Allotment using borders of agricultural site (10)
I believe the answer is:
allocation
'allotment' is the definition.
('allocation' can be a synonym of 'allotment')
'borders of agricultural site' is the wordplay.
'borders of' suggests removing the centre.
'site' becomes 'location' (I've seen this before).
'agricultural' with its centre taken out is 'al'.
'al'+'location'='ALLOCATION'
'using' acts as a link.
(Other definitions for allocation that I've seen before include "Distribution, assignment" , "Share" , "Allotment" , "Apportionment" , "budget" .)