Many growers are in the habit of leaving fallow land until September when they will seed it with winter rye. Seeding a cover crop now will produce lots of organic matter; add soil nitrogen (if you use a legume) and help to keep weeds from going to seed. All of the cover crops mentioned above will perform much better if they are seeded with a grain drill.
Here are some options:
Oat
This is a very useful cover crop for us in Massachusetts. Unlike winter rye, oat will grow very vigorously and straight up when seeded in the spring or summer. We frequently seed this cover crop during the summer months at the Research Farm in S. Deerfield on land that is not in production. It is readily available, but beware that you do not get oats that have been cooked (used for animal feed). Oat seeded this early will probably produce viable seed before frost. For this reason you might want to incorporate it (or simply mow it) before it goes to seed.
Seeding rate: 100 lbs/acre.
Sorghum x sudangrass
As the name implies, this cover crop is a cross between sudangrass and forage sorghum. Different companies use different trade names (‘sudex’ being one). One nice characteristic of this cover crop is that it produces a sterile seed so there is no concern of it reseeding. This plant is frost sensitive, so it can be seeded any time now. If you have land that you are trying to ‘build up’ this is a good choice since it produces a tremendous amount of organic matter. When seeded in mid June it can get eight feet high by the fall. We did some work at the UMass Research Farm demonstrating that the addition of a small amount of nitrogen at planting can produce a much bigger plant. I would not apply more than 50 lbs/acre. Sorghum X sudangrass does not grow well at low pH. Do not plant after July since it will die with a frost and not grow enough to justify the cost of the seed. There has been some concern about how to manage sorghum x sundangrass in the fall. My experience with this cover crop was that it was not difficult to manage, however you may want to seed a little of it the first time in order to get some experience with it. It will die with a hard frost. You can either leave it until the following spring or incorporate it after a frost and seed rye. After a hard frost I let the plant residue dry down and then mowed it with a brush hog and then disked it in to seed winter rye.
Seeding rate: 40 50 lbs/acre.
Hairy Vetch
Hairy vetch is a cover crop that is being used by a lot of growers in the late summer and fall. This crop can also be planted in the spring and early summer and will do well. When vetch is seeded this early it will not usually survive the winter (whereas it will survive the winter when seeded in late August or September). The following spring the nitrogen from the dead vetch will become available, so this is when we want the cash crop in the ground to be able to take up the available nitrogen. It can be seeded alone or in combination with oat.
Seeding rates:
2530 lbs/acre (using a grain drill);
3540 lbs/acre (broadcast); 40 lbs/acre of oat when seeded with vetch.
Buckwheat
This is another cover crop that growers will seed in the summer months. It is frost sensitive so it can be planted any time now. It is used by some growers to suppress weeds since it grows very quickly, however it will not add much organic matter. Be sure to mow or incorporate before it goes to seed.
Seeding rates: 60 70 lbs/acre.
Frank Mangan, Department of Plant, Soil and Insect Sciences, University of Massachusetts
Updated July 2006