« Scenarios on the Downslope: Insights from Greer’s The Ecotechnic Future | Home | How the Maximum Power Principle affects living systems »
Biochar – a Critical View Through the Ecosystemic Lens
By Karl North | October 30, 2017
I have been following the biochar story since it began to gain visibility over a decade ago. I view it from the perspective of forty years of farming informed by study of systems ecology. My understanding of both of these pursuits has evolved over that time in ways that will inform this critique. I began to study ecology in a unique graduate program in anthropology that regarded the knowledge of a society as incomplete without an understanding of its ecological foundation. However I still saw the study of ecosystems as one field of knowledge among others. Gradually I have come to see it as the master or umbrella discipline, one that that provides an essential framework for all other inquiry.
Similarly, in farming I first saw the enterprise I was creating as sheep farming. As the wellbeing of my sheep and draft horses was heavily reliant on the health and productivity of perennial grasses, it began to make more sense to think of the enterprise as grass farming. But as forage quality and productivity in turn depends on the state of the soil and its food web, I ultimately came to see myself as a carbon farmer, as it became increasingly apparent what an important role the level of soil organic matter (and its carbon) plays in the fitness and success of the farm as an agroecosystem. Others have experienced this evolution, and now there exist increasing numbers of self-proclaimed carbon farmers, for whom a central question is to design a farming system that insures the best regeneration of soil carbon.
Getting past the Greenwash
Given the background described above, it should not surprise the reader to learn that I have tended to regard with the healthy skepticism of a student of science the promotion of a form of charcoal as a soil amendment. A fad enhanced with an intriguing story of terra preta, the dark earth residue of a mysterious ancient Amazonian civilization, appears designed to enlist environmentalists desperate for a solution to climate change and to entice business people who are always looking for a new way to make a profit. With agricultural soil organic matter levels typically down in the 1-2% range due to conventional tillage agriculture, there is no doubt of a need to rebuild soil, and since it sequesters atmospheric carbon in the process, so much the better. However, as ecological farmers, we have studied the many ways both mankind and nature have generated and regenerated soil. Rodale’s excellent long term trials demonstrated one way. An example of dark earths that evolved in natural ecosystems is the muck soils sought by growers of heavy feeders like onions. The real question for us should be: What is the most effective way that integrates with ecosystem processes and does no harm in the larger context?
The first tipoff of an attempt to create a new fashion is to dress up something old with a more attractive label. The term “Biochar”, like ‘clean propane’ or ‘clean coal’, is an attempt to make a substance and a process sound greener than it really is. Biochar is no more nor less biological than any other form of charcoal. All charcoals are made from biomass (any substance that is or once was part of a living thing) by pyrolysis, which is oxygen-starved combustion, a rather violent process by comparison with the ways biomass is decomposed in most ecosystemic carbon cycling. I am using the term biochar in this article only because that is how the general public recognizes it. A more neutral term used in the scholarly literature is black carbon.
A lengthy review of the literature on the subject only tended to confirm my skepticism. Currently it is mostly blatant promotion – garden variety advertising; I could find few attempts to view the subject critically with the habitual skepticism necessary to scientific appraisal. A common kind of statement is the following: “Biochar is increasingly being recognized by scientists and policy makers for its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation, and as a soil amendment.”[1]
As the biochar feeding frenzy has reached new heights, even the scientific papers tend to begin on a promotional tone, with just enough ambiguity in the language to cover for the caveats buried deep in the studies. For example, Biochar is often described as if it were a fertilizer. A website of Cornell University, a hot spot of biochar research, postulates “the soil fertility benefits of biochar”.[2] To the lay reader that carries the implication that it is a fertilizer. The fact that biochar is not a fertilizer and makes little direct contribution to soil fertility is often buried deep in the scientific literature.
Again for the lay reader, the literature also tends to confuse biochar with terra preta/dark earth by using the properties of the latter to promote the former. The properties of earth darkened with carbon from any source are the result of a complex systemic process of interaction between the carbon and the other soil constituents over a long time frame; they vary in the extreme with the nature of a specific soil and climate and cannot be deduced from the properties of charcoal alone or in a short term laboratory trial.
Stoked by the desire to defy the limits to growth on a finite planet, the business-oriented literature is also full of glowing expectations that biochar production will deliver yet another agro-fuel to replace fossil fuels as the end of cheap oil starts to bite into the global economy. Given the disastrous boondoggle of corn ethanol and soy diesel, production of which steals land from food production and exists only with the prop of massive subsidies because it can never deliver any appreciable net energy, it is surprising that anyone has the nerve to suggest another agrofuel project.
Finally, the treatment of this subject, as with most others, suffers from the limitations of narrow focus of the dominant reductionist way of doing science. Big questions like sustainability and climate dynamics require a systemic approach. I could find few attempts in the literature to compare biochar use with alternative solutions, or to make the full life cycle energy calculations necessary to any investigation of energy production or consumption in complex systems like ecosystems and human economies.
In this article I will address the following claims of the biochar promoters:
- Biochar has the unique ability to indirectly enhance soil fertility by encouraging the growth of soil microbial populations and store and retain plant nutrients.
- It is more stable than more naturally occurring carbonaceous compounds, and therefore a better option for sequestration to mitigate climate change.
- Some of the gaseous byproducts of biochar production could replace fossil fuel use, also mitigating climate change.
I will demonstrate that the first claim, while true, is misleading because it ignores other, better ways of providing the same benefits. Regarding the second claim, while the relative stability of biochar appears true, I will show that properly designed agroecosystems can achieve the same carbon sequestration results while better serving overall system health and productivity. Regarding the third claim, I will argue that while pyrolysis produces burnable methane, so do other less violent processes. Moreover, like all energy alternatives, it will fail to reduce fossil fuel use due to the Jevons Paradox[3]. As with all attempts to produce biofuels, whether the consequences for society and the planet are good or bad depends greatly on the choice of biomass feedstock and where it comes from. As I will argue, there are no biochar feedstocks produced in any ecosystem on the planet whose massive expropriation would not damage the normal, necessary function of the carbon cycle in that ecosystem. Unless of course one is counting on sourcing them from Mars.
Seeing the issue through the ecosystemic lens
The ecosystemic lens is the worldview that frames all inquiry in terms of the dynamics and health of the ecosystem processes. The health of these processes and obedience to their laws are essential to the long term survival of all species within its system, including us. Although we have been led to believe since the Book of Genesis that Nature is our plaything, Nature rules us, not the other way around.
Using the ecosystemic lens, students of ecosystems soon realize and must come to terms with the complexity of our environment, which derives from the interaction and interdependence of so many of its parts. Within ecosystemic wholes they see further layers of complexity: social wholes and organisms, especially ours. They discover that there is no simple answer to any problem because all problems are ultimately connected and consequences of actions are multiple. They realize that when intervening in complex systems, one can never do just one thing! There are always ripple effects, and consequences distant in space or time are commonly far different from immediate ones. In my view a critical assessment of any human activity or technology needs to be undertaken through the ecosystemic lens. That is how I intend to explore the question of biochar.
Farmers who see agriculture in an agroecological framework know that the health of ecosystem processes includes proper carbon and other mineral cycling. The biochar literature consistently refers to biochar feedstocks as “wastes” or “residues”, a first tip-off of the narrow unecological lens through which promoters are viewing the subject.
I still remember hearing sustainability pioneer William McDonough[4] in a keynote address to the Pennsylvania Association for Sustainable Agriculture years ago stating, “There’s no such thing as waste!” Ecosystems, whether managed or natural, must follow the ‘law’ of the ecosystem food web: waste=food=waste=food. The level of ecosystem health and sustainability depends on how well this law is obeyed. In the language of systems ecology, there exists a mineral/nutrient cycle that must not fail or be broken, and if possible must be enhanced.
1. Biochar has the unique ability to indirectly enhance soil fertility by encouraging the growth of soil microbial populations and store and retain plant nutrients.
The main trouble with this claim is not with the truth of the functions of black carbon in the soil, but of with the claim of uniqueness of biochar to serve these functions. A typical statement is: “The application of bio-char (charcoal or biomass-derived black carbon (C)) to soil is proposed as a novel [my italics] approach to establish a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems.”[5] It should not be necessary to remind readers of The Natural Farmer that ways of getting soil carbon up to optimal levels and keeping it there are hardly new.
There exist numerous ways to get black carbon into the soil and keep it there. However the biochar literature rarely considers these other ways of obtaining dark earth and its benefits, hence, what is worse, it rarely compares them to its favorite, biochar production, an industrial process that occurs outside the agroecosystem. So let’s do the comparison.
From the viewpoint of conventional chemical fertilization – soluble salt fertilizers that can contain as much as 40% of N, P or K – neither compost nor pyrolysis rate as fertilizers. Both processes lose nutrients, especially nitrogen amd carbon. Figures vary in the scholarly studies, so the following are some purely illustrative figures from different studies to compare nutrient retention in the two processes:
- Composting: high C/N ratios obtained using deep litter bedding limit N losses to 12-18%,[6] and losses can go as low as 5%.[7] C losses range from a high of about 40% – same as in pyrolysis – down to 19%, again depending on how well the compost is made.[8]
- Pyrolysis. N losses ranged from 10.4% to 72.6% depending on the N concentration in the feedstock. The higher the N concentration vs. C, the higher the loss. “The amount of N conserved ranged from 27.4% in the PL biochar to 89.6% in the PC biochar and was inversely proportional to the feedstock N concentration.”[9] PC and PL refer to different feedstocks.
Unlike pyrolysis (a chemical process), composting is a biological process, a version of carbon cycling time-tested through several billion years of natural history. Ongoing vegetation die-off and regrowth in natural ecosystems in many locations slowly build soil organic matter and its black carbon content up to maintenance levels that due to constant renewal can be permanent, barring disturbance – natural ones like landslides or erosive floods or man-made ones like tillage. In the US Northeast these levels commonly attain 5-6% soil organic matter (SOM).
Based on this ecosystemic knowledge, the well-known 30-year project of organic farming research pioneer, Rodale Institute, demonstrated that a combination of animal integration, legume-based forage rotations, cover-cropping and herbicide-free minimal tillage can even improve on natural SOM levels in the Northeast and quicken the process. And regarding the carbon sequestration potential of their system, Rodale concluded,
“Simply put, recent data from farming systems and pasture trials around the globe show that we could sequester more than 100% of current annual CO2 emissions with a switch to widely available and inexpensive organic management practices, which we term “regenerative organic agriculture.” These practices work to maximize carbon fixation while minimizing the loss of that carbon once returned to the soil, reversing the greenhouse effect.”[10]
The work of two holistic scientists, French farmer-researcher André Voisin and range ecologist Alan Savory brought more insights from natural ecosystems to bear, and demonstrated systems that accelerated the ability of Rodale’methods to regenerate soil even more, permanently raising soil carbon levels in the same way.
Unfortunately, most US readers of Grass Productivity, Voisin’s chef d’oeuvre, absorbed only the rotational grazing component of the effort in healthy agroecosystem design that his title implies. Using long term studies from different European farming systems, Voisin showed that a system that integrated careful manure management, planned grazing and the potentially productive ‘wet meadows’ common to many European coastal plains could rebuild soil and produce a surplus of fertility that, applied to crop fields, in many cases had sustained those farming systems and their soil carbon levels for hundreds of years.[11]
While Voisin’s system was designed to work well in cool wet, temperate environments like New England and Europe, Savory adapted it to work in arid, seasonal rainfall environments like rangelands in Africa, Australia and the US western plains. Studies of the performance of the Savory system on grasslands all over the world bear out Savory’s conclusion:
By restoring grasslands through Holistic Planned Grazing we have the potential to remove the excess atmospheric carbon that has been the result of both anthropogenic soil loss over the past ten thousand years and industrial-era greenhouse gas emissions. This sequestration potential, when applied to up to 5 billion hectares of degraded grassland soils, could return 10 or more gigatons of excess atmospheric carbon to the terrestrial sink annually thereby lowering greenhouse gas concentrations to pre-industrial levels in a matter of decades. This while restoring agriculture productivity, providing jobs for thousands of people in rural communities, supplying high quality protein for millions, and enhancing wildlife habitat and water resources.[12]
In all three regeneration systems, permanently renewing carbon pools, especially lower ones, function to provide the same increase of sites for bacteria and mineral capture that biochar offers. Not often mentioned in the biochar literature is the fact that all soils with appreciable clay content perform the same mineral and microbial site functions.
However, high organic matter soils created by these regeneration systems go beyond the functions of biochar to provide better tilth, air and water capacity, and an essential feedstock of energy and minerals in organic form for the growth of the soil microbial food web. In that sense a dense soil microbial/fungal community acts like a keystone species in regard to ecosystem function. Without decomposing organic matter, soil microbial population densities remain relatively low. The crucial importance of high microbial populations in the soil food web to overall agroecosystem health and productivity has finally been recognized by the agricultural research community after generations of focus on only the chemistry.
2. Charcoal is more stable than more naturally occurring carbonaceous compounds, and therefore a better option for sequestration to mitigate climate change.
About That Carbon Cycle: A proper comparison of biochar with other methods described above requires at least an elementary understanding of the carbon cycle that must work properly in all of them. First, carbon is lost to the atmosphere in all processes that reduce complex carbonaceous organic matter to simpler forms – everything from the rapid, violent extreme of normal burning to pyrolysis to bacterial decomposition, to metabolism in humans and other animals. So those losses need to be subtracted from any calculations of the sequestration potential of a system that uses any of the above biomass reduction processes.
Second, soil organic matter decomposition proceeds through stages that scientists describe as carbon pools of increasing carbon loss as CO2 but also increasing stability in the carbon that remains. A typical biochar research paper states, “Although little research has been published on the long-term stability of biochar, studies suggest a mean residence time (MRT) for charcoal in soil in the order of millennia, compared to 50 y for bulk soil organic matter.”[13] So apparently the lowest, most stable soil carbon pools from microbial decomposition cannot match the stability of the black carbon in biochar. However, what is missed in the comparison is the ability of managers to constantly renew soil organic matter and maintain rebuilt soil carbon levels and therefore the sequestration, once brought to full potential, as in the agroecosystem designs already described above. Hence the constant renewal in these systems serves the same stability/sequestration function of biochar, and provides many more benefits as well.
3. Some of the gaseous byproducts of biochar production could replace fossil fuel use, also mitigating climate change.
First, let’s take a closer look at pyrolysis. Burning anything at all seems an unlikely cure for an overheating planet. No matter how it is done, or what is burned, combustion creates pollution — air pollution, particulates, ashes, various toxins and soot, the second largest warming agent created after C02. Pyrolysis is much dirtier in particulate and other pollutions than normal high-oxygen clean burning.
As already mentioned, pyrolysis also destroys some of the nutrient-value in the biomass feedstock. Even at the lowest temperatures adopted recently in the production of biochar, 50% of the nitrogen in the biomass can be lost. Compare that with well-made (high C/N ratio) compost that can retain larger quantities of nitrogen.
Also, a trade-off exists between fuel and biochar production. Pyrolysis can be done at different temperatures with more biochar production at lower temperatures and more fuel production at higher ones. The same process cannot maximize both.
In the evaluation of any complex production process through the ecosystemic lens, a full life cycle calculation is called for, not only of energy and carbon outcomes, but all other short and long term effects on the health of larger systemic wholes. I found only one such evaluation of pyrolysis in the literature:[14]
Yet even this attempt is flawed: Where in this picture is the 40% of co2 in the biomass feedstock that is lost to the atmosphere as greenhouse gas during pyrolysis?
The real agenda of the business community for biochar seems to be the creation of yet another agrofuel boondoggle, dressed up in the green garb of carbon sequestration to save the climate. The capture of fuel gases as a byproduct of pyrolysis will not scale up to any significant degree without further expropriating agricultural land, especially in less developed countries. Already the activists and critics who exposed the disastrous consequences, particularly for the less developed world, of the corn ethanol and other agrofuel projects, are exposing attempts at land grabs for the harvest of biomass feedstocks in the global south for industrial scale pyrolysis and fuel production.
A paper entitled “Land Grabs for Biochar” describes “carbon grabs” as one of the most recent forms of land grab being resisted by the less developed countries, partly because it “threatens a re-run of ‘biofuels vs. food’ controversies and resource appropriations, yet with a new twist as carbon grabs for other biofuels and for biochar feedstocks threaten to compete with each other too. NGO activists and African governments alike have seized on the land grab spectre to mount vociferous critiques of biochar as a whole.”[15] To what degree that “spectre” will fulfill itself is unclear due to many variables, not least the grinding to a halt of the industrial civilization juggernaut as scarcity looms for its main energy source, oil.
There exists one method of biofuel production that, unlike biochar, returns a large amount of mineral fertility as a soil amendment, and can be designed to serve useful functions as an integral part of an agroecosystem when kept small in scale. Anaerobic digesters small and simple enough to have seen wide adoption in peasant communities on several continents produce enough methane for families to cook and light with, and fit well into the carbon cycle of farms that produce wet manures such as from pigs, poultry, and humans. Figure 1 is an example of such a design.
Part of the hype of biochar promotion is its proposed provision of carbon credits. As one scholarly paper states, “Bio-char soil management systems can deliver tradable C emissions reduction, and C sequestered is easily accountable, and verifiable.”[16] This too is surprising in a scientific paper, because carbon trading has been exposed for years as a scam used by big business to greenwash itself while allowing it to continue to pollute.
What seekers of alternate energy sources fail to understand is that the present excessive level of energy consumption is the problem. It inevitably entails the resource depletion and damage to essential ecological services that have initiated catabolic collapse of industrial civilization and the way of life it supports. Resource analyst Tim Murray conveys well the meaning of the limits to growth in his blog, Canada the Sinking Lifeboat: “The greatest calamity that could ever be inflicted on human and non-human species alike would be the discovery of an abundant, cheap and perpetual energy source, or unlimited availability of cheap food and universal and uninhibited access to bountiful water supplies.”[17] Those who fight off the fog of denial and willful ignorance that currently blankets most of humanity know that to end the suicidal industrial destruction of the planetary resource base, we need to “power down”[18], not try to replace current energy sources with others.
Niche uses for biochar
Arguably there exist niche uses for biochar in less developed countries where most cooking is done by burning biomass. Cookstoves designed by Worldstove for less developed countries are an example. They burn the combustible gases from pyrolysis to cook, leaving biochar instead of ash for the soil. If biochar claims are true, the longterm benefits of charcoal are potentially better than ash as a soil amendment. Biochar cookers have tradeoffs and limitations: hot burning stoves reduce particulate air pollution and cook faster but leave less biochar. Cookstoves that use pyrolysis produce biochar but cook more slowly and still smoke somewhat. However, better cooking solutions than biochar cookers exist. Solar cookers use simple technology and materials, directly address forest depletion, and eliminate biomass burning and its pollution and soil carbon loss entirely.
Biochar also has been proposed as a transitional stop-gap measure. Many areas of production in industrial society are chewing through the global natural resource base at a rate that is unsustainable for much longer. But as long as their termination is not politically feasible, conversion and sequestration of their byproducts (termed “wastes” in the language of the ecologically uninformed) as charcoal makes some sense. Low temperature pyrolysis of papermill byproducts is an example.[19]
Conclusion
Apart from the major objections described above, the truth of the claimed benefits to agriculture from biochar application is far from proven. According to one review of the literature, “Fifty percent of the reviewed studies reported yield increases after black carbon or biochar additions, with the remainder of the studies reporting alarming decreases to no significant differences.”[20] Also, in a German comparison of plant growth with pure compost vs. a mixture of compost and biochar, the pure compost trial came out ahead.[21]
Digging deep into one scientific paper I found a long list of sustainability criteria that pose obstacles to adoption.
“Biochar can be produced sustainably or unsustainably. Our criteria for sustainable biochar production require that biomass procured from agricultural and silvicultural residues be extracted at a rate and in a manner that does not cause soil erosion or soil degradation; crop residues currently in use as animal fodder not be used as biochar feedstock; minimal carbon debt be incurred from land-use change or use of feedstocks with a long life expectancy; no new lands be converted into biomass production and no agricultural land be taken out of food production; no biomass wastes that have a high probability of contamination, which would be detrimental to agricultural soils, be used; and biomass crop production be limited to production on abandoned agricultural land that has not subsequently been converted to pasture, forest or other uses. We further require that biochar be manufactured using modern technology that eliminates soot, CH4 and N2O emissions while recovering some of the energy released during the pyrolysis process for subsequent use.”[22]
In sum, the biochar fad seems to be one more of the increasing frenzy of wishful attempts to prolong the inevitable decline of the industrial way of life. Biochar is promoted as one more technological silver bullet. Seen through the ecosystemic lens, silver bullets don’t exist. Seen through the ecosystemic lens, we do not have a shortage of anything, we have a longage of expectations. Hence the human overshoot of planetary carrying capacity and its consequences – the accelerating destruction of the natural resource base. We need to stop grasping at straws like agrofuel from pyrolysis and reduce our energy use to the level for which the biosphere was designed.
[1] Kookana, R.S., et al. 2011. Biochar application to soil: agronomic and environmental benefits and unintended consequences. Advances in Agronomy, Volume 12, Chapter 3. Elsevier, 2011.
http://store.elsevier.com/product.jsp?isbn=9780123855381
[2] http://www.css.cornell.edu/faculty/lehmann/research/biochar/biocharmain.html
[3] Capitalist manufacture of desire trains consumers to override all attempts to conserve resources by making gains in efficiency or development of alternatives. Conservation gains are wiped out by increased consumption. William Stanley Jeavons first explained this historical human behavior pattern in 1865, in regard to coal consumption.
[4] Braumgart, Michael, and William McDonough. 2002. Cradle to Cradle: Remaking the Way We Make Things. Northpoint Press. 2002.
[5] Lehmann, Johannes, et al. 2006. Bio-char sequestration in terrestrial ecosystems – a review. Mitigation and Adaptation Strategies for Global Change, Vol. 11, Issue 2, 2006.
http://link.springer.com/article/10.1007/s11027-005-9006-5
[6] Sommer, S.G. 2001. Effect of composting on nutrient loss and nitrogen availability of cattle deep litter. European Journal of Agronomy 14 (2001) 123 – 133.
http://mie.esab.upc.es/ms/informacio/residus_ramaders/Nutrient%20loss%20composting%20manures.pdf
[7] Sommer, S.G. and P. Dahl. 1999. Nutrient and Carbon Balance during the Composting of Deep Litter. J. Agric. Engng. Res., 74, 145-153. 1999.
http://mie.esab.upc.es/ms/informacio/residus_ramaders/CN%20balance%20deep%20composting.pdf
[8] Ibid.
[9] Gaskin, J.W., et al. 2008. Effect of low temperature pyrolysis conditions on biochar for agricultural use. Transactions of the ASABE, vol. 51(6), 2061-2069. 2008. http://www.researchgate.net/publication/237079730_Effect_of_Low-Temperature_Pyrolysis_Conditions_on_Biochar_for_Agricultural_Use
[10] http://saveoursoils.com/userfiles/downloads/1398168006-RegenOrgAgricultureAndClimateChange_20140418.pdf
[11] Voisin, André. 1959. Grass Productivity. Island Press, 2nd edition, 1988.
[12] Savory Institute. 2013. Restoring the climate through capture and storage of soil carbon through holistic planned grazing. http://savory.global/assets/docs/evidence-papers/restoring-the-climate.pdf
[13] Shackley, Simon, and Saran Sohi, eds. 2010. An assessment of the benefits and issues associated with the application of biochar to soil. UK Biochar Research Centre, School of GeoSciences, University of Edinburgh. 2010
[14] Roberts, K., et al, 2010. Life Cycle Assessment of Biochar Systems: estimating the energetic, economic and climate change potential. Environmental Science and Technology. Vol. 44 (2), Pp. 827–833. http://pubs.acs.org/doi/abs/10.1021/es902266r
[15] Leach, Melissa et al. 2011. Landgrabs for biochar: narratives and counter narrratives in africa’s emerging biogenic carbon sequestration economy. Conference on Global Land Grabbing. University of Sussex, April 2011. http://www.future-agricultures.org/papers-and-presentations/conference-papers-2/1091-land-grabs-for-biochar-narratives-and-counter-narratives-in-africa-s-emerging-biogenic-carbon-seque/file
[16] Ibid.
[17] http://sinkinglifeboat.blogspot.ch/2010/02/ten-ecological-reasons-to-oppose-mass.html
[18] Heinberg, Richard. 2004. Powerdown: Options and Actions for a Post-Carbon World. New Society Publishers, 2004. http://www.amazon.com/Powerdown-Options-Actions-Post-Carbon-World/dp/0865715106/ref=tmm_pap_title_0?_encoding=UTF8&sr=&qid=
[19] Van Swieten, L. et al. 2009. Effects of biochar from slow pyrolysis of papermill waste on agronomic performance and soil fertility. Plant and Soil, Vol. 327, Issue 1-2, February 2010.
http://link.springer.com/article/10.1007/s11104-009-0050-x
[20] Spokas, Kurt, et al. 2012. Biochar : a synthesis of its agronomic impact beyond carbon sequestration. J. Environ. Quality, 41, 2012. http://www.extension.uidaho.edu/nutrient/culturalpractices/PDF/Biochar%20A%20synthesis%20of%20its%20agronomic%20Impact%20beyond%20carbon%20sequestration..pdf
[21] Schulz, Hardy and Bruno Glazer. 2012. Effects of biochar compared to organic and inorganic fertilizers on soil quality and plant growth in a greenhouse experiment. J.Plant Nutr. Soil Sci., 000, 1-13, 2012. http://www.researchgate.net/profile/Hardy_Schulz/publication/259451692_Effects_of_biochar_compared_to_organic_and_inorganic_fertilizers_on_soil_quality_and_plant_growth_in_a_greenhouse_experiment/links/004635373280742279000000.pdf
[22] Woolf, Dominic, et al. 2010. Sustainable biochar to mitigate climate change. Nature Communications, v1, n5. 2010. http://www.nature.com/ncomms/journal/v1/n5/pdf/ncomms1053.pdf
Topics: Agriculture, Northland Sheep Dairy, Systems Thinking Tools, Uncategorized | No Comments »
