Perhaps endlessly treating with chemical fertiliser (7)

I believe the answer is:

nitrate

I'm a little stuck... Click here to teach me more about this clue!

'chemical fertiliser' is the definition.
'nitrate' can be an answer for 'fertiliser' (I've seen this before). I am not sure about the 'chemical' bit.

'perhaps endlessly treating' is the wordplay.
'perhaps' indicates an anagram.
'endlessly' means to remove the last letter.
'treating' with its last letter removed is 'treatin'.
'treatin' anagrammed gives 'NITRATE'.

'with' is the link.

Can you help me to learn more?

(Other definitions for nitrate that I've seen before include "Fertilizer" , "Fertiliser chemical" , "following 28 [SILVER]" , "Compound" , "Tear tin up for fertiliser" .)

I've seen this clue in the Evening Standard.

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