Disc and fertilize just before you plant. Which, I'm guessing, should be late April or early May. Watch the local farmers. They will know when it's right. Don't worry about leaching unless you on sand. Fertilizing just before planting ensures the plants will use it. Make sure you choose something that will do well with wet feet. Red clover is what is usually planted on low ground for hay. There are other options. Check with you co-op.