MINISTRY OF AGRICULTURE AND COOPERATIVES, THAILAND

STATUS OF CASSAVA IN THAILAND:
IMPLICATIONS FOR FUTURE RESEARCH AND DEVELOPMENT

Department of Agriculture (DOA) Bangkok, Thailand

C. Ratanawaraha, N. Senanarong and P. Suriyapan

International fund for Agricultural Development (BFAD) Rome, Italy

The objectives of the study are:

To analyse the past and present situation of cassava in Thailand, with a view to describing the lessons learned from past development interventions and their implications for a strategy of future investment in cassava research and development

EXECUTIVE SUMMARY

Cassava (Manihot esculenta Crantz) is considered one of the most important economic crops in Thailand. However, cassava is not a staple food for Thai people; it is a cash crop produced by small farmers. Nearly all the harvested roots are processed into dry chips and pellets for export as animal feed, as well as into starch, both for domestic use and export. About 80% of the production is exported. The most important market is the European Union (EU). The production has steadily increased during the 1970s and early 1980s through expansion of the planted area to about 1.6 million ha in 1988/89, after which the area decreased again to about 1 million ha during the 1990s. The national average yield has been about 14.5 t/ha, which is higher than the world average, yet low compared with the potential of the crop. While the EU sets an upper limit to cassava importation from Thailand, it is widely felt that Thailand can no longer afford uncontrolled production increases by limitless area expansion.

Major production problems are declining soil fertility, soil erosion and the strong fluctuation of the cassava root price. Previous research by the Department of Agriculture (DOA) has resulted in the identification of a high yielding and very versatile local cultivar, Rayong 1. More recently several new high-yielding and high-starch cultivars have been developed. Latin American germplasm provided by CIAT is now well incorporated into the breeding population. The Department of Agricultural Extension (DOAE) and DOA have cooperatively created the cassava stake multiplication program to accelerate the distribution of the new high-yield and high-starch content varieties throughout the country. Agronomic practices, such as land preparation, stake selection and optimal planting time, have been studied.

Cassava roots are utilized by making dry chips, pellets, native starch, modified starch, and some other industrial products. Modified starch has been used for the paper, textile, food and beverages, plywood, glue, and alcohol industries. These products are exported to many Asian countries.

RESEARCH AND DEVELOPMENT

ABSTRACT

Cassava is one of the most important economic crops in Thailand. It is produced by small farmers on marginal land and its products are exported mainly to the European Union (EU). Production has steadily increased during the 1970s and 1980s through expansion of the planted area, but has decreased again since the early 1990s. The national average yield has been stagnant at about 14.5 t/ha, which is higher than the world average, yet low compared with the potential of the crop. While the EU sets an upper limit to the amount of cassava imported from Thailand, it is widely felt that Thailand can no longer afford uncontrolled production increases by limitless area expansion. For that reason, the government established a policy in 1993 to reduce the cassava growing area by at least 20%.

Major production problems are declining soil fertility, soil erosion and limited genetic diversity of the crop. Previous research conducted by the Department of Agriculture (DOA) has resulted in the identification of a high-yielding and very versatile local cultivar, Rayong 1, and more recently, the breeding and selection of several high-yield and high-starch cultivars. Latin American germplasm provided by CIAT is now well incorporated into the breeding population. High yielding capacity, high-starch content and early maturity are important selection criteria. Agronomic practices, such as land preparation, stake selection and storage, planting method, planting time, fertilization, crop rotation, intercropping and weed control have been studied. More emphasis is now being given to soil fertility maintenance, erosion control and labour-saving technologies. All these will lead to more efficient and more stable production, thus enhancing the competitiveness of Thai cassava products in the world market.

1.INTRODUCTION

Thailand is located in Southeast Asia, and is bordered by Myanmar on the west and north, Laos in the north and northeast, Cambodia in the east, and Malaysia in-the south. The-total area is about 518 000 km². The population was about 60 million in 1997. The northern part of the country consists mainly of mountains, which form the watershed from which rivers flow down to the Central Plain, where Bangkok, the capital, is located. Thailand has a wide range of topographical features, so the country can be divided into four ecological regions: the North, the Central Plain, the Northeast and the South.

During the decade from 1986 to 1996 Thailand produced annually between 18 and 24 million tonnes of cassava fresh roots. The area under cassava progressively increased from 1.2 million ha in 1985/86 to about 1.6 million ha in 1988/89; this was followed by a decrease to 1.1 million ha in 1997/98 (Table 1) (Figure 1).

After rice and maize, cassava occupies the largest planted area in Thailand. In the early 1970s cassava was grown mainly in the eastern part of the Central Plain, with only 30% grown in the Northeast, 6% in the North and 4% in the South (Table 2). Since then, however, the cassava production area has shifted from the Central Plain to the Northeast, while the area in the North has also increased gradually. Presently, about 60% of the cassava area is located in the Northeast, 27% in the Central Plain and 13% in the North (Figure 2).

The Northeastern region has a total area of 171 000 km² and accounts for about 33.1% of the total area of the country; it is about 150 m above sea level. There are only a few rivers in the area. The Southwest monsoon comes from the Indian Ocean and the Gulf of Bengal, providing rain to the region for about six months, i.e. from May to Oct. From Nov to Feb cold air comes from mainland China, resulting in a cool and dry climate. Consequently, drought is a frequent occurrence in this part of the country, giving cassava a certain competitive advantage over other crops.

2. CASSAVA PRODUCTION IN THAILAND

2.1 Climate, topography and soils

Thailand is located between 97.5° and 105.5° E longitude and 5° and 19° N latitude. The average annual rainfall is 1200 mm. The rainy season normally starts in May and terminates in Oct; the following six months are predominantly dry with each month less than 100 mm precipitation. The topography in the cassava growing areas is generally level to undulating. Soils have a pH between 4.5 and 6 in the surface and tend to be of low fertility, very low in N, low in K and rather low in P (Table 3). Soils recommended for growing cassava have a sandy loam to loamy sand texture. Drainage is moderate to excessive, but can also be poor if there is a subsurface hardpan. The mean soil temperature is about 20°C year-round.

2.2 Varieties and production practices

There are now several recommended cassava varieties in Thailand. Almost all cassava grown is of the bitter type, used for the production of animal feed and starch. Previously, the most popular variety was the local variety. It was introduced about 40 years ago. A selection from this local variety was named "Rayong 1" and was released in 1975. Its average yield is about 14 t/ha. According to the most recent report of the Field Crops Promotion Division, DOAE, in 1997 Rayong 1 variety covered only about 37% of the cassava growing area throughout the country. The rest of the cassava area was planted with several new improved varieties; the distribution of those varieties is shown in Table 4.

Table 1. Cassava planted and harvested area, production, yield, and farm gate root price in Thailand from 1977 to 1998.

¹⁾Yield based on harvested area

²⁾Average exchange rate during year of harvest

³⁾FAO, preliminary data

⁴⁾Estimated by Thai Tapioca Trade Association (1999)

Source: Office of Agriculture Economics, Agricultural Statistics of Thailand Crop Years 1976/77 to 1996/97

Source: Office of Agriculture Economics, DOA. 1975–1998.

Cassava area, production and yield in Thailand from 1975 to 1997. Source: Office of Agriculture Economics, DOA,1999.

Distribution of cassava growing areas in Thailand in 1995/96. Each dot represents 1000 ha of cassava. Source: Dept. of Agriculture Extension, 1998.

Table 3. Chemical and physical properties of soils in the main cassava growing areas of Thailand.

Source: Duangpatra, 1988.

Table 4. Area grown with various cassava varieties in Thailand in 1997.

Source: Field Crops Promotion Division, DOAE, 1999

To grow cassava on small farms, land is usually prepared by using animal power or small implements, such as a hand tractor, on larger farms land is prepared by four-wheel tractors. Custom service or hired tractors for plowing are now widely available. Ridges used to be made by oxen-drawn implements, but now mainly by tractor. It is customary to plow 15-20 cm deep once or twice with a tractor to bury residues of the previous crop. This is followed by harrowing once or twice. Cassava stakes can be planted directly in the soil when the land is prepared this way; there is no need to make furrows. In poorly drained land it is recommended to plant cassava on ridges. In Thailand, about 23-31% of the crop is planted in May, followed by 10-20% and 11-17% in April and June, respectively. Another 10-20% is planted during October or November, at the end of the rainy season. The most suitable time to plant is in May, June or July. There is a large reduction in yield if planting is delayed beyond July. Planting during the dry season from January to March is also practised, usually immediately after an occasional rainstorm.

Planting material is obtained from the previous crop or from neighbours' fields. Long stems are usually cut from 10 to 12 month old plants. At harvest, these stems are bundled and stacked upright, or are piled up horizontally. They are stored in the field under shade or in the open, sometimes covered with leaves until required for planting. Planting material taken from 6–12 month old plants produced over 90% survival of planted cuttings. When ready to plant, the immature top part as well as the woody part at the base of the stems are cut off. Stakes of desired length, usually 15–25 cm, are cut. Yields are not significantly affected by the length of cuttings within the range of 10–20 cm with 5-7 nodes, but less plants survive if shorter cuttings are used. Stakes are not treated with chemicals before planting.

Cassava planting is done either on the flat or on ridges, depending upon rainfall, soil texture, weeds, and method of harvest and tradition. Cassava is planted on ridges when the soil is likely to be wet, when weed problems are severe, or when the crop will be harvested by tractor-mounted digging tools; this makes the harvest easier. Planting on the flat is cheaper, it is also preferred in low moisture soil, or in areas with less assured rainfall. The method of planting varies depending on the moisture content of the soil, ease of operation and tradition. Vertical and inclined (slanted) planting are much more common than horizontal planting. Depth of planting is variable. With horizontal planting, the depth is about 3–5 cm, while in vertical planting it is about 8–10 cm.

There is a wide variation in row widths of cassava, mainly because of differences in soil fertility. It is usually 70-100 cm between rows with a plant-to-plant distance of 60-100 cm. Normally, a spacing of 100 × 100 cm is recommended. However, in low-fertility soils and on sloping land a spacing of 80 × 80 cm is recommended to obtain a higher yield and to reduce erosion.

More and more cassava is now being fertilized. A survey conducted in 1990/91 indicated that about 50% of cassava farmers applied some chemical fertilizers. Fertilizers are usually applied at the time of first weeding. Previously, the general recommendation was 50 kg/ha each of N, P₂O₅ and K₂O for fertile soil and 100 kg/ha each for poor soil. Presently, the use of a fertilizer grade in the ratio 2:1:2 is being recommended.

Weeding is usually done 2–3 times during the crop cycle, using a hoe or oxen-drawn plow; or, more recently, using herbicides. The first weeding should be done at 1–1.5 months after planting, followed by a second and third weeding at 2 and 3 months after planting, respectively. About 75% of all cassava is harvested in the five dry months of Nov to March (Figure 3).

The national average yield of cassava is about 14.5 t/ha. The average yield in the experiment station is about 25 t/ha, while the potential yield of the crop is between 50 and 80 t/ha (Cock, 1985).

Figure 3. Percent of cassava area harvested in each month in 1992 for the whole of Thailand.

2.3 Socio-economic conditions

The average land holding of cassava farmers in Thailand is 8.9 ha, of which 4.0 ha is under cassava, 1.47 ha under irrigated or rainfed rice and 0.57 ha under other upland crops. Most cassava farmers (68%) plant cassava in areas ranging from 1.0 to 5.75 ha.

Labour demand peaks occur in July for weeding and in Feb for harvest. If weeding is done manually, there is scope to decrease the labour requirement by introducing animal-drawn or tractor-mounted implements for inter-row cultivation, or by the use of herbicides.

In the early 1990s the total production cost was about US$320-350/ha (Table 5B). With an average yield of 14.0 t/ha, the production cost would be US$23-25/t fresh cassava. Average gross income from cassava for 1991 to 1994 was about US$437/ha. Annual net income during the same period was about US$106/ha or about US$425 per family of 5-6 persons (Table 5).

Table 5. Average production costs, income and profits from cassava production in Thailand for 1986/87 to 1994/95.

Source: Office of Agriculture Economics, Agriculture Statistics of Thailand, Crop Years 1988/89, 1993/94 and 1994/95.

In 1997 the production cost had increased to US$400/ha with labour accounting for about 75% of variable costs (Table 6). Cash inputs were equivalent to US$60/ha; this indicates the amount of credit needed by the farmers.

From Table 6 it is clear that labour costs in 1997 accounted for about 65% of the total cost, and one can imagine that in the future the labour cost may increase even more. Unless labour saving technologies are developed, cassava may not be grown anymore in this country (Yangmood, 1994).

The average labour requirement for cassava production was found to be about 96 man-days per hectare, of which family labour accounted for 50 man-days. The rest was hired labour, principally for harvesting, weeding and planting (Yangmood, 1994). The total labour cost (including imputed cost of family labour) was US$261/ha (Table 6). Labour demand peaks occur in July for weeding and in Feb for harvest. High-competition for labour occurs during the harvest season, because many other crops are harvested-at the same time, such as rice, sugarcane, and some fruits.

Table 6. Details of cassava production costs in Thailand in 1997.

¹⁾ US$1 is about 25 Baht in early 1997.

Source: Office of Agricultural Economics, 1997.

2.4 Constraints in cassava production

A survey of 259 cassava farmers conducted in 1997 indicate the following major production constraints (Rojanaridpiched and Sriroth, 1998):

1. low soil fertility
2. low yields
3. weeds
4. shortage of labour
5. shortage of planting material

2.4.1 Low soil fertility

As mentioned above, cassava is grown on sandy or loamy soils and on slightly or moderately undulating land; these soils tend to be of low fertility and are very susceptible to erosion. Serious erosion may result even on gentle slopes. Soil fertility has also declined by the growing of cassava continuously for many years without adequate fertilization. As such, cassava agronomy research is being conducted to reduce soil erosion and maintain or improve soil fertility.

2.4.2 Low yield

Being a low-value crop that is also well adapted to areas of poor soils and low or unpredictable rainfall, cassava is pushed more and more into the least favorable areas, mainly in the northeastern part of the country (Tables 2 and 3). Even with the use of improved varieties and cultural practices yields have therefore not increased.

2.4.3 Weeds

Cassava is quite susceptible to competition from weeds, especially at the early growth stage. Failure of timely weeding can cause a total loss of harvest. Weed control is traditionally done by animal drawn implements or by hand. Labour for weeding accounts for about 40% of total labour used, thus representing a major part of production costs (Table 6). To prevent heavy infestation by weeds during the rainy season, it is advised to weed 2-3 times during the first 2-3 months after planting.

2.4.4 Shortage of labour

With the industrial expansion of the late 1980s and early 1990s, much labour, especially young people, was drawn from the countryside to the cities. This has led to an acute shortage of farm labour, and increased wages. The economic crisis since 1997 has temporarily reversed that trend.

2.4.5 Shortage of planting material

Cassava is an annual crop that is propagated vegetatively. It is usually planted within one to two months after the roots of the previous crop have been harvested. Cassava farmers therefore produce their own planting material. Farmers who purchase cassava stakes are those who: (1) are planting cassava for the first time; (2) have stopped planting cassava, were unable to conserve planting material, and want to plant again; (3) wish to change varieties; and (4) wish to significantly increase the size of their plantings. A stake producer's volume of sales depends on the rush to obtain newly-released varieties or the need to rapidly increase the area planted, which, in turn, depend on trends in root prices.

PROCEEDINGS OF THE VALIDATION FORUM ON THE GLOBAL CASSAVA DEVELOPMENT STRATEGY

Rome, 26–28 April 2000

3. CASSAVA UTILIZATION IN THAILAND

3.1 Main uses

In Thailand rice is a staple food, while cassava has traditionally been considered as a snack food or for making starch used in desserts. The crop was usually planted in small areas near the house to dig up some fresh roots for making Thai traditional desserts.

Since the 1960s cassava roots are increasingly being used for production of dry chips and pellets, mainly for export. However, in some small villages in Northeastern Thailand farmers are experimenting with cassava chips as a substitute for more expensive cereals (mainly maize and broken rice) in animal feed. Local consumption of chips for animal feed was estimated at 800 000 tonnes in 1998 (Sriroth and Oates, 2000). Two to two and a half kg of fresh roots can produce about one kg of dry chips (14% moisture content).

Presently, more and more cassava roots are utilized for production of starch, both for export and domestic use (Table 7). About 40% of cassava starch is used domestically (Table 8), mainly as chemically or physically modified starch, as sweeteners or as native starch in various industries (Table 9). The remaining 60% is exported, mainly in the form of native or modified starch (Table 10). Exports of cassava starch and starch-derived products have increased dramatically, especially during the past ten years (Table 7 and Figure 4).

Table 7. Quantity (tonnes) of cassava products exported from Thailand from 1966 to 1998.

¹⁾ January-November only

Source: Thai Tapioca Trade Association, 1999.

Table 8. Total production and use of cassava roots in Thailand in 1994.

Source: Thai Tapioca Hour Industries Trade Association, 1994.

Table 9. Estimates of domestic uses of cassava starch in Thailand, by industry and in terms of native starch or fresh root equivalents (tonnes) in 1993 and 1994.

Source: Thai Tapioca Flour Industries Trade Association, 1994.

Table 10. Estimates of exports of cassava starch and derived products from Thailand in 1992.

Source: Thai Tapioca Flour Industries Trade Association, 1994.

Figure 4. Quantities of cassava products exported from Thailand from 1966 to 1997.

4. PROCESSING

Fresh roots are usually transported to cassava chip or starch factories on the same day of harvest. Storing period of fresh roots at the factory depends on the capacity of the factory and the amount of roots received. Roots are usually processed within 2–5 days. Chipping and drying of the roots or the processing into starch should be done not later than 4 days after harvest. The starch content was found to decrease from 24% at harvest to 20% at 4 days and to 11% at 6 days after harvest. The starch quality is also affected by delays in processing.

4.1 Chips

Cassava chipping and drying yards are small-scale enterprises often belonging to farmers; they are located near the cassava growing areas. The equipment consist of a chipping machine and a front-end loader, and chips are dried on a cement floor often covering more than one hectare.

The production of cassava chips involves two steps, i.e. chippings and sun drying. Fresh cassava roots are fed into the hopper of a chipping machine, mounted on wheels to facilitate the distribution of chips on the drying floor. These chipping machines have a rotating circular steel plate about 100 cm in diameter. The blade consists of a 1.0–1.5 mm steel plate which is corrugated at the cutting edge. The chipping machine produces about 3-cm diameter size chips. This can be reduced by narrowing the opening in the cutting plate. The capacity of these chipping machines could be increased if the feed rate and the cutting blade were more uniform (Thanh, 1974). This could be achieved by the use of a conveyor belt, as used in the starch factories for feeding the rasper (Manurung, 1974).

The common practice in Thailand is to chip the roots early in the morning. The fresh chips are distributed by pulling the chipping machine across the drying floor while chipping; the chips may also be spread out manually with the use of a rake. The spread-out chips are turned over every 1–2 hours, using a small vehicle with a special tool attached to the front, to speed up sun drying. The duration of sun drying is dependent on the weather, the chip size, and loading rate on the floor. Usually, without rain, it takes three days to dry the chips to 12-14% moisture content.

4.2 Pellets

The production process for cassava pellets is shown in Figure 5. There are approximately 200 pellelizing factories in Thailand with a total capacity of about 10 million tonnes per year. Because of lack of sufficient markets they operate at only about 50% of capacity (3–4 months per year) (Sriroth and Oates, 2000).

After removal of sand and other impurities, the dry chips are ground in a hammer mill. Cassava particles together with steam are forced through holes in the die. The compressed material emerges hot from the other side of the die; after cooling the strands are cut to length to produce pellets. The pellet diameter ranges from 5 to 6 mm and the length from 15 to 20 mm.

4.3 Starch

In 1996, Thailand had 41 modern cassava starch factories registered with the Thai Tapioca Flour Industries Trade Association. The peak of the starch processing season is from Oct till March, when most farmers harvest their cassava roots. During the processing season many starch factories have a shortage of working capital to buy cassava roots. Due to a lack of capital the millers have no choice but to sell the cassava starch as soon as possible. This reduces the price. To improve the situation, loans have to be provided by the government.

The production process for cassava starch is shown in Figure 6. Production of one tonne of native starch requires 4–5 tonnes of fresh roots and 30–40 m³ of water.

Figure 5. Process for production of cassava pellets. Source: Sriroth, 1999.

4.4 Modified starch

There are three methods to make modified starch in Thailand, i.e.:

1. Degradation or conversion: starch is rendered less sticky in three ways:
   1. Acid conversion: Hydrochloric and sulfuric acids react with starch liquid to decrease the degree of stickiness, and to reduce the temperature of gelatinization. This starch is called “acid modified starch”.
   2. Oxidization: Starch reacts with chloride in alkaline starch liquid. The starch thus derived will become less sticky with the degree of chloride used and the reaction time. This starch is called “oxidized starch” or “hypochlorite modified starch”.

   3. Dextrinization or pyroconversion: Starch is roasted in a drum under high temperature, while certain acids are sprayed to react with it. This process will make the starch less sticky. The product is called “dextrin”, which consists of three types: white dextrin, popular yellow dextrin, and British gums. The converted starch is suitable for the glue industry.

2. Pregelatinization: Liquid starch in 40–50% concentration is drum-dried. Starch is cooked and dried to form a thin crispy layer. It is ground and sifted to obtain a fine powder, which immediately becomes a glue when cold water is added to it. The starch at this stage is called “cold water soluble starch” or “alpha starch”.

3. Derivatives: These are processed starches whose molecular structures havebeen altered through chemical reactions. Examples in this group include esters (acetated starch and phosphoric acid ester), starch ether (carboxymethyl etherand hydroxy-ethyl starch), and cross-linked starch. (Thai Tapioca Flour Ind.Trade Assoc., 1994).

5. MARKETING

The principal market for Thai cassava products is the EU, which in 1997 absorbed about 64% of the total Thai cassava exports (Tables 11 and 12). The EU has set an annual quota for Thai cassava imports of 5.25 million tonnes for the years 1995 and 1996, with a possible reduction in the future. Within this quota the cassava products can enter the EU market at the current preferential tariff of 6%, and beyond the quota it will be subject to a 30% tariff. However, due to competition from other feed grains the price paid for cassava pellets in the EU has decreased, making it less attractive to produce and market cassava pellets. For that reason Thailand has not met its quota for the past five years (1994–1998).

Figure 6. Flow diagram of cassava starch manufacturing process. Source: Sriroth, 1999.

5.1 Fresh cassava roots

Within the cassava plant, starch accumulates mainly in the swollen roots. The moisture content of the root is about 60–65% by weight. The farm gate price for fresh roots has been highly variable, fluctuating from about 800 to 2000 Baht per tonne, with a starch content of 25% (Figure 7); farmers are usually paid a higher or lower price according to the starch content of the roots. The low price of fresh roots in 1996/97 was caused both by overproduction (stimulated by the high price in 1995/96) and the low price of cassava pellets and starch on the world market, due to an ample supply of relatively cheap corn, wheat and potato starch.

5.2 Dry cassava chips and pellets

In Thailand cassava dry chips are used exclusively for production of animal feed. Each year Thailand exports dry cassava chips and pellets to the EU market (maximum of 5.25 million tonnes under the quota system), while the rest is exported to non-EU markets (Tables 11 and 12).

The price of chips and hard pellets is highly fluctuating (Figure 7), depending on the price of competing commodities on the world market, such as wheat, barley, maize etc. This in turn influences the price paid for fresh roots, which is also highly variable. The latter, however, is also determined by the price of starch, as both the starch and pellet industries compete for the same raw material (Figure 7).

Table 11. Trends in the exports ('000 t) of cassava chips, pellets and starch from Thailand to the EU and outside the EU.

Source: Customs Department and Board of Trade of Thailand.

Table 12. Quantity (tonnes) and destination of cassava products exported from Thailand during 1996 and 1997.

Source: Board of Trade of Thailand, 1998

Figure 7. Monthly variation in domestic price of fresh cassava roots (Baht/kg) and the FOB Bang] price (US$/tonne) of cassava starch and hard pellets from Dec 1993 to Dec 1998. Source: Thai Tapi Trade Assoc. (TTTA), Yearbook 1998.

5.3 Starch and its derivatives

Cassava starch is not only produced for domestic use but also for export, which produces annual revenues of about 250–300 million US$ (Table 10). Products with the fastest growing export markets are modified starch and sorbitol. Producing modified starch adds about 60% to the price of native starch and nearly 200% to the price of roots required for its production (Table 13).

Native starch can be consumed directly, but can also be used as a raw material in a variety of industries, e.g. food, sago pearl, transparent vermicelli, instant noodles, seasoning powder (monosodium glutamate), sweetener, paper, plywood, textile and bread (Table 9).

Starch plays a significant role in the daily lives of consumers, either directly or indirectly, in the form of processed products and as an ingredient for the production of many other products. But, its potential uses have not been exhausted. At present, there is a lot of research being conducted with the aim of converting starch into other value-added products.

Table 13. Price links among modified starch, native starch, and roots as well as marketing and processing costs, obtained from a 1991 industry survey.

¹⁾ Exchange rate is 25.50 Baht = US$1.00 in 1991. Source: Titapiwatanakun, 1996.

6. RECENT PROGRESS IN CASSAVA RESEARCH

All cassava research undertaken in Thailand aims to improve production and processing efficiency and to broaden markets.

The national average yield of cassava is 14.5 t/ha in Thailand, but experimental yields may be 50 t/ha or more. There are now new clones with much higher yield and root dry matter content than Rayong 1. Hence, there is still much room for yield improvement through breeding and improved cultural practices under Thailand's conditions.

6.1 Germplasm collection, evaluation and improvement

In Thailand, cassava breeding is the responsibility of the Rayong Field Crops Research Center (Rayong-FCRC) of the DOA, as well as of Kasetsart University (KU).

6.1.1 Germplasm collection and evaluation

Before 1960 some twenty cultivars were introduced, mainly from Malaysia, Indonesia and Mauritius. During the 1960s more clones were introduced, from Indonesia in 1963, and from the Virgin Islands in 1965. The first introduction from CIAT was in 1975.

Thailand has presently a collection of 348 cultivars, including three local cultivars, five from Indonesia, 21 from the Virgin Islands, 14 from CIAT and 305 clones from open pollinated and hybridized seeds. Out of these 305 clones, 89 are progenies of hybrid seed from CIAT/Colombia and 216 clones are from the Thai breeding program. Seedlings obtained were selected according to yielding ability, disease and insect resistance, and plant type. Only high performance clones are maintained and further observed.

The germplasm collection is maintained by annual planting in the field at Rayong Field Crops Research Center located in the east, while some accessions of the collection are duplicated at Khon Kaen Field Crops Research Center, located in the northeastern part of the country. The DOA also plans to use tissue cultures for germplasm conservation and exchange. A few cassava clones were introduced from CIAT in the form of tissue culture. This cassava germplasm has been extensively utilized in the breeding program.

Cassava germplasm accessions are being observed and evaluated for root yield, starch content, dry matter content, HCN content, harvest index, disease and pest incidence, germination, vegetative vigor, plant height, branching habit, earliness, daily yield, number of roots/plant, root colour and shape, root perishability, flowering habit, stem colour, leaf colour and shape. Chemical analysis for protein content, HCN content, starch content, and fiber have been done for some accessions in the breeding program.

The introduction of cassava germplasm from CIAT through sexual seed started in 1975. From this first introduction, Rayong 3 was selected. Ten clones were also introduced in the form of meristem culture form CIAT in 1979. Introductions from CIAT of seed populations from better-defined cross parents started in 1982. Many of these introductions have since been utilized in the breeding program.

6.1.2 Germplasm improvement

Cultivar Rayong 1
Cassava breeding research began with the collection of local cultivars throughout the country and their systematic evaluation in 1956 at Rayong-FCRC, Rayong province. There were not many genotypes, and many cultivars from different locations were identified to be the same genotype. This was called “Local Rayong” to be used in comparison with introduced cultivars. It was found that “Local Rayong” had higher yields than all introduced cultivars from Indonesia, the Virgin Islands and CIAT. So, this cultivar was named “Rayong 1” by the Department of Agriculture in 1975.

The breeding program based on open-pollinated seeds from Rayong 1 and introduced cultivars, started in 1971. Not much was gained from the selections of open-pollinated seeds. Controlled hybridization started in 1975 by utilizing a limited number of germplasm accessions from Indonesia, the Virgin Islands and from CIAT. Large introductions of cassava germplasm from CIAT, mostly as sexual seed, have contributed to increased genetic variation. Many crosses are being made between Thai and CIAT clones every year, supplemented by a fewer number of crosses among Thai clones. Many hybrid seeds from CIAT have been directly incorporated into the testing program. From CIAT hybrid seeds introduced in 1975, two cultivars were selected: Rayong 3 selected from CM 407, and HP 6 from CM 305 (Sinthuprama and Tiraporn, 1984).

With the return of several researchers trained at CIAT since 1977, the breeding program at Rayong-FCRC began to form into a core of the national program (Sinthuprama and Tiraporn, 1984).

Breeding objectives. The major objectives of cassava breeding are:

1. high yield potential, in terms of dry matter and starch
2. early harvestability
3. diversification of genetic base
4. resistance to pests and diseases

Breeding to produce high yielding cultivars is based on high yield, high harvest index and high root dry matter content. High yielding cultivars will contribute to higher productivity, hence lowering the cost of production per tonne and improving the competitiveness of cassava vis-à-vis other feed grains. Higher root dry matter content will lead to a reduction in the cost of processing.

Breeding for early harvestability is done by selection for high yield at an early harvest date. Early cultivars will increase the opportunities for more efficient land use by allowing double cropping and crop rotations; these may also improve soil fertility and reduce erosion (Sinthuprama et al., 1993). Breeding for pest and disease resistance includes resistance or tolerance to CBB and red spider mite.

Breeding cultivars suitable for intercropping has been another selection target.

Methodology of the varietal improvement program
The Thai cassava breeding program includes every step of varietal improvement, including germplasm collection, hybridization, F₁ seedlings trial, single-row trial, preliminary yield trial, standard yield trials, regional trials and on-farm trials.

15 000 to 20 000 F₁ seedlings are evaluated annually and about 10% of these plants are selected for the single-row trial. About a 5% selection rate is practised in the single-row trial, as well as in the following stages of selection, up to the regional trial. All the trials, up to the preliminary yield trial, are conducted at Rayong-FCRC. Standard yield trials are planted in three major research stations, and regional trials are conducted throughout the country in major cassava growing areas. While the majority of the experiment stations are located on rather fertile soils, the soil fertility at Rayong-FCRC is generally low, so that it can well represent the majority of cassava growing areas (Sinthuprama and Tiraporn, 1984).

Promising clones from regional yield trials, usually three to five, are tested in on-farm trials. The trials are conducted by using farmers' land and labour, but the management input is contributed by the researchers. The number of trials depends on the resources available.

The best clone(s) is/are compared with the farmers' crop in farmers' fields using farmers' agronomic practices. Many large plots are required and extension workers participate in the evaluation.

The best selection is named and released as a new variety by the Department of Agriculture.

From 1975 until 1998, Rayong-FCRC of DOA and KU have released six cultivars for industrial use and one cultivar for human consumption. The background and the outstanding characteristics of those cultivars are described in Table 14.

6.2 Agronomic research

The objective of the agronomic research is to develop improved production technology that will lead to high and stable production using the best available cultivars. The major recipients of the technology are small farmers; thus, the technology must be suitable and affordable for the majority of small farmers.

The principal research topics have been land preparation, quality of planting material, planting time, planting methods, plant populations, replanting, weed control, fertilization, stake multiplication, harvesting, as well as the mechanization of harvest.

Cassava fertilization and soil conservation research aimed at increasing or conserving soil fertility and enhancing the sustainability of production. Rotation experiments aimed at controlling water erosion and replenishing or recycling nutrients that were removed by the crop or were leached down the profile.

Research on the long-term effect of various soil management practices on cassava production was conducted by planting continuously for 15 years in the Northeast; it showed that cassava planted in rotation with sequentially planted peanut and pigeon pea could maintain a high relative yield of 87% of that obtained by the same cropping system during the first year of planting. Also, application of some lime and fertilizers could reduce the rate of yield decrease.

Research about the optimum period of weed control for Rayong 60 and Rayong 90, planted either in the early or late rainy seasons in the Northeast, indicate that both cultivars need to be free of weeds at least during the first three months after planting.

Weed control research also aimed to develop weed control practices to reduce labour requirements during periods of high labour demand. The most appropriate weeding method for cassava intercropped with either mungbean or peanut was to control weeds at planting by the application of a pre-emergence herbicide like Metholachlor at a rate of 1.50 kg/ha, followed by that of a post-emergence herbicide like Paraquat at a rate of 0.50 kg/ha by spot treatment whenever necessary.

Table 14. Background and outstanding characteristics of cultivars released in Thailand.

Source: Limsila et al., 1996.

Cropping systems research aimed to develop practices for soil nutrient conservation and soil erosion control. The research emphasized on intercropping cassava with grain legumes. Studies have been conducted to identify the best legumes to be grown in association with cassava, that will cause a minimum reduction of cassava yield, requires minimum additional inputs and have economically attractive returns.

Some specific findings are as follows:

• Land preparation. Zero tillage combined with application of a post-emergence herbicide (Paraquat) to kill the existing weed population gave a similar cassava yield as traditional land preparation, which includes one plowing by tractor plus furrowing by animal. Minimum tillage may be introduced for the control of soil erosion and for reducing production costs.

• Stake storage. Stems stored up to 30 days in the field had a survival rate of more than 80%. Storage under shade tended to be better than storage under full sunlight.

• Stake size and planting method. Yields were not significantly affected by the length of the stake in the range of 10–30 cm, even though shorter stakes gave a lower survival percentage. Root yields were not different for cassava planted on the ridge, on the flat, or on the flat followed by earthing up 30 days after planting. Horizontal planting gave lower yields than vertical or inclined planting (especially when planted in the dry season); the latter two methods were not statistically different in terms of yield. Depth of planting (5, 10 and 15 cm) had no significant effect when stakes were planted either vertically or inclined (Tongglum et al., 1992).

• Planting time. A study on planting time and age of harvest, carried out for three years from 1976 to 1978, indicate that the root yield was highest when cassava was planted in June and decreased if planted later than June. Root yields increased with age of harvest from 8 to 18 months.

• Fertilization. Fertilizer trials show that cassava in Thailand responded mostly to application of N, moderately to P and less significantly to K. In one experiment, the root dry matter yield responded positively to 90 kg/ha each of N, P₂O₅ and K₂O, but beyond that level it responded negatively. Broadcasting, banding under the stake, or sidedressing at 20 or 50 cm were found to be equally good fertilizer placement methods.

  The long-term effect of fertilization on cassava grown on three soil series has been studied since 1975. The effect of application of municipal compost applied annually at the rate of 12.5 t/ha or incorporation of crop residues (stems and leaves) on root yield was highly significant. It was concluded that high root yields of cassava could be maintained by the annual application of 50 kg/ha each of N, P₂O₅ and K₂O, and a further response could be obtained if compost or crop residues were incorporated before planting. On sandy loam soils in Khon Kaen, K was the most limiting nutrient (Howeler, 1995).

• Crop rotation. Long-term rotation experiments in three research stations showed that in the two rotation patterns of cassava/peanut and cassava/mungbean, cassava yields in the fifth and sixth crop year were higher than when cassava was planted continuously without rotation. After six years there was a slight increase in soil organic matter due to crop rotation.

• Intercropping. Land use efficiency and restoration of soil fertility through intercropping have been studied since 1970, using peanut, mungbean and soybean. The most promising intercropping system appears to be cassava and grain legumes, which were shown to have a combined economic yield of 170% relative to cassava monoculture. This was also confirmed in large plots on farms.

• Weed control. Application of the pre-emergence herbicide Diuron, at the rate of 1.5 kg/ha, caused no crop injury using either vertical or horizontal planting methods of cassava. These practices were as effective as three times of hand weeding.

• Erosion control. Since cassava gives a good yield in sandy soil, but has slow initial growth, soil erosion may occur, especially on sloping or slightly sloping land. During the past 15 years the DOA, DOAE and CIAT have worked together closely to develop effective methods to reduce soil erosion in cassava fields. In 1987 an experiment was set up in Pluak Daeng which included 16 treatments to reduce soil erosion in cassava fields. The treatments varied from zero tillage to ridging and intercropped with mungbean, soybean and cowpea etc. It found that preparing the soil with a seven disk-plow and intercropping with mungbean (four rows) gave the best result in terms of preventing soil erosion (Tongglum, 1994).

  Since 1994, DOA and DOAE have worked closely with CIAT in the execution of the Nippon Foundation-supported project. This project introduced a rather new approach of farmer participatory research (FPR), in which researchers help farmers conduct their own experiments on their own farms. This approach is particularly effective in enhancing the adoption of soil conservation practices, as it gives the farmers the opportunity to see with their own eyes the magnitude of soil erosion in their fields, and how certain agronomic practices can markedly reduce these soil losses.

6.3 Processing Research

Experiments are being conducted (Sriroth, 1999) for the use of cassava starch in making biodegradable plastic bags, or some other plastic materials to substitute for conventional plastics. The latter are causing serious environmental problems, since they are difficult to decompose. When buried into the soil, they do not biodegrade; when burned, the incandescent heat damages incinerators and they pollute the air with toxic gases. Recently, the use of aliphatic polyesters is becoming very important for the production of starch-based plastics. The commercial biodegradable plastics composed of gelatinized starch contain a lot of polycaprolactone (PCL). Today, two types of biodegradable plastics are commercially available, i.e. starch-based plastics and aliphatic polyesters. Cornstarch can also be used as raw material. Last year, Japan's National Institute of Bio-science and Human Technology began work with the Thai's TTDI and Mahidol University in a joint Thailand-Japan International Research Project, the goal of which is to develop a useful biodegradable plastic using cassava starch (Tokiwa, 1997).

7. GOVERNMENT POLICIES CONCERNING CASSAVA

Agriculture has maintained its importance in the Thai economy in the past and present, and will undoubtedly be in this position for a long time in the future. A major component of Thailand's exports still consists of primary commodities of agricultural origin. The output of some major crops, such as rice, cassava, rubber, sugar, etc. have been planned to gradually increase. However, the quantities exported depend on the amount of surplus supply over domestic consumption.

Prices of most agricultural products are dependent on world prices. As Thailand has become a member of the WTO, we have to consider the effect of free competition of commodities. To help poor cassava farmers, our government has to stabilize the cassava price by guaranteeing a minimum domestic price. Most of the price uncertainty is usually passed on from those who have strong market power to those who have weak bargaining power, i.e. usually the farmers. To help these farmers, the government has taken a lot of measures to stabilize the price and raise the income of farmers.

7.1 Production policies

More than half of Thai cassava products are exported to the EU, where, since 1993 they have to compete with cheap domestic grain in the production of animal feed. This has led to a marked reduction of exports of cassava pellets, which in turn reduced the price of cassava roots in Thailand. The planted area must therefore decrease to prevent over-production and hardship for farmers. With that objective the cassava growing area in Thailand has been divided into “favourable” and “non-favourable” zones. Only the growers in the “favourable” zone will receive government promotion services.

Growers outside the zone will be encouraged to replace cassava with other crops. Research is under way to find crops to replace cassava in these regions. Thus, the future trend of cassava production will depend strongly on the market, and the market will be dependent on production costs. If no improvement in production-efficiency is attained, there will be little hope for improving cassava's competitiveness in the international market. At the present, market demand is largely dependent on EU policies. If, however, a significant reduction in prices-of cassava products can be achieved through improved production efficiency, then there will be increased opportunity to create new export markets.

In 1992 the Thai Tapioca Development Institute (TTDI) Foundation was established, using funds collected by the government from cassava exporters. The objective of this institute is to help in stake-multiplication of new cassava cultivars and to distribute these free of charge to farmers. The institute also trains cassava farmers in the use of new cost-saving technologies. Every year about 7 000 cassava farmers receive a two-three-day training at the TTDI Research and Training Center in Huay Bong, Nakhon Ratchasima.

In 1991, The Department of Agricultural Extension (DOAE) and the Department of Agriculture (DOA) also created the “Cassava Stake Distribution Program” to accelerate the dissemination of high-yielding and high-starch varieties throughout the country.

7.2 Marketing policies

In Thailand, cassava is produced mainly for export rather than for domestic use. Most cassava output is exported to the EU. However, the amount of cassava exported to the EU is limited by an annual quota of 5.25 million tonnes. Under this quota the exportation is subject to an especially low import tariff. The high cassava pellet price in the EU has in the past been quite attractive to exporters. In turn, exporters have been able to pay a reasonable price for fresh roots of cassava. This has resulted in the expansion of the cassava growing area. But since 1993 the Common Agricultural Policy (CAP) of the EU has been reformed, resulting in a gradual lowering of the support prices for European domestic grains, thus making these grains more attractive than Thai cassava pellets in the formulation of animal feed. As such, the amount of cassava produced in Thailand is larger than the amount sold in the EU market. The price of cassava products has fluctuated drastically depending on market demand at any particular time. This in turn, affected the price of cassava roots which the farmers received (Figure 7).

Before 1997 the only important market for Thai cassava was the EU, which absorbed more than half of the Thai cassava exports. To stabilize the price, the government allocated a certain export quota to each exporter based on two criteria:

1. The amount of cassava dry chips and pellets in stock by each individual exporter
2. The amount of cassava products the company had exported to non-EU markets

Now the policy has changed, the export quota of cassava products has been lifted. The concerned members of the cassava trade associations (the affiliate members of the Thai Chamber of Commerce) jointly agreed that quota allocations based on stock-checking and previous quotas should not be continued, as it leads to monopolization by those companies that were awarded quotas in the past, and it will not stimulate the buying of-cassava roots from farmers.

In 1996/97 cassava fresh root production reached about 18 million tonnes. If nine million tonnes of fresh roots were used to produce starch, there would be a balance of fresh roots to produce chips and pellets of about nine million tonnes, equivalent to about 3.6 million tonnes of pellets, which would not be enough to fulfil the cassava quota in the EU.

8. FULFILLMENT OF OBJECTIVES AND SCIENTIFIC ADVANCES

8.1 Varietal improvement

From 1975 to 1999 six new cultivars have been released for industrial use, i.e. Rayong 3, Rayong 60, Rayong 90, Rayong 5, Sri Racha 1, and Kasetsart 50. All these recommended cultivars are widely adopted by the farmers, but the area planted with improved cultivars was increasing rather slowly due to the low multiplication rate of cassava. For that reason, in 1992 the government approved the allocation of 11 million US$ for the DOA and DOAE to rapidly multiply stakes of those cultivars and distribute them to the farmers. New varieties are now being grown on about 660 000 ha, or 64% of the planted area.

8.2 Improvement of cropping systems with cassava

Normally cassava in Thailand is grown as a sole crop. Intercropping of cassava is practised to a very limited extent. It can be intercropped with either maize or leguminous crops. In turn, cassava can also be intercropped between rows of young oil palm or rubber trees.

Legumes, mostly soybean, peanut and mungbean have been successfully intercropped with cassava in experimental systems. Yields of both legumes and cassava are usually reduced due to crop competition, but total yield or income may be quite high. Peanut is the most suitable crop, followed by mungbean. Soybean is the least suitable because of its poor adaptation to the type of soils in which cassava is grown. It is recommended that two rows of peanut spaced at 10 × 10 cm be planted between cassava rows spaced at 1 m. (Sinthuprama et al., 1993). Cassava farmers are well aware of the problem of soil erosion, and many are now adopting certain measures to control erosion. In one pilot site of the FPR project, in Sra Kaew province, about 30 farmers have already planted contour hedgerows of vetiver grass to prevent soil erosion; they may also intercrop with mungbean or peanut to increase their income.

8.3 Improvement of cassava harvest and post-harvest handling techniques

To encourage farmers to develop a new, suitable machine for digging or harvesting roots of cassava, TTDI, DOAE and DOA organized a contest of cassava harvesting implements attached to an 87 horsepower tractor in 1998. Many farmers and mechanics entered their inventions in the contest, and one to two most suitable harvesting tools were selected for further production and dissemination.

9. LESSONS LEARNED FROM PAST EXPERIENCES AND FUTURE STRATEGIES

9.1 Labour

The labour requirement can be divided into two parts, i.e. labour in the field to produce cassava roots, and labour needed for production of dry chips and pellets or cassava starch. Nowadays, the high cost of labour is a topic of daily discussion. Growing cassava is presently done mainly by hired labour. To improve production costs it is absolutely essential to reduce the labour requirements for production, through the development of more effective weed control practices (both mechanical and chemical), and planting and harvesting tools. Harvesting with a tractor-mounted cassava digger is now practised in some parts of the country.

9.2 Role of women in cassava production

In Thailand, growing cassava is usually carried out by both men and women. Nowadays, the cassava planting has become more and more mechanized. This results in less time spent on preparing the land and in the harvest of the fresh roots. The harvest uses female labour mainly for pulling up plants and cutting-off roots, while male labour is used for pulling up plants and loading of trucks. Since cassava is not a staple food of Thai people, Thai women are not much involved in the processing of starch or the preparation of cassava dishes.

9.3 Cassava research capacity building

Cassava research personnel has gradually increased over the years; a total of 18 researchers are now working on cassava, six in varietal improvement, four in cultural practices, five in soil science, one in entomology, one in postharvest technology and one in stake multiplication. In addition, there are some people working part-time on regional trials at research stations in different parts of the country.

CONCLUSIONS

Major cassava production problems in Thailand are declining soil fertility, soil erosion and limited genetic diversity of the crop. Previous research conducted by the DOA has resulted in breeding and selection of high-yielding and high-starch content cultivars. Latin American germplasm provided by CIAT is now well incorporated into the whole breeding system. Agronomic practices, such as land preparation, stake selection and storage, planting method, planting time, fertilization, crop rotation, intercropping and weed control have been studied. More emphasis is now being given to soil fertility maintenance, erosion control and labour-saving technologies. And also to enhance farmers' awareness of soil erosion by the introduction of a rather new approach of farmer participatory research, in which researchers help farmers conduct their own experiments on their own farm. This approach is effective in enhancing the adoption of soil conservation practices, as it gives the farmers the opportunity to visualize the magnitude of soil erosion in their fields, and to develop agronomic practices that can markedly reduce these soil losses.

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