Limitations of charcoal as an effective carbon sink

[phantom power]

I was hoping to see confirmation that this would work. Disappointing. I wonder if helped in South America because the Amazon soil is nutrient poor to begin with?

They found that when charcoal was mixed into humus, there was a substantial increase in soil microorganisms (bacteria and fungi). These microbes carry out decomposition of organic matter (carbon) in the soil, and consistent with this, they found that charcoal caused greatly increased losses of native soil organic matter, and soil carbon, for each of the three forest stands. Much of this lost soil carbon would be released as carbon dioxide, a greenhouse gas. Therefore, while it is true that charcoal represents a long term sink of carbon because of its persistence, this effect is at least partially offset by the capacity of charcoal to greatly promote the loss of that carbon already present in the soil.

http://www.slu.se/?ID=704&Nyheter_id=8497

[izquierdista]

1. Yes

Tropical soils tend to be poor in organic matter and nutrients because of the fast rate of decomposition. Areas with fertile black soils, like Iowa and the Ukraine are frozen over for much of the year and the organic matter is not broken down quickly.

I couldn't follow your link, but if the experiments were done in Sweden the temperature effect probably explains it. Charcoal in humus rich cold soils acts to increase surface area available for bacteria to grow, increasing the rate at with they decompose organic matter.

[phantom power]

2. Strange, that link does work for me. It was in Sweden. Here's more:

However, a new study by Professors David Wardle, Marie-Charlotte Nilsson and Olle Zackrisson at SLU, the Swedish University of Agricultural Sciences, in Umeå, scheduled to appear in this Friday’s issue of the prestigious journal Science, suggests that these supposed benefits of biochar may be somewhat overstated. In their study, charcoal was prepared and mixed with forest soil, and left in the soil in each of three contrasting forest stands in northern Sweden for ten years.

[kristopher]

3. Don't shoot the horse yet

They aren't saying that it doesn't work only that the carbon released should be considered.

I don't know much about it, so I'd like to ask a few questions.

Do you know of any information on how terra preta affects the use of fertilizers?
How much is too much; is there a 'saturation point' for the percentage of charcoal in the soil where it begins to have negative effects on plant growth?


Final paragraph from study:
Previous short-term laboratory studies have shown that charred plant material causes accelerated breakdown of simple carbohydrates (10). Our results extend these findings by indicating that charcoal can promote rapid loss of forest humus and belowground C during the first decade after its formation. Fire often causes substantial losses of ecosystem C, and our results provide evidence for a previously unreported mechanism that could contribute to these losses. Our results are specific to boreal forests and to the type of charcoal that we used, and further work is needed to determine the importance of this mechanism in other biomes and for other types of charcoal (11). Although several studies have recognized the potential of black C for enhancing ecosystem C sequestration (2, 3), our results show that these effects can be partially offset by its capacity to stimulate loss of native soil C, at least for boreal forests. The effect of charcoal on native soil C needs to be explicitly considered to better understand the potential of black C as an ecosystem C sink and agent of C sequestration.

http://www.sciencemag.org/cgi/content/full/320/5876/629

[izquierdista]

4. Another factor to consider is water

As anyone who has hiked through deserts can tell you, charcoal from fires lays around for years. Of course, in deserts, there is very little soil carbon to be released.

I wouldn't think there would be a 'saturation point'. At some point, the charcoal just becomes inert granules, like silica sand. Unlike silica sand though, it does have to ability to adsorb and desorb a lot of compounds. Many of those compounds could, in turn, stimulate or inhibit plant growth. The hardest part of that experiment would be to start with clean charcoal and keep it clean.

[phantom power]

5. In the Amazon, the charcoal was thought to increase nutrient retention...

so it increased the effectiveness of fertilizers, I would assume. But my reading of this article is that it wasn't working out that way in the swedish study. That might be the result of a saturation effect. Or some other thing. One thing I've learned on E/E is that soil biology and chemistry is very complicated, and I don't understand much about it.

I agree that this doesn't prove it's ineffective, but does seem to indicate that its effectiveness is location dependent, which makes sense. It also might mean that temperate soils are already sequestering nearly as much carbon as they can.

:shrug:

[NickB79]

6. Damn, I was going to try some terra preta production this year

Now I'll have to reconsider, if adding it to temperate, already-fertile soils might actually decrease fertility.

[kristopher]

7. Test it.

Plant half with and half without.

I'm going to do it also. I live in an area with sandy, fast draining soil, so I expect it to help.

Now I think I'll also do a control area - just to check my expectations.