Turn into a messy mush, as a soil constituent (5)
I believe the answer is:
humus
'soil constituent' is the definition.
'humus' can be an answer for 'soil' (thesaurus). I am not certain of the 'constituent' bit.
'turn into a messy mush as a' is the wordplay.
I cannot really understand how this works, but
'turn' could be 'u' (a 'U-turn' is a kind of turn) and 'u' is present in the answer.
an anagram of 'mush' is 'hmus' which is present in the left over letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for humus that I've seen before include "Organic stuff" , "Rich organic material from dead leaves, plants etc" , "Soil's organic component" , "Organic matter in topsoil" , "Decomposed vegetation" .)