As the 2013 Feeding Cities conference unfolds this week in Philadelphia, Next City, a media partner for the event, will feature regular updates from bloggers covering its talks and workshops. Click here to see a rundown of our coverage.

In an eye-opening presentation today, Zhengxia Dou, a specialist on Agricultural Systems at the University of Pennsylvania School of Veterinary Medicine, described the immense pressure China’s population rise will put on the country’s — and the planet’s — agricultural resources.

Since the disastrous Great Leap Forward of the 1960s, when 30 to 40 million Chinese died of hunger, China’s growth has been a phenomenal agricultural success story. Per-capita grain production has doubled over last 30 years, while arable land decreased. China, today, feeds 19 percent of world’s population using only 9 percent of its arable land. Dou also credited China’s controversial population controls. “If it was not for the one-child policy, there would be 400 million more people in China,” she said. “That’s more than the total population of the U.S.”

But the progress of the last three decades comes at a heavy price. With efficiency gains depleting in recent years, Dou said China is more and more relying on increasing crop acreage by converting more land for agricultural use. That leads to diminishing returns, pollution and soil degradation. China’s agricultural labor force has also been depleted by by the migration of young people — particularly young men — to growing megacities. This migration has created what she calls “C-O-W” villages, with populations consisting largely of children and older women.

In the mean time, demand is only growing. China’s population is projected to peak somewhere between 1.47 and 1.5 billion people around 2030. About 1 billion of those will live in cities, and about 500 million will be in the ranks of the country’s growing middle class. Dou projected that the grain demand around this time will be around 700 to 800 million tons per year. The record is about 517 million tons, and gains per year have been falling.

It’s possible that technological progress and increased efficiency could help fill this demand, but more likely China will have to rely on imports. The international market accounts for 80 percent of the soy consumed in China, and the country recently became a net importer of corn. Of course, China’s international agricultural practices are not without controversy. Its move to buy a Luxembourg-sized swath of Argentinian farmland has provoked a political backlash in that country and African governments have become increasingly wary of what they term “land grabs.”

Plus, this isn’t even the nightmare scenario. If China’s growing urban population were to start eating they way middle-class Americans do, Dou said the yearly grain needs would reach 1,700 million tons, rather than 700 million. Or, in her words, “If the Chinese adopt an American diet, it would be a global disaster.”