TREE-BORNE OILSEEDS IN AGROFORESTRY
J.N. Daniel and N.G. Hegde
Abstract
Among the many favourable attributes of agroforestry is its suitability for degraded land. It is an alternative available for the rehabilitation and utilisation of the vast expanse of wastelands in the country. Another matter of great concern is meeting the energy needs of the rapidly-growing economy of the country. Biodiesel has emerged as one of the promising options and production of its raw material, oilseeds, is now gaining importance. The use of wastelands to produce tree-borne oilseeds can realise the twin objectives of rehabilitation of a vital land resource and obtaining an energy substitute. Although there are definite advantages in this approach, achieving the desired outcome is not easy. The major constraint is the lack of accurate information about the requirements and cultivation practices of the species, their potential yields and income. There are several trees yielding oilseeds, but Jatropha curcus, Pongamia pinnata and Azadirachta indica are the species of high potential. Not all the claims made about these species at present are backed by actual field data. Therefore, a systematic approach backed by scientifically validated information is necessary in the promotion of these species. These aspects together with the need for realistic expectations are discussed in this paper.
Keywords: agroforestry, jatropha, pongamia, tree-borne oilseeds, wastelands
2007. Proceedings of the National Seminar on Changing Global Vegetable Oils Scenario: Issues and Challenges before India. ed. D.M. Hegde. Indian Society of Oilseeds Research, Hyderabad, India: 263-276.
1. Introduction
The significance of agroforestry as a land use system has been highlighted extensively in recent years. Among the many favourable attributes of agroforestry is its suitability for degraded land. In India, the area of land that belongs to this category is considerable. Commonly known as wastelands, the total area of such land in the country is variously estimated at less than 70 million to more than 170 million ha (Radhakrishna, 2006). Even to allow the figure at the low end of this range to remain idle is ill-affordable to the country as the pressure on natural resources is immense. A systematic approach is necessary to rehabilitate wastelands because they are a national wealth remaining underutilised. Agroforestry is a potential alternative suggested by many for the rehabilitation of wastelands. Their current fertility status is such that the probability of success of annual cropping systems is low whereas agroforestry has a reasonable chance to succeed. Along with the material harvests from the perennial component, soil fertility improvement is a benefit of agroforestry. Thus, fertility restoration is a key objective of agroforestry.
Meeting the energy needs of a rapidly-growing economy is another matter of apprehension for India. Issues associated with conventional petroleum energy are fluctuating global prices, depletion of reserves, dependence on imports and environmental pollution. Understandably, efforts have been intensified to identify alternative sources of energy. Biodiesel has emerged as one of the promising options and production of its raw material, oilseeds, is now gaining wide publicity. Although all oils can be used, edible oils as a source for biodiesel production have to be ruled out because they are required for cooking and food purposes. Therefore, non-edible oils are the premier raw material for biodiesel production in India. Seeds rich in these oils are mostly produced by perennial species. Hence these trees are referred to as Tree-Borne Oilseed Species (TBOS) and they produce Tree-Borne Oilseeds (TBOs).
Production of TBOs on wastelands meets the twin objectives of rehabilitation of a vital natural resource and obtaining an energy substitute. This is a highly appealing combination because it includes a number of ecological and economic benefits. Establishment of agroforestry systems with TBOS on vast areas of barren or scrub land as well as less fertile farm land will change the rural landscape and bring with it many environmental benefits. Environmentally, the gains can be in the form of reduced erosion, improved micro-environment for intercrops, enhanced soil fertility, production of raw material for less polluting biofuel and by-products for various uses. The economic benefits being highlighted are increased rural income, reduction in expenses on petroleum imports and energy at lower cost.
Although there are definite advantages in promoting TBOS-based agroforestry on barren wastelands and marginal farmland, achieving the desired outcome is not easy. The major constraint, in this regard, is the lack of accurate information about TBOS, their cultivation practices, potential yields and income. In the absence of reliable sources on the topic, interested growers have to rely on whatever information that comes their way. Unfortunately, most promotional literature available at present tends to exaggerate the returns and understate the efforts required to succeed. In the wake of the publicity jatropha and other TBOS are receiving, there is a proliferation in the number of stakeholders. Unfortunately, a majority of them are misled by promoters who are overenthusiastic or are taking advantage of the prevailing euphoria. At stake are the feasibility of agroforestry as a production system and the suitability of TBOS as a source of energy. Among the many issues to be addressed is the need for a systematic effort to develop and disseminate appropriate production packages so that an excellent opportunity is not lost.
2. Agroforestry in India
2.1Systems
Agroforestry is a traditional practice among farmers in India. The practices adopted may not be well-defined systems like those evolved scientifically in recent times. Nevertheless, they too have followed the same principles and realised the benefits. A comprehensive description of all these practices and systems is found in the documentation of Tejwani (1994). There are many traditional agroforestry systems in practice in arid regions of India (Nandal and Narwal, 1994). Presence of Acacia nilotica and Dalbergia sissoo is very common in northern parts of the country. In the humid tropical areas along the south-western coast, systems which combine several perennial species are a common occurrence. The inclusion of several spice crops in these intensively-managed systems makes them highly remunerative.
TBOS have not been a key component of any traditional agroforestry system and often they may not have been established deliberately by farmers. The exception is jatropha, which is established by farmers as a live fence. This requires planting them in a row at close spacing. Other species like Pongamia pinnata, Madhuca species and Calophyllum inophyllumprobably came up as wildlings and were retained by farmers. Their presence is usually limited to a few trees in the middle of crop fields or along the borders. Oilseed production is not the intention of retaining these trees and they are mostly there for service functions like providing shade and protection as fence.
Agroforestry technology development has been an active programme in the country for many years (NRCAF, 2004). In recent years, several agroforestry systems have been successfully introduced and accepted by farmers in India. Systems based on poplar (Populus deltoides) in the north-western region of the country are highly intensive and are suitable for irrigated conditions. An agri-horti-forestry system - where the component species are horticultural crops like mango and cashew, annuals as intercrops and multipurpose trees along the border of the farm - has gained acceptance in Maharashtra and Gujarat (Mahajan et al., 2001). Additionally, there are many innovative farmers who have developed or modified existing agroforestry systems to suit local conditions. TBOS can fit into most of these systems, contributing positively towards the overall productivity and farm income.
2.2Limitations
Wastelands belonging to farmers that can be brought under TBOS is available in plenty. The present production levels of some marginal farmlands are so low that farmers will be happy to try out alternative crops. Therefore, land availability for oilseed production is unlikely to be a constraint. The vital resource that will determine the area eventually brought under oilseed production is water. Although most TBOS are hardy, they will still require adequate water to produce satisfactory yields. Because priority allocation of available water would be for food production, oilseed production has to be concentrated on land where competition for water does not occur.
3. Tree-Borne Oilseed Species
Seeds of many tree species contain high levels of oil and their use for bioenergy generation has been a topic of interest for long (Raina, 1986). Those popularly known as TBOS are Jatropha curcus (jatropha or ratanjyot), Pongamia pinnata (pongamia or karanj), Madhuca latifolia and M. indica (mahua), Calophyllum inophyllum (undi), Azadirachta indica (neem) and Simarouba glauca (simarouba). Simarouba has been studied to standardise various aspects of it cultivation (Joshi and Joshi, 2004). It is not a very familiar species in India. It produces edible oil and probably requires relatively better growing conditions compared to others in this group. Mahua oil is also edible and is used by tribal communities. Undi probably has the highest seed oil content among these species, but its major limitation appears to be the restricted environmental niche of sandy soil with humid environment. Moreover, mahua and undi are very slow-growing species and hence may not fit into an agroforestry system. Neem has recognition more for its pesticidal uses than seed oil. Thus, the list narrows down to jatropha, pongamia and neem. Jatropha appears to be the frontrunner at present.
There are several reasons for the greater interest in jatropha. It already has a domestication record as research on it has been carried out in India and other countries. Seed oil characteristics of jatropha are superior to others for biodiesel production. Besides its faster growing attribute when compared to most other TBOS, it also has the ideal size for agroforestry. Thus, jatropha has emerged as the premier TBOS. Unlike most other perennial species, jatropha has a shorter gestation period and regular seed harvests are possible within four years of establishment. Being a small tree with a lax canopy, it is ideally suited for small farm agroforestry systems. Its natural distribution throughout India is indicative of its adaptation to diverse agro-climatic conditions. Farmers are also familiar with jatropha as a hardy fence plant that can survive with very little inputs or management. These advantages notwithstanding, it should not be assumed that jatropha can succeed under any condition.
Another advantage of jatropha is the properties of its oil for biodiesel production. Its low free fatty acid content, almost similar to edible oils, makes it ideal for transesterification and the oil to biodiesel conversion ratio is higher than in other non-edible oils. A higher ratio means better profit margins and hence jatropha oil is a more desirable raw material than others. Combustion studies have also shown jatropha biodiesel to be superior to others as its emissions are less polluting.
Pongamia has its own merits as a TBOS. Rural communities in India are familiar with this species because its oil has been used traditionally for lighting lamps in households. It grows well in most parts of the country. A particular merit of this species is its ability to withstand both waterlogging and extreme drought conditions. In dry areas, it is one of the few species remaining green during the summer season. Its ability to fix atmospheric nitrogen is another advantage of this species. Domestication work on this species to identify elite genotypes and standardise cultivation practices is still at an early stage. Because this species is native to India, most of the information related to its use as an economically important plant and contribution to scientific knowledge has to be generated locally.
Neem is a species that combines two environment-friendly themes of current interest in the form of biopesticide and biodiesel. It is a hardy species that not only suvives, but produces reasonable quantities of seed in all types of environments. Of particular significance is its ability to grow on saline soils. Its wood is of reasonably good quality timber that can be used for making farm implements and construction purposes. It can also combine well with many annual crops as well as small trees like jatropha in agroforestry systems.
3.1Profiles of Important TBOS
3.1.1Jatropha curcas (BAIF, 2004)
Considered to be a species of high potential for oilseed production, jatropha is an ideal species for wasteland development programmes. It is a small tree of about 6.0 m height belonging to family Euphorbiaceae. Its natural distribution is in Mexico and the Amazon region. It has a short trunk with thick branches spreading into a crown of dark green leaves. The bark is pale brown and the leaves are attached to long petioles. Native to humid zones under arid and semi-arid conditions, jatropha thrives under a wide range of soil and climatic conditions. It grows under annual average rainfall of 480 mm to 2400 mm and its daily average temperature range is 20-28oC. It tolerates extreme temperature conditions as well. It is drought tolerant and can withstand slight frost. Jatropha can grow on almost any site, ranging from gravel, sandy to clayey soils. But its growth form is stunted in highly eroded soils of low fertility and in alkaline soils. It tolerates drought by shedding the leaves. This, however, results in decreased growth. It grows at altitudes ranging from sea level to 1000 m. Jatropha comes into flowering during September to December and fruits mature 2-4 months after flowering. However, in irrigated or high rainfall areas, a main harvest in October and a second harvest in March/April are possible.
Jatropha can be established with seeds or cuttings. Seeds can be sown directly at the onset of the rainy season or seedlings can be raised in polybags and transplanted. Branch cuttings grow vigorously when used as planting material. Cuttings of 45-100 cm in length and 3-4 cm in thickness taken from the base of the stem are the best for vegetative propagation. Plants raised from cuttings start bearing within one year whereas those propagated from seeds bear in 3-4 years. Canopy development by periodic pruning in the first three years is necessary to ensure high yields subsequently. Flowering occurs on one-year old branches. Therefore, after the tree enters the seed production phase, selective pruning must be done after harvesting the crop so that the new flush is mature enough to bear seeds during the next rainy season.
Apart from the use of seedoil for biodiesel production, parts of jatropha have several other uses. The latex, oil, twigs, wood and leaves have medicinal value. Leaves are used as a fumigant for bed bugs. Different parts of jatropha are also used as pesticides. There are reports of leaves being used as a feed for silkworms. A dye extracted from leaves and tender stems is used for colouring cloth and fishing nets. Tender foliage and oil cake of jatropha can be used as organic manure.
3.1.2 Pongamia pinnata (Daniel, 1997)
Pongamia pinnata, belonging to family Leguminosae,was earlier known as Derris indica and Pongamia glabra. It is a nitrogen fixing tree that produces seeds containing 25-30% oil. It is often planted as an ornamental and shade tree. It is native to India and is receiving a widespread attention at present as a TBOS. Pongamia is a medium-sized tree that generally attains a height of about 8.0 m and a trunk diameter of more than 50 cm. The bark is thin, gray to grayish-brown, and yellow on the inside. The alternate, compound pinnate leaves consist of 5 or 7 leaflets which are arranged in 2 or 3 pairs, and a single terminal leaflet. Pods are elliptical, 3-6 cm long and 2-3 cm wide, thick walled, and usually contain a single seed. Seeds are 10-20 cm long, flat, oblong, and light brown in color.
Pongamia thrives in areas having an annual rainfall ranging from 500 to 2500 mm. In its natural habitat, the maximum temperature exceeds 38oC and the minimum can be as low as 1oC. Mature trees can withstand water logging and slight frost. This species grows in elevations of 1200 m, but in the Himalayan foothills it is not found above 600 m. It can grow on most soil types ranging from stony to sandy to clayey, including dry sands and saline soils. The natural distribution of this species is along coasts and river banks in India and Burma.
The average seed oil content is about 25%, but higher percentages are claimed nowadays because of its use for making biodiesel. The oil is thick and yellow-orange to brown in colour. Traditionally, besides the cooking and lighting uses in rural areas, it was used as a lubricant, water-paint binder, pesticide, and in soap making and tanning industries. The oil is known to have value in folk medicine for the treatment of rheumatism as well as human and animal skin diseases. Wood is beautifully grained and medium to coarse textured, but is not durable as it is susceptible to insect attack and tends to split when sawn. Therefore, it is used as fuelwood and cheap timber. The leaves are not readily eaten by animals, but it has some fodder value in dry areas. Leaves are also used as insect repellent in stored grains. The oilcake has use as poultry feed and also as manure with nematicidal value.