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Please cite
as:

Fearnside, P.M. & N. Leal Filho. 2001. Soil and
development in Amazonia: Lessons from the Biological Dynamics of Forest
Fragments Project. pp. 291-312 In:
R.O. Bierregaard, C. Gascon, T.E. Lovejoy & R. Mesquita (eds.) Lessons
from Amazonia: The Ecology and Conservation of a Fragmented Forest. Yale
University Press, New Haven, Connecticut, E.U.A. 478 pp.

Copyright:
Yale University Press

The original publication is available from  Yale University Press, New Haven,
Connecticut, U.S.A.

SOIL AND DEVELOPMENT IN AMAZONIA:  LESSONS FROM THE BIOLOGICAL DYNAMICS OF
FOREST FRAGMENTS PROJECT

Philip
M. Fearnside and Niwton Leal Filho

National
Institute for Research

in the Amazon (INPA)

C.P. 478

69011-970
Manaus, Amazonas

BRAZIL

Fax:
55 (92) 642-8909

Tel: 55 (92) 643-1822

Email:
[email-masked]

Contribution to:

R.O.
Bierregaard, C. Gascon, T.E. Lovejoy and A.A. dos Santos (eds.) Lessons from Amazonia: The Ecology and
Conservation of a Fragmented Forest.
Yale University Press, New
Haven, Connecticut, U.S.A.

3
May 1998

17 June 1998

3 July 1998

1 Oct. 1999

TABLE OF CONTENTS

ABSTRACT
...................................................

I.) INTRODUCTION

A.)
RELEVANCE OF SOILS TO PLANNING ....................

B.)
SOIL CLASSIFICATION ...............................

C.)
SOIL VARIABILITY ..................................

D.)
ECONOMIC-ECOLOGICAL ZONING ........................

E.)
IMPORTANCE OF SOIL PROPERTIES

1.)
Soil texture
................................

2.)
Available water capacity .....................

3.)
Phosphorus ...................................

4.)
pH, aluminum and cations .....................

5.)
Nitrogen .....................................

6.)
Zinc .........................................

7.)
Manganese ....................................

8.)
Other elements ...............................

II.) THE BDFFP SOILS SURVEY

A.)
OVERVIEW OF THE DATA SET ..........................

B.)
FIELD METHODS .....................................

C.)
LABORATORY METHODS

1.)
Sample preparation, soil color, textural                        appearance
and consistency ..................

2.)
Soil texture .................................

3.)
Bulk density .................................

4.)
Organic carbon and organic matter ............

5.)
Available water capacity .....................

6.)
pH in water and KCl ..........................

7.)
Macro and micro nutrients ....................

8.)
Total nitrogen ...............................

9.)
Total carbon (%C) ............................

D.)
SUMMARY OF RESULTS ..............................

III.) LESSONS FOR DEVELOPMENT

A.)
AGRICULTURAL POTENTIAL ............................

B.)
PROSPECTS FOR RESILIENCE ..........................

C.)
DISTRIBUTION OF NATURAL VEGETATION ................

D.)
POTENTIAL FOR RELEASE OF GREENHOUSE GASES .........

E.)
PROBABLE RESPONSE OF FOREST TO FRAGMENTATION ......

F.)
PROBABLE RESPONSE OF FOREST TO CLIMATIC CHANGE ....

IV.) CONCLUSIONS
...........................................

V.) NOTES
..................................................

VI.) ACKNOWLEDGMENTS
.......................................

VII.) LITERATURE CITED
.....................................

FIGURE LEGEND
..............................................

ABSTRACT

Soils data from the
1000-km2 area covered by the Biological Dynamics of Forest Fragments
(BDFFP) reserves (north of Manaus, Amazonas) provides detailed information of
the type used in development planning, such as the economic-ecological zoning
of the region now being carried out by the Brazilian government.  The soil in the reserves is typical of
vast areas of Brazilian Amazonia that are likely to be increasingly deforested
for agriculture and ranching.  These
soils have low fertility, are acid and have high levels of toxic aluminum ions.  They also have limitations due to
topography, generally very high clay content, and low values of available water
capacity.  Agricultural potential is
low, and the prospects for resilience are not bright given the reality of
changing land-use patterns in the region.
The soils under forest also give indications of the environmental impact
of converting these areas to pasture and other uses, including the potential
for release of greenhouse gases (which depends on forest biomass, a feature
related to distribution of natural vegetation and favorability of soils for plant
growth), the probable response of forest to fragmentation, and the probable
response of forest to climatic change.
Our soils research indicates that areas like this would produce little
if converted to agriculture or ranching, and point to land uses that maintain
forest cover intact as preferable.
The value of the environmental services provided by the standing forest
far exceeds the returns that can be expected from clearing it for agriculture
or ranching.

I.)
INTRODUCTION

A.) RELEVANCE OF SOILS
TO PLANNING

Soil quality is
obviously fundamental to the potential of any area to produce and sustain
agricultural yields.  If planning
decisions are made to encourage agriculture in areas with soils that are not
suited to this purpose, crops can be expected to fail.  Planning decisions opening vast areas to
settlement are frequently made in a near vacuum of information on soils.  For example, when the POLONOROESTE Project
opened Rondônia to settlement through a World Bank-financed regional
development program centered around paving the BR-364 (Cuiabá-Porto
Velho) Highway, the soils information available for Rondônia (Brazil,
Projeto RADAMBRASIL, 1978: Vol. 16) was based on only 85 soil cores.  Such events are recurring today quite
near the Biological Dynamics of Forest Fragments Project (BDFFP) reserves: on
24 June 1997, president Fernando Henrique Cardoso announced in his weekly radio
program "Palavra do Presidente" that six million hectares (ha) along
the BR-174 (Manaus-Caracaraí) Highway would be opened to settlement, and
suggested that the area farmed there would be "so colossal that it would
double the nation's agricultural production" (de Cássia,
1997).  Despite almost certain
hyperbole in both the expected production and the area likely to be settled, the
intention of initiating a major program on the BR-174 Highway appears to be
real.  The announcement of the
BR-174 settlement program came as a surprise, as the paving of the highway (in
1996 and 1997) had been presented as a surgical cut through the forest that
would allow the city of Manaus to trade with Venezuela and have access to that
country's ports.

Neither studies of
soils and agronomic potential nor assessment of environmental impact were done
prior to the announcement of the BR-174 agricultural project.  As is true for most of Brazilian
Amazonia, information on soils used in planning is essentially restricted to
the results of the RADAMBRASIL Project, which, in the early 1970s, mapped soil,
vegetation and other features based on side-looking airborne radar (SLAR)
imagery (Brazil, Projeto RADAMBRASIL, 1976: Vol. 10, 1978: Vol. 18).  Original imagery was at a scale of
1:250,000 and was published at a scale of 1:1,000,000.  Areas with the same appearance on the
images were mapped as the same, with field checking to identify vegetation and
soil in many of the units.  The
BR-174 area has been identified by the Amazonas state government as a priority
for economic-ecological zoning (Pinheiro, 1997).

The portion of the
BR-174 to be opened for agriculture lies over the Guianan Shield, and can
therefore be expected to be more fertile than those in the BDFFP reserves.  However, the Landless Rural Workers'
Movement (MST) has recently invaded some ranches in the SUFRAMA (Manaus Free
Trade Zone Superintendency) Agriculture and Ranching District (not those under
study by the BDFFP), raising the possibility that some of these ranches may be
distributed to small farmers for agriculture (Pacífico, 1997).

B.) SOIL CLASSIFICATION

The BDFFP reserves are
located 80 km north of Manaus (2o30'S, 60oW), and are
spread over a 20 X 50 km (1000 km2) area.  The site is approximately 25-50 m above
mean sea level; mean annual temperature at Manaus is 26.7oC and mean
annual rainfall (30-year average) is 2186 mm with a three-month dry season
lasting from July to September (Lovejoy and Bierregaard, 1990).  The site of the BDFFP reserves is
typical of much of central Amazonia.

The RADAMBRASIL maps
classify the BDFFP reserves as allic yellow latosols, which are Allic
Haplorthoxes (Oxisols) in the US soil taxonomy and haplic or xanthic Ferralsols
in the FAO/UNESCO system (see Beinroth, 1975).  The classification as a latosol(1)
relates to the type of clay minerals present.  The relative amounts of clay minerals
composed of silicate (kaolinite), iron (goethite) and aluminum (gibbsite)
determine the structural stability, the natural fertility and the effect of
applying fertilizers (Sombroek, 1966: 73).

Oxisols are the most
common soil in the Amazon Basin, covering 220 million ha or 45.5% of the total
(including areas outside of Brazil); most of the remainder is covered by
Ultisols (such as the red-yellow podzolic soils of the Brazilian system),
covering 142 million ha or 29.4% (Cochrane and Sánchez, 1982: 152).  Oxisols are distinguished from Ultisols
by lack of higher clay content with depth; Ultisols have at least a 20%
increase in clay content in the lower (B) horizon (United States, Department of
Agriculture, Soil Survey Staff, 1975).
At a high level of generality, Ultisols are considered less appropriate
than Oxisols for mechanized agriculture due to susceptibility to soil
compaction and their frequent occurrence on more steeply sloping terrain
(Sánchez, 1977: 539).
However, the broad range of characters within either of these great
groups (as illustrated, for example, by the results of the present study)
indicate the need for caution in applying such generalizations to specific
management decisions (see Fearnside, 1984).

Oxisols and Ultisols (i.e.,
yellow latosols and red-yellow podzolics) often occur in close proximity in
Amazonia and frequently intergrade with each other (Sombroek, 1966: 68).  Profiles in nearby sites confirm this
(Chauvel, 1982; Ranzani, 1980).
However, since both Oxisols and Ultisols are similar in being acid,
infertile soils that are indistinguishable from each other without information
on differences in the B horizon (which is outside the rooting zone of most
crops), taxonomic differences between them generally have little relevance for
agriculture as practiced in Amazonia.

The BDFFP reserves are
located about 50 km south of the edge of the Guianan Shield (the Balbina
hydroelectric dam is located at the edge of the Shield).  The reserves are within the basin bounded
by the Brazilian and Guianan Shields.
This basin covers approximately 1.2 X 106 km2 in
Brazil, or about 25% of Brazil's 5 X 106 km2 "Legal
Amazon" region.  It is known as
the Alter do Chão Formation (formerly called the Barreiras
Formation).  The soils are derived
from sedimentary deposits from the bottom of a shallow sea that occupied the
center of the Amazon Basin during the Tertiary (Falesi, 1974; Jordan,
1985).  The soils derived from these
sediments have been exposed to heavy rainfall and high temperature over most of
the approximately 60 million years since the region was uplifted at the time
that the Andes mountains were formed; most of the nutrients have therefore been
leached out of the soil (Sombroek, 1984).
Younger soils, such as those derived from igneous rocks in the Guianan
and Brazilian Shields, have higher fertility than those of the BDFFP area,
although they too are far from being classed as fertile for agriculture.

The general
characteristics of the origin of soils are closely associated with their
overall fertility.  In the case of
the BDFFP area soils, this history rules out occurrence of high-fertility
soils, with the exception of patches of anthropogenic black soil (terra
preta do índio), which was not found in the project area.  However, great variation in some
characters occurs within any given area, such as the BDFFP reserves, that
appears as uniform at the scale considered by the RADAMBRASIL survey (the
maximum level of detail that can presently enter land-use planning decisions);
in reality, not even this level of detail is considered when many actual
decisions are taken.  Perhaps the
clearest example of this was the complete ignoring of existing soil maps when
government decisions were taken on the location of settlement areas in
agriculturally unpromising areas of Rondônia (Fearnside, 1986a).

C.) SOIL VARIABILITY

The BDFFP soil survey
offers a unique opportunity to assess fine-scale variability in Amazonian soils
and the potential significance of this variability for development
planning.  Fine-scale variability
can be expected to affect agricultural success; it also affects the natural
vegetation, both in influencing what trees (and thereby other life forms) occur
and the stress placed on those trees when they find themselves isolated in
forest fragments.

Variability in initial
soil quality, as well as in other factors, is a key determinant of human
carrying capacity (Fearnside, 1986b).
In the Transamazon Highway colonization area, for example, soils vary
from fertility levels similar to those found in the BDFFP area to considerably
higher levels in terra roxa (Alfisol) areas, as well as in much smaller
patches of terra preta do índio (anthropogenic black soil)
(Fearnside, 1984).  The occurrence
of fertile patches, even if small in area, is important in the success of
colonist agriculture, as is the ability of farmers to identify these patches by
knowledge of the tree species that typically grow on them (Moran, 1981).

D.) ECONOMIC-ECOLOGICAL
ZONING

Brazil's 1988 constitution
calls for zoning of the entire country, after which land-use decisions for each
area would have to be made in accord with the zone assigned to it.  This provision was supported by the
"environmental caucus" of constitutional delegates, and was viewed as
a great victory for increasing the amount of protection against excessive
environmental impacts of development modes such as those that result in
tropical deforestation.  However,
the question of zoning soon became a controversial one, with those who
implement zoning at the level of state governments often viewing it more as a
means of "opening up" areas to development rather than as a means of
containing development excesses (see Fearnside and Barbosa, 1996, for examples
from Roraima).

Following the October
1988 constitution, an inter-institutional struggle ensued for control of the
zoning at the federal level; the principal contenders were the Brazilian
Institute for Geography and Statistics (IBGE), the Brazilian Enterprise for
Agriculture and Ranching Development (EMBRAPA), and the Ministry of Science and
Technology (MCT) (Régis, 1989).
The matter was settled by a 1991 presidential decree giving
responsibility to the Secretariat for Strategic Affairs (SAE), which had
formerly been known as the National Information Service (SNI): a much-feared
internal espionage agency.  This
institutional setting can potentially affect both the priority assigned to
environmental concerns and the degree of popular participation in the zoning
process.

The methodology to be
used in the zoning has been the subject of long controversies.  A series of very general maps was
prepared at a scale of 1:2.5 million using data from the RADAMBRASIL surveys;
additional data collection was not undertaken for these "diagnostic"
maps, but some additional data collection is foreseen in state-level zoning
projects.  The zoning projects and
the strengthening of the state-level agencies that have begun to carry them out
is being done with assistance from G7-Pilot Program to Conserve the Brazilian
Rainforest (with funds administered by the World Bank).

Increasing the level of
detail of data on characteristics such as vegetation and soils is obviously
important in order to increase the degree of confidence in zoning
conclusions.  It is also important
to achieve a better understanding of how to scale down from general zoning maps
to the fine-scale variation that exists on the ground where development
actually takes place.  One approach
proposed to interpreting soils information in conjunction with information on
vegetation, topography and other features is the "land units"
approach (Sombroek, 1966; see Sombroek et al., 1999).  Land units use naturally co-occurring
sets of these characters as the basis for defining the categories into which
the landscape is divided for purposes of planning.

E.) IMPORTANCE OF SOIL
PROPERTIES

1.)
Soil texture

One of the most
important characteristics of the soil is its texture: for example, the balance
between sand and clay fractions.
Very sandy soils are poor for plant growth because they lack sites for
holding cations (which are consequently leached away, leaving the soil
infertile), and because sandy soils do not hold water well, exposing plants to
drought stress during dry periods.
Clays have more sites for cations, largely because clay content is
positively correlated with organic matter when comparing surface samples taken
at different locations (as distinct from comparisons made between different
depths in the soil profile).  Clay
also holds cations directly, independent of its effect on organic matter.  Organic matter is especially important
in contributing to cation exchange capacity (CEC) in soils with clay minerals
of low activity, such as the Oxisols and Ultisols of Amazonia (Lenthe, 1991: 121).  Cation exchange capacity is a measure of
the negatively charged sites on the surfaces of clay and humus molecules; these
sites may be occupied either by nutrients needed for plant nutrition (Ca2+,
Mg2+, K+ and Na+) or competing ions in acid
soils (H+, Al3+ and Fe2+, but only the first
two of these are included in the CEC).

Clays also hold water
better in the smaller pores in the soil matrix.  However, very heavy clays can have
disadvantages because they have a higher proportion of very small micropores
from which removing water requires an undue exertion of force by the plant
roots (i.e. water requires a tension of more than 15 atmospheres to
remove).  The large percentage of
water at tensions above 15 atmospheres (bars) in very clayey soils, which can
be as high as 30% by weight, has a positive role as well: it increases the
stability of organic matter, contributing to the positive relationship between
clay content and organic matter (Bennema, 1977: 35).  The relationship between clay and plant
growth can be complicated by the effect of aluminum ions, which are toxic to
most plants in high concentration.
The allic (high aluminum) clays that are common in Amazonia lead to a
strong positive correlation between clay content and aluminum.  Because most of the effects of clay are
beneficial to plants, one can expect a positive association between aluminum
and plant growth even though the effect of aluminum per se is negative.

Excessively heavy clays
can also pose a physical impediment to the growth of tree roots.  Soils for citrus trees, for example, are
considered best if they have a mix of sand and clay rather than being pure or
almost pure clay.  For cacao, the
best soils have 30-40% clay, 50% sand, and 10-20% silt (Smyth, 1966 cited by
Alvim, 1977: 289).  The various
effects of clay content on plant growth are summarized in Figure 1.  In causal loop diagrams such as this,
the sign at the head of each arrow indicates the direction of change in the quantity
at the head of the arrow given an increase in the quantity at the tail
of the arrow.

[Figure
1 here]

Clay content of the
surface soil is relevant to the susceptibility of soils to erosion,
particularly laminar (sheet) erosion (see Fearnside, 1980).  Clay, being composed of particles of the
smallest dimensions, is more easily carried away by runoff water than are
coarser particles such as sand.
Clay can make the soil less permeable, leading to greater amounts of
runoff for a given amount of rainfall, but in well-aggregated clay soils, such
as those in the BDFFP area, drainage can be good despite high clay
contents.  In typical yellow
latosols (Oxisols) the soil aggregates are not covered with silicate clay skins
or linings, and the soils are little subject to gully erosion (Sombroek, 1966:
77).  Oxisols with low iron content
(a feature indicated by the yellow color of the BDFFP reserve soils) are the
ones most susceptible to topsoil deterioration when exposed to sun and rain
under agriculture, making them more susceptible to erosion when the surface
becomes impermeable and runoff consequently increases (Bennema, 1977: 35).

2.)
Available water capacity

"Available water
capacity," also known as "available water," is a measure of the
amount of water that the soil can hold in a form that can be extracted by plant
roots.  It is calculated as the
difference between field capacity (total moisture content of soil after gravity
water has been allowed to drain away) and wilting point (the moisture content
at which plants wilt and do not recover on re-wetting) (Young, 1976: 40).  Water held in fine pores cannot be
extracted from the soil at the pressures that plants are able to exert through
their roots.  Field capacity is
determined at 0.33 atmospheres (bars) of tension, and wilting point at 15 bars.

The available water
capacity calculated by this standard procedure is really only an index of
availability for several reasons.
One is that the ability of plants to extract water from the soil varies
among species, which may differ from the sunflower--the plant taken as a
standard by soil scientists.  A
second is that the 0.33 bar pressure used as a standard operational definition
of field capacity underestimates water holding capacity: 0.1 bar is believed
more appropriate, meaning that the standard method leads to an underestimation
of available water capacity by about 35% (Sánchez, 1976: 111).  A third is that intact soil cores taken
from the side of a soil pit are the ideal material for the measurements, and
results using dried material from traditional soil samples (as in the present
study) provides only an indication of these parameters in the field.

Some indications exist
that available water capacity may pose a restriction on use of water by the forest
in soils similar to those in the BDFFP reserves.  A study of undeformed cores in INPA's
"Model Basin" (30 km south of the BDFFP reserves) indicated that,
while pores make up 60% of the soil volume at 10 cm depth, only 17% of the
water contained in the pores is available to plants, while 50% is bound water
and 33% is lost at a pressure less than 0.33 bar and drains away by gravity
(Ferreira, 1997: 168).

3.)
Phosphorus

Phosphorus is a
limiting element for agricultural crops and cattle pasture in Brazilian
Amazonia.  For example, P
fertilization is the key to increasing pasture grass growth in technical
packages formulated by EMBRAPA (e.g. Koster et al., 1977;
Serrão et al., 1979).
Phosphorus is low in virtually all soils in Brazilian Amazonia, even including
relatively fertile ones such as the terra roxa (Alfisol) occurrences in
settlement areas along parts of the Transamazon Highway in Pará and the
BR-364 Highway in Rondônia (see Fearnside, 1984, 1986b).  Furthermore, the prospects are poor for
maintaining vast areas of agriculture dependent on phosphate fertilizer in
Amazonia because of limited deposits of rock phosphate in Brazil and worldwide;
virtually all of Brazil's modest supplies of this mineral are located outside
of Amazonia (see de Lima, 1976; Fenster and León, 1979; Fearnside,
1997a,b; Beisiegel and de Souza, 1986).

It is available
phosphorus (PO4, actually the anion H2PO4-),
rather than total P, that is most directly related to plant growth.  Phosphorus availability in latosols is generally
very low because most of it is in highly insoluble Fe and Al compounds
(Kamprath, 1973a: 139).  Phosphorus
availability in agriculture is usually stated in terms of phosphoric anhydride
(P2O5);
considering analyses made with the North Carolina extractant (0.05 N HCl
and 0.025 N H2SO4) that is standard in Brazil, 1
milliequivalent (m.e.) of PO43-/100 g of dry soil is
equal to 103 parts per million (ppm) of P or 23.7 mg of P2O5/100
g of dry soil (e.g., Vieira, 1975: 451-453).  While the total soil P obviously sets a
limit on the amount of available phosphorus that can be present, a variety of
soil characteristics and processes determine the available phosphorus present
within this limit.  Values of pH below
5.5 are generally associated with marked decrease in phosphorus availability
(Young, 1976: 299).  Organic carbon
and Fe2O3 both are positively related to available
phosphorus (P2O5) in Brazilian Oxisols (Bennema, 1977:
43).  Since both carbon and iron are
associated with high clay content, the granulometric structure of the soil
relates to plant growth through phosphorus, as well as through other nutrients
and through water.  Micorrhizae are
important in mobilizing P into available forms (St. John, 1985).  Micorrhizal associations have been found
in many, but by no means all, of the few Amazonian trees that have been
examined (St. John, 1980).

4.)
pH, aluminum and cations

Little information
exists on the response of Amazonian trees to different soil characters.  One important exception is the case of
cacao, which is a native Amazonian tree that has been the subject of much more
research than other species due to its economic importance.  It is noteworthy that, while most
Amazonian trees appear to be highly tolerant of very acid soils, soil pH (soil
reaction) is the best predictor of cacao yields (Hardy, 1961; see Fearnside,
1986b).  Under the acid conditions
that prevail in most Amazonian soils, soil pH is the single most important
influence on yields for many crops, such as maize (see Fearnside, 1986b).  In agricultural settings, soil pH at the
time of planting is dependent not so much on the initial pH of the soil as on
the quality of the burn that the farmer obtains when preparing the land for
planting (Fearnside, 1986b).  The
relations of soil pH to plant growth are included in Figure 1.

Cation exchange
capacity of soils rich in iron and aluminum oxides (such as those of the BDFFP
reserves) is pH dependent (Young, 1976: 95).  In addition, low pH leads to increased
concentrations of ions that are toxic or useless to plants (Fe2+, Al3+
and H+), which occupy some of the reduced number of binding sites
that do exist.  "Base
saturation" is the percentage of the sites that are occupied by useful
cations, or exchangeable bases (Ca2+, Mg2+, K+
and Na+, the sum of which is "total exchangeable
bases").  Cation exchange
capacity is normally calculated as total exchangeable bases + Al3+ +
H+, all in units of m.e./100 g of dry soil (Guimarães et
al., 1970: 85).  Cation exchange
capacity, total exchangeable bases and base saturation are, in practice, often
calculated without data on Na+ (e.g., Young, 1976: 426-429);
the results are little altered as sodium ions are normally present in low and
fairly constant quantities (around 0.01 m.e./100 g of dry soil).

The importance of low
pH to agriculture is often due to its close relationship to toxic aluminum ions
(Al3+).  Aluminum ion
concentration normally has a negative logarithmic relationship with pH (see
Fearnside, 1984; Sánchez, 1976: 225).  It is generally believed that aluminum
saturation, rather than the absolute concentration of aluminum ions, is most
closely related to plant growth (Primavesi, 1981: 100).  Aluminum saturation can be computed in
two ways, with or without including exchangeable acidity (H+).  Including H+, the sum of Al3+
+ H+ is divided by the total exchangeable bases plus Al3+
and H+, and the result is expressed as a percentage (Sánchez,
1976: 224).  This is the same as
100% minus the base saturation, so only one or the other need be used in
analyzing relations with plant growth when defined in this way.  In Brazil, however, aluminum saturation
is usually calculated without H+, it being Al3+ divided
by the exchangeable bases + Al3+, expressed as a percentage (Brazil,
SNLCS-EMBRAPA, 1979).  Aluminum
saturation calculated in this way of over 25% indicates inhospitable soils for
cacao (Alvim, 1977: 291).

Crops vary widely in
their sensitivity to aluminum toxicity: in terms of aluminum saturation with H+,
maize can tolerate up to 60% aluminum saturation, while sorghum is restricted
even at very low levels of aluminum saturation (Sánchez, 1976:
231).  Aluminum ions also have a
detrimental effect as one factor affecting fixation of phosphorus into
unavailable forms (Kamprath, 1973b: 127).
Aluminum toxicity itself acts partly through phosphorus, as aluminum
tends to accumulate in the roots and impede uptake and translocation of both P
and Ca to the aerial portion of the plant (Sánchez, 1976: 231).  Aluminum in the soil solution depends
not only on pH but also on organic matter content of the soil: aluminum ions
decrease as organic matter increases because organic matter forms strong
complexes with aluminum (Sánchez, 1976: 226).

The difference between
pH in potassium chloride (KCl) and water, or delta pH, indicates the charge
status of an oxide system (a soil in which entire clay particles consist of
iron and aluminum oxides, or allophanes, or a soil in which stable coats of
these oxides cover silicate particles)(Sánchez, 1976: 140-141).  If pH in KCl is less than that in water
(delta pH is negative: the usual case), then there is a net negative charge
(cation exchange capacity), whereas if the reverse is the case there is a net
positive charge (anion exchange capacity).
The magnitude of the charge affects the soil pH at the isoelectric
point, or zero point of charge.
This, in turn, determines the cation exchange capacity (CEC) at any
given soil pH level.(2)
The organic matter content of the soil has a strong influence on these
relationships and resulting CEC (Bennema, 1977: 39; Sánchez, 1976:
146).  Delta pH is often used as an
indicator of organic matter.  If pH
in KCl is higher than pH in H2O (delta pH is positive), then organic
matter is low.  Delta pH is normally
positively associated with C/N ratio in Amazonian soils, especially when
disparate soils are compared with wide differences in delta pH values (Tanaka et
al., 1984: 55).

5.)
Nitrogen

Nitrogen is
traditionally considered to be the major nutrient deficiency in tropical
agriculture (National Academy of Sciences, 1972: 8; Webster and Wilson, 1980:
220).  Leguminous trees are able to
fix nitrogen with the aid of symbiotic bacteria, which probably gives members
of this superfamily a competitive advantage over species in families that lack
this capability.  This helps explain
why legumes are a common group in the BDFFP reserves, but hardly a dominant
one: Burseraceae, Sapotaceae and Lecythidaceae are all more common
(Rankin-de-Merona et al., 1990: 574).  In a model developed by the BIONTE
(Biomass and Nutrients) project for INPA's "Model Basin" (located on
the same soil type about 30 km south of the BDFFP reserves), N was assumed to
be limiting for the forest as a whole (Biot et al., 1997: 284).  In the BDFFP reserves, total N was found
to be positively correlated with forest biomass (Laurance et al., 1999).

Sollins (1998: 23)
reviews literature on relation of soils to lowland rainforest composition, and
suggests that soil factors in decreasing order of importance would be: P
availability, Al toxicity, depth to water table, amount and arrangement of
pores of different sizes, and availability of base-metal cations,
micronutrients (e.g., B, Zn), and N.  Nitrogen is listed last because most
lowland tropical soils are relatively N-rich.  On the other hand, studies in tropical
montane forests in Venezuela, Jamaica and Hawaii have found relations of tree
occurrence and growth with nitrogen (Tanner et al., 1998).  Work on tropical montane forests is more
advanced than that in lowland forests, as some montane forest work includes
manipulative experiments rather than relying exclusively on correlation.  Tanner et al. (1998) speculate
that many lowland forests are limited by P and many montane forests by N.

6.)
Zinc

Zinc deficiency can be
caused by fixation by crystalline sesquioxides (Bennema, 1977: 36).  Since sesquioxides (Fe2O3
and Al2O3) are the hallmark of latosols (Oxisols), zinc
deficiency may pose a problem for plant growth.  Zinc solubility bears a negative
exponential relation to pH (pH values represent an exponent), and increases
rapidly at soil pH values below 5 (Coelho and Verlengia, 1972: 58).  Critical values for zinc in agriculture
are between 1 and 2 ppm when extracted with 1 N HCl (Cox, 1973a: 183).

7.)
Manganese

Manganese is a
micronutrient required in small quantities by plants (Young, 1976: 291).  However, at high levels it is toxic and,
like aluminum toxicity, can inhibit plant growth.  The availability of Mg to plants is
closely tied to pH, with highest solubility at low pH.  Manganese toxicity is a common problem
for legume production in Brazilian agriculture on acid soils (Cox, 1973a: 87).

8.)
Other elements

The above discussion
has been restricted to elements believed to be potentially limiting for forest
growth and for agriculture and ranching implanted on soils like those in the
BDFFP reserves.  The data set for
the BDFFP reserve soils includes information on sulfur and copper.  Boron, molybdenum and chloride were not
analyzed.  Total potassium was not
analyzed: this measure is ordinarily not correlated with plant uptake and thus
is primarily just of academic interest (Cox, 1973b: 162).

II.) THE BDFFP
SOILS SURVEY

A.) OVERVIEW OF THE
DATA SET

The soils data set
contains surface samples from 1693 locations under forest in the BDFFP reserves
(272 of which have additional samples taken at later dates), plus 41 soil
profiles and 1693 soil density cores.
This allows the effects of "fine scale" variation to be
investigated in a way that would not be possible at the scale of soil maps used
for zoning and other planning exercises, such as those based on the RADAMBRASIL
surveys.  The BDFFP soils data
indicate substantial variability within an area that is all mapped as having
identical soil on the RADAMBRASIL maps.
The differences among sampling locations in the BDFFP reserves are
sufficient to have an impact on agriculture were these areas (or areas like
them) cleared and planted.  The
differences are also likely to affect the distribution of tree species within
the forest, the biomass of the forest, and the susceptibility of the forest to
drought stress if exposed to climatic variability (such as that provoked by the
El Niño phenomenon), to the effects of edge formation through
fragmentation and to the effects of probable climatic changes such as global
warming and reduced rainfall due to loss of evapotranspiration.

B.) FIELD METHODS

Surface samples (0-20 cm)
were taken using a screw-type soil auger, each sample being a composite of 15
cores taken at haphazardly chosen locations within a 20 m X 20 m quadrat.  Quadrats were delimited by permanent
markers at the corners (PVC pipes with numbered aluminum tags), thereby
allowing the same locations to be resampled in additional studies.

A soil density sample
was taken at the center of each quadrat where surface samples were taken.  Volumetric cylinders were used 20 cm in
length and 6.9 cm in diameter.  The
cylinder fits into the end of a soil corer on the shaft of which a movable
weight slides up and down.  The
weight was raised and dropped repeatedly to pound the cylinder into the ground.  Once in place, the cylinder was removed
by digging around it with a digging tool, taking care that the cylinder is
removed completely full of soil (which requires that the cylinder not be pulled
out from above).  The soil was
removed by hitting the outside of the cylinder with a blunt instrument.  Samples were placed in double plastic
bags for transport to the laboratory and weighing.

A profile to 1.5-m
depth was taken at the center of a subset of the quadrats using a
"Dutch"-type soil auger.
Each profile was divided into eight layers, the first seven samples
corresponding to layers 20-cm thick (to a total of 1.4 m) and the last sample
representing a 10-cm layer.  The
samples were laid out on a plastic tarp beside the hole to allow identification
of horizons (by color, texture and plasticity).  These descriptions follow the methods of
Vieira and Vieira (1983: 60-81).
The samples were then placed in separate plastic bags for transport to
the laboratory.  The sites of the
profiles were identified by PVC pipes with numbered aluminum tags.

C.) LABORATORY METHODS

1.)
Sample preparation, soil color, textural appearance

and consistency

When surface and
profile samples arrived from the field they were classified in the wet state
for color (using a Munsell color chart), wet consistency (stickiness and
plasticity), and textural appearance.
These descriptions followed the methods of Vieira and Vieira (1983:
60-81).

The samples were then
dried in a solar dryer, followed by 24 hours in an electric oven at 1050C.  After this drying, charcoal fragments
were removed by hand, weighed and stored.
The dry sample was then ground by hand (using a board and rolling pin),
passed through a 20-mm and then a 2-mm mesh sieve.  Stones and lateritic concretions removed
in the sieves were weighed and recorded.
A 300-g subsample of the dried soil was stored in a glass container in
the voucher collection ("soloteca").  Additional 300-g subsamples were
prepared for the INPA (National Institute for Research in the Amazon, Manaus,
Amazonas) and CENA (Center for Nuclear Energy in Agriculture, Piracicaba,
São Paulo) soils laboratories.
Analyses of granulometric characters, bulk density, organic carbon,
available water capacity and pH in H2O and KCl were done at INPA;
total N, total C, Al3+, H+, Ca2+, Mg2+,
K+, PO43-, Cu, Fe, Zn, Mn were done at CENA.  The INPA soil texture results were
checked by comparison of 10 blind samples that were also analyzed by the
EMBRAPA soils laboratory in Manaus; no significant differences were
encountered.  The CENA laboratory
sends 10 samples every two months to one of a group of cooperating Brazilian
laboratories to obtain an independent check on its chemical analyses.

2.)
Soil texture

Textural
(granulometric) analysis separated material into four fractions: coarse sand
(grains 0.2-2.0 mm diameter), fine sand (grains 0.05-0.2 mm diameter), silt
(particles 0.002-0.05 mm diameter) and clay (particles < 0.002 mm diameter)
(Vieira and Vieira, 1983: 68).  The
particle size limits in these classes observe the United States Department of
Agriculture standards, rather than those of the International Society of Soil
Science.  The pipette method was
used (Brazil, SNLCS-EMBRAPA, 1979).

The clay fraction was
determined by mixing soil in NaOH solution in an electric agitator.  The mixture was then placed in a 1-liter
sedimentation cylinder (graduated cylinder), mixed by successive inversions,
and allowed to settle.  After a
period of time determined from a table depending on the temperature (e.g.,
3 hours and 33 minutes for 25oC) a 25-ml sample is drawn at a depth
of 5 cm, using a pipette.  The
material was placed in a tared container, dried in an electric oven at 105oC,
and weighed.

Total sand (coarse +
fine) was determined by sieving with a 0.053-mm mesh, followed by washing, oven
drying and weighing the material.
This material was then sieved in a 0.2-mm mesh sieve.  The fine sand was weighed and the coarse
sand determined by difference from the total sand.  Silt was determined by difference of the
total sample weight from the sum of the other three fractions.

3.)
Bulk density

The samples were dried
to constant weight in an electric oven at 105oC.  Fine roots and charcoal were removed
from these samples immediately after dry weight determination.  Roots were then washed, oven dried, and
weighed.  Charcoal was stored after
weighing.

4.)
Organic carbon and organic matter

The modified
Walkley-Black method was used at INPA, in which volumetric measurements are
made by potassium bichromate and titration with ferrous sulfate.  The method (Walkley and Black, 1934)
included the modifications employed by EMBRAPA (Brazil, SNLCS-EMBRAPA,
1979).  Organic matter was derived
by multiplying the result by the constant 1.72 (Brazil, SNLCS-EMBRAPA, 1979), a
common practice (Young, 1976: 102).
The C/N ratio is organic carbon (Walkley-Black) divided by total
nitrogen.

5.)
Available water capacity

Field capacity and
wilting point were determined indirectly on a pressure membrane apparatus (Soil
Moisture Equipment Co., Santa Barbara, California), field capacity
corresponding to moisture content under a suction of 0.33 atmospheres (bars)
and wilting point to the corresponding value at 15 atmospheres.  The difference in the amount of water
held by the soil between these two points is the available water capacity.  Moisture content and available water
capacity are expressed as percent water by weight on a dry basis (Klar, 1984:
71).  Note that, following the
standard procedure, the soil was dried and sieved before being placed in the
pressure plate rings, thereby altering its structure.

6.)
pH in water and KCl

Soil reaction (pH) in
distilled H2O and in 1-N KCl solution were measured using a pH
meter. The ratio of oven-dried soil to water or KCl solution is 1:1 on a
volumetric basis (20 ml soil in 20 ml of water or solution).  Work in tropical soils elsewhere has
found soil reaction to increase by about 0.3 pH units in dried samples as
compared to field conditions; pH is unaffected by storage once dried (Gillman
and Murtha, 1983).

7.)
Macro and micronutrients

The CENA methodology
for micronutrient determination has been described by Zagatto et al.
(1981) and Jorgensen (1977).
Samples were digested using the EMBRAPA methodology: 0.0025 N HCl and
0.005 N H2SO4 (SNLS-EMBRAPA, 1979).  K+ was measured by atomic emission
spectrophotometry in an air-acetylene flame, using a Perkin-Elmer AAS 306; Al3+,
Ca2+, Cu, Fe, Mg2+, Mn2+, Na+ and
Zn+ by atomic absorption spectrometry with plasma induced in argon,
using a computerized spectrometer system (Jarell-Ash Plasma Atomcomp Direct
Reading Spectrometer), and S (as barium sulphate) by turbidimetry, using a flow
injection system.  PO43-
was determined in an autoanalyzer using the molybdenum blue method (Jorgensen,
1977: 10).

8.)
Total nitrogen

Total nitrogen was
determined with Kjeldahl digestion, using a mixture of H2O2,
Li2SO4 and concentrated H2SO4 to
break down the organic matter and transform the nitrogen in the sample into NH4+
(Parkinson and Allen, 1975).  The
distillate was titrated with H2SO4.

9.)
Total carbon (%C)

Total carbon (%C) was
determined at CENA by the "dry" method, which converts the forms of
soil carbon into CO2 by combustion at 1100oC.  The gas was then sent to a standard
sodium chloride cell, where the difference in electrical conductivity between
this solution and one carbonated with CO2 was detected, and the
result is expressed in milligrams of carbon (Cerri et al., 1990).

D.) SUMMARY OF RESULTS

Results presented here are
restricted to the 54 non-contiguous ha in which tree surveys were carried out
in the BDFFP project.  The reserve
area lacks patches of the best Amazonian soil types (anthropogenic black soil
"terra preta do índio" and Alfisol "terra roxa
estruturada"), and of the worst types such as white sand campina
soils (podzols or Spodosols).
Nevertheless, the data indicate a substantial variation in soil quality
despite its uniformity at the level of general soil maps.  Table 1 presents descriptive statistics
on the hectare-level means.

[Table
1 here]

Clay content (mean
value = 54.7%) varies greatly from 18.0-68.8%; since clay content is closely
tied to several indicators of soil fertility, the general fertility level also
varies substantially.  The mean soil
would be classed in the middle of the "clay" category (Vieira and
Vieira, 1983: 68).  The soil has a
significant percentage of silt-sized particles (mean value = 21.2%), making the
soil differ from some Amazonian soils where particles are concentrated in sand
and clay fractions, with very little in between.  However, it is possible that incomplete
dispersion of clay aggregation could result in an apparent abundance of
silt-sized particles when, in fact, this size class is present in much smaller
amounts (Thierry Desjardins, personal communication, 1998).  The statistical analyses were therefore
performed lumping the clay and silt categories.

The terrain is
undulating, with a mean slope of 10.8%.
A portion of the area with steep slopes would be prone to erosion
problems, in addition to not being appropriate for mechanized agriculture.  Land-use capability classifications
consider slopes of 0-2% to be without limitations, 2-8% to be slightly limited,
8-30% to be moderately limited, and >30% to be very limited (Benites, 1994:
215).  By these criteria, of the 373
points with slope measurements in the data set used in the current study, 57.1%
had no limitation, 23.6% had slight limitation, 23.1% had moderate limitation,
and 2.7% had severe limitation from slope.
In addition, the clay/sand content ratio of 2.6 (or 3.1, considering
clay+silt) in the BDFFP reserves is considered an impediment to mechanization,
the maximum value of this ratio considered appropriate being 2.0 (Vieira and
Vieira, 1983: 123).  However, this
classification of mechanization limitations based on clay content represents an
average for all of Brazil; W. Sombroek (personal communication, 1998) believes
that yellow latosols in Amazonia, such as those in the BDFFP reserves, soils
with higher clay contents could be mechanized.

The soil is quite acid,
with a mean pH in water of 4.0 (range 3.4-4.4).  However, it should be remembered that
what is of interest to agriculture is not the level of nutrients in the soil
under forest, but rather the level that will be present when the forest is
cleared and burned.  Especially in
the case of pH, the values are increased by an amount that varies with burn
quality (Fearnside, 1986b).

The delta pH (mean
value = -0.3) indicates a net negative charge (a cation exchange
capacity).  This also confirms a
reasonable level for soil organic matter by the standards of tropical
agricultural soils.

Aluminum saturation
(excluding H+), with a mean value of 92.4%, is clearly high, while
base saturation (without Na+) is low, with a mean value of only
7.6%.  Al saturation (without H+)
< 50% is classified as low and > 50% is classified as high (Vieira and
Vieira, 1983: 144).

Total carbon had a mean
value of 1.96%.  Organic carbon, as
determined by the modified Walkley-Black method, had a mean value of
1.58%.  Organic matter had a mean
value of 2.72%.  While these values
may appear low for agricultural soils, they are typical of Amazonia.

Total N levels are
moderate, with a mean value of 0.16%; values less than 0.1% are considered
"low" with a probable response to fertilization in crop plants, while
values in the 0.1-0.2% are in the "moderate" range where responses
are possible (Young, 1976: 291).
The C/N ratio (mean value = 9.9) indicates a reasonable, but not ideal, quantity
of nitrogen available to plants (values over 15 indicate little N in available
forms).

Phosphate levels are
very low (mean value of PO43-=0.030 m.e./100 g of dry
soil).  PO43-
is considered "insufficient" for crop plants with levels <0.097 m.e./100
g of dry soil (equivalent to <2.30 m.e. of P2O5/100 g
of dry soil); "fair" levels of PO43- are
0.097-0.253 m.e./100 g of dry soil (equivalent to 2.30-6.00 m.e. of P2O5/100
g of dry soil), while "good" soil has >0.253 m.e. of PO43-/100
g of dry soil (>6.00 m.e. of P2O5/100 g of dry soil)
(Vieira and Vieira, 1983: 144)

Exchangeable potassium
(K+) is low, with a mean value of 0.06 m.e./100 g of soil; values
below 0.2 m.e./100 g of dry soil are considered to be low, with fertilizer
response probable in crop plants (Young, 1976: 291).  A land-use capability rating system used
in Brazil (Vieira and Vieira, 1983: 144) classifies K+ levels <
0.11 m.e./100 g of dry soil as "insufficient," 0.11-0.37 as
"fair" and > 0.37 as "good."  The absolute minimum level required by
crop plants is considered to be 0.10 m.e./100 g of dry soil (Boyer, 1972:
102).  Of the nutrient cations,
potassium is the one which is in greatest demand by crops (Webster and Wilson,
1980: 74).  Lack of exchangeable
potassium may therefore affect plant growth on these soils.

Calcium ion
concentrations are very low (mean value = 0.058 m.e./100 g of dry soil).  For crops, < 1.50 m.e./100 g of dry
soil is "insufficient," 1.50-3.50 m.e./100 g of dry soil is
"fair," and > 3.50 m.e./100 g of dry soil is "good"
(Vieira and Vieira, 1983: 144).

Magnesium ion
concentrations are fair (mean value = 0.076 m.e./100 g of dry soil.  For crops, < 0.50 m.e./100 g of dry
soil is "insufficient," 0.50-1.00 m.e./100 g of dry soil is
"fair" and > 1.00 m.e./100 g of dry soil is "good"
(Vieira and Vieira, 1983: 144).

The cation exchange
capacity (expressed as the CEC of clay) is very low, with a mean value of 14.4
m.e./100 g of clay after correction for carbon.  With a correction for carbon (each 1% of
carbon is considered to correspond to 4.5 m.e. of CEC), a CEC of
24 m.e./100 g of clay is the dividing line between "low" and
"high" activity clay (Vieira and Vieira, 1983: 38).  The value of 24 m.e./100 g of clay is
considered low for agriculture (Benites, 1994: 231).

Base saturation >50%
is considered as indicating high fertility, provided that CEC of the clay is
> 24 m.e./100 g of clay; base saturation < 50% indicates moderate
fertility like these (Benites, 1994: 215; see also Vieira and Vieira, 1983:
46).  The mean value of 7.6%
(without Na+) in the study area is obviously low, as is the maximum
value of 12.2%.  The Na+
levels found appear to be unusually high (mean = 0.052 m.e./100 g dry soil);
combined with very low values for Ca2+ (mean = 0.058 m.e./100 g dry
soil), Na+ makes an unusually large contribution to exchangeable
bases.  However, due to the much
less complete data set for Na+, cation measures excluding sodium
were used in the statistical analyses.

The relationships among
soil characters in the BDFFP data set are summarized in Table 2 for total
exchangeable bases, organic matter, aluminum ions and available water
capacity.  Some of the other
relationships shown in Figure 1, although known to hold generally, did not
emerge as significant regressions in the BDFFP data set.  Total exchangeable bases was not
predicted significantly better by including pH (or log10 pH) in the
regression, although higher pH values are known to be associated with greater
amounts of cations such as Ca2+ and Mg2+ (see Fearnside,
1986).  Phosphate was not
significantly related to pH, Al3+ and Fe in the data set.

[Table
2 here]

III.) LESSONS
FOR DEVELOPMENT

A.) AGRICULTURAL
POTENTIAL

Our knowledge of the
BDFFP reserve area greatly exceeds the level of knowledge that can be expected
to be available for zoning decisions in the rest of Amazonia.  If we can't come up with well-founded
recommendations for this area, then we can't expect such suggestions to be
obtainable for the vast majority of the rest of the region.

Wide differences of
opinion exist as to whether a given fertility level means that an area should
be opened up for agriculture, or that it should be maintained under forest
cover.  The data make clear that
soil fertility is low and impediments to agriculture, such as aluminum
toxicity, are substantial.  This
suite of problems leads some authors to conclude that soils such as these
should not be used for agriculture.
Irion (1978: 519), for example, concludes for soils on the Barreiras [or
Alter do Chão] formation, such as those of the BDFFP reserves,
"extensive cultivation .... is impossible, as the quality of the soil is
insufficient.  Any such cultivation,
aiming at export of agricultural products, would result in an impoverishment of
the soil within a few years, thus making the soil agriculturally unusable for
many decades."  Van Wambeke
(1978: 233) warns of the potential for "irreversible destruction of soils
and the creation of fertility deserts."  On the other hand, Serrão and
Homma (1993: 287), look at the same situation and conclude that 70% of the land
in Brazilian Amazonia is "appropriate for crop production," and
assert that "regions with low fertility and acidic soils have not been
transformed into deserts, as some have foreseen....  On the contrary, such regions have been
very dynamic in terms of agricultural development" (Serrão and
Homma, 1993: 288).  Whether these
regions can be described as "very dynamic" is open to question; certainly
the cattle ranches on which the BDFFP reserves are located are
less-than-dynamic.

Amazonia in general,
and particularly the state of Amazonas, has been protected from deforestation
by impediments that include poor soils, human diseases (particularly malaria),
and difficulty of access from densely populated portions of Brazil.  But disease is no longer the barrier
that it once was; for example, if opening areas today required the sacrifice of
lives that opening the Madeira-Mamoré railway in Rondônia did at the
beginning of the 20th century, then the threat of deforestation would be much
less.  Poor access is also rapidly
changing: many settlers have gone directly from Rondônia to Roraima,
bypassing the state of Amazonas through which they passed, a phenomenon explained
both by somewhat better soils on the Guianan Shield in Roraima and by
inducements offered by the government of Roraima.  The paving of the BR-319 Highway linking
Rondônia with Manaus, expected in 1998 or 1999, will open the flood gates
to an influx of prospective settlers to central Amazonia, including the general
area of the BDFFP reserves.

What happens when an
area like the BDFFP reserves is cleared depends on what is done with the
land.  Some options are better than
others from the standpoints of maximizing sustainability and minimizing
environmental impact.  Agroforestry,
for example, is better in many respects than either annual crops or cattle
pasture.  However, severe
limitations exist for widespread use of agroforestry in the vast areas of
degraded lands that have already been created in the Amazon region, let alone
the even larger areas that would exist if more forest were to be cut in the
belief that agroforestry can solve the problems of sustaining production to
support the human population (Fearnside, 1998).

The political discourse
surrounding the announcement of new settlements in Amazonia is invariably
permeated with images of permanent prosperity emanating from the agricultural
systems to be implanted in the cleared areas.  However, governmental decisions to cut
the forest and implant agricultural settlements in areas with soils like those
of the BDFFP reserves, which are typical of vast expanses of Amazonia, imply
one of two things: either the government must be willing to provide or
subsidize regular inputs of fertilizers for the indefinite future (a highly
improbable scenario), or the decision-maker must accept responsibility for
trading the forest for a landscape of degraded cattle pastures and second
growth stands.  Unfortunately, this
responsibility is frequently avoided by recourse to histrionic devices such as
the platitude that agriculture or ranching will be sustainable with
"adequate management," the implication being that, if the project
fails at some future date, then it will be the farmers who are to blame for not
having applied "adequate management."

Two of the principal
crops that are currently in fashion for promotion in Amazonia are not likely to
be successful in areas like the BDFFP reserves.  One is oil palm (e.g., Smith et
al., 1995).  In areas with a
significant dry season (such as the Manaus area) the yield of oil drops quickly
in comparison with optimal yields.
In Brazilian Amazonia the two locations with optimal climatic conditions
for oil palm are the area near Belém (Pará) and Tefé
(Amazonas).  Plantations in the
Belém area suffer the effects of shoot rot disease (Fearnside,
1990).  Because most of the costs of
establishing and maintaining plantations are similar on a per-area basis
regardless of the yield, plantations located in suboptimal areas are unlikely
to be competitive.

The other crop that
figures heavily in current discourse on Amazonian development is soybeans.  Unfortunately, the social benefits from
this crop are small for the local population, and the mechanized agriculture it
requires is capital and chemical intensive.  Although mechanization in areas like the
BDFFP reserves is not impossible, the area would be less-than-ideal for these
methods due to undulating terrain and high clay content of the soil.

Low soil fertility can
be compensated by application of fertilizers.  However, a series of severe constraints
limits the extent to which agriculture based on a supply of nutrients from
fertilizers can be extended to wide areas in Amazonia.  The best example of this is the history
of the "Yurimaguas technology" developed for continuous cultivation
in Amazonian Peru (Sánchez et al., 1982; see Fearnside, 1987,
1988; Walker et al., 1987).
Despite a long list of subsidies ranging from chemical inputs to free
soil analyses and technical advice on a field-by-field basis, this high-input
management package did not gain popular acceptance in the area.  The limits of physical resources, such a
phosphate deposits, as well as financial and institutional restraints, make
widespread use of such systems unlikely (see Fearnside, 1997a).

Application of
fertilizers is only one means by which soil fertility limitations can be
addressed.  One must consider the
extent to which the agricultural prospects of areas like the BDFFP reserves
would change if other kinds of technical advances were to occur.  For example, recent progress has been
made on removing aluminum saturation limitations through development of
transgenic crop plants (Barinaga, 1997; de la Fuente et al., 1997).  It is not inconceivable that phosphorus
limitations could be relaxed by development of crop plants with appropriate
micorrhizal associations.  Nitrogen
limitations of various non-leguminous crops may be relaxed through
pseudosymbiotic relationships with a variety of types of nitrogen-fixing
bacteria, an area in which significant advances have been achieved in Brazil
through the work of Johanna Dbereiner (e.g., Dbereiner, 1992).

Today, however, it is
not viable to sustain agriculture and ranching in vast areas of Amazonia due to
limits of markets, phosphate deposits, and funds.  Therefore one should not count on a
"technological fix" to solve the problems of sustainability until
such time as the technological advances in question are actually achieved.  Not "counting one's chickens before
they hatch" is a universal precautionary principle that is a basic rule
for avoiding unwise adventures in myriad situations in addition to this
one.  One should also remember that
the environmental costs of forest loss must be considered, and that these costs
do not change much if the agriculture implanted is productive or not (see
Fearnside, 1997a).

The soils in the BDFFP
reserves are clearly infertile: indicators of soil fertility such as pH, cation
exchange capacity, total exchangeable bases and PO43- are
low, while aluminum saturation is high.
Under such circumstances, it is logical to maintain these areas under
forest rather than converting them to short-lived low-productivity land uses.  But to what extent would the situation
be different if the soils were more productive?  What level of soil quality would make it
worthwhile to sacrifice the forest?
There are no simple answers to these questions.  Rational decision-making will require
assessment of the value of both the agricultural production that can
realistically be expected from the area and the environmental cost of
sacrificing the forest.

So what is the
lesson?  These researchers are of
the opinion that the main lesson is that the returns from converting areas like
the BDFFP reserves to agriculture or ranching are minimal when compared the
true value of the environmental services of the intact forest.  Even though the amount that countries
like Brazil may one day be able to collect on the basis of supplying these
services is much less than the true value of the services, the returns from
agriculture and ranching are also meager when compared with the amounts that
might, in fact, be collected (Fearnside, 1997c; see Chapter ____[Laurance]).

B.) PROSPECTS FOR
RESILIENCE

The relationships found
among the various soil characters follow patterns that are consistent with what
is generally known about tropical soils.
These relationships (Figure 1 and Table 2) give an indication of some of
the changes that are likely to occur in the face of human interventions such as
selective logging, formation of edges through forest fragmentation, and removal
of forest for implanting agriculture and ranching.

In the case of logging,
changes normally found include soil compaction along logging tractor paths
(Veríssimo et al., 1992).
Nutrients are exported in the biomass removed (Ferraz et al.,
1997), and soil cations are lost through leaching and runoff (Jonkers and
Schmidt, 1984).

Outright removal of the
forest has major impacts on soil nutrients and structure (see review in
Fearnside, 1986b).  Soil characters
important for plant growth can be expected to change together: as they adjust
to a new equilibrium they will tend to maintain the same relationships among
each other that were found in the forest soil.  Burning raises pH and provides inputs of
nutrients to the soil, but cultivation usually leads to losses of organic
matter and clay that gradually reduce the ability of the soil to hold cations.  Some of the changes, such as loss of
organic matter content and increase in soil compaction, can be reversed through
periods under fallow.  How much this
capability for recovery of the soil, as well as capability for recovery of the
forest, compensate for the impacts of deforestation is an important area of
debate.  Unfortunately, the
theoretical possibility of recovery if areas are abandoned for many decades or
even centuries has little relevance to the real impacts that are caused by the
continued advance of deforestation in the region.

"Resilience"
is a term that is fashionable in discussions of Amazonian development, and
refers to the ability of a system to recover its original characteristics if
perturbed (e.g., Smith et al., 1995).  Are the soils of the BDFFP reserves
likely to be "resilient" if they are converted to pasture and
degraded?  Reasons to doubt this
include the already low levels of key elements that would be further
depleted.  Among the changes that
normally occur are loss of clay and carbon, together with the cations that are
tied to these components.  Carbon
can be regenerated under extended fallows, but, in practice, it is doubtful
that fallows would be left for sufficient periods for this to happen
(Fearnside, 1996a).

Different people can
look at the same set of facts and arrive at radically different
conclusions.  Serrão et al.
(1996: 8), for example, take the regrowth of secondary forest in abandoned
pastures to indicate that "the Amazonian upland forest ecosystem is fairly
resilient to current uses," whereas others would disagree (e.g.,
Fearnside and Guimarães, 1996).

C.) DISTRIBUTION OF
NATURAL VEGETATION

On a broad scale, a
relationship between soil and tree species and biomass is evident, such as the
difference between campina and campinarana vegetation with low
biomass that grows on white sand soils in the Manaus area, versus the upland
forests with high biomass on more clayey soils like those in the BDFFP
reserves.  Within more similar
soils, such as those in the reserve system, differences are more subtle but are
likely to be present.

Studies in various
parts of the tropics indicate relationships between tree species occurrence and
soils.  In a review by Sollins
(1998) of 18 studies in tropical lowland forests, relations between species
occurrence and soil drainage regimes were common.  Notable is the study by Lescure and
Boulet (1985) of 16.8 ha of forest in French Guiana, which found that 69% of
the tree species showed response to soil drainage conditions.

Only three of the 18
studies reviewed by Sollins (1998) were able to detect relationships of tree
species occurrence to chemical properties: Ashton and Hall (1992) found
relationships with P and cations in Sarawak and Brunei; Clark et al.
(1995) found relationships with P, Al and pH in Costa Rica, and Van Schaik and
Mirmanto (1985) found a relationship with pH in Sumatra.  The three studies that reported
relationships with chemical properties were those with the largest ranges of
values for the chemical indicators of fertility (the independent
variables).  Sollins (1998) believes
that the limited range of soil fertility within the areas in which studies have
been attempted to relate species occurrence to chemical properties is a primary
reason for the elusiveness of demonstrating significant relationships.  Other confounding factors include
seasonal variation in some key fertility indicators, especially available
phosphorus, cations and pH.  Both of
these restrictions apply to the BDFFP data set as well.

Soil fertility and
water relations can be expected to be related to seedling survival and to the
growth rates of trees.  Species
associations with soils may be related to forest biomass if species
characterized by larger individuals are found on certain soils.  Any soils effect on the occurrence of
species that become large canopy emergents would have a great effect on biomass
because a large part of forest biomass is often held in only a few very large
individual trees (Brown et al., 1995; Clark and Clark, 1985).  Independent of species effects, general
favorability of the soil for plant growth can be expected to be positively
associated with forest biomass.  An
ordination analysis relating biomass to soils in the BDFFP reserves indicates
that 53% of the variation in biomass is explained by a gradient in clay content
(and positively associated levels of total N, organic C, exchangeable bases, K+,
Mg2+, Ca2+, Al3+, H+ and
CEC)(Laurance et al., 1999).

D.) POTENTIAL FOR
RELEASE OF GREENHOUSE GASES

Carbon stocks in soil
and in forest biomass in Amazonia are very large due to high per-hectare
loading and to the vast areas of Amazonian forest still standing.  Release of these stocks is a significant
contributor to global warming at present rates of deforestation (Fearnside,
1996b, 1997d), while the large remaining stocks mean that the potential future
importance of avoiding emission is even greater (Fearnside, 1997c).  Converting each hectare of forest to the
equilibrium landscape that replaces it releases approximately 8.5 t of soil
carbon to the atmosphere considering soil to 8-m depth over 15 years, or 7.4 t
C/ha to a depth of 1 m (Fearnside and Barbosa, 1998).

The fine-scale spatial
variability in soil carbon distribution indicated by the BDFFP soil survey
suggests a substantial amount of uncertainty is inherent in studies of soil
carbon change based on "chronosequences," where the effects of land
uses (such as pasture) are inferred from comparison of roughly simultaneous
samples taken at a series of sites with different land-use histories (see
Fearnside and Barbosa, 1998).
Substantial differences among these sites could be due to natural
spatial variation, rather than to the effect of land use.

E.)
PROBABLE RESPONSE OF FOREST TO FRAGMENTATION

The BDFFP has provided
undeniable evidence that creation of edges results in greatly increased
mortality of trees located near the edges (Laurance et al., 1998;
Lovejoy et al., 1984).  These
edges have drier air than the forest interior (Kapos, 1989; Kapos et al.,
1993).  Tree mortality near the
edges leads to a "biomass collapse," releasing carbon to the
atmosphere (Laurance et al., 1997).

Soils are likely to
play a role in mortality of trees under these conditions.  Soils with greater amounts of sand can
be expected to retain less water, leading to greater drought stress when
conditions are dry due to edge proximity.
However, sandy soils are associated with valley bottoms, which would be
expected to have some additional water as compared to higher locations.

F.) PROBABLE RESPONSE
OF FOREST TO CLIMATIC CHANGE

Climatic variations and
changes of several types exist or are predicted.  The El Niño-Southern Oscillation
event, a periodically recurring phenomenon which is not caused by human action,
results in droughts that can have significant impact on Amazonian forest.  Tree species that are specialized on
wetter sites are particularly vulnerable to drought stress.  For example, such species in the forest
on Barro Colorado Island, Panama, suffered extraordinarily high mortality
during the 1982-1983 El Niño event (Hubbell and Foster, 1990: 531).

Archeological evidence
suggests that catastrophic fires have occurred in Amazonia at the times of
major El Niño events four times over the past 2000 years: 1500, 1000,
700 and 400 B.P. (Meggers, 1994).  Human
action could now turn less-intense El Niño events, such as the 1982-1983
and 1997-1998 events, into major catastrophes.  Such less-intense events are much more
frequent than major ones, but these would be added to the effects expected from
climatic changes such as reduction in rainfall from lowered evapotranspiration
caused by continued deforestation (Salati and Vose, 1984) and the effect of
temperature and rainfall changes caused by global warming (see Fearnside,
1995).  While neither of these
changes is expected to result in radical reductions in rainfall, the effect is
added to that of natural variability such as that caused by El Niño
events and disturbances such as logging and edge formation.  Logging is rapidly increasing in
Amazonian forests, leading to more flammable conditions from accumulation of
slash and accidentally killed trees in the logged-over forests (Uhl and
Buschbacher, 1985; Uhl and Kauffman, 1990).  The continued advance of settlement and
deforestation in the region means that many more opportunities exist than in
the past for fires to enter adjacent forests.  These effects are added to those of
climate variability and climatic change, increasing the risk of fire entering
standing forest.

Soils play a role in
the forest's response to these events.
As in the case of edge-related drought stress, trees on soils with
little available water are more likely to succumb to extreme events.

IV.) CONCLUSION

The soils of the BDFFP
reserves are typical of vast areas of Brazilian Amazonia that are likely to
come under increasing pressure for deforestation.  These soils have low fertility, are acid
and have high levels of toxic aluminum ions.  They also have limitations from rolling
topography, high clay content, and low available water capacity.  The soils data indicate that they would
produce little if converted to agriculture or ranching, and point to land uses
that maintain forest cover intact as preferable.  Although the value of the environmental
services provided by standing forest currently provides no source of cash
income, the potential value of these services far exceeds the returns that can
be expected from cutting the forest for agriculture or ranching.

V.) NOTES

(1)
The defining criterion for latosols is that the B horizon must be
"latosolic," as opposed to "textural" (i.e.,
clayey).  The criterion for
identifying "latosolic" character in the Brazilian soil
classification system is that the ratio of silicon and aluminum oxides (SiO2:Al2O3)
must have a value less than two (see Sombroek, 1966: 69).  Values below two generally indicate that
the silicate clay minerals have a 1:1 lattice structure (Sombroek, 1966:
80).  The ratio refers to the number
of sheets of silica tetrahedra to sheets of alumina octahedra, and is one of
the primary determinants of the properties of the clay (Young, 1976: 73).  The lower amount of silicate in these
soils, as compared to those with a 2:1 lattice structure, is a consequence of
removal of silicon from the soil column (along with most weatherable minerals,
including important nutrients for plants) over millions of years of
leaching.  In the absence of
analytical data on SiO2 and Al2O3, clay
mineralogy of subsoil horizons (which are low in organic matter) can be deduced
from the cation exchange capacity (CEC) of the clay fraction, which is
calculated as the CEC of the soil divided by the percent clay, multiplied by
100; values below a cutoff point of 16-20 m.e./100 g clay indicate absence of
2:1 lattice minerals (Young, 1976: 95-96).

(2)
The pH of the extracts used in laboratory analyses affects the values obtained
for the cations that make up the CEC and, since the determinations are not
normally made at the natural pH of the original soil, the values only represent
an index of the true CEC.  In
Brazil, the extracts used for the determinations are buffered to pH 7.0
(Brazil, SNLCS-EMBRAPA, 1979).
Values for CEC determined at the pH of the soil (effective CEC) are much
lower than those determined either at pH 7.0 or at the pH 8.2 standard
sometimes used in the United States (Sánchez, 1976: 150-151).

VI.) ACKNOWLEDGMENTS

Field
collections were done by Irene Tosi Ahmad, Celso Paulo de Azevedo, Ronaldo
Gomes Chaves, Fernando Moreira Fernandes, Jorge Gouveia, Marcelo Vilela Galo,
Michael Keller, Evaldo Moreira Filho, Manuel de Jesus Barros Nogueira, Fernando
José Alves Rodrigues, Joel Costa Souza, Wilson Roberto Spironello. Sample
preparation was performed by Félix de Almeida, Raimundo Matos.  Soil analyses performed at INPA were
done by Rosinéia Gomes da Silva, Newton Falcão and Eduardo White
Martins.  Takashi Muroaka
coordinated analyses at the Centro de Energia Nuclear na Agricultura (CENA), in
Piracicaba, São Paulo.  The
EMBRAPA soils laboratory in Manaus analyzed samples for comparison with the
INPA soil texture results.  Susan G.
Laurance and William F. Laurance helped with data coding and checking.  Theirry Desjardins, Wim Sombroek, Ed
Tanner, Summer Wilson, and two anonymous reviewers commented on the
manuscript.  Financial support was
provided by World Wildlife Fund-US and the Smithsonian Institution, by the
National Institute for Research in the Amazon (INPA PPIs 5-3150 and 1-3160) and
the National Council of Scientific and Technological Development (CNPq AI
350230/97-98).  This is contribution
No. _____ in the BDFFP technical series.

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FIGURE LEGEND

Figure 1 --   Relations of soil clay content and pH to plant growth.

LIST OF TABLES

Table 1 --    Variation in soil properties in the BDFFP reserves
(0-20 cm).

Table 2 --    Relationships among soil parameters.

TABLE
1:  VARIATION IN SOIL PROPERTIES
IN THE BDFFP RESERVES (0-20 cm)

(descriptive
statistics of site means)

Category

Soil
character

Units

Mean

SD

Minimum

Maximum

N

---------

---------

---------

---------

---------

---------

---------

---------

---------

GRANULOMETRIC
CHARACTERS

Clay

%

54.7

13.5

18.0

68.8

54

Silt

%

21.2

4.3

8.3

32.5

54

Fine
sand

%

5.6

3.9

1.3

18.1

54

Coarse
sand

%

18.5

12.5

4.4

56.6

54

AVAILABLE
WATER

Soil
moisture content @ 1/3 bar

%
H2O by weight

31.8

6.8

13.0

41.2

45

Soil
moisture content @ 15 bars

% H2O
by weight

24.3

5.8

9.1

31.9

45

Available
water capacity

%
H2O by weight

7.6

2.0

3.3

12.0

45

TOPOGRAPHY

Slope

%

10.8

8.9

1.4

38.7

36

CARBON

Organic
matter

%

2.1

0.7

0.8

3.3

50

Organic
C (Walkley Black)

%

1.6

0.3

0.8

2.2

40

Total  C

%

1.96

0.45

1.27

3.07

51

C/N
ratio

dimensionless

9.9

1.6

8.4

17.0

38

C
stock to 20 cm

t/ha

SOIL
REACTION

pH
in H2O

pH
units

4.0

0.3

3.4

4.4

53

pH
in KCl

pH
units

3.8

0.2

3.2

4.3

53

Delta
pH

pH
units

-0.3

0.1

-0.5

0.0

53

PRIMARY
NUTRIENTS

N
(total)

%

0.16

0.03

0.10

0.21

38

PO43-

m.e./100
g dry soil

0.030

0.005

0.022

0.041

38

K+

m.e./100
g dry soil

0.060

0.011

0.032

0.077

38

SECONDARY
NUTRIENTS

Ca2+

m.e./100
g dry soil

0.058

0.026

0.015

0.131

38

Mg2+

m.e./100
g dry soil

0.076

0.031

0.013

0.125

38

Na+

m.e./100
g dry soil

0.052

0.018

0.026

0.106

18

S

ppm

13.0

1.4

10.6

15.0

13

MICRONUTRIENTS

Cu

ppm

0.33

0.12

0.10

0.54

24

Fe

ppm

137

31

77

185

24

Zn

ppm

1.48

0.78

0.61

2.99

24

Mn

ppm

1.81

0.49

0.87

2.49

24

OTHER
IONS

Al3+

m.e./100
g dry soil

1.63

0.29

1.03

2.22

38

Al sat. w/ H+, w/ Na+

%
of CEC

89.4

1.0

86.3

90.5

18

Al sat. w/ H+, w/o Na+

%
of CEC-Na+

92.4

1.7

87.8

96.2

38

Al sat. w/o H+, w/ Na+

%
of Base sat.+Al3+

85.2

1.2

82.4

86.5

18

Al sat. w/o H+, w/o Na+

%
of Base sat.+Al3+

89.5

2.2

84.3

94.4

38

H+

m.e./100
g dry soil

0.70

0.12

0.39

0.85

38

CATION
MEASURES

Cation
exchange capacity (w/ Na+)

m.e./100
g dry soil

2.7

0.2

2.5

3.0

18

Cation
exchange capacity (w/o Na+)

m.e./100
g dry soil

2.5

0.4

1.7

3.3

38

CEC
of clay (w/o Na+)

m.e./100
g dry clay

5.1

1.6

3.7

10.5

38

CEC
of clay (w/o Na+) w/ C correction

m.e./100
g dry clay

14.4

1.7

10.9

18.2

38

Total
exchangeable bases (w/ Na+)

m.e./100
g dry soil

0.3

0.0

0.2

0.4

18

Total exchangeable bases (w/o Na+)

m.e./100
g dry soil

0.2

0.1

0.1

0.3

38

Base
saturation (w/ Na+)

%
of CEC

10.6

1.0

9.5

13.7

18

Base saturation (w/o Na+)

%
of CEC

7.6

1.7

3.8

12.2

38

TABLE 2: RELATIONSHIPS AMONG SOIL PARAMETERS

-----------------------------------------------------------------

TOTAL EXCHANGEABLE BASES (without Na+):

TEB  =
1.86 X 10-3
CS  + 3.88 X 10-2
OM - 5.20 X 10-2

(p
< 0.00001, r2=0.84, n=38)

where:  TEB = Total exchangeable bases (without
Na+)

(m.e./100g
dry soil)

CS  = Clay + silt (%)

OM  = Organic matter (%)

ORGANIC MATTER

OM  =
2.13 X 10-2 CS + 1.12

(p
< 0.00001, r2=0.73, n=38)a

where:
OM = Organic matter (%)

CS = Clay + silt (%)

ALUMINUM IONS

Al3+
= 7.66 X 10-3 CS - 7.70 X 10-1 log10 pH + 5.64

(p < 000001, r2=0.78, n=38)

where:  Al3+ = Al3+
(m.e./100g dry soil)

CS   = Clay + silt (%)

pH   = pH in water (pH units)

AVAILABLE WATER CAPACITY

AWC
=  5.24 X 10-2 CS + 3.66

(p
< 0.01, r2 = 0.43, n=45)

where:
AWC = Available water capacity (% H2O by weight)

CS
= Clay + silt (%)

-----------------------------------------------------------------

a.) With elimination of one outlier.

Fig.
1