'Magic bean' transforms life for poor Jacks of Central America

In the nursery tale, a handful of magic beans rescued Jack's family from poverty. In Central America, there are tens of thousands of poor Jacks whose fortunes have been transformed by planting beans; and that is no fairy story. This magic bean is called mucuna, or the velvet bean, and extraordinary claims are being made for it: maize crops have been tripled, erosion has been halted, destruction of the rainforest curtailed, and migration to the cities reversed.

The origin of this "magic" bean is obscure. It is thought to have come from southern Asia and spread through the tropics and beyond. In the 1930s, two million acres were grown in the US as fodder for cattle; and it was probably American plantation owners who brought it to Central America where it has now become part of what Professor James Pretty of Essex University calls " a new agricultural revolution".

Professor Pretty points out that, while the majority of the world's population benefited from the high productivity of industrial agriculture, two billion poor people were left out. "Poor producers [of food] cannot afford expensive technology ... they will have to find solutions based on existing resources."

One of those resources is the mucuna bean. In recent years, its use has been promoted by non-governmental organisations working among the rural poor in Guatemala and Honduras. They chose it because it provides the best solution to their biggest problem: how to improve crop yields on steep, easily eroded hillsides with depleted soils.

Farmers first plant mucuna, which produces masses of vigorous growth. When the beans are cut down, maize is planted in the resulting mulch. Subsequently, beans and maize are grown together. Very quickly, as the soil improves, yields of grain are doubled, even tripled.

The magic of mucuna is that it produces 100 tonnes of organic material per hectare, creating rich, friable soils on rocky hillsides in just two or three years. It is also so vigorous that it almost wholly suppresses weeds. The land never needs to be ploughed and, as if that is not enough, mucuna produces its own fertilizer. It takes atmospheric nitrogen and stores it in the ground where it can be utilised by other plants. Mucuna can fix up to 150kg of nitrogen a hectare, enough to triple maize yields.

In Honduras, results like that can turn abject poverty into modest prosperity. Twenty years ago, the small town of Guinope, two hours' drive from the capital, Tegucigalpa, was seen as a dying community, as many of its small farmers gave up the struggle to feed their families and fled to the cities. Today, some of those farmers are returning to their abandoned land and making it productive, with little investment other than knowledge.

So far, that knowledge has mostly come from non-governmental organisations led by inspirational figures such as Roland Bunch. He has been promoting sustainable agriculture in Central America for 15 years and, although he's wildly enthusiastic about the virtues of mucuna, he believes there are many other cover crops and green manures waiting to be discovered. "In Brazil, they're using over 65 species right now ... in another 15 years I would expect us to have 150 different species we can use, depending on the particular needs of the farmer."

Julian Pettifer's report on the mucuna bean can be seen on 'Correspondent' on BBC2 tonight at 6.15pm