Even as farmers across Wisconsin leave the agricultural industry, the volume of crops they produce keeps growing dramatically, according to a report.

There are 50,000 fewer farmers and 23% less farmland in Wisconsin than in 1970, but yields of milk, corn and soybeans are up more than 80% over that period, the report says.

But agricultural experts note that the continuing loss of farmland to development could increase demands on the remaining soil while reducing green space and wildlife habitat.

The report, released last week by the nonprofit Wisconsin Taxpayers Alliance in Madison, said the state’s total agricultural output was $912 million in 1970 and rose to $3.36 billion in 2004. But as a percentage of gross state product, farming slipped from 4.5% to 1.6% over that time.

Alliance spokesman Ryan Parsons said the numbers show farming is an ever-shrinking factor in the state’s economy, but that may not be cause for alarm.

“We’re never going to get back to when the state used to be predominantly farming,” he said, “but farmers in Wisconsin and nationally are still producing what the country needs.”

Parsons said the state’s statistics mirror a national trend. For example, from 1970 to 2005, corn yields increased 80% from 82 bushels per acre to 148. Farmers nationwide increased production from 72.4 bushels per acre to 147.9, an increase of 104%.

According to the report, there were 1.24 million cows in Wisconsin in 2005, about 32% fewer than the 1.81 million cows in 1970, the first year for which reliable data were available. Yet milk production jumped 24% in that same period, as production per cow went to 18,500 pounds a year from 10,200 pounds.

The alliance attributes such increases to improved technology and a greater willingness among farmers to apply new techniques.

The findings aren’t surprising since agricultural science has always showed a trend toward improvement, said Richard Barrows, professor emeritus in the University of Wisconsin-Madison department of agriculture.

“But the two concerns for Wisconsin are, one, that families transitioning out of agriculture have other opportunities to move into. And two, for the families that remain, agriculture has to remain profitable,” he said.

The alliance report noted that total farmland in the state was 15.5 million acres in 2004, down from 20.1 million acres in 1970. Much of the lost land was turned into commercial housing, said state Department of Agriculture spokeswoman Jane Larson.