Some other mod crops will plant properly, but PizzaCraft's pop right off after placing. I would guess there would be similar results with other modded farmland.
Edit: They also can't be planted on the bonemealed farmland from Better with Mods or the Fertilized Dirt from Random Things. In the case of the Random Things soil, they can't be planted at all (right clicking does nothing.)
Some other mod crops will plant properly, but PizzaCraft's pop right off after placing. I would guess there would be similar results with other modded farmland.
Edit: They also can't be planted on the bonemealed farmland from Better with Mods or the Fertilized Dirt from Random Things. In the case of the Random Things soil, they can't be planted at all (right clicking does nothing.)