Terra Preta
Ever since I heard of it the first time the black earth phenomenon in the Amazon has always fascinated me, according to the wikipedia article terra preta will give a 38-45% higher yield of rice without fertilization when compared to fertilized ferralsol and the Biochar Fund gives an even higher figure of 840% (the figure is given in an unclear manner, it’s likely it refers to total biomass of the plants, not yield). Wherever the truth may be it’s obvious that this is powerful stuff that can simultaneously increase the crop yields in tropical countries while at the same time eliminating the need for expensive artificial fertilizers.
This is all well and fine but it’s the side effects that might be the most important thing. Since the whole process basically is about converting plant matter into non degradable biochar it will result in a reduction of atmospheric CO2. According to Nature:
That means turning unimproved soil into terra preta can store away more carbon than growing a tropical forest from scratch on the same piece of land, before you even start to make use of its enhanced fertility. Johannes Lehmann of Cornell University in Ithaca, New York, has studied with Glaser and worked with Sombroek. He estimates that by the end of this century terra preta schemes, in combination with biofuel programmes, could store up to 9.5 billion tonnes of carbon a year — more than is emitted by all today’s fossil-fuel use.
That would basically mean a complete reversal of global warming if it is the CO2 that is the culprit. Needless to say, the worst possible scenario will not come to pass either. So what would it take in practice to achieve for instance sequestering one billion tons of CO2 per year to win the Virgin Earth Challenge? According to Desmond Radlein of Dynamotive Energy Systems in a SciAm article it’s far from impossible.
I developed this rough back-of-the-envelope calculation of what it would require if one were to [attempt the Virgin Earth Challenge] with the agrichar concept,” Radlein explains. “One would need about 7,000 plants each processing 500 tons of biomass per day, which is a large number, but it’s not outside the bounds of possibility.” Such facilities would produce four parts bio-oil to one part carbon sequestered, so it would rake in money as well as carbon.
But apparently it’s not as easy as it seems to achieve the really, really good stuff.
In addition, scientists are finding it hard to replicate the original terra preta soils. “The secret of the terra preta is not only applying charcoal and chicken manure—there must be something else,” says Bruno Glaser, a soil scientist at Bayreuth University in Germany. Field trials in Amazonia using charcoal with compost or chicken manure find that crop yields decline after the third or fourth harvest. “If you use terra preta you have sustaining yields more or less constantly year after year,” he says.
“I’m skeptical about adding just a pure carbon source,” says Stanley Buol, a professor emeritus from the Department of Soil Science at North Carolina State University’s College of Agriculture and Life Sciences who spent 35 years studying Amazonian soils. “It will be black and look good,” but will it contain enough inorganic ions, such as phosphorus and nitrogen, essential to plant growth?”
Luckily just about anyone can easily experiment with this stuff, I will start myself this weekend. The plan is to try various amounts of charcoal mixed with ferralsol in order to hit upon the right mix, according to wikipedia the amount of C in current soils is as high as 9% so that will be a starting point.
However the coal needs to be prepared, I plan on soaking it in urine for a month or two first. Adding other organic material is also probably a good idea. Finally different levels of continuous additions of P and N to the mix has to be tested. I won’t use pots because organisms need to be able to freely move into the mix from the surrounding earth. Did I forget something?
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Tags: Agriculture, black earth, fertilizer, Global Warming, terra preta