PARIS/HAMBURG (Reuters) - European Union counter-tariffs on U.S. goods starting next week are set to halt a large flow of U.S. corn to Europe and raise costs for buyers chasing alternative supplies of the feed grain, traders and industry representatives said.

Grain market reaction has been restrained so far with traders unsure if a barrage of tariffs, including tit-for-tat U.S. and Chinese duties, will stay in place or be removed following negotiations.

The EU will impose a 25% duty on corn (maize) from April 15 in response to U.S. steel and aluminium tariffs. U.S. soybeans, which the EU imports in much bigger volumes than corn, will be subject to tariffs from December 1.

European countries mainly use corn to feed cattle, poultry and pigs.

The retaliatory measures, approved by EU countries on Wednesday, will price U.S. corn out of European markets where buyers have scooped up abundant and cheap U.S. supplies this season.

Between July 1, 2024, and April 6, 2025, the EU imported 3.4 million metric tons of U.S. corn, up from just 114,000 tons a year earlier as the United States leapfrogged Brazil to become the EU's No. 2 supplier behind Ukraine.

EU importers will still be able to find supplies in Ukraine and Brazil. But prices there are currently higher than in the United States and could rise further until Brazil's next crop arrives starting in July.

"I think corn tariffs is a cost story rather than a supply problem. There are alternative supplies in the Black Sea and South America but I calculate at least $6-$7 a ton additional costs for corn importers," one European trader said.

European feed industry association FEFAC has warned that tariffs on feed ingredients could add some 2 billion euros in costs, calling instead for the EU to use its import requirements as a way to expand trade with the U.S.

Spain has led EU imports of U.S. corn this season, including a new purchase of 240,000 tons announced by the U.S. government on Tuesday.

There was relief that some feed products such as soymeal have not been put on the EU tariff list, said Stephane Radet, director general of French feed industry association SNIA.

But the sector is concerned that feed additive lysine has been included, with separate EU anti-dumping tariffs on Chinese lysine raising the prospect of rising prices, he said.

The proposed EU duty on U.S. soybeans is potentially a bigger issue, as the U.S. is the EU's largest supplier at over 5 million tons annually.

But the deferred December 1 date for the soybean duty is seen by traders as leaving time for trade talks and letting EU importers continue buying U.S. beans while No. 1 importer China focuses on Brazilian supplies.