Ferns produce spore capsules contained in the sporangium (plural: sporangia), a structure localized on the undersides of the leaves. Moreover, the sporangia are borne in clusters known as sori (singular sorus). The spores are single reproductive cells that, when mature, are released from the sporangium to germinate on soil and produce new ferns. In a fern sporangium, the maximum number of spores is 64, although this number depends on the species.
Crop rotation helps to maintain soil structure and nutrient levels. If you don't rotate crops, the soil in that field will inevitably begin to lose the nutrients plants need to grow.