Group Title: Communiqués TropSoils.
Title: Communiqués TropSoils
Full Citation
Permanent Link:
 Material Information
Title: Communiqués TropSoils
Series Title: Communique´s TropSoils.
Alternate Title: Communiqués
TropSoils communiqués
Physical Description: v. : ill. ; 28 cm.
Language: English
Creator: Soil Management Collaborative Research Support Program -- Management Entity Office
Publisher: Management Entity, Soil Management Collaborative Research Support Program
Place of Publication: Raleigh NC
Publication Date: July/August/September 1987
Frequency: quarterly
Subject: Soil management -- Periodicals -- Tropics   ( lcsh )
Soils -- Periodicals -- Tropics   ( lcsh )
Genre: periodical   ( marcgt )
General Note: Title from caption.
General Note: Description based on: Vol. 4, no.1 (July/Aug./Sept. 1987).
 Record Information
Bibliographic ID: UF00080618
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 104807875
lccn - 2007229054

Full Text

Study finds CRSPs on right track

study undertaken by the U.S.
Agency for International
development (AID), has con-
cluded that the four Collaborative Re-
search Support Programs (CRSPs) in-
vestigated, including TropSoils, are
conducting research "of excellent
quality and quantity" and should be
The study, initiated by AID to
provide an objective look at the
programs' effectiveness, covered the
four oldest CRSPs-TropSoils,
Sorghum and Millet, Bean and
Cowpea, and Small Ruminant. A
report from the study acknowledges
that the CRSPs' first five to eight years
have been largely "exploratory," and
that there have been some "growing
pains," but states that this period has
also been "marked by some solid ac-
complishments, both in terms of re-
search progress and institution build-
The study's report calls the CRSP
concept "a magnificent idea whose

'solid accomplishments'

in research and


time has come," and discusses a
number of strengths the programs
exhibit, including:
relevant, high-quality research
conducted at a reasonable cost
strong collaboration with interna-
tional research centers and host-
country institutions
effective management
well-rounded, multi-disciplinary

an ability to train large numbers
of young scientists, whose impact in
government, universities and business
will be "large and positive" in develop-
ing countries.
The study also found some areas in
which the CRSPs could improve. For
example, the report says the CRSPs
should disseminate more research
results to host-country agencies for ap-
plication, and should establish strong
networks for sharing and applying
research results. However, the report
cautions the CRSPs not to stray too far
from their research objectives into
extension or technology-transfer

TropSoils is 'already

having an impact'
on agriculture

On the subject of budgets, the
study found that the CRSPs will
require reliable, long-term support in
order to reach their potential. The
report states that the "greatest danger
at this stage would be to impose any
further cutbacks in budget."
The study found that TropSoils
appears to have "the highest immedi-
ate relevance and impact on tropical
agricultural development." The report
states that TropSoils is already having
an impact largely because it draws on
a history of tropical research, and
because of a "cadre of highly qualified
professionals involved in the pro-

TropSoils publishes

technical report

T ropSoils has published a 268-
page technical report covering
96 research projects conducted
to help solve soil-related constraints to
crop production in developing nations.
The TropSoils Technical Report, 1985-
1986 presents research led by four uni-
versities in three agro-ecological
zones-the humid tropics, the acid sa-
vannas and the semiarid tropics.
The report covers significant
results in a number of key areas, in-
continued next page

New soils network
Ethnic factors & research
Video & variability

U .

JULY/AUG/SEPT, 1987 VOL. 4, NO.1

TropSoils Communiques is published quarterly by the Management
Entity, Soil Management Collaborative Research Support Program,
Charles B. McCants, director. It is available free on request from
TropSoils, Box 7113, North Carolina State University, Raleigh, NC
27695-7113. Telephone number (919) 737-3922. Neil Caudle, editor.
Jennifer Austin, administrative assistant.

TropSoils is a collaborative research program whose goal is to develop
improved soil-management technology for developing countries in the
tropics. Primary funding is provided by the U.S. Agency for Interna-
tional Development through Grant DAN 1311-G-SS-6018-00. This
action is in support of Title XII, "Famine Prevention and Freedom
From Hunger" of the U. S. Foreign Assistance Act. The formal col-
laborators are:

Agency for International Development-USA
Center for Soils Research-Indonesia
Cornell University-USA
Empresa Brasileira de Pesquisa Agropecuaria-Brazil
Institute National de Recherches Agronomiques du Niger-Niger
Institute d'Economie Rural-Mali
Institute Nacional de Investigation y Promocion Agraria-Peru
International Crops Research Institute for the Semi-Arid Tropics-India
North Carolina State University-USA
Texas A&M University-USA
University of Hawaii-USA

For more information
Acid savannas
Dr. Douglas Lathwell
Department of Agronomy
Cornell University
Ithaca, NY 14853

Humid tropics/Indonesia
Dr. Goro Uehara
Dept. of Agronomy & Soil Science
University of Hawaii
Honolulu, HI 96822

Semiarid tropics
Dr. Lloyd Hossner
Dept. of Soil and Crop Science
Texas A&M University
College Station, TX 77843

Humid tropics
Dr. P. A. Sanchez
Soil Science Department
Box 7619, N.C. State University
Raleigh, NC 27695-7113


technical report
A low-input cropping system
developed and tested as an alternative
to shifting cultivation has produced
seven continuous crops over three
years with a total yield of 13.8 t/ha of
rice and cowpea grain, without the ap-
plication of lime or fertilizers, in a soil
with pH 4.4 and 68% Al saturation.
A system of classifying soils by
characteristics that affect crop produc-
tivity has been successfully tested at a
number of sites through a soil-manage-
ment research network.
Crop-simulation models and
prototype expert systems are being
developed and tested to extrapolate
research and to apply soil-management
techniques under a range of tropical
Several studies by social scientists
have contributed a large amount of
information about how transmigrant
farmers in West Sumatra, Indonesia
live and work. The results of these
studies are being used to develop
farming systems and soil-management
recommendations tailored to the
settlers' needs.
Research in the acid savannas has
shown that leguminous green manures
can contribute large amounts of
organic nitrogen to succeeding food
crops, while improving soil structure
and water availability.
Work in the semiarid tropics has
developed several practical techniques
for capturing and retaining moisture in
the soil, promoting crop growth and
the natural reseeding of forests. Other
studies are compiling data bases that
will help scientists characterize the
critical relationships of soil, climate
and plants in the harsh semiarid zone.
The technical report, which was
more than a year in production,
presents data in some 300 figures and
tables. Individual project reports are
grouped according to topic, and
research topics are introduced with de-
scriptions of the settings and goals of
the research.
Single copies of the TropSoils
Technical Report, 1985-1986 may be
obtained free on request. An order
form is printed on Page 7 of this issue.

Soils network links projects in Latin America

Scientists in eight Latin American
countries have joined a collabor
ative research network whose
goal is to improve the management of
tropical soils.
Jot Smyth of North Carolina State
University (NCSU), who coordinates
technical backstopping for the net-
work, says that RISTROP (the Tropical
Soils Research Network) grew out of a
21-day workshop conducted during
September, 1986, in Yurimaguas, Peru.
The workshop drew 31 participants
from 15 national institutions in 10
Smyth says that the network's main
goal is to spread new soil-management
technologies beyond NCSU's primary
TropSoils site in Yurimaguas, Peru.
"We felt it was time to share what
we'd learned at Yurimaguas, so that
researchers in other countries would
have a chance to validate our results at
the local level," Smyth says.
Smyth says that participants in the
workshop reviewed the progress of re-
search conducted at Yurimaguas and
other TropSoils sites, then planned ex-
periments for their respective coun-
tries. The experiments have also been
designed to provide useful feedback to
the network, and to TropSoils.
"One of our interests is to have
some feedback from Latin America,"
Smyth says. "We want to know how
applicable our work is in other areas."
Each participant in the network
finds research support locally. Trop-
Soils provides assistance for coordina-
tion, for the selection and characteriza-
tion of research sites, for analyses and
interpretation of data, and for the
exchange of information among
Smyth says the first experiments
are just getting under way, and it will
be months before the network begins
to produce results. But he feels the
work is off to a good start.
"So far, I've been impressed with
how the scientists have been able to
take our suggestions and adapt them to
their own locations," Smyth says.

Tingo Maria
Puerto Makl

0 Network Training Center
* Initiated Experiments
0 Approved Plans

Porto Velho

S Chapare

Y \\

i '

Figure 1. Distribution of network sites for RISTROP in Latin America.

Airborne cameras focus on the Sahel

ropSoils scientists from Texas
A&M University are using a new
form of remote sensing-video
infrared-to take a broader look at
spatial variability in soils of Africa's
Video infrared detects changes in
soils by highlighting the corresponding
changes in vegetation. Such changes
can be subtle and difficult to detect
from the ground.
Soil scientists Larry Wilding, and
Anne Pfordresher and Andrew Manu
have teamed with Robert Maggio,
A&M's expert in video-infrared
remote sensing, to study areas that
represent the major land-resource types
in the Sahel. The team is flying
transects over the sites, videotaping the

terrain, and will ground-truth the
results by sampling and analyzing
Variability is a major problem in
the Sahel because it confounds the
management of fields and crops and
complicates research. Results of the
study are expected to help scientists
understand how much soil variability
exists in these major land-resource
types, and some of the factors causing
the variability. One product of the
study will be a map depicting the
extent and patterns of variability at the
sites observed.

'11"eS~ftffitws tVe9t shre wwe'd
learned at )"Itriiaoua'J mi~lth ^

Danli 0
L ,Iue 0


Ethnic differences can make

a difference in agriculture

By Carol J. Pierce Colfer, Barbara J. Newton and Herman Agus

Agricultural scientists, reasona-
bly enough, concentrate their
efforts on the nitty gritty of ag-
ricultural experimentation, in most
cases. But many are becoming increas-
ingly interested in ways to ensure that
their technologies, to which they've
devoted so much energy, are adopted
by people. The TropSoils/Indonesia
project has used a "farming systems"
approach to agricultural research and
development as one way of trying to
match agricultural technology to the
people who will use it.
Although farming-systems work
has recognized the importance of
matching technology to environments
(often including the economic aspects
of local conditions), there has been
comparatively little recognition of the
patterned human variation that can
exist in one area. Over our three-year
experience living in Sitiung, West
Sumatra, conducting farming-systems
research on a soil-management project,
this oversight became ever more
glaring to us.
Sitiung is a 100,000-hectare area
with acid soils (Ultisols, Oxisols and
Inceptisols), and receives about 2500
mm of rainfall per year. The area is
occupied by a mix of Javanese and
Sundanese settlers (transmigrants) and
the indigenous Minangkabau-virtu-
ally all farmers.
Residing as we did in the villages
where we worked, differences in the
agricultural practices and preferences
among these groups of farmers became
clear to the TropSoils team. Because
such differences are important in the
design of agricultural technologies, we
conducted a quantitative study of
people's different views of soil. The
type of study we used is called a
Galileo (Woelfel and Fink 1981). The
purpose of the Galileo was first to
identify the "concepts" that people

relate to soil, and then to "map" them
by having people judge the distances
between concepts. We compared the
cognitive maps of different ethnic
groups, to see if there were significant
Although there is not space for a
complete discussion of our findings,
some of the highlights can be pre-
sented here. Certainly the observable
differences in the farming systems of
the three groups were largely sup-
ported by the data we gathered. For
instance, the important place of rice
and rubber in the Minang systems
showed up consistently. And Sun-
danese view a close association of men
to vegetables, whereas the other ethnic
groups viewed vegetables as a
women's crop. The distance between
each of 21 concepts and every other
concept has been measured in three
ethnic groups. We will focus on only
two important findings here.

Distances between con-

cepts differ importantly

between ethnic groups

Although the plots in Figure 1 are
distortions of the data, since they only
represent two dimensions (out of a
theoretical 21), they serve well to
indicate the comparative distances
between concepts for the three groups.
The Minang have an average distance
of 44, the Javanese, 30, and the Sun-
danese, 22. This difference appears to
reflect two aspects of their farming
The first relates to the degree of
integration evident in their approach to
agriculture. The transmigrants'
systems are very integrated. For
instance, cattle are kept on home
gardens; manure can be applied to the

About the authors
Carol J. Pierce Colfer is on leave
from the department of Agronomy
and soil science, University of
Hawaii, Honolulu. She was previ-
ously team leader of the TropSoils-
Indonesia project.

Barbara J. Newton is head of the
Department of Psychology at the
University of Hawaii's west Oahu
College in Pearl City, Hawaii.

Herman Agus is a recent graduate of
Andalas University in Padang, West
Sumatra, Indonesia.

gardens, which sometimes provide
feed for the cattle. These systems are
labor-intensive, and farming is the sub-
sistence base around which the
transmigrants organize their lives.
The Minang System is composed
of quite separate components. Water
buffalo are kept in a communal
grazing area, and their manure is
burned nightly to ward off mosquitos.
Fruit trees are grown in separate
orchards, or in the home garden. Wet
rice fields are in another area, and the
swidden fields (which are first cut for
upland rice, then planted with rubber
or rubber and coffee, and end as forest)
are in yet another place. There is very
little interaction among the compo-
nents of the system, except insofar as
they all feed into family subsistence in
one way or another, and even that sub-
sistence is supplemented wherever
possible by non-agricultural work.
The second aspect of the respective
systems relates to simple geographical
dispersion. The Minang have practiced
agriculture in a situation of minimal (if
any) land scarcity. Until the transmi-
grants came, anyone needing land had
access to it one way or another. Even
now the Minang have access to
considerably more land than transmi-
grants. The transmigrants are limited
to 1.75 ha per family in Sitiung, and
have recently moved from Java, where
land is extremely scarce. One of our


Figure 1.
Cognitive maps of three ethnic groups showing
relationships of concepts related to soil. Plots
are of the first two dimensions of rotated coor-
dinates (from Colfer, Newton and Agus, 1987).



Studies by the authors underscore
the importance of women in settlers'
farming and gardening systems.

surveys found that half the respondents
had been landless in Java, and the re-
mainder reported having left very
small holdings (in 10m2 units). The
Galileo distances inversely reflect
population densities in the home areas
of the three ethnic groups.

The labor-intensive sys-

tems of the transmi-

grants are clearly differ-

entiated from the exten-

sive farming strategy of

the Minang

A number of the people's concepts
(water, fertilizer, pests, yield, cultiva-
tion) are also important concepts for
soil scientists conducting soil-manage-
ment research. Table 1 shows these
concepts paired with related concepts,
to show the patterned difference in
views of soil management, by ethnic
group. The most glaring difference, not
surprisingly, is between the Minang
and the transmigrants. Only three of
these concept pairs do not significantly
differentiate the Minang from one of
the transmigrant ethnic groups.
This kind of data can be used, in
conjunction with soil-science consid-
erations, to help determine research
priorities. Someone interested in inves-
tigating the impacts of tillage on yields

might want to do a comparative study
(as TropSoils did, on the basis of ear-
lier observational findings by Wade,
Agus and Colfer in 1985) with differ-
ing ethnic groups.
Three simple principles may make
the utility of this kind of information
more clear:
1. If the distance between two con-
cepts is already close, persuading
people to work on collaborative ex-
perimentation on these topics should
be comparatively easy. The same
notion applies to observational data. If
people are already using a crop and are
hoeing the soil prior to planting, they
will more readily understand the goals
of an experiment involving tillage on
that crop.
Fertilizer is viewed as significantly
closer to three of the four soil-manage-
ment concepts by the transmigrants
than by the Minang. Perhaps studies of
fertilizer's interaction with these other
soil-management concepts might most
easily be carried out with transmi-
2. Conversely, if distances per-
ceived by the farmers are great
between two concepts (and scientists
consider them close). This may be an
opportunity for useful extension work.
The fact that the Minang men perceive
fertilizer as distant from themselves
suggests an opportunity to increase fer-
tilizer use-if indeed that is deemed
Those interested in increasing fer-
tilizer use might want to consider some
special effort devoted to women
farmers of the Minang and Javanese
ethnic groups, since they are active

farmers yet are perceived as far
removed from fertilizer. Indeed,
working with women as well as with
men of all three groups in soil man-
agement is warranted by these data
(and others): Note the similarities in
the distances between the sexes and
the others of these concepts.
3. Lastly, indigenous farmers' per-
ceptions of great distances, vis-a-vis
scientists' perceptions, should also
strike a warning bell. It may well be
that the farmers' longer experience in
that environment has taught them
things that the scientists can use and
build on. The low-level management
possible with the Minang system,
which relies on a mix of food crops
and tree crops, has many apparent ad-
vantages. But as population densities
increase, creating the necessity to
either shorten the swidden cycle or
intensify production on each field, the
Minang system will require scientific
research to remain feasible.

Wade, Mike, Fahmuddin Agus, and C.
J. P. Colfer. "The Contribution of
Farmer-Managed Research in Tech-
nology Development." Paper pre-
sented at the International Workshop
on Farming Systems Research,
Sukarami Agricultural Research
Institute, West Sumatra (10-13) De-
cember, 1985.

Woelfel, J.D. and E.L. Fink. Science
and Human Communications: A
Theory of Cultural Processes. New
York: Academic Press, 1981.

Table 1. A measure of values relating to selected soil-manage-
ment concepts at Sitiung, West Sumatra, 1985.

Good and Minang (M) Javanese (J) Sundanese (S)

Water JS 46 M25 M 24
Fertilizer S34 S28 MJ 16
Pests JS 68 MS 52 MJ 26
Yield JS 61 M 26 M 27
Cultivation JS 66 M 23 M 24

Note: The smaller the number, the more highly valued the concept. If there is a letter
before the number, there is a significant difference between ethnic groups. For
example, in the Minang column, the distance between "good" and "water" (46) is
significantly greater than that perceived by Javanese (J) and by Sundanese (S).

Ed Runge, head of the Department of
Soils and Agronomy at Texas A&M
University, has been elected chairman
of the TropSoils board of directors,
succeeding Ed Oyer of Cornell.

Frank Calhoun, former TropSoils
program coordinator at Texas A&M
University, has joined the faculty of
Ohio State University. Lloyd Hossner
of the Department of Soil and Crop
Science at A&M has been named
interim program coordinator for
TropSoils' Semiarid Tropics Program.

Jose Benites, project leader in N.C.
State University's TropSoils research
at Yurimaguas, Peru since 1982, has
joined the Food and Agriculture
Organization (FAO) in Rome.
Benites' new title is technical officer
of the Soil Resources Management and
Conservation Service of the Land and
Water Development Division. His re-
sponsibility is to promote organic-
matter management and the use of
alternatives to shifting cultivation in
Latin America.

Several changes have been announced
in TropSoils staff in Indonesia. Carol
Colfer, an anthropologist, is currently
on leave from the University of
Hawaii. Mike Wade, a soil scientist
formerly of N.C. State University, is
now in private business. The research
team on-site in the Sitiung transmigra-
tion settlements on West Sumatra now
includes Lalit Arya, a soil physicist,
and Ron Guyton, an agronomist, both
of the University of Hawaii.

Walter Bowen of Cornell University,
who conducted TropSoils research into
nitrogen fixation by green manures in
the Cerrado of Brazil, has completed
his PhD and has joined the faculty of
Comell as a senior research associate.
Bowen will help extrapolate research
results from Cornell's acid-savannas
program to other tropical locations.

Andrew Manu has joined the Trop-
Soils Semiarid Tropics Program as
technical assistant to the INRAN Soil
Laboratory in Niamey, Niger. Manu, a
native of Ghana, received his PhD
from Iowa State University.

Zoumana Kouyate has been assigned
as TropSoils' country coordinator in
Mali. Kouyate received his MS in
agricultural engineering in Algeria.

r--- ------ -------- ------------- i
K Readers may receive the TropSoils Technical
S Report, 1985-1986 by filling out the form
ST rops below, and by clipping and mailing it to:
STropSoils Report
Box 7113, N.C. State University
TECHNICAL REPORT, 1985-1986 Raleigh, NC 27695-7113

Languages you read (1st) (2nd) (3rd)
EO Business O Librarian
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L -------- -------------------------------------- J

The editor has been advised of the
following publications produced as a
result of TropSoils research:

Alegre, J.C., D.K. Cassel and D.E.
Bandy. 1986. Reclamation of an
Ultisol damaged by mechanical land
clearing. Soil Sci. Soc. Am. J.,

Alegre, J.C. and D.K. Cassel. 1986.
Effect of land-clearing methods and
post-clearing management on aggre-
gate stability and organic carbon
content of a soil in the humid tropics.
Soil Sci., 142:289-295.

Alegre, J.C., D.K. Cassel and D.E.
Bandy. 1986. Effects of land clearing
and subsequent management on soil
physical properties. Soil Sci. Soc. Am.
J., 50:1379-1383.

Alegre, J., D.K. Cassel, D. Bandy and
P.A. Sanchez. 1986. Effect of land
clearing on soil properties of an Ultisol
and subsequent crop production in
Yurimaguas, Peru. In: R. Lal, P.A.
Sandchez and R.W. Cummings, Jr.
(eds.). Land Clearing and Develop-
ment in the Tropics, pp 167-177. A.A.
Balkema Press, Boston.

Bandy, D.E. and P.A. Sanchez. 1986.
Post-clearing soil management alterna-
tives for sustained production in the
Amazon. In: R. Lal, P.A. Sanchez and
R.W. Cummings, Jr. (eds): Land
Clearing and Development in the
Tropics. pp 347-362. A.A. Balkema
Press, Boston.

Benites, J.R. 1987. Transfer of acid
tropical soils management technology.
In: P.A. Sanchez, E.R. Stoner and E.
Pushparajah (eds): Management of
Acid Tropical Soils for Sustainable Ag-
riculture. IBSRAM Proceedings 2:245-
260. Bangkok, Thailand.


Buol, S.W. and P.A. Sanchez. 1986.
Red soils in the Americas: morphol-
ogy, classification and management.
In: Proceedings of the International
Symposium on Red Soils. Institute of
Soil Science, Academia Sinica,
Science Press, Beijing, China. pp 14-

Hiebsch, C.K. and R.E. McCollum.
1987. Area-x-time equivalency ratio: a
method for evaluating the productivity
of intercrops. Agron. J. 79:15-22.

Lopes, A.S., T.J. Smyth and N. Curi.
1987. The need for a soil fertility
reference base and nutrient dynamics
studies. In: P.A. Sanchez, E.R. Stoner
and E. Pushparajah (eds): Management
of Acid Tropical Soils for Sustainable
Agriculture. IBSRAM Proceedings
2:147-166. Bangkok, Thailand.

Nair, P.K.R. and E. Femandes. 1986.
La agrosivicultura como alternative a
la agriculture migratoria. In: Sistemas
mejoradas de prduccion como alterna-
tiva a la agriculture migratoria.
Servicio de Recursos, Manejo y Con-
servacion de Suelos Direccion de

Fomento de Tierras y Aguas, FAO,
Rome. pp 183-197.

Nicholaides, J.J., Ill, D.E. Bandy, P.A.
Sanchez, J.H. Villachica, A.J. Coutu
and C.S. Valverde. 1986. De la agric-
ultura migratoria a la explotacion
agricola continue en la cuenca del
Amazona. In: Sistemas mejoradas de
prduccion como alternative a la
agriculture migratoria. FAO, Rome.

Ritchey, K.D., F.R. Cox, E.Z. Galrao
and R.S. Yost. 1986. Disponibilidade
de zinco para as cultures do milho.
Pesq. Agropec. Bras., 21:215-225.

Sanchez, P.A. 1987. North Carolina
State University's Tropical Soils
Program. INTERCOL Bul. 14:55-58.

Sanchez, P.A. and R.H. Miller. 1986.
Organic matter and soil fertility man-
agement in acid soils of the tropics.
Trans. 13th Int. Congr. Soil Sci. (Ham-
burg) (in press).

Sanchez, P.A. and J. Benites. 1986.
Opciones technological para el manejo
racional de suelos en la selva Peruana.
In: lo Simp6sio do Tr6pico Umido,
1:399-435. EMBRAPA, Belem, Para,

Sanchez, P.A. 1987. Management of
acid soils in the humid tropics of Latin
America. In: P.A. Sanchez, E.R.

Stoner and E. Pushparajah (eds): Man-
agement of Acid Tropical Soils for
Sustainable Agriculture. IBSRAM
Proceedings 2:63-107. Bangkok,

Sanchez, P.A. and T.J. Smyth. 1987.
Acid Tropical Soils Network: a
progress report. In: Land Development
and Management of Acid Soils in
Africa--IBSRAM proceedings. (in

Sanchez, P.A. 1987. Edaphic parame-
ters for characterizing IBSRAM's Acid
Tropical Soils Network sites. In: M.
Latham (ed): Land Development-Man-
agement of Acid Soils. IBSRAM Proc.
4:113-123. Bangkok, Thailand.

Sharpley, A.N. and S.W. Buol. 1987.
Relationship between minimum ex-
changeable potassium and Soil Taxon-
omy. Commun. in Soil Sci. Plant Anal.

Szott, L.T. and C.A. Palm. 1986. Soil
and vegetation dynamics in shifting
cultivation fallows. In: lo Simp6sio do
Tr6pico Umido, 1:360-379. EM-
BRAPA, Belem, Para, Brazil.

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