Fields can be archived from within the field details screen.
To do this, you will need to select the field you wish to archive and click on Archive this Field -
Click OK on the following pop-up to confirm -
You will then be taken back to the fields screen.
Please Note - Archiving a field will hide it from the Fields screen and any displayed list of available fields. Any historical crops grown in the field will still be visible in the Crop History.
The following guide will tell you how to permanently delete a field.
To unarchive your field, select the Archived Fields tab within the Fields screen - 
Select the field you wish to unarchive and click Unarchive this Field - 
You will be prompted with a pop up to confirm that you wish to unarchive it. Click OK to continue - 
You will then be returned to the active fields tab.