I agree with Buckhunter, the turnips and rape shouldn't be planted till mid to late July.
With 1 acre remaining your best bet would probably be some kind of clover, such as white clover.
You could buy a mix or make your own with something like 5 lbs/acre of durana clover,7 lbs/acre of red clover,and 50 lbs/acre of wheat oats or rye.
Or you could just plant a solid stand of white clover.
It would be fairly easy to get started and easy maintenance to keep it going for several years.
Genesis 27:3 Take your bow and quiver full of arrows out into the open country, and hunt some wild game.....