i know for a fact that soil ph can make a difference. a few years ago i cleared out most of the brush/saplings/trees from an abandoned pasture, then i limed/fertilized and planted it as a dove plot for the last few years. this spring i cleared out another small section of the field. i was not able to lime it, but was able to fertilize it.

the sunflowers growing in the new spot are dinky, stunted, yellowish and generally look poor. 10 yards away in the areas that i limed, the sunflowers are about twice as tall, have a stem 3x the diameter, and are generally a much better looking plant.

same soil, same fert, except one area didn't have lime. i think the starting ph was 5.8 or 6.0.