U.S. soybean farmers are witnessing a generational shift in domestic use as demand for soy oil by renewable diesel refiners continues to grow.

Despite this, many farmers find profitability in soybean production to be elusive, said Scott Gerlt, chief economist for the American Soybean Association, speaking at a commodity conference hosted by the Iowa Farm Bureau Federation last month.

“Historically, soy sales growth has been export-driven — especially starting in the 2000s, when the Chinese market really...