Farmer Participatory Selection of Vetiver Grass as the Most Effective Way to Control Erosion in Cassava-based Cropping Systems In Vietnam and Thailand1

Reinhardt H. Howeler2 , Nguyen The Dang3 and Wilawan Vongkasem4

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 Farmer Participatory Approach to Soil Conservation

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 Sasakawa Foundation FPR Project

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.

Results of FPR Soil Erosion Control Trials

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