COLONIA BERLIN, Bolivia — A few months ago, a representative from Cargill traveled to this remote colony in Bolivia’s eastern lowlands in the southernmost reaches of the vast Amazon River basin with an enticing offer.

The American agricultural giant wanted to buy soybeans from the Mennonite residents, descendants of European peasants who had been carving settlements out of the thick forest for more than 40 years. The company would finance a local warehouse and weighing station so farmers could sell their produce directly to Cargill on-site, the man said, according to local residents.

One of those farmers, Heinrich Janzen, was clearing woodland from a 37-acre plot he bought late last year, hustling to get soy in the ground in time for a May harvest. “Cargill wants to buy from us,” said Mr. Janzen, 38, as bluish smoke drifted from heaps of smoldering vegetation.

His soy is in demand. Cargill is one of several agricultural traders vying to buy from soy farmers in the region, he said.