels and reduced aluminium toxicity on the red ferrosol soils of the trial.
“Soil biology improved, the need for added fertiliser reduced and water holding capacity was raised,” he said. The trials also measured gases given off from the soils and found significantly lower emissions of carbon dioxide and nitrous oxide (a greenhouse gas more than 300 times as potent as carbon dioxide).
“For the environment, it means soil carbon emissions can be reduced because rapidly decomposing carbon forms are being replaced by stable ones in the form of agrichar.”
NSW DPI environmental scientist Steve Kimber said an added benefit for both the farmer who applies agrichar and the environment is that the carbon in agrichar remains locked up in the soil for many years longer than, for example, carbon applied as compost, mulch or crop residue.
“We broadly categorise carbon in the soil as being labile (liable to change quickly) or stable – depending on how quickly they break down and convert into carbon dioxide,” he said.
“Labile carbon like crop residue, mulch and compost is likely to last two or three years, while stable carbon like agrichar will last up to hundreds of years.
“This is significant for farmer costs because one application of agrichar may be the equivalent of compost applications of the same weight every year for decades.