seperated by a common language.
as a YANK, I didn't really understand much...AG operator? departure?
I am guessing you are flying from an UNCONTROLLED FIELD using UNICOM or MULTICOM procedures AKA CTAF.
Departure is more a term used with an IFR clearance. I would say TAKEOFF...I might say, with a right standard departure.
I would say: SuperDuper123 taking off runway 31, back taxiing for full length
AT best I might hear...wind 320 at 7, reported traffic on the left downwind a tiger moth.
Be cool next time...let people know you plan to BACK TAXI as we call it...but I will tell you this...your AG operator is not a flight instructor or controller, so next time he says something you don't agree with just say:
You were blocked...say again
until he won't say it no more!