The 'double agent' is also accused of sharing excerpts from an official government document on Germany's relationship with Russia after its annexation of Crimea.
Ralph G. today declined to speak, but will do so at the next hearing on September 1.
The accused soldier was a reserve lieutenant colonel who also worked as a sales manager for an international engineering company in western Germany, Der Spiegel reported.
After his arrest in 2020, he admitted to having supplied information to the Russians, but claims not to have known his contacts were working for the country's military intelligence, the newspaper added.
He was charged in April with leaking information on a variety of sensitive areas for the Federal Republic of Germany.
Last year, a German court sentenced a Russian man to life in prison for shooting dead a former Chechen commander in a Berlin park in broad daylight, a murder prosecutors say Moscow ordered.
A Russian man also went on trial in Munich in June charged with plotting to kill a Chechen dissident living in Germany on the orders of Chechen leader Ramzan Kadyrov.
Ralph G. is the latest in a string of suspected Russian spies uncovered on German soil.