The color of chlorophyll, the photosynthetic pigment made by plants, has become an
international symbol of sustainable production, ecosystem health, and biodiversity. But
production of the plants on which human livelihoods depend isn’t always green. Some
practices rob soil of nutrients or trigger erosion. Pesticide overuse pollutes water,
contaminates food, and kills nontarget organisms. And chemical fertilizers, often a
necessary production input for sustainable farming, consume nonrenewable fossil and
mineral resources.
How can we bring about the greening of
agriculture while reducing poverty and strengthening food security? A large part of the
answer lies in creative use of local resources and technology, combined with science-based
solutions, such as integrated pest management, biofertilizers, disease-resistant crops,
and plants that use soil and water more efficiently. Here we provide some concrete
examples of how innovative research, often relying on high-tech tools as well as direct
farmer participation, is helping tropical agriculture live up to the promise of its
natural color.
Rice growers with green attitude
Over the last three decades, Latin America has
experienced a rice revolution that has transformed landscapes, farming practices, and even
national economies. With the debut of improved rice varieties (243 of them based on
germplasm from CIAT), yields have climbed, while unit production costs and rice prices
have fallen. Poor consumers, both urban and rural, have benefited immensely. The
cumulative value of additional rice production made possible by CIAT-related varieties has
been estimated at US$5.5 billion (in 1990 dollars). Moreover, millions of hectares of land
that otherwise would have been put under the plow to feed a rapidly growing population
have been left undisturbed.
The region’s rice boom saw a new breed of
grower emerge—rice specialists with a keen eye for technology and profit. With them
came intensive cultivation practices and chemical fertilizers, elements of the new
technology. Unfortunately, these created an ideal home for insect pests, weeds, and
diseases. Not wanting to risk their investment, farmers sometimes applied far more
insecticides, herbicides, and fungicides than were needed or recommended.
The new commercial producers tended to be
highly organized into groups, and rice was their prime focus of agricultural interest.
That pattern, going back more than half a century in some countries, persists in much of
Latin America today. Local producer associations and national federations provide channels
to rice markets, high-quality seed, a forum for discussion, and access to innovations from
CIAT and its partners, the national rice research programs. They include not only
producers but also other links in the field-to-table chain: seed producers, milling
enterprises, and exporters.
At the regional level, industry interests are
catered to by the Fund for Latin American Irrigated Rice (FLAR). It is headquartered at
CIAT’s international science park in Colombia, and CIAT itself is a founding and
active member. The fund supports research, based on financial contributions from farmers
and others; thus the rice industry, as a collective client, sets the science agenda. As
FLAR’s executive director, Luis Sanint, says: "The customers of technology are
the ones giving the signals to the generators of technology."
Sanint believes there is a positive connection
between the highly integrated nature of Latin America’s rice sector and the
significant success it has had in mitigating the environmental risks of intensive,
high-input production. The use of more environmentally friendly production methods, such
as integrated pest management (IPM) options from CIAT and its partners, is enhanced by
strong farmer organization and unity of purpose. National policies, especially shifts from
pesticide subsidies to pesticide taxes, also play a key role.
"In countries with strong grower
organizations and a national rice strategy, the reduction of pesticide use has been more
rapid," says Sanint. "If an association sets up a demonstration plot showing the
difference between, say, 10 pesticide applications and no application, then the farmers
see the benefit for themselves." They get a feel, he explains, for the thresholds of
biotic stress below which there is no need to spray.
"Farmers are conscious of the fact that
pesticides, applied in a water-intensive production system, easily get washed into streams
and can hurt the quality of the resources they depend on. They worry about killing the
goose that laid the golden egg. And they worry that laws will be passed restricting the
use of water for irrigated rice because of the threat of pollution."
Data from Tolima Department in central
Colombia, a country with a highly organized rice industry, show a strong pattern of
pesticide reduction. Insecticide use, mainly to fight the insect pest sogata and a
leafhopper that transmits rice hoja blanca virus, dropped dramatically between 1981 and
1997—from 4.2 liters per hectare to just 0.6 liters. Reductions in fungicide use were
comparable.
While herbicide use has been cut by 20 percent,
the 1997 level of 4 liters per hectare in Tolima is still high. This is probably due to
the nature of land tenure, says Sanint. As many farmers rent rather than own fields,
they’re not motivated to invest in weed control, which requires rented machinery and
whose benefits would accrue in part to the next tenant. "They just give up the plot
and move on."
Data from Venezuela, for 1989-92, also show
sharp cuts in pesticide use. "In other countries," says Sanint, "we know
this has also happened, but we haven’t yet studied it in detail." Apart from
economic necessity and the increasingly "green" attitudes of organized farmers,
another reason for pesticide reduction is the availability of rice varieties that not only
yield well but also resist major diseases.
Know your enemy
Observed reductions in pesticide use bode well
for the environmentally sustainable future of rice production in Latin America. And so
does CIAT’s on-going biotechnology research. One example is our use of molecular
markers in the quest to make rice more resistant to blast, the most important disease of
the crop.
The fungus responsible for blast affects both
irrigated and upland rice, though the latter is more susceptible. The organism is hard to
fight because it is a moving target: There are many strains and they mutate rapidly.
Resistant rice varieties usually become susceptible to new strains within 2 or 3 years of
their official release. As a countermeasure, farmers often apply heavy doses of fungicide.
This not only is very costly but also damages the environment.
Scientists at CIAT and Purdue University in the
USA are jointly working on an integrated approach to fighting blast. The strategy combines
conventional plant breeding and pathotyping (distinguishing individual strains of a
pathogen) with the use of two types of molecular markers, RAPDs and RFLPs.
Through conventional breeding, CIAT spent many
years developing a fully resistant rice cultivar in a Colombian hot spot of rice blast.
This was done in collaboration with Colombia’s National Rice Federation (FEDEARROZ)
and the Colombian Institute for Agricultural Research (ICA). The variety Oryzica Llanos 5
has now been grown for about a decade without the resistance breaking down.
The CIAT-Purdue strategy centers on exploiting
this hard-won genetic resistance. The aim is to produce new rice cultivars that have
long-lasting resistance to whole families of blast rather than single strains. For Latin
America the potential economic benefits of such resistance stability in rice are estimated
at US$1.6 billion over 15 years.
In the early 1990s, CIAT used conventional
pathotyping assays, the only diagnostic tool then available, to identify 56 pathotypes of
blast from Colombian samples (or "isolates"). More recently, genetic
fingerprinting has allowed more in-depth analysis of this material. The results reveal a
serious chink in the fungus’s armor: The various pathotypes fall into just six
genetically distinct families or lineages. On average, fingerprints for different isolates
within each lineage are 92 percent similar. These findings are a major advance in the
quest to "know your enemy," as one CIAT scientist put it.
Fortunately, each blast lineage turns out to be
strongly associated with a specific subset of rice cultivars. Molecular markers are now
being used to identify rice breeding lines with specific resistance genes. So far, the
scientists have succeeded in identifying rice genes associated with resistance to one of
the six blast lineages. The results suggest their strategy is on the right track. This
research will produce rice varieties with durable blast resistance that enables farmers to
further reduce pesticide use without sacrificing production gains.
Beans with a nose for phosphorus
As with rice, the impact of CIAT’s
cooperative research on beans has come mainly from improved yields and disease resistance.
Since 1970 national agricultural research programs in 39 countries have released 362 bean
varieties—238 in Latin America and 111 in Africa—based on germplasm provided by
the Center. These varieties are planted on an estimated total area of nearly 2.4 million
hectares and have generated cumulative benefits of almost US$1.3 billion (in 1990
dollars).
A major obstacle to further progress is the
widespread phosphorus, or P, deficiency of tropical soils. This is a major hurdle for
Latin American farmers, half of whose growing areas are critically low in this nutrient.
The problem is not so much the absolute quantity of P in the soil as the fact that it is
bound up in chemical compounds difficult for beans to absorb and use for grain production.
For each ton of food grain produced on fertile
soil, beans have to take in about
10 kilograms of P—much more than for other major food crops. For example, maize needs
only about half as much P per ton of yield as common beans, and rice a little less than a
third.
Given that most bean farmers cannot afford to
apply large doses of fertilizer, a vital strategy for overcoming P deficiency is to
genetically alter the plants themselves. The goal is to identify and harness genes that
allow beans to tap and use scarce P more efficiently and then combine them with disease
resistance genes.
During the 1990s, CIAT screened thousands of
bean samples from the huge germplasm collection it safeguards in Colombia. A major payoff
was the identification of materials with superior yield even under low-P conditions. Some
bean lines are producing 400 kilograms per hectare more than Carioca, a commercial variety
regularly used as a check in experiments. Given average Latin American bean yields of
around 700 kilograms per hectare, this large genetic advantage has opened the door to
major increases in bean production.
Part of CIAT’s strategy is to understand
the specific mechanisms that allow beans to tolerate the stress of low P levels. One
superior bean accession, G 21212, appears to have an unusual ability to mobilize plant
phosphorus for grain production. This was crossed with another bean line, BAT 881, that
yields extraordinarily well as long as P is not deficient in the soil. Among the progeny,
one superior line yields as well as the Carioca check under more favorable soil conditions
and outyields it by 600 kilograms per hectare under the stress of low P. In all, six
advanced bean lines are being used by CIAT as parents in crosses with commercial
varieties.
CIAT researchers have been using molecular
markers called RAPDs to analyze the most promising bean crosses. Recently they discovered
several gene combinations with a remarkably strong influence on yield when P is low. One
long segment of DNA in particular accounts for more than 300 kilograms of yield per
hectare. The scientists now suspect that the genes responsible for P deficiency tolerance
also shield beans against drought.
As CIAT bean breeder Steve Beebe says,
"molecular markers are helping us get deeper into the genetics of tolerance to
abiotic stresses." Some markers, however, are better than others as tools to speed up
breeding and make identification of valuable genes more precise. Beebe and colleagues are
therefore now using two more powerful types of markers, SCARs and SSRs, to identify useful
stretches of the bean genome. The idea is to space out the markers evenly over the full
bean genome.
What are the implications of the improved
germplasm for farmers? First, combining the trait of high bean yield under low P with
genetically based tolerance to diseases like bean golden mosaic virus (see pages 38-40)
means that bean growers can expect more stable yields. Second, the amount of fertilizer
needed to make a P-deficient field produce a good crop can be brought to within the
economic reach of poor farmers.
CIAT plant nutritionist Idupulapati Rao
cautions, though, that the use of P-efficient germplasm isn’t a complete substitute
for P fertilizer. Relying only on better seeds would mine the soil of its P, degrading
fertility. The trick, he says, is to combine "strategic" applications of P
fertilizer with better germplasm. Eventually, P in a form readily available to plants will
build up in the soil, decreasing the size and frequency of fertilizer amendments needed to
sustain production.
Soil conservation through participation
Besides nutrient deficiencies like low
phosphorus, a major headache for small farmers in the tropics is gradual loss of farm
productivity through soil erosion. Farming in hillsides is a constant tug-of-war with
gravity and rainfall. When the two team up, they can quickly carve out ruts and ravines,
carrying off tons of precious soil to lower elevations. Or, worse, they can trigger
devastating mudslides, leaving steep farm fields denuded of vegetation, as happened 2
years ago in Central America during Hurricane Mitch. The scars can last for years. But
erosion and declining soil fertility can also be silent demons, slowly eating away a
community’s natural resource capital year after year.
For several decades now, soil degradation,
especially from erosion and continuous cropping, has been recognized as a widespread
threat to sustainable world agriculture. Proven conservation and management practices,
such as terracing, have been available for centuries. And a whole range of new options has
been added to the menu over the past 25 years. These include improved contour cultivation,
grass strips, cover crops, green manures, live fences, microcatchments (water and soil
nutrient traps), and a host of innovative tree-crop combinations coming out of
agroforestry research. But in most low-income countries, farmer adoption of these improved
practices has been low. During the 1990s a lot of effort, including research by CIAT, was
spent trying to find out why farmers weren’t responding.
The answer centers on at least three factors.
First, farmers have tended to rank poor soil fertility lower on their list of agricultural
constraints than biotic stresses, whose effects are more obvious and dramatic. Second,
many of the newer soil-related technologies represent extra costs for farmers without
giving them short-term spinoff benefits like more food, fodder, fuel, or income. Third,
farmers have had little sense of technology ownership. Many new methods were designed by
researchers on-station, and sometimes on-farm, but with only token farmer participation.
As a result, there was a blockage in a key channel of technology dissemination:
"spontaneous" adoption, whereby farmers pass on new ideas to each other and try
them out without direct intervention by extension agents.
A 1992-94 study by Jacqueline Ashby
(CIAT’s director for research on natural resource management) and colleagues clearly
showed that participatory methods can dramatically boost adoption of soil conservation
practices. The study involved 261 farmers in an area of southwestern Colombia where nearly
half the land is steeper than 30 degrees. To supplement their income from coffee, many
farmers cultivate cassava, maize, and beans on steep, erosion-prone slopes.
The researchers trained local extension agents
in participatory methods. The agents then worked with core groups of farmers,
demonstrating eight different plant species that could be used as live barriers to protect
soil along hill contours. As part of the study’s strategy, the farmers themselves
decided what to plant, and where, in their on-farm experiments.
A key research element was to have farmers rank
the various options. Among the species evaluated were sugarcane, a cut-and-carry forage
grass called pasto telembi, and vetiver grass, which livestock don’t eat. From the
scientists’ point of view, the best option for soil conservation was vetiver grass.
However, the farmers ranked it low, preferring especially the sugarcane and pasto telembi,
which they use as animal forage. For them it was a matter of finding an acceptable
compromise between soil conservation and direct use of the barrier plants.
Results from the final phase of the study were
surprisingly positive. Follow-up interviews showed that participating farmers were
spontaneously passing on their chosen technology to others. By 1994, 146 farmers were
reported to have planted barriers, at their own expense, on the recommendation of other
farmers. For Ashby, this is strong evidence that "soil conservation programs can use
participatory research methods to improve their recommendations and their likelihood of
future success."
Lessons learned from that participatory study
and similar work in Uganda are now being systematically applied by CIAT and its partners
in soil conservation research in Latin America and Africa. For example, in our hillside
research "reference site" in Colombia’s Cauca Department, where the
original study was conducted, student researchers are now working with farmers to examine
the nutrient content of local plant species that could be used as biofertilizers.
Tithonia: A low-cost nutrient trap
Whether native plants are "weeds" or
"biofertilizers" depends mostly on your perspective. For farmers they are
usually considered weeds when they aggressively compete with crops for soil nutrients,
moisture, and sunlight; act as reservoirs of disease and pests; and aren’t useful as
food, fodder, or fuel.
In southwestern Colombia researchers from CIAT
and Colombia’s Universidad Nacional are conducting participatory research aimed at
identifying, cataloging, and testing native and nonnative plants that might help reverse
soil nutrient depletion and prevent erosion on hillside farms. One promising species is
Tithonia diversifolia, a member of the sunflower family often seen growing by roadsides.
While many people consider it a weed, it has been shown to have several traits that are
useful in soil management.
Farmers are now testing the hypothesis that
tithonia is particularly good at trapping moisture and soil nutrients that would otherwise
be lost through erosion and offers a convenient, low-cost option for soil fertility
management. Farmers plant the species along the lower edges of sloping fields, cut and
carry tithonia prunings, and then apply them, stems and all, as a biofertilizer on crops.
"By thus recycling nutrients," says CIAT soil scientist Edmundo Barrios,
"farmers can lessen the need for chemical fertilizers, thus reducing their production
costs and lowering the risk of contaminating water."
In preliminary tests tithonia, which has the
advantage of decomposing quickly, was gently incorporated into the soil around maize
plants. Researchers from CIAT and the Universidad Javeriana in Bogotá were pleasantly
surprised to find that some maize roots easily penetrated the decomposing stems.
"It looks like there may be a direct
nutrient transfer from the tithonia to the maize," says CIAT soil scientist Richard
Thomas. "The soil is essentially bypassed." If that’s so, then the
application of tithonia could slow down the soil nutrient depletion typical of demanding
crops like maize. Thomas suspects that the nutrient transfer is mediated by mycorrhiza, a
mutually beneficial relationship between soil fungi and plant roots. Among other things,
this bond promotes the uptake of phosphorus by plants.
"We know that poor farmers won’t use
much fertilizer because of the cost and because it isn’t always available," says
Thomas. "So, we have to look at better nutrient management methods—recycling
what’s already available on farms rather than relying entirely on outside
inputs."
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Best-bet green
manures for Uganda
Like many areas of Latin America, eastern and
central Africa also suffer from widespread soil degradation. Since the early 1990s, CIAT
has been using participatory research to identify, test, and perfect new soil management
strategies with farmers in eastern Uganda. Some of these innovations have since been
packaged as "minikits" for grassroots use.
The minikits contain seeds of legumes that can
be grown as "green manures" or cover crops to improve soil fertility as well as
decision guides on how to use them. Over the past 2 years, 3,000 kits have been
distributed in Uganda through a national project—Investment for the Development of
Export Agriculture (IDEA)—and several NGOs.
The decision guides are the result of
collaboration between CIAT, Uganda’s National Agricultural Research Organisation
(NARO), and farmers in the Ikulwe area of Iganga District. With a population of one
million—about 200,000 farm families—Iganga is one of the country’s most
densely populated areas.
Over the years the size of the farmer group
active in research at any one time was 25 to 30 people. Together, the scientists and
farmer-researchers identified crop production constraints and options for improving soil
fertility. They then designed on-farm experiments to test various legumes in association
with crops such as banana, coffee, cassava, sweet potato, maize, and bean or in some
instances as a sole cover crop or pest control measure. While the experiments were done by
the farmers, who collected data and recorded detailed observations in notebooks, both
scientists and farmers evaluated the results.
The decision guides cover five leguminous
plants—canavalia, mucuna, lablab, crotalaria, and tephrosia—which capture
nitrogen from the air and fix it in the plant. Once cut and incorporated into the soil,
they provide a rich source of organic matter for crop growth and make the soil easier to
cultivate. The main guide, called "Best-Bet Options," contains easy-to-follow
instructions for 11 different cropping scenarios. A separate guide is also available for
each legume, explaining its advantages and disadvantages, how to grow it, and how to
incorporate it into the soil for various crops.
One serious pest problem identified in the
participatory research was root rats, tunneling rodents that destroy sweet potato and
cassava crops. The legume Tephrosia vogellii provides a practical method of control.
Indigenous to Uganda, this deep-rooted perennial shrub, which is easy to establish from
seed, contains a natural toxin. It can be planted in a scattered pattern in fields or
around them to serve as a barrier. Once the root rats are gone, the shrubs can be
uprooted. Tephrosia also has bonus traits. Its leaves can be picked and used to control
insect pests in stored grain, and stalks can be used as stakes for climbing beans.
Systematic dissemination of the results of the
green manure and cover crop experiments, as well as from related participatory research on
other topics like bean and cassava production, began in 1996. Farmers are playing an
active role. They multiply seed, host groups of visiting farmers, participate in
agricultural exhibitions, and organize farmer workshops. Some have been so motivated by
their experience of being full partners in research that they’re now experimenting
with other technologies on their own.
A farmer’s repertoire of soil management methods
Alex Bukenya has 4 hectares of
land, from which he and his wife feed themselves and their seven children. The Ugandan
farmer participates in a multipartner soil conservation research project with CIAT and
also finds time to experiment on his own.
Bukenya grows the legumes lablab and canavalia
to improve soil fertility. These are intercropped with maize, as part of a research
experiment. He’s also testing fertilizer applications.
"I’ve gained a lot of new knowledge
to improve productivity," says Bukenya. "Before, I used to just plant
anyhow—and the rain took the fertile soil away. Now I conserve the soil and
water."
His entire farm is surrounded by vetiver grass,
as an erosion barrier. But it’s also useful as thatch and for mulching crops. He has
constructed irrigation ditches around the farm, which the vetiver grass helps stabilize,
and he has planted another legume, mucuna, to fix nitrogen in the soil and combat weeds.
Fallowing of land and applications of farmyard manure are likewise part of his repertoire
of soil management methods.
"Although he joined the group late, Alex
now trains other farmers on their farms and gives them seed from his vetiver and
mucuna," says Anthony Esilaba, a CIAT researcher. One European development worker,
visiting Bukenya’s farm at the same time as CIAT staff, commented that this farmer
deserved a doctoral degree for his innovative work!
Ugandan
farmer Alex Bukenya.
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Reversing soil degradation in Africa
Building on success with the legume minikits,
CIAT recently embarked on a new participatory project on soil nutrient management in
collaboration with the Tropical Soil Biology and Fertility Programme (TSBF). Following a
diagnosis and analysis exercise in late 1999, farmers proposed 11 experiments for
March-August 2000, during the long-rains growing season. They’re testing farmyard
manure, compost and rock phosphate as fertilizer, deep tillage techniques, mulching,
fallowing, and the use of trenches and grass strips to control erosion. This work, which
also extends the earlier research on green manures, is funded by Germany’s Federal
Ministry of Cooperation and Economic Development (BMZ) and is a component of the
CGIAR’s Soil, Water, and Nutrient Management Program.
One partner in this ambitious effort to reverse
nutrient depletion is the Africa 2000 Network, an initiative of the United Nations
Environment Programme (UNEP). The network supports grassroots community interests,
environmental protection, and sustainable development in 13 African countries, including
Uganda. "When we came here, we found that the CIAT technologies were exactly in line
with the objectives of our project," says Africa 2000’s Drake Ssenyange.
Collaboration with such like-minded organizations is a pillar in CIAT’s strategy to
multiply the impact of its work elsewhere in Uganda and in other countries.
CIAT’s work with the farmers of Iganga has
had an impact not only on soil conservation and cropping practices but also on farmer
confidence and knowledge. "Working with the researchers has been very useful,"
says Livingstone Mumbya, a local community leader and active participant in the research.
"Now we have new knowledge about compost, good varieties, fertilizers, and green
manure. We know how to take measurements in our fields, and we recognize diseases of
plants and harmful insects. Also, the group has inspired some people who thought they were
weak to be more confident."
Besides that, says Mumbya, the food situation
has improved. "Now we have enough food and even a surplus to sell, to help pay for
school fees. Our maize has done better where we used farmyard manure. Right now we wish
our fellow farmers in villages could adopt the same techniques—to achieve something
very good for posterity!"
How and whether such farmer-based research will
have broad and deep development impact in the coming years is difficult to predict. Major
intervening forces—political turmoil, delayed rains and recurring drought, the AIDS
pandemic, and even the economic repercussions of liberalized trade in coffee—are at
work in eastern and central Africa. But like the soil conservation strategies now
available, participatory research and organizational partnerships are among the
"best-bet options" for promoting sustainable farming in this region. They give
poor rural people a fighting chance to build viable, dignified livelihoods based on
self-reliance and learning rather than food aid and inappropriate technology handouts.
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