What should your cover crop accomplish if you are applying fall manure? First, a live plant that survives the winter and absorbs nitrogen, phosphorus, and reduces soil erosion. Fibrous fine roots systems are better than tap roots which may allow manure nutrients to leach into tile or surface water. The cover crop should be easy to kill, and it’s a bonus if it can be used for forage (but not allowed under the H2Ohio program rules).
Generally, grass cover crops with fibrous fine roots absorb manure nutrients the best. Legumes and clovers make their own nitrogen and readily absorb free nutrients but are generally a little less efficient at absorbing soil manure nutrients. Brassicas like radish, have deep roots and are efficient at absorbing manure nutrients, but winter kill and release nutrients quickly and may cause water quality problems. Kale and rape seed (brassicas) have deep roots, survive the winter.
Brassicas should be used at low seeding rates and always in a mixture with winter grass cover crops.
Summer annuals include oats, radish, and Sorghum Sudan varieties; which effectively absorb manure nutrients. However, these cover crops die with a frost, so they should be minimized in a fall planted cover crop mixture. Winter grass cover crops are cereal rye, annual ryegrass, barley, triticale, and wheat; which can be planted alone or in mixtures. Winter legumes include vetches (hairy, common), clovers (red, sweet, crimson, Balansa), and peas (true winter peas or Canadian pea) which need to be inoculated. Follow H2Ohio program cover crop mixtures guidelines to qualify for payment.
Seed quality can be harmed by weed seed (purity) and low germination. NRCS requires adjustment factors (need more seed) if seed purity (too many weeds seeds) or seed germination is less than 86%. Farmers can use bin run seed or their own seed, but seed testing or seed tags are required for purity and germination to get payment.
There are several seeding methods to plant cover crops at the proper seeding depth and rate to get fast germination. Drilling cover crops and getting good seed to soil contact is usually the best method, but because the farmer needs to harvest the main crop first, this can be difficult. Broadcast seeding with airplanes, helicopters, high boy applicators, or with a broadcast seeder can be successful if done early with adequate moisture to get fast seed germination. Some farmers incorporate seed with tillage equipment, but depth control may be variable. Broadcast seeding can be done quickly and on large acres, but the seeding rate should be at least 20% higher to account for lower germination rates (H2Ohio program rules).
Most fall planted winter cover crops can be planted from August 1st until around mid-September in Ohio with good results. Farmers located close to Lake Erie have a shorter planting window than those located closer to the Ohio River. NRCS allows farmers to compensate for up to two weeks of planting after the ideal planting window by increasing the seeding rate 20% to compensate for reduced germination and to increase plant biomass. If you plant more than 2 weeks later than recommended, NRCS does not pay. The longest planting window for grasses is cereal rye (November 1st) followed by wheat, triticale, and spelt (Oct. 22), and barley (Oct. 10).
Since each cover crop seed has a different size and density, seeding rates are based proportionally on the recommended seeding rate for each specie. For example, if equal parts winter rye, winter triticale and hairy vetch mixture was selected use the 1/3 proportional rate of the full seeding rate for each (17, 19, and 5 lb/ac respectively). Insure the sum of the proportions equal at least 1 (1/3 + 1/3 + 1/3 = 1). If addressing water quality (nutrients in surface and ground water) as part of a conservation plan, at least half of the proportional seeding rate must be non-winter killed cover crop species.