Karadzic, the former Bosnian Serb leader, is on trial at the International Criminal Tribunal of the former Yugoslavia (ICTY), where he faces charges of genocide, war crimes and crimes against humanity stemming from the 1992-5 war.
He has denied all charges against him.
Prosecutors say Karadzic led a campaign to make Bosnian Muslims "disappear from the face of the earth" during a war that killed an estimated 100,000 people.
Zulic's testimony was intended to illustrate the brutal campaign, early in the war, to carve out an ethnically pure Serb mini-state in Bosnia.
Although Zulic did not mention Karadzic in the early part of his testimony, prosecutors allege the former Bosnian Serb leader orchestrated the plan.
The first day of testimony came months after Karadzic's trial started in October.
Karadzic boycotted that hearing to protest what he claimed was lack of time to prepare his defence against the 11-count indictment.
In his opening statement to the court on March 1, the former leader denied involvement in the four-year siege of Sarajevo by Serb forces, where 10,000 died, and the killing of some 8,000 Bosnian Muslim men and boys at Srebrenica in 1995.
Presiding judge O-Gon Kwon warned Karadzic on Tuesday that the court would not tolerate delays and could limit the length of witness cross-examination.
Karadzic's plan to spend 14 hours on one cross-examination was neither responsible nor realistic, he said.