[Terrapreta] The Science of Terra Preta Formation
Gerald Van Koeverden
vnkvrdn at yahoo.ca
Tue Apr 8 13:48:33 CDT 2008
One thing we do know from the writings of the first European
explorers in the Amazon, is that farmers did a lot of burning on the
fields. Note that, in the Mexican study quoted below, the subsequent
increase in the amounts of N and P available to plants, was
determined to come from the heating of the soil itself, not the ash
of plants burned.
Slash-and-burn clearing of forest typically results in an increase in
soil nutrient availability. Throughout the tropics, ash from consumed
vegetation has been accepted as the primary nutrient source for this
increase. In contrast, soil heating has been viewed as a secondarily
important mechanism of nutrient release. Through the use of multiple
burn plots and intensive pre-burn and post-burn sampling of mineral
soil, this study quantified changes in total P and N, P fractions,
and KCl-extractable N in soil during the slash-and-burn conversion of
a Mexican dry forest to agriculture. Slash burning resulted in large
transformations of non-plant-available P and N in soil into mineral
forms readily available to plants. Anion-exchange resin, NaHCO3-
extractable P, and KCl-extractable N in soil increased by 37 kg P
ha-1 and 82 kg N ha-1. Organic and occluded P (sequentially extracted
with NaOH, sonication + NaOH, and NaOH fusion) and organic N (total N
minus KCl-extractable N) decreased after burning by 25 kg P ha-1 and
150 kg N ha-1. Immediately after burning, ash from consumed
aboveground biomass contained 11 kg P ha-1 and 27 kg N ha-1, of which
55 and 74%, respectively, were quickly transported off the site by
wind. At this dry forest site, soil heating had a much larger
influence on soil P and N availability than inputs of ash.
http://soil.scijournals.org/cgi/content/full/64/1/399
Gerrit
On 8-Apr-08, at 1:39 PM, Robert Klein wrote:
>
> the problem with rainforest soils as I have understood it is not
> that nutrients are not available but that they are transported by
> rainwater to the water table at least, leaving the surface
> depleted. What is more, plant material is degraded at a very fast
> rate releasing that source of nutrients back to the water table.
> The magic of terra preta is that it intercepts this cycle and holds
> nutrients at the surface available for cropping. The most
> important aspect of terra preta is its powerful nutrient retention
> capability allowing success in adding even fish waste to the soil.
> The archaeological data makes no mention of this, but I suspect
> that legumes were also grown heavily here besides maize and manioc.
>
> Please read my blog postings on the making of terra preta with
> stone age technology to understand both the how and the natural
> restraints.
>
> google arclein
>
> ----- Original Message ----
> From: David Hirst .com <david at davidhirst.com>
> To: Terrapreta <terrapreta at bioenergylists.org>
> Sent: Tuesday, April 8, 2008 9:54:30 AM
> Subject: Re: [Terrapreta] The Science of Terra Preta Formation
>
> Jim,
> It may be that there are a few nutrient recycling opportunities
> that are
> natural, although how far they apply in the Amazon I do not know. For
> example;
> 1. The bodies of Salmon bring nutrients from the sea far up
> river, and,
> after spawning, usually get caught by bears. They tend to take a
> few bites,
> and leave the bulk of carcass in the forest, where the nutrients
> recycle.
> The forests seem to suffer from the loss of salmon. Do any Amazon
> fish swim
> upriver from the sea so brining up nutrients (perhaps via several food
> chains)?
> 2. Aeolian dust. Quote significant volumes of dust get blown
> about, and
> land far from where they originated. In the Amazon, I guess most
> traces get
> lost in the forest but I though Laos was build on blown dust. Some
> of the
> dust is alive, and even scorched islands seem quite quickly to have
> seeds
> land and germinate. Some spiders use threads to fly off and travel
> long
> distances.
> 3. Volcanoes. They are also a contributor to dust.
> 4. Sulphur is also cycled from the sea as particulates (and cloud
> condensation nuclei). Algae, when they get too hot tend to release
> DMS,
> which helps form clouds (and so cools them).
> 5. Tectonic movements. Upriver, there are the Andes, which are
> still
> being pushed up, and so can carry on eroding and feeding nutrients
> downstream.
> Many of these are quite slow acting, but most nutrients get
> recycled close
> to home. I understand that most rain is from evaporation within the
> forests.
> I imagine that forest fires do occasionally occur during dry
> spells, and
> would tend to leave some charcoal.
> Most sources seem to think that TP is anthropogenic, and I am not
> arguing.
> But natural sources cannot be entirely ruled out on nutrient cycling
> grounds.
> Cheers
> David
>
> David Hirst
>
> direct: +44 (0) 1723 570113
>
> mobile: +44 (0) 7831 405443
>
> email: david at davidhirst.com
>
>
> -----Original Message-----
> From: terrapreta-bounces at bioenergylists.org
> [mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of Jim Joyner
> Sent: 08 April 2008 16:02
> To: Terrapreta
> Subject: Re: [Terrapreta] The Science of Terra Preta Formation
>
> If I might add a few things:
>
> I find it very difficult to believe that dark earth in Amazonia had a
> natural start. Much of the muck soils in the US Midwest were due to
> catastrophic events through the ice ages. These nutrients became a
> treasure trove of nutrients that farmers are still mining. There is
> nothing comparable in the tropics that I know of. (Well, there the
> occasional guano deposits found, but even these are not soils)
>
> There is practically no way that carbon can naturally accumulate in
> the
> tropics for any length of time. The one exception to that seems to be
> charcoal but that is not what we would call natural.
>
> Also, in terms of nutrient (I'm speculating, but bear with me). For
> thousands, many hundreds of thousands of years, nutrient has flowed
> into the Amazon from the mountains above. Some of these nutrients are
> soaked up into above ground jungle/rain forests. Some, of course, are
> bound up in aquatic life. Most are washed out to sea. But there is no
> source of nutrient in the tropics to "mine" like there are in the
> temperate zones. There is no soil deposit to mine simply because,
> if it
> had existed, it would have quickly disappeared.
>
> This means, I think, to have supported what seems to have been huge
> populations, there had to be a serious form of economizing and cycling
> of nutrient. Basically, people had to take from the rivers and some
> from
> the forests (so far that is gather-hunting which will not support
> large
> populations), but in time as they keep their waste (somehow), they
> recycled and accumulated nutrient. This recycling is not unusual
> (Asians
> ahve done for millenia), but it is difficult in the tropics simply
> because the medium that is necessary (for the most part) to hold these
> nutrients, in a usable way, is carbon. And most carbon under normal
> natural conditions in the tropics will will simply evaporate
> (actually,
> the process is burning or oxidation).
>
> Somehow, it seems the people discovered a medium to collect, hold and
> recycle nutrients and carbon. Our guess, of course, some form of char.
>
> Jim
>
>
>
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