With the current version of Farm Site Mobile each line will have its own log file. Thus when you stop one line and start a new line you will start a new logfile. This means that either you will need to create several different logfiles (which can all be loaded onto the same layer in Farm Site), or create one large log file that includes some unneccesary lines (these lines can be deleted with the Pointer Tool in Farm Site).
We are planning some very major changes to Farm Site Mobile over the Summer. One of these changes will definitely be adding the ability to have as many lines as you want within a single log file.