Plant a legume in the plots next summer... They will help replinish soil nutrients. Some sort of forage soybeans will be good, just don't forget your innoculant.
I'm not a huge fan of fancy mixtures that cost an arm and a leg. Every bag of seed (even the fancy bags) has a label of contents and percentages. You'll come out a lot cheaper if you make your own mix. Just my two cents
If you can make the initial investment and get it established clover is your best bet. Let it head out, mow high enough to knock the heads off, let it reseed it self. If you take care of it you can get 3 years out of it. They make certian selective chemicals to help keep.the weeds out of the plot. You local county agent can help depending on what you plant
