It was advertised as Brazil’s “new frontier,” the vast savanna running alongside the Amazon jungle that would help meet China’s insatiable demand for food. The farmers of Brazil heeded that call, razing trees, plowing virgin land and planting soybeans at a frenetic pace for much of the past decade.

Now, soybean demand from China has slowed and the world supply has increased amid a record U.S. crop, denting international prices. In parts of northeastern Brazil, so little rain has fallen in the last four years that farmers find themselves stuck in what is the worst agriculture crisis to hit the country in a decade. Productivity in the new frontier in the latest season fell 40 percent below the country’s main soybean-growing region, known as the Center-South. A year ago, the northeast trailed by 6 percent, according to Conab, Brazil’s crop-data agency.