CBOT corn futures ended firm after trading close to unchanged for much of the day. Short-covering continued to underpin prices even amid expectations of a bumper US crop flooding the market with supplies in the coming weeks. Technical support for the benchmark CBOT December corn contract was noted at the 10-day moving average. But prices hit resistance near the 50-day moving average, which the contract has not broken through since July 25. USDA said the US corn harvest was 38 percent complete, up from 28 percent the previous week but behind the five-year average of 59 percent.