The small village of Miririnyi village lies in the sun-baked province of Arusha in northern Tanzania.

The ancient crop jatropha grows wild here. It is extremely hardy and can survive in dry, barren soil - even though other plants cannot.

It used to be considered as bush with no commercial potential.

But the global search for clean energy has changed all that.

That is because the seeds can be harvested to make biofuel. It has meant that farmers are now taking to the crop with gusto.

Child’s play

Samson Nasary is one such farmer, and he is looking to jatropha as an important source of income.

He harvests the seed and takes it to a collection point where he meets an agent for a firm called Diligent Tanzania. The product is weighed and valued, then a deal is struck.

Mr Nasary says it was school children looking for extra pocket money who first led the way in raising awareness of the commercial potential.

"Initially, it was actually the kids who’d sell the seeds - and we really got interested and thought - why can’t we get the seeds and sell them,” he says.

"That’s why we’ve been collecting the seeds and selling them to Diligent.”

A few miles away from the farm, we come to a factory run by Diligent. The company doesn’t grow jatropha itself.
It buys seeds from farmers through its local agents.

Many uses

The heart of the operation is a hot, noisy, sticky place. The seeds are crushed, processed and turned into crude jatropha oil.

Once its been refined it can be used to power electric generators and cars.

Diligent run some of their vehicles on the stuff. Jatropha oil from this factory has even been used as fuel in a 747 making an experimental flight.

It can also be used to make other products like soap and candles. Researchers are looking into possible medical applications.
But here is the rub.

The government is facing complaints that food production is being threatened because so many farmers are focusing on jatropha rather than edible crops .

And that’s something a poor country like Tanzania can ill afford.

‘Green gold’

Faustina Manang works for Diligent. Her job is to liaise with the farmers and encourage efficient management of the crop.

The company is facing real pressure from the government to make sure jatropha does not squeeze out food production.

"The government is shouting about this because some of the farmers they plant only jatropha without food production,” she says.

"We try to tell them to to mix it with food production, like maize, like beans. They agree and they do that.”
The message does seem to be getting through, at least to some farmers.

Mr Nasary says he’s determined to continue growing food alongside his jatropha - and will only grow it where food cannot flourish.

But critics still question whether jatropha really can be the "green gold” its supporters claim.

Production is still small scale - most cultivation around the world is on plots of less than 12 acres.

Current production is certainly not enough to make a real dent in our demand for fossil fuels.

It can grow in poor conditions - but some scientists say that the amount of oil produced under such condition will also be poor.

So while the farmers of this small village continue to exploit this new source of income - the status of jatropha as wonder biofuel - remains uncertain.

BBC