If you use grain rye it will out compete alot. It’s fall planted anyways and will grow into the winter and be going again in the spring.
Possible draw backs. It will grow vigorously. It will want to seed out and the best time to kill it is at the beginning of heading out. So this may not work for all areas, especially somewhere you want to get things planted early the next spring. If done this way though it will lay down a nice amount of litter on the soil.
Another to consider would be sorghum sudan. It’s a hybrid, not just sorghum. It grows a ton and you could mow it down a few times through the summer and lay down alot of litter to build soil.