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Definition
"Most soils in the tropical region are highly weathered
and infertile. A sustainable crop production system must adopt
an ecological approach, using balanced nutrient inputs from
inorganic, organic and biological sources. Achieving food
security for a rapidly expanding population in the tropics
means intensifying food production on existing cropland through
enhanced nutrient input and recycling. While nitrogen may
be generated through biological N fixation, other nutrients,
especially phosphorus, must be supplied from external sources
to achieve higher crop yields and to replace nutrients which
are exported and lost during cropping. Continuous, use of
mineral fertilizer can have detrimental effects on soil properties.
In temperate regions, continuous monocropping of cereals with
optimum fertilizer use can sustain crop yields on fertile
soils such as Mollisols and Alfisols with high activity clays.
But on the strongly weathered, poorly buffered soils of the
tropics (e.g. kaolinitic Alfisols, Ultisols and Oxisols) continuous
monoculture of cereals, using chemical fertilizers as the
main source of nutrients, can lead to a significant decline
in yields after only a few years of cropping because of soil
acidification and compaction. The use of organic inputs is
essential to maintain adequate physical, chemical and biological
properties of [these] soils." (Hossner and Juo, Soil
nutrient management for sustained food crop production in
upland farming systems of the tropics. Crop Sciences Department
College Station, Tennessee, 77843, USA).
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Related topics
Background information on soils
Soil health management
Soil conservation (erosion
control, tillage, moisture conservation)
Integrated nutrient management
(INM): Overview
INM: Replenishing soil organic
matter
INM: Replenishing mineral nutrients
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Relevant literature
Available in PDF format
 Scientific
references: replenishing mineral nutrients
Available on the Internet
Efficient fertilizer use
- Website: Land
and water publications series directory
The above link takes you to the directory; then select or
scroll down to Fertilizer and Plant Nutrition Bulletins,
where #11 is this 5,541 KB/ 46 page PDF.
- Reference: De, Rajat. 1988. Efficient fertilizer use in
summer rainfed areas. Rome, FA0 Fertilizer and Plant Nutrition
Bulletin 11.
- Description: This book covers the principles of fertilizer
use under rainfed conditions and gives good coverage of
strategies for increasing fertilizer use efficiency.
Acid soils of the tropics
Many acid tropical soils suffer from mineral toxicities (Al
and Mn) and deficiencies (P and Ca) and require special management
approaches, which are discussed in the documents below as
well as on our  P-efficient
legumes (China/Mozambique) project page.
- Website: Acid
soil problem (FAO problem soil site)
- Description: Defines the scope of problem worldwide,
indicating the major soil groups most apt to be affected.
- Website: Land
and water publications series directory
The above link takes you to the directory; then scroll down
the page to find the link Fertilizer and Plant Nutrition
Bulletin No. 10. (71 page pdf)
- Reference: von Uexkull, H. 1986. Efficient Fertilizer
Use in Acid Upland Soils of the Humid Tropics. Rome,
FAO Fertilizer and Plant Nutrition Bulletin No. 10.
- Description: This book gives thorough coverage of
acid tropical soils. It also contains extremely useful
and detailed practical information on special considerations
for fertilizer use in these soils.
- Website: Acid
soils (Hawaii profs)
- Reference: Hue, N. and H. Hikawa. Acid soils in Hawaii:
Problems and management.
- Description: University of Hawaii professors illustrate
the problems associated with soil acidity in highly-weathered
soils and discuss management solutions.
- Website: Echo
technical notes
- Reference: Harter, R. 2002. Acid soils of the tropics.
- Description: The above link will take you to a list
of Echo Technical notes, where the acid soils PDF is near
the top of the alphabetical list.
N management
Nitrogen is probably the most universally deficient nutrient
in tropical cropping systems; increased use of nitrogen inputs
(via biological nitrogen fixation of legumes or fertilizer)
will almost always boost crop productivity. But nitrogen is
easily lost from the system, so, there is a need to understand
why, how, and where these losses occur in order to minimize
them.
- Website: Vision
learning/the Nitrogen cycle
- Description: Improving nitrogen-use efficiency requires
a good understanding of the nitrogen cycle.
- Website: Cornell
University/Nitrogen fact sheet
- Reference. Trautmann, N., K. Porter, and R. Wagenet.
?. Nitrogen: the Essential Element. Cornell University
Coopertative Extension Fact Sheet.
- Description: General review of N and N fertilizers
- Website: Purdue
University/types of N fertilizers and their uses
- Reference: Mengel, D. 1986. Types and uses of nitrogen
fertilizer for crop production. Purdue University Cooperative
Extension. AY-204.
- Description: An extension pamphlet from Purdue University.
Biological N fixation (BFN) and agriculture
- Website: FAO/practical
BFN information
- Reference: Mulongoy, K. 1992. Technical paper 2: Biological
nitrogen fixation. In: Tripathl, B. and Psychas, P.
(Eds.) The AFNETA alley farming training manual - Volume
2: Source book for alley farming research
- Description: A good general introduction to biological
fixation in agriculture, with a slant towards leguminous
agroforestry species.
- Website: Cantho
University/theoretical BFN
- Description: Lecture material from Cantho University,
Vietnam, by Iwao Watanabe.
- Website: National
Academy Press/BFN research
- Description: A review (circa 1994) of grants funded
by USAID. Executive summary. Chapter 1: Global Investments
and research needs; Chapt. 2 Review of Grants; Chapt.
3: Recommendations; References.
P management
Phosphorus is limiting in many tropical soils, either due
to inherently low levels or due to P-fixation. More info on
different management options (fertilizers, including rock
phosphate and Tithonia diversifolia) and plant adaptation
to low P conditions, as well as mycorrhiza can be obtained
from the sources below.
Mineral fertilizers
- Website: University
of Minnesota/ Phosphorus fertilizers
- Reference: Rehm, G., M. Schmitt, J. Lamb, G. Randall,
and L. Busman. 2002. Understanding phosphorus fertilizers.
Extension pamphlet FO-06288-GO
- Description: Extension pamphlet from University of
Minnesota.
- Website: Land
and water publications series directory
The above link takes you to the directory; then scroll down
the page to find the link to Fertilizer and Plant Nutrition
Bulletin No. 13. (172 page, 10,212 KB pdf)
- Reference: Zapata, F. and R. Roy. 2004. Use of phosphate
rock for sustainable agriculture . Rome. FAO Fertilizer
and Plant Nutrition No. 13.
- Description: An excellent, up-to-date source of information
about all aspects of rock phosphate use.
- See the publications on efficient fertilizer use in acid
soil and in rainfed cropping systems for P fertilizer management
under those conditions.
Organic P fertilizer
- Website: Improving
crop yields with Tithonia plus fertilizer
Scroll down to Chapter 23 and click the link for the PDF.
- Description: Tithonia diversifolia (Mexican sunflower)
is a weedy shrub that grows (vigorously!) along the roadside
in humid and sub-humid regions of Africa. It is very efficient
at extracting otherwise unavailable soil P. It has been
the subject of extensive research by ICRAF in Western Kenya.
Adaptation to low soil P
- Website: P-efficient
legumes (China/Mozambique)
- Description: Check out the research that McKnight
grantees are conducting in this area.
- Website: Jonathan
Lynch Lab
- Description: Lynch, a collaborator on the above CCRP
project, and his colleagues focus on "understanding
the genetic, physiological, and ecological basis of
plant adaptation to infertile soil." Check out
the abstracts of some of their recent publications.
Mycorrhizal fungi
- Website: Mycorrhiza
and agriculture
- Description: Mycorrhizal fungi form a symbiosis with many
plants and this plays a major role in plant P nutrition
in phosphorus poor or phosphorus-fixing soils. This site
uses information from Mark Brundrett el al.'s excellent,
and highly recommended book, "Working with mycorrhizas
in Forestry and Agriculture". Nice photos…
- Website: Mycorrhizal
research
- Description: The INVAM site, targeting mainly researchers
and students, documents the largest centralized collection
of Vesicular Arbuscular Mycorrhizzal fungi in the world.
"Basic tools of fungal biology, taxonomy, and ecology
are needed to maximize the success of the collection, so
they are explored in these pages."
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Relevant links
Nutrient management self-study course
- Website: University
of Montana
- Description: a 15 module course on nutrient management
from Montana State University Extension service. Modules
include: separate units on cycles of individual nutrients,
plant nutrient functions, soil OM and pH, commercial fertilizers
and soil amendments, etc. Test your understanding after
completing a module by taking the quiz provided.
International Fertilizer Development Center
Mycorrhiza information exchange
- Website: Mycorrhiza
information exchange
- Description: See literature section. Contains bibliographic
lists of journal refs (1970's-present) (quite a few citations
have links to abstracts or full text pdfs), as well as theses
and book chapters.
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