Dark soil disturbed in trade route (4,4)
I believe the answer is:
silk road
'trade route' is the definition.
(I know that Silk Road is a trade route)
'dark soil disturbed' is the wordplay.
'disturbed' is an anagram indicator (the order of letters is disturbed).
'dark'+'soil'='darksoil'
'darksoil' anagrammed gives 'SILK ROAD'.
'in' acts as a link.
(Other definitions for silk road that I've seen before include "Ancient trade route from China" , "Caravan route" , "Old trade route to China" .)