Planting annual ryegrass or other cover crops in the fall is tricky. Weather determines when the harvest arrives. If the ground is wet, the harvest can be delayed. If winter arrives early, there may not be enough time to plant a cover crop. That leaves the field subject to erosion, unless you’ve protected it with no-till and prior cover crops.
Farmers find aerial seeding of cover crops a better fit with their schedule. While there are issues involved with aerial seeding – how to avoid wind-drift onto neighboring farms; the cost of hiring a plane or finding a high-clearance rig with a seeder – the advantages seem to outweigh the hurdles.
By seeding annual ryegrass into standing corn or beans, you have a better chance of getting the cover crop established before winter. There are risks, of course. Seeding when rain is expected will give the annual ryegrass something to germinate into…although annual ryegrass seed can lay on top of the soil for weeks without rain without any harm. The risk is that the crop germinates and then you experience a dry spell.
Once the harvest is taken from the field, the annual ryegrass can then flourish in full sunlight. This often gives you extra weeks for the crop to establish before cooler weather sets in and stunts the top growth.