Can turn on speed to make the land more productive (7)
I believe the answer is:
nitrate
'make the land more productive' is the definition.
I can't tell whether this definition defines the answer.
'can turn on speed' is the wordplay.
'can' becomes 'tin' (both are metal containers).
'turn' says the letters should be written in reverse.
'on speed' becomes 'rate' (the speed at which something happens. I am not sure about the 'on' bit.).
'tin' backwards is 'nit'.
'nit'+'rate'='NITRATE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for nitrate that I've seen before include "following 28 [SILVER]" , "salt" , "Natural or synthetic fertiliser" , "Nattier (anag.)" , "Fertiliser chemical" .)