Table Of ContentMANAGING ORGANIC MATTER IN TROPICAL SOILS:
SCOPE AND LIMITATIONS
Managing Organic Matter in
Tropical Soils:
Scope and Limitations
Proceedings of a Workshop organized by the Center for Development Research at
the University of Bonn (ZEF Bonn) - Germany, 7-10 June, 1999
Edited by
C.MARTIUS
H. TIESSEN
and
P.L.G. VLEK
Reprinted from Nutrient Cycling in Agroecosystems, Volume 61, Nos. 1-2 (2001).
SPRlNGER-SClENCE+BUSINESS MEDIA, B.V.
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ISBN 978-90-481-5947-5 ISBN 978-94-017-2172-1 (eBook)
DOI 10.1007/978-94-017-2172-1
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Originally published by Kluwer Academic Publishers in 2001
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Contents
MANAGING ORGANIC MATTER IN TROPICAL SOILS:
SCOPE AND LIMITATIONS
Proceedings of a Workshop organized by the Center for Development Research at the University of Bonn
(ZEF Bonn) - Germany, 7-JOJune, 1999
1. The management of organic matter in tropical soils: what are the priorities?
C. Martius, H. Tiessen & P.L.G. Vlek 1
2. The role and function of organic matter in tropical soils
E.T. Craswell & R.D.B. Lefroy 7
3. Soil organic carbon sequestration in tropical areas. General considerations and analysis of some
edaphic determinants for Lesser Antilles soils
e. Feller, A. Albrecht, E. Blanchart, Y.M. Cabidoche, T. Chevallier, e. Hartmann, V. Eschen
brenner, M.e. Larre-Larrouy & J.F. Ndandou 19
4. (Tropical) soil organic matter modelling: problems and prospects
H. van Keulen 33
5. The role of soil microorganisms in soil organic matter conservation in the tropics
D.S. Powlson, P.R. Hirsch & pe. Brookes 41
6. SOM management in the tropics: Why feeding the soil macrofauna?
P. Lavelle, E. Barros, E. Blanchart, G. Brown, T. Desjardins, L. Mariani & J.-P Rossi 53
7. Management of organic matter in the tropics: translating theory into practice
e.A. Palm, K.E. Giller, P.L. Mafongoya & M.J. Swift 63
8. Critical aspects of organic matter management in the Tropics: the example of India
J.e. Katyal, N.H. Rao & M.N. Reddy 77
9. Problems with and local solutions for organic matter management in Vietnam
Nguyen The Dang & e. Klinnert 89
10. Organic matter turnover and management in low input agriculture of NE Brazil
H. Tiessen, E.V.S.B. Sampaio & I.H. Salcedo 99
11. Management of soil organic matter in semiarid Africa for annual cropping systems
F. Ganry, e. Feller, J.-M. Harmand & H. Guibert 105
12. Soil management under no-tillage systems in the tropics with special reference to Brazil
P.L.O. de A. Machado & e.A. Silva 119
13. Soil organic carbon management for sustainable land use in Sudano-Sahelian West Africa
A. Bationo & A. Buerkert 131
14. Soil organic carbon (SOC) management for sustainable productivity of cropping and agro-forestry
systems in Eastern and Southern Africa
S.M. Nandwa 143
15. Organic matter management for soil conservation and productivity restoration in Africa: a con
tribution from Francophone research
E. Roose & B. Barthes 159
16. Preserving tropical soil organic matter at watershed level. A possible contribution of urban organic
wastes
C. Binder & N. Patzel 171
17. Social, economic and policy dimensions of soil organic matter management in sub-Sahara Africa:
challenges and opportunities
E.T. Ayuk 183
18. Farmer's view on soil organic matter depletion and its management in Bangladesh
Md. Z. Hossain 197
19. Farmers' perceptions and management of soil organic matter - a case study from West Africa
C. Quansah, P. Drechsel, B.B. Yirenkyi & S. Asante-Mensah 205
20. Organic matter management in family agriculture of semiarid Paraiba, Brazil
L.M. da Silveira, H. Tiessen & J.P. Tonneau 215
21. Organic soil fertility management in family agriculture of Zimbabwe
H. Tiessen, D. Billo & S. van Oosterhoud 225
22. Terra-aqua vitae: the role of soil and water in supporting civilization
D. Hillel 231
Nutrient Cycling in Agroecosystems 61: 1--6,2001,
© 2001 Kluwer Academic Publishers.
The management of organic matter in tropical soils: what are the
priorities?
C. Martius, H. Tiessen & P.L.G. Vlek
Rheinische Friedrich-Wilhelms-Universitiit, Zentrum for Entwicklungsforschung (ZEF), Walter-Flex-Str. 3, 53113
Bonn, Germany
Introduction and a 'healthy' soil biological activity reduces soil
fertility, degrades soil structure and water holding ca
Soil degradation is one of the most serious environ pacity, and utlimately leads to desertification. SOM
mental problems. Soils represent a resource that is holds the key to sustainable soil management and,
essential to life on this planet (Hillel, 2001). They therefore, the prevention or reversal of soil degrad
are the interface between rocks, biota, water and the ation. The estimated total loss of carbon through
atmosphere and are therefore a pivotal element of soil degradation since the advent of agriculture about
ecosystems. Dryland soils are particularly vulnerable 10 000 years ago (of 243 Gt; Rozanov et aI., 1990) rep
(Katyal and Vlek, 2000) - a problem recognized by resents 16-20% of the present-day global soil carbon
the establishment of the Convention to Combat Deser stocks (of 1200-1500 Gt; Haider, 1999).
tification (www.unccd.org) in 1994. Seventy to 80% A limited view of soils as a dead substrate hold
of the world's drylands are affected by desertifica ing nutrients for agricultural production has dominated
tion. The degradation of soils is typically a 'creeping during the world-wide expansion of intensive agricul
environmental problem' (CEP); i.e., a cumulative en ture with its heavy reliance on industrial fertilizers.
vironmental change that evolves at an imperceptibly This has placed added demands on the soils to provide
slow pace, which hinders the initiation of counterbal the nutrient balance. Conventional land preparation
ancing measures (Glantz, 1998). Soil losses have been methods (reviewed by Machado et aI., this issue) have
increasing with the growth of the human population. had a negative impact on soil organisms and the soil
It is particularly troubling that soils today are des structure built and maintained by them. Thus, in
troyed at a much faster rate than they can be formed tensive agriculture has amplified and accelerated the
by natural processes. age-old problem of soil degradation (Hillel, 1991).
Soil organic matter (SOM) or humus, and its asso Soil degradation is reflected in declining agricultural
ciation with soil minerals is essential to soil function: productivity and utility (Katya1 and Vlek, 2000). Ever
it forms during the biological decomposition of or growing inputs required to maintain agricultural pro
ganic detritus of plants, animals and microbes; keeps duction are the price for the disregard for the functions
plant nutrients and water in the upper soil where roots of soil organic matter in modem agriculture.
can access them; and provides tilth - making the soil The proper management of soil organic matter is
easier to work. Also, SOM-rich soils generally retain important to food security and the protection of mar
more water than SOM-poor soils. Soils come to life ginallands (Scherr, 1999). To define the steps needed
through SOM: highly diverse communities of microor to understand and manage organic matter in tropical
ganisms and soil animals (e.g., earthworms, termites, soils is a major challenge for soil science. SOM man
mites, millipedes and others) provide important 'eco agement practices in temperate and tropical climate
system services', in particular the recycling of carbon zones differ. Much scientific attention has been fo
and plant nutrients. cused on temperate zones (most recently in Cadisch
SOM, however, is rapidly lost when organic mat and Giller, 1995; Carter and Stewart, 1996; Drozd,
ter inputs are reduced upon cultivation (Jenkinson and 1997; Swarup et aI., 1998; Davies and Ghabbour,
Ayanaba, 1977); losses can be as high as 70% in 1998; Lal, 2001) rather than on the tropics, although
fragile environments (Jenny and Raychaudhuri, 1960; degradation is most severe in tropical regions (cf.,
The Dang and Klinnert, this issue). The loss of SOM however, IBSRAM, 1990; Elliott et aI., 1997; Rees
2
et aI., 2001). Existing knowledge about the man Quansah et ai. of the farmers' views and perceptions
agement of organic matter in the tropics has found of OM in Ghana.
astonishingly little practical application - what went At the end, Hillel (2001) discusses historical as
wrong? pects of soil degradation related to the decline of
ZEF organized a workshop (7-10 June 1999) to ancient and modern cultures, and explains why soil
provide insight into the management of SOM in trop management and preservation are so important.
ical soils. The participants had been asked to answer The workshop closed with a plenary discussion in
why, when and how SOM should be managed in which the participants discussed three central ques
tropical areas, and to review the needs for further tions:
research, but also for policy changes. The results rep 1. What are the issues of highest priority?
resent the state-of-the art of our knowledge on SOM 2. How can SOM research and management best be
management in the tropics. linked to practical application?
Heading the introductory session, Craswell and 3. What are the best entry points to develop a higher
Lefroy outline roles and functions of organic matter in public awareness for the need of SOM manage
tropical soils, and Feller dicusses the ecological and ment and research in the tropics?
agricultural determinants of carbon sequestration in The answers were obtained in a moderated process
tropical soils. Van Keulen debates the problems and that catalyzed discussions and provided opportunit
advances of modelling tropical SOM. ies for all participants to express their views in a
Powlson then clarifies the role of soil microorgan differentiated manner (Klebert et aI., 1995).
isms in soil organic matter conservation in the tropics,
and Lavelle et ai. provide a compelling answer to the
question: 'Why feeding the soil macrofauna?' Follow Conclusions
ing this, Palm et ai. translate 'theory into practice',
almost a foreword to the subsequent papers that are
The results of the final workshop discussion about the
dedicated to management options and regional as three questions above are summarized in the follow
pects. Several regional case studies are presented: a
ing.
review by Katyal et ai. of SOM management in India
starts the session; the possibilities for SOM manage
What are the key priorities in SOM management and
ment with particular reference to erosion control on
research?
hillsides of northern Vietnam are reviewed by The
Dang and Klinnert; Tiessen et ai. discuss the role of The development of and agreement upon indicat
subsistence agriculture in the Brazilian Northeast, and ors and thresholds for SOM quantity, quality and
no-till systems in Brazil are reviewed by Machado and its degradation are urgently needed. These indicat
Silva. Ganry et aI., Bationo and Buerkert, Nandwa, ors should be reliable, easy-to-use and uniform (at
and Roose and Barthes review different aspects of least within specific purposes or environments). They
SOM management in cropping systems of Africa. Two should ideally be able to provide early warning signals
papers (Silveira et aI., 2001; and Tiessen et aI., 2001) to identify stressed soils. Indicators should allow to
exemplify the problems encountered with SOM man assess nutrient- as well as non-nutrient effects. Once
agement and its measurement on the farm, both in established, the indicators should be used as a basis
Africa and Brazil. for SOM inventories in critically affected regions or
The following analysis of the carbon budget and countries (in the time since the workshop, a use
its management on a watershed level, a case study ful contribution to this topic has been presented by
from Colombia presented by Binder and Patzel, as Stocking and Murnaghan (2000».
sesses the - surprisingly low - contribution of organic Many participants stressed the need for databases
returns from urban areas to OM conservation in the and information centers and for the development
countryside. of strategies and concepts for transferring scientific
The last section starts with a contribution by Ayuk knowledge to practice. A synthesis of existing data and
on social, economic and policy dimensions of trop models is needed, and common databases, decision
ical SOM management. Hossain gives an insight into support systems, and models must be developed to
the activities of an NGO promoting OM management be able to establish, for example, C flows and their
in Bangladesh, and the final chapter is a study of management at regional levels (an elegant example
3
of regional C flux budgeting is given in Binder and One suggestion is to let stake holders, not donor
Patzel, this issue). Local scientific knowledge should agencies, contract the researchers so that they be
be included in these data bases. The Organic Resource come owners of the scientific results. Alternatively a
Database set up by Wye CollegefTSBF (Palm et aI., protocol might be established to ensure stakeholder
this issue; ORD, 2001) could be adopted as a standard. involvement in the research projects, e.g., by holding
Palm and her co-authors demonstrate convincingly meetings to establish roles in the process, or to facilit
how decision support systems can be made available to ate perception and assimilation of management altern
both farmers and scientists, and van Keulen (this issue) atives through farmer-participatory and on-farm re
outlines the prospects and problems of modelling of search. Regional programs should involve researchers
SOM. and stake-holders from the start, ideally in the form of
A greater stakeholder involvement is urgently partnerships and alliances between researchers, farm
needed. Stakeholders are farmers, decision makers, ers, international, government and non-government
and every citizen concerned with land use or ecolo organizations, communities, the private sector and
gical sustainability. Only participatory research will donor agencies. Scientists should be involved in ex
guarantee that the client's true needs will be con tension work, e.g., by the generation of information
sidered; e.g., that research on OM is based on farmer and teaching materials for the public, farmers and
demand, that tools (indicators, management options) politicians.
are usable by the stake holder (cf. World Neighbors, A network for the management of tropical SOM
2000), or that a policy environment sensitive to the should be developed by linking to or widening the
need for investments in SOM is created. Eventually, existing national and international networks and pro
a protocol to guarantee stakeholder involvement could grams (such as IBSRAM, TSBF, GCTE-SOMNET,
be developed, to be used by scientists as a guideline WWI) and by linking to national agricultural research
(cf. the recent paper by Stocking and Murnaghan, services. Bringing different disciplines together in
2000). working groups, connecting global coordination with
The monitoring of SOM quantity and quality local task forces, and linking developed and devel
(ideally including some measures of stability, turnover oping countries can help address specific problems.
and carbon sequestration) must be intensified, and this Such networks can be organized into regional nodes
requires the development of suitable indicators. and include research sites dedicated to particular eco
The often conflicting goals of agricultural produc regions. Networks could be dedicated to specific tasks,
tion, such as SOM preservation versus the short-term e.g., participatory organic matter conservation and
maximization of agricultural production, must be har preservation; the development of indicators; SOM
monized, or non-competitive forms of OM manage monitoring, the development of methods and tools and
ment should be fostered. Site-specific nutrient man the coordination of data bases and models. A network
agement is to be enhanced as a strategy to increase would facilitate workshops and training programs. Ex
OM production. Additional carbon sources must be isting institutions that are well-established in SOM
incorporated into the farming systems locally, because research should take the lead.
due to high transport costs OM can not be dislocated
over long distances.
What 'entry points' are able to promote SOM
An explicit economic valuation of SOM (including preservation?
non-nutrient values, e.g., ecological sustainability or
reduction of poverty) must be established through in Global aspects such as carbon sequestration of soils
tegrated agrotechnical and economic analyses in order in the context of climate change may appeal to policy
to evaluate trade-offs between different land use sys makers particularly in the developed world, but in
tems and competing issues of agricultural production degradation-affected regions, the clear demonstration
and SOM preservation. of how SOM management and preservation may im
pact poverty and improve livelihoods of the rural pop
How can SOM research best be linked to practical ulation would represent a strong entry point. A sys
application? tematic representation of data across climatic gradi
ents (a SOM inventory of critically affected regions or
There is little doubt that the practical use of SOM countries, based on existing long-term experiments)
research will be facilitated in a client-driven process. should outline regional constraints to SOM manage-
4
ment and allow for the definition of regional land linization, compaction and anthropogenic pollution,
use alternatives (e.g., specific techniques to reduce have resulted in far-reaching changes in landscape
erosion). Benchmark research sites could be estab function. Addressing soil conservation directly is a
lished to meet this goai. Process models can be used to difficult task. Soil degradation can be slowed and
synthesize data and to show temporal changes that go reversed only if sustainable cropping systems are in
unnoticed because their time scale is too long for the troduced based on the conservation or enhancement of
human observer. soil organic matter. Such systems could take advantage
High visibility indicators of stress should be de of diversification in space (intercropping: hedgerows,
veloped. However, reliable, easy-to-use indicators shelterbelts and agroforestry) and time (crop rotation
of SOM change and, perhaps more importantly, in systems). Making better use of the 'ecosystem ser
dicators accessible to farmers, are largely missing vices' provided by the agroecosystem, including the
(Quansah et ai., this issue, suggest some potentially preservation and management of soil biota that pro
good indicators for farmers). These indicators must be duce and maintain organic matter (Lavelle et ai., this
landscape- or soil-type specific. Thresholds must be issue) is one important element in the conservation
identified, and monitoring criteria be set. strategies to be adopted. The negative effects of in
Farmer involvement is key because farmers repres tensive agriculture on the diversity of beneficial soil
ent a direct interface of human intervention on soils. organisms are not easily documented - however, they
However, farmers' needs must be pinned against envir eventually will become much more devastating for the
onmental and societal goals. Human capacity for local maintenance of essential ecosystem functions than the
research must be strengthened and local constraints - lamentable - loss of bird or mammal diversity
be assessed. Location-specific, farmer demand-based (e.g., Hofer et ai., 2000). Soil organisms are today
experiments could be helpful on demonstration sites. seen as ecosystem engineers, important if not central
Farmers are subject to decisions of policy makers, and to ecological function (Jones et ai., 1994; Lavelle et
therefore, can not be treated in isolation. Management ai., 1997), and soil fertility maintenance (Stork and
options for OM maintenance or sequestration with low Eggleton, 1992). Generally, the diversity of soil or
competition with other objectives (e.g., production) ganisms is drastically reduced in man-made land use
should be outlined. Within-farm transfers, budgets and systems, but the role of soil biota is rarely considered
gradients need be elaborated. The multiple benefits or understood in agricultural studies (Hanne, 2001).
of SOM such as the ecological services SOM and Appropriate management of SOM in the tropics
soil biota provide, or the often not obvious links to still requires considerable research into the regional
poverty reduction and development must be explained differences and the variability of SOM quantity, qual
to farmers. ity and function; the importance of the quality of input
The human, social, and economic costs of neglect material; the role of below-ground versus mulched
ing soil conservation are difficult to calculate but are organic matter (particularly the importance of roots
undoubtedly high. SOM is not only a major determin and root exudates); the role of recalcitrant materi
ant of rural livelihoods, but its conservation is related als (e.g., charcoal) in building a stable SOM fraction
to three main areas at the interface between nature and in the long-term; and how to balance the need for
human activities. These are: agricultural productiv stable forms against the need for short-term nutrient
ity, the maintenance of ecological services including availability. The question remains how to find altern
biodiversity, and carbon sequestration. Productivity ative sources or how to balance competitive uses for
related issues include nutrient- and non-nutrient ef SOM (feed, construction etc.). The definition of reli
fects of SOM. SOM storage and release and the in able and easy-to-assess indicators of SOM should be
tricate web of short- and long-term processes related given high priority as they would allow the design
to immobilization and mineralization of nutrients are of a appropriate policy approach. Regional organic
primary determinants of soil fertility. matter budgets must be established (e.g., Binder and
Patzel this issue) to be able to assess SOM avail
ability. Farmers need to balance SOM management
Outlook against agricultural management that maximizes goals
other than SOM (crops, pest control, etc.). Resources
Desertification processes ongoing world-wide, with should be channeled into research on direct and indir
their components erosion, loss of organic matter, sa- ect SOM management techniques (cropping systems;
