1 Paper presented at the International Conference on Vetiver, held in Chiang
Rai, Thailand,
Feb 4-8, 1996
2 CIAT Regional Cassava Program in Asia, Dept. of Agric., Chatuchak, Bangkok 10900,
Thailand.
3 Agro-forestry College Bac Thai, Thai Nguyen Univ., Thai Nguyen, Bac Thai,
Vietnam.
4 Rice and Field Crops Promotion Div., Dept of Agric Extension, Bangkok, Thailand
Research has identified various effective ways to reduce erosion in cassava-based cropping
systems, including the use of vetiver grass contour hedgerows. However, few of these
practices are presently used by farmers. To enhance the adoption of soil conservation
practices by cassava farmers, a Farmer Participatory Research (FPR) methodology was used
in two pilot sites each in Thailand, Vietnam, China and Indonesia to test and select the
most effective practices. Farmers in Thailand and Vietnam selected vetiver grass contour
barriers as one of 4-5 treatments they wanted to test on their own fields. After
harvesting all trials and discussing the results, farmers in all three villages in Vietnam
selected the vetiver grass treatment as the most effective in increasing income and
reducing erosion. Although in one site in Thailand the vetiver grass treatment did not
result in high cassava yields or income, farmers in both sites selected the vetiver grass
treatment as the most useful. In both countries, participating farmers, after seeing the
benefits of vetiver grass barriers, requested additional planting material to plant on
their fields.
Cassava (Manihot esculenta Crantz) is the third most important food crop grown in
southeast Asia, both in terms of area planted and production of dry matter, following rice
and either maize or sugarcane (FAO, 1993). In Thailand the crop is grown mainly for the
production of dry cassava chips and pellets, as well as for that of cassava starch. The
former are mainly exported while the latter is used for both domestic consumption and
export. Cassava is generally among the three most important agricultural export products
of Thailand. The crop is grown mainly in the northeastern and eastern part of the country
in rather infertile lighttextured soils and under unpredictable rainfall conditions.
In Vietnam cassava is grown mainly for on-farm feeding of pigs, for direct human
consumption, and for production of starch, maltose, noodles, cakes etc. Most of the starch
is produced by small-scale family units, but in the past few years some large-scale search
factories have been established in South Vietnam. Cassava is grown by small farmers
throughout the country, but especially in the hilly and mountainous areas of North and
Central Vietnam, on light textured and infertile soils which are very susceptible to
erosion. Chemical fertilizers are seldom applied, but many farmers apply pig manure to
maintain soil productivity.
Cassava is known to grow well on poor soils and under low rainfall conditions, but also
has the reputation to exhaust the remaining soil nutrients and to cause serious erosion
when grown on slopes. Research has shown that cassava extracts large amounts of soil
nutrients only when yields are very high, but that per ton dry matter produced the crop
extracts less N and P, and similar amounts of K as other crops (Howeler, 1991). Whether or
not the crop causes more erosion than other crops depends largely on the soil and climatic
conditions as well as on its management. Under the soil and climatic conditions of
Thailand, Putthacharoen et al. (1992) found that the planting of cassava caused about
twice as much erosion as that of mungbean, and three times as much as that of maize,
sorghum or peanut grown only once a year. However, Wargiono et al. (1992) and Howeler
(1995) reported that cassava grown in southern Sumatra of Indonesia produced similar
amounts of soil loss as peanut and slightly more than maize or upland rice. Because of its
wide spacing and slow initial growth, cassava plants leave considerable soil surface
exposed to rainfall impact during the first three months after planting, and this can lead
to serious erosion when the crop is grown on steep hillsides. However, the fact that
cassava is often grown on eroded hillsides does not necessarily mean that the crop has
been the cause of the erosion. It may also be that the growing of this crop is the result
of erosion, since cassava can still be productive on degraded and eroded soils where other
crops can not grow anymore, as shown by recent research in Colombia (CIAT, 1996). In any
case, numerous erosion control trials, conducted both in Colombia and various parts of
Asia, have shown that soil erosion in cassava can be reduced substantially by good
management. Many management practices have been identified that can reduce soil erosion,
such as minimum or zero tillage, mulching, fertilizer application, closer plant spacing,
intercropping, as well as the growing of contour hedgerows of grasses, legumes or
multipurpose tree species (Howeler, 1987 and 1994). The effectiveness of vetiver grass
(Vetiveria zizanioides) contour hedgerows in reducing erosion losses in cassava fields in
Colombia has already been reported by Laing (1992) from work done by Ruppenthal (1995).
Similar trials conducted in Nanning, Guangxi province of China (Table 1) again showed that
among various soil/crop management treatments, the planting of vetiver grass contour
hedgerows produced the lowest amount of soil loss due to erosion as well as the highest
cassava yields.
Many of the practices shown to reduce erosion, however, have certain advantages and
disadvantages as they may require additional capital, labor or land, and thus may or may
not increase the net income for farmers (Table 2). Since most cassava farmers are poor,
and their main concern. is to feed their families, they will not adopt soil conservation
practices unless they themselves are convinced that these practices bring immediate
benefits as well as protect their soil from long-term degradation (Fujisaka, 1991). Which
management practices are most effective and beneficial is very site-specific and depends
very much on the local soil and climate, the farmers' socio-economic conditions, as well
as the traditional production practices. The testing and selection of the best management
practices can thus best be done by the farmers themselves, in close collaboration with
researchers and extension agents.
The adoption of new technologies, such as new varieties or management practices, is often
limited because the recommended practices were developed by researchers, who may not
always know the farmers' specific needs and limitations. The recommended technologies may
thus not fulfill the farmers' needs or may not be adapted to fit the local conditions.
Farmer Participatory Research (FPR) methodologies have been developed by CIAT in Colombia
(Ashby et al., 1987) and Rwanda (Sperling, 1992), and were shown to increase substantially
the adoption of new bean (Phaseolus vulgaris) varieties. A similar approach is presently
being used to improve the efficiency of cassava variety selection (Hernandez, 1991) as
well as to enhance the adoption of better integrated pest management (IPM) practices for
cassava in the northeast of Brazil, and that of better soil conservation practices in
Colombia (CIAT, 1996) and southeast Asia (Howeler, 1996).
In 1993 the Sasakawa Foundation in Japan (now known as the Nippon Foundation) decided to
fund a 5-year project, with the objective of enhancing the adoption by farmers of more
sustainable management practices in cassava-based production systems in Asia, through the
development and use of an FPR approach to soil conservation extension. The approach is
based on the following basic principles of soil conservation:
1. Soil conservation is not an end in itself, but an integral part of good soil and crop
management, including effective agronomic practices as well as the use of more productive
germplasm.
2. Soil conservation must be done through a bottom-up program, planned and executed with
the full knowledge, cooperation and participation of farmers.
3. Any proposed soil conservation practices must offer short-term benefits to farmers in
order to be accepted, and must be suitable for the local soil and climatic conditions and
fit the local cropping patterns.
The project started in 1994 with the organization of an informal consortium of
collaborating research and extension institutions from the four participating countries,
i.e. Thailand, Vietnam, China and Indonesia. In Thailand the project is conducted with
participation of the Field Crops Research Institute of the Department of Agriculture, the
Rice and Field Crops Promotion Division of the Dept. of Agricultural Extension, and the
Thai Tapioca Development Institute (TTDI). In Vietnam the project is conducted in
collaboration with the Agro-forestry College in Thai Nguyen, Bac Thai province, and the
National Institute for Soils and Fertilizers in Hanoi. After the training in FPR
methodologies of participating researchers and extensionists from the four countries, the
project started with the conducting of Rapid Rural Appraisals (RRA) in potential pilot
sites, so as to select the most appropriate sites and learn about the bio-physical and
socio-economic conditions as well as the current production practices in each site; these
data were used to identify farmers' needs and constraints. From the results of these RRAs,
two pilot sites were selected in each country, based on the present and future importance
of cassava in the region, the seriousness of soil erosion, and the interest of farmers to.
participate in the project. Table 3 shows that the selected pilot sites differ markedly in
terms of soil, climate, cropping systems and farm size.
Before the next planting season started, farmers from the selected pilot sites were
invited to a farmers' field day to see demonstration plots that had been established by
researchers on a uniform slope, usually at an experiment station, with a large number of
soil and crop management practices. Soil losses due to erosion had been determined in each
treatment by weighing at monthly intervals the sediments collected in plastic-covered
channels at the bottom of each plot (Figure 1). Farmers could see with their own eyes the
amount of soil that had eroded into these ditches as a result of each treatment. Farmers
were asked to discuss the advantages and disadvantages of each treatment and to score the
treatments in terms of general usefulness, based on yields of cassava and intercrops as
well as effectiveness in reducing erosion.
Table 4 shows the ranking of the management practices considered most useful by the
farmers of each pilot site. It is clear that farmer preferences vary greatly between
countries, and even between sites within the same country, depending on the local
conditions, farm size, and traditional cropping patterns (see Table 3). The use of vetiver
grass hedgerows was the first choice among farmers from both pilot sites in Thailand,
possibly because of their knowledge about the interest of His Majesty the King, King
Bhumibhol Adulyadej of Thailand, in this "miracle grass" as an effective means
to reduce erosion. Vetiver grass hedgerows was also among the first three preferences of
farmers in the two pilot sites in Vietnam. It was not a preferred option in China and was
not even used in the demonstration plots in Indonesia, as researchers considered that
farmers would reject it as unsuitable for feeding their cattle, and would therefore prefer
to plant elephant-grass barriers instead.
Upon return to their village, the farmers that were interested in conducting FPR trials
met with researchers and extensionists to decide on the 4-5 most useful practices that
they wanted to try in their own fields. In Vietnam, farmers in Pho Yen district of Bac
Thai chose four common treatments (including one of intercropping cassava with peanuts and
establishing permanent vetiver grass contour hedgerows) and one "farmer's"
practice consisting of their individual current practice. In the other site, in Thanh Hoa
district of Vinh Phu, seven farmers each planted two replications of one selected
treatment in adjacent plots on 40% slope; one treatment involved cassava/peanut
intercropping with vetiver grass contour hedgerows. In Thailand, farmers in both Soeng
Saang district of Nakorn Ratchasima province and in Wang Nam Yen district in Sra Kaew
province chose 2-3 common practices (among which vetiver grass hedgerows), the farmer's
current practice as well as a farmer selected practice. The latter was the farmer's
individual choice of what he/she considered a most useful practice. This sometimes
included cassava intercropping with sweet corn or pumpkin, the use of dry grass mulch, or
contour barriers of mulberry bushes for feeding silkworms. Besides soil erosion control
trials, those farmers having mostly flat land participated in the project by conducting
trials on varieties, intercropping or fertilization practices (Table 5). The FPR teams,
consisting of researchers and extensionists, helped the participating farmers select the
most suitable site for each type of trial, to set out contour lines, stake out the plots
and construct the plastic-covered erosion channels at the bottom of each plot in the
erosion control trials (Figure 1). Planting material of new cassava varieties and the
selected hedgerow species, as well as fertilizers for the trials were usually provided by
the project, but farmers were responsible for the planting, weeding and maintenance of
their own trials. FPR team members visited the trials regularly to see the progress,
discuss any problems and try to find solutions. They also helped the farmers collect and
weigh the eroded soil sediments in each erosion channel, and to take samples of these
sediments to be dried and weighed to determine the moisture content, in order to calculate
soil losses on a dry weight basis.
1. Thailand
In both pilot sites, erosion was particularly severe in 1995 due to unusually heavy rain.
In Soeng Saang district, where cassava is planted as a monocrop on gentle (5-10%) but very
long slopes, large amounts of rain water ran down the slope along natural drainage
channels. This caused the formation of small gullies and washed out and exposed cassava
roots. The diversion ditches and bunds constructed above each trial were often inadequate
to stop this deluge, and sediments brought in from outside the plots often filled the
erosion channels, making it impossible to accurately measure the effect of each treatment
on erosion. In Wang Nam Yen district, slopes tend to be steeper but shorter and the
clay-loam soil has much greater aggregate stability, which resulted in less serious
erosion and less problems of sediments from outside the plots filling the erosion
channels.
Cassava as well as the vetiver grass hedgerows grew well in both locations. Other
hedgerows, like sugarcane (for chewing) or mulberry bushes did not establish so well and
left wide spaces between plants, causing water to run unimpeded down the slope. When asked
what practice they considered most effective in reducing erosion, almost all farmers in
both pilot sites mentioned the vetiver grass barriers. Some, however, considered sugarcane
or mulberry as attractive alternatives, since these crops can provide additional income.
One farmer also mentioned that mulch of dry grass was more effective in reducing erosion
than his vetiver grass barriers.
At the time of harvest, in each site a field day was organized to harvest together,
farmers, researchers and extensionists, the various FPR trials, to determine in each
treatment the average height of plants, and to pull out ten plants to weigh the fresh
roots and determine starch content using a Reihman scale. The results were tabulated and
written on large paper sheets to present to and discuss with the farmers.
Tables 6 and 7 show the average results of six FPR trials on erosion control harvested in
Wang Nam Yen district and nine trials in Soeng Saang district, respectively. Since only
4-5 treatments had adequate replication, only those will be considered. In both locations
cassava yields and starch contents were quite high (yields were about twice the national
average), while soil loss due to erosion was low to medium. However, the latter are only
rough estimates of erosion losses due to treatments, as some "additional"
sediments that were believed to have come with runoff from outside the plot (as discussed
above) were excluded.
In Wang Nam Yen district (Table 6) highest cassava yields and net income were obtained
with the "farmers' practice" of up/down ridging; however, this practice also
resulted in the highest soil losses due to erosion. Contour ridging produced slightly
lower yields but significantly lower erosion losses. Vetiver grass hedgerows produced
still lower cassava yields (partially due to space occupied by and competition from the
hedgerows) and net income, while being only intermediately effective in reducing erosion.
In spite of this, farmers overwhelmingly selected the vetiver grass as the best treatment,
probably in the expectation that once the grass is better established, the hedgerows will
become increasingly more effective in reducing erosion, while a better infiltration of
runoff water will reduce fertilizer loss and result in better soil moisture during the dry
season, while the mulching of vetiver leaves on the soil surface will help control weeds
and erosion and also conserve soil moisture, which may lead to improved yields. Thus,
farmers hope that the use of vetiver grass leaves as in-situ mulch, will give benefits
similar to those obtained in the grass mulch treatment (T7), but without the hard work of
carrying grass mulch onto the field from elsewhere.
In Soeng Saang district (Table 7) the "farmers' practice" of up/down ridging
produced the lowest yield and the highest erosion losses. Although this practice is
cheaper than any of the other practices tested, it still produced the lowest net income,
clearly showing to farmers that this practice is counter-productive. The vetiver grass
hedgerows produced the highest cassava yield and a high net income, while being the most
effective in reducing erosion. Contour ridging and planting sugarcane hedgerows were also
quite effective in reducing erosion and increasing net income. Based on these results
farmers from Noon Sombuun also overwhelmingly selected the vetiver grass as the best
treatment, with contour ridges and sugarcane hedgerows as second and third best,
respectively.
Most farmers were very interested in continuing the trials next year and requested
additional vetiver planting material to plant in their cassava fields outside the FPR
trials. That is probably the best sign of spontaneous adoption of the vetiver grass
technology. However, it still needs to be seen how extensive actual adoption is, because
farmers also mentioned that tractor drivers contracted to plow their cassava fields charge
considerably more for plowing along the contour than for plowing up and down the slope,
even on gentle slopes of less than 10%. This will be a deterrent for any farmer who wants
to establish contour hedgerows to control erosion. Thus, the benefit of contour hedgerows,
including that of vetiver grass, must also be conveyed to contract tractor drivers that
often determine the method of land preparation for cassava farmers.
2. Vietnam
Field days were also organized in Vietnam to harvest and discuss the results with farmers
in three pilot sites, i.e. in Kieu Tung village of Thanh Hoa district in Vinh Phu
province, and in Dac Son and Tien Phong villages of Pho Yen district in Bac Thai province.
During the field days, farmers looked at and discussed the amount of sediments in the
erosion channels of each treatment (sediments had been collected from the channels only
during the first two months, in order to let farmers see the erosion losses during the
rest of the year), and pulled up at random ten plants in each plot and weighed the roots
to estimate cassava yields.
Table 8 shows the results of total soil loss due to erosion, yields of cassava and peanut,
and the gross and net income from each treatment in Kieu Tung village. Soil losses did not
vary much among treatments, but were highest in those treatments with cassava monoculture,
or where cassava was intercropped with peanut, but without fertilizer application. Soil
loss was lowest in the treatment of vetiver grass barriers and cassava/peanut
intercropping. This treatment also provided the highest cassava and peanut yield and thus
the highest gross and net income. When asked, farmers overwhelmingly selected this as the
best treatment and requested additional planting material of vetiver grass to plant in
their own fields outside the trial plots. Similar results were obtained in Dac Son and
Tien Phong villages of Pho Yen district in Bac Thai province (Table 9). In both villages,
the treatment of cassava/peanut intercropping with vetiver grass hedgerows produced the
lowest amount of erosion and the highest or second highest net income. Based on these
results, farmers from both villages in Pho Yen district voted overwhelmingly for the
cassava/peanut intercrop with vetiver hedgerows as the most effective treatment to
increase their incomes and protect the soil from erosion. They too requested additional
planting material of vetiver grass for planting on their cassava fields next year.
During the course of the year, non-participating farmers from the village and those from
neighboring villages often visited and talked about the FPR trials. Several asked to join
the project in the coming year. It is hoped that when farmers themselves develop the soil
conservation technology that is most suitable for their particular conditions, and they
are able to see with their own eyes and through their own work what effect each practice
has on. crop yields and erosion, that they are more likely to adopt those practices
considered most effective. In the case of both Vietnam and Thailand this included the
planting of vetiver grass contour barriers to slow down run-off, enhance water
infiltration into the soil and thus reduce erosion.
Once farmers are convinced of the need to reduce erosion and committed to use soil
conserving farming practices, they will show their neighbors and teach their fellow
farmers about the best soil conservation practices for their region. We believe that
through a bottom-up approach and farmer participation in the development of effective soil
conservation practices for a particular region, farmers become more aware of the problem
of erosion and the need for soil conservation practices. Farmers are the stewards of our
soil resources - so essential for present and future food production - and thus should be
the ones directly involved in the development of practices that maintain the soil's
productivity for future generations.
The authors want to acknowledge the contributions and active participation in the project
by the following persons: Mr. Tran Ngoc Ngoan, Mr. Le Sy Loi, Mrs. Dinh Ngoc Lan and Mr.
Duong Van Hung of Agro-forestry College Bac Thai; Dr. Thai Phien, Dr. Nguyen Tu Siem and
Mr. Tran Quang Thong of the Nat. Inst. for Soils and Fertilizers in Vietnam; Mr. Anuchit
Tongglum, Mr. Danai Suparhan, Mr. Somphong Katong and Mr. Preechaa Saengsoda of the Dept.
of Agric.; Mr. Kaival Klakhaeng and Mr. Somnuek Hemwichit of the Dept. of Agric.Extension;
Mr. Chaawrai Kaanchanoomay of TTDI in Thailand; as well as the participating cassava
farmers in Vietnam and Thailand.
The authors also gratefully acknowledge the financial support for the project by the
Sasakawa Foundation in Tokyo, Japan.
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Referenced tables available on request The Vetiver
Network