Erai Maggi does not look like a villain who is destroying the planet; nor does he look like a hero who is saving the world's poor. Wearing jeans and work boots, he can be found on a typical day driving a battered Fiat car on one of his farms south of the Amazon rainforest.

For someone who excites extreme views he seems miscast, neither Darth Vader nor Indiana Jones. But the 48-year-old Brazilian farmer is protagonist in a drama about climate change, globalisation, poverty and hunger.

Maggi owns more than 200,000 hectares (494,000 acres) of soyabean plantations in Mato Grosso state. It is reckoned to be the biggest such holding in the world, making him the king of soya.

"What really makes me feel happy is seeing the beans in the fields," Maggi said recently, shading his eyes from a tropical sun while gazing over yellowing fields ready for harvest.

According to environmentalists, Maggi also knows how to accelerate deforestation of the Amazon, at least indirectly. By buying up the savannah for soya cultivation, he forces cattle ranchers north into the rainforest where they slash and burn, releasing millions of tonnes of carbon dioxide into the atmosphere, said Paulo Adario, the Amazon director of Greenpeace in Brazil. "It is an indirect but fundamental impact."

There is another version of Maggi: a pioneer who helped turn a sea of barren scrub fit only for some cattle into highly productive farmland - and in the process turned Brazil into an agricultural superpower which is expected to overtake the US as the world's leading food exporter while the global population surges towards 9 billion people.
Brazilian government scientists discovered that the acidic soils of the savannah could be made fertile with phosphorus and lime, a momentous technological breakthrough that Maggi and other migrants from the south exploited when they moved to Mato Grosso in the 1970s and 1980s.

Not so long ago, Maggi's story would have been cast in terms of development versus ecology. Now a new dimension has complicated the picture. An upward surge in commodity prices has created, what the United Nations last week called, a "new face of hunger".

Annual global food price increases of up to 40% are hitting the poor and raising the spectre of urban malnutrition. Food riots have broken out in Morocco, Yemen, Mexico, Guinea, Senegal and Uzbekistan. Emergency price controls have been declared.

Surging demand for meat and other foodstuffs from a new middle class in China and India is the main cause, followed in part by the transfer of land and grains to the production of biofuel and the hikes in energy costs. Volatile weather linked to climate change is a small but growing factor, said the International Food Policy Research Institute.

For Maggi, this prompts a dramatic conclusion: Brazil's soya producers, without subsidies, are helping to save humanity. "We are a vital part of the food chain," he said. "We are producing the cheapest and healthiest protein there is."

Soya, a legume native to East Asia, has been called a "miracle bean" owing to its high protein content. Popular with vegetarians, it is now valued as a cheap and safe animal feed.

Maggi started out with a small plot and bought up neighbours, building an empire requiring a two-prop plane to keep tabs on its outer reaches.

His firm, Bom Futuro, uses 300 combine harvesters and 500 tractors to produce more than 600,000 tonnes of soya a year, most of it to feed livestock which will end up as meat in China and Europe. He denies any responsibility for deforestation. Soya farmers kept 35% of the savannah untouched, as mandated by law, and did not operate in the rainforest, said Maggi.

Erai Maggi has put his name forward for Brazil's senate because he wants to accelerate Mato Grosso's development by paving roads and harnessing rivers. "That will mean cheaper food for China, for India, for everyone," he said.

For critics, this is the self-serving claptrap of a deluded or cynical tycoon. That producers are striving to keep prices low is implausible as they squealed in unison when prices plunged three years ago before recovering in 2007.

Nor is there much doubt about the link with deforestation. Soya producers buy up land already cleared by cattle ranchers who then acquire cheaper land deeper in the Amazon jungle, replacing virgin forest with pastures.

The rocketing of soya prices has been widely blamed for the accelerating clearances. Soya is also directly penetrating the Amazon, accounting for up to 10% of national production according to most estimates.

There are also concerns about labour conditions. This year Brazilian officials extracted 41 workers from what were described as "slave-like" conditions on one of Maggi's farms.

Regardless of whether Maggi is a hero or villain there is no doubting Brazil's importance in the global food chain. Across the savannah new towns built on soya have fancy hotels with clocks showing the time in Chicago, home to the world commodities market.

Prices fluctuate according to the unpredictable zig-zag of weather, investment and production data. Brazil's soya farmers like to point out that when the bell sounds at the end of a trading day there is one number which always, without fail, shows a relentless, remorseless rise: that of mouths to feed.