Jatropha curcas seeds yield oil that can be processed into biodiesel, but scientists at the International Crop Research Institute for the Semi-Arid Tropics (ICRISAT), Hyderabad, have found that Jatropha plantations can also sequester carbon in abundant quantities.
The findings, reported in October in Agriculture, Ecosystems and Environment, may reignite the 'fuel-versus-food' debate where critics argue that Jatropha cultivation diverts lands that could be used to grow food crops and affect food security.
ICRISAT scientists, led by Suhas Wani, assistant research programme director, studied Jatropha plantations in six different locations in India and measured the amount of carbon dioxide – a greenhouse gas – they removed.
Jatropha plantations older than four years added as much as 1,450 kilograms of organic carbon per hectare per year through leaf fall, pruned twigs and residue after removal of oil, the study said.
Also, by increasing organic carbon in soils and live root activity Jatropha plants encouraged growth of the soil's microbe population – a key indicator of soil health.
Nutrient availability also improved through recycling of the biomass back into the soil. Nitrogen increased by 85 kilograms per hectare, potassium by 44 kilograms, and phosphorus by eight kilograms.
Previous experience has shown that commercial farming of Jatropha is fraught with problems, including non-availability of quality seeds and the need for inputs such as irrigation and fertilisers.
At the current productivity levels of 1–1.5 tonnes of oilseeds per hectare, commercial Jatropha cultivation for producing biodiesel is not as economically viable as other crops, Wani said. Hence, it is better used for restoring degraded lands, he said.
"Our emphasis is on reducing the burden of degraded lands and problems such as runoff, siltation and receding groundwater. If we could rehabilitate degraded lands, it may lead to improved carbon sequestration, soil fertility and greening," Wani told SciDev.Net.
Vijay Gour, associate professor at the Jawaharlal Nehru Agricultural University, Jabalpur, says the initial hype over Jatropha resulted in several multinational companies investing in large plantations for oil production without proper planning.
More studies, as well as crop improvement through such methods as genetic manipulation, are needed before Jatropha can become a viable source of biofuel, Gour told SciDev.Net.