Scientists say a jatropha plantation in an arid region of Madagascar has helped increase the organic matter of degraded soil from 0.2 percent up to 3 percent, making it possible to grow other, protein-producing crops between rows, according to a report in SciDev.net.

Jatropha, a hardy biofuel crop, needs little water. Planting trees in coastal deserts could capture carbon dioxide, reduce harsh desert temperatures, boost rainfall, revitalize soils and produce cheap biofuels, the report said.

Large-scale jatropha plantations could help sequester carbon dioxide through a process known as carbon farming, according to a study based on data gathered in Mexico and Oman that was published in Earth System Dynamics.

In the Madagascar plantation, local people now harvest beans planted between the trees, providing protein and creating a symbiotic exchange of nitrogen – fixed from air by beans – and shade provided by the jatropha trees.

“Previously, no one had the idea of using uncultivated land to plant these kinds of leguminous beans because they would not grow there. But after four or five years of applying cultivation techniques, the soil quality increases dramatically,” said Klaus Becker, the study’s lead author and director of carbon sequestration consultancy Atmosphere Protect.

Each hectare of jatropha could soak up 17-25 tonnes of carbon dioxide a year at a cost of about $56-$84 per tonne of gas, making the technique competitive with high-tech carbon capture and storage, scientists say.

A jatropha plantation covering 3 percent of the Arabian Desert could absorb all the carbon dioxide produced by cars in Germany over two decades, Becker said.

“Our models show that, because of plantations, average desert temperatures go down by 1.1 degree Celsius, which is a lot,” Becker said.

Plantations would also induce rainfall in desert areas, Becker added.

He envisages a role for sewage in such large-scale plantations. Billions of liters of sewage are discharged into the oceans every week, but instead that water could be sent to the desert to water planted trees, eliminating the need for expensive artificial fertilizer.

Carbon farming is a common-sense approach to rising carbon dioxide levels, says Alex Walker, a research assistant at the Center for Environmental Policy at Imperial College London, U.K. “It will grow on non-arable land, and so not compete with food production, but it is more difficult to process.”

Egypt is pioneering an experiment in desert farming using sewage water after basic treatment to produce wood, woody biomass and biofuel crops, such as casuarina, African mahogany, jojoba, neem, and jatropha.

“In Egypt, there are 15,000 acres planted with trees of good quality but so far they have not been sold to create economic value,” Hany El Kateb, a professor at the Technical University of Munich in Germany.

Egypt produces more than 6.3 billion cubic meters of sewage water a year, and 5.5 billion cubic meters of this would be enough to forest more than 650,000 hectares of desert lands and store more than 25 million tonnes of carbon dioxide annually in new forests, El Kateb said.

Trees grow more than four times faster in Egypt where the sun shine most of the year than European countries that are leaders in forestry, such as Germany, he said.

The biggest challenges to planting forests in arid areas are lack of experience, lack of expertise and lack of technical personnel in the management of forest plantations, said Mosaad Kotb Hassanein, director of the Central Laboratory for Agricultural Climate in Egypt.