Landowners have the option of reallocating the base acres on each of their FSA farm units. The choice is between the current base acres on the farm, or reallocating based on the crop acreage planted from 2009 to 2012. These articles discuss the base acre reallocation decision.
2014 Farm Bill: Reallocating Base Acreage
2014 Farm Bill Decisions: Base Acre Reallocation Option
Base Acre and Yield Updating Tool: A Release of Spreadsheet to Aid in Making Farm Bill Decisions
Documenting Yields for Updating Under the 2014 Farm Bill Using RMA Records