The senate vote itself was not enough to cancel the tax increase because it has been issued by executive order.
Julio Cobos, the vice-president, cast the deciding vote against the government-backed bill to break a 36-36 tie in the senate, sparking outrage among the president's allies.
Kirchner had sent the proposal to congress after months of strike action by farmers following her initial decree raising taxes on soy and grain exports issued in March.
Strong opposition
The bill passed the lower chamber of deputies on July 5 where it faced stronger than expected opposition.
It proposed to raise grain export tariffs from 35 to 47 per cent, on a sliding scale linked to global prices.
The vote came after rival protests for and against the bill on Tuesday, with hundreds of thousands demonstrating in the streets.
With the vote carried live on national television, hundreds of opponents of the bill gathered in the Palermo district to watch the proceedings.
They erupted in celebration when the bill went down to defeat.
Farm leaders welcomed the tax-increase cancellation.
"The conflict is over," said Luciano Miguens, head of the Argentine Rural Society,