A state, newly treed and irrigated (7)

I believe the answer is:

watered

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'irrigated' is the definition.
('water' can be a synonym of 'irrigate')

'a state newly treed' is the wordplay.
'a state' becomes 'wa' (I can't explain this - if you can you should believe this answer much more).
'newly' indicates an anagram.
'treed' with letters rearranged gives 'tered'.
'wa'+'tered'='WATERED'

'and' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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