ORIGINAL: haystack

Grass is one of the worst enemies of clover. Sprays that kill grass is by far the best method to ensure the clover has a chance to grow. The roots of the grass must be killed or it will bounce right back, with burning especially. You could possibly kill the grass by disking, but you would need to disk every couple weeks, all summer. It is getting late to plant clover in your area Mar20-May15. Sprays are expensive, but vital in a situation like yours. How large is the field? You might be able to hire somebody to spray it, in my area the going rate is $7 bucks an acre. If you used Poast or Arrow it would kill the grass only, leaving the clover and there will probably be clover sprout from seed already in the ground. I would not attempt to plant clover without killing the grass first. Just my 2 pennys

You could also use Gly to kill every thing, and it would be cheaper than the other methods mentioned.