Aha, that's what I needed. The "FertileSoils" part, I assume the rest of the functions match the import name?
import mods.agricraft.growing.Soil.set(<AgriCraft:seedDandelion>, <minecraft:dirt>);
EDIT: ninja'd by @nimO
My mutations go based on type of veggie : Bushcrop, Vines, Stalks...