Up to cultivate the land (4)
I believe the answer is:
till
I believe this is a double definition.
'up to' is the first definition.
(up to or till a certain time)
'cultivate the land' is the second definition.
(Other definitions for till that I've seen before include "Cash machine" , "Container for money" , "Work the land for cultivation" , "Cultivate - cash drawer" , "Drawer holding money in shop." .)