Farmers in tractors block roads and set off fireworks in Brussels outside a summit of European Union leaders as protesters rally against a major free trade deal with South American nations.Farmers fear that the deal will undercut their livelihoods, and there are broader political concerns that it could also help drive support for the far right.Thousands of farmers are also expected at twin rallies planned by unions that are set to converge on Place Luxembourg, a stone’s throw from the European Parliament and the Europa Building where leaders of the 27 EU nations are meeting.They are to discuss amending the trade pact or delaying its signing.