Farmer's opening furrow, turning sod (4)
I believe the answer is:
turf
'sod' is the definition.
('turf' can be a synonym of 'sod')
'farmer's opening furrow turning' is the wordplay.
'opening' suggests taking the first letters.
'furrow' becomes 'rut' ('rut' can be a synonym of 'furrow').
'turning' shows that the letters should be reversed in order.
The first letter of 'farmers' is 'f'.
'f'+'rut'='frut'
'frut' backwards is 'TURF'.
(Other definitions for turf that I've seen before include "Grassy earth" , "Layer of matted earth and grass" , "Grass; slab of peat" , "Bit of grass with roots and earth" , "Cover over with grass" .)