Can a field boundary polygon be a multi-part polygon? Would it make sense to explode the polygon and assign it a new number? What would the processes of assigning it new land use information based on the new geometry look like?
While it would be possible to use a multipart polygon as a field, it is not recommended. Many of the tools in the ACPF use the individual field boundaries to calculate statistics…like mean field slope. Calculating a mean field slope across multiple, disparate polygons would likely return faulty or inconsistent results. I would strongly encourage you to use a single-part polygon structure for field boundaries. Regarding the assignment of new land use information, please look at the Update Edited Field Boundaries tool in the Utilities tool drawer. This tool will take update the Crop History (CH) and Land Use (LU6) tables using an edited field boundary feature class and the existing land use data (wsCDL20xx) in the file-geodatabase (fgdb). This tool is intended to allow users to refine the watershed’s field boundary feature class and update the relationship between the feature class and the Crop History and Land Use tables. This is necessary because the relationship between the feature class and the tables is based on the FBndID field, a unique field identifier. This FBndID field will be corrupted if the field boundaries are edited, and the relationship will no longer be valid. You should also take a look at the Get NASS CDL data by Year tool. This tool allows the user to add individual years of NASS Cropland Data Layer data to the watershed’s fgdb. The currently available HUC12 database carries NASS CDL data for 2009-2014. You can use this tool to add new (2015) or historic (pre-2009) data to the fgdb. If you update the NASS CDL data holdings and then use the Update Edited Field Boundaries tool, the crop History table will be expanded to hold the new data and the LU6 table will use the most recent 6 years of data. Together these tools enable the user to maintain the most current field boundaries and land use information. Let me know if you have any questions.