Excessive rains across the central United States over the past week have slowed the harvest of corn and soybeans, while rising water levels closed at least three locks on the Upper Mississippi River, a key artery for shipping Midwest grain to U.S. Gulf exporters.
Cash bids for corn shipped by barge to the Gulf firmed on Tuesday, reflecting exporter demand and dwindling pipeline supplies as rising river levels slowed barge traffic.
The United States is the world's top corn supplier, and sales of the yellow grain represent one U.S. agricultural market that has been relatively immune from trade spats.
U.S. soy shipments to top global buyer China have declined due to the Trump administration's ongoing trade dispute with Beijing, but world demand for corn has stayed strong amid tightening global supplies.
Meteorologists predicted more showers this week in the western Midwest, including Iowa and Minnesota, before a break at midweek.
"You are going to have at least a two-week period where nothing is going on, basically from St. Louis to Davenport (Iowa)," a barge industry source said. "It's not pretty. We need to be getting the crop out of the field."
On the Mississippi River, three locks between Davenport, Iowa, and Quincy, Illinois - locks 16, 17 and 20 - were already closed as of Tuesday due to high water, and at least three others nearby were likely to close, a U.S. Army Corps of Engineers official said.
The closures halt the movement of barges laden with corn and soybeans and headed for export terminals at the U.S. Gulf.
The Midwest harvest got off to a quick start, aided by fast-maturing crops, before rains stalled progress. The U.S. Department of Agriculture late Tuesday said the U.S. corn harvest was 34 percent complete, ahead of the five-year average of 26 percent. But the soybean harvest, at 32 percent complete, lagged the five-year average of 36 percent.
Big crops are still in the offing. The USDA last month projected record-high U.S. corn and soybean yields.
But along with harvest slowdowns, the excessive moisture is degrading the crop quality in some areas. Corn stalks in some fields are weakening, causing plants to lodge, or fall over.
"With a combination of lodging, where the ear is now below where the combine head can pick it up, plus ears dropping on the ground, we are starting to see that yield potential disappear," said Mark Licht, an Iowa State University crop specialist.
(Reporting by Julie Ingwersen)
