Karanj for Wastelands
The need to search for alternative sources of energy which are renewable, safe & non polluting assumes top priority in view of the uncertain supplies & frequent price hikes of fossil fuels in the international market.
Among the many species, which can yield oil as a source of energy in the form of biodiesel, Pongamia pinnata has been found to be one of the most suitable species due to its various favorable attributes like its hardy nature, high oil recovery and quality of oil, etc. It can be planted on degraded lands through Joint Forest Management (JFM), farmer's field boundaries, wastelands / fallow lands.
Indigenous production of Pongamia oil will save foreign exchange worth of several million dollars & also generate employment opportunities in rural areas.
Pongamia pinnata belongs to the family Fabacese (Papilionacease). It is also called Derris indica & Pongamia glabra. It is a medium sized evergreen tree with a spreading crown and a short bole. The tree is planted for shade and is grown as ornamental tree. It is one of the few nitrogen fixing trees producing seeds containing 30-40% oil. The natural distribution is along coasts and river banks in lands and native to the Asian subcontinent. It is also cultivated along road sides, canal banks and open farm lands.
Native to humid and subtropical environments, pongamia thrives in areas having an annual rainfall ranging from 500 to 2500 mm, in its natural habitat, the maximum temperature ranges from 27 to 38o C and the minimum 1 to 16o C. Mature trees can withstand water logging and slight frost. This species grows naturally to an elevation up to 1200 m, but successful trials of Pongamia have been conducted in Zambia, at 1,277 and 1,363 metres indicating that this is not a hard constraint on growth.
Pongamia can grow on most soil types ranging from stony to sandy to clayey. It does not do well on dry sands. It is highly tolerant of salinity. It is common along waterways or seashores, with its roots in fresh or salt water. Highest growth rates are observed on well drained soils with assured moisture.
Bark is smooth, grey and thin. Leaves imparipinnate, leaflets opposite, 5 to 9 in number, ovate to ovate elliptic, shortly accuminate, glabrous bright green in colour, petiole 4.5 cm long. Inflorescence of axillary racemes, shorter than leaves, about 20 cm long. Flowers one cm across, zygomorphic, style incurved. Pods obliquely oblong, 3-6 cm long and 2-3 cm wide thick walled, woody, compressed, indehiscent. Pongamia starts flowering from the 4th or 5th year of planting. White and purplish flowers in axillary recemes appear in April to July.
Out of the two ovules in the ovary, invariably only one will develop into seed. After fertilization the early fertilized ovule suppresses the subordinate one by the strong sink activity. The abortion of embryo is due to manifestation of sibling rivalry.
Pods are 4.5 cm long & 1.5-2.5 cm wide broad, pointed at both ends, yellowish grey when ripe, 1 or 2 seeded. Seeds are elliptical, reniform, compressed, reddish brown, fairly hard, 2-3 cm long. The pods ripen from February to May in the following year.
Oil: The seeds are largely exploited for extraction of a non edible oil commercially known on India as ‘Karanja oil' or Honge oilW which is well organized for its medicinal properties. The yield of fruit varies from 9 to 90 kg per tree for different age trees. There is no systematic organized collection of seeds. Mixture seeds consist of 95% kernel and is reported to contain about 27.0% oil. The yield of oil is reported to be about 24 to 26.5% if mechanical expellers are used for the recovery of oil from the kernels, but it is only 18-22% from village crushers. The crude oil is yellow orange to brown in colour which deepens on standing. It has a bitter taste and disagreeable odour, thus it is not considered edible.
The oil is used as fuel for cooking and lamps, and has possibilities as biodiesel. The oil is also 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. It is effective in enhancing the pigmentation of skin affected by leucoderma or scabies.
Wood: With a calorific value of 4600 - 4800 kcal per kg, pongamia is commonly used as fuel wood. Its wood is beautifully grained and medium to coarse textured. However, it is not durable, is susceptible to insect attack, and tends to split when sawn. Thus the wood is not considered a quality timber. The wood is used for cabinet making, cart wheels, posts, agricultural implements, tool handles and combs, etc.
Fodder and feed: Opinions vary on the usefulness of this species as a fodder. It is reported in some places that the leaves are eaten by cattle and readily consumed by goats. However, in many areas it is not commonly eaten by farm animals. Its fodder value is greatest in arid regions. The presscake, remaining when oil is extracted from the seeds, is used as a poultry feed.
Other uses incorporation of leaves and the presscake into soils improves fertility. Dried leaves are used as an insect repellent in stored grains. The presscake, when applied to the soil, has value as a pesticide, particularly against nematodes.[verification needed]
Pongamia is a drought resistant, nitrogen fixing leguminous tree. It is also salt tolerant and to some extent tolerant to slight frost. It is a good shade tree. The shade provided by this tree is said to have cooling effect (?? wouldn't it?) and is good for health.
Pongamia is often planted in homesteads as a shade or ornamental tree and in avenue plantings along roadsides and canals. When planted as a shade or ornamental tree, branch pruning may be necessary to obtain a trunk of appropriate height. It is a preferred species for controlling soil erosion and binding sand dunes because of its dense network of lateral roots. Its root, bark, leaf, sap, and flower also have medicinal properties[verification needed].
Seed Collection & Storage
Pongamia is easily established by direct seeding or by planting nursery-raised seedlings or stump cuttings of 1-2 cm root-collar diameter. Propagation by branch cuttings and root suckers is also possible. In peninsular India, the seeding season is April to June, and the seed yield per tree ranges from about 10 kg to more than 50 kg. There are 1500-1700 seeds per kg. The pods are dried in sun & seeds are extracted by thrashing the fruits. They remain viable for about a year when stored with the fruit shell un opened in air-tight containers / stored at 5 0 C.
Generally seeds do not require any pretreatment before sowing. But, soaking the seeds in hot water for 15 minutes improves germination percent & vigour. Seeds are sown in seed beds / polypots / sand trays with the micropyle facing downwards. Seed germinates within two weeks of sowing. Seedlings attain a height of 25-30 cm in their first growing season. Transplanting to the field should occur at the beginning of the next rainy season when seedlings are 60 cm in height. Seedlings have large root systems. Soil should be retained around the roots during transplanting. Seedling survival and growth benefit from annual weed control for the first three years after transplanting. Pits of 30 cm3 are appropriate for planting in a plantation scale at an espacement of 3 M X 3 M
The spacing adopted in avenue plantings is about 8 m between plants. In block plantings, the spacing can range from 2 x 2 to 5 x 5 m. Pongamia seedlings withstand shade very well and can be interplanted in existing tree stands. In nurseries and in the field the presence of root nodules on uninnoculated pongamia seedlings are common.
Two or three weedings are required per year for the first 3-4 years of sowing / planting.
Pests and diseases
There are about 30 species of insect pests recorded to cause damage to pongamia raised usually as avenue planting & strip plantations on marginal lands. They include gall inducers, leaf miners, foliage feeders, shoot bores, sap suckers, flower feeders and fruit seed borers. Of these, gall inducers and leaf miners rank predominant position because of their destructive potential and ubiquitous occurrence. However, it has also been shown that galls increase the photosynthetic capacity of the plant by increasing the surface area of leaves.
Yield & Economics
Some varieties of Pongamia in the wild may take over 7 years before yielding any pods, and may produce pods only every other year. It is necessary to ensure good selection of grafted saplings with high annual yields to ensure early (year 3) first yields, which increase to maturity after year 10.
The plant starts give economically viable yields from the fifth year onwards and the benefits increase over the years and stabilizes in the 10th year. The financial analysis has been done with the above parameters of the investment cost & yields, the BCR & IRR works out to 2.18 & 31.77% respectively.
Pongamia is often listed as being unsuitable for agroforestry because it produces root suckers profusely. It should be planted preferably in the forest & non-forest wastelands & community lands etc. However, pruning of roots is a simple matter and there is plenty of evidence of farmers in S. India having Pongamia trees along boundaries and in fields, and cropping is carried out almost up to the trunk of the tree. Soils near to the tree benefit most from the cumulative effects of N-fixing.