exactly, Mick. there is a farmer up the road that burned his with glyo BUT he didnt run a crimper over it to lay it down. he has some weeds in his fields. you also dont get the moisture retention benefits of laying it down.
the board doesnt need to be over 2ft long maximum, any longer and the force spreads out over the board and doesnt give a good crimp. the angle iron needs to be 1 1/4 inch and a grinder to put an edge on the downward part makes it even better(not a razor sharp edge, just an edge). the reason i did it 3 times was because i really planted a tad too much oats and ended up with about a 4" mat. suprisingly it wasnt a whole lot of work and once i got the hang of it it took maybe an hour. you dont have to do strictly no till but the least you disturb the soil the better. like i said, my method is low till and hopefully after layers of the black soil is built up then i should be able to do no till. after the crimp stayed down, i weedeated my rows for the row crops. then i took the outside tines of my front tine tiller and made ONE pass for each row. then i laid a furrow for the seeds and covered, then i pulled the weedeated much over what i had tilled. this was a shallow till, 1-2 inches max. for hill crops and transplants i just pulled the covers back some and used a garden spade to dig a hole and plant. hard clay is a chore to build up but once you do you have the benefits of the clay soil combined with better drainage. clay is good soil but it retains more water for longer.
this makes it a lot easier than it sounds. for a till garden you would have spray, till once, wait 10 days and till again to remove any weed sprouts. then if you dont use hay mulch you will have to run a tiller or hoe down the middle to combat grass and weeds. with a cover crop map, any weeds that make it thru can easily be pulled up and left laying for additional mulch as long as there are no seeds on them. if they are seeded remove them from the garden.
daveb, you could approach a larger plot 2 ways. first you could build a cheap crimper either with an old water filled seed compactor(just weld angle iron to it and pull it with a lawn tractor) or do like Mick suggested drag a 6x6 piece of lumber(the corners should knock it down)
you could also do like Jeff Poppen and use a small harrow and chisel plow to incorporate into the soil without turning the soil. someone with 5 acres is usually going to have a small tractor and harrow anyway. i know i did.
