Producing biomass: Biomass types: Trees: Pongamia
The pongamia (Millettia pinnata) plant is a leguminous tree that is found through much of Asia, northern Australia and the Pacific Islands. It is a species of the legume family and grows large pods that are rich in triglyceride oils that may be converted into biodiesel and aviation fuel.

The tree is not currently grown commercially in Australia. However, there is considerable interest in its seeds to produce oil, provided the cost is low enough.

Evaluating the economics

A Common View of the Opportunities, Challenges and Research Actions for Pongamia in Australia [PDF, 2.5 MB] published in Bioenergy Research in 2012, provides a comprehensive review of the production costs, revenue and benefits of Pongamia oil production systems.

For annual seed yields ranging from 20 to 80 kilograms (in shell) per tree, the delivered cost of pongamia oil was estimated to be between $2.22 and $0.64 per litre.

The seed yield range of 20 to 80 kilogram per tree is roughly equivalent to between 7 and 29 tonnes per hectare at a planting density of 357 trees per hectare.
Pongamia seed pods are rich in triglyceride oils
Major components of the delivered cost of oil are:
  • the capital expenses of land acquisition
  • plantation establishment
  • operational costs include mechanical harvesting; fertiliser and weed control, pests and diseases
  • crushing plant construction
  • transporting raw oil to a plant for further processing to biodiesel or aviation fuel.

Table 1 is adapted from A Common View of the Opportunities, Challenges and Research Actions for Pongamia in Australia [PDF, 2.5 MB].

It shows the cost of production of Pongamia oil for two different yield scenarios over a 40 year life cycle.

Both scenarios are based on a 500 hectare plantation with 500 trees/ha. Scenario A assumes 40 kg pods/tree/year when trees are 10 years old; Scenario B assumes 10 kg pods/tree/year when trees are 10 years old.

Table 1. Cost of production of Pongamia oil for two different yield scenarios over a 40 year life cycle.
Cost Category Scenario A Scenario B
land $/ha over 40 years Oil Cents/litre land $/ha over 40 years Oil Cents/litre
Capital (excludes value of land)
Establishment of site, planting of trees, crushing plant, machinery 9,384 6.00 9,384 24.00
Opportunity Costs
Foregone net returns from alternative land use (e.g. grazing) 656 0.42 656 1.68
Variable Costs
Machinery – tractor, implements (fuel, oil, parts, repair and maintenance) 1,128 0.72 1,128 2.88
Fertiliser and mulch 3,975 2.54 3,685 9.42
Control and management of weeds, pests and diseases 2,237 1.43 2,237 5.72
Pruning labour 2,487 1.59 2,487 6.36
Harvesting 7,977 5.10 6,182 15.81
Crushing seeds to extract oil 448 0.29 593 1.52
Fixed Costs
General repair and maintenace 267 0.17 267 0.68
Power, fuel and oil 347 0.22 347 0.89
Administration and wages of manager and staff 6,786 4.34 6,786 17.35
Total Costs 35,691 22.82 33,751 86.31
Carbon revenue 3,246 2.07 3,246 8.30
Total costs less carbon 32,445 20.74 30,506 78.01
Equivalent Annual Value – Total Costs ($/ha/year) 2,677 2,532

Benefits

Pongamia is suited to the northern tropical and subtropical regions in Australia and can be grown in marginal conditions.

As a legume, it produces its own nitrogen thereby displacing approx $200 per hectare/pa of nitrates applied as compound fertiliser. Decreased requirement of fertilisers and reduction of cultivation results in lessening of potential soil and chemical runoff.

Research shows pongamia’s potential for increasing Australia’s current low level of plant oil production using a non-food crop [PDF, 2.5 MB]. Pongamia seeds contain oils and fatty acids.

Pongamia oil has traditionally been used for lanterns, cooking stove fuel, medicines, fodder, beautification, shade, and environmental protection and is currently of major interest for biodiesel production and aviation fuel. Starch from the meal is also suitable for ethanol production.

Other useful products from Pongamia trees include:
  • Wood, which has been used for stove top fuels, poles, and ornamental carvings
  • Bark, which has been used for paper pulp, twine and as a medicine to reduce swelling of the spleen
  • Flowers, which are considered good sources of pollen for honey bees, and have been described as having anti-diabetic properties
  • Leaves, which have been used as cattle fodder, as an infusion to relieve rheumatism and coughing, as an extract to treat itches and herpes and as a source of poison used by Australian Aborigines for fish spears
  • Oil extracted from the seeds, which has been used as lipids for commercial processes, as an ointment for skin diseases, as a liver medicine, as a lamp fuel in India, and for the production of biodiesel (see below)
  • Seed cake leftover after oil extraction, which has been used as ‘green manure’ as it is rich in protein and nitrogen.

Supplying

To produce an efficient biomass, it is critical to minimise the supply chain and delivery costs of the oil to the refinery.

A model for growing Pongamia trees and harvesting, crushing and transporting the oil from its seeds to a refinery is described in the collaborative study Bioenergy in Australia: Status and opportunities [PDF, 9.1 MB], published by Bioenergy Australia in 2012.

The study also outlines, potential markets for by products from the oil extruding process. Pongamia meal (also known as karajin cake) has been used successfully as green manure, a natural pesticide and a fungicide.

There has also been extensive research into finding ways to use Pongamia meal as livestock feed however this has been less successful due to the cake being highly unpalatable.

The University of Queensland are also investigating the potential to develop and establish new types of production systems for Pongamia, as well as the value chains – for example for conversion of oil to aviation fuel.

The potential exists for exploring production systems combining Pongamia plantations, grazing and carbon farming which could provide enterprise diversification, reduction of risk, and reduced GHG emissions for the grower.

Growing

Pongamia trees have a mature height of 10 to 15 metres. They prefer humid tropical and subtropical climates.

In Australia, Pongamia are found in northern tropics and subtropical east coast ranging from the coastal fringe around Darwin through Cape York and as far south as northern NSW. Records further inland are from locations along major rivers including the Wenlock, Archer and Holroyd Rivers in the Cape York area, and the Norman River in the Gulf of Carpentaria.

Origin Energy owns and operates the largest commercial trial site (300 ha) near Roma in central Queensland. The crop consists of 170,000 trees, which are irrigated with treated Coal Seam Gas water from the Spring Gully reverse osmosis treatment plant.

Field trials have also been conducted to measure the growth of Pongamia in south-east Queensland, Western Australia and the Northern Territory.

A Common View of the Opportunities, Challenges and Research Actions for Pongamia in Australia [PDF, 2.5 MB], published in Bioenergy Research in 2012, provides a comprehensive review of these trial’s results with regards to:
  • Optimal rainfall
  • Critical high and low temperatures
  • Frost tolerance
  • Suitable soil conditions
  • Fertiliser application
  • Best practices for managing pests, diseases and weeds.
Pongamia experts recommend that, for the first three years grazing livestock be excluded from the plantation in order to protect the trees from being damaged. This will necessitate mechanical control and removal of pasture from under and between the trees as well as some chemical control of weeds.

After that period sheep can be introduced into the plantation to manage the grasses and weeds. This will in turn provide a secondary income from the plantation (Section 10.6.5 of Bioenergy in Australia: Status and opportunities [PDF, 9.1 MB], published by Bioenergy Australia in 2012).

Table 2 is adapted from A Common View of the Opportunities, Challenges and Research Actions for Pongamia in Australia [PDF, 2.5 MB]. It shows that pod production starts around 4 to 14 years of age.

Trees can produce anywhere from 0 to 30 kg of seed each year which can be stored up to 12 months. Growers with trees that yield 20 kg of seed per year can expect to 7 tonnes seed per hectare per year on the basis that 350 trees are planted per hectare.

Table 2. Summary of reproductive and yield variables based on Australian observations to date.
Variable Unit Range based on all observations in Australia Average
Time to reproductive maturity Years 4 to >14 5 years
Full development of seeds Months 10-11 months 10 months
Flowering episodes per year Number 1-2 1
Seed production per tree kg/year 0 – 30 20a
Seed oil content % 31-45 40
Seed viability months < 12
Tree per hectare Number 320-500 350b
Yield estimate (if all trees are productive) tonnes/ha/yr 7*
* Calculated from a and b

Harvesting the seeds

Pongamia plantations are not labour intensive. They require one harvest per year and minimal upkeep, especially if interrow cropping or livestock are employed to manage weeds.

Mechanical harvesting is the cheapest and most efficient harvesting option. Growers can use either Collossus harvesters or umbrella harvesters, the same as those used in the olive and tree nut industry.

Colossus harvesters with associated bins and trailers cost around $900,000. A single Colossus harvester is capable of harvesting a 500 hectare plantation (Section 10.8.4 of Bioenergy in Australia: Status and opportunities [PDF, 9.1 MB], published by Bioenergy Australia in 2012).

Table 3. Operating costs of the harvester for 20 kg seed per tree yield scenario.
Cost item for harvesting Value
Total annual harvest cost (including cost of two drivers) $202,677
Operating cost per hectare per year $405
Operating cost per tree per annual harvest $1.1
Average cost kilogram of seeds in shell $0.06

Umbrella shaker-style harvesters require a minimum of 7 metres of spacing between rows. The optimal arrangement for accommodating a gantry style shaker with maximum trees per hectare is 7 m spacing between rows and 4 m between trees within the row, which gives approximately 320 trees/ha.

Some pruning is required during the establishment phase (first 3 years) of the plantation to control tree shape. Plants are generally pruned following harvest with the aim of maintaining trees at a height of approximately 6 metres (Element 7: Agronomy A Common View of the Opportunities, Challenges and Research Actions for Pongamia in Australia [PDF, 2.5 MB], published in Bioenergy Research, 2012).

Crushing and transporting

Oil can be extruded from the seed using the same crushing equipment used in the oil and nut industry. As part of the Bioenergy in Australia: Status and opportunities study [PDF 9.1 MB], researchers estimated the operational costs for operating a seed crushing and oil extrusion plant.

A crushing plant with a crushing capacity of 3,345 tonnes of seed in shell each year under the yield scenario of 20 kg of seed per tree is estimated to cost $716,000. This includes:
  • building and plant housing
  • storage bins for seed and meal
  • mechanical press
  • oil tanks
  • power source for press
  • civil works and costs of connection for electricity, water etc.
  • seed dehuller and cleaner
  • filtration equipment, valves, pumps and plumbing

Operating costs per litre of extruded oil are estimated to be $0.27. Freighting oil to a refinery within a 100 km distance from the crusher is estimated at $0.10. In total, seed crushing to extrude the oil and the delivery of oil with tank containers to a refiner account for 13% of the costs.

Contacts

Heather Bone

RebusJ Sustainability

50 Willowvale Drive, Willow Vale , Queensland 4209
Phone: 0400473733

heather.bone@hotmail.com
George Muirhead

BioEnergy Plantations Australia

Caboolture, Qld, 4510,
Phone: 0411 619 722

Prof. Peter Gresshoff

ARC Centre for Excellence for Integrative Legume Research

Queensland University of Technology, Brisbane, Queensland, 4072,
Phone: 07 3365 3550

p.gresshoff@uq.edu.au