Fecundify is a rather uncommon word, which means "to make fertile or productive." If you're looking for a more widely used alternative, you could say "fertilize" or "enrich the soil." If you're talking about animals, you might use "breed," "mate," or "reproduce." In a more figurative sense, "stimulate" or "encourage growth" could also work. Other options include "proliferate" (to increase rapidly), "generate" (to bring into existence), or "prolific" (producing a large quantity of something). Ultimately, there are many words that could be used to convey the same general idea as "fecundify," and the best choice will depend on the context of the situation.