If you are running a patch on ground you do not own, the answer is almost always yes, and you will usually need it before anyone hands you a gate code.
What a certificate actually is
A certificate of insurance is a one-page summary showing that a policy is active, what kind of coverage it is, and what limits apply. It is not the policy itself. It is proof the policy exists, issued by the insurer or its agent so the property owner does not have to take your word for it.
Why landowners ask for one
If a visitor turns an ankle stepping off a hay wagon, the landowner wants to know your policy is the one that responds, not theirs. A certificate is how they confirm that in September rather than finding out in November.
Additional insured versus certificate holder
These two get mixed up constantly. A certificate holder simply receives a copy of the certificate, usually so the landowner has it on file. Additional insured status goes further, extending part of your liability coverage to the landowner for claims arising out of your operation on their property. The additional insured guide covers the difference in more detail.
When to request one
As soon as you know the address. Issuing a certificate is quick once a policy is bound, but it cannot happen before the policy exists. If a farm owner wants proof of coverage three weeks before you move equipment in, get the application submitted early rather than waiting on a countersigned lease.
Keep a copy on the property
Print one and keep it in the ticket booth or the cash box. A property manager or a county inspector who asks on a Saturday afternoon is not going to wait while you find an email on a phone with one bar of signal in the middle of a field.