Brian Schilling, a specialist in agricultural policy at Rutgers Cooperative Extension, is unequivocal in his support of a tax differential system for farmers. “Without farmland assessment,” he said, “we wouldn’t have any viable agricultural activity in this state.” But he acknowledged that “enforcement of the law is not always as rigid as it could be.”

The state Division of Taxation offers local tax assessors a handbook and seminars on the Farmland Assessment program, but better guidelines would be welcome, said Patricia Wright, who oversees the program.

“The Department of Agriculture could give more guidance on what is or is not a farm,” said Ms. Wright, a property tax administrator with the tax division, “but it needs to come from them. They are the farmers; we are the tax people.”

New Jersey has about 982,000 acres of farmland, according to Ms. Wright, who added that 10 years ago it had 1.1 million. In a 2008 study, Mr. Schilling’s department looked at the potential impact of raising the revenue threshold on state farmlands and local tax coffers. A $10,000 threshold would remove about 398,000 acres of farmland from eligibility for the farmland assessment, while raising $51 million in new taxes. A $1,000 minimum would make 47,378 acres ineligible, while adding $2 million in taxes.

But Mr. Schilling noted that imposing the $1,000 threshold wouldn’t mean losing as much farmland as those numbers suggest, because “I fully would expect every landowner to find every way possible to increase productivity to generate $1,000 and meet the new threshold.”

According to Richard Motyka, a tax assessor in seven towns in Warren and Passaic Counties, doubling the threshold will not present much of a challenge for those currently eligible for the exemption. “Going from $500 to $1,000?” he said. “That’s just a stroke of a pen. It’s not very hard to buy a book of receipts.”

Over the years, Mr. Motyka has challenged many who have claimed to be running farm operations, only to lose most of his challenges in court. “I’m a little jaded,” he said. “I just sign off on them unless you’re outright doing nothing. The bar is so low, it’s not worth fighting.”