How good would turnips and clover grow without going over the seed bed with a roller?

Good seed/soil contact will give the best results. A good rain will do the same thing. Maybe a light cover with a disc or harrow?
Brian

Soil contact is the best way to get the most from your seed. But you don' t need a roller. Run over the field with your 4 wheeler, back and forth to press as much seed as you can. It won' t compact the soil too much and it just takes a little time and gas.
Russ

Drag an old set of bed springs behind the atv. It increases your surface contact.

Dan O.

I' ve rolled all my plantings, but have had a couple of areas that were too wet and got the ATV stuck. What I found was that if it was too wet to roll, or a little iffy, you experienced great germination and growth, but if it was dry enough to roll, it needed to be. Pre-roller, I just dragged my ATV ramp sideways through the field and it worked just fine.

Jeff...U.P. of Michigan

If you live in an area with cedar trees, they also make a good drag to cover the seed. Those seeds will germinate well with a modest rain as mention earlier without covering or rolling them.

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After working the soil up it is best to pack the soil to give a good seed bed. Some seeds can be lightiy dragged in.