“What about sunbathing?”
Well if he’s sunbathing, it doesn’t matter if he’s a farmer or not. The only way a farmer, as a farmer, can make use of photons is to plant crops.
“But anyway: Imagine it was raining donuts and you sat on the ground and caught them as they fell from the sky (the origin is unknown). Now let’s say someone taller than you came along and held a basket above you, thereby catching the newly falling donuts. You have the donuts you caught before, and he has the donuts he caught after placing his basket there. Do you have a rightful claim on his donuts purely because you caught the donuts that fell before them?”
I would probably say that the guy sitting there first has a better claim to the ones falling towards him than the tall guy. I don’t spend too much time worrying about scenarios like this though. Perhaps a better question is who owns the land the guy is sitting on.