The terminal outside Belem in Para state will have an initial annual capacity of 1.5 million tonnes of grain and will expand to 6 million tonnes per year by 2016.
"The first trucks are already unloading soy," ADM said in a statement on July 31.
About 80% of the initial volume will move on waterways mostly in Brazil’s interior while the rest will be trucked in until a railway is finished.
ADM said the new route will take 34% off its freight costs from shipping out of Brazil’s main port of Santos, which is thousands of kilometers south.
ADM received approval for terminal use from waterway regulator Antaq last month in what it said was the first contract awarded under Brazil's new port law, which was passed in 2013.