There is a bug in the current version (i.e. 2.72) of the game (and probably in the previous versions too).
When using a barrenness potion in 2 cases (depending of your current fertile status), the number of barrenness potions is not decreased.
Instead, the number of "Recipe Barrenness Potion" is decreased. This is a "Key item" which is to be unique; which means that the recipe for this potion will just disappear from your inventory.
Attached a patch to fix this bug for the version 2.72 (it will not restore the recipe in your inventory if it has already disappears; you'll need to use a save editor for that). Download, decompress and replace the ""CommonEvents.json" file in the "\www\data" sub-folder of the game (do backup the original file first).
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