WASHINGTON — Corn’s global trade over the next decade is expected to increase by 30% while soybean global trade is expected to expand by almost 40%, said Joseph W. Glauber, chief economist for the U.S. Department of Agriculture. He added that he expected to see a 15% increase in global trade of wheat during the same time period.

In his prepared comments at the Feb. 20-21 U.S.D.A. Agricultural Outlook Forum, Mr. Glauber said the United States could expect robust export competition from Brazil in soybeans and corn and the Black Sea Region in wheat and corn. Nevertheless, favorable income growth in China and elsewhere should keep export demand strong over the next 10 years, he said.

Mr. Glauber predicted that 2014-15 U.S. corn and soybean acreage is expected to total 171.5 million acres, about 400,000 less than in 2013. He said projections are that corn plantings will fall to 92 million acres, down 3.4 million acres from 2013. Soybean acreage was projected at 79.5 million acres, up 3 million from 2013.

Prices in 2014-15 are projected to fall to their lowest levels since 2009-10, Mr. Glauber said. Corn prices are expected to fall to $3.90 a bu, the lowest season average price for corn since 2009-10. Soybean prices are forecast at $9.65 a bu in 2014-15, the lowest season average since 2009-10. Wheat prices are estimated to fall to $5.30 a bu, down 22% from 2013, Mr. Glauber said.

“Record global crops for grains and oilseeds have contributed to significant price declines over the past year and it is expected these trends to continue into 2014,” he said. “Because global stocks continue to be tight, markets will remain sensitive to global production, both in the United States and abroad.”