BUENOS AIRES, March 29, 2008 (AFP) - Argentine farmers restarted their damaging national strike over a hike in export taxes Saturday, barely 24 hours after it ended, after negotiations with the government broke down.

The four major farming groups said in a statement that President Cristina Kirchner's government had refused their demand to suspend an increase in the tax on soya products, Argentina biggest export, for at least 90 days.

They suspended their 16-day strike, which had seen roads blocked across the country, on Friday after Kirchner called for talks over their concerns about the increase of taxes on soyabean exports from 35 to 44.1 percent.

But five hours of negotiations overnight Friday ended in failure, and the groups ordered a resumption of the protests that had caused nationwide food shortages and prompted clashes between farmers and truckers.

Half of Argentina's fertile farmland is used for soyabean cultivation, and the country is the biggest soya exporter in the world, sending 13 billion dollars' worth annually to China, India, southeast Asia and Europe.

The strike became the biggest test so far of Kirchner's mandate, which started in December.

She and other ministers had labeled the farmers 'extortionists,' and pointed out that sky-high commodities prices on the world market, coupled with Argentina's devalued peso, have made many rural landowners very wealthy.

But farmers complain the tax hike, combined with income taxes, transport costs and the high cost of land, would push many of them out of business.