At a news conference, agricultural leaders said the freeze on selling goods such as corn and soybeans would last until May 15.
Eduardo Buzzi, president of the Argentine Agrarian Federation, one of the four groups that led March's strike, said: "After 57 days, we haven't advanced. The government has chosen the road of confrontation.
"It's the only reason we haven't reached an agreement."
News of fresh protests, which affects grains shipments, sent US soy futures soaring on Wednesday.
Farmers manned roadblocks and stopped selling grains and beef for 21 days in March after the government introduced a sliding scale of export taxes that substantially raised the levies on soy and sunseed products.
That protest caused food shortages in Argentina's supermarkets and has been the biggest challenge faced by Cristina Fernandez, the president, since taking office five months ago.
Soon after Wednesday's announcement, Alberto Fernandez, the cabinet chief, called on farmers to show "good sense" .
"We've got to be more sensible. And that's coming from someone who ... feels he's had too much faith in them. I would have loved to have kept on negotiating," he told Radio 10.
Even before a new wave of protests was announced, farmers staged roadside protests across the country.
Argentina is the world's second biggest exporter of corn, the third-biggest soy supplier and the number four provider of wheat and beef.
Fernandez has refused to scrap the sliding-scale tax system and has defended high export taxes on farm goods as a way to redistribute wealth and combat inflation in a country where a quarter of the population lives in poverty.
| Cristina Fernandez is facing her biggest |
challenge since taking office [EPA]
Increased revenue from export taxes has helped the government maintain budget surpluses and keep the peso currency weak to stimulate exports.
However, the tax announced on March 11 was one of a several policies that have angered farmers, including price controls and repeated export restrictions on wheat and beef.
The new system pins export taxes to international prices, raising levies on soybeans to about 40 pe rcent at current prices from the previous fixed rate of 35 per cent.
Soy exports earned the country $13.47bn last year while sales of farm goods abroad accounted for 52 per cent of total Argentine exports, totaling $29.13bn.