Just did a small patch that I intend as a vegetable garden. It was hard pack, and my neighbor, trying the same task on his property, had used a disc with a couple of 6X6" posts strapped across such for weight - only scratched the surface, but after 1 zillion passes got some decent 6" grooves in the soil. So .... I used my subsoiler, which I had purchased for laying electric cable. Got about 18" into the ground, behind an L3410 4WD, and the only time I had traction problems was when a tree root was snared. So, after 1/4 zillion passes, I had the ground really torn up, and deeply too. Then, I layed a couple of loads of good topsoil onto that broken ground, and finally use the discs to mix things up (if I'd had access to a tiller, it'd be even better) - you only have to really deeply tear up the ground once, and thereafter yearly maintenance is a lot easier.