"We sell at less than 30 per cent the cost of production. The cost to produce a ton of wheat is euro134, but the price of a ton is less than euro100," he said.
"Two years ago, the production cost was euro110 and the price was euro200."
The Paris protesters were among an estimated 50,000 people with 7,000 tractors who rallied in the streets, disrupting traffic for the demonstrations, FNSEA, France's main farmers' union said.
Outside of Paris, farmers on tractors clogged streets outside the southwestern city of Toulouse, while protesters threw soil in front of public buildings and released small farm animals in the western city of Poitiers.
FNSEA said in a statement on its website: "Mr Sarkozy, agriculture merits as much as the banking or automobile sectors."
The statement referred to emergency aid the French president's administration has offered to banks and car makers to help them through the global financial crisis.
Jean-Michel Lemetayer, the head of FNSEA, told France's RTL radio that he has appealed to the government for an "emergency plan", including tax cuts to help French farmers compete with European rivals.
Bruno Le Maire, France's agriculture minister, has said he will urge the president to reduce the tax burden on farmers this year.