Pongamia pinnata (aka Indian Beech Tree, Honge Tree, Pongam Tree, Milletia Pinnata) is a medium-sized evergreen tree with a spreading crown and a short bole. The tree is planted for its shade and is grown as an ornamental tree. It is one of the few nitrogen fixing trees (or legume trees) producing seeds containing 30-40% oil. Its dense network of lateral roots and its thick, long taproot make it drought-resistant and well-suited to the intense heat and sunlight.

The natural distribution of Pongamia is along coasts and riverbanks in lands and native to south-east Asia and India. The tree is introduced in humid tropical regions all over the world including the US and Australia. It is cultivated along roadsides, canal banks and open farm lands. It is a preferred species for controlling soil erosion and binding sand dunes because of its dense network of lateral roots.

Its root, bark, leaves, sap, and flower also have medicinal properties and traditionally used as medicinal plants. Concentrated fruits or seeds extract can be found in various herbal preparations which are widely available in the market today. Analysis resulted in more than 18 flavonoid compounds in the bark alone.I

In India, where there is the most experience with this tree, the seeds are collected to obtain Karanja or Honge oil. The non-edible oil is known for its medicinal properties. There is a long history of using the oil as a fuel for lamps and cooking stoves. The pressed cake is used as an insect repellant and as an organic fertilizer because it contains fixed Nitrogen (4%), Phosphorus (1%) and Potassium (1%).

Recent research on Pongamia suggested its name should be changed to Millettia pinnata. Since the 1990s the tree is under research as a source for biofuels in India. Grafting is necessary because it can take as long as ten years for a tree in the wild to reach full seed-bearing maturity. The researchersII studied thousands of Pongamia variants, identifying and collecting the best sources of high-quality grafting stock. This not only removed the uncertainty from the yield, it also reduced the time to harvest from ten years to as little as three. The tree will increase yield until age 15 and will continue having reliable yields until age 50. The total lifespan of the tree is between 85 and 100 years.

The theoretical projected yields depend on many factors including rainfall, temperature, soil conditions, age of tree, density of trees, irrigation, specific variety (seed weight), and many others. Therefore the estimations of the potential yield in the field vary from 15 to 50 ton of seed (in pods) per hectare. This relates to an oil yield of 3 to 10 ton/ha. Indian sources are more conservative in this respect than some of the Australian projections, as the growing conditions are different. One important factor is irrigation. The tree can resist drought but will yield better if there is enough water available, as is the case with any other crop.

The University of Queensland ARC Center of ExcellenceIII for Integrative Legume Research is working on selection and developing higher yielding cultivars by using genetic diversity tests and transgenic methods to improve the oil biosynthesis by understanding root biology, nodulation, nitrogen fixation, domestication genes, grafting, salinity tolerance, and the genetics of the oil production pathways.

The 1.5 cm long seeds also contain 30% starch which can serve as a feedstock for ethanol production and simple proteins usable as fodder.

Key advantagesIV

1. Drought resistant (500-2500mm rainfall per year)
2. Heat resistant (-1 to 50 degrees Celsius)
3. Mechanical harvest is possible
4. Synchronized flowering and harvesting
5. Tolerates saline conditions
6. Timber producing
7. Wood suitable for burning as a fuel
8. Particularly ornamental
9. Tolerates alkaline soils
10. Legume (Nitrogen fixing tree)
11. Fast growing 15 m high trees at age 15
12. High oil yields per tree
13. High oleic acid content (C18:1) of the extracted oil
14. CO₂ sequestrating of the perennial tree (estimated at 30 ton/ha/a)
15. Tolerant to water logging

Here is one tree that can become an important second generation biofuel crop. It can produce inedible oil (biodiesel), starch (ethanol) and by fermenting the pressed cake, biogas. The tree itself can be used as wood fuel and thus prevent soil erosion by replacing wood cutting in the wild. This tree can be grown sustainable on marginal lands and does not need to compete with food production. More detailed studies on the biology, genetics and silviculture are required in order to give us essential information about the successful cultivation and management techniques of growing well-selected top varieties of Pongamia pinnata.