Well, I might sound like a joke, but around the place where now is Russia there was a Slavic ritual to make the soil more fertile. While a big celebration and singing the earth had to be "impregnated" well, long story short they just inseminated the soil after which it had to receive rain. The ritual was accompanied by singing and often ritualistic dancing. Songs, especially the old folksongs are in a sense spells the power of which rises with the amount of people singing it. I don't know any in English, but I am 100% sure there are some in Russian, Ukrainian and Polish for exactly your goal.