Looking on the internet deeply has found these results:

Work on the farm is the most popular phrase on the web.

Work at the farm 18,250,000 results on the web	Work on the farm 18,930,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
17, pretty, works at the city farm. Most of the competitors, they work for him back at the farm. He works at the farm where I was last year. Did they ever send you to work at the Elliston farm? Our work at the farm prohibits any political activity so if our superiors were to find out about my meetings As you can see, this pupil did not do his homework... because he had to work at the farm. We have to go work at the duck farm. I want to live with my children and work at the farm.	Yes, and I do all the work on the farm I let him stay there in return for a bit of work on the farm. By labour is meant all persons who have been engaged on work on the farm during the accounting year (see hereafter). total expenditure in respect of work on the farm carried out by agricultural contractors. I could go work on the farm. In return, I'd find him work on the farm. total expenditure in respect of work on the farm carried out by agricultural contractors. By labour is meant all persons who have been engaged on work on the farm during the accounting year (1) (see hereafter).

Work at the farm

18,250,000 results on the web

Work on the farm

18,930,000 results on the web

More popular!

17, pretty, works at the city farm.
Most of the competitors, they work for him back at the farm.
He works at the farm where I was last year.
Did they ever send you to work at the Elliston farm?
Our work at the farm prohibits any political activity so if our superiors were to find out about my meetings
As you can see, this pupil did not do his homework... because he had to work at the farm.
We have to go work at the duck farm.
I want to live with my children and work at the farm.

Yes, and I do all the work on the farm
I let him stay there in return for a bit of work on the farm.
By labour is meant all persons who have been engaged on work on the farm during the accounting year (see hereafter).
total expenditure in respect of work on the farm carried out by agricultural contractors.
I could go work on the farm.
In return, I'd find him work on the farm.
total expenditure in respect of work on the farm carried out by agricultural contractors.
By labour is meant all persons who have been engaged on work on the farm during the accounting year (1) (see hereafter).