Annual ryegrass dies out after one year, although some of the seed planted the first year may come up for the next two or three. Use it when you need a green manure that germinates quickly, loosens the soil, and prevents soil erosion. Annual ryegrass won't tolerate flooded conditions for long. Annual ryegrass germinates well in cool soils. It does well in a wide range of soil pH and textures, but prefers loamy or sandy soils.
Annual ryegrass releases substances toxic to other plants.
That trait makes it good for weed control, but means you can't plant small-seeded crops such as lettuce and radishes just after turning annual ryegrass under. Transplants and large-seeded crops aren't affected. You can plant it along with a legume. Cover with about half an inch of soil, then tamp down the soil. Alfalfa is the best legume for fixing nitrogen, if the soil is adequately fertile.