Agroforestry Systems 36: 83-104, 1997. © 1997 Kluwer Academic Publishers, Printed in the Netherlands.

Imperata management strategies used in smallholder rubber-based farming systems

H. B A G N A L L - O A K E L E Y 1, C. C O N R O Y z, A. F A I Z 3, A . G U N A W A N 4,

A . G O U Y O N 5, E. P E N O T 6, S. L I A N G S U T T H I S S A G O N 7, H. D. N G U Y E N 8

a n d C. A N W A R 9 ~ Natural Resources Institute, UK; ZNatural Resources Institute, UK; 3Rubber Research Institute of Malaysia; 4Rubber Research Institute, Sembawa, Palembang, South Sumatra, Indonesia; sCIRAD - CP, Paris, France; 61CRAF Regional Office, Bogor, Indonesia; 7Office of Rubber Replanting Aid Fund, Bangkok, Thailand; 8Rubber Research Institute of Vietnam; 9 Rubber Research Institute, Sembawa, Palembang, South Sumatra, Indonesia

Key words: farming systems research, Hevea brasiliensis, lmperata cylindrica, jungle rubber, rubber, smallholder, Southeast Asia, transmigration, weed control

Abstract. A large proportion of global natural rubber production takes place in Southeast Asia. The majority of this rubber is produced by smallholders. Thailand, Indonesia and Malaysia are the three principal countries involved. In Malaysia and Indonesia the smallholder sector accounts for 72% and 84% of total rubber production respectively. In other countries rubber plays a significant role on a more local basis, lmperata is a serious problem for the smallholder rubber farmer in most of Southeast Asia in three respects: the high cost (labour and/or capital) of opening lmperata-infested land, its competitive effect on rubber and annual intercrops, and the fire hazard that it poses during the dry season as a major source of combustible material. The costs of lmperata to smallholders are substantial in terms of a direct loss through fire and revenue foregone or delayed as a result of competition. Most smallholders intercrop their rubber during the first 1-3 years after planting it, and during this period lmperata is reasonably well controlled. Intercropping is only feasible for a limited period because of limited soil fertility and/or the shading effect of the rubber trees. After intercropping, lmperata tends to establish itself for a few years until it too is shaded out by the rubber. This is the problem period, during which farmers practise only limited weed management, if any.

A large amount of research has been done on methods of controlling lmperata, but the recommended methods have been generally spurned by smallholders unless they have been given subsidies to apply them. This paper describes the precise nature of the Imperata problem, with reference to some of the smallholder rubber-based farming systems within Southeast Asia; the different lmperata control strategies currently practised in these farming systems; and some of the constraints on the adoption of currently and recently recommended practices. It then proposes a ten-point agenda for research on lmperata control, including two ways in which current research programmes could be usefully reoriented: first, they need to take greater account of smallholder farming systems and constraints; and second they should shift their emphasis from single-method to integrated control systems.

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Introduction

Contribution of rubber smallholders in Southeast Asia

The principal rubber-producing countries in Southeast Asia are Indonesia, Malaysia and Thailand. In all three countries smallholders produce more than half of the rubber. In Indonesia, the 1992 total rubber production was 1,293,860 tons, of which 959,481 tons (74.2%) were produced in Sumatra and 229,935 (17.8%) in Kalimantan (Direktorat Jendral Perkebunan, 1992). There are about 1.3 million households relying on rubber production in Indonesia. The smallholder sector accounts for 84% of the country's rubber area, and 72% of the rubber produced. This contribution is expected to increase: both the second 25 year plan and the sixth 5 year plan (PELITA VI) have established the expansion of smaltholder production as a national priority.

In Malaysia rubber is one of the major crops apart from oil palm and cocoa. The area planted with rubber in Peninsular Malaysia was 33.1% of the total cultivated area (RRIM, 1993). The rubber growing areas can be classed into estates or smallholdings, the latter being 4 hectares or less. The rubber estates covered 292,470 hectares while smallholdings totalled 1,174,736 hectares or about 80% of the area planted with rubber. Rubber smallholdings produced 774,778 tonnes of rubber compared to 291,736 tonnes by estates. Hence the smallholders sector produced 72% of rubber in peninsular Malaysia. Unfortunately, the yield and quality of rubber produced in smallholdings was lower than in estates. Smallholdings in Peninsular Malaysia are scattered throughout the peninsula.

In Thailand 95% of rubber is produced by smallholders, production being located mainly in the south and southeast of the country. The total area under rubber is 1.8 million hectares.

In Vietnam there has been no private sector until recently: 90% of Vietnam's plantations are state owned companies. However, the government's open policy and a more favourable economic and policy climate are expected to lead to a major expansion of smallholder rubber production.

The Imperata problem in smallholder systems

In many smallholder rubber-based farming systems in Southeast Asia, lmperata cylindrica constitutes a problem at two points in the rubber pro- duction system (see Figure 1): first, in rehabilitating unproductive sheet Imperata grassland; second, between the harvest of the last intercrop and canopy closure. The majority of farmers usually plant rubber and an inter- crop simultaneously. The area planted with rubber is intercropped for one or two seasons, the duration of intercropping often being limited by low and declining soil fertility. During this period farmers regularly weed, and there

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Land Clearance from forest, scrub or lmperata Grassland Rubber planted

perata Problem (Competition)

1-3 years of Inte]eropping

Potential lmperata Problem (Fire)

I I 1 I I 3 I I 0 2 4 5

Canopy Closure

Tapping commences

I I I I I 6 7 8 9 10

Years after planting rubber

Figure 1. The periods in the first 10 years of a smallholder rubber plantation (from planting to canopy closure) when Imperata is likely to be a problem.

is little Imperata present. It is after intercropping that the immature rubber plantation is prone to invasion by Imperata cylindrica and other weeds.

The duration of the period to canopy closure varies, depending on the type of rubber planting material used and the level of inputs and maintenance. Canopy closure may occur after five or six years in a well-kept clonal rubber plantation, and after 10-12 years in a seedling rubber plantation in which there has been little weeding or fertiliser application.

Land opening Vast areas of land in Southeast Asia are infested with sheet Imperata. This land could in principle be used for agricultural or forestry production. One of the reasons why it is not used for these purposes is the high cost of effec- tively removing the Imperata. Some rhizome fragments are inevitably left in the soil, allowing the Imperata to rapidly regrow and establish itself again. For these reasons, smallholders tend to prefer opening forest land. It should be recognised, however, that there are often other reasons why much Imperata- infested land is not utilised by smallholder rubber producers (see discussion of farming systems).

Imperata in immature rubber

Competition It is well known that Imperata competition can have a severe retarding effect on rubber trees during the first few years after planting, although there has been only one published piece of research on this subject (Anon, 1938). It may also reduce latex yields, although there has not been any published research on this subject.

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Fire If Imperata becomes established in a block of immature rubber, fire can be a serious risk during the dry season, when the lmperata becomes a potential source of fuel. This depends very much, however, on the characteristics of a given location (Gunawan et al., 1994). A low risk site might be a plantation bordered on all sides by a water course and/or mature parcels of rubber, whereas one surrounded by large tracts of sheet Imperata would be a high risk site.

Soil fertility Soil fertility is a key issue. The red-yellow podzolics are the predominant soils in the rubber growing areas of South Sumatra. These soils are characterised by very low fertility. A recent soil analysis gave the results below:

Nitrogen 1.6 g/kg Phosphate 2.0 mg/dm 3 Potassium 0.1 cmol/kg (me/100 g) pH 4.7 Aluminium 4.2 me/100g Cation Exchange Capacity 10.0 cmol/kg (me/100 g)

These data show that these soils are very acid and contain very high levels of exchangeable aluminium. Furthermore the soil is very low in cations and other macro nutrients, particularly phosphate.

In this soil Imperata cylindrica is well adapted, moreover it can compete readily with farmers' crops. Farmers can and do apply fertiliser, but only infre- quently. Large quantities are required. To correct the aluminium imbalance large quantities of lime will be required. In Indonesia, lime is difficult to obtain and expensive. Urea and potassium chloride (KC1) are readily available and inexpensive. Triple super phosphate (TSP) is also available, but is perhaps inappropriate for tree crops, where a slow-release phosphate fertiliser (Syofyan and Fairhust, 1994) would be more appropriate. The latter is difficult to obtain in South Sumatra.

In Thailand the Office of Rubber Replanting Aid Fund administers credit schemes to promote wider use of fertilisers. Likewise in Malaysia organisa- tions such as FELCRA and RISDA have schemes to promote better fertiliser use. In Indonesia urea and potassium are readily available through private sup- pliers or government-sponsored development schemes.

Smallholders have relied primarily on manual control methods, both for opening Irnperata-infested land and weeding parcels of immature rubber. However, manual control methods tend to require massive amounts of labour, particularly given Imperata's propensity for rapid regrowth. Consequently, Irnperata control is often neglected by smallholders, and parcels of immature rubber commonly suffer from the competitive effect and from fire damage.

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Imperata in mature rubber

In plantat ions with 450-500 trees/ha lmperata is not considered to be a problem. At lower rubber-tree planting densities it may be a problem. The area beneath the trees is heavily shaded and Imperata is intolerant of shade. In this envi ronment other more shade tolerant weed species replace the Imperata.

Recommended control practices and constraints to their adoption

During the last few decades there has been a considerable amount of research on alternatives to manual control. Extension services and rubber improvement projects have encouraged smallholders to adopt one or more alternative control methods, i.e. legume cover crops and herbicides. Much of the research has ignored the fact that many farmers incomes are less than the World Bank ' s designated minimum income ($1,000/year). These farmers are thus attempting to control Imperata when confronted with serious financial constraints. Consequently, a large proportion of smallholders have not adopted them unless they have received financial assistance to do so; or unless their adoption has been a condition for grants or low-interest loans for improved planting material. The recommended practices and the reasons for their non-adoption will now be discussed.

The basic control technology adopted by rubber (and oil palm) estates involves a combinat ion of herbicides and perennial legume cover crops. Herbicides are used to clear the land of Imperata. The legume cover crop (LCC) is then planted and establishes itself before the Imperata is able to regrow. The LCC' s competi t ive effect on rubber is less than that of Imperata, and it tends to be less of a fire problem.

Legume cover crops

Legume cover crops have been promoted by the Agricultural Extension Service and large development projects in Malaysia and Indonesia, but the vast majority of smallholders have not adopted them.

Constraints In Indonesia perennial LCC ' s were promoted by the earlier rubber improve- ment projects, but farmers resisted planting them. Instead, they continued to plant other crops with their rubber that would provide food or cash. The reasons for non-adoption do not appear to have been thoroughly researched and merit further study. However , it seems likely that the major reasons were that perennial legume cover crops do not provide a direct return on the f a rmer ' s investment , as they can be neither consumed on the farm nor marketed - there do not appear to be any significant markets for legume fodder

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crops. Investment includes the costs of purchasing the seed and planting it, and then the labour required to maintain it so that it does not smother the rubber: in Vietnam the crop requires cutting 3-4 times every wet season (Hai Duong, pets. comm.). LCC's have also been promoted in Malaysia, but only about 15% of independent smallholders have adopted them (Rahim et al., 1990). The reasons for this included: no direct benefit and the lack of avail- ability and poor quality of the seeds (Faiz, 1995). Another potential disad- vantage of perennial LCC's is that during an extended dry season they could represent a source of combustible material and hence be a fire risk: it is unlikely, however, that this is an important reason for their non-adoption.

Herbicide control

It is not known what percentage of smallholder rubber producers in the various Southeast Asian countries use herbicide either to open lmperata-infested land or to keep their immature rubber clean. There appears to be a very gradual shift from manual control to herbicides taking place throughout the region, which may reflect growing pressures to adopt labour-saving technologies as the opportunity cost of labour rises and as people's incomes grow. Never- theless, it appears that a substantial proportion of smallholders still do not use herbicides. Glyphosate is by far the most widely used herbicide in the control of Imperata cylindrica in Southeast Asia.

Opening land In the past, where sheet Imperata grasslands have been present, farmers in Indonesia have followed two approaches to land opening. One approach is to burn the Imperata at the start of the dry season and then dig it over with a cangkul (a mattock-like agricultural implement). This exposes the rhizomes to the sun so that they become desiccated. The process is then repeated after 4 - 6 weeks, the clods of soil being chopped up into smaller chunks. Then a month or so later a third cultivation breaks down the chunks of soil com- pletely, to make a suitable seedbed, and the rhizomes are knocked loose from the soil (Terry et al., this issue). The farmer then plants an annual crop and rubber before the Imperata has had time to re-establish itself. The second approach is to wait until the Imperata has been suppressed through the natural succession of woody vegetation, such as Melastoma spp. This process is long term, taking five years or more; and repeated fires may sustain Imperata grass- lands for 10-20 years or more.

The first approach is very labour-intensive, and has been becoming less acceptable to farmers. Furthermore, as land becomes scarcer there will also be a greater need to open Imperata-infested land rather than abandon it or open forest land instead. For both these reasons the use of herbicide for opening land is becoming more widespread and this trend can be expected to continue. To rehabilitate an area of Imperata grassland, the recommended practice is to burn or slash the Imperata and 20 days or so later to apply

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5 1/ha glyphosate: this should then be followed by a 1 1/ha correction spray (Terry et al., this issue).

A substantial proportion of farmers in Indonesia's Batumarta transmigra- tion area in South Sumatra are using glyphosate for this purpose, but some- times in ways that differ from the recommended practice. The majority burn the area first, although a substantial minority do not. (Slashing the Imperata prior to spraying is regarded as requiring too much labour.) However, a large proportion of them apply significantly less than the 5 1 of glyphosate blanket application recommended to control one hectare: in interviews many have stated that they cannot afford to purchase the recommended quantity.

Herbicide control in immature rubber

A survey of independent smallholders in Malaysia found that only a minority of independent smallholder rubber producers use glyphosate in their immature rubber: 24% and 33% of those with smallholdings of < 2 ha and 2-4 ha respectively (Rahim et al., 1990). No comparable figures are available for other .Southeast Asian countries, but it would not be surprising if herbicide users are also in a minority in other countries, although this is likely to depend to some extent on labour availability. For example, herbicide users may be in a majority in Thailand as the rubber industry there has a shortage of labour, labour costs are high and the Office of Rubber Replanting Aid Fund paid for over a million litres of glyphosate in 1994 (Liangsutthisagon, 1995). In Indonesia nearly all smallholders whodo not use glyphosate in this situation say that they cannot afford it.

The recommended practice for herbicide use is essentially the same as the one described above, except that the amount of glyphosate applied per ha should be reduced if the Imperata only covers a certain percentage of the land (D. Laycock, pers. comm.). In the Batumarta transmigration area some of the poorest herbicide users follow the recommended practice of slashing before spraying, whereas relatively rich ones regard slashing as requiring too much labour and spray instead.

Farming systems and lmperata management

Imperata is the principal weed problem in immature rubber, both in relation to competition and dry season fires, for most smallholder rubber-producers in Malaysia (Faiz, pers. comm., 1995), Thailand (Liangsutthisagon, pers. comm., 1995)and Vietnam (Hai Duong, pers. comm.). In Indonesia it is probably not the main problem weed for the majority of smallholders, who employ the traditional 'jungle rubber' farming system, although it is the main problem for a substantial proportion of smallholders. We do not have an overview of the situation in the Philippines, but in one particular farming system there the problem posed by Imperata is minimal.

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Some of the smallholder rubber farming systems encountered in Southeast Asia will now be briefly described, and the Imperata situation discussed in relation to each. The first four are quite widespread. The last two are unusual, but have been included because they illustrate circumstances in which the Imperata problem can be largely overcome.

Indonesia's jungle rubber system

These are the traditional smallholder systems (Gouyon and Nancy, 1993). In Sumatra, the introduction of rubber at the beginning of the century gave the opportunity to farmers to shift from swidden cultivation to sustainable complex agroforests based on rubber. More than two million hectares of jungle rubber cover the central plains of Sumatra, and around 700,000 ha in the dry lowlands of Kalimantan.

The soils of large areas of Sumatra and Kalimantan where this system is found tend to be very infertile red/yellow podzolics. Farmers use a modified slash and burn system to clear existing plantations, primary forest, or secondary forest. Seedling rubber is planted into the burnt residue, initially intercropped with annual crops. Farmers allow the secondary forest to grow among the rubber trees. Trees with a food or economic value (fruit or timber) are encouraged. This increases the natural biodiversity of these systems. About 40 years after tapping commenced the mature rubber is cleared and replanting takes place.

The intercrops with the immature rubber are mainly subsistence ones, primarily upland rice. Intercropping in Sekayu, South Sumatra is normally only for one season. Farmers give two reasons for this: one is that yields would be too low in a second season (because of poor soil fertility); and the other is that Imperata would become a problem if they had a second season of inter- cropping. Off-farm sources of income tend to be limited.

Jungle rubber smallholders regard rubber as the most important of their crops: it is usually their principal source of income, providing cash on a weekly basis. They tend to be among the poorer rubber smallholders in Indonesia. Their system is an extensive, low-input-low-output system, with few, if any, external inputs being used. The rubber planting material is free, collected as seed or seedlings from existing mature parcels of rubber, but its poor genetic quality means that latex yields are low.

Prevalence o f Imperata Sheet Imperata is rarely found in areas where this system predominates. Imperata is less of a problem in immature rubber in this farming system than it is in areas and farming systems where sheet Imperata is present. There are several possible reasons for this:

I. Farmers say that the reason they intercrop only for one season is that Imperata would establish itself if they intercropped for a longer period.

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II. Weeds in general are less of a problem on land which was previously primary forest or old mature rubber, than on land that was previously sheet lmperata or scrub - presumably because the seed banks of the weeds have declined, and the propagules of secondary forest species are more abundant.

III. The absence of sheet Imperata may mean that the quantity of wind-borne Imperata seeds is reduced.

IV. It may be relevant that jungle rubber producers plant rubber at densities (e.g. 1,000 trees/ha) that are well above the recommended practice of 500-600 trees/ha, because they expect a high seedling mortality rate - primarily because of damage from wild pig, but also potentially cattle and tapirs.

A secondary factor related to point IV may be that the high planting density also helps to achieve a degree of early weed control by accelerating canopy closure, although this will only happen if the mortality rate is low.

Imperata control in immature jungle rubber Farmers do not regard Imperata as a serious weed in their immature rubber. Their approach to Imperata control is essentially one of prevention, i.e. aban- doning intercropping after one season. Their main problem weed in immature rubber after intercropping is a broadleaf creeper (Mikania sp.), known locally as Serambas, which they say can kill rubber trees if it is not removed.

Improved rubber group-smallholding farming systems

The principal rubber-producing countries in Southeast Asia have been oper- ating schemes of various kinds to improve and modernise smallholder rubber production. Indonesia has implemented block-planting schemes, in which a large number of smallholders own adjacent parcels of land (e.g. 2 ha) in a large block, which may be anything from 100 to 1,000 ha in area (Tomich, 1990). To participate farmers must be organised into groups. Projects head- quartered on these administered blocks provide extension, high-yielding rubber clones, fertiliser, pesticides, and herbicides - all financed by credit and mar- keting assistance. Participants are obliged to accept the whole of the input package, so they have to purchase herbicides for lmperata control. Origi- nally, the package included cover crops, but farmers objected to this. Inter- cropping of various subsistence or cash crops is now accepted. About 15% of Indonesia's smallholder rubber producers have participated in schemes of this kind. In this farming system, the farmer is likely to regard rubber as his most important crop, particularly if the clonal rubber has already reached the tapping stage.

Malaysia's group smallholdings are operated by major land development agencies such as the Federal Land Consolidation and Rehabilitation Authority (FELCRA) and Rubber Industry Smallholder Development Authority

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(RISDA). Smallholdings which are non-contiguous are developed in situ and RISDA provides the necessary resources. Small holdings which are contiguous may be developed as mini estates where possible. In this case RISDA per- sonnel developed the holdings with the service of hired labour. This approach provides more effective management, and new technologies can be easily and effectively implemented.

FELCRA is responsible for rehabilitating State fringe schemes (which were unsuccessful), opening fringe schemes, opening up new land to cater espe- cially to youth settlers, and developing in situ projects aimed at a total group farming effort in the traditional villages (Juman and Teng, 1979). Settlers under FELCRA's management operate on a group basis and become share holders in the scheme. With the group farming approach each scheme is able to adopt and implement new technologies and agricultural practices more effectively. The smallholders are required to plant legume covers in the inter-rows, or intercrop with annual or perennial crops, or practice mixed cropping.

Prevalence of Imperata This varies in South Sumatra, depending on the area in which the rubber devel- opment project is situated. In Pangkalan Balai (South Sumatra), where the Smallholder Rubber Development Project operates, there are many parcels of sheet Imperata - although the reasons for this are not known, and need to be investigated. Dense stands of Imperata are found in some farmers' parcels of immature rubber. In other project areas, sheet Imperata may be relatively uncommon. Imperata in immature rubber may also be less of a problem.

Imperata control in immature rubber In Indonesia certain herbicide control technologies are promoted by the projects, but this does not necessarily mean that the farmer implements them. Although project participants are obliged to buy the herbicide they sometimes sell it instead of using it. One would expect that block project participants, with their clonal rubber, herbicides and extension guidance, would be more diligent and effective in controlling their Imperata than non-participants with seedling rubber. We are not aware of any surveys on this; but we have come across several cases where participants' parcels of immature rubber were not well weeded and whole blocks have been lost to fire.

In Malaysia's organised smallholdings, Imperata cylindrica is less preva- lent than in its independent smallholdings. This is due to planting of legume covers or intercrops in the early phase and good maintenance for weed control, as a result of sound central management and better adoption and implemen- tation of appropriate technology (Faiz, pers. comm., 1995). Imperata is gen- erally controlled with herbicide.

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Transmigration systems

Some transmigration projects in Indonesia have included a rubber production component. The discussion of this system draws on data collected by the authors from transmigrants of Javanese origin in the Batumarta area of South Sumatra, through a combination of surveys and a programme of on- farm research. The transmigration project cleared large areas of primary and secondary forest in Batumarta, and each transmigrant family was given a house and 3.5-5 ha of land by the Scheme, including 1 ha of mature rubber. Subsequently farmers have been planting their own rubber - clonal, rather than seedling, Rubber is regarded by farmers as their most important crop (Anwar and Conroy, 1993). The intercrops in immature rubber gardens are primarily subsistence ones, the most important of which is upland rice. This is sometimes followed by a second crop around the end of the rainy season. Off-farm sources of income are limited, with the possible exception of share- tapping and wage labour on estates.

A similar kind of scheme can also be found in Malaysia, where the Federal Land Development Authority (FELDA) has been involved in developing jungle land for crops such as rubber, oil palm, sugar cane and cacao (Lamin, 1979). Planting and maintenance are done by contractors for more than two years after which the land is handed over to the settlers. A typical scheme has an area of about 2,000 ha and can settle 400 families. Each settler is given about four hectares of agricultural land and 0.1 hectare for a house lot. Each scheme is provided with basic infrastructure. The scheme is operated by trained management personnel and appropriate technologies on rubber pro- duction are provided by the Rubber Research Institute of Malaysia (Faiz, pers. comm., 1995).

Prevalence of Imperata Imperata is generally the most serious weed in immature rubber. Sheet Imperata is widespread in Batumarta, particularly in relatively new units, and is probably more prevalent in these systems than in any other, for two reasons. First, the land was cleared by the transmigration authorities before the farmers moved into the areas. As a result, sheet Imperata established itself before farmers were able to plant any crops. Second, in some transmigration areas, farmers were not initially allowed to grow perennial crops. Since the soils are of low fertility, the farmers had to abandon their plots after growing annual crops for one or two years. These plots then became colonised by sheet Imperata, and many have remained so, since fires have destroyed the woody species which would have shaded out the Imperata.

Rehabilitating Imperata grasslands Immediately after their relocation, transmigrants used manual methods to rehabilitate an area of sheet Imperata. Nowadays, very few farmers use

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manual methods, as these are regarded as too laborious. Some use draft animal power; but a significant proportion will only open up Imperata-infested parcels using herbicide. If they cannot afford herbicide they leave the parcel uncultivated.

Imperata control in immature rubber The vast majority of farmers in Batumarta use herbicide to control Imperata in immature rubber, in conjunction with some form of complementary manual control practice (Gunawan et al., 1994). However, sub-optimal application practices (e.g. low dose rates, inappropriate sprayer nozzles) mean that there may be substantial amounts of Imperata present in many farmers crops after intercropping has ended.

Independent semi-modernised smallholdings

The information in this section describes the situation in Malaysia. No com- parable data are available for Indonesia, although a substantial proportion of its smallholders probably fall in this category - i.e. they are neither jungle rubber producers nor participants in rubber improvement projects. One dif- ference is that the vast majority of Malaysia's independent smallholders adopted clonal rubber, with government support, many years ago; whereas in Indonesia they have not received such support and many continue to plant seedling rubber.

A survey of more than 500 holdings throughout Peninsular Malaysia found that the size of at least 90% of independent (i.e. non-group) smallhoidings is 4 ha or less (Rahim et al., 1990). About 85% of Malaysia's independent small- holders intercrop: the other 15% plant legume cover crops such as Pueraria phaseolides, Calopogonium caerulum, Centrosema pubescens and Mucuna pruriens var. cochincinensis in the inter-rows. About 75% of intercropping is for subsistence and 25% commercial (Rahim et al., 1990). The common inter- crops are bananas, vegetables, maize, groundnuts, tapioca, pineapple and chillies: some, such as maize and groundnuts, may be planted twice a year. Most smallholders prefer to plant annual intercrops which require low input for establishment. They may also rear sheep, cattle and bees to supplement their income.

Imperata prevalence and control Sheet Imperata is common in Malaysia's independent smallholdings, espe- cially during the immature phase of rubber. One of the main reasons is lack of sufficient income during this period to purchase herbicides and also to employ workers. Prior to land preparation, Imperata is controlled by spraying herbicide. Manual weeding, such as circle weeding and slashing, is also prac- tised, especially during the early stages of planting.

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Constraints In Malaysia these include financial constraints, especially during the immature phase of rubber; uneconomic size of the holdings, labour shortage, and low level of education. Imperata control by glyphosate is still considered expen- sive, despite a recent decrease in its price (Faiz, 1995): a few years ago it was only used by 24% of smallholders with holdings of less than 2 ha and 33% of those with 2--4 ha (Rahim et al., 1990). (The percentages of small- holders using paraquat to control other weeds was approximately double the figures cited for glyphosate use.) Adoption of weeding technology is related to the provision of a subsidy from government agencies such as RISDA. Most independent smallholders are more than 50 years old and cannot carry out heavy maintenance work in the field (Rahim et al., 1990). Most do not receive any assistance from children on their holdings. Thus, there is a shortage of young workers to carry out maintenance work in the field.

Multiple cash crop farming systems

In the systems described here the farmers have not participated in rubber development projects. In these systems the intercrops with immature rubber are primarily cash crops. This discussion draws on on-farm research with chilli (Capsicum longum) producers in the Pangkalan Balai district of South Sumatra; but many of the system's characteristics may also apply to small- holders producing other cash crops, such as pineapple and banana (and, in the past, pepper).

In this kind of system the farmer often regards his intercrops as more impor- tant than his rubber, as the proportion of his income that is derived from rubber is substantially less than in the jungle rubber system (Faiz, pers. comm., 1995). The farmer's mature rubber is probably jungle rubber. The planting material used in his immature rubber is more likely to be clonal than seedling. This may be partly because there is a rubber smallholder development project in the district, and because it is near to the Indonesian Rubber Research Institute's station at Sembawa, which has been promoting the adoption of clonal rubber.

Farmers who opt to cultivate chilli are risk takers, since chilli prices are subject to large fluctuations, both within a season and from one season to the next. This is an intensive, high-input-high-output system, requiring large amounts of labour and large quantities of chicken manure (6 tonnes/ha) and inorganic fertilisers (N, P and K). Chilli production can be highly profitable, and some of the chilli farmers are relatively rich. The wealthier farmers plant about a hectare of chilli. Poorer farmers entering chilli production for the first time begin by cultivating it in very small areas, approximately 1,000 m z, that can be managed by the farmer and his family, without impinging on other essential activities; and for which he can afford the necessary purchased inputs

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costing about $240/ha. Revenue from chilli production often enables the farmer to expand the area cultivated in succeeding seasons.

Prevalence o f Imperata There are more than expected sheet Imperata areas - although the reasons for this are not known, and need to be investigated. Dense stands oflmperata are also sometimes found in plots of immature rubber.

Rehabilitation of Imperata-infested parcels Herbicide-based technologies are rarely used. To open land infested with sheet Imperata for chilli production, the area is normally hand-cultivated twice. For areas of between 1,000-2,000 m 2 family labour is used although some may also be hired. Richer farmers cultivating larger areas hire labour. The second cultivation serves as a weeding and to construct rudimentary ridges which serve as planting beds and are progressively developed throughout the growing season. This also serves as a weeding as the rhizomes are removed. Farmers prefer to use manual labour for cultivating chilli: deep cultivation is required for chilli production, so the land has to be dug over anyway and spraying is regarded as unnecessary.

Imperata control in immature rubber Imperata is a serious problem at this stage, but for a shorter period of time (see below). The wealthier farmers are more likely to use herbicide-based technologies but some of them still use predominantly manual control prac- tices, particularly during the intercropping period. The poorer farmers still use manual methods.

A rubber-based farming system in the Philippines

The system of smallholder rubber cultivation described here is found in one particular part of southern Mindanao (Gouyon, 1995). It is not necessarily representative of the problem of Imperata cylindrica in Mindanao as a whole.

Ecological and socio-economic environment The ecological conditions of the rubber growing area of the Philippines are very different from those in the large cultivated areas of Indonesia i.e. the Sumatran peneplains as defined by Scholz (1983). In the Province of Cotabato rubber is mostly cultivated in the middle upland area, i.e. in a hilly environ- ment. Soils are developed on recent volcanic material, and are far more fertile than the leached, ferralitic soils in the rubber cultivated plains of Indonesia.

Up to the early 1950s, most of the hilly and upland part of Cotabato was covered with forest, cultivated through slash and burn by the sparse, native population (Manobo tribe). This changed rapidly with the massive inflow of migrants from the more crowded islands of Luzon and Visayas, who came from areas cultivated with annual crops (maize and rice), where they were

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using continuous cultivation methods involving the use of ploughing with draft animals (buffaloes).

The migrants, however, started cultivating the forest with slash-and-burn techniques which require less labour. They planted upland rice without land preparation. Yet after 15 to 20 years, repeated cultivation and shortened rota- tions resulted in an increasing weed population (including Imperata), leading migrants to resort to ploughing with animal draft. They also shifted from rice cultivation to maize, which is easier to weed using a plough. Hence the basic cropping system now includes two crops of maize per year, or upland rice followed by maize, depending on the conditions. The fertile soils permit these annual crops to be cultivated on a continuous basis in most cases, without long fallows. It was only during the 1960s and 1970s that farmers started planting rubber, with assistance from estate companies and the Development Bank of the Philippines; although only a minority, usually the more wealthy, are able to withstand the long unproductive period prior to the commence- ment of tapping.

Farming system Rubber in Cotabato is usually intercropped with the upland rice-maize or the maize-maize cropping system. This association lasts for two to three years, then shade prevents good development of the annual crops. In areas with good access to markets, these intercrops are sometimes followed by more lasting crops like banana, Gmelina arborea for timber, coffee, cacao, or fruit trees (like Lansium domesticum). When this is not judged worthwhile by farmers, the area between rubber rows is left uncultivated. It is then usually invaded either by Imperata cylindrica or, more often, by Pueraria javanica (Kudzu) which is naturally prevalent in the area.

Management of Imperata cylindrica In the majority of cases, the nature of the farming system and the soils is such that Imperata a minor problem, not requiring specific control methods (Gouyon, 1995).

Discussion of farming systems and Imperata management

Indonesia's traditional jungle rubber system is an ecologically sustainable and successful agroforestry system, with a high level of biodiversity (Gouyon et al., 1993), that has minimised the lmperata problem. However, the system is under threat in some parts of Indonesia, such as West Kalimantan; and as land becomes scarcer, pressures grow to increase the productivity and intensive- ness of the system. One option for achieving this, without losing the system's biodiversity, is discussed later in the section on research.

The jungle rubber system is a low-input (cost)-low-output (benefit) system, whereas the improved smallholder systems promoted by projects are high-

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input-high-output systems. Financial analyses have shown that the improved project systems give a better return on investment. Nevertheless, for most smallholders the jungle rubber agroforestry system is probably more congruent with available farmer resources (in terms of labour and capital). Whilst the project systems provide higher latex yields and hence higher revenues in the medium to long-term, Imperata control exacerbates demands on already con- strained labour and cash resources during the years before tapping commences; and when tapping does commence smallholders may be obliged to adopt over- intensive tapping practices to pay off loans they have incurred to finance their high-cost inputs.

The farming system in which there is the most widespread (almost 100%) adoption of herbicides is the transmigration system in South Sumatra. However, most of these smallholders face a capital constraint that results in them applying less herbicide than they would like to apply. There is also a labour constraint that leads most of them to substitute a herbicide application for the recommended practice of slashing Imperata before spraying, the result being that they spray twice instead of once. These transmigrants will gener- ally have had no previous experience of growing rubber themselves, but were exposed to the plantation system when they arrived in Batumarta. Thus, their widespread adoption of herbicides could, therefore, be due to them being more receptive to adopting an 'estate'-like system than indigenous farmers who have previously used the jungle rubber system.

Despite the fact that they use clonal rubber and a considerable amount of herbicide, Imperata control is a major problem in immature rubber, and there are numerous parcels of land that remain infested with sheet lmperata. There are two reasons for the latter situation, apart from the fact that sheet lmperata is difficult to rehabilitate. One is the threat of fire to their immature rubber, which they may regard as too great in relation to certain parcels to make the opening of the land worthwhile; and in locations near to forests the threat of damage to immature rubber (and/or intercrops) from wild animals (such as wild pig, monkeys or tapirs) may be regarded as too great.

Nevertheless, as their original mature rubber approaches the end of its economic life, and as the utilisation of the most convenient land (e.g. near the farmer's home) reaches saturation point, the pressures to open up the remaining parcels of sheet Imperata are increasing.

The multiple cash-crop farming system shows that where substantial profits can be made from a short-term cash crop there is an increased incentive for farmers to open Imperata-infested land. This system also illustrates how the period for which Irnperata is a problem in immature rubber can be short- ened, due to the following factors:

• the planting material is mainly clonal, which grows faster than seedlings, leading to earlier canopy closure;

• the high levels of fertiliser applied to the chilli also accelerate the growth of the rubber;

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• the intercropping period tends to be longer, due to the fertiliser inputs - three years rather than the usual 1-2 years.

This kind of farming system is only possible in areas with good access to markets, which tend to be near large cities. The Pangkalan Balai chilli farmers are about an hour's drive from the South Sumatran capital of Palembang, as is the main pineapple-growing area. Traders come to the farmers' fields to buy the chilli on a pre-arranged date. Most of them are based in Palembang, although they may often be acting as middlemen for wholesalers or retailers in Jakarta. When there is a poor harvest in Java or Padang (West Sumatra), traders also come from these regions to purchase chillies for their local markets.

For the smallholders of Cotabato Province, Mindanao, the Imperata problem is minimal due to the following factors:

• the fertile soils minimise the problems of competition between Imperata cylindrica and the crops, making it easier for the cultivated species to overcome the Imperata;

• the soil preparation and ploughing, repeated over years, limits Imperata growth;

• even when Imperata becomes established after the intercropping cycle, its growth is suppressed after 1-2 years, by the shade of rubber, since farmers use quick growing clones (RRIM 600) with a relatively good standard of plant preparation in nurseries.

It can be seen that the South Sumatran cash crop system and the Cotabato system have a lot in common in their implications for Imperata, both bene- fiting from high or increased soil fertility and from fast-growing, clonal rubber. The specific conditions pertaining to each system mean that they cannot easily be reproduced elsewhere, although the adoption of clonal rubber and the increased use of fertilisers could be (and have been) promoted by govern- ment subsidies. (The issue of soil fertility management and the reclamation of Imperata grasslands is discussed further in another article in this issue (Santoso et al., this issue).) Nevertheless, the examples of these farming systems help to improve general understanding of the problem and may provide insights into ways of overcoming it.

Although these two systems point to improved soil fertility as a factor in reducing the Imperata problem, it should not be forgotten that the jungle rubber system overcomes the Imperata problem in a situation of poor soil fertility, by preventing it from establishing in the first place. Indeed, one of the great virtues of rubber production is that it is viable in conditions of low fertility. Thus, methods of enhancing the jungle rubber system, and promoting a modified version of it in certain Indonesian conditions, should be consid- ered. This is discussed further in the next section.

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Research on Imperata m a n a g e m e n t

In recent years most research in Southeast Asia on Imperata and its control has been concerned with the evaluation of herbicide control methods - for example:

• herbicide mixtures and herbicide plus surfactants; • different concentrations of chemicals for different soil types; • the volume of water required and the application apparatus; • time of treatment, to achieve the most effective control, and research into

the treatment cycle. (See Terry et al. (this issue), for a description of some of the research undertaken in Indonesia.)

There has been relatively little research into integrated Imperata manage- ment practices for smallholders, such as mechanical, chemical, and cover crops used in conjunction with each other. There has been even less participatory on-farm research that takes account of smallholders' views in the develop- ment of technologies for their use.

Proposals for a revised research agenda

1. Identify and carry out research within a farming systems context, recognising the constraints facing smallholders as these affect Imperata control

As was discussed earlier, the adoption rates for recommended weed control technologies are generally low in most of Southeast Asia. We believe this is primarily because a clear understanding of smallholder farming systems, and constraints on the availability of cash and/or labour, has been lacking in much of the research. A farming systems approach to research that takes account of the resources available to, and constraints faced by, different types of small- holders should facilitate the development of weed control technologies that better fit farmers' circumstances and hence stand a better chance of being adopted. This is one of the objectives of a joint project between ODA/NRI and the Indonesian Rubber Research Institute currently being undertaken by the authors in South Sumatra.

2. Identify and research more integrated approaches to Imperata control In any farming system, apart from estates, it is doubtful whether any Imperata control method will be appropriate used on its own. More probably a combi- nation of different control methods will be more acceptable to smallholder farmers. A control strategy using a combination of different operations may see a degree of synergy. For example, the use of fertiliser to increase the vigour of the intercrop will also accelerate the growth of the rubber trees, particu- larly if they are improved varieties, leading to earlier canopy closure and suppression of Imperata.

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3. Draft animal power and Imperata control Ploughing using animal traction is not widely practised in any of the farming systems discussed, except for the one in Cotabato Province in the Philippines. It is also used by some farmers in Batumarta, however, for opening Imperata- infested land and during the first year or so of intercropping. Hiring draft animal power for this purpose is apparently cheaper than hiring labour, although the expenditure may be more lumpy. Farmers say that after the first year, ploughing in parcels of immature rubber becomes problematic, causing root pruning, which leads to bleeding and ingress of pathogens. The fact that the Cotabato farmers use animal power for longer than this is interesting and merits further investigation. Research into the current use of draft animal power in these and other farming systems should provide insights into the scope for increasing its contribution elsewhere.

4. Research on the competitive effect of Imperata on rubber and other crops Since there has been a vast amount of research on Imperata in Southeast Asia, and since most weed research is concerned with the competitive effect of weeds, one would expect that this subject would have been well-researched. It appears, however, that it has not, the only substantive reference being an article published in 1938 (Anon, 1938). Almost 60 years later, more detailed research into the degree of Imperata's competitive effect on rubber and other tree crops over time (and hence the benefits of controlling it at different points in time) is long overdue and should be a priority. The competitive effect is known to decrease as the rubber trees develop, and there will probably be a point in time, therefore, at which Imperata control ceases to be financially worthwhile for the smallholder.

5. The economics of Imperata control in immature rubber There has been very little research on this subject. Since the physical effects of Imperata on immature rubber of different ages have not been quantified it is not currently possible to apply cost-benefit analysis to different control methods. Once the former information becomes available research on the eco- nomics of different methods should be undertaken.

6. Research on Imperata control in the context of the fire hazard The relationships between Imperata in smallholdings, its control, and the risk of fire have not been researched at all as far as we are aware, although the ODA/NRI/IRRI project has begun to look at this issue in South Sumatra (Gunawan et al., 1994, 1995). This is surprising, and a serious omission, given that the risk of fire is regarded by many smallholders as a problem that is as serious, if not more so, than the competition problem. Its neglect can probably be explained by the fact that fire-related issues are not normally addressed by agricultural research programmes. Consequently, fire is not recognised by researchers as a research issue; not recognised by research institutes as being within their mandate; and if it is recognised as a legitimate subject, the

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organisation may decide not to investigate it because of a lack of relevant expertise. Fire issues meriting investigation include: the implications of the fire risk for the timing and nature of Imperata control measures; optimum control measures for minimising the damage caused by fire; the degree to which severe dry seasons increase the risk, and whether their occurrence is cyclical or random.

7. Legume cover crops The reasons for low adoption levels are not fully understood. It is interesting that 15% of independent smallholders in Malaysia have adopted legume cover crops, whereas almost none have done so in Indonesia. A survey of factors affecting adoption in Malaysia could be particularly useful in shedding light on the circumstances in which legume cover crops may be appropriate.

8. Shading Another potential means of Imperata control is shading, although it does not appear to be used in the farming systems discussed earlier. Research into the intercropping of shade trees, and their effect on Imperata, could be useful, with a view to identifying species that would have relatively limited compe- tition with rubber, but would provide direct benefits to the farmer. Coffee and mulberry are being promoted in Vietnam, and banana is quite widely inter- cropped in South Sumatra.

9. Increasing the productivity of the jungle rubber system In Indonesia jungle rubber is still the most widespread smallholder rubber system, and has the twin virtues of being high in biodiversity and low in Imperata. However, for reasons mentioned earlier, its productivity needs to be increased if it is to continue as a major farming system. The experience of rubber estates shows that latex yields increase dramatically (by up to a factor of three) if non-selected seedling rubber is replaced by improved clonal varieties. ICRAF is currently researching the introduction of clonal rubber into jungle rubber systems in Kalimantan and Sumatra (Penot, pers. comm.). It will be interesting to see how clonal rubber performs in this very different farming system, with its much lower inputs of fertiliser and limited weed control and maintenance.

10. International collaboration The earlier descriptions and discussions of various farming systems suggest that comparisons between them of the Imperata situation can yield useful insights into the nature of the problem and means of minimising it. A cross boundary co-operation programme involving researchers from various South- east Asian countries, enabling them to share their experiences and to meet with farmers, could prove very useful in the development of practicable and improved methods of Imperata control in the region.

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