philip Wick

I’d suggest, if the soil is cold and wet, that you plant oats and then till under later to enhance your cover crop and then plant your other mix of covers in late spring. A bag of whole (uncrimped oats) will grow quickly and add vegetative matter). Most clovers won’t do much the first year so if added to the mix there isn’t as much of a benefit, through you might add inoculated mammoth “one cut” red clover.
Normally rye and daikon radishes are fall grown: the daikon radishes root enters the soul deeply and the rye will put on a lot of growth in the fall and colder weather and lower light conditions. The crimson clover may add some benefit but the growth will be modest and unable to compete with radish and rye. The latter two collect nitrogen that would otherwise be lost.

It seems to me that what you are really asking is what to do with the residue.  The residue for a season's long planting can get out of control and be very woody and difficult to plant through because of the fact that it can take time for decomposition to occur.   When you raise a crop like beans (bean seed from the supermarket which you add inoculant to would be fine) and you let the crop grow to flowering, you are cover cropping and, if you chop up the bean plant and add it to the soil, you are adding a green manure.  When you cover crop, you need to be conscious about what you want or expect the following crop to be and plan accordingly.  If you want to plant early, you can plant in late summer a crop of oats if zone 6 or above.  You can then leave the dead oats in place to help protect the soil and add the remnants in the spring.  If you want a summer cover crop but want to grow something later in the summer you can dependably choose buckwheat.  If you cut its weak stems with a hoe as it begins to flower, you will get the benefit from that.  But if you wait a bit, buckwheat will self seed and if you cut it down later, you can grow a second crop of buckwheat from the seeds of the first.  

Even some pretty  difficult crops like sudan grass can be kept more or less succulent if mowed during the growing season and it will die with the first hard frost.  You can also use an out of season crop (winter rye in spring) which needs the cold vernalization to grow  and cut it in when small and succulent (though then it acts like a green manure and won't have the longer acting soil building effects like woody crops would).

There are many cover crops out there and it makes sense to experiment with those that you can obtain cheaply.  Supermarket wheat berries, beans (but not pearled barley, etc) will all come up and give you some good effects.

I found it gummy and starchy even when small or when ears are immature.

This is old and late but oats will winter kill at zone 6 and lower.
Tillage radishes will winterkill and leave largevhilrs in the soil for water and air as well as adding some pathways for worms. When combined with peas, you will get some nitrogen through the nodes on the peas if the peas or inoculated or if peas have been grown recently.
Sudan grass or sorghum will put on tremendous growth in the warm summer but will easily winterkill at the first frost. Some Sudan grass I had on an acre this year was higher than the muffler of my general purpose JD 630 when I mowed it .
When you think about integrating a cover crop or green manure, you also have to think about the incorporating any debris left next year.  In areas where I am going to grow a garden crop, I like radishes

I’ve had bocking Comfrey for years and I’ve never found any sort of cover helpful or necessary as the stuf has explosive growth after the first year and the plants literally crowd out anything near the base.

I tried Sunn Hemp a few years ago, with inoculant.  I found that it did not do well for me (zone 6 CT)  and it did not out compete the local weeds even at the height of summer when temperatures are hot.   I reverted to using other types of cover crops or green manures.  For my money, piper sudan grass or sorghum is a better choice.  I planted just over an acre of it in a fallow field at 50 lbs to acre and mowed it once in the middle of summer when it was a couple of feet tall with a drum mower.  I let it alone and regrow (too busy to get back to mow again though I could have) and when I mowed it over a week ago, the plants were at least 10 feet tall in places.  

The nice thing about this grass is that it winter kills and will begin to rot down prior to plow down next spring.

One way to do it is to overseed in later winter with clover. If the grass is shortened in the fall--mown close or eaten--you can overseed medium red clover over the field and you will have clover mixed with the grasses. Alfalfa grows too weakly at first so not a good choice. On our small farm, I have a hayfield that was last plowed and reseeded from field corn in 1964. I've contained to get ok yields from it until this past year when I finally decided to plow and reseed it.

I'm in CT so we have typical NE weather. All of my legumes are clover based since alfalfa doesn't grow as well here and it is hard to dry as hay.

When I do reseed by plowing in the fall, I use rye or spelt as a fall companion crop. You get a crop of straw that is sale able and then a crop of clover. You could use oats but they winter kill here. I like to seed in mid august when the plants can get started and there is more certainty of fall rains.

I've grown spelt as a late fall and winter to spring crop meaning I seed by broadcasting after plow down of old hayfield. . It makes nice straw. I've not grown it just for grain but the grain is more tightly bound and isn't easily removed from its envelope. It grows taller than wheat and fills out nicely too.

I am in a like situation. The farm is 12 acres in ct, part of a 80 acre farm that was dairy until the early 1960s. I make a little hay on about 3/4 of the land (remainder is wood lot) and a couple of acres of adjacent land trust land that I have life use of. In my experience, without animals, you need to practice fallow periods as well as rotations where green manures are rotated through the land. I've had good luck discing down weedy, run down fields and planting nurse crops (winter rye or oats) with Timothy, fescue and medium red clover and alfalfa. I get some income from the straw(runs $5.00 a two string bale here, sometimes more) and a like amount for good quality 1-2nd cutting). I will sometimes cut, at end of summer, the hay on the field and let it rot; seems to enrich the soil.
Anyone who thinks that hay is a path to wealth probably needs to do more homework; unless you have a full contingent of equipment--tractor(s), mowers, Tedder, rake, baler, etc--you won't make much money. I use a bunch of old two cylinder tractors that aren't too bad but even so, they don't sip gas. Plus, you need to keep everything going. Lots of hard work which I do mostly to keep the fields neat and to work outside in comparison with my office job.

Try Sudan or sorghum Sudan grass. Grows great, enriches the soil and can be cut a couple of times during the season. With the first hard frost it dies and it is easy to work the ground in the spring. Adds tons of organic matter to the soil.