The title the Master Farmer is unlocked by purchasing the "Farm deeds (+titles)" reward for 250,000 beans in the Farmers' Market. The reward also unlocks the Granny, Potterington, and Grandpa/Grandma titles.
Purchasing the "Farm deeds (+titles)" reward will prompt the following messages:
Granny P has retired - You now have full ownership of the farm!
Less importantly, you now have unlocked the title 'the Master Farmer'.
(Also some other titles, but let's not talk about those...)
This title changes according to the language of the server on which RuneScape is played, as shown below:
||[Name] der Meister-Landwirt / [Name] die Meister-Landwirtin
||[Name] le Maître fermier / [Name] la Maître fermier
||[Name] o Agricultor Mestre / [Name] a Agricultora Mestra
|This information has been compiled as part of the update history project. Some updates may not be included - see here for how to help out!