Quote: “Jatropha curcas Linn was promoted as miracle crop capable of producing biofuel”
At first jatropha was grown not as a commodity, but for the intrinsic value of the tree. Traditionally it is, for instance, used for medicinal purposes and the production of soap (1, 2). Jatropha planted in rows forms an effective hedge protecting crops from browsing livestock, serving as wind and fire barriers (3, 4).
Jatropha is used in contour planting to prevent soil erosion or to rehabilitate eroded watersheds. Examples of such use can be found in Ethiopia, Mali and Tanzania. The situation changed in 2004/2005, when jatropha began to be viewed globally as a possible source of biofuel. The aim of this article is to introduce Jatropha curcas and to explain what uses it has for biofuel and beyond.
A description of jatropha
Jatropha curcas L. is a monoecious shrub or small tree of on average 3-5 and up to 8 m height, with a single main straight stem and multiple secondary branches with leaves arranged alternately on the stem (3, 4). The crop belongs to the genus Euphorbiaceae and can be found in many tropical and subtropical regions, roughly between 30°north and 35°south. Jatropha grows in arid and semi-arid areas, e.g. in India, and is therefore known as drought tolerant, but for seed production sufficient water is needed.
Rooting patterns are influenced by propagation methods, with direct seeding leading to one taproot, four lateral roots and many secondary roots, and propagation by cuttings generally leading to more superficial secondary roots only. The root system affects jatropha’s drought tolerance as taproots can tap into deeper soil water layers. The limitation of soil fertility hampers crop growth and production, as has been shown by fertilizer trials on waste lands in India(5). As a perennial crop, jatropha stands may reach maturity and full production three to four years after planting. Over time jatropha invests a lower proportion of its assimilates into wooden standing biomass and, if properly pruned, most assimilates become available for the seasonal growth of branches, leaves, flowers, fruits and seeds. Although singular jatropha trees seem to be free from pests and diseases, serious problems have been reported with fungi, viruses and insect attacks in jatropha plantations.
Pollination is by insects. The female flowers form fruits which normally contain three seeds. Abortion of flowers and fruits may be as high as 60%, depending on soil water and nutrient availability (6). Seeds have a hard shell with a soft, white kernel, their weights 35-40% and 60-65% respectively. Dry seeds have an oil content of between 25% and 35% (3, 4, 7), making them a potential source of biodiesel. With the exception of some non-toxic or low phorbol ester accessions identified in Mexico, all parts of the plant, including the seeds, are inedible (for man and livestock) due to the presence of various toxic phorbol esters, curcin, trypsin inhibitors, lectins and phytates.
Jatropha yields have been estimated by many, but have only been measured by a few. Furthermore, many seed yields have been extrapolated from single trees or provenance trials to fields. A further complicating factor is that commercial varieties do not exist yet; hence when you plant seed from a single source, you may end up with a field of trees that show high variability in architecture, size and productivity. Maximum seed yields in mature stands of improved populations of jatropha reach 3t/ha in Indonesia (8). These seed yields per hectare are low compared to expectations (12 tons seed/ha reported in Jongschaap et al. (7); 5 tons seed/ha in (2)) and calculated potential yields based on crop physiological characteristics and growing conditions (1.5-7.8 tons seed/ha, according to Jongschaap et al.(7)).
Jatropha can be cultivated as a single tree, in hedges, in intercropping with other crops, or as a monoculture. Jatropha productivity can suffer from competition for water, nutrients and sunlight when planting densities within jatropha fields or hedges are high, or when the planting distance between jatropha and other crops is low. In certain situations jatropha is primarily used as a barrier to prevent soil and water erosion, or to rehabilitate eroded watersheds. Then plant density is only related to its effectiveness as a barrier, and the production of seeds is, at most, an added bonus of the tree.
Biofuels are classified into three basic groups. In the first group, biomass is produced by converting edible crops using conventional technology to produce bioethanol, biodiesel and biogas. Sugarcane, cassava, sweet sorghum and beetroot sugars are fermented to produce bioethanol. Edible oils extracted from oil palm, soybeans, rapeseed and sunflowers, and inedible oils from jatropha, Pongamia, Castor and Calophyllum, are processed into biodiesel via a transesterification process (1). Anaerobic digestion of non-edible biomass is used to produce biogas. The second group includes the production of diesel from lignocellulosic biomass, crop residues and municipal waste, using advanced process technology. The third group includes biodiesel or kerosene grade alkane, derived from microalgae biomass containing lipids or oil.
Fuel uses of jatropha
The seeds are pressed to produce crude oil, which can be used as a substitute for kerosene for cooking and lighting. The oil can also be used directly in diesel engines, although it has a high viscosity, acid composition and free-fatty-acid level; therefore, these engines need to be adapted. The oil can be transformed into biodiesel through the use of methyl or ethyl esters in a transesterification process (2). Biodiesel can easily be blended into diesel and be used in the existing combustion engines of cars. The press cake, remaining after oil extraction, can be burned directly or pressed into high-energy briquettes. The press cake, fruit exocarp, seed shell and pruning materials can be used for biogas production (4). The pruning and, at the end of its productive life, the woody stem, too, can be used as fuel wood, although the wood takes a long time to dry. Woody parts and nutshells can be transformed into charcoal. It is also possible to use the whole fruits or whole nuts as an energy source, to be burned for household cooking or to fuel industrial processes in brick making, bakeries, et cetera.
Non-fuel uses of jatropha
Jatropha products from different phases of the production and processing process can be used for non-fuel purposes (1, 2, 4). During jatropha cultivation, therefore in the field phase, biomass is pruned to increase the productivity of the plant. This biomass consists of branches and leaves and can be used as firewood (fuel), mulch (also having a fertilization effect), building material or cuttings for new plantings. Bees are responsible for pollination; hence the jatropha flowers can serve as a substrate for honey. Tannins can be extracted from the bark and nutshell to treat leather. In some countries leaves are also used as feedstock for silkworms. During the oil-producing process a press cake is produced in which the seed’s proteins (c.25% of the seed), carbohydrates and most of the minerals are present. The press cake, containing 3.2-4.4% Nitrogen, 1.4-2.1% Phosphorus and 1.2-1.7% Potassium (9), can therefore be used as fertilizer to replenish the soils. When the jatropha variety is non-toxic, or when toxic elements have been removed, the protein fraction (about 50-62% of the press cake) can be used as animal feed. In the biodiesel production phase glycerine and soap are produced, whereas the methanol and magnesium silicate used in the process can be recovered for reuse.
Jatropha can also be valuable as contour planting to prevent soil and water erosion, or to rehabilitate eroded watersheds. Furthermore, the climate change debate has drawn attention to jatropha’s ability for carbon sequestration, potentially tapping into the voluntary payments for carbon credits.
The potential for jatropha to provide a renewable source of energy technically exists, and different forms of energy can be produced from different components of the plant. The production of plants and their seeds can be hampered by insufficient water and nutrients, and by pests and diseases. The regular fruit harvests and removal of prunings require regular nutrient supply to the plants for continuous production. These nutrients can, at least in part, be supplied through the reuse of press cake and prunings as fertilizers, and mulch in the jatropha fields. Jatropha can not only be used for renewable energy, but for many other things besides.
So far the seed yields per hectare are low, both compared to expectations and in absolute terms, and they are also unpredictable, being subject to many pests and diseases, and do not always respond favorably to pruning, fertilizer and water applications. This makes the production of jatropha for biofuels an unrealistic business proposition currently. The price of a liter of jatropha-based biodiesel is too high to compete with fossil-fuel diesel. For businesses, but especially for smallholders, the additional non-energy uses of jatropha might add value and turn it into a viable enterprise, especially in the longer term.
If jatropha is to be successful as a biofuel and as an additional source of income for smallholders and commercial plantations, then continued agronomic research and the development of high-yielding varieties is urgently required to increase both the yield per hectare and the stability of the yield over time. Furthermore, the development of non-toxic varieties, or a cheap and simple method of detoxifying seeds or press cake, is essential to enabling the use of the seeds’ high protein content. To capture the value of biofuel and other jatropha products, the entire supply chain (including seed collection, transport, processing and market) needs to be present for each of the products, and the market prices need to be conducive.
1. G. M. Gübitz, M. Mittelbach, M. Trabi, Exploitation of the tropical oil seed plant Jatropha curcas L. Bioresource Technology 67, 73 (1999).
2. K. Openshaw, A review of Jatropha curcas: an oil plant of unfulfilled promise. Biomass and Bioenergy 19, 1 (2000).
3. J. Heller, “Physic nut. Jatropha curcas L. Promoting the conservation and use of underutilized and neglected crops. 1” (IPGRI, Rome, Italy, 1996).
4. A. Kumar, S. Sharma, An evaluation of multipurpose oil seed crop for industrial uses (Jatropha curcas L.): A review. Industrial Crops and Products 28, 1 (2008).
5. J. Patolia et al., “Provenance trials for selection of high yielding Jatropha curcas on wastelands.” Expert seminar on Jatropha curcas L. Agronomy and Genetics, Wageningen, the Netherlands, March 26-28, 2007. Published by FACT Foundation, Eindhoven, the Netherlands.
6. A. Kumari, A. Kumar, “Influence of growth regulatiors on flowering and fruiting in Jatropha curcas.” Expert seminar on Jatropha curcas L. Agronomy and genetics, Wageningen, the Netherlands, March 26-28, 2007. Published by FACT Foundation, Eindhoven, the Netherlands.\
7. R. Jongschaap, W. Corré, P. Bindraban, W. Brandenburg, “Claims and Facts on Jatropha curcas L.: Global Jatropha curcas Evaluation, Breeding and propagation programme” (Plant Research International, Report 158, Wageningen UR, the Netherlands, 2007).
8. R. D. Purwati, “Improvement of jatropha productivity through conventional breeding”. After the Hype: Learning from Experiences Jatropha in Indonesia. JARAK Cluster Research: The Commoditization of an Alternative Biofuel Crop in Indonesia, October 10-12, 2012, Yogyakarta, Indonesia.
9. J. D. Montoya, E. P. Tejeda. “Potential multipurpose agroforestry crops identified for the Mexican Tropics,” in G. E. Wickens, GE, Haq, N., Day, P.(Eds), New Crops for Food and Industry, pp.166-173. (Chapman and Hall, London, 1989).