In our past few sessions, my group has started
working on really bringing everything together, synthesizing the information
that we have found so far, and developing the plan that we will eventually
give in our final presentation. Simultaneously, we worked together
to come up with a format for our group website, which parallels the progression
of our work. The web page's first section will be the background information
that we found in our preliminary research, which includes facts on logging,
mining, ranching, agriculture, and industry in the Amazon Basin area. (My
part in this was primarily research on agricultural practices and on exactly
what sort of agriculture is practiced in the Amazon.) Our second section
is the one where we define and quantify (as much as possible) the development
problems in the Amazon. Finally, we will have the "solutions"
section, which will contain all the best ideas that we can come up with to
solve the problems that we have identified.
Marion (another member of my team) and I have been talking outside of class
about the agricultural component of development in the Amazon. Our
data show that incorrectly managed agriculture is one of the major causes
of deforestation, and we are looking for ways to remedy that. Marion
has been looking into agroforestry practices. I have been looking into
terra preta, which is described in last week's update. My idea right
now is that terra preta could be used to make development in the Amazon more
sustainable and rational by 1) making it possible to farm a single plot for
an extended period of time, instead of having to move from plot to plot and
waste land 2) increasing the productivity of a single plot, so that
farmers don't need to clear as much land to get the yields that they need,
or so that, if they have easy access to big markets, they can produce more
goods and increase their profits, and 3) keeping the overall condition of
the soil much better even after farming, so that the forest can move back
into abandoned plots much faster than it normally could. It would also
be interesting to find out whether terra preta could eventually be used to
revive plots of land that already have been mostly depleted, which would
drastically reduce the necessity to cut down the rainforest at all.
I have been looking for more information on terra preta on several websites.
The website of the
International Workshop on Anthropogenic Terra Preta Soils
lists, among other things, many professors and researchers who are involved
in projects with terra preta, and I am working on contacting some of them
right now, because, despite my best efforts, I have been hard-pressed to
find any more solid facts on terra preta than the ones that I already have.
Also, when I was reviewing the facts that I have
collected to put on our team website under the "background" section, I began
to realize that there are still some facts that we are lacking... simple
things like statistics on what percentage of agriculture is done by whom.
This is something that we included in our inital definition of an A
(development: by whom and how?) and it should not be overlooked. I
plan to work on filling in some gaps in the next few days, by revisiting
the goals that we initially set for ourselves and seeing whether we are going
in the right direction to fufill all of them. I have checked out a
number of books from the library, and I have a lot of old bookmarks that
I can also use for this. I realize that maybe I should have done that
by now, but.... bad week. :o(
This week, I have somewhat shifted the focus
of my research to a topic which I had noted earlier but had not examined
in depth. This topic is something called "terra preta
," or dark earth, which is the subject of a good deal of current scientific
research. I have found a number of relevant web site and articles, but
the bulk of my information here comes from an article by Charles C. Mann called
"The Real Dirt on Rainforest Fertility" which was published online in Science
Magazine in 2002.
What is terra preta?
Terra preta is the name given to a special kind of soil that is found in
the Amazon, which is strikingly different from all other soils in the area.
Most soils in the Amazon are oxisoils, which are very ill-suited for
agriculture. They are highly acidic, and they are low in organic matter
and nutrients, because the carbon and nutrients are primarily stored in the
vegetation covering the oxisoils. Therefore, when land is cleared for
agriculture, oxisoils are left with few nutrients, so they become completely
depleted after they are used for agriculture for only 2 or 3 years.
Terra preta, on the other hand, yields great productivity and long-lasting
fertility. Furthermore, it seems to actually be the product of previous
intensive agricultural activity in the Amazon. This indicates that some
kind of sustainable, intensive agriculture is possible in the Amazon. Bruno
Glaser, a chemist at the Institute of Soil Science and Soil Geography at
the University of Bayreuth, Germany, says that "[Precontact Amerindian populations]
practiced agriculture here for centuries. But instead of destroying
the soil, they improved it--and that is something we don't know how to do
today" (C.C. Mann, Science Magazine).
Terra preta has more "plant-available" nutrients (P, Ca, S, N) and more
organic matter than oxisoils. It also retains moisture and nutrients
There are three major factors that make terra preta different from regular
- CHARCOAL-- Terra preta contains
up to 70 times as much charcoal as oxisoils. Charcoal prevents organic
matter from being rapidly mineralized. It also partly oxidizes over
time, which keeps providing sites for nutrients to bind to. Experimentally,
when plots of rice and sorghum were treated with different combinations of
fertilizers and charcoal over a period of three years, the charcoal "was really
making a difference" by the second year, and in the end, plots treated with
a combination of charcoal and fertilizers yielded as much as 880% more than
plots with only fertilizer.
- NUTRIENTS -- Charcoal alone
is not enough. In the experiment mentioned above, plots with charcoal
but without fertilizer did not produce very much. High nutrient inputs
are also key.
- MICROFAUNA -- Janice Thies,
a soil ecologist from Cornell, says that "there are indications that microbial
biomass is higher in terra preta" (C.C. Mann, Science Magazine). These
special soil microorganisms probably also play a role in terra preta's persistent
How is it created?
In the past, terra preta was probably created through a method that scientists
are calling "slash-and-char," as opposed to slash and burn. In this
method, farmers only burned organic matter incompletely, and then stirred
it directly into the soil. They also added nutrients via excrement and
waste such as animal bones. In the Amazon today, the creation of "ingredients"
for terra preta might be an excellent use for unwanted waste and excrement
from cattle and from cities.
These days, scientist are hard at work trying to create new terra preta.
It is possible that they could create a "package" of charcoal, nutrients,
and microfauna that could be added to regular oxisoils the transform them
into terra preta. If this could be done economically and distributed
efficiently, it would have a very positive effect on sustainable agricultural
development. If farmers could use less land to get the same end product
as before, and could remain on a single land plot indefinitely, then the rate
of deforestation due to agriculture could be slowed dramatically.
What's the catch?
Although it's easy to get excited about terra preta, there are some complications
with using it. First, it would be essential to develop new techniques
to control tropical weeds. Soil that is conducive to the growth
of crops is also conducive to the growth of weeds, so crops on terra preta
fields can be completely overwhelmed by weeds. If this happens, farmers
have to abandon their fields and clear new sites for agriculture, which is
exactly the problem that we are trying to eliminate.
Second, terra preta has to be managed competently. When it is poorly
managed, its nutrients can decline back to near-oxisoil levels.
Third, concerns have been expressed that terra preta might not be economically
viable in remote parts of Amazonia, because the benefit of increased yields
depend on quickly transporting produce and fruit to large markets. I
would argue that this is not necessarily an issue, though; farmers do not
necessarily have to produce more just because they have more productive land.
The other option is to simply farm on less land.
Finally, is is possible that success with terra preta will simply encourage
more people to farm the Amazon, and forest will be cleared due to that. This
seems to me like a valid concern, and it is something that we will have to
keep in mind.
Despite possible complications, I think that terra preta holds some exciting
possibilities. I plan to continue researching it for a while longer,
both by browsing the web for more detailed articles and by contacting, via
email, some of the scientists who have been involved in terra preta projects
Over the past couple of weeks, our group has
been working to organize itself and focus in on our key ideas. My
recent research has focused primarily on Brazilian agriculture. I
have been trying to find details on agricultural practices, but these are
hard to come by. I have, however, found information about Brazil's
agricultural production and its past and present land use, and information
about agricultural practices in general.
These are some statistics on land use in Brazil, from the
Instituto Brazileiro de Geografia e Estatistica (IBGE)
. These numbers do not distinguish between land that is and is not
part of the Amazon, but they do give a decent sketch of the way land is
used in Brazil in general and they show how land use patterns have changed
|total (in millions of
|"productive land" not
The IBGE defines each of these terms as follows:
It is important to note here that IBGE does
not define "temporary" crops in the same sense as we have been. Our
group tends to think of temporary crops as the ones that will be abandoned,
leaving the land fallow, after several years, but here they are simply defined
as crops that require re-seeding. This does connect to our group's idea
of temporary crops, but it is not exactly the same. Some interesting
trends in the data are: productive land not in use is steadily decreasing,
natural pastures are being replace by planted pastures, there was a decrease
in fallow land between 1985 and 1995, and the area of temporary crops has
been steadily and rapidly increasing.
- Permanent crops - comprising the
area planted or being prepared for planting long-term crops that after harvesting
do not require new seeding and keep producing during successive years. Areas
occupied by nurseries of permanent-crop seedlings have been included in
- Temporary crops - included the
area planted or being prepared for planting short-term crops (usually less
than one year) and requiring new seeding after each harvesting. Also included
in this category were areas with green fodder to be cut
- Fallow land - land habitually used
for planting temporary crops, which on the 31st of December 1995 were left
uncultivated, for a period not longer than four years counting from the
last year it was utilized.
- Natural pasture - formed by areas
suitable for grazing, not planted, even those receiving some kind of treatment.
- Planted pasture - included areas
especially cultivated for grazing.
- Natural woods - formed by areas
with natural forests and woods used for extracting products or preserved as
- Planted woods - comprised areas
cultivated or being prepared for planting forest essences (black acacia, eucalyptus,
pine etc.), including the areas occupied by seedling nurseries of forest
- Productive land not in use - those
areas suitable for crops, pasture or woods which were not being used to
such ends. Land not used during more than four years was included here.
The IBGE also has a breakdown of land use by state, telling each state's
total land use, permanent and temporary crops, natural and artificial pastures,
natural and planted woods, and fallow lands and productive lands not in
use. This can give us a more geographically precise idea of how land
is used, and can be viewed here:
I also found (again on IBGE) a list of the quantities of different farm
products that were harvested in 2001, the quantity that will be gathered
in 2002, and the percent change between these years. I will not reproduce
the entire chart, but will give the numbers for the ten most produced farm
Area (in ha, rounded
to nearest 1,000)
|harvest gathered in
|harvest to be gathered
1) Soybeans (grain)
2) Corn (grain) 1st harvest
3) Sugar cane
4) Rice (in husk)
5) Corn (grain) 2nd harvest
6/7) Coffee beans
7/6) Beans (grain) 1st
10) Beans (grain) 2nd
We can see from this that soybeans and corn alone make up more than 50%
of the harvest of farm products by area. Also, since we are trying
to minimize deforestation, it makes sense for us to focus on the crops that
take up the most area. Therefore, I have tried to find some information
about best practices for soybeans and corn. So far I have not found
any information that is specific to the Amazon, but I have found that the
Ohio Agronomy Guide (link coming very soon) has good information about soybean
production in general, including issues such as fertilization, disease control,
planting dates, weed control, and variety selection.
This week I did some independent research
on agricultural practices in the Amazon. I focused on this topic because
I found in my general research that one large contributer to deforestation
is ill-managed agriculture, so one way to reduce deforestation greatly could
be to find ways to make agriculture more efficient and environmentally friendly.
That way, necessary agricultural development could continue with
minimal damage to the ecosystem.
From Sustainable Settlement
in the Brazilian Amazon1
High productivity farming tends to have two effects:
1) Retention of land is high, so deforestation is contained to a certain
2) There is high deforestation on the plots that are occupied; the forest
will probably never grow back there.
The enviromental costs that arise from this sort of farming are loss
of biodiversity and erosion of soil. These things are difficult to
measure, but it is possible to identify the conditions under which they are
reduced. (For instance, when there is greater yield per acre of land,
enviornmental costs will be lower.)
Three measures that would promote sustainability
1) Reduce environmental cost per private benefit.
2) Increase private costs of deforestation.
3) Decrease private cost of environmental alternatives such as
alternative tropical farming technology.
From Amazonia: Agriculture and Land
Little has been done to understand the Amazon's potential adaptability
for annual food crops. Some information suggest that, with adequate
scientific knowledge, it would be possible to gradually develop the Amazon's
agricultural potential, through the careful manipulation of existing conditions
and through the generation of an equilibrium between different types of
crops (annual, perrenial, forest).
Different agricultural methods:
"Shifting agriculture," commonly known as slash and burn, is
the most widely used method in the humid tropics. As you would expect,
it consists of cutting down the vegetation in an area, burning it, farming
the plot for 2 or 3 years until the soil is depleted, and then moving on
to a new plot. Unfortunately, when the population of an area increases
enough, this practice becomes disruptive of the ecological balance. Additionally,
its average yields are relatively low.
Mechanized clearing (i.e. bulldozing)
is even worse than slash and burn in many ways. In the slash and burn
method, ashes return to the ground and replenish the soil's (very important)
nutrients. This doesn't happen with the mechanized clearing. Mechanized
clearing also causes problems of soil compacting (causing water infiltration
rates to decrease from 10.5 cm/hr to only 0.5 cm/hr in one study), and disrupts
the fragile surface layer of soil.
A number of systems for continous
cropping of annual plants exist, which are all improvements over these two
Intercropping--the cultivation of multiple crop species simultaneously
in the same area.
Experimentally, implementations of this give figures such as 50% and
60% better yield per unit of land. This system minimizes competition
for light, water, and nutrients, allows for more efficient management of
diseases, insects, weeds, and soil, permits better diversity of crops, and
just uses land more efficiently. This works best on small farms, although
the author states that intercropping of annuals and perennials "offers
Relay system--the planting of a second crop before the flowering
or harvesting of a first
This gives better yields than intercropping because it reduces the periods
of competition between crops, but it also seems to create environments that
encourage the spread of pathogens.
Sequential rotational system for annual
This is often used commercially, and is viable for an extended period
of time (7+ years in one study). Of these three systems, it seems
to be the most efficient and effective in large scale operations.
Regardless of the system, certain things
are always important, such as:
- weed control
- use of fertilizers (farmers increased
yields by more than 90% just by using fertilizers and lime)
- knowledge of soils, climate, and
indigenous resources (This is knowledge that locals often have but
that many settlers do NOT possess.)
Conclusions that can be drawn are:
When population density is high enough,
agriculture with annual crops should be permanent and continuous instead
of shifting. The step from shifting to continuous agriculture requires:
- management of soil through clearing
- management of plant production
through genetic selection of crops well disposed to the conditions, sequential
intercropping and relay cropping systems, and control of insects, diseases,
- indirect management of climate
through the coordination of planting with the climate patterns and good
use of rainwater
Continuous cultivation in the Amazonia
is feasible if these things are all taken into account.
There is still much research that needs
to be done. Some relevant fields of research are better farming technology
and genetic studies/selection of other crops that could be grown sucessfuly
in the Amazon area.
1. Sustainable Settlement in the Brazilian Amazon. Anna
Luiza Ozorio de Almeida and Joao S. Campari, Oxford Universtiy Press, New
2. Amazonia: Agriculture and Land Use Research. ed. Susanna Hecht,
Cali. Columbia, Centro Internacional de Agricultura Tropical, 1982.