Place rows of plants on terrain.

I am wanting to build a large (2km x 2km) farm of row crops on a non-smooth terrain. I don't want to place them by hand for obvious reasons. I figured I could make a prefab of the crop building up to a grid, but then the crop would be floating or below the ground.

Is there a way to either make objects in a prefab follow the terrain under them, or a script I could write to place plants in large rows? I am still fairly new to Unity so I would like all the guidance I can get.