A First Amendment lawsuit over the rights of protesters to rally at Central Park could turn, in part, on the lawn care strategies of dueling turf management experts.

In a ruling on Tuesday, a federal judge paved the way for a trial on whether the city uses concerns over the grass at the Great Lawn as a pretext to discriminate against political organizations.

Both the city and the plaintiffs have turned for help to professors who specialize in grass growing.

In depositions and reports from 2005, the expert witnesses for both sides show that there can be sizeable differences of opinion when it comes to predicting how much damage a certain concert or event will cause the 13-acre stretch of ball fields and Kentucky bluegrass and perennial ryegrass known as the Great Lawn.

At the heart of the case is the city’s claim that an anti-war protest is likely to cause damage to the lawn of the same magnitude as a rock and roll concert where the audience is standing and stamping its feet. The experts were called on to discuss whether the audiences of the regular Philharmonic and Metropolitan Opera performances at the Great Lawn affect the grass any differently than would concertgoers at a Dave Matthews Band or Joan Baez show.

In a deposition, whose transcript is more than 200 pages long, the city’s expert witness, A. Martin Petrovic, a professor of turfgrass science at Cornell University, said events such as rock concerts and war protests should be considered “high-impact events” for the potential they have to damage a grassy field.

Other events, such as outdoor symphony performances, should be classified as “passive” because they would likely take less of a toll on the grass, Mr. Petrovic, who was part of the team that renovated the Great Lawn in the 1990s said.

The theory has come under attack by a lawyer for the National Council of Arab Americans, an organization that was denied an event permit for an anti-war rally in 2004. The lawyer, Carl Messineo, argues that Mr. Petrovic’s reasoning doesn’t shed much light on whether his group’s proposed rally would have harmed the lawn. In the deposition, Mr. Messineo tested the limits of Mr. Petrovic’s distinction.

“Do you agree, is it your hypothesis that, for example a Joan Baez concert would not likely be a passive event,” Mr. Messineo, asked Mr. Petrovic at the 2005 deposition.

Mr. Petrovic said he could not answer the question as he had seen only an indoor performance by the folksinger.

Mr. Messineo pressed on, asking whether an outdoor anti-war concert by Pete Seeger would do damage to the Great Lawn.

Mr. Petrovic’s response was inconclusive.

“Could he stir the crowd to be very flamboyant? I don’t know,” Mr. Petrovic said.

The plaintiff’s expert witness, John Rogers III, a professor at Michigan State University whose career began in golf course management, filed a report to the court in 2005 saying that the city’s decision to reject one political rally was unnecessary. The rally by the National Council of Arab-Americans was intended to be a “family event” that would likely have had no more impact on the lawn than events routinely approved for the Great Lawn, such as concerts by the Philharmonic or Metropolitan Opera, Mr. Rogers wrote in his report.