Cover crops accomplish many things:
- help protect soil from erosion
- increase its resilience against soil compaction
- boost the organic matter content
- feed soil organisms
- provide some weed control
- produce the mulch for next year's crop
- hold and recycle nutrients
- produce extra forage this fall or next spring
Cover crop options:
Oats mixed with rye
Drill a mix of about two bushels per acre oats and 1.5 bushels per acre rye, one to two inches deep. The oats produce more biomass for a fall forage harvest than rye. The rye doesn't winterkill and will be present next spring when it can be terminated or harvested for silage. Establish late July/early August.
Annual ryegrass can be drilled at 15-20 pounds per acre, 1/4 to 1/2 inch deep. Establish late July/early August to take a cut or graze this fall. If annual ryegrass goes into the winter with more than four to six inches of top-growth, it is likely to winterkill. If you want to have ryegrass only as a cover crop (no forage), establish it in the second half of August (central Pennsylvania) or first part of September (south).
If established late July/early August, the forage radish (also called "tillage radish") puts on a lot of growth. The roots can grow two inches thick, 18 inches long. These roots drill holes in the soil which provide entryways for next year's crop. The deeper rooting of the next crop is likely to make it more drought resistant. Drill at 8-12 pounds per acre, 1/4 to 1/2 inch deep. We recommend mixing with a cover crop that will provide mulch next year -- oats if you want a dead mulch next spring, rye if you want a live cover in spring. If seeding with a companion, reduce forage radish seeding rate to five pounds per acre. The brassica/cereal mix can be grazed in late fall. Radishes can be planted up until September 15th in southern Pennsylvania, but after September 1st growth will be limited.
Hairy vetch/oat mix
Vetch is a winter-hardy legume that can fix substantial amounts of nitrogen for next year's crop. The oats provide protection for young vetch plants, increasing its winter survival, but don't compete with vetch in the spring. If established too early, it puts on a lot of top growth and winterkills. For greatest success, I recommend establishing hairy vetch in the first half of August in the central part of the state, and in second half of August in the south. Drill approximately 20 pounds per acre of vetch seed with one bushel per acre oats, 1/2-1 inch deep. This mix is not recommended for northern locations. Inoculate with pea/vetch rhizobium strain. Count on planting your late corn or forage sorghum in these fields next year. The vetch comes on slowly in the fall, but grows very fast in the spring. It can supply most of the nitrogen for a corn crop.
Crimson clover is a legume, and fixes substantial amounts of nitrogen, although not as much as hairy vetch. It grows fast in the fall and, therefore, does not profit much from a companion seeded with it. Just like vetch and annual ryegrass, it may winterkill if established too early in the fall. For greatest success, plant by September 1st in the central, and September 15th in the southern parts of the state. Drill 15 pounds per acre of seed, 1/4 to 1/2 inch deep. It's then likely to provide at least 80 pounds per acre nitrogen for next years' summer crop. Use crimson/berseem Rhizobium inoculant.
While it is still early for rye establishment, it is worthwhile to get the seed in the barn to be ready whenever there is an opportunity. Seed two bushels per acre, one to two inches deep. 'Aroostock' is a variety well adapted to Pennsylvania winters.
Mix with oats to get a forage cutting this fall. Seed ten pounds per acre red clover, and two bushels per acre oat, 1/4 to 1/2 inch deep (avoid burying the red clover seeds).
Make sure to eliminate all weeds before establishing the cover crop and wait with establishment until after a rain event.