The Importance of Tropical Forages
Worldwide, livestock use 3.4 billion hectares of grazing land as well as the production
from about a quarter of the land in crops. This amounts to more than two-thirds of total
agricultural land area and a third of total land area. Forage species are thus a prominent
feature of agricultural landscapes around the world.
In the humid and subhumid tropics, most pastures are in native species of inferior
nutritional quality. As a result, livestock productivity in native pastures tends to be
quite low, and the possibilities for sustainable intensification are limited. In recent
decades, though, forage specialists have identified a wide variety of tropical forage
grasses and legumes that are highly productive, show superior nutritional quality, and are
well suited to marginal agroecosystems characterized by low soil fertility and drought. In
Latin America much progress has been made toward commercializing and promoting these
improved forages, notably the grass Brachiaria decumbens, which is of
African origin. Despite heavy pest pressures and other limitations, introduced grasses
have had a significant impact on livestock productivity across the region. Efforts to
introduce improved forages are also under way in Africa and Asia but are less advanced.
The need for improved forages in all regions of the developing world can only increase
with continued massive growth in global demand for livestock products. According to many
economists, a "livestock revolution" is under way, which will continue well into
the next century. From 1983 to 1993, meat consumption in the developing world leaped from
14 to 21 kilograms per capita, while milk consumption rose from 35 to 40 kilograms. The
increases were particularly notable in Asia. Consumption of livestock products also grew
in Latin America, while declining in sub-Saharan Africa.
Increased demand is driven largely by population growth, rapid urbanization, rising
incomes, and diversification of human diets. Given current trends, demand for meat in the
developing world is expected to grow from the current 206 million tons to 275-310 million
tons or more by the year 2020.
This is good news for rural people in the developing world. Increased demand for
livestock products could provide small farmers with new opportunities to increase incomes
through more intensive production. Hundreds of millions of them already depend heavily on
livestock for income. Often, animals are their only means of accumulating and saving
capital and of obtaining insurance against crop or other losses.
As the incomes of the poor in both rural and urban areas rise, they will be able to
improve their diets by consuming more livestock products. Meat and milk provide protein,
calcium, vitamins, and other nutrients that are lacking in many of the staple crops on
which poor consumers mainly depend.
What remains to be seen is whether economic conditions and agricultural policies will
be conducive for small farmers to intensify production in response to growing demand.
Often, these farmers will be competing with highly efficient industrial production systems
located near urban markets. In order for small farmers to thrive in this environment, they
will need to move away from the traditional patterns of low-input, extensive livestock
production.
Another concern is that greatly increased livestock production will incur unacceptably
high environmental costs. Though some livestock production systems actually result in
better management of natural resources, others have led to widespread degradation of
pasture land, involving serious soil erosion, or to deforestation, resulting in
biodiversity loss.
Appropriate combinations of superior forage grasses and legumes could provide some of
the answers to these and other concerns. Much recent experience in Latin America and Asia
has demonstrated that new forage-based technologies are highly effective for intensifying
meat and milk production on small farms. They also show potential as partial substitutes
for concentrate supplements in feeds, thus lowering production costs.
In addition, many forage species contribute to more sustainable land management by
helping regenerate degraded soils and replenish the nitrogen supply of the production
system. Forage plants also help reduce erosion and control weeds. Moreover, since many of
the new forages are well adapted to poor soils, they can intensify livestock production
even under marginal conditions, thus freeing more favorable environments for cereals and
other crops. Some recent experience in a hillside environment of Central America further
suggests that improved forages, by permitting more intensive livestock production on areas
already in pastures, can remove some of the pressure on adjacent forest land.
That is why CIAT scientists refer to tropical forages as a "multipurpose genetic
resource." These plants have tremendous potential and appeal as a way of improving
the lot of small farmers as well as poor consumers, while having benign effects on natural
sources.
Research for Development
Challenge
Nearly 3 decades of tropical forage research at CIAT have confirmed the effectiveness
of various grass-legume combinations both for improving livestock nutrition and
recuperating degraded land. Focusing initially on the vast tropical savannas of South
America, this research has gradually expanded in scope to include the forest margin and
hillside agroecosystems of tropical America.
The savannas are characterized by extensive cow-calf operations with low management
input and little use of purchased fertilizers or seeds, with corresponding low
productivity. The savanna area planted to improved grass pasture has expanded, but the
proportion of degraded pastures has also increased alarmingly.
At the forest margins, land is used initially for subsistence agriculture after the
felling and burning of native forest. The decline of soil fertility and growth of weeds on
cleared land leaves farmers with little choice but to clear more land. Many of these
smallholders eventually convert cleared land to the production of dual-purpose cattle in
grass pastures, characterized by low productivity and rapid degradation.
Livestock production in hillside areas is limited by steep and irregular slopes subject
to soil erosion. Often, when farmers have not raised enough forage during the growing
season to feed their cattle during the dry season, they allow them to graze in forested
areas. The overgrazing that may result from this practice exposes the soil to further
degradation, while animal weight gain and milk production are severely curtailed.
Though dealing mainly with these three agroecosystems in tropical America, CIAT forage
scientists also provide new germplasm for the uplands of Southeast Asia through the
Center's work on cropping systems in that region and for sub-Saharan Africa in cooperation
with the International Livestock Research Institute (ILRI).
With such a diversity of target environments, it obviously takes more than one or a few
forage species to meet the needs and fit the conditions of many individual production
niches. Thus, the central challenge of forages research is to provide an extensive
portfolio of germplasm options for multiple uses in smallholder production systems.
To accomplish this requires a substantial effort in germplasm evaluation, aimed at
generating information on key traits of the most promising grass and legume species,
including their quality attributes, response to pests and diseases, and adaptation to soil
and climatic conditions. In selected cases we must also undertake forage breeding to
supply combinations of traits that do not exist in the germplasm currently available.
As described in the sections that follow, CIAT forage scientists and their national
partners have come far indeed toward the goal of making a rich array of forage diversity
available for improving livestock production and land management.
Genetic Resources
Grass-legume mixtures are subtle combinations, which must be created to fit the
conditions of specific environments. One legume, for example, may promote better nutrition
for calves, while another is useful in places with extended dry seasons, and another is
drought tolerant and adapted to acid soils.
In searching for suitable species, CIAT researchers and their
partners draw on an extensive collection of over 22,000 forages
(including some 18,400 samples of 654 different legume species
and about 1,900 samples of 178 grasses). This germplasm is
held in trust at Center headquarters for the Food and Agriculture
Organization (FAO)
of the United Nations. Safeguarding, studying, and sharing
the germplasm are fundamental responsibilities implied by
CIAT's global mandate for tropical forages research within
the Consultative Group on International Agricultural Research
(CGIAR).
To facilitate the evaluation and targeting of forage grasses
and legumes, Center scientists have developed core collections
of key species. These are small but representative samples
of the complete germplasm holdings.
Nutritional Quality of Forages
Recent research at CIAT on the quality attributes of forages has focused on the role of
antinutritional factors, particularly condensed tannins (CTs). These substances occur at
high levels in many herbaceous and woody legumes and are known to reduce the intake,
digestion, and utilization of these forage species by ruminant animals.
The aim of our research on CTs is to gain a better understanding of how they affect
ruminant nutrition, so we can develop more efficient procedures to screen legumes for
nutritional value and design better strategies for incorporating these species into
livestock feeding systems. Improved screening methods have been developed and are now
being used to characterize a wide range of legumes. Based on the results, we are compiling
a list of legume species indicating their quality attributes as feed sources.
Another vital part of this work involves measuring the impact of selected legumes on
livestock performance at the farm level, based on factors (such as live-weight gain and
milk production) that are closely associated with the quality attributes of legumes.
Obviously, farmers will not adopt legumes just to regenerate degraded soil but to achieve
significant improvement in their livestock production.
Recent results confirm that legumes can have a sizable impact on meat and milk
production, when used in different feeding systems on dual-purpose cattle farms. On-farm
trials have consistently demonstrated that, for example, the herbaceous legume Arachis
pintoi, combined with grasses, can increase the milk yield of cows by 10 to 15
percent, compared with feeding cows on grasses alone.
Genetic Improvement of Brachiaria
The forage germplasm now available satisfies many of farmers' requirements but by no
means all. Some important traits are lacking, as is the case with resistance to the
ubiquitous grassland spittlebug in Brachiaria spp. CIAT researchers have embarked
on breeding of this trait for two compelling reasons. First, Brachiaria grasses
are the most widely grown forage species in tropical America. And second, the spittlebug
dramatically reduces forage productivity and persistence, contributing to extensive
pasture degradation in the region.
Brazilian researchers have released a spittlebug resistant cultivar of B. brizantha,
but this species lacks tolerance of acid soils. Particularly in tropical savannas, this
trait is one of the main reasons for the huge popularity of B. decumbens, which
dramatically increases beef production, boosting weight gain per hectare per year by a
factor of 10, compared with native grasses. The challenge is to combine the spittlebug
resistance of B. brizantha with the desirable traits of B. decumbens in
a wide range of cultivars that give farmers multiple options for different environments.
One complication in breeding Brachiaria is that the grass normally reproduces
through apomixis, a process involving the production of asexual seed. Two decades ago,
Belgian scientists provided a way around apomixis by creating a polyploid sexual Brachiaria
plant that serves as a bridge for combining attributes from distinct, naturally asexual
parents.
Through field evaluation of a Brachiaria population consisting of sexual
genotypes, 11 were selected for resistance under artificial infestation and were
recombined to form a new cycle of the population in 1998. Crossing of elite apomictic
genotypes to this population is now generating large numbers of superior,
spittlebug-resistant clones, which will be evaluated for commercial release.
The use of molecular markers for apomixis, spittlebug resistance, and other traits
shows promise for further improving the efficiency of selection. For this purpose CIAT
scientists are now generating a large, segregating Brachiaria population to
identify molecular markers that are associated with desired traits.
Anthracnose Resistance
Another major constraint being addressed by forage researchers at CIAT is the
anthracnose fungus (Colletotrichum gloeosporioides), which is a serious obstacle
to wider use of Stylosanthes spp. This is a legume of South American origin that
shows much potential for improving livestock production and land management in the tropics
and subtropics. Anthracnose is also becoming a problem on another important forage legume,
Arachis pintoi.
Center scientists are screening Stylosanthes germplasm for anthracnose
resistance, while examining pathogen diversity and the geographic distribution of its
various races, work that is vital for developing effective programs for breeding
anthracnose resistance.
Endophytes for Plant Protection
A novel approach to plant protection in tropical forages centers on endophytes,
microscopic fungi that grow between the cells of plant tissues. Commonly used in forage
and turfgrasses of the temperate zone, endophytes help the host plant by making it drought
tolerant and resistant to insect pests. However, in some species the toxicity that repels
pests also sickens cattle that graze on the grass. The challenge for research is to
identify the endophyte strains that are safe for use in pasture grasses. Once improved
grasses such as Brachiaria are artificially infected with these safe strains, the
association will be permanent, since the endophytes are passed on through the seeds.
Though considerable research has been conducted on endophytes in grasses of the
temperate zone, little is known about these fungi in tropical grasses. One of the first
tasks of research on endophytes was to develop protocols for detecting the fungi. Such
methods are now available and have been used to identify endophytes in Brachiaria
similar to those reported in temperate grasses. Molecular analysis has revealed genetic
differences among the endophytes isolated in Brachiaria. Surveys are now under
way to detect endophytes in both Brachiaria spp. and native grasses to determine
the distribution of these fungi in tropical America.
Another key step has been to identify methods for artificially inoculating Brachiaria
with endophytes. In addition, our scientists are examining the effects of these fungi on
other fungi that cause diseases in tropical grasses. The results so far show that
endophytes can provide effective control. To further explore their potential benefits,
researchers are testing Brachiaria clones containing endophytes for tolerance to
other pathogens as well as insect pests and drought.
Adaptation of Forages to Soil and Climate
Forage evaluation at CIAT would be decidedly incomplete without a major effort to
determine and document the tolerance of key species to the main abiotic stresses of
grasses and legumes in savannas, forest margins, and hillsides.
One major limitation of forage production across environments is the limited supply of
nutrients, especially phosphorus, in acid soils. Many tropical forages are well adapted to
these soils and thus offer one of the best options for managing them. Collaborative
research at CIAT has shown that the ability of some forages to tolerate low soil fertility
is associated with certain root and shoot attributes. Both grasses and legumes adapt to
low nutrient supply by partitioning increased dry matter to the roots at the expense of
leaf and shoot growth. There appears to be significant genetic variation for this ability
in Brachiaria spp. and Arachis pintoi.
A major constraint of small-scale livestock production in hillsides and forest margins
is shortage of forage during the dry season, which leads to overgrazing. If smallholders
are to intensify production in these environments, it is vital that they have new forage
species with tolerance to a long dry season. Toward this end CIAT researchers are
conducting extensive evaluations of promising species, particularly the shrub legumes Cratylia
argentea and Calliandra calothyrsus.
Partnerships
Forage researchers at CIAT rely heavily on partners in national agricultural research
systems, the private sector, and advanced research institutes.
National Programs
Throughout the 1980s testing of promising grass and legume species in Latin America
took place through the International Network for the Evaluation of Tropical Pastures
(RIEPT), which involved 95 institutions in 22 countries. The RIEPT marked a decisive break
with historic neglect of tropical forages in the region's agricultural research. The
network was highly successful in building national research capacity and in establishing
close ties among national programs and between them and CIAT. A similar network was formed
for evaluating pastures in West Africa.
Although these networks are no longer active, intensive forage evaluation and related
research continue today under other types of cooperative arrangements. In this work CIAT
naturally maintains especially close ties with the Colombian Corporation for Agricultural
Research (CORPOICA) and with
various universities in its host country. Given the vast areas planted to pastures in
Brazil, CIAT also works closely with centers of the Brazilian Agricultural Research
Enterprize (Embrapa), particularly in
germplasm collection and evaluation and in genetic improvement of Brachiaria. For the
benefit of these and many other national programs, Center scientists offer training and
organize regional workshops on key forage species, research methodologies, and related
themes.
Networks for Participatory Evaluation of Forages
The RIEPT model for cooperative research has been succeeded by a new kind of network
centering on farmer evaluation of forages. Under this new model, national partners in
selected countries of a region develop and evaluate forage technologies with farmers for
specific livestock systems.
The Tropileche
project, for example has focused on dual-purpose livestock production in Central America
and the Andean zone. Throughout the humid and subhumid regions of tropical America, dual
purpose ruminants—cattle, sheep, and goats raised for both meat and milk—account
for most animal production on small farms. Dual-purpose cattle make up 78 percent of the
region's total herd and produce 41 percent of its milk. Under CIAT coordination Tropileche
worked to provide smallholders with new options for intensifying livestock production,
while improving natural resource management. Part of a wider international research
effort—the CGIAR's Systemwide Livestock Programme, which is coordinated by ILRI—the project has involved
researchers, extensionists, and farmers in Costa Rica, Honduras, Nicaragua, and Peru.
Another example of this networking approach is the Forages for Smallholders
Project (FSP), which was jointly coordinated by CIAT and the Commonwealth Scientific
and Industrial Research Organisation (CSIRO)
of Australia. The national partners involved in the project have used participatory
research approaches with farmers in Indonesia, Laos, Philippines, Thailand, and Vietnam.
Together, they have designed, developed, and tested forage systems with broadly adapted
grasses and legumes identified by the project.
To provide stronger support for such projects, CIAT scientists have formed an
interdisciplinary team that will develop improved methods for targeting forage germplasm
in hillside environments, drawing on participatory approaches and geographic information
systems (GIS).
Private Sector
CIAT is building strong ties with the private sector in forage research and
development. For example, in Colombia's Caquetá Department, we collaborated with Nestlé in a project
designed to recuperate degraded pastures, using forage legumes, in the forest margins. In
upstream research on endophytes, we are working with the US company BioWorld on methods for detecting
these fungi in tropical grasses.
Advanced Research Institutes
Center collaboration with advanced research institutes in the developed world is
especially vital for resolving the methodological challenges in forages research. In work
on antinutritional factors in legumes, for example, we work closely with colleagues at the
Institute of Grassland and Environmental Research (IGER) and Oxford Forestry
Institute (OFI) in the UK.
Endophytes research at CIAT depends on strong relationships with Japan's National
Grasslands Research Institute and with the University of Rutgers in the USA. Finally, our efforts to identify
forage attributes that are associated with adaptation to acid soils has benefited greatly
from cooperation with the Universities
of Hohenheim (Germany) and Vienna (Austria)
as well as Japan's
Hokkaido University.
Impact
Since 1970 national programs in 14 countries have released 45 tropical forage cultivars
that were derived from germplasm selections provided by CIAT. Most of these cultivars are
grasses, which have been widely adopted in Latin America for pasture improvement.
When expressed as a percentage of the total pasture area in specific countries, the
adoption rates seem low; the highest, for Costa Rica, is just 10 percent. But the figures
for area planted to these varieties are impressive. In Brazil, for example, where the area
in pastures is vast (180 million hectares), the percentage of that area sown to
CIAT-related cultivars amounts to more than 5 million hectares.
The total area planted to CIAT-related cultivars in Latin America is estimated at about
6.8 million hectares. And the cumulative value of the meat and milk production increases
made possible by these improved cultivars is estimated at $1.4 billion in 1990 US dollars.
The internal rate of return to the Center's forage research is a respectable 36 percent,
indicating that the work has been quite effective.
Even so, given the low percentage of total pasture area planted to improved varieties,
there is obviously a lot of scope for further impact. It is estimated that 90 percent of
the grazing land in tropical America is still in native pastures. The pace at which new
forage technology continues to spread, however, will depend on broad trends in the
livestock sector, which are heavily influenced by government policies.
In Latin America increased livestock production has been brought about during recent
decades mainly by expanding the area used for cattle, particularly in tropical savannas,
forest margins, and hillsides. Farmers have had little incentive to adopt technology that
increases production per unit of land. Nonetheless, the proven ability of improved grasses
to boost livestock productivity by a factor of 16 over native grasses is a considerable
enticement. And adoption of these grasses will no doubt increase as demand for livestock
products continues to grow. This will happen a lot faster, though, if government policies
are designed to encourage intensification rather than area expansion of domestic livestock
production.
Adoption of forage legumes has been fairly limited so far, again because farmers lack
incentives to intensify production, but also because many do not recognize the long-term
benefits that forage legumes bring by enhancing the soil and making production more
sustainable. Nonetheless, recent experience has revealed many opportunities in tropical
Asia and America for integrating forage legumes into different production systems.
In southern China, for example, a CIAT selection of the tropical American legume Stylosanthes
guianensis is currently sown on about 50,000 hectares as a cover crop for rubber and
fruit trees. It reduces the need for chemical fertilizers, helps conserve moisture, and
controls both erosion and weeds. In addition, farmers harvest the Stylosanthes
leaves and use them as an ingredient in highly nutritious animal feeds. Other forage
species, including Centrosema acutifolium, C. macrocarpum, and Arachis pintoi,
are also being used as cover crops in banana, coffee, palm, pepper, citrus, and other
commodities in several Latin American countries.
Since 1996 the above-mentioned Tropileche project has demonstrated the potential for intensifying
small dual-purpose livestock production (i.e., for meat and milk) through the introduction
of various grass-legume combinations. At the same time, the Forages for Smallholders
Project in Southeast Asia has led to the adoption of improved germplasm in a wide variety
of upland production systems. Perhaps most important, these projects have enabled us to
devise farmer participatory research methods, which have proved highly effective in
creating appropriate forage technologies for diverse production niches.
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