As you drive along old Mazowe Road, northwest out of Harare, your attention is drawn to a large, colourful billboard: it announces the existence of a new bio-diesel plant, "the first in Africa".

The huge plant was commissioned amid pomp and fanfare by President Robert Mugabe recently.

The billboard says: "Bio-Diesel Processing Plant in Zimbabwe: Towards food self-sufficiency; oiling the wheels of the nation."

There is no smoke billowing from the tall chimneys. A few technicians mill around the silent plant.

The plant will become operational in two years when the Jatropha planted last year matures.

Touted by political leaders as the panacea to the fuel crisis, the plant probably deserves little of the hype.

Haunted by an eight-year fuel crisis caused by the foreign currency crunch, the government sees the project as a likely solution.

The plant is a joint effort between the government and Yuon Woo Investments of South Korea.

But experts are hesitant to sound as enthusiastic as the politicians.

The government has no capacity to support farmers to grow enough Jatropha, cotton, sunflower and soya bean seed to produce bio-diesel, say the experts.

They say the project will take "several years" to contribute to the country's fuel needs, if ever it will.

It's ironic that the plant was commissioned a month after a United Nations food expert called for "a five-year moratorium" on bio-fuel production.

But the government insists that the plant will ease fuel shortages.

That would happen when the plant is operating at full throttle, producing 100 million litres of bio-diesel a year.

Reserve Bank of Zimbabwe governor Dr Gideon Gono, at the same high-profile, glitzy ceremony, noted that the success of the bio-diesel project, to produce 90-100 litres of diesel annually, would depend entirely on agriculture.

"These peak production levels impose a challenge on the farming community to produce adequate feedstock of oil seeds to meet demand throughout the year," he said.

But an agriculture expert said it would take years for the bio-diesel plant to produce "meaningful quantities" of diesel.

"Right now we don't have enough seed for soya beans and cotton and where would they get the Jatropha? It would be another white elephant," said the expert who refused to be named, as this was a "sensitive issue".

Another expert said: "We would need a separate Zimbabwe to do that. We cannot convert arable land to grow Jatropha; otherwise we would experience serious food shortages. There is no land for that."

Zimbabwe has planted 100 hectares of Jatropha since last year, according to reports.

The land invasions of 2000 reduced oil seed production: soya bean from 150 000 to 60 000 tonnes; sunflower from 40 000 in 1994 to 20 000 tonnes in 2006; groundnuts from about 95 000 to 90 000 tonnes.

"But still," said the expert, "these figures are too little to make any meaningful contribution to produce diesel. What they did (inaugurating the plant) is like celebrating a still-birth."

Land expert Professor Sam Moyo described the project as "quite good" but said the general fear was that uncontrolled and unregulated growing of Jatropha would have serious implications on food production and the environment.

A UN independent expert, Jean Ziegler, last month condemned the increasing use of crops to produce bio-fuels as replacement for fossil fuels, saying it was creating food shortages.

Ziegler called for a five-year moratorium on bio-fuel production to stop what he called a growing "catastrophe" for the poor, which he called "a crime against humanity". Ziegler said it caused hikes in prices leading to more hunger.

Ziegler is a sociology professor at the University of Geneva, Switzerland, and the University of the Sorbonne in Paris, France.

Among the negative effects of fuel production from corn, sugarcane and other crops are indiscriminate deforestation, resulting in the high price and shortage of food, says his report.

Many species of trees would disappear, so ecosystems that absorb carbon from the atmosphere would be destroyed, leading to an increase in polluting emissions, the report says.

Research has shown that countries such as India, Mali, China, the Philippines and Malaysia are starting huge plantations, betting that Jatropha will help them to become more energy independent and even export bio-fuel.

It is too soon to say whether Jatropha will be viable as a commercial bio-fuel, scientists say, and farmers in India are already expressing frustration that after being encouraged to plant huge swaths of the bush they have found no buyers for the seeds.

The scientists say countries that struggle to feed their populations, like Mali, can scarcely afford to give up cultivable land for growing bio-fuel crops.

Already, World Food Programme estimates in Zimbabwe indicate that 4.1 million people need food aid.