Spot basis bids for corn at US Midwest river elevators were steady to up as much as 7 cents per bushel on Friday, fuelled by tepid farmer sales, said grain merchants. Corn movement slowed after farmers focused on finishing planting crops. US government data last Monday showed US corn 85 percent planted. Producers resisted selling corn in the belief that hot dry weather in Midwest will again return nearby Chicago Board of Trade corn futures above the $4 per bushel level. On Friday, the CME raised corn futures margins by 13.3 percent effective on Monday.