(Reuters) THe USDA is estimating that U.S. farmers will plant 90.0 million acres of soybeans this spring, down from 90.1 million last year, and reduce corn acres to 90.0 million acres from 90.2 million in 2017, projected on Thursday. The USDA at its annual Agricultural Outlook Forum projected U.S. wheat plantings for 2018 at 46.5 million acres, up from 46.0 million a year earlier. A Reuters poll of analysts estimated that soybean plantings would rise to 90.6 million acres and corn seedings would drop to 89.9 million acres. Some analysts were surprised that the government projected a drop in soybean acres. The price ratio between new-crop November soybean futures SX8 and December corn CZ8 futures on the Chicago Board of Trade is near 2.6-to-1, high enough they believe to encourage farmers to plant more soybeans than corn.