The main reason to not farm between solar panels is irrigation and harvesting. Modem farms tend to rely on big equipment to accomplish those sorts of tasks.

Now, with giant arrays of power production, you could theoretically make a rail system with an electric motor/s running the farm equipment up and down the rails. That would be custom equipment (Though it could be standardized). The irrigation would still be a challenge. Pivot irrigation works so well because it's a single tube carrying all the water. That makes for much lower maintenance. I'm not sure how you could get similar maintenance with panels. The naive approach would be tubing carrying water under all the panels. That, however, would frequently clog requiring someone to constantly go around fixing nozzles and plugged pipes.