Just came back from a seminar with William I. Woods of the University of Kansas about Terra Preta. He has spent a lot of time on this and the seminar was very interesting. William was rather provocative and made a number of bold statements such as
- all the fertile steppes (pampas, the Norh American prairies and the Pontic steppe, i.e. are of man-made origin, having been forests burnt down by people
- composting is very bad as most of the carbon is lost
- the best strategy to deal with climate change is to cut down the Amazon forests and to make bio char from it, let it grow again - and make more bio char etc.
The latter statement is closely linked to his research which states that contrary to what most believe the Amazon was rather populated in the history AND it was to a large extent deforested. He stated that the "little ice age" partly was caused by the return of forests in the Amazon (gulping up the carbon in the atmosphere) as a result of post 1491 decline in population. Interesting thought-I do agree with him to some degree. We tend to overlook how much humans have transformed ecosystems in the past. The fact is that also large scale transformation took place long before "modern" society and industrialism. Ruddiman has also pointed that out in a good way.
I have written before about that the relationship between man and nature is a bit more complex than we mostly beleive:
Climate; doing the things right or doing the right thing?
http://gardenearth.blogspot.com/2010/04/reminder_17.html
http://gardenearth.blogspot.com/2009/09/we-are-part-of-nature.html
How fertile are terra preta soils?
When it comes to the power of Bio Char I am less convinced. There is a lot of promotion of BioChar today and like many other techno-fixes it seems somewhat over-promoted in my view. We now have multi-million research programs and (of course) biochar standards and certification.
From the presentation of William Woods, I realise that the terra preta soils of the Amazon are not only a result of charcoal use and making, but perhaps even more of a large scale import of nutrients from a hinterland, not much different from the infield-outfield system of Sweden or Plaggen soils of Germany. It is not difficult to maintain high productivity of soils when there is a constant import of nutrients. Also the soils will improve over the years. For me, it appears as if this aspect is more important to understand the fertility of terra preta soils than charcoal. I might be wrong, but I am still waiting for the evidence of the opposite. In addition, the fertility of the terra preta soils as measured by professor Woods wasn't really too impressive.
As a carbon sequestration technology I am sure it works quite well, having the possibility to sequester carbon as the only parameter for measuring success - but I don't think we can manage our world with such one-dimensional criteria. In general, I am afraid about all messianic ideas of simple solutions to climate change - allowing us to continue with "business as usual" as expressed by professor Woods.
Svensk källa för biokol: http://www.geo.uu.se/biokol/
I have been a professional nurseryman for over 40 years and have grown everything organically. I was introduced to charcoal by my grandfather who was a charcoal burner in England. I have found that charcoal, inoculated with worm compost tea ( or any other organic tea) works best but only on soils that are already nutrient rich. If the organic matter that is used as compost or as a fertilizer has not been grown on organic rich soils then the amount of nutrients it is able to add to the soil is diminished. I do believe bio-char is beneficial to the organic grower but I think there are even more benefits if sewage and organic garbage were converted to bio-char and either sequestered in the soil or used as fuel to create power. this goes for the gases and bio-oil also produced in the process. Using these ingredients I don't think we would ever run out of fuel!--and would not have to grow crops to make bio-char. It may not slow global warming but it sure would clean up the planet and possibly take us off our dependency on oil.
ReplyDeleteKen, that sounds pretty much what I believe as well - and what I felt the Amazonian Terra Preta experience tells us. Charcoal doesn't convert bad soils without nutrients to fertile soils (just look at the growth in a an old fireplace on a beach...). But mixed with other stuff, it can help to retain nutrients.
ReplyDeleteI know William Woods since 10 years and do not believe that he proposed to carbonize Amazon pristine forests. Slash and char was proposed as an alternative to slash and burn practiced by approximately 500 million farmers worldwide. This would also exclude pristine forests but may carbonize re-growing fallow vegetation as done in many slash and burn cycles.
ReplyDeleteThe fertility of Terra Preta is impressive when compared to adjacent soils. You are right that the majority of nutrients came from other sources than charcoal. However it is remarkable that the Terra Preta soils are still dark and rich in organic matter hundreds and thousands of years after their creation. This is responsible for the high cation exchange capacity (the ability to hold nutrients) and good physical properties. To maintain high levels of organic matter is very challenging in a hot and humid climate such as in the Amazon. Even in temperate zones soils have lost 30 to 70% of their organic carbon content due to intensive cultivation.
CS, I believe William's point was that most of the Amazon isn't "pristine" in the first place. I think we agree on that carbon in soils can do very good, when combined with a supply of nutrients in some way. Equally there are other production systems in tropical countries that maintain high productivity over long periods of time - without carbon.
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