Growers already have been struggling with declining farm incomes because of high input costs, global competition and low commodity prices.

Cargill Inc. took a revenue hit of almost 10% in its most recent fiscal year, a decline that comes amid signs of profit struggles at the world’s biggest crop trader.

The cost to transport America’s harvest from the Midwest to the rest of the world is soaring as shrinking water levels on the Mississippi River drive up barge freight rates.